Abstracts No.52: 12th Victorian Universities Geosciences Conference, 1998

Geological Society of Australia

ABSTRACTS Number 52

Victorian Universities Geosciences Conference La Trobe University 4th September 1998

THE ORGANISERS OF THE 12th VUGC EXPRESS SPECIAL THANKS TO THE MAJOR SPONSORS

Rio Tinto La Trobe University Faculty of Science and Technology Australian Geodynamics Cooperative Research Centre CSIRO Division of Exploration and Mining

ISSN 0729-1IX © Geological Society of Australia Incorporated 1998 Copies of this publication may be obtained from the Geological Society of Australia Incorporated. 706 Wynyard House, 301 George St, Sydney, NSW, Australia, 2000. Example citation for papers in this volume: White, S., 1998. Karst of the Cainozoic limestones of the Otway Basin, Southeastern Australia. Geological Society of Australia, Abstracts No. 52, pp 40.

1Victorian Universities Geosciences Conference LaTrobe University, September 1998

i^TROBE ••UTTTVERSTTY

Opportunity for excellence

A meeting organised by the post graduates of the School of Earth Sciences, LaTrobe University

Geological Society of Australia Abstract Volume Number 52 Edited by W P. Noble

THE FOLLOWING ORGANISATIONS ARE THANKED FOR THEIR KIND SPONSORSHIP OF THE 12th VUGC DEPARTMENT OF EARTH SCIENCES

ABERFOYLE RESOURCES LIMITED

LA TROBE UNIVERSITY FACULTY OF SCIENCE & TECHNOLOGY

ACACIA RESOURCES

LA TROBE UNIVERSITY AUSTRALASLVN INSTITUTE OF MINING

FACULTY OF SCIENCE

& METALLURGY

MONASH UNIVERSITY

AUSTRALL^M GEODYNAMICS

NATIONAL CENTRE FOR PETROLEUM

COOPERATIVE RESEARCH CENTRE

GEOLOGY AND GEOPHYSICS

CHOICE CONNECTIONS

NORMANDY EXPLORATION LIMITED

CSIRO

NORTH LIMITED

DIVISION OF EXPLORATION & MINING

Esso AUSTRAUA LIMITED

PASMINCO EXPLORATION

GEOLOGICAL SOCIETY OF AUSTRAUA

RIO TINTO

GEOLOGICAL SOCIETY OF AUSTRALLV.

SHELL AUSTRALIA LIMITED

( V I C T O R L ^ DIVISION) SPECL^LIST GROUP IN GEOCHEMISTRY,

GEOLOGICAL SURVEY OF VICTORIA

MINERALOGY & PETROLOGY GEOTRACK INTERNATIONAL LIMITED

STOCKDALE PROSPECTING LIMITED

GREAT CENTRAL MINES LIMITED

VICTORIAN INSTITUTE OF EARTH & PLANETARY SCIENCES

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GEOLOGICAL SOCIETt'OF AUSTRALIA, ABSTRACTS No. 52 12th Victonan Universities Geosciences Conference, La Trobe University, September 1998

FORWORD The Victorian Universities Geosciences Conference is now well established as a key date in academic calender for Victorian earth sciences. The success of each conference relies on the commitment shown in previous years by students as both organisers and participants. Their energy and effort have enabled the VUGC to become an important platform for student research, and in 1998 we are building on this solid foundation. For many students this event represents their debut as presenters of science to a wider audience, so our aims as organisers of the Victorian Universities Geosciences Conference are twofold: we hope to provide a forum for fledgling scientists to present the results of their research, and in doing so, introduce the student delegates, both as presenters and audience, to the rewarding experience of the conference environment. The benefits to students at this stage of their career are many. Younger colleagues have the opportunity to see where their undergraduate toils are leading them; peers discover the object of a student's obsession; supervisors learn if students have finally grasped true meaning; and maybe a future employer has seen the right person for the job. None of these outcomes is guaranteed but all have happened at one time or another, and most participants come away enriched. The VUGC was the brainchild of Dr Kevin Hill, who as a postgraduate student recognised the pool of talent that made up the student population of La Trobe, Melbourne and Monash Universities Earth Science departments. This inclusive approach provided sufficient numbers to give the initial conference a critical mass, and a richness in the breadth scientific pursuit to ensure its success. This year we have built on that theme of "inclusive not exclusive". Delegates from as far away as Adelaide and Sydney are participating, although the organisation remains the responsibility of the original three VIEPS departments. We have also encouraged contributions from students of non-geology departments working in earth surface processes such as geomorphology and hydrogeology. Perusal of this volume will show that we have endeavoured to apply the "inclusive" theme to the science as well. This year presentations include topics ranging from tectonics in Oman (Miller) to channel morphology in suburban Melbourne (RossRakesh). We believe that such diversity can only strengthen the role of the VUGC. While we, as organisers, may have a vision for the conference as a stepping stone in the professional development of students, it is our sponsors who provide the funding to make it all happen. Thanks are due particularly to Rio Tinto, the major sponsors along with the Australian Geodynamics CRC, CSIRO Division of Exploration and Mining, and the Faculty of Science and Technology at La Trobe University, for their exceptional support. Generous financial support for the running of the conference, provision of prizes as well as logistical backup and a wealth of in-kind support was provided by a host of sponsors, listed on the previous page, to whom we express our thanks. We trust that delegates, be they undergraduate or postgraduate students, seasoned academics or industry geologists, will all gain something from this event. David Belton on behalf of the VUGC Student Organising Committee, September, 1998

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GEOLOGICAL SOCIEn OF AUSTHALIA, ABSTRACTS No. 52 12th Victonan Universities Geosciences Conference, Ui Trobe University, September 1998 THE APPLICATION OF STREAMING POTENTIAL METHODS TO CONTAMINANT TRANSPORT IN GROUNDWATER FROM MINE TAILINGS Baker, S.F. Depanment of Eanh Sciences, VIEPS, Monasb University, Clayton, Victoria 3168 Acid mine drainage (AMD) is a source of contaminated groundwater, producing waters with low pH and high contaminant concentrations. AMD commonly develops from weathering of pyrite-rich mine tailings (e.g. Taylor, et al. 1996). Groundwater contaminant flux from AMD is usually tracked by direct sampling from piezometer fields placed to intercept groundwater flow from tailings sites. A contaminant plume flowing from the site may not be intercepted by the monitoring field, as reactive transport of acidic metal rich waters may change porosity and hydraulic conductivity by an order of magnitude, resulting in changes to contaminant flow paths (Blowes, et al, 1991).The monitoring field may not clearly measure the depth of the contaminant zone, making estimate of total contaminant flux uncertain. The King River, Tasmania, has been subject to deposition of mine tailings consisting of predominantly quartz grains with 5% pyrite, and typically groundwater from its sediment banks has a pH of between 3 and 4 and concentrations of Iron and Copper up to 2g/l and I4mg/1 respectively (Green, 1997). Self-potential is a geophysical method that measures the electric potential at the surface. Changes to electrical properties of the groundwater from changing flux and contaminant concentrations may also change self-potential readings (Baker, et al, 1998). Self-potential is measured using a high-impedance voltmeter and two non-reactive electrodes.The area of interest has its self-potential measured by progressive movement of the electrodes over the surface using a "leap-frog" technique. A contour map of selfpotential values for the surface is generated, and can be compared with groundwater hydraulic gradients. From previous work on sediment banks of the King River, self-potential gradients as high as IV per metre of depth and IV over 800m of bank surface were found (Baker, op cit.). Streaming potential is a source of self-potential from groundwater flow (Hunter, 1981; Ishido and Mizutani, 1981).The streaming potential is a function of the zeta-potential, the electrical potential between the mineral surface and the layer of fixed ions adsorbed onto the mineral surface from the fluid, and of fluid flow through the medium.The mathematical relationship between a pressure gradient and streaming potential is derived from theories of irreversible thermodynamics (Nourbehecht, 1963). The general equation used to define the ratio of the gradients of streaming potential V and hydraulic pressure P is: AV/AP=Li2/Ln =e^/r|af where L^ is the electrical conductivity (which equals the fluid conductivity. Of in most waters), and L12 is the streaming potential coupling coefficient, expressed as a measure of the electrical field change for a unit hydraulic pressure drop of the aquifer (Hunter, 1981, Journaix and Pozzi, 1995). In this equation, G{ is the fluid electrical conductivity, e and r| are the electrical permittivity and shear viscosity of the fluid and ^ is the zeta potential of the materials surface. At the midpoint of the bank, a self-potential change of 350mV is associated with a hydraulic pressure change of 500mm of water. Assuming this is solely from streaming potential, and a measured value of 1.5 mS for the fluid conductivity, the coupling coefficient, L12 , measured near the midpoint of the bank was therefore about 1 juA/Pa. For quartz minerals, and fluids at low ionic concentrations and a pH of 4, a value of 2.25 )LiA/Pa is obtained from Ishido and Mizutani's work (op cit.).The obvious discrepancy is an important part of this current work.The above equation for AV/AP is not suitable for high ionic strength fluids due to changes of the thickness of the zeta-potential layer, and also assumes a capillary model for fluid flow through the porous media which is not appropriate to this situation. Recent work by Journaix and Pozzi (op cit.) also found streaming potential to be dependent on permeability of the media, and explained this as due to changes to surface conductivity, which are not taken into account in the above equation. While the ability for self-potential to locate contaminated groundwater is shown, further work is needed to refine the method for detecting the depth of the contaminant plume and quantifying groundwater contamination fluxes. REFERENCES: Baker S.E, McPhail, Dr. D.C., and Hooper, C., International Groundwater Conference, 1998. Blowes D.W., Reardon E.J., Jambor J.L., Cherry J.A., Geochimica et Cosmochimica Acta, Vol. 55, pp. 965-978, 1991. Green, D.K., and McPhail, D.C.,VUGC Abstracts Vol 46, Geological Society of Australia, 1997. Hunter, R.J., Zeta potential in colloidal science - principles and applications. Academic Press, 1981. Ishido,T., Mizutani, H., Jnl. of Geophysical Research. B86;3, pp. 1763-1775,1981. Jouniaux, L. and Pozzi, J. P, Geophysical Research Letters 22; 4, Pages 4 8 5 - 4 8 8 , 1 9 9 5 . Norbehecht, B. PhD Thesis, 1963Taylor, J. R., Weaver T. R., McPhail D.C., Murphy N.C., Report of the Office of the Supervising Scientist No. 105, 1996.

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GEOLOGICAL SOCIETi'OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trohe University, September 1998 MESOZOIC TECTONICS AND STRUCTURE IN THE LIMPOPO BELT: EVIDENCE FROM APATITE FISSION TRACKS D.X.Belton, R.W.Brown Victorian Institute ofEaith and Planetaiy Sciences, Depanment ofEaitb Sciences, La Trohe University, Bimdoora 3083, Victoria Australia. (D3elton @la trobe.edu .a 11) The Limpopo Belt is one of the most extensively studied mobile belts in the world. Ready access and abundant outcrop provide geologists with a wealth of information about this major Archaean deformation zone. The Limpopo Belt also records evidence of more recent tectonism, though less research has been directed at the Phanerozoic. Rocks of this age are either absent or restricted to localised basins where exposure is severely limited. Much of the stratigraphy in these basins is obscured by extensive and partly diachronous) basalts. On the cratons bordering the Limpopo Belt, little or no sedimentary record is preserved between the Archaean and the early Mesozoic. The lack of traditional geological markers can be overcome by using apatite fission tracks. The technique derives thermal histories for upper crustal samples (< ~6km ). This allows us to identify regional tectonic episodes by quantifying parameters such as burial depth and denudation rates. Locally, significant differences in thermal histories between nearby samples may imply some intervening, structural discontinuity. Thus, the method provides a means of identifying (sometimes cryptic) structures such as fault displacements in otherwise massive lithologies. Re-activation of much older structures may also be detected. A suite of samples from the Limpopo region in southern Zimbabwe and Mpumalunga (formerly the Northern Transvaal) with elevations between 400 m and 1000 m, was selected for apatite fission track analysis. These were predominantly basement samples of granitic and gneissic origin with Archaean protolith ages. A micro-granite of Mid-Jurassic age was also included. The suites were chosen to provide transects running normal to the structural trend of Belt. In addition to a cooling event at around 200 Ma, we describe significant cooling events for the Neocomian (~140 Ma), the Cenomanian ( - 1 0 0 Ma) and most recently at the end of the Cretaceous ( - 6 5 Ma). Modelling provides robust estimates of erosion in the Central Zone of some 4 km of material removed since the Early-Cretaceous (~150Ma). Values of 3.5 to 4 km of overburden removal appear consistent for most of the Limpopo. We include a comparison with published gravity data (Gwavava et al., 1996) in the form of an isostatic anomaly map that provides corroboration of the fission track analysis and may prove a useful exploration tool. Finally we look at a structural mechanism that may explain some of the local-scale variation seen in the data. REFERENCES Gwavava, O. et al., 1996, Geophys.J. Int (127): 635-650

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GEOLOGICAL SOCIETY' OF AUSTRALIA, ABSTRACTS No. 52 12th Victoiian Universities Geosciences Conference, La Trohe University, September 1998 CONTRASTING CHARACTERISTICS OF PROTEROZOIC AND PHANEROZOIC MANTLE TYPES: PRELIMINARY RESULTS Eloise E. Beyer Key Centre for Geochemical Evolution and Metallogeny of Continents (GEMOCj School ofEanh Sciences, Macquane University Fundamental differences in the composition of Archean and Phanerozoic lithospheric mantle have been well documented over the last decade, but little attention has been paid to the nature of Proterozoic mantle and how it compares with mantle of different ages. To establish a basis for comparison of Phanerozoic and Proterozoic mantle in Australia sampling was carried out at several localities across Tasmania. Sampling was carried out on either side of theTasman Line, which delineates the surface expression of the younger Palaeozoic Tasman Fold Belt in the east from the older Proterozoic Central Australia Mobile Belt in the west, to determine any differences in mantle composition beneath the two tectonic regimes. Lithosphere mapping represents a methodology which allows the construction of geological sections of the subcontinental lithospheric mantle (SCLM) and follows the evolution of the lithosphere through time (O'Reilly and Griffin, 1996). The basis of lithosphere mapping in Tasmania is the direct evidence for the petrology and geochemistry of the upper mantle provided by xenoliths entrained in Tertiary basalts. Results from in-situ microanalysis for major element abundances in spinel-bearing xenoliths and their constituent minerals make it possible to determine the distribution of temperature with depth; the depth to the crustmantle boundary; and the stratigraphic distribution of rock types Electron microprobe analyses have been carried out on xenoliths from two localities; Blessington (east of theTasman Line) and South Riana (west of theTasman Line).The mantle wall-rock xenoliths from both localities are exclusively Iherzolites ± spinel. EMP data has delineated two distinct geochemical populations (I0W-AI2O3 vs high-Al203 in clinopyroxene) in xenoliths from Blessington.The I0W-AI2O3 group is defined byAl203 contents <4.0 wt% while the high-Al203 group contains >4.0 wt% Al203.This dichotomy is also reflected in olivine composition.The magnesium numbers (Mg*) for olivines from the I0W-AI2O3 group are uniformly high (91.5-91.7) and all lie in the Proterozoic field of a Boyd diagram. The high-Al203 group display much lower Mg# (89-90.8) and plot in Boyd's Phanerozoic field. Preliminary work on South Riana has revealed two main xenolith types. The majority of South Riana samples are fine-grained and cpx-poor (<3.0%) with rarer coarse-grained cpx-rich (>15%) xenoliths. AI2O3 content of clinopyroxene is significantly higher in the coarse-grained samples though both types overlap the high-Al203 group of Blessington. Mg# for South Riana samples ranges from 89.2-90.3 placing them in the Phanerozoic field of a Boyd diagram. Temperature calculations from EMP data indicate that the two South Riana groups have originated from different thermal regimes indicating sampling from different depths.The fine-grained samples range in temperature from 850-900°C whereas the coarse-grained group are considerably hotter at 990-1000°C. Reasonable temperature estimates could not be calculated for Blassington due to disequilibrium problems. On results so far the more depleted peridotites (I0W-AI2O3 group) give lower temperatures.The absence of garnet-bearing xenoliths at the two localities prevents direct pressure calculations. An approximate depth of origin can be found by plotting known temperatures on the southeastern Australian geotherm.The finegrained xenoliths of South Riana give an estimated depth of 30-35km.This depth is inferred to be the distance to the crust-mantle boundary at this locality. In contrast the coarse-grained South Riana group appears to have originated from depths between 45-52km. REFERENCES O'Reilly, S.Y. and Griffin, W.L. 1996.4-D lithosphere mapping: methodology and examples.Tectonophysics 262, 3-18.

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GEOLOGICAL SOCIETY'OF AUSTRAUA, ABSTRACTS No. 52 12th Victohan Univemties Geosciences Conference, Lci Trobe Universitw September 1998 ARSENIC GEOCHEMISTRY AT WALHALLA Jean Cciuzid Department of Ecinh Sciences, \1EPS, Monash University, Clayton, Victoria 3268 Walhalla is a former gold mining town where major mining activity ceased around 1915. The possibility of new gold mining operations has been studied from 1984 to 1990 by the Intrepid Mining Company which owns the mining lease on this land.The ore is a mesothermal gold deposit in which quartz is associated with Pyrite and arsenopyrite are the dominant sulphides, and little has been done to prevent contamination resulting from the release of arsenic from primary or secondary arsenic minerals. Subsequent contamination of groundwater and surface waters, as well as soils and sediments may have occurred. This work aims to identify arsenic sources and sinks in the Walhalla area by measuring arsenic concentrations in waters and sediments in the township. Moreover, if new mines open, this study will give a first understanding of the geochemical processes and the initial state necessar)^ to monitor the environmental impacts likely to happen. Previous work by the Intrepid Mining Company showed that mine was contaminated, as well as soils in some areas. Arsenic geochemistry is complex and dependent on the redox, pH, moisture content and temperature of the media. Four valence states are possible : -III for the gaseous species, O for native arsenic and some primary minerals, +III in aqueous and soil reductive conditions and +V in aqueous and soil oxidative conditions (Boyle andjonasson, 1973).To understand arsenic speciation in Walhalla, many types of samples have been collected: mine, spring and creek waters for the aqueous species; bottom sediments, bank sediments, soils, country rock, mine clays, mine iron stalactites and iron precipitates for the solid phases. Analytical methods included field measurements of pH, Eh and electroconductivity; sediment and soil digestion; and sediment, soil and water analysis with High Resolution - Inductively Coupled Plasma - Mass Spectrometer (HR-ICP-MS). Preliminary analysis of surface waters showed a 2 to 30 ppb range levels of arsenic in the stream ; however, a 2 ppm level in one spring coming from the stream bank was detected, that is 40 times above the Australian and New Zealand Environment and Conservation Council (ANZECC) drinking water guideline (ANZECC, 1992). The arsenic content of the mullock heaps, township soils and stream sediments is being measured. At this time, contamination in this area seems to be limited to water that is currently not used for human consumption or other purposes. Sediments and iron precipitates may complex or adsorb aqueous arsenic (Peters et al., 1996).The low levels of arsenic may be a result of the drought conditions experienced during the past several years. In this case, usual rainfalls changing the Eh and pH conditions in the oxidised ore zone may lead to an increased leaching of arsenic. More geological and mineralogical data on ore rock, country rock, soils and sediments are required to ascertain and/or monitor the arsenic concentrations and distribution at Walhalla. REFERENCES ANZECC (1992). Australian water quality guidelines for fresh and marine waters. Australian and New Zealand Environment and Conservation Council, 158 pages. Boyle, R.W. and Jonasson, I. R. (1973) The Geochemistry of Arsenic and its Use as an Indicator Element in Geochemical Prospecting. Journal of Geochemical Exploration, 2, 251-296. Peters, G. R. et al. (1996) Environmental Aspects of Arsenic Toxicity. Critical Review in Clinical Laboratory Sciences, 33(6), 457-493.

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GEOLOGICAL SOCIETy'OF AUSTRALIA, ABSTRACTS No. 52 12th Victomin Universities Geosciences Conference, Ui Trobe University, September 1998

HIGH-RESOLUTION SEQUENCE BIOSTRATIGRAPHY OF THE MID-MIOCENE SECTION IN BARRACOUTA 1,GIPPSLAND BASIN Louise R. Chiistian National Centre for Petroleum Geology and Geophysics lchristi@ncpgg.adelaide.edu.au

Since the 1920's, foraminifera have been widely utilised as a means of determining age correlative surfaces and depositional palaeoenvironments. More recently, results from foraminiferal analyses have been integrated with wireline logs and seismic sections, in order that biozones and depositional environments may be more accurately interpreted. Discrepancies occur between the mid-Miocene biozonation of Barracouta 1 and Barracouta 4. Approximately 50 samples from Barracouta 1 were analysed, with over 700 foraminifera picked from each sample. Wireline logs and seismic sections were studied in detail, in order to develop a sequence stratigraphic model, which could be used to extrapolate sequence stratigraphic packages from the two wells deeper into the basin. Preliminary results are presented herein. An interpreted basal mid-Miocene sequence boundary is marked by a break in foraminiferal succession between samples at 930m (N4) and 922m (N8b). A significant wireline log break is evident at 929m, and channel cutting is apparent at this depth on the seismic section. Deeper within the basin, older horizons are truncated and overlying sediments downlap onto the sequence boundary. Calcareous quartz sands which directly overlie the sequence boundary are poorly-sorted, coarse to fine-grained, and display blocky character on the gamma-ray log. Foraminifera are generally rare, although outer shelf faunas such as Cibicidespseudoungerianus, Astrononion centroplax and Gyroidinoides sp. are observed. The presence of abundant relict elpbidiids and Lepidocyclina within this succession may be attributed to reworking of inner-shelf sediments. Channel sands are interpreted to have been deposited on the outer-shelf. Downslope deposits comprise slope fans and basin floor fans, and pelagic drape is evident within the deeper regions of the basin. Foraminiferal indices fluctuated markedly throughout this interval, possibly as a result of sporadic sediment influx within the channel complex. However, peaks in plankton diversity, plankton to benthos ratio (P:B) and Gg. woodi to Gg. bulloides correlate with those described from the Lakes Entrance Oil Shaft (McGowran and Li, 1993), and are related to the Miocene Climatic Optimum. Sediment containing faunas from Zones N9 to N11 (795-713m) succeed the channel deposits. They are interpreted as outer shelf sediments, based on the abundance of C, pseudoungerianus, Globocassidulina subglobosa, A. centroplax and lagenids. A series of slope fans, basin floor fans and pelagic drape are again interpreted basinward. A significant unconformity truncates the N9-N11 sediments at 713m. Foraminifera from Zones N12 and N13 are absent from the succession. Furthermore, a significant log break at 713m is apparent, and channel cutting is also evident on seismic at this level. The base of the channel is interpreted as a highfrequency sequence boundary. This surface is interpreted to represent the relative sea-level fall associated with the Mi3 glaciation which signalled the end of the Miocene Climatic Optimum, and is supported by increases in global S^^O values (McGowran and Li, 1993). Basinward, deposition is represented by a lowstand prograding wedge with basin-floor fans and pelagic drape. Stacked channel deposition (713-521m) overlies the N9-N11 package, and is related to minor fluctuations in sea-level. Deposits are dated as being N14-N15. The base of each channel is interpreted as a high-frequency sequence boundary, although these surfaces have not yet been extrapolated basinward. Within each cycle of deposition, the infaunal to epifaunal ratio increases steadily and wireline log character shows typical fining-upward packages. A transgressive systems tract (TST) is interpreted from 521-498m. The transgressive surface (TS) is recognised on logs by a maximum gamma-ray value. Planktonic foraminifera above this depth are dominated by cool water species, including Gg. bulloides, while the benthos comprises abundant deep-water forms such as Spbaeroidina bulloides and A. centroplax. Inner shelf faunas, including abundant abraded miliolids, are present. This faunal assemblage agrees with the microfossil attributes for TST's proposed by Holdgate and Gallagher (1996). A combined transgressive surface-maximum flooding surface is recognised on seismic profile at Barracouta 1. However, the TST is interpreted to thicken considerably basin wards.

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GEOLOGICAL SOCIETY^ OF AUSTRAUA, ABSTIMCTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

The end of the mid-Miocene at Barracouta 1 is interpreted as a maximum flooding surface (MFS). A significant wireline log break marks the MFS within Barracouta 1 and Barracouta 4. On seismic section, downlapping onto this surface is evident. Unfortunately, only cuttings samples are available from this interval, and thus the foraminiferal characteristics of the MFS could not be distinguished from those of theTST Hence, mid-Miocene deposition at Barracouta 1 is interpreted to comprise lowstand systems tract (LST) deposition, largely as channel-fill packages. Basinward, LST slope fans, basin-floor fans and prograding wedge complexes are observed on seismic sections. The lowstand channel-fill packages display the following foraminiferal characteristics: P:B ratios between 30-40%, with plankton dominated by Gg. woodi Benthos dominated by deep-water forms, such as C pseudoungerianus, Sp bulloides, Globocassidulina suhglohosa and A. centroplax Abundant relict inner-shelf faunas, such as elphidiids and miliolids, along with high proportions of dominant mid-shelf faunas, including C. mediocris, C. refulgens and discorbids Relatively low abundances of infaunal faunas, although infaunal abundance increases as channel pack ages fine upwards In Barracouta 1, mid-Miocene deposition is succeeded by Nl6-aged highstand deposition. Problems with biozone correlation between Barracouta 1 and Barracouta 4 remain unresolved, as analysis of Barracouta 4 samples has not yet been completed. However, on wireline logs and seismic sections, correlation appears sound. At present, the top of Zone C (equivalent to N14-N15) in Barracouta 4 is placed at 635m (Taylor, 1977). It is expected that this biozonation will be extended up to the maximum flooding surface at 500m, once examination of relevant samples has been carried out by the author. REFERENCES Holdgate, G. and Gallagher, S. (1996). Microfossil palaeoenvironments and sequence stratigraphy of Tertiary coolwater carbonates, onshore Gippsland Basin, Southeastern Australia. In Cool-Water Carbonates. SEPM Special Publication 56. McGowran, B. and Li, Q. (1993). Miocene planktonic foraminifera from the Lakes Entrance in Gippsland: Mid-latitude neritic signal from a transforming ocean. Memoir of the Association of Australasian Palaeontologists, 55, p 395-405. Taylor, D.J. (1965). Esso Gippsland Shelf No. 1. The mid-Tertiary foraminiferal sequence. Barracouta 1 Well Completion Report. Esso Australia (Unpublished). Taylor, D.J. (1977). Foraminiferal sequence, Barracouta 4. Barracouta 4 Well Completion Report. Esso Australia (Unpublished).

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GEOLOGICAL SOCIETY' OF AUSTRALIA, ABSTRACTS No. 52 12th Victonan Universities Geosciences Conference, La Trobe University, September 1998

AEOLIAN VS. FLUVIAL ORIGIN FOR THE BOROVIKI MEMBER, KOTELNICH UPPER PERMLVN FOSSIL TETRAPOD LOCALITY, VYATKA BASIN, RUSSLV Depanment

Andre A. Coffa ofEcmh Sciences, Moncish University, Clayton 3168, email: Andre.Coffa@mail.eanb.monasb.edii.au

Australia

The Boroviki Member at the Kotelnich terrestrial tetrapod locality is an orange fine to medium grained subarkosic arenite (Coffa, 1997; Coffa, 1998). It is found in a near continuous section on the Western bank of the Vyatka River, in Upper Permian sediments of the Russian platform. The member's thickness is up to 17 metres and its width is up to 10 km. Because of its different sedimentary structures, both fluvial and aeolian origins have been argued for the sandstone. On the basis of large scale, high angle cross-bedding, very well sorted grain size, sub-rounded to rounded grains, a homogenous texture and a compositionally mature lithology, an aeolian origin for the sediment is a more consistent interpretation for the Borovikov Member's mode of deposition. REFERENCES: Coffa A. A. (1997) Stratigraphy and Correlation of the Continental Redbed Sequence at the Kotelnich Upper Permian Fossil Tetrapod Locality, Russia. Geol. Soc. of Aust., Abstracts No. 46, pp.15 &17. Coffa A. A. (1998) Sedimentology, Stratigraphy and Correlation of the Continental Redbed Sequence at the Kotelnich Late Permian Fossil Tetrapod Localit>^ Russia. Intern. Symp. Upper Permian Stratotypes of the Volga Region, Abstracts, pp. 23-

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GEOLOGICAL SOCIET)' OF AUSTRAUA, ABSTI^CTS No. 52 12th Victorian Universities Geosciences Conference, La Trohe University, September 1998 RECONSTRUCTING LATE QUATERNARY ENVIRONMENTS AROUND LAKE BOLAC, WESTERN VICTORIA FROM SEDIMENTOLOGICAL, PALAEOECOLOGICAL AND FINE RESOLUTION i^c ANALYSES OF LUNETTE-LAKE SYSTEMS Ellyn Cook Centre for Paiynology' and Palaeoecology^ Depanment of Geography and Environmental Science Monash University Comprised of lakes (depositional basins) and their lunettes (dunes on the eastern shores) built from sediments deflated from the lake floor during arid periods, lunette-lakes have the potential to provide palaeoenvironmental records which are two-fold - the palaeoecological record from lake sediments and the somewhat independent geomorphological and sedimentological record from lunettes. Both sorts of record have been demonstrated to contribute substantially to our understanding of late Quaternary environmental change (e.g. Bowler, 1976; D'Costa et al., 1989). Additionally, these systems have preserved the oldest evidence, to date, for people in south-eastern Australia (Bowler, 1990). At the northern margin of the volcanic Western Plains of Victoria, Lakes Bolac and Turangmoroke and their respective lunettes are representative of many in the semi-arid area. Located within the drier part of the Western Plains, the lakes in this area are expected to be sensitive to subtle climate and vegetation variability and have long been recognised as archaeologically rich, bearing stone tools, hearth and other cultural materials dated to the late Pleistocene (Horton, 1984; former Victorian Aboriginal Survey, unpublished data). The area is currently the focus of detailed archaeological research (Bird and Frankel, work in progress). This study aims to produce a detailed single-site reconstruction of late Quaternary environments around these lakes through the integration of sedimentological and palaeoecological data. A critical component of this integration is the development of fme-resolution chronological control. This aspect of the project is well underway and recent dating results have substantially increased chronostratigraphic interpretation of the work in progress and added chronological context to the palaeoecological results of an earlier study (Crowley and Kershaw, 1994). In this presentation emphasis is placed on palaeoecological results from cores exceeding double the length of cores previously available (Crowley and Kershaw, 1994) and an outline is given of the sedimentological and fme-resolution i^c work in progress. REFERENCES: Bowler, J.M. (1976) Aridity in Australia: Age, Origins and Expression in Aeolian Landforms and Sediments Earth-Science Reviews 12, 279-310. Bowler, J.M. (1990) 'Human Occupation and Environmental Change:The Ancient Record from the Wiilandra Lakes' in Noble,J.C.,Joss, RJ. and Jones, O.K. (eds) The Mallee LandsA Conservation Perspective Proceedings of the National Mallee Conference, Adelaide, April 1989 CSIRO, Melbourne. Crowley G.M. and Kershaw,A.R (1994) Late Quaternary environmental change and human occupation around Lake Bolac, western Victoria, Australia J. Quaternary Science 9, 367-377. D'Costa, D.M., Edney, R, Kershaw,A.R and De Deckker, R (1989) Late Quaternary palaeoecoiogy ofTower Hill,Victoria, Australia J. Biogeography 16,461-482. Horton, D.R. (1984) 'Red Kangaroos: Last of the Megafauna' in Martin, RS. and Klein, R.G. (eds) Quaternary Extinctions University of Arizona Press,Tuscan.

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GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 52 I2tb Victoiian Universities Geosciences Conference, La Trobe University, September 1998 AN ALTERNATIVE MODEL FOR THE TECTONIC EVOLUTION OF THE FRIEDA RIVER MINERAL DEPOSITS, NW PAPUA NEW GUINEA P.V. Crowhurst, K.C. Hill, and D.A. Foster Victoiian Institute of Faith and Planetaiy Sciences, Depamnent of Faith Sciences, La Trobe University, Bundoora 3083, Victoria Australia. Recent structural mapping in the Frieda River area has delineated three different structural styles, which can be interpreted in terms of different deformation events. They include an early, ductile, tight folding event, overprinted by later thrusting and subsequently by sinistral strike-slip movement. The separate events can be related to changes in the convergence vectors betv^een the Pacific and Australian plates. Apatite fission track ages for the Frieda River area suggest that the rocks cooled below 120°C in the last 2-4 Ma, which means they were at elevated temperatures prior to this time and therefore buried at depths > 3-4 km, based on normal geothermal gradients. This contrasts with 7 Ma cooling ages for the adjacent Landslip Ranges block, to the west across the Mount Kasa Lineament. Using a K-Ar minimum age for mineralisation at Frieda of - 1 2 Ma and coupled with the high erosion rates in Papua New Guinea it could be suggested that the Frieda River mineral deposits were overthrust in the Late Miocene, preserving the rocks at >120° C for ~7 Ma. They were then exposed after Mio-Pliocene thrusting by Pliocene uplift and erosion perhaps associated with renewed sinistral wrench faulting, that was oblique to the deep-seated Mount Kasa lineament, with the Landslip Ranges acting as a buttress. Mineralisation in the Frieda River area may be related to the westerly subducting Solomon Sea Plate during the Middle Miocene. Where this area was over a relatively deep point on the slab tapping the mantle and providing mineralised melts that could have been focused by the Mount Kasa lineament into, what is now the Frieda River Mineral District.

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GEOLOGICAL SOCIETY' OF AUSTIMLIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998 THE IMPACT OF FREEWAY RUNOFF ON THE HEAVY METALS IN AN URBAN STREAM: CARDINIA CREEK, MELBOURNE Brad Cuitis Department of Eanh Sciences, VIEPS, Monasb University, Clayton, Victoria 3168 Runoff from major roadways is an important process that can result in heavy metal and poly aromatic hydrocarbons (PAHs) contaminating receiving waters (Brockbank and Batley 1996). Heavy metals such as Cu, Zn, Pb, Ni, and Cd that are deposited onto road surfaces as a result of traffic activities and vehicular wear are subsequently transported into the stream system where even relatively low concentrations of metals could impact on the stream biota. The Princes Highway and Princes Freeway two major arterials out of Melbourne, both cross Cardinia Creek, located approximately 40km east of Melbourne, which drains into Westernport Bay Hence, this is an ideal system to study effects of road runoff. Concentrations of heavy metals in the surface and interstitial waters and bed sediments are being measured to examine the effects of road and urban runoff on Cardinia Creek. Metal speciation is being measured in the sediments using sequential extraction techniques and sediments analysed for their bioavailable metal content. Cardinia Creek begins at Cardinia Reservoir and flows under the Princes Highway and Freeway within a 2km stretch. Grab samples of water and sediment were taken at six sites along an 8km stretch starting 1km above the Princes Highway and ending 2km below the Princes Freeway with sites concentrated above and below the two major roadways. A cross-section of core samples will be taken at one site to determine any changes in metal concentrations with depth and this sediment will also be sequentially extracted. Surface water was also sampled over time and may be sampled during a storm event to determine changes with time and increased stream flow. Field measurements of waters included temperature, pH, Eh and electrical conductivity using portable meters and electrodes. Laboratory analysis of surface and interstitial waters include measuring concentrations of dissolved and suspended metals (Cd, Pb, Mg, Cr, Ni, Cu, Zn, As) and dissolved major cations (Mg,Al, Si, Ca,Ti, Mn, Fe) using HR-ICP-MS. Major anions (CI", HCO^', SO^^', NO^") were measured using ion specific electrode, titration and flow injection analysis with Na and K analysed using AAS. The sediments will be analysed for bulk and bioavailable metal concentrations using a combination of HR-ICP-MS and AAS as well as particle size analysis and sequential extraction. Field measurements gave a range of values for temperature (10°C - 16°C), pH (7.18 - 7.93), Eh (114.5 152.1 mV) and E.C. (295 mS - 398 juS) Preliminary results of surface waters show that some sites have dissolved phase concentrations over the recommended freshwater quality guidelines (ANZECC 1992) for example Cd (4|Lig/l) was up to 20 times higher at one site and Zn (4.8 - 250.2 pg/l) up to 5 times higher at one site. Also in surface waters alkalinity ranged from 20.9 to 32.7 mgCaC03/L and chlorine 119.7 to 151.3 mg/L. Preliminary results of bulk metal concentrations in sediments show between ~4 ppm levels for Co up to 174 ppm for Mn. The results of this preliminary analysis show that the road surfaces are not contributing significantly to heavy metals in the stream water but they did show highest concentrations of selected metals at the control site above the roads which may indicate another source of heavy metals. REFERENCES ANZECC (1992). Australian water quality guidelines for fresh and marine waters. Australian and New Zealand Environment and Conservation Council, 158 p. Brockbank, C. I. and Badey G.E. ( 1 9 9 6 ) Road runoff and its impact on the aquatic environment: Literature review update. CSIRO.

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GEOLOGICAL SOCIET\' OF AUSTRALIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998 HYDROGEOLOGY OF LITHIA SPRING Katblyn Czapn ik Eanb Science, University of Melbourne Lithia Spring is located near Daylesford in Central Victoria and forms part of a suite of mineral springs that occur within the region. Mineral springs in Central Victoria are generally recognised as being effervescent with high bicarbonate and carbon dioxide. Formally known as Elevated or Soda Spring, Lithia Spring is noted for being relatively high in Lithium (up to 9.2 mg/L) and tends to also show high discharge. The spring is piped and issues through recent alluvium that rests on an anticlinal axis of steeply dipping Ordovician sandstones, siltstone, slates and shales, of which some are graphitic. The Ordovician bedrock forms essentially a fractured rock aquifer and is heterogeneous and anisotropic. Previous investigations at Lithia Spring were conducted in 1975 by the Geological Survey of Victoria, and resulted in 18 wells of depth up to 40 metres being placed 10 to 20 metres apart on either side of the anticline. In this research we we monitored, ten wells and the spring to identify variations in chemistry and hydraulic gradients in the flow system. Chemical parameters were measured in the field since the mineral water is reactive with the atmosphere. These parameters include pH, Eh, CI", Alkalinity, dissolved CO2, dissolved oxygen and electrical conductivity. Based on these parameters and stable isotope data the groundwater can be divided into two different compositions with some mixing apparent.To the northern part of the Lithia Spring Catchment there is a more "mineral water" signature with groundwater having high electrical conductivity, alkalinity, chloride and carbon dioxide contents. This contrasts with significantly lower values for these parameters in groundwater from the southern end. It appears that this system responds to rainfall both in terms of hydraulic head and chemistry. After intense precipitation events, the southern body of the fresher water migrates north, pressurising the mineral water area. Increased discharge from the spring and a slight increase in water levels further indicates this pressurisation.There was a change in chemistry in the freshwater region associated with these changing water levels. Dilated joints and fractures that developed during unloading of the Ordovician sediments form conduits for the movement of water. Hydraulic gradient measurements suggest that the flow is not towards the topographical low of the stream or along the bedding as would be expected in most hydrological systems. Instead, it appears that the gradient is parallel to the stream and runs perpendicular to bedding. It is most likely that these dilated joints facilitate the movement of mineral water in this system. The flow system at Lithia Spring is responsive to rainfall events and therefore shows seasonal variation. It is characterised by two groundwaters of different chemistry, separated by a mixing zone. Mineral water is typical of the mineral water in the entire region of Daylesford and is probably recharged in the Great Dividing Range.The fresher water may reflect more local recharge processes and is likely to have a shorter residence time.

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GEOLOGICAL SOCIETY' OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

TRANSFER FAULT ZONES IN CONTINENTAL EXTENSION AND ITS IMPLICATION IN HYDROCARBON EXPLORATION:A REVIEW Pradipta Kumar Das and Nick Lemon NCPGG, Thebanon Campus, The University Of Adelaide, 5005 Pb- (08) 83034302, Fax- (08) 83034345

This paper reviews the current understanding of transfer fault development which is an important element of continental extension and the resulting extensional basins. Several examples of extensional basins from the literature e.g. the Viking Graben of North Sea, the Gulf of Suez, Lake Tanganyika, the Reconcavo Basin in Brazil and the Offshore Canning Basin of Australia are compared to show the typical structural styles of these transfer fault zones and their influence on the stratigraphy at various scales. Evidence of transfer zones from analogue clay and sand box modelling experiments are also presented. Transfer fault zones (accommodation zones) are important structural elements in allowing displacement changes from one rift segment to another. Sedimentary basins formed in the extensional stress regime will exhibit transfer fault zones at various scales. The fundamental unit of any extensional basin, a half-graben, may switch polarity across these transfer zones. Two half-grabens with opposing tilts in their hanging wall blocks may interfere along intra-basinal transfer fault zones. Strike-slip or oblique-slip movements are commonly induced along these transfer faults. The linking of the half-graben units along strike in an extensional basin interwoven with these transfer zones will determine the evolving topographic disposition during the initial evolutionary history of the basin.The transfer fault zones may continue to influence the basin evolution even into later stages also. They will thus constitute major controlling factors in the development of the drainage patterns and sediment transport direction and dispersal.The resultant stratigraphy in the basin is thus controlled by the location, quantity and nature of clastic sediments. Major inter-basin transfer zones may act as conduits for large rivers transporting sediments to the adjacent depo-centres. Small scale intra-basin transfer zones linking individual fault segments within a half-graben may control local sediment distribution and character of reservoir scale lithology.Transfer zones are generally sites of large scale accumulation of coarse clastic sediments whereas the border faulted margins in the down-thrown side are sediment starved bypass margins.These are preferential sites for carbonates or organic rich deposits. The hydrocarbon fields associated with such transfer zones in petroleum basins around the world demonstrate that they are sites of hydrocarbon accumulation. Careful study of these structural elements during basin analysis may contribute to the understanding of the syn-rift stratigraphy and help in predicting additional accumulations.

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GEOLOGICAL SOCIETY OF AUSTRALIA. ABSTRACTS No. 52 12th Victohcin Universities Geosciences Conference, Lci Trobe University, September 1998

REGOUTH MAPPING AND ITS IMPLICATIONS FOR LANDSCAPE EVOLUTION OF THE BEAUFORT 1:100 000 MAPSHEETAREA Vicki-Ann Dimas School of Earth Sciences, Tloe University of Melbourne, Parkville, Victoria 3052

The aim of this project is to map the regolith and geomorphology of the Beaufort 1:100 000 sheet area. This area provides an ideal opportunity to assess the regolith and geomorphological history of a representative section of the West Victorian Uplands with Palaeozoic bedrock, granitic rocks, a possible Mesozoic palaeosurface,Tertiary gravels. Newer Volcanics and Quaternary alluvial and colluvial deposits. This area is also ideal for studying and developing ideas about the relationship of granite composition, weathering and landform development. Detailed descriptions of Regolith Landform Units (RLU) as used in current AGSO field surveys are being carried out for the area. Extensive use of radiometric and magnetic data is helping define RLU boundaries which is supplemented by air photos, Landsat imagery and bedrock maps. Field mapping is being used together with laboratory methods, assumptions and hypotheses, particularly the relationships between landform characteristics of each RLU and the geology, regolith and soils. The nature of radiometric images make them particularly suitable in regolith study as ninety percent of gamma-rays emanate from the top 40cm and the technique effectively "sees through" the vegetation. Gamma-ray spectroscopy therefore measures the geochemical nature of the material at this depth. By recognising the elemental response and the relationship between bedrock and regolith, information including mineralogy and chemistry of the regolith can be gained. Further, it is possible to infer aspects of the nature of weathering from this. From the Late Devonian to the mid-Mesozoic there is evidence of tectonic stabilit)^ consequently erosion was dominant. By the middle of the Mesozoic, erosion had produced a landscape of low to gentle relief over most of southeastern Australia.The break-up of the Gondwana supercontinent began in the midCretaceous. This produced major subsidence in the Gippsland and Otway basins with major uplift of a broad belt fringing the coast. Regional uplift in the Late Cretaceous was then followed by rapid dissection during the Palaeocene when the present continental divide was established. A high rainfall and poorly vegetated environment gave rise to large volumes of coarse gravel, now termed the White Hills Gravel (WHG). Climate changes in the early Tertiary possibly halted this gravel deposition and slowed the rate of erosion. Deep weathering and soil formation followed. A radial drainage pattern, previously identified and centered on a possible domal uplift on Mount Buangor within the Mount Cole pluton, may instead be related to the weathering resistance of the granitic rocks.This weathering is controlled by a strong modal biotite percentage relationship with pluton sample elevation. Although there has been uplift, the domal nature of the Mount Buangor area may be best related to the felsic nature of the Mount Cole pluton and its subsequent resistance to weathering and erosion. The landform of the granitic rocks takes two different forms.The first is a positive relief pluton (eg. Mount Cole, Ben Nevis, Langhi Ghiran) which rise above their surrounding hornfels aureoles and Palaeozoic sedimentary^ rock.The second is a negative relief pluton (eg. Glenlogie, Eversley, Amphitheatre) which has a low relief and is surrounded by prominent hills representing the hornfels aureole of this pluton. Higher plagioclase and biotite contents in granites are more susceptible to weathering and erosion thus they form negative relief features. In contrast, positive relief features are characterised by lower plagioclase and biotite contents.Therefore plutons with positive and negative relief are a result of differential weathering of granites. The granitic areas of the Western Uplands of Victoria and their relationship to the regional landscape evolution is a particularly interesting study in resolving regolith features and the uplift history of the area. Little is known about the nature and extent of old landsurfaces and associated regolith within Victoria. Many of these surfaces are particularly well preserved as plateaus within granitic terrains and may provide valuable insights into the geological and landscape erosion of Beaufort.The plateaus are thought to be parts of a regional erosion surface which was uplifted to its present level in the late Mesozoic, following the breakup of the Gondwana supercontinent (Cayley & McDonald, 1997). In summary, the regolith mapping of Beaufort will help identify the landscape sequence which may be used to solve environmental problems such as soil erosion and salinisation in the local landscape. REFERENCE

Cayley, R.A. & McDonald, R.A. 1997. Beaufort 1:100 000 Geological Report. Geological Survey ofVictoria, Report 104. The 12^'-' VUGC is proudly sponsored by Rio Tinto

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GEOLOGICAL SOCIETl'OF AUSTRALIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, Lci Trobe University, September 1998 FLAKING PROPERTIES OF POLISH FLINT SAMPLES Mark Domanski School o/Eaith Sciences, La Trobe University, Biindoora. \7C 3083 Extensive mechanical testing of heated and unheated microcrystalline and macrocrystalline siliceous lithologies has defined the flaking properties of raw materials used in the manufacture of stone tools.The experimental studies have shown that fracture toughness is the most objective and important measure of the quality of raw materials shaped by either flaking or pecking/grinding. Lithic materials most amenable to blade manufacture and pressure flaking (obsidian) have low values of fracture toughness, whereas those shaped by pecking and grinding (greenstone) have very high values. Forty flint samples from various geological formations in South Australia (Gambier, Andamooka and Wilson Bluff Limestones), northwestern Queensland (Thorntonia Limestone) and central Poland were tested for compressive strength, modulus of elasticity, tensile strength and fracture toughness. The mechanical tests of the flint samples produced moderate median values of elastic modulus between 45000 and 63000 MPa, high median values of compressive strength between 470 and 1140 MPa, high median values of tensile strength between 48 and 105 MPa, moderate median values of fracture toughness between 49 and 83 MPa.mm-2, ^nd high rankings of uniformity Archaeological records show that the selected three flint types of central Poland have different Uthological properties and were used for different tool t^^pes and for different reduction sequences. Chocolate flint represents stone artefact materials used for the manufacture of blades (long narrow flakes with parallel margins) and micro-blades. Grey white-spotted flint represents raw materials used for the manufacture of blades, macro-blades (up to 30 cm long) as well poUshed axes shaped by flaking, grinding and polishing. Banded flint represents a lithology used for the manufacture of polished axes shaped by flaking, grinding and polishing. The mechanical tests of chocolate flint produced a relatively low median value of fracture toughness of about 53 MPa.mm-2.The tests demonstrated that the low fracture toughness and uniform microstructure of chocolate flint may explain its excellent flaking properties and preferential use for the manufacture of blades and microblades. Grey white-spotted flint displays median values of fracture toughness between 60 and 65 MPa.mm-2 and the highest rankings of uniformity. A slightly higher fracture toughness suggests that it requires more force to detach flakes from grey white-spotted flint than from chocolate flint. Its uniform microstructure and moderate fracture toughness values may help to explain its universal technological properties and widespread use for the manufacture of long blades and the production of polished axes by flaking, grinding and polishing. Of the Polish flint samples tested, banded flint displays the highest fracture toughness, between 67 and 83 Mpa.mm-2, and the lowest rankings of uniformity The high fracture toughness coupled with its nonuniform microstructure make the banded flint difficult to flake and less suitable for blade manufacture and shaping axe preforms. The high fracture toughness also makes banded flint more durable and less susceptible to breakage during heavy-duty activities. It may help to explain its mechanical superiority in heavy-duty use such as tree felling and may also help to explain its common use for the production of polished flint axes in the Neolithic period.

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GEOLOGICAL SOCIETl'OF AUSTIMLIA, ABSTRACTS No. 52 22th Victonaii Universities Geosciences Conference, La Trobe University, September 1998

REGIONAL GEOLOGY OF THE BALLARAT -AVOCAAREA - WITH REFERENCE TO THE AVOCA FAULT ZONE,VICTORLV Heath Doodie Deakin University

Lacated in central western Victoria, the Avoca Fault Zone is an area dominated by deep marine CambroOrdovician turbidite sequences. Consisting of unfossiliferous quartzose sandstone, shales and slate, the sediments are structurally controlled by a high angle westerly dipping reverse fault (Avoca Fault) which has resulted in repeated folding of the sediments at many localities. Generally striking NNW-SSE to N-S, the units exhibit structural features that are a result of wide-scale deformation and west to east cross shortening. These include, overturned units to the south of Avoca at Hamclough, Green Hill Creek and south of Lexton.These units dip to the east in the order of 70° and young to the west.These areas also contain north and south plunging folds at angles of 30-40°.There is generally only one cleavage visisble which tends to be discordant to the major bedding in the finer mudstone and shale units. A lineationis also present within the bedding planes which appears to be stretched carbonate spotting porphyryblasts.A highly weathered igneous dyke is also present south of Lexton. A model for the structures present within the western Avoca Fault Zone indicate that the high -angle nature of the Avoca Fault has resulted in movement of the sediments west to east and "ramping up" the fault, subsequently becoming overturned.

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GEOLOGICAL SOCIETY'OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998 THE BOTSWANA AND GAIRDNER DYKE SWARMS AND THEIR RELATIONSHIP TO SUPERCONTINENT BREAK-UP AS. Goldberg Depanment of Eanb Sciences, Monash University, Melbourne, Australia email: golciberg@eajth.monash.edii.au The Botswana dyke swarm is a massive array of dykes intruded into southern Africa during the initial stages of the breakup of Gondwana.The swarm is interpreted as a failed arm of a three-armed rift system. Similarily, the Gairdner dyke swarm of southern-central Australia is interpreted as a failed arm of a rift system which led to break-up of Rodinia. Botswana Dyke swarm- The Botswana dyke swarm (BDS) ~180Ma extends for over 1150km across Zimbabwe, Botswana, and Namibia. The strike of the dyke swarm is roughly N 110° (Reeves, 1979). The maximum width of the swarm is ~250km.The swarm can be subdivided into two bands across the swarm width. Maximum dyke density occurs in the main band, a 110km wide zone which narrows to 55km at the western end of the swarm (Hunter and Reid, 1987). South of the main band, dyke intrusion is less abundant and more widely spaced. Several spaced dykes, which may be related to the BDS, occur north of the main swarm. The main band exhibits two slight kinks northwards in orientation.The first occurs as the swarm leaves the Limpopo Belt.The second kink occurs as the swarm leaves the Magondi sub-province and enters the Damara Fold Belt and enters the Zimbabwe Craton. The southern zone of dykes displays a more constant change in orientation from roughly E-W at the triple point to ~N 294° at its western end. A regional stress field with a minimum compressive stress orientation of 020° may have been in existence at the time of the swarm intrusion. It is inferred that the magma source for the dykes lies at the triple point, because of fanning outwards of the swarm to the west, and pinching inwards of the swarm at the triple point.The initial estimates of crustal extension across the swarm are a minimum of 2% in the main band, and a minimum of 1.5% right across the swarm. It is inferred that the BDS is a failed arm of a rift system that resulted in the breakup of Gondwana.The two successful arms lie along the Lebombo and Sabi monoclines. Dyke intrusion in the form of the Lebombo swarm also occurred along the Lebombo monocline. Several dykes in southern Mozambique may be a continuation of the Sabi swarm.The triple point is located at the intersection of the eastern edge of the Kaapvaal craton, the Limpopo belt and the Mozambique Belt. Gairdner Dyke Swarm- The Late Proterozoic Gairdner Dyke Swarm (GDS) (827 Ma (Wingate et al., 1998)) in Australia that is associated with the breakup of Rodinia exhibits several similarities and differences to the BDS. Both swarms are inferred to be failed rift arms of triple junctions. However a main difference is the geometry of the swarms. While the swarms are of approximately the same length, the BDS has a well defined main band of dykes which is a fairly narrow, fanning slighly to the west.The GDS has a less well defined main band with diffuse bands either side.The GDS fans markedly. Both swarms cut straight through major lithological boundaries including cratons with no noticeable change in orientation, dyke abundance or amount of anastomosing in the swarms. However the GDS does exhibit a regional deflection near its source, and several dykes in the diffuse southern band in the BDS tend to change orientation along their length, with some marked deflection across the Ghanzi Ridge. Another major difference between the swarms is the presence of the Adelaide geosyncline sub-parallel to the GDS, which began to develop shortly after the intrusion of the GDS. The geosyncline developed as the Curnamoona craton rifted away from the Gawler craton. No geosyncline occurred sub-parallel to the Botswana Dyke Swarm.The Limpopo belt may have been stable enough to prevent the Zimbabwe craton rifting from the Kaapvaal craton. Gravity measurements in the region of the triple junction display well defined highs along the Lebombo and Sabi monoclines. A less intense high is developed along the Botswana Dyke Swarm. Gravity highs along rift arms may be due the upwelling of an axial megadyke as suggested by Gunn (1997).The less intense anomaly under the BDS also suggests rifting did not proceed far enough to produce the upwelling of a major axial dyke. REFERENCES Gunn, P.J. 1997. AGSO Journal of Australian Geology & Geophysics, 17(2), 115-131. Hunter, D. R. and Reid, D. L. 1987. Geological Association of Canada Special Paper 34, pp. 445-456. Reeves, C. V. 1978. Nature 273, 222-223. Wingate, M.T.D., Campbell, I.H., Compston,W. and Gibson, G.M. 1998. Precambrian Research 87, pp. 136-159.

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GEOLOGICAL SOCIETY'OF AUSTRALIA, ABSTRACTS No. 52 12th Victoncin Universities Geosciences Conference, Ui Trobe University, September

1998

ICHNOLOGYAND GEOLOGICAL SIGNIFICANCE OF THE MELBOURNE FORMATION AT STUDLEY PARK, MELBOURNE A. Grassy Department of Geology, Rusden Campus, Deakin Un iversity

Silurian sediments at Studley Park, Kew, Melbourne contain numerous trace fossils. The main objectives of the project are centred around the identification and description of the trace fossils which are in turn, very useful in environmental reconstruction. Ichnofossils, as they are otherwise known, have restricted geographic distribution due to their slow evolution and narrow adaptations to particular environmental conditions. Field work encompasses the completion of graphic logs, sketching, photographing and mapping the trace fossils in relation to the Park geology. A possible seven different groups of trace fossils have been preserved including; Chondites, Skolithos (worm burrows), Gordia, Diplocraterion, Planolites, grazing trails, shell casts and Helminthopsis. The interbedded sandstone and mudstone of Dight's Falls contain trace fossils whose normal habitats would be shallow coastline/sandy shore.These trace fossils would have been transported by high turbidity currents to a deep marine environment.

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GEOLOGICAL SOCIETY' OE AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

SEDIMENTOLOGYAND STRATIGRAPHY OF THE EARLY TRIASSIC REWAN GROUP, BOWEN BASIN P.V. Grech National Centre for Petroleum Geology & Geophysics University of Adelaide e-mail: pgrech@ncgpgg.adelaide.edii.an

This study of the Early Triassic Rewan Group in the Bowen Basin was an integrated approach using seismic stratigraphic principles with outcrop, wireline log, biostratigraphy and core data. It resulted in a coherent and useable stratigraphic framework that assisted in defining facies and potential reservoirs below seismic resolution within the Rewan Group. The Rewan Group consists of the Sagittarius Sandstone and Arcadia Formation. Depositional systems of the Sagittarius Sandstone and Arcadia Formation were affected by major tectonic and climatic changes. Each formation is marked at its base by a third-order sequence boundary. The Sagittarius Sandstone unconformably overlies the Late Permian Blackwater Group, the boundary being erosive and sharp, and overlain by a lag of extraformational poly-mictic rounded gravel and pebbles. On seismic sections valley incision and erosional truncation can be seen on the shallower western flank while in the deeper parts of the trough, the sequence is conformable. Westward prograding wedges recognized on seismic data at the base of the Sagittarius Sandstone are interpreted as the lowstand systems tract (LST) deposited in a fluvio-lacustrine environment. Grey to green fine-grained sediments are interpreted from cored sections to represent the transgressive systems tracts (TST) deposited in a lacustrine environment, with flat laminated grey clay being deposited during maximum flooding. Acritarchs, conchastracans and lingula also mark this event. The highstand systems tract (HST) displays an overall upward-sanding pattern on wireline logs, suggestive of regressive sedimentation. The base of the overlying Arcadia Formation is marked by the Brumby Sandstone Member. The medium to coarse-grained quartz-rich Brumby Sandstone Member is interpreted as a fluvial dominated shoreface unit deposited during a forced regression. The Arcadia Formation is a thick unit of fine-grained, volcanolithic sediments that often form red-beds interpreted as interfluvial palaeosols and lenticular channel sands. It forms the TST and the HST of the second depositional unit, of which the Brumby Sandstone Member is the lowstand. Most of the sediments were deposited in a fluvial environment, with only the sand to shale ratio defining the separate tracts. Lacustrine facies are rare. High-frequency channelfill make up the uppermost section of the HST. The Arcadia Formation is in turn erosively overlain by pebbly sandstone of the Clematis Group. The Rewan Group has been largely ignored by explorers as a prospective stratigraphic unit because sand bodies are generally beyond seismic resolution and difficult to correlate. This study has provided a method for defining the stratigraphy of sand bodies within the Rewan Group based on an integrated approach using seismic, outcrop, wireline and core data, allowing mapping of possible reservoir and seal distribution across the Bowen Basin. Sandstone-filled incised valleys at the base of the Sagittarius Sandstone and in the upper Arcadia Formation offer the best reservoir potential in the Rewan Group. Good reservoir potential also exists within the fluvial and shoreface facies of the Brumby Sandstone Member. The sequence stratigraphic approach adopted by this study does not only provide a basis for identifying possible traps in existing fields but more importantly a framework to extrapolate the interpretation presented here to previously unexplored areas of the Bowen Basin.

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GEOLOGICAL SOCIETY' OF AUSTRALIA, ABSTRACTS No. 52 12th Victonan Universities Geosciences Conference, La Trobe University, September 1998

THE SIGNIFICANCE OF YOUNGER THERMAL EVENTS IN THE WILLYAMA INLIERS: USING 40AR-39AR THERMOCHRONOLOGY Michael J. Haitleyl David A. Foster^, David R. Gray^ Australian Geodynamic Cooperative Research Centre ^School o/Eanh Sciences, La Trobe University, Bundoora, Victoria 3083, Australia ^Depaitment of Eanh Sciences, Monash University, Clayton, Victoria 3168, Australia

The Broken Hill, Clary and Mount Painter Block (Willyama Inliers) are the main Precambrian basement inliers that outcrop extensively in western New South Wales and South Australia, and form part of the north/northeastern margin of the Adelaide Fold Belt. These terrains, comprised of Palaeo to Mesoproterozoic metasedimentary and metaigneous rocks (Willyama Group), have experienced several orogenic events that have resulted in a complex structural and metamorphic history The presence of younger tectonic events in the Broken Hill Block have been recognised from ^OAr/^'^Ar thermochronology Apparent muscovite ages constrain a pattern of broadly Grenvillian (Musgravian) resetting of the basement in the northern part of the Broken Hill Block (Poolamacca Inlier) with temperatures reaching the order of -350°C. The samples, although limited, begin to show the tectonic influences of younger thermal overprints, the effects of which may be spread over the entire inlier. Willyama Group rocks of the Broken Hill, Olary and Mount Painter Block exhibit some similarities that enable them to be correlated, lithologically structurally and metamorphically These terrains underwent peak metamorphism between -1700 and l600Ma and reached metamorphic grades of upper amphibolite to granulite facies (Willis et al, 1983). Collectively, the Willyama inliers form part of an extensive intracratonic basin complex that remained active until the late Proterozoic (Grenvillian), triggering the commencement of deposition of an unconformably overlying thick succession of terrestrial and shallow marine rocks known as the Adelaidean Supergroup. Believed to be part of a single intracratonic basin, significant variation in relief of fault blocks was sufficient enough to produce isolated regions of outstanding relief (Broken Hill, Olary and Mount Painter Blocks) which were the primary sources for localised Adelaidean sedimentation from -llOOMa (Preiss, 1981; Stevens, 1986). Following basin infill, the Adelaidean cover underwent widespread deformation at low grade (subgreenschist facies) during the Delamerian Orogeny (~500Ma). Although not pervasive throughout the cover sequence, zones of polydeformation are prevalent along and proximal to basement/cover interfaces (for example, Poolamacca Inlier). The preservation of polydeformation within the Adelaidean implies that the Delamerian Orogeny may not be confined to a single phase tectonic event as previously thought for this area. Apparently restricted to the Adelaidean cover sequence, the Delamerian Orogeny also affected Willyama basement rocks. Folding of pegmatites and the development of an overprinting (latest?) fabric within the basement show very similar orientations to the north-south folds of the cover sequence, suggesting that the cover and basement structures developed synchronously, during the Delamerian. One hypothesis may imply that initial Delamerian deformation was most likely confined to displacement along zones of weakness (for example basement/cover contacts and/or shears) until attainment of sufficient shortening achieved gentle buckling and minor reverse faulting of the Adelaidean cover. However, results suggest that folding of the basement preceded the shearing event. Final cooling of the basement due to early Delamerian(?) folding is recorded at ~550Ma at -350°C with shearing occurring at ~500Ma with an estimated temperature of -280°C. Further reactivation of the shear zones occurred at 280Ma coinciding with the Alice Springs Orogeny Furthermore, folding of the thin Adelaidean strata over the Willyama Inliers is also believed to be attributed to the renewed movement of ancient shear zones within the Willyama Complex (Marjoribanks et al, 1980). The main aim of this study is to analyse muscovite, K-feldspar and whole rock chips by the ^OAr/^^Ar dating method (in progress) to elucidate the late temperature-time history and tectonics of the Broken Hill, Olary and Mount Painter Blocks by targeting shear zones and the geology that abounds them. Previous results, in particularly around the central to southern portion of the Broken Hill Block, revealed through 40Ar/39Ar thermochronology, have shown that the basement was effected by a single tectonic "pulse" at 520±40Ma with temperatures in the order of -350°C (Harrison and McDougall, 1981), after the high grade metamorphic event at 1590±10Ma. Contrary to previous results, current results show that at least the northern part of the Broken Hill (i.e. Poolamacca Inlier) terrain has recorded several events post-dating the high grade metamorphism.

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GEOLOGICAL SOCIETY' OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference. Lci Trobe University. September 1998

Unlike previous work, where sample coverage was limited, this project has focused on systematically sampUng along 3 separate traverses in the Broken Hill region, which include the 1996 AGSO seismic traverse, Wendelpa traverse (north-central portion of the inlier) and the Poolamacca Inlier traverse (northern most part of the block "proper"), an area which shows interesting basement/cover relationships. Similar sampling strategies have also been accomplished in the Olary and Mount Painter Blocks in an attempt to determine the extent of the younger thermal events affecting the basement. The new results will be integrated with previous geochronological and thermochronological data to focus on the nature, origin and significance of the younger tectonothermal events active in the Broken Hill, Olary and Mount Painter Blocks. Constraints on the timing and patterns of deformation may have implications for metallogenesis in the Willyama Inliers and contribute to a broader understanding of the Adelaide Fold Belt. REFERENCES: Harrison T.M. & McDougall 1.1981. Excess ^^Ar in metamorphic rocks from Broken Hill, New South Wales: implications for

age spectra and the thermal history of the region. Earth and Planetary Science Letters 55, 123-149.

Marjoribanks R.W., Rutland R.W.R., Glen R.A. & Laing W.R 1980. The Structure and Tectonic Evolution of the Broken Hill Region,Australia. Precambrian Research 13,209-240. Preiss W.V. & Forbes E.G. 1981. Stratigraphy Correlation and Sedimentary History of Adelaidean (Late Proterozoic) Basins in Australia. Precambrian Research 15,255-304. Stevens B.P.J. 1986. Post-depositional history of the Willyama Supergroup in the Broken Hill Block, NSW. Australian Journal of Earth Sciences 33,73-98. Willis I.L., Brown R.E., Stroud W.J. & Stevens B.P.J. 1983. The Early Proterozoic WUlyama Supergroup: stratigraphic subdivision and interpretation of high to low-grade metamorphic rocks in the broken Hill Block, New South Wales. Journal of the Geological Society of Australia 30,195-224.

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GEOLOGICAL SOCIEW OF AUSTIMLIA, ABSTIMCTS No. 52 12th Victoncm Universities Geosciences Conference, La Trobe University, September 1998

BIOCHEMICAL AND GEOBOTANICAL ASSOCIATIONS WITH REGOLITHATTHE THACKARINGA SERPENTINITE,WEST OF BROKEN HILL, N.S.W LJ. Hill Depaitment of Geography and Environmental Studies, Tide University of Melbourne, Parkville, Victoria, 3052.

Vegetation and regolith cover large parts of the Australian landscape while exposures of bedrock are often less prominent. The surface expression and chemical signatures of covered bedrock are therefore reliant upon an understanding of the chemical dispersion pathways for specific elements through biological processes and within the regolith. The anomalous chemistry of serpentinites provides an opportunity to examine the vegetation and regolith expression of this bedrock type in surficial environments, such as at Thackaringa near Broken Hill. The Thackaringa Serpentinite is situated 36 km WSW of Broken Hill in the Barrier Range of western New South Wales. The geology of the study area (approximately 5km2) features two masses of serpentinite surrounded by schists and pegmatites of the Proterozoic,Willyama Supergroup. The bedrock in the area is mostly fresh to moderately weathered where it crops out, although over half of the area is highly weathered with areas of alluvial, colluvial and aeolian derived regolith. The areas of serpentinite bedrock form distinct hills, with valley systems extending eastwards from the Mundi Mundi faultline escarpment mostly incised into the surrounding schists. The recording of geobotanical associations, and regolith and plant leaf sampling programs were undertaken in the area to test for the geobotanical and biogeochemical associations with the Thackaringa serpentinite and its associated regolith. One hundred regolith samples (53 from areas with serpentinite bedrock and 47 from the surrounding area) and 30 leaf samples were analysed for Ca, Mg, K, Na, Cu, Mn, Fe, Zn, Pb and Ni using an Atomic Absorption Spectrometer. Environmental site characteristics and vegetation quadrat surveys were recorded for each sampling site, along with a record of GPS position. The regolith overlying the serpentinite bedrock showed much higher Fe (almost two times) and magnesium (five times) contents, but lower Na, K and Mn contents than adjacent areas. This is consistent with analyses of serpentinite-derived regolith from other parts of the world, suggesting a strong bedrock control on regolith chemistry here. Landscape controls could also be contributing factors here with highly soluble elements such as Na, K and Mn accumulating in the adjacent valley systems. Surprisingly however, exchangeable metals such as Cu, Ni, Zn, and Pb are at similar or slightly lower concentrations in the regolith overlying the serpentinite compared to adjacent areas. An important feature of the comparisons of the regolith chemistry for the two lithologies is that although exchangeable Ca concentrations are higher in the regolith overlying the serpentinite, the Ca:Mg is much lower (1.6 compared to 2.9 for adjacent regolith). This has implications for the nutrient status of the vegetation in these areas as a high Ca:Mg reduces the toxicity of other elements, and also accounts for the abundance of the secondary mineral magnesite in preference to calcite in the regohth overlying the serpentinite. The difference between the vegetation communities on the two substrates clearly reflects the differences in the regolith resulting in striking geobotanical anomalies. The main vegetation community in the adjacent area is open Acacia aneura (mulga) / Heterodendrwn oleifolium (rosewood) woodland with low-lying shrubs dominated by Bassia spp. (copperburrs). Casuarina cristata sp. pauper (belah) and Eucalyptus gillii (curly mallee) are restricted to the serpentinite areas with mulga and rosewood absent. The leaf chemistry of the curly mallee and the belah show a high Ca:Mg (4.273 and 3.012 respectively) despite the low quotient for the underlying regolith. The leaves of the belah also contain far lower levels of Fe, Cu and Pb in relation to the curly mallee and vegetation in non-serpentine areas. Although Maireana pyramidata (black bluebush) and Solatium ellipticum (velvet potato-bush) are located on both substrates, their leaf chemistry varies according to the underlying regolith chemistry. Individuals overlying the serpentinite feature lower Fe, Ca and Mg contents, higher Ca:Mg, and higher K contents. Both species also express levels of metal accumulation and exclusion in serpentine areas, with higher levels of Ni and Pb and lower levels of Cu in leaf tissue of the velvet potato-bush, but lower levels of Ni and far higher levels of Cu in the black bluebush leaf tissue. The absence of mulga and rosewood, and the presence of belah and curly mallee are therefore good geobotanical indicators of regolith with serpentinite bedrock in this area. The vegetation in the area exhibits an ability to process and differentiate certain chemical elements by accumulation and exclusion. The occurrence of metal species such as Ni, Pb and Cu appear to be controlled by biogeochemical processes. This has major implications for geochemical cycling and dispersion pathways in surface and near surface environments, and could be of value to geochemical sampling surveys in regional mineral exploration programs. The 12^'^ VUGC is proudly sponsored by Rio Tinto

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GEOLOGICAL SOCIET\' OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

EARLY PERMIAN BRACHIOPODS OF THE CANARVON BASIN, WESTERN AUSTRALIA Tanya Hogeboom Deakin University

The Canarvon Basin is one of several sedimentary basins which can be found in Western Australia that contain Permian sediments that are highly fossiliferous. Within this basinare four sub-basins in which two, the Merlinleigh and the Byro, contain the same Early Permian stratigraphy It was within these sub-basins that the brachiopod specimens were collected. The formations in which the brachiopods were collected are known as the Callytharra Formation and the Billidee Formation. The Billidee Formation is a part of the Wooramel Group. Within the Billidee Formation is a small subdivision known as the Jimba Jimba calcarenite which has a striking resemblence to the Callytharra Formation which is also calcarenite. Much debate in the past has been whether the Jimba Jimba is actually a part of the Callttharra Formation or of it wat a separate environment within the Wooramel Formation. The brachiopods collected indicate the formations are Early Permian ranging from Late Samarian (Sterlitamakian) to Early Artinskian (Artastinian) and indicate the environemnt to be subtemperate to temperate within a shallow to medium depth marine.

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GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 52 12th Victomin Universities Geosciences Conference, Lci Trohe University, September 1998

METAMORPHISM AND STABLE ISOTOPES OF THE DANBA DOMAL METAMORPHIC TERRAIN, SICHUAN PROVINCE, WEST CHINA M. H. Huang and 1. S. Buick Depanment ofEanh Sciences, La Trobe University, Bundoora, Vic. 5085, Australia

In the east of the Songpan-Garze Orogenic Belt, the Danba domal metamorphic terrain (DDMT) crops out among the regional low-grade Triassic flysch sediments and consists of Mesoproterozoic basement migmatites; Neoproterozoic-Triassic covering metasediments and syntectonic granites. Isograds have defined within the DDMT based on the distribution of index minerals, namely biotite, garnet, staurolite, kyanite and sillimanite and cordierite. The metamorphic isograds, although concentric around the domes, form a asymmetric outcrop pattern, with the highest grade sillimanite (-corderite) zone in the north. In metapelitic mineral assemblages, three metamorphic phases have been distinguished: (1) conditions up to amphibolite facies grade at moderate pressures (Grt+St+Rut+Ilm+Ky+Mu+Qtz) characterize the Ml phase, as a result of the Indonesian-Yanshanian N-S shortening (Dl) marked by the E-W isoclinal folding and top-to-south detachment; (2) pressure release and/or temperature increase due to the Himalayan E-W compression and the formation of the gneiss domes (D2) in the Danba area, as shown by N-S directed fibrolite, and migmatized granite cores and syntectonic intrusives, define the M2 phase; and (3) finally during uplift of the DDMT, a minor retrogressive M3 phase is characterised by the overprint of low temperature assemblage Qtz-i-Ser+Chl. This generation of minerals grew preferably in the NW fault and shear zones and variably developed SE-NW crenulation cleavages during the regional shearing and compression (D3-D4) in the Songpan-Garze Orogenic Belt. P-T conditions were estimated on the metapelites and amphibolites from the different zones using the geothermobarometers and thermodynamic data set and updated THERMOCALC computer program. Temperatures of 530-560°C and pressures of 6-6.5 kbars were calculated for the garnet zone, 570-590°C and 6.5-7.5 kbars for the staurolite zone, and 580-6l0°C and 6.5-7.9 kbars for the kyanite zone, while the peak conditions of the sillimanite zone are estimated at 600-640°C and 4-5 kbars. Pressure calculations on metapelites containing kyanite and sillimanite suggest a decrease in pressure from the Ml to M2 ( - 7 to 3-5 kbars), as corroborated by fibrolite replacing kyanite, staurolite and garnet. In light of the metamorophic texture reactions in metapelites, a petrogenetic grid for the sillimanite zone was constructed in the KFMASH system. It is most likely that the cordierite-bearing assemblages maintained peak metamorphism at temperatures of > 650°C and pressures of ca. 3 kbars.The results in conjuction with the retrogression temperatures of 250-350°C suggest a clockwise P-T path. Strong evidence for the infiltration of hydrous fluid into the marble and calcsiliocate rocks is provided by the occurrence of modally abundant hydrous minerals in rocks with hydrate-free peak minerals. For example, retrograde tremolite formed around the prograde clinopyroxene and amphibole. Similarly, clinozoisite forms a major part of the retrograde breakdown products of some calcsilicate rocks.The XCO2 of peak metamorphic fluids is estimated at <0.10, 0.07 and 0.04-0.2 for staurolite, kyanite and sillimanite zones, respectively. Retrograde assemblages consistently record fluid compositions of XCO2 <0.06, with the staurolite zone having the lowest values of <0.02. It seems that fluids became more and more water-rich with decreasing temperature and pressure. A detailed oxygen and carbon isotope study has been carried out on the major rock types in order to examine fluid flow during the metamorphic events. Quartzites and gneisses show relatively homogeneous and low S^^O values (+I6.6 to 18.4 and +l4.2-l4.6%o, respectively), whereas metapelites vary in b^^O systematically, rising from +11.9%o in the sillimanite zone to +15.8%o in the lowest grade chlorite-sericite zone, as expected from the devolatilatization of the pelites. Around the granitic basement migmatized metapelites and gneisses have been strongly S^^O depleted (+7.9-9.2%o), which is very close to the basement migmatite S^^O values of ca.+8.3%o. The two kinds of marbles (calcite and dolomite) that occur in the Danba area show similar isotope signatures. Apart from the thin (few cm) bands in which oxygen isotopes were homogenized, approaching the bulk 51^0 values of +12-l4%o of surrounding metasediments, individual marble layers have 20-80 cm thick calcsilicate zones which are well developed on both sides.The b^^O values of calcite or/and dolomite across the marble layer increase steeply from marginal values of +12-13%o to cores values (of +20-22%() for The 12^'^ VUGC is proudly sponsored by Rio Tinto

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GEOLOGICAL SOClET\'OF AUSTRALIA. ABSTRACTS No. 52 12tb Victorian Universities Geosciences Conference, Lci Trohe University, September 1998

calcite marbles and ca.+30%o for dolomites). The h^^C values display a similar change, but heterogeneous from layer to layer ranging from 11 to -4%o.The lack of covariation between percentage and 5i«0 values and percentage and values of carbonates indicates most of the rocks may not have been greatly affected by decarbonation during metamorphism.The development of boundary zones is interpreted to result from the infiltration of fluids probably channelled along the contacts.These fluids were derived from dehydration of graphite-bearing pelites during prograde Ml phase. Tremolite vein networks (2 mm to 5 cm thick) were observed in the Neoproterozoic dolomites in the sillimanite zone, crosscutting the layers and prograde assemblages. The isotopic compositions of calcite from the veins are +7.7%o for 5 i « 0 , and + 1 . 4 4 % o for which are similar to those of the contiguous unaltered pure dolomites.The oxygen isotope is in the range of migmatites, migmatized metasediments and pegmatites. The alteration associated veins result from peak to post-peak infiltration of very water-rich fluids that drive decarbonation reactions.These fluids were most probably produced from the crystallizing partial melts formed during the prograde M2 metamorphism and migmatization.They are thought to have 5180 < +7%o and 8i3C of 0%o.

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GEOLOGICAL SOCIETY'OF AUSTRALIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, Lci Trobe University, September 1998

PETRO-ACOUSTICS OF COOPER BASIN SANDSTONES Abbas Kbaksar •National Centre for Petroleum Geology and Geophysics, Thebanon Campus, University of Adelaide, South Australia, email: akhaksar<Wncpgg.adelaide.edu.au

To date more than half of the proven and probable estimated conventional gas has been exploited from the sandstone reservoirs in the Cooper Basin. Hydrocarbon production causes changes in dynamic reservoir properties such as pressure and fluid saturation. Knowledge of the magnitude of such variations is essential for the exploration of unaccessed reserves and the optimising of the performance of existing fields. A petro-acoustic study was carried out to investigate the influence of effective pressure and fluid saturation on the compressional and shear wave velocities on a set of representative samples from gas producing fields in the Cooper Basin. The suite of samples consists of 22 sandstones from 1917m to 2564m depth with porosity ranging from 2.6% to 16.5%. A reflection technique was used to measure the ultrasonic wave velocities in dry and water saturated cores under effective pressures of 5 MPa to 60 MPa. Both Vp and Vs in the Cooper Basin sandstones increase non-linearly with effective pressure with the pressure influence being stronger below 40 MPa. The increase of velocity with effective pressure is due to the closure of crack-like pores which hardly affects the porosity but significantly increases the bulk and shear moduli of the samples. For water saturated rocks the finite modulus of the water increases the bulk modulus of the rock and resists the closures of cracks. Vp in dry samples shows the greatest stress sensitivity whilst there is no significant difference between the pressure dependency of Vs in dry and water saturated samples. The stress sensitivity of the Cooper Basin rocks appears to be large when compared with data in the literature. A 10 MPa increase in the in situ effective pressure causes up to 12% increase in the wave velocities in the studied samples. A wire-line sonic log could detect such a change of velocity with effective pressure. At 2500 m depth in the study area, a gas producing reservoir may show effective pressure of ranging from 28 MPa (non-depleted) to 50 MPa (highly depleted). There are examples of apparent low sonic porosities in partially pressure depleted gas fields in the southern Cooper Basin. Combining field data with the results of laboratory acoustic measurements confirms that the velocity anomaly due to higher effective stress causes the sonic log to read too low in pressure depleted reservoirs. Neglecting this pressure effect results in anomalously low sonic porosities if the porosity is calculated by conventional sonic porosity methods.A mechanism is proposed to calibrate the sonic tool response to the reservoir pressure variations for the Cooper Basin rocks. The strong stress sensitivity and the distinct Vp/Vs values for dry and water saturated Cooper Basin cores suggest that the dynamic changes in pressure and saturation of the reservoir rocks may also be detectable from other field velocity data such as VSP and time-laps seismic (4D) surveys. This study also has implications for direct hydrocarbon detection techniques and seismic reservoir characterisation in the Cooper Basin and similar regions.

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GEOLOGICAL SOCIETY OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

EVALUATION OF SEAL EFFECTIVENESS IN CAP ROCKS AND FAULTS: A REVIEW Tom Kivior National Centre for Petroleum Geology^ and Geophysics Thebanon Campus, University of Adelaide,

Top seals and fault seals are significant geological components of traps in petroleum systems. Whether a lithology or fault seals or not depends on the interaction between the capillary pressure of the seal lithology and the buoyancy pressure of the upward moving hydrocarbons acting on the brine. The three main aspects to an effective top seal are capacity, integrity and geometry Seal capacity depends on the capillary pressure vs. buoyancy pressure, lithology and ultimately determines the column height a seal can hold. Seal integrity can be directly related to the ductility of the sealing lithology as well as the possibility of seal breach by micro fracturing. Lateral extent and thickness are important factors of seal geometry, which is a major control on the effectiveness of regional seals. Understanding the properties of a fault plane and rocks juxtaposed by faulting is a seal capacity issue. Sealing properties examined when studying top seals are also applicable to fault related seals. The main factors controlling fault related seals are the fault zone properties and the lithology of the units juxtaposed by faulting. However over geological time, a fault plane is only completely sealing to lateral hydrocarbon flow under certain conditions such as clay smear and juxtaposition of sealing hthologies.

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GEOLOGICAL SOCIETY' OF AUSTRALIA, ABSTRACTS No. 52 12th Victoiicin Universities Geosciences Conference, La Trohe University, September 1998

TITLE: KIMBERUTIC INTRUSION OF THE MERLIN PLATEAU Ben MacGregor Deakin University, Riisden Campus.

Overview: Located approximately 800 kilometers south of Darwin (Boomerang Creek), the diamond bearing Merlin Plateau, occupies an area adjacent to the massive McArthur River Zn-Cu deposit and within the Batten trough region and stands to be one of the richest economic deposits of its kind in Australia. Overlying Proterozoic bedrock (Proterozoic consisting of the Tawallah, McArthur, Nathan and Roper Groups) the Plateau exposure is dominated by Cambrian Bukulara Sandstone. Secondary siliceous and bioturbated units crop out overlying the Cambrian sequences. There is however significant debate over the age of theses secondary units. The secondary units play major host to the Kimberlitic intrusives which signifies the economic importance in their clarification. Placement of the Kimberlites: The McArthur River District lies on the Eastern margin of a Northwest trending belt of Middle Proterozoic sediments deposited as a result of the formation of an intracratonic rift basin. Rifting/stretching of the plates, subsequent thinning of the crust and refinement of mantle processes resulted in the intrusion of magmatic/basaltic/ kimberlitic bodies through fissures/fractures. The intrusives seem to have been placed post depostionally or contemporaneously to the before mentioned secondary units. The lack of a clearly defined metamorphic aureole is suggestive to a cool entr}^, supported by secondary brecciated/conglomeratic unit directly overlying the diamond bearing clay. This contact breccia is comparative to the Argyle and Ellendale Lampriorite systems.

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GEOLOGICAL SOCIETY' OF AUSTRAUA^ ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

EXHALATIVE CARBONATE-BARITE-SULPHIDE MINERALIZATION IN THE DEVONIAN REEF COMPLEXES OF THE CANNING BASIN, WA Rebecca Mason and Nicole De Kever School of Eanh Sciences University of Melbourne

Mississippi Valley-type Zn-Pb deposits are present throughout the Upper Devonian reef complexes of the Lennard Shelf.The Goongewa, Kapok and Pillara Zn deposits are now being mined, while the Cadjebut deposit was previously worked (Tompkins et al., 1994). Less well known is the exhalative carbonate-baritesulphide mineralization which is associated with Frasnian basinal carbonates (Gogo Formation). Mounds and mound complexes consisting of carbonates with abundant barite and sulphides (mainly FeS, ± ZnS and PbS) are commonly present around the margins of inter-reef basins on the south-eastern portion of the Lennard Shelf. Stratigraphically, the mound complexes occur near the contact between the Gogo Formation and the overlying Virgin Hills Formation and generally occur in close proximity to (or on) Pillara Formation platformal carbonates. Individual carbonate mounds are several meters in diameter and display a stromatolitic fabric in outcrop. In detail, the carbonate and barite has a radiating crystalline texture and shows no clear microbial fabrics (e.g. filaments). Stromatolitic and dendritic textures are also well developed in iron sulphides. The general order of precipitation within the mounds is, from oldest to youngest, 1. calcite, 2. barite, and 3. sulphides, although there is considerable overlap in the timing of these phases. All of the phases have been precipitated in the synsedimentary or early diagenetic environment and are commonly overgrown by early marine calcite cements.This indicates that the mineralized mounds were either precipitated on the sea floor, or close to the sediment/water interface. This also suggests that the mineralized mounds are not directly related to regional Mississippi Valley-type Zn-Pb mineralization, which occurred during the early Carboniferous (350 Ma, McManus and Wallace, 1992) when the Upper Devonian reefs were buried to some considerable depth (perhaps 1 km or more). The mineralized mounds may represent paleo-vent sites where diagenetic fluids have exhaled onto the Devonian sea floor. Submarine hydrocarbon or methane seeps found in modern oceans may be good analogues for these Devonian mounds. References McManus, A., & Wallace, M.W., 1992, Age of Mississippi Valley-Type sulfides determined using cadiodoluminescence cement stratigraphy, Lennard Shelf, Canning Basin, Western Australia.: Economic Geology, v. 87, p. 189-193. Tompkins, L.A., M.J. Rayner, D. I. Groves, and M.T. Roche, 1994, Evaporites; in situ sulfur source for rhythmically banded ore in the Cadjebut mississippi valley-type Zn-Pb deposit, Western Australia: Economic Geology^ , v. 89, p. 467-492.

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GEOLOGICAL SOCIEW OF AUSTIMLIA, ABSTRACTS No. 32 12th Victohan Universities Geosciences Conference, La Trohe University, September 1998 THE TECTONIC EVOLUTION OF THE OMAN MARGIN - NEW INSIGHTS FROM STRUCTURAL AND 40AR /39AR AGE DATA J. McL. Miller^, R. T Gregoiy^, D. R. Grciy^ and D. A. Foster^ ^ Dept. ofEanh Sciences, Monash University, Clayton, 3168 ^ Dept. of Geological Sciences, S. M. U. Dallas, U.S.A., 25275 Dept. ofEanh Sciences, La Trobe University, Bundoora, 3083 Continental crustal rocks, now structurally beneath the Samail ophiolite, underwent blueschist to eclogite facies metamorphism prior to the emplacement of the ophiolite onto the Arabian margin. These rocks now occur as stacked fold-nappes within a less deformed upper plate and a strong-to-intensely deformed lower plate separated by a major, ductile, crustal discontinuity. The lower plate rocks have higher grade metamorphic assemblages that locally reach eclogite facies. 4<>Ar/39Ar ages on high pressure fabric elements in the lower-plate range from 131 Ma to 82 Ma. The majority of these ages are inferred to represent cooling by the progressive emplacement of colder units during convergent margin tectonism, prior to emplacement to higher structural levels. Some of the ages are older than the crystaUisation of the Samail Ophiolite ( - 9 5 Ma,Tilton et al. 1981). ^OAr/^^^Ar correlation plots for the older ages provide good fits with ^OAr-^^Ar ratios close to atmospheric and excess argon does not appear to be present. 4()Ar/39Ar age data supports a two stage exhumation process for the high-pressure rocks. In the lower plate, 82-79 Ma 40Ar/39Ar ages are associated with lower grade assemblages defining both transposition fabrics and C-type shear bands which have overprinted the high-P assemblages during intense NE-directed shearing. Partial exhumation of these lower plate sequences resulted in the formation of regional sheathlike closures that are truncated by the structural break separating the two plates. This is in contrast to carpholite-bearing upper plate rocks that have been folded into large recumbent nappe structures which exhibit a marked increase in deformation intensity towards the boundary with the lower-plate. Biostratigraphic data suggests the allochthonous ophiolite and sediments overlying the high-P rocks were emplaced between 80 and 75 Ma (Warbuton et al. 1990). 40Ar/39Ar crystallisation ages on lawsonite schists suggest high-P metamorphism in the upper-plate occurred at - 8 0 Ma (El-Shazly and Lanphere 1992). The lower plate ^OAr/^^Ar cooling(?) ages related to exhumation of the lower-plate sequences overlap with these age constraints. Hence, emplacement of the lower-plate units to shallower crustal levels may have occurred prior to, or synchronously with, high-P metamorphism of upper-plate units, and also with the emplacement of the allochthonous units overlying the continental rocks. Juxtaposition of the two plates is constrained by 76 Ma to 70 Ma crystallisation ages on mica from axial surface fabrics to upper-plate fold nappes. These nappes formed during the exhumation of the upper-plate units and their northeast-directed transport over the higher grade lower plate units. The younger mica crystallisation ages are very close to the deposition age of Maastrichtian units that unconformably overly all of the sequences ( - 6 8 Ma). This suggests the upper-plate nappe forming event may have been synchronous with the south-directed movement of the overlying ophiolite, and structurally higher low angle normal faulting and/ or rapid erosion of the nappe pile. REFERENCES

EL-SHAZLY, A. K. & LANPHERE, M. A. 1992. Two high pressure Metamorphic events in NE Oman: evidence from 40Ar/39Ar dating and petroiogical data.The Journal of Geology 100, 731-751. TILTON, G.R., HOPSON C. A. & WRIGHT, J. E. 1981. Uranium-lead isotopic ages of the Semail OPhiolite, Oman, with applications toTethyan ridge tectonics. Journal of Geophysical research, 86, 2763-2775. WARBUTON, J., BURNHILL,T J., GRAHAM, R. H. & ISAAC, K. P 1990. The evolution of the Oman Mountains Foreland basin . In: ROBERTSON, A. H., SEARLE, M. P, & RIES,A. C. (eds).The Geology and Tectonics of the Oman Region. Geological Society of London Special Publication 49,419-427.

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GEOLOGICAL SOCIETY' OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, Ui Trohe University, September 1998

THE FORMATION OF ALBITE VEINS DURING EXHUMATION OF HIGH-PRESSURE TERRANES Jodie A. Miller Depanment of Eaitb Sciences and VIEPS, Monash University, Melbourne, Australia

Albite veins are a common feature of high-pressure terrains but the processes by which they form are not clear.The veins are generally thought to reflect the presence of fluids during exhumation of the rocks. Hov^ever, the source of this fluid is problematic given that high-pressure rocks have normally been substantially dehydrated during subduction. It is also unclear what influences the precipitation of albite in veins under high-pressure conditions. Here, we put forward some ideas about the formation of albite veins in two high-pressure complexes, the Alpine Corsica, France and the Zermatt-Saas ophiolite zone, Switzerland. Alpine Corsica (France) and the Zermatt-Saas ophiolite (Switzerland) are part of the Pennine zone of the internal units of the Alpine chain. Both areas comprise ophiolitic and sedimentary material that have undergone high-pressure metamorphism during the Alpine orogeny to produce lawsonite-blueschist, blueschist, and eclogite facies mineralogies. On Corsica two high grade metamorphic episodes have been identified: 1) early eclogite facies metamorphism (1.2 GPa, 530°C); and 2) pervasive blueschist facies metamorphism (0.7-0.9 GPa, 4 0 0 X ) . In the Zermatt-Saas ophiolite, the highest grade metamorphic event reached 1 . 7 - 2 . 0 GPa and 500 - 600 at 50-70 Ma producing eclogitic mineral assemblages and other cofacial parageneses. On Corsica and around Zermatt-Saas, a late stage greenschist facies overprint that is often spatially related to the distribution of albite veins occurred at 0.5 GPa, 450°C and 0.8 GPa, 450 °C respectively. Albite veins from Alpine Corsica typically occur in blueschist facies metabasalts composed of lawsonite, omphacite, garnet, albite glaucophane and clinozoisite.The rocks are locally retrogressed around laterally discordant, near-monomineralic coarse-grained albite veins that may reach 20 cm in width. All the albite veins have alteration haloes up to Im wide, characterised by the formation of albite -i- chlorite + clinozoisite/epidote -i- tremolite/actinolite at the expense of glaucophane and lawsonite, suggesting that the alteration haloes formed under greenschist facies conditions. In comparison, the higher-grade Zermatt-Saas metabasalts are composed of paragonite, omphacite, garnet, glaucophane, clinozoisite, late albite and minor lawsonite pseudomorphed by clinozoisite and paragonite. Albite-rich veins (>90% albite) with minor chlorite and ankerite, and up to 10% clinozoisite occur both as narrow (<10 cm) conjugate shear-veins and as broader (>20 cm) en echelon dilatant fractures that bisect the shear-veins. They locally have alteration haloes up to 2 m wide but more commonly <lm, with similar mineralogies to the Corsican albite veins. Oxygen isotope data suggests the fluids were derived from within the ophiolite or from a fluid that equilibrated isotopically with the ophiolite rocks. In the second case the fluids may have been derived from the overlying Schistes Lustres. However, given that the Schistes Lustres on Corsica are dominated by calcareous metasediments containing both calcite and quartz veins, it is unlikely that the albite veins within the ophiolite units were formed from fluids derived from these units.The more likely scenario is that the fluids involved in vein formation were derived from the ophiolitic rocks since, in addition to being similar isotopically to the albite veins, they are also compositionally more compatible as ophiolitic rocks are often enriched in Na by early seafloor hydrothermal alteration prior to subduction. The lowering of 5i«0 values in the vicinity of the vein suggests either that the fluid had a lower S^^O value than the host rock or that the fluid was derived from "hotter" rocks. Both of these explanations are consistent with the fluids being derived from units lower down in the ophiolite pile possibly from high-pressure hydrous minerals such as lawsonite. Overall, the oxygen isotope data suggest that large scale fluid flow between different Corsican Alpine nappes did not occur. A similar pattern is observed for the Zermatt-Saas albite veins. The formation of albite veins requires that fluids associated with vein formation contain aqueous Na, Al, and Si. In order to transfer chemical components from one part of a rock to another, a driving force such as a chemical potential gradient, pressure or temperature gradient is required. In the case of albite veins, since the solubility of Al is pressure sensitive, albite precipitation is likely to be driven by a pressure gradient. This suggests that fluids may dissolve Al at medium to high pressures. The precipitation of albite may occur via: Na-H -H 3Si02 + Al(OH)-4 = NaAlSi30g -I- 2H2O with the precipitation of albite favoured at lower pressures. Two factors may facilitate albite precipitation; 1) the pressure drop associated with the

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GEOLOGICAL SOCIET\' OF AUSTRALIA. ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trohe University, September 1998

blueschist to greenschist transition during uplift; and 2) the drop in fluid pressures associated with the opening of fractures. While it is not clear whether a drop in fluid pressure is sufficient to cause albite precipitation, the pressure change associated with uplift of the Corsican alpine nappes may be sufficient to drive albite precipitation. While albite veins are common in many high-pressure terrains, the processes that lead to their formation are complex. The devolatilisation of hydrous minerals such as lawsonite at medium to high pressures may provide an important fluid source for the formation of albite veins.This is also supported by stable isotope data that indicates fluids involved in the formation of albite veins from Corsican and Zermatt-Saas metabasalts were probably derived from within the ophiolites.The precipitation of albite from a fluid is favoured by a decrease in pressure. Alteration haloes around the veins are characterised by greenschist facies minerals suggesting that albite precipitation may be driven by the drop in pressure associated with the blueschist to greenschist transition possibly during exhumation and core complex formation.

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GEOLOGICAL SOClETi'OF AUSTRALIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998

THE ROLE OF HYDROTHERMAL DISSOLUTION IN THE FORMATION OF THE U-LENS ORE AT NAVAN, IRELAND Wendy Peace School of Eanh Sciences, University of Melbourne

The Navan Zn-Pb orebody is situated near the northern margin of the Dublin Basin, approximately 50 km northwest of Dublin. Mineralisation is hosted within a shallow water carbonate sequence of Lower Carboniferous (Courceyan) age formally known as the Meath Formation (Strogen et al., 1990), but more commonly referred to by the informal name of the Pale Beds (Philcox, 1984). The host sequence lies on the northern flank of a strongly faulted, northeast trending anticlinal structure at the southwestern margin of the Lower Palaeozoic Longford-Down inlier (Ashton et al., 1986). Mineralisation occurs as a series of six stratabound lenses which dip up to 15-20° to the southwest. The stratigraphically highest (and most recently discovered) of these is the U-lens. U Cupper'>lens mineralisation is defined as mineralisation which occurs in the stratigraphic interval between the base of the Upper Sandstone Marker (USM) marker horizon, and the overlying Shaley Pales [Moathill Formation (Strogen et al., 1990)]. The thickness of this unit varies from a maximum of approximately 40 m, to completely absent due to faulting or excavation by the pre-Arundian (Ashton et al., 1986) submarine erosion surface and associated Boulder Conglomerate debris flows. The U-lens is stratabound in nature, with a pod or lens-like morphology. Lateral continuity of the mineralisation has been affected by offsets due to post-mineralisation movement of E-NE trending extensional faults. As in the rest of the deposit, sphalerite is the dominant sulphide, with lesser galena, pyrite and marcasite present. Due to the nature of the mineralisation, gangue minerals are relatively rare, but where present the gangue is typically a combination of barite, saddle-dolomite, and calcite, with barite normally dominant. Sulphide mineralisation is mainly by replacement of the carbonate host, and disseminated sulphides in inter-particle voids. The remaining sulphides occur as open-space cements, both cavity and vein/fracture fill, and to a lesser extent, as internal sediments. Hydrothermal dissolution (also known as 'hydrothermal karsting') has had a significant influence on sulphide mineralisation within the U-lens. Although replacement of the carbonate host is the dominant style of sulphide mineralisation, a significant proportion of these replacement sulphides are found as breccias within cavities formed by hydrothermal dissolution of the host rock. These cavities vary in size, from a few centimetres to several metres. The edges of cavities (and some clasts) are coated by space-filling sulphide cements, and the remaining space is often filled by mineralisation-phase barite and saddle dolomite. The presence of these cements demonstrates that brecciation of the sulphides occurred during mineralisation, and not at some later time. Internal sediments within the cavities are often laminated and display grading, and contain fine-grained sulphides, as well as brecciated clasts of replacement and spacefilling sulphides which are truncated at the edges. This indicates that the internal sediments were deposited during mineralisation, and not earlier. These textures show that cavity formation must have occurred during mineralisation. Such relationships between the sulphides, internal sediments and cavity walls preclude a model of mineralising fluids taking advantage of pre-existing palaeokarst caverns. On the evidence available, cavity formation during sulphide mineralisation by hydrothermal dissolution is favoured. REFERENCES Ashton, J. H., Downing, D.T., & Finlay, S., 1986.The geology of the Navan Zn-Pb orebody In Andrew, C. J., Crowe, R.W.A., Finlay, S., Pennell, W.M., «& Pyne, J.E, eds., Geology and genesis of mineral deposits in Ireland, p. 243-280. Philcox, M. E., 1984. Lower Carboniferous lithostratigraphy of the Irish Midlands. Dublin, Irish Association for Economic Geology, 89 p. Strogen, P, Jones, G.L., & Somerville, I.D., 1990. Stratigraphy and sedimentology of Lower Carboniferous (Dinantian) boreholes from West Co. Meath, Ireland. Geological Journal, v. 25, p. 103-137.

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GEOLOGICAL SOCIEW OF AUSTRALIA. ABSTRACTS No. 52 12th Victohan Universities Geosciences Conference, La Trobe University, September 1998 CRUSTAL STRUCTURE BENEATH NORTHERN TASMANIA FROM WIDE-ANGLE SEISMIC DATA N. Rciwlinson^'^, G.A. Houseman^, TO. Semenova^-^ & C.D.N. Collins^ ^^ ^Australian Geodynamics Cooperative Research Centre ^Depaitment of Eanh Sciences, Monash University, Clayton \TC 3168 "^Australian Geological Suivey Organisation, Symonston ACT2609 Established in 1994, the TASGO project is a multidisciplinary study with the aim of understanding Tasmania's geology at depth and how this relates to its mineral and petroleum systems. The seismic component of the TASGO project was completed in 1995, when AGSO's research vessel Rig Seismic performed a circumnavigation ofTasmania during which approximately 36,000 shots were fired from its air guns. A network of 38 portable analogue recorders and 6 digital observatory stations distributed throughout the island recorded seismic energy from these shots. Marine deep reflection profiles, which are not considered in this paper, were also recorded as part of the survey. The 3-D refraction and wide-angle reflection dataset provides us with an opportunity to analyse the deep crustal structure ofTasmania much more comprehensively than has previously been possible. Results in the form of 1-D refraction interpretations and 2-D and 3-D forward modelling using data collected in northern Tasmania are discussed below. The 1-D refraction interpretations assume that the first arrivals are head waves which travel along horizontal planar interfaces separating constant velocity layers. The models that are produced have layer thicknesses and velocities that best satisfy, in a least-squares sense, the observed traveltimes. Consequently, each model represents the vertically averaged seismic structure of the region spanned by the data used to constrain it. The following description of Tasmania's crustal structure is based on these interpretations. Along the north coast, from just south of Three Hummock Island to Forth River, reversed profiles show the crustal thickness to be relatively uniform at about 31 km with an average crustal P-wave velocit}^ of 6.0 km/s and a Pn velocity (the P-wave velocity of the mantle beneath the Moho) of about 7.9 km/s. Two crustal layers that are separated by an interface at approximately 8 km depth are discernable from the data; the upper crustal layer has a P-wave velocity of 5.6 km/s while the lower crustal layer P-wave velocity is approximately 6.3 km/s. In addition, a 1-3 km thick layer with a P-wave velocity of about 4.5 km/s overlies the two main crustal layers; this represents the clastic carbonate sequence known as the Rocky Cape Group. Further east, across the Tamar Fracture System, the crustal thickness decreases to 27 km and remains at this value as far as Banks Strait. Inboard from both the eastern and western north coasts, the crust appears to thicken by several km towards the centre of the island. A 2-D crustal model of the western north coast of Tasmania has been constructed using both refraction and wide-angle reflection traveltimes from a shot line that runs between Three Hummock Island and Forth River to a receiver located near each end of the line. The model is parameterized in terms of uniform cubic B-spline interfaces in parametric form and layer velocities that are allowed to vary linearly with depth so that ray paths consist of circular arc segments. The most prominent lateral feature of the model is an upward deflection of both the Moho and the mid-crustal interface in the vicinity of the Arthur Lineament.The model is supported by free-air gravity data, in which the Arthur Lineament is expressed as a gravity high. The 2-D raytracing program used to construct the model described above has been extended to 3-D. Now, each interface is a surface described by a mosaic of uniform bi-cubic B-spline surface patches which are C2 continuous across suture.A model of the Rocky Cape Element (NWTasmania) has been constructed using the 3-D raytracing program in a forward modelling capacity. The starting model was based on the 2-D model which runs across the northern section of the crustal element.The final model shows that the Moho surface beneath the Rocky Cape Element dips approximately SE, with the crustal thickness increasing from about 25 km south of Three Hummock Island to over 30 km beyond the eastern margin of the element.This dip is much less pronounced along the northern edge of the element, where the 2-D model remains valid. The Arthur Lineament features in the final model as an upward deflection in the lower crustal layer which trends approximately NE-SW. 1-D refraction interpretations of data collected in northern Tasmania point to a relatively thin continental crust with lower than average crustal P-wave velocity.The coupling of these two factors suggest that this region ofTasmania has experienced significant extension.The 2-D and 3-D models of the Rocky Cape Element show a Moho surface dipping approximately SE and a NE-SW trending Arthur Lineament. Our long term goal with this very large dataset is to invert traveltimes for 3-D crustal structure and velocity to produce a high resolution tomographic image of the whole island to at least Moho depth. Such an image will undoubtedly enhance our current understanding of Tasmania's deep geology and tectonic evolution.

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GEOLOGICAL SOCIEW OF AUSTIMUA, ABSTIMCTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998 IMPACT OF HISTORICAL GOLD MINING IN THE UPPER GOULBURN RIVER, NORTH EASTERN VICTORLS. Emma L. Reid Department ofEaitb Sciences, VIEPS, Monasb University, Clayton, Victoria 3168 Historical mining of mesothermal gold deposits in the Woods Point Dyke Swarm Upper Goulburn River, north eastern Victoria, has resulted in metals being released to the river system over a hundred year period. Mercury was introduced into the river system for ore processing and has been the focus of previous work (eg.Tiller, 1989). At the peak of gold production up to 60 mines operated at any one time, with alluvial gold recovery occurring up until the late 1980's. Sulphide minerals, present in mine tailings, are rich in As, Sb, Cu, Pb and Zn, and as a result of reworking, the metals have also entered the system. The aims of this project are to track histroical mining activity using metals present in sulphide minerals and to determine whether the metals are present at levels above the recommended water and sediment quality guidelines as set by the Australian and New Zealand Environment Conservation Council (ANZECC). The Upper Goulburn River flows approximately 60 km from its headwaters near Woods Point to the Goulburn Inlet arm of Lake Eildon. Water and grab samples of stream sediments were taken at sites along the Upper Goulburn River and Raspberry and Gaffneys Creek. Sampling focused on sites upstream and downstream of tributaries with 'clean' sediment and potentially contaminated sediment, to determine the influence of sediment dilution and mixing. This will allow dispersal patterns to be ascertained with distance downstream of source. Sediment cores were taken from floodplain deposits in meanders of the lower reaches of the river and in the dry bed of the Goulburn Inlet arm of Lake Eildon to determine whether metals are stored in these sediments, and if an association between grain size and metal concentration is evident. Waters were measured in the field for temperature, pH, Eh (redox potential) and electrical conductivity, using portable meters and electrodes. Laboratory analysis of waters include measuring concentrations of dissolved metals and major cations, and bulk metals in sediments, using HR-ICP-MS for:Ti, Mn, Fe, Ni, Cu, Zn, As, Pd, Ag, Cd, Sb, Cs, Pt, Au, Hg, Pb; and major cations: Mg, Al, Si, Ca. Current analyses of waters include major anion (CI", HCO^", SO4O, Na and K measurement (using AAS, specific element electrode, titration and gravimetric techniques), and for sediments include metal speciation (using sequential extraction), grainsize analysis and mineralogical studies (using petrography) of all sediments and downcore patterns in floodplain and lake sediments. Field measurement results indicate a range of values exist for all parameters, such as 8.5 - 20°C for temperature, pH from 6.47 to 8.08, with one site measuring 5.60, Eh ranging from -58 to 215 mV and conductivity from 38 to 600 |uS. Preliminary results indicate that the majority of water samples have Cu and Zn concentrations above (20 times and 2 times, respectively) the upper limit of the recommended water quality guidelines (ANZECC, 1992). A number of sediment samples have As, Hg, Sb and Ni concentrations above (90-, 3-, 2.5- and 1 times) the upper limits of the recommended sediment quality guidelines (ANZECC, 1997). The highest metal concentrations in both waters and sediments are found adjacent to old mine sites, tailings dumps and downstream of tributaries with mines, with concentrations generally decreasing with distance downstream of source. This trend could be attributed to the accelerated release of metals from sulphide minerals due to mining activity, which are persisting in the river system decades after the cessation of gold mining. REFERENCES ANZECC, 1992. Australian Water Quality Guidelines for Fresh and Marine Waters, Australian and New Zealand Environment and Conservation Council. ANZECC, 1997. Interim Sediment Quality Guidelines. Environmental Research Institute of the Supervising Scientist,Australian and New Zealand Environment and Conservation Council. Tiller, D. G., 1989. Mercury in the Freshwater Environment, A Legacy of Gold Mining in Victoria. Water, 16:20-22.

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GEOLOGICAL SOCIEW OF AUSTRALIA, ABSTRACTS No. 52 12th Victonan Universities Geosciences Conference, Lci Trobe University, September 1998

ARCHAEAN CRUSTAL SHEAR ZONES;AN EXAMPLE FROM THE YILGARN CRATON,WA James Richardson Depanment ofEanh Sciences, VIEPS, Monash University, Clayton, Victoria 3168 The Koolyanobbing shear zone is a large northwest trending, crustal scale ductile shear zone located within the Archaean granitoid-greenstone terrain of theYilgarn Craton in Western Australia.The shear zone is between 6 and 15 km in width and so is highly likely to cut through the entire crust.The shear zone is laterally extensive for a distance of 300km southeast of Koolyanobbing, almost to the southern boundary of the Yilgarn Craton, and 60km northwest of Koolyanobbing before losing definition around the western margin of the Marda greenstone belt (Libby et al, 1991). However it is believed to be in excess of 650km in length based on geophysical data, while another important aspect of the Koolyanobbing shear zone is its paralleUsm to the fundamental crustal structures defined by recent geophysical surveys (Libby et al, 1991). At Koolyanobbing, the shear zone is best exposed along the northern shore of Lake Deborah East, w h e r e it is seen as continuous outcrop of approximately 6 kilometres.The outcrop ranges from undeformed granitoid in the west, through to banded gneiss and mylonite in the east. The Koolyanobbing shear zone itself separates areas of high grade metamorphism in the southwest from low to medium grade metamorphic grades in the northeast (Libby et al, 1991). There is a large granitoid body known as the Ghooli dome, to the southwest, which may be responsible for the increasing metamorphic grade through contact metamorphism, and it is believed that the Koolyanobbing shear zone is in part due to the emplacement of this granitoid body. The main lithology of the Koolyanobbing shear zone is one of strongly foliated to mylonitic monzogranite containing deformed sheets and enclaves varying from granite to tonalite, with the ranges of granites increasing towards the centre of the shear zone (Libby et al, 1991). To the west, the granites are generally less deformed, preserving distinct magmatic layering of felsic and mafic compositions within the granites.The deformed granites of the Koolyanobbing shear zone show distinctive S-C fabrics towards the east; therefore w e have an overall progressive change in deformation from the west leading to the development of shear banding in the east.This progressive deformation is seen within the grains of the granite, as kink bands, twinning and widespread sub grain formation within the feldspar and quartz grains. In the east a change from magmatic textures to solid state deformation occurs with shearing, mylonitic bands, and dramatic grain size reduction. Kinematic criteria for assessment of this shear zone include sigmoidal grains, S-C mylonites, C indicators, and within the greenstones, well developed boudinaged layers of the banded iron formation. These indicators are present throughout the foliated granitoids, pegmatites and mylonites of the exposure along the northern margin of Lake Deborah East. Lineations within the deformed granites stay within a range of 10° to 25°, and all plunge generally towards the north. All of these kinematic indicators give us a sinistral strike slip sense of movement for the shear zone. REFERENCES. Libby Groves and Verncombe (1991).The nature and tectonic significance of the crustal-scale Koolyanobbing shear zone,Yilgarn Craton,Western Australia.Aust. J. Earth Sci. 38, pp 229 - 245,1991.

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GEOLOGICAL SOClET\'OF AUSTRALIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, La Trobe University, September 1998 THE EFFECT OF FLOOD RETARDING BASINS ON DOWNSTREAM CHANNEL MORPHOLOGY Shajyn RossRakesb Depaitment of Civil and Environmental Engineering, The University of Melbourne It is generally accepted that urbanisation leads to channel enlargement due to an increase in the frequency and magnitude of flooding (Hammer 1972). Flood retarding basins are used to mitigate downstream flooding by attenuating flood peaks but the impact of the altered flow regime on the downstream channel morphology is not well known.The aim of this paper is to present some of the issues raised in the literature concerning the potential adverse effects of flood retarding basins on channel morphology. A case study is presented describing the differences in channel morphology upstream and downstream of Blackburn Lake, a long established flood retarding basin. Results show that both the channel upstream and downstream of the lake have enlarged since urbanisation and the construction of the Lake.The altered flow regime downstream of the lake has, however, mitigated to some extent the effects of urbanisation, resulting in a smaller channel downstream compared with upstream. Flood frequency appears to play a greater role in upstream channel forming processes while flood duration is more critical downstream of the storage. Other retarding basins around Melbourne, all designed for flood mitigation, were rapidly assessed to compare with the situation observed at Blackburn Lake.The results were variable with no consistent pattern indicating that there are a number of factors effecting channel stability. The incorporation of artificial storages (detention basins, retarding basins, ponds, etc) into stormwater management was first introduced in the 1950s as a means of compensating for the loss of natural storage. Flood mitigation has been the priority in most urban areas inorder to protect assets.The use of storages for other objectives such as water quality improvement and erosion control have more recently been recognised. Flood retarding basins are typically designed to reduce the magnitude of the post-developed 100 yr ARI event to the pre-developed level and the effect of storage control diminishes for all other flood frequencies. So although peak discharges for large events are reduced and flood mitigation is achieved, release rates for smaller events are higher and last longer than pre-urban flow rates. It is recognised that this may lead to adverse impacts such as downstream channel degradation. It has also been reported that even storages designed specifically for downstream erosion control have failed to meet the desired objective (MacRae 1993).The design approach usually includes attenuating a more frequent flow such as the 1 in 2 year peak event. MacRae (1993) has proposed a procedure for the design of storage facilities for instream erosion control in urban streams by taking into consideration the role of moderate flows and the transverse variability of shear stress along the perimeter of a cross section. However, more work is required in both assessing the current effectiveness of these stormwater management measures and developing methods for validating proposed design procedures. The results of this case study revealed notable differences in channel morphology upstream and downstream of Blackburn Lake. Determination of a reach average bankfull discharge from 3 cross sections upstream and 3 downstream revealed a 65% smaller peak discharge below the lake. Partial flood series analysis using 2 years of concurrent data suggests that the upstream bankfull discharge occurs more frequently (6 times per year) than downstream bankfull discharges (once every 2 years). The average duration of bankfull discharges is however significantly longer downstream (5 hrs) than upstream (10 mins). Velocity, shear stress and stream power at bankfull are higher upstream than downstream. So although bankfull discharges occur for a much longer duration downstream, they do not occur as often or appear to have the erosive power of upstream bankfull flows. In the case of Blackburn Lake, downstream channel enlargement due to urbanisation has been moderated. It is difficult to establish if the channel has reached a state of quasi-equilibrium or if it is still responding to landuse changes in the catchment. A second wave of urbanisation is possible in the future, through sub-division of residential properties.This will continue to alter the rainfall runoff regime and may prevent stabilisation of channel morphology, both upstream and downstream of the storage. Using bankfull width as an indicator of channel change, four other flood retarding basins were rapidly assessed. In two of the cases the downstream channel was larger than upstream.These results show there is a need to address the potential negative impacts of flood retarding basins on channel morphology, particularly where they aggravate the effects of urbanisation. REFERENCES MacRae, C.R. (1993) 6th International Conference on Urban Stormwater Drainage Niagara Falls Canada. Hammer,T.R. (1972) Water Resources Research Vol. 8, No. 6,1530-1540.

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GEOLOGICAL SOCIET}'OF AUSTRALIA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, Ui Trobe University, September 1998

STRUCTURAL ASSOCIATION OFTHE AMADEUS BASIN AND ARUNTA BLOCK, CENTRAL AUSTRALLV: FROM REPROCESSING AND INTERPRETATION OFTHE 1985 AGSO DEEP SEISMIC REFLECTION SURVEY Antony Riidge Depaiiment ofEcutb Sciences, \1EPS, Moncish University, Clayton, Victoria 3168

TheAmadeus Basin in Central Australia, is one of Australia's most productive and prospective basins for the accumulation of hydrocarbons. However, much of it has been unexplored because the structure and tectonic evolution is relatively unknown or poorly understood. TheAmadeus Basin started to form at around 900 Ma and has a complex tectonic history with at least two compressional events and two extensional events. No single mechanism can be responsible for the multiple stages of subsidence recognised in the basin. Stage 1 from 900 Ma to 590 Ma, is considered to be the major extensional event. The Heavitree Quartzite and Bitter Springs Formation were deposited in this period, and there is evidence for major glaciation. The most significant tectonic event within this period is the Petermann Ranges Orogeny. Stage 2 subsidence due to a single event of extension and thermal relaxation occurred from 590 Ma to 450 Ma. It is during this stage that the Central Ridge began to form and affect the evolution of the basin by causing the starvation of clastics to the eastern sub-basins and causing carbonates to form. Stage 3 is considered to be a foreland basin type development, with molasse type sediments being deposited. The major tectonic event during the period 450 Ma to 300 Ma is the Alice Springs Orogeny which is responsible for the present day landscape and morphology. There was a major occurrence of shortening of approximately 50-100km, which produced the basin margins and are thought to be structural and erosional rather than depositional. In 1985, AGSO (then BMR) recorded a deep reflection seismic transect through the Ngalia Basin, Arunta Block and the Amadeus Basin. This data was processed by AGSO, but in large areas of the line, the structure remains unresolved. Using different techniques and methodology, a greater proportion of the structure is now being resolved. Two of the regions where very little structure is apparent on the survey are the region where the Amadeus Basin has its contact with the Arunta Block, and the region called the Central Ridge. The latter is a peripheral bulge which has been thought to be one of the main controlling factors involved in the formation of the basin. It runs more or less east-west through the basin, and it is of economic interest because its structure controls some of the traps, which contain oil and gas plays. The reflection seismic data indicates considerable amounts of crustal deformation within the region, particularly across the Red Bank thrust zone, a structure which cuts the entire crust and offsets the Moho. How did this occur? Was it due to an intra-continental collision, or collision on the present continental margin? Reprocessing the AGSO seismic lines, combined with interpretation of gravity and magnetic surveys through this region, will be used to better constrain the structure and tectonic evolution of the region. Preliminary reprocessing of the AGSO seismic data has resulted in better resolution of the structure, especially along the Arunta-Amadeus contact, and should lead to better constraints on the tectonic history of the region.

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GEOLOGICAL SOCIETY OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, Lci Trohe University, September 1998

THE GEOLOGY OF THE WALKERVILLE - BIRD ROCKAREA:THE SEDIMENTOLOGY OFTHE ORDOVICIANAND DEVONIAN LIMESTONES AT BIRD ROCK Gavin Scherer Deakin University

This honours thesis aims to gain a detailed understanding of the sedimentology of the carbonates and geology of the Bird Rock field site, in order to produce a detailed geological map, stratigraphic section and geological thesis on Bird Rock and attempt to add more detail to and clarify many of the maps that have already been produced. The methods that were used to meet the aims of this thesis are largely based on field work, observation from field mapping, laboratory work and contributions from previous work. These combined methods were then used to produce a geological map and stratigraphic sections, to gain insight into the geology of the Bird Rock field site.The data collected can then be used to determine the source environment of the sediments and mode of deposition of the Bird Rock field site.

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GEOLOGICAL SOCIET}'OF AUSTRALIA, ABSTRACTS No. 52 12th Victohan Universities Geosciences Conference, Lci Trobe University, September 1998 NEW OCCURRENCES OF INTERMEDIATE PRESSURE METAMORPHIC ASSEMBLAGES WITHIN GREENSTONE BELTS: IMPLICATIONS FOR THE TECTONIC EVOLUTION OF THE LACHLAN OROGEN,VICTORLV Catherine V. Spaggiari, Australian Geodynamics Cooperative Research Centre Depajtment Eanh Sciences, Monash University, Melbourne MC. 3168, Australia. ST-cath@earth.mon ash .edu.au The Heathcote and Mount Wellington greenstone belts (MWGB) are located at the boundaries of major structural zones in Victoria.The greenstones are predominantly mafic to ultramafic meta-igneous rocks of PCambrian age associated with marine sediments and are exposed along generally N/S trending thrust systems. The Heathcote fault is the leading fault for the Ballarat Bendigo Zone and the Governor Fault (MWGB) is the leading fault for the Tabberabbera Zone. Gently folded Silurian to Lower-Devonian Melbourne Zone sedimentary rocks lie between the two fault zones. Both the central segment of the Heathcote fault zone and the Howqua area of the Governor fault zone (MWGB) include strongly sheared, veined and boudinaged black-mud matrix or serpentinite-matrix melanges with pronounced anastomosing "scaly" foliation in the hanging walls. Amongst chaotic blocks of turbidite, chert, and greenstone are blocks of blue metavolcanic rocks consisting of metamorphic assemblages transitional between blueschist and greenschist facies.These are similar to exotic blocks with high or intermediate pressure mineral assemblages described in the Franciscan of California, which occur in melanges in a subduction-accretionary complex.The assemblage in the Heathcote and Howqua rocks is sodic or sodic-calcic amphibole, albite, chlorite, epidote, Mg-Cr spinel, stilpnomelane, ±quartz. Electron microprobe analyses have shown that the amphibole in the Heathcote rocks is winchite, a sodic-calcic variety transitional between actinolite and glaucophane. Analyses of the Howqua rocks show that both winchite and glaucophane are present. Both these amphiboles are typical of blueschist facies metamorphism. Geobarometry using this assemblage indicates pressures of around 6 kbars for Heathcote and 7 kbars for Howqua, translating to depths of approximately 18 km and 21 km respectively. Maruyama et al (1996) have classified blueschists into two associations,"Type-A" and "Type-B" according to their protoliths. Type-A are typical of continental margin collision, have passive margin protoliths, and form ultra-high pressure (up to 45 kbars) metamorphic rocks. Type-B are more typical of ocean-ocean and/or ocean arc collision, and have active margin protoliths consisting of rock assemblages which form in accretionary complexes. Maximum pressure metamorphism is 12 kbars.The occurrences described here in the turbidite dominated thrust system of the Lachlan orogen are of the Type-B. Detailed mapping at Howqua has shown that the melange zone is structurally overlain by a layer of upper oceanic stratigraphy. This consists of a basal layer of sheared serpentinite, overlain by relatively undeformed and pillowed metabasalts, which pass up into bedded cherts and siliceous black shales, overlain by turbidites. Both the black shale and chert unit, and the base of the turbidite unit contain Lower Ordovician fossils (VandenBerg & Stewart, 1992, Harris & Thomas, 1938). This whole sequence dips and youngs to the northeast, is apparently conformable, and is interpreted as a slice or duplex of oceanic stratigraphy. The oceanic rock associations, intermediate pressure metamorphism, and structural relationships (melange and duplex formation) can be explained in terms of subduction-accretionary processes in a "Type-B" setting. Melange may be produced by decollement related shear as oceanic crust is subducted. Intermediate pressure metamorphism suggests accretion to the base of an accretionary complex, rather than the toe. Fault-bounded slices of greenstone and associated marine sediments may form by underthrusting and duplexing of subducting oceanic crust. This study has shown that both Heathcote and Howqua have been subjected to similar processes. REFERENCES: Harris W.M. & Thomas D.E. 1938. Notes on the geolog>^ of the Howqua valley. Mining and Geological Journal Department of Mines, Victoria 1,81-84. Maruyama S., Liou J.G.,Terabayashi M. 1996. Blueschists and eclogites of the world and their exhumation. International Geology Review 38,485-594. VandenBerg A.H.M. & Stewart I. R. 1992. Ordovician terranes of the southeastern Lachlan Fold Belt: stratigraphy structure and palaeogeographic reconstruction.Tectonophysics 214, 159-176.

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GEOLOGICAL SOCIETY OF AUSTIiAUA, ABSTRACTS No. 52 I2th Victorian Universities Geosciences Conference, La Trobe University, September 1998

SILCRETE FORMATION IN THE MTWOOD HILLS AREA, NORTHWEST NEW SOUTH WALES Michelle Tait Depaiiment of Eanb Sciences, La Trobe University, Bundoora. Victoria 3083

The Mt.Wood HiUs area is situated in the Sturt National Park, northwest NSW, 20 km east ofTibooburra. The landscape is dominated by scarps up to 30 m high that run approximately N - S through the area.The barren regional landsurface has a shallow easterly dip of 4 - 5°, and is covered extensively in silcrete and lateritic gibber. Exposed, strongly weathered and silicified Early Cretaceous sediments deposited in the Eromanga Basin dominate the regional geologyA thin, partially silicified Early Tertiary cover of the Lake Eyre Basin sediments is seen in places. At least three separate episodes of silcrete formation have been recognised in this area. The oldest recognised silcrete, the 'columnar silcrete', commonly has pedogenic features such as columns, candle wax drippings and a concretionary top layer. It is pale-coloured and formed at or near the landsurface within the exposed, folded and faulted Early Cretaceous sediments. It outcrops as pavements in eroded gullies and as prominent blocks along scarp edges, where thicknesses can reach 5 m.The silcrete has been gently deformed, with sheets tilted under flat-lying younger sediments. A younger silcrete, the 'sandstone silcrete', has silicified quartzose gritty red sandstone deposited over the Early Cretaceous sediments and columnar silcrete, and incorporates eroded water-worn columnar silcrete clasts reaching 50 cm in diameter. This silcrete often infills joints or depressions in the columnar silcrete, and outcrops on scarp and valley sides reach 3 m thick. It is predominantly massive, but can show pedogenic candle wax drippings that terminate at the silcrete clasts. Its age is probably Late Cretaceous, as it is overlain by Early Tertiary Eyre Formation sediments.There is no evidence of post-silcrete deformation. The youngest silcrete has been named the 'white pebble silcrete', as it contains shiny rounded milky vein quartz pebbles, often in lenses or bands, as well as petrified wood. It has silicified Early Tertiary (Palaeocene to Middle Eocene) Eyre Formation gravels and older weathered sediments that have incorporated relict Eyre Formation pebbles. Its outcrop is sparse, massive and shows no pedogenic features. Silica cement varies from yellow opaline to grey or buff quartzose to blue-grey anatase-rich.

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GEOLOGICAL SOCIETY'OF AUSTRALIA, ABSTRACTS No. 52 12th Victoncm Universities Geosciences Conference, Ui Trobe University. September 199S THOSE MYSTERIOUS MEGAFAUNAL EXTINCTIONS: THE CASE FOR KING ISLAND, BASS STRAIT Sanja Van Hiiet Depcinment ofEcinb Sciences, Moncish University, Clayton, VIC. 3168. e-niail: ST-h11et@eanh.monasb.edii.au King Island is a small continental island off the south-east coast of mainland Australia. It represents a geographically isolated biota that has been subjected to repeated periods of connection and separation with the Australian mainland during the late Quaternary/Holocene Gennings 1959). Fluctuations in sea-level, attributed to glacial to interglacial climates, are linked to changes in precipitation and temperature in southern Australia (Bowler 1982, Galloway and Kemp 1984). Evidence for these changes can be seen in the sediments and fossils deposited at a number of sites on King Island (D'Costa, Grindrod and Ogden 1993, Van Huet pers. observ.). Evidence suggests that the absence, or the local extinction, of megafauna* after approximately 70,000 ybp can be correlated to climate-related change in habitat. Pollen analysis (D'Costa 1997), Uranium/Thorium, Electron Spin Resonance and conventional Carbonl4 dating (Grindrod, pers. comm.) combined with sedimentary, taphonomic and faunal analysis (this study) provides an insight into the disappearance of the megafauna from King Island. Two possible scenarios are: • The King Island extinctions were due to glacially-dominated changes in climate, which resulted in the evolution of habitat unsuitable for supporting the megafauna. • The migration of free-ranging megafauna away from an unsuitable habitat on King Island, to suitable habitat; via a land bridge exposed during a period of low sea-level. Human intervention has been discounted as a factor in this study, as there is no evidence for the inhabitance of indigenous people in the area during this period of time.

*Megafauna are defined as extinct animals over 45 kg. in weight (Murray 1984). REFERENCES Bowler J.M. (1982). Aridity in the late Tertiary and Quaternary of Australia, pp. 35-45 in Barker,W.R. and Greenslade, P.J.M., eds. Evolution of the flora and fauna of arid Australia. Frewville: Peacock Publications. D'Costa D. M. (1997).The reconstruction of Quaternary vegetation and climate on King Island, Bass Strait, Australia. (Unpublished PhD. thesis) Monash University, Clayton. D'Costa D.M., Grindrod J., and Ogden R., (1993). Preliminary environmental reconstructions from late Quaternary pollen and mollusc assemblages at Egg Lagoon, King Island, Bass Strait. Australian Journal of Ecology 18:351-366. Galloway R., and Kemp E, (1984). Late Cainozoic environments in Australia, pp. 69-81 in Archer M., and Clayton G., eds. Vertebrate zoogeography and evolution in Australia. Carlisle:Hesperian Press. Jennings J.N. (1959). The coastal geomorphology of King Island, Bass Strait, in relation to changes in the relative level of land and sea. Records of the Queen Victoria Museum 11. Murray P (1984). Extinctions down under: A bestiary of extinct Australian late Pleistocene monotremes and marsupials, in Martin PS., and Klein R.G., Quaternary Extinctions, pp. 600-628. University of Arizona Press, USA.

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GEOLOGICAL SOCIET\'OF AUSTRAUA, ABSTRACTS No. 52 12th Victorian Universities Geosciences Conference, Lci Trobe University, September 1998

KARST OF THE CAINOZOIC LIMESTONES OF THE OTWAY BASIN, SOUTHEASTERN AUSTRALIA Susan White School ofEanh Sciences, La Trobe University, Biindoora, Victoria 3083

The Tertiary and Quaternary limestones of the Otway Basin in south western Victoria and south eastern South Australia include Miocene and Oligocene marine limestones and Pleistocene calcareous dune and beach facies. These highly variable limestones of high primary porosity and high permeability show diverse karst features both in surface expression and underground, presenting particular problems with regards to the usual concepts of speleogenesis. Although there have been some studies of karst development in the Tertiary, the Pleistocene dune karst areas (White 1994) and of the some of the surface karst (Grimes, 1994), these are generally of small areas Oess than 100 km^ ) and show some interesting contrasts in features. The Otway Basin is a large karst area where there is the potential to understand the regional patterns of karst development in particular the times taken for karst development in Pleistocene calcareous dunes. Karst development in these limestone lithologies shows substantial variation across the basin and between the different lithologies. The karst shows important differences in the number and type of cave present per volume of limestone, total passage length, passage orientation, passage size, and cave form. Substantial differences in other karst features such as the presence of distinctive cenotes and other surficial features in some areas and their complete absence in others are also evident. Although environmental factors such as relief and climate do not vary greatly across the basin, there are significant changes in lithology, structure and underground water conditions. The variation in karst features can be explained partly by lithological variation; especially in such highly variable karst host rock. The overall regional view can add some important insights into concepts of speleogenesis. REFERENCES Grimes K.G. (1994) The South-East Karst Province of South Australia. Environmental Geology 23:134 - 148. White S. (1994) Speleogenesis in aeolian calcarenite:A case study in western Victoria. Environmental Geology 23: 248 - 255

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GEOLOGICAL SOCIET}'OF AUSTRALIA. ABSTRACTS No. 52 12th Victonan Universities Geosciences Conference, Lci Trohe University. September 1998 AUTHOR INDEX BAKER

HARTLEY

BELTON

HILL

19

BEYER

HOGEBOOM

22

BROWN

HOUSEMAN

33

9,21

BUICK

23

HUANG

23

CAUZID

4

KHAKSAR

25

CHRISTIAN

5

KIVIOR

26

COFFA

7

LEMON

12

COLLINS

33

MACGREGOR

27

COOK

8

MASON

28

CROWHURST

9

MILLER

29, 30

CURTIS

10

PEACE

32

CZAPNIK

11

RAWLINSON

33

DAS

12

REID

34

DEKEVER

28

RICHARDSON

35

DIMAS

13

ROSSRAKESH

36

DOMANSKI

14

RUDGE

37

DOODIE

15

SCHERER

38

FOSTER

9,19,29

SEMENOVA

33

GOLDBERG

16

SPAGGLVRI

39

GRASSY

17

TAIT

40

VANHUET

41

WHITE

42

GRAY

19,29

GRECH

18

GREGORY

29

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