Issuu

Clausthal-Zellerfeld 2013

I6Abb.,

Clausthaler Geowissenschaften

5-44

|6Taf,3 Tab]

Dolomite in the Triassic Dolomites WotrcanG BLevpinarR, ALBERTO Bertini, StePitaNIE

Loreta & Epwi MEISSNER

Abstract: Middle Triassic dolomite of the Pale di San Martino and San Lucano a typical. up to 1.6 km thick, platform carbonate. Calcareous parts comprise 2-3% and occur narrow (tens to a few hundred metres wide, hundreds of metres long and high) corridors in dolomite following synsedimentary fractures (with NNE trends), Dolomite mainly suerosic. The calcareous parts are composed of about 45% micritic crusts and 35% early cements, the remainder is micrite, blocky calcite, and other allochems. Reliet fabrics in dolomite suggest similar but unquantified composition of the precursor. Porosities and permeabilities average 1% and 0,07 mD for limestone, and 7%and 0,03 mD for dolomite. Capillary pressure measurements indicate pore throat radii mostly between 0,1 and pm, Higher dolomite porosities are partly an artefact caused by recent boring organisms. Tight rock properties were acquired during surficial diagenesis The average difference in 2!!C between dolomite and limestone of the Pale is 1,3%» (PDB), similar to the theoretical fractionation caused by a difference in MgCO, of 50 mol%. Average limestone 2'C is ca. 2,2%o heavier at Latemar and Marmolada, where dolomite only 0,4% heavier than limestone. Almost all (95%) dolomite îs near-stoichiometric (average 49 mol% MCO, and shows a higher degree of chemical compaction than limestone. 2"O shows a wide range to -11%e) without trend over the entire platform thickness, where vitrinite reflectance data indicate a temperature difference of >30°. Avi ‘erage @S0 limestone and dolomite do not show the difference predicted by fractionation, but nearly identical values (ca. 4,5%). Tight rock properties, geometries and geochemical data suggest that dolomite was not ercated by fluid flow. Instead, a recrystallization product a high-Mg calcite precursor possibly bacterial origin Preserved limestone was either deposited as a Mg-poor polymorph lost its Mg and other elements preferentially in near surface fracture zones. The controls on possibly different depositional mineralogies cannot clarified with geochemical data, because external factors (artesian [reshwater influence, ),) and mineral specific effects (fractionations, loss of Mg ‘magmati and associated reversal of stable isotope fractionation) form unsolvable unknowns.

and

)

Keywords: Dolomite,

Triassic, Pale di San Lucano, Pale di San Martino, stable isotopes, porosity. perme-

ability, capillary pressure, fractionation, fracture zone, 3D modelling

Ansehrift der Autoren:

Blendinger, Stephanie Lohmeier

Technische Universit Clausthal, Institut Rir Geologie und Paltontologie Leibnizstr. 10, D-38678 Clausthal-Zellerfeld Alberto Bertin Viale Sommariva 38

N-3020 Trondheim

Kurzfassung: Der mitteltriassische Dolomit der Pala-Gruppe (Pale di San Martino, Pale di San Lucano)

typisches Plattformkarbonat mit M&chtigkeiten bis 1,6 km. Kalkige Bereiche machen nur etwa schmale Korridore vor, die Breiten im Zehnermeterbereich und Lingen und aus und kommen Machtigkeiten von mehreren hundert Metem erreichen und synsedimentiren Briichen mit NNE und NE-Streichen folgen. Dolomit ist meistens zuckerkòrnig. Die kalkigen Bereiche bestchen aus ctwa 45% Mikritkrusten und 35% frihdiagenetischen Kalzitzementen, der Rest aus Mikrit, Blockkalzit und anderen Allochemen. Relikttexturen im Dolomit zeigen cine schr inliche Zusammensetzung, die bisher aber nicht quantifiziert ist. Durchschnittswerte von Porositàit und Permeabilitàt sind 1% und 0,07mD im Kalk und 7 % und 0,03 mD im Dolomit. Kapillardruckmessungen ergeben Porenradien, deren grofte Haufigkeit im Bereich zwischen 0,1 und um liegt. Die hheren Dolomit-Porositaten sind cin tcilweise durch rezente Bohrorganismen (Bakterien, Pilze) verursachtes Artefakt. Die dichten Gesteinseigenschaften wurden whrend der oberflichennahen Frihdiagenese erworben Der Unterschied der 2"C -Durchschnitiswerte von Dolomit und Kalk betriigt 1,3%o (PDB) und ist damit tibinlich der theoretischen, durch Fraktionierung erzeugten Differenz zwischen einem Karbonat mit 50 bzw. 0 Mol% MgCO,. An der Marmolada und am Latemar betriigt diese Differenz jedoch nur 0,4 %o, wobei die Durchschnitswerte Kalk ca. 2,2%n schwerer sind als die der Pale. Fast alle Dolomite sind mit einem Durchschnitt von 49 mol% MgCO, beinahe stéchiometrisch. Der Grad der chemischen Kompaktion, erkennbar an Stylolithen, st im Dolomit hoher als im Kalk, aber bisher nicht quantifiziert dSO zeigen insgesamt cine hohe Streubreite und reichen von Werte ca. 0 bis -11%a. Einvertikaler, nicht erkennbar, obwohl Vitrinitreflexionsdaten Temperaturunterschiede temperaturabhaingiger Trend von mindestens 30° wvischen Plattformbasis und -op belegen. Im Gegensatz zu 2C zeigen die 2*0Durchschnittswerte Kalk und Dolomit nicht den eigentlich zu erwartenden, fraktionierungsbedingten Unterschied, sondern fast identische Werte um -4,5%o. Die dichten Gesteinscigenschaften, Geometrien und geochemische Daten machen es sehr unwahrscheinlich, dass der Dolomit der Pale durch das Gestein durchstròmende Fluide erzeugt wurde. Er ist besser als Rekristallisationsprodukt eines Hoch-Mg-Kalzits mit mehr als 50 Mol% MSCO, erkliren, bei dessen Genese Bakterien cine wesentliche Rolle gespielt haben diurften. Die heute als Kalk vorliegenden Bereiche wurden entweder als priméir Mg-arme Polymorphe wie Aragonit oder Niedrig-Mg-Kalzit gebildet oder verloren wdhrend der Frihdiagenese Mg und andere Elemente oberflichennahen Bruchzonen. Es blcibt jedoch spekulativ, dic genauen Ursachen auf geochemischem Weg zu ergriinden. Externe Faktoren wie der synsedimentire Einfluss von artesischem Sùfwasser oder magmatischem CO, und mineralspezifische Fffekte wie Isotopenfraktionierung und deren Umkehr wihrend der Diagenese bilden gegenwartiu unlosbare Unbekannte. {

cin

als

2-3%

ist

Schlusselwòrter: Dolomit, Trias, Pale di San Lucano, Pale di San Martino, stabile Isotopen, Porositàt, Permeabilitàt, Kapillardruck, Fraktionierung, Bruchzone, 3D Modellierung

Monte San Luò

Gc ®.,

decton

» FiMaomani

rate Les)

HE strata dolomite (Contrin formation) IEEE]

stracci dlomite (aggradational platform interior)

[IT] pooriy stratified dolomite (mainly EBBE b0cdg dolomite ABBI b:asin21 imostone

(progradational)

clinostratitied)

em 1000m

A vocone die |

tractreriaut

( dolomite breccia pipe ®°

clinoform dip direction

reflectance (number oî Table 1)

122% (8) vitriinite

verticaliy to scale

The geologica! map of the platform carbonates and correlative basinal rocks of'the Pale shows the narrow sorridors mainly composed of limestone, occurring both in the platform interior and the clinoforms. The cross section documents the structurally uncomplicated setting of the platform and the absence of major faults, The inset rectangle at Pale di San Lucano delîncates the area covered by the detailed 3D model of Fig. 6.

Fig. 2.

dolo!

problem and scope of the

Setting of the type area of the mineral dolomite and previous work

dolomite problem results from the so called of dolomite in ancient sedimentary rocks contrasting with the scarcity of dolomite in recent

The Triassie Dolomites show two main stratigraphic intervals dominated by dolomite: the Middle Triassic, generally isolated, carbonate platforms, and the Dolomia Principale or Hauptdolomit, now erosional remnants of a large Upper Triassic shelf. covered by Only the Middle Triassic interval will the present study. The Middle Triassic outerops are a thin up to 1,6 km thick, and are time equivalent basinal sediment. sequence Older studies of dolomite in various platforms the Dolomites concluded that dolomitization oeof curred mainlyby brines sinking from the Upper Triassic Raibl Formation, which is locally evaporitic Leonarbi 1968). It was clear that dolomite (Rossi formation a post-depositional phenomenon, because the basinal rocks adjacent to the platforms contain boulders which are nearly always limeimmediate stone, whereas platform outerops

The

study The

‘abundance

restricted to a few and environments which not compavery specific table with dolomite in ancient carbonate platform al. 1994), It is unanimously assettings (Punser sumed that dolomite is the result of a dolomitization process by which Mg added to a Mg-poor precursor byfluid flow (e.g., MacWeL 2004). AI models do not plausibly explain, however, why a chemical reaction, which cannot be replicated the laboratory, should have worked the deep and the fluid flow exists or an past. Whether evidence altemative for the explanation of massive dolomite is necessary will be tested în a unparalleled natural of the mineral, the Dololaboratory, the type mites in northem (Fig. 1). settings.

Modem dolomite

are

for

area Italy

Rosengarten-Schlem Bozen

Langkotet

1.1

the

7 tx

Na ge Marmolada

Cda x

T_T Cemera

moro

Triassic intrusioni Middle Triassie cerbonata platforms mainly dolomite bi mainly imestone

10 km

‘a:

The crosional relicts of calcareous and dolomitie platforms Fig. the Triassic Dolomites shows that most platforms are dolomite, whereas calcareous platforms form a ENE trending belt in he central parts ol'ihe Dolomites and overlap the main volcanie centres. Inset rectangle delineates the map arca ol Fiu. 2 1.

di is Bose

vicinity are often dolomite. By contrast, (1989) infers seawater-freshwater mixing as consi quence repeated subaerial platform exposure as the reason dolomitization. AII modem studies based largely are on geochemical analyses and have been carried out at the Latemar, where dolomite vecurs sporadically in the platform interior. A model with the opposite flow direction to that proposed has been by Rossi forward, in which warm to hot fluids, driven by the nearby Predazzo intrusion, were forced through the platform causing dolo: mite fingers branching from vertical, partly bre ated, stems (Wirsov ct al. 1990; CARMICILALI et 2008; CarmiciaLi & Ferry 2008). More recently, dolomitization temperatures were calculated using clumped isotope thermometry, and a crystallization temperature between ca. 40° and 70° obtained (Frrnv et al. 2011). not elear, however, whether the Latemar dolomite can considered typical for the process of dolomite formation in general, given the that most totally dolomitic platforms, including the principal area of this study, lic outside the volcanie centres and are, therefore, difficult to explain as dolomitized by hydrothermal processes (Bosrtuni 1989)

for

put

Itis

fact

1.2

The

studied platforms

data of this study come from a largely dolo-

San Martino-Pale di San platform, the Pale Lucano arca (here called “Pale” if both areas are taken together), and a mainly calcareous platform, the Marmolada. The principal mineralogica! differences have been known long time (Mossisovics 1879). Castiuioni (1939) recognized some limethe Pale di San Lucano and noted unspecistone differences with the Marmolada limestone. The two platforms differ not only in their prevailing mineralogy, but also in the structural setting. The Pale (Fig.2) is the largest coherent remnant of Triassic platform în the Dolomites. It strueturally uncomplicated, with slight dip (5-7°) towards NE, and no major faults, but the SE and W higher dip angles prevail (15-259). The Pale di San Martino area preserves up t0 1,6 km Middle Triassic platform dolomite, with very limited occurrences of limestone. The lower part of the platform is the so-called Contrin formation, Which entirely dolomitic. The Contrin is brackbetween eted the base and terrigenous sequence the Buchenstcin beds at the top, which are absent in the central parts of the overlving Upper Anisian t0 Lower Ladinian platform, 400-800 m thick. The Pale di San Martino area used for the documenta

fora

tion of property variations at the platform scale. The Pale di San Lucano about 1,3 km thick and shows a remnant of an aggrading platform terior, about 400 m across, and well exposcd progradational platform top, only rivalled by the geometries ofthe Capitan reef in North America 1948). The platform foundation a ca. 500 m thick dolomite of the Contrin formation, The progradational part, <110 m thick, grades laterally înto clinoforms cut by a number of listric fractures with very limited displacement (a few metres) and a few sub vertical fractures without mappable offset of strata (Fig. 3). The bedded progradational part terminates with a massive, < 4 m thick, marker bed, which facilitates a bed-by-bed logging, and overlain by another 120 m of bedded limestone and dolomite. The Pale di San Lucano provides the main reference for limestone-dolomite transîtions at the bedding to

in-

(Ka

microscopic scale. The Marmolada

consists of about | km thick Middie Triassic limestone, but structurally more fragmented and now rotated northward by 30-35°. The platform consists mainly of clinoforms, but an about 100 m thick succession of well bedded interior rocks is easily accessible at Pian dei Fiacconi. This outerop provides petrographical and geochemical data of a platform with only little dolomite.

2 Material 2.1

and methods

Field mapping and logging

The mineralogy of the Pale di San Martino was mapped and spot sampled addition to the logging of long section covering the entire preserved platform thickness, with a sample spacing of stratigraphic metres (Milletornanti, Pradidali, Vallon delle Lede, Fig. 2). At Pale di San Lucano, the progradational platform top was logged in sections. In 5 of these (Profil A, B, H, I, M) field logging was carried out on a bed-by-bed basis. Mineralogy was logged as 5 discrete according to the estimated dolomite content (0, 25, 50, 75. 100%). Samples were collected at cach macroscopically detectable change în mineralogy, otherwise every 2 stratigraphic metres. The Pian dei Fiacconi outcrop at the Marmolada was spot sampled onls:

classes

2.2

Quantitative petrography

Three hundred six! four thin sections (5x5 cm), highly polished and double stained with Alizarin red-S and K-ferricyanide for the identification of dolomite and iron-bearing carbonate minerals. respectively, and impregnated with blue dye resin for

= recognition of porosity, were manufactured (302 from the Pale, 44 from the Marmolada). Of these, 315 were point counted using a standard petrographie microscope and a point counting device of own manufacture. Three hundred points were counted with per sample at low magnification (50-100x), method bulk 1 The mm. increment ofca. graîn an voids in partiwhere 1962) applied, was Munsav classes were Nîneteen cles are counted particle, 3 non-carbonate, open distinguished (15 carbonate,

of the set injection pressure over this period then

equilibrium was assumed. If the pressure dropped below 99,5% then the pressure was reset, and monitored again over the equilibration time. This was each repeated until equilibration was achieved at atreduced pressure, The injection pressure was and removed mospheric and the penetrometer was It weighed with the sample and mercury in place. the chamber was then loaded into a high-pressure to maxia was injected Autopore system. Mercury 2000 psia. ‘mum pressure pore spaces) Sample weight, sample and penetrometer weights calculate with and without mercury were used Porosity and permeability measurements of Volumes mercury grain density and bulk density. recorded. were each at injection pressure injected Eighty-nine samples of limestone (79) and dolobe Initial apparent intrusion at low pressures may and for permeabilporosity mite (10) were analysed surface the the result of mercury conforming Geophysik of the Technische ity at the Institut regularities of the core sample. These irregularities Universitàit Clausthal. Core plugs with a diameter of the pore structure. The of 2em and varying length were analysed for poros- are not representative threshold pressure, where mereury injection into and ity by weighing dry state, fully saturated state the pore structure begins, is identified at the presArchimedes weighing in a water basin. A gas per\creases sure where the rate of mercury injcetion own manufacture was used for permemeameter rapidly. Cumulative apparent injection up to this ability measurement using nitrogen as flowing fluid subtracted as surface porosity threshold pressure and applying the Klinkenberg correction (Scnetfrom measured data before subsequent caleulations negGER 1957). mercury injected are made. Cumulative volumes total of pore volume are expressed as a fruction the 24 Capillary pressure measurements of the sample. At any mercury displacement pressure the miniFora quantification of pore throat sizes, capillary mum radius of pore throat that can be penetrated by for one dolomite pressure curves were determined mercury is given by: sample and one limestone sample (2 cm diameter and length) at Core Laboratories, Aberdeen. The dry core trim samples were weighed and cach placed 24» cosf+C to) {hat the pore the bulb of a penetrometer selected Pe volume of the sample was approximately 70 - 80% vher the penetrometer stem. The sample offthe volume = pore throut radius, um 1 together. and penetrometer were weighed interfacial tension between air and mercury, 0 The penetrometer containing the sample was dynesiem loaded into the low-pressure chamber of a Micontact angle between air and mercury, degrees = The 6 9520 IV porosimeter, cromeritics Autopore capillary pressure, psia less penetrometer was evacuated to a pressure of € conversion constant (0.145) than 50 um ofmercury, and then filled with mercury at a pressure of 0.5 psia. The bulk volume of the fraction of Using this relationship, a graph sample was determined at this point, Mercury was radius pore volume injected (v) versus pore throat injected into the core plug at increasing incremencan be constructed. The differential of this gives a tal pressures from 0.5 to 25.0 psia, At each pressure while the pore throat size distribution (PSD) function: point, mercury intrusion was monitored identidv pressure was held constant. Equilibrium was ) PSD= Fogm: fied when the rate of intrusion dropped below 0.001 that The pressure and the total volume ul PSD smoothed using - 2 - smoothing: identified on was point were recorded. Equilibrium pressure over a time basis. Monitoring the change 5) PSD, = (PSD,, 2PSD, PSD,)/4 identified seconds) time of a specific period equilibrium. If the pressure remained above 99.5%

ir-

Pe=

for

(60

PSD

then normalised

to as follows: 1

PSD,

Normalised PSD is presented in graphical form along with saturation against pore throat radius and permeability distribution function against pore throat radius. Swawson"s (1981) parameter is a method to correlate capillary pressure with permeability. The technique involves determining Swayson*s parameter (Sb:Pc), (where Sb = mercury saturation, % bulk volume) which is related to the effective pore space ontributing to fluid Mow and the corresponding indeteriection pressure. The Swawsoy parameter mined by calculating (SbiPc) all pressures for any sample and taking the maximum these values. Theoretical cumulative permenbility, K, of a sample with a given pore size distribution, (r, tor), can be expressed as (PL&chi:, 1949):

Ki=Yr 48

then normalised such that the maximum value is 1.0. A cumulative Permeability Distribution Function (PDF) is given by the following equation: Kt

PDF 2.5

‘veni

Kt Kt,

(O)

For the purpose better quantifying the minerdatabase, alogical X-ray diffractometry was carried out on 706 carbonate samples (503 dolomites and 203 limestones), 693 of which organized stratigraphie sections plus 13 spot samples, For the X-ray phase analyses a Philips PW1710 with Cu K-radiation (1.5418 nm; Ni filter) under 30 kV and 30 mA wasused. The samples were powdered to analytical fineness in a vibratory disc mill using a tungsten carbide grinding set. In order to achieve randomly oriented aggregates which allow compare relative intensities for series series of peaks, the powder was carefully scraped into the cavity of he aluminium holder and only gently pressed with a glass slide to counteract the tendency of particles to lie parallel to the glass surface. For the semi-quantitative determination of content of different carbonates in the samples, CaF, was admixed internal standard in ratio of 1:5 because the main fluoride and carbonate peaks adioin directly but do nol interfere with cach other. By means of the evaluation softwarc APD (Automated Powder Diffraction, Philips) the relevant peak areas of internal standard and car-

molesCaCO,-

(333:33*d-spacinu în degress_ol_20)-911,99(7)

2.6 Isotopes hundred sixty six carbonate samples (473 dolomites, 133 limestones and cements from the Pale, 54 limestones and cements and 6 dolomites from the Marmolada) were analysed the Isotope Unit of the University of Reading, U.K., and the Isotope unit of the Universitàt Géttingen for determination of and d50. The powdered samples (0,5-1 g) were drilled with a mm bit from surfaces. polished Aliquots of 100 mg were digested in 100% H,PO, and the purified CO, was analysed in a SIRA Series II (Reading) and Finnigan Delta Plus (Gòttingen) mass spectrometer after calibration with a marble internal standard. Duplicate samples indicate a reproducibility of 0.05% for dC and 0.09% d"O. The isolope analysis was performed using standard procedures (MCCrea 1950; Craig 1957). The 3'C measurements were reported as deviation (%e) from the PeeDeeBelemnite (PDB) standard, those of 250 as deviations (%o) from the Standard Mean Occan Water (SMOW) standard. In be order able use identical units in the text and SMOW diagrams, values were recalculated to PDB values using the equation:

2!5C

drill

for

X-ray diffractometry

the

bonates were integrated and recaleulated on basis of the known content of CaF,. Furthermore, the shift of the d (104) peaks with 3.04 A (for pure calcite) and 2.89 À (for stoichiometric dolomite) to lower and higher values, allowed the determination of the molar content of MgCO, both phases. For a more determination dolomite accurate of stoichiometry, 24 samples were analysed with step size of 0,004° following the analytical method and equation of Kaczuarex & StoLy (2011)

a'O(PDB) = 0.97002 *2"O(SMOW) -29.98

(8)

account for potential acid fractionation cf fects during {he mass spectrometry measurements. the data were corrected according to the equation To

aO(com)= @"O(PDB)-((dolomite

All PDR

percentage’100)*1,1)

(9)

è'0 values used in this article are corrected

values.

Seventy seven carbonate samples (42 dolomites,

35 limestones and calcite cements) were analysed for ‘'Sr:#'Sr at the Scottish Research and Reactor Centre in Glasgow, U.K. The material analysed was

= microdrilled from polished slab surfaces. Samples were accurately weighed into PFA teflon screwtop beakers (Savillex*) and leached in IN ammonium acctate to remove readily exchangeable Sr (GoroxHiov et al. 1995). 7Rb and "Sr spikes were added quantitatively to determine Rb and Sr concentrations. Samples were then dissolved using 2.5N HCI. Rb and were separated in 2.5 N HCI cation X8 200-400 mesh Bio-Rad AGSOW using Rb and exchange resin. Total procedure blanks Sr are typically <200 pg for carbonate samples. Sr samples were loaded onto single Ta filaments with N phosphoric acid, Rb samples were loaded onto triple Ta filaments and analysed on a VG Sector 5430 multiple collector mass spectrometer. The "Sr #Sr ratio was corrected for mass fractionation us0.1194 and an exponential law. The ing *Sr'#Sr mass spectrometer was operated in the peak-jump15 blocks of ing mode with data collected tios. NBS987 gave 0.710257 18 (2SD, n=14). Rb VGS4E samples were analysed on a single collector mass spectrometer. 3 sets of ratios are collected and the mean and standard error computed. Rb and Sr isotope ratios are adjusted for mass fractionation and spike contribution and concentrations calculated using adaptations of the standard algorithms of Kkovca & Hurtev (1968). Rb concentrations were analysed on an Agilent 7500ce ICP-MS using a self aspirating PTFE nebuliser with an uptake rate of 0. 1ml'mn. 115In was used as an internal standard to monitor instrumental sensitivity. Rb concentration was determined on the Rb peak using 5 integrations of 0.2 A solution of the geostandard BCR-1 ‘was under the same conditions as the samples and gave [Rb] = 47.2 ppm which is identical the certified value of 47.2+0.6 ppm.

for

ra-

run 2.7

Vitrinite reflectance

In order to obtain an independent estimate of maximum temperatures during burial, 10 sites were sampled for vitrinite reflectance analysis (Fig. 2). Nîne samples come from organic rich facies at the base and the middle part of the platform succession One sample from the top ofthe platform was seleeted on the southern part the Civetta massif (Palazza Alta), 1,5 kilometres NE of the Pale di San Lucano. The samples were prepared and analysed following the method described in Litxe et al.

site

(012).

2.8 3D modelling Construction

of 3D models was necessary for

first was to correctly position all

two reasons. The parameters, measured

at the platform scale from dif-

ferent locations, relative to their stratigraphic provenance. The second was to determine the geometries

the limestone-dolomite transitions by transform-

5 the point data obtained from stratigraphic logSan ging of the progradational interval of the Pale Lucano înto a spatial distribution The 3D models created for this study are puremodels. The outerop modelling technique static ly used here is similar t0 modelling subsurface hydrocarbon reservoirs using a deterministic framework transformed of stratigraphic layers which a volume composed cells possessing properties Modelling was performed using (he commercial ly available software IRAP-RMS (version 2012) by

into

Roxar (www.roxar.com).

A simple 3D model was construeted for the entire platform of the Pale. The model consists of only two horizons, one for the platform base, and one the platform top (corresponding to the stippled line in the cross section of Fig. 2). The scattered property data were loaded as point data defined by y and plus the properties (mineralogy, isotopes, porosity). The long logged sections were loaded as artificial well paths with the properties. The model with cell was then transformed into a crements of 20x20 m and 500 layers, which corresponds to an average layer thickness of about 3 m in the area of maximum platform thickness, and 0 where the clinoforms are wedged out. The resulting cell properties were then plotted on x,y diagrams (x corresponding to property, y to stratigraphic posidocumenting variations of tion) with the purpose properties as function of stratigraphic position. For construction of the detailed model, 7 stratigraphic sections were loaded using accurate (40,1m) GPS data exact path definition plus the logged data (bed thickness, mineralogy, dolomite type, isotopes, porosity). The beds were modelled with the accurate bed thicknesses but interpolated beyond the sections to cover the model area. result surface forms the top of'one bed, and the resulting layers were transformed into a modelling grid covering 0.55 km? with rectangular cell geometry and dimensions of 3x3 m (x, y) and cell thickness corresponding to the bed thickness, resulting in 1134106 cells. Those coinciding with the stratigraphic sections were assigned a diserete value of the property. Carbonate geometries (limestone, sucrosic dolomite, cyele cap dolomite, tepees) were calculated using a simple interpolation algorithm with search radius x, of 1000 m to avoid undefined cells in the model volume, and a vertical search radius of 0.01

for

grid

for

Fach

in y,

494 (83)

500

“i

HE coiomite

IE] ankerite (number

E z

of observations in parentheses)

5 8

5Ò

129 (23)

® 99 0 PA

21 (5)

100

dolomite/ankerite percentage

Frequency distribution of mineralogies measured by X-ray diffraction of carbonates from the Pale in inerements of 10%. Numbers indicate total numbers of observation, those in parentheses and yellow bars represent the ankerite, Almost pure calcite and dolomite/ankerite prevail, whereas intermediate compositions are much rarer.

Fig.

to avoid interpolation into neighbouring beds)

interpolation between the sections and was carried out separately for each bed. The circular search geometry was chosen because of the unconstrained geometry (x, y) of'the dolomite and limestone bodies. Finally, the cells of property models above the actual topography and below the progradation plane were to undefined, resulting in realistic 3D model of the actual field situation. for

set

mally white with shades of grey, tan and yellowish. Macroscopically visible porosity is generally very low and confined to isolated voids, occasionally with centimetre sizes. Sedimentary structures are lacking, but some beds exhibit tepee structures (PI. 1) consisting of partially totally dolomitic beds containing centimetre thick crusts of fibrous calcite (PI. 2). Tepee structures are up to a few decimetres height, are onlapped by bedded limestone and dolomite, and can occur superimposed several beds which grade laterally into breccia cemented by fibrous calcite. Breccia beds grade laterally unbrecciated beds. The second dolomite type is an fine grained cardonate with typical conchoidal fracture planes when hammered in addition to an odour of kerogene. ‘occurs as centimetre to decimetre thick interbeds of sucrosie dolomite, less commenly of limestone. X-ray diffraction indicates that 63% (26 of 41 analyses) of these carbonates are pure ankerite, the remainder similar to the sucrosie dolomite. Therefore, the wheathering colour typically yellowish, but white and light grey also occurs. Millimetre size voids filled with calcite and parallel lamination are typical. Clasts of this dolomite type occur in beds of sucrosic dolomite. This facies is similar to the so-called cyele caps, which are parily calcitic at the Latemar. In the modelled progradational interval, the cumulative thickness varies between and 27% of the total stratigraphic thickness (Fig. 5)

Results* 3.1

Dolomite and limestone

into

Dolomite occurs în 2 basic facies mappable in the field with a hand lens and HCI. Most common is a sucrosic type with occasional fossil moulds. Xray diffraction indicates pure dolomite in the majorîty of analyses, but many consist of an unquantified mixture of dolomite and Fe-rich dolomite. Ankerite ((Ca(Fe, Mn, Mg)CO,),) makes up 17% of'the analthe long secyses (Fig. 4), but virtually absent the di Pale tions of San Martino consisting of nearly 100% dolomite. Ankerite and dolomite cannot be differentiated the field, because the colour nor-

Rane data in table format (point count data, isutopes, vîtrinite reflectance data, 3D model data files) cam be obtained from

the principal author upon requesi

1 iydwy

uo]Op

deo “OS

Aj9f9

St 10q

JO 99

2 SastALIM9IO

tyduny

"9 Bi

ut pur

poroidap

sARRIDUI

sammioez

DOG

seviuI

dor

@ Md

MOId

9g 9110)

IMOId

indu

Furpinoad

‘5221

Pur

(SAMO suor9as

‘9

Ft UL

GIOTOP/E MENTE dEI SAO

‘6

[RIOT

Fit %LT

suonoas

Limestone is a macroscopically dense rock lacking visible porosity and similarto a mudstone. Dasyeladacean thalli, gastropods, sponges and corals are occasionally recognizable. Oncoids can have diameters of 5 cm, but cm îs a more common figure. Sedimentary structures such cross bedding have not been found in the Pale, but the Marmolada few cross beds with decimetre thick foresets occur. The maîn difference between the limestones of the Marmolada and those ol'the Pale are the conspicu0us, locally metre sized botryoids of fibrous calcite cement. These occur mainly, but not exclusively, in the clinoforms of the Marmolada but are nearly absent from the Pale. Grains floating fibrous calcite cement characterize many beds in the Marmolada, but have noi been quantificd. Discordant dolomite breccia bodics are normally elongated (Vallon delle Lede, Pradidali) to subeircular (Pale di San Lucano) and funnel to saucer shiaped cross section. The breccia consists of doJomite blocks in sucrosic dolomite ranging in diameter from a decimetre to metres, but blocks of limestone occur (Pradidali, Pale di San Lucano) The dimensions (x, v) of these breccias ranges from a few metres to 200 m across such at Pale di San Lucano and nearly a kilometre in length such as at Pradidali, where the breccia overlaps a conspicuous subvertical fracture, The proportions between dolomite and limestone can be estimated the Pale di San Martino from mapping. The platform carbonates now cover an area of about 135 km?, of which about 2,5 km? are mainly calcitic, which translates into a limestone abundance about 2-3%. The limestone percentage the Pale di San Lucano less certaîn, because the mainly vertical, partly calcareous, cliffs could not be sampled continuously. The progradational interval consists of about 30% limestone. Contrin, aggradational core and an estimated 50% of the clinoforms are dolomite. 1

as at

cubic

for

3.2.

Dolomite-limestone transitions

Transitions from dolomite to limestone shows basic geometries and always occur within millimetres t0 a few decimetres. One is parallel to bedding including lateral transitions within a bed, the other a transition subperpendicular and crossoutting bedding. The prevailing abrupi transition îs mirrored in the mineralogica] data obtained from XRD (Fig. 4). In the bed parallel transitions the mineralogy changes with planar or undulating boundary (PI. 3 A), Altemation of beds of pure limestone and pure dolomite are common as well. Some limestone beds

contain millimetre thick dolomite layers, traceable Jaterally for tens of metres. Lateral transitions within a bed show digitate geometry (PI. 3B). Crosscutting dolomite îs associated with fractures and shows a gradual transition from totally dolomitic fracture haloes into pure limestone (Pi 4). Perpendicular the fracture this transition zone decimetre thick dolomite fingers parallel develops bedding. This type is observed only a few locations The orientation of the larger limestone bodies (x,y) is subparallel to mappable fractures (Fig. 2). The calcitic areas of the Pale di San Martino, between Pizzo Micl and the Fradusta, parallel the ENE-WSW and NE-SW striking fracture system. Thiekness comprises about half of the platform carbonates, ca. 500 m, whereas the lower 600 m (Contrin formation) are dolomite. The limestonedolomite transitions of the Pale di San Lucano parallel the listric fault system (Fig. 3, 6). The presence of these fractures is not documented by oftset and faulted strata, but rather by gradual thickness variations of individual beds and intervals. The most conspicuous thickness changes from 0,8 to 4 m is observed in the marker bed providing a figure for the displacement caused by the listric fractures in the progradational interval. The width of limestone bodies is 50-100 m perpendicular fracture strike, with a thickness generally less than the total thickness of the progradational interval. The marker bed is [imestone in almost the entire Pale di San Lucano. Parallel to the fractures, limestone bodies range kilometre (Fradusta, Pizzo Miel) in length from ‘about 300 m (Pale di San Lucano). The distribution of limestone the northem Îlank, the depositional platform slope, of Pale di San Martino îs unknown access, but in at elevations reasons lower than 2000 m limestone prevails. This contrasts markedly with the southeastern flank (Croda Granda — Feltraio area), which entirely dolomitic for localized except occurrences of limestone, very Platform and flank carbonates are crosscut by subvertical sedimentary dikes, which can a metre wide and tens of metres long, and consist 0: rOUS cement and fine grained internal sediment. AII dikes strike NNE-SSW E-W (Zawpiri 1987) and part of conspicuous fracture system with steep southward (80°) dips, which is mappable the altopiano of the Pale.

exact

for

the

3.3.

tion

are

Petrography and quantitative composi-

The microfacies of limestone îs dominated by a

RBBBE

sccosc dolomite

REMI tepoos

[eye cap ankeriteldolomite

Fig.

oblique aerial view rom SSE

6, The 3D model of the progradational platform top of Pale San Lucano în map view and two oblique

with stationary limestone dolomite transitions (arrowed). Tepee fracture occurrences conspicuously overlap the systematie zone, whereas the cycle cap dolomite shows dolomite, limestone and fractures. Model location îs Fig. 2. relationships with Views. Limestone is present in narrow corridors

| 0

E--Fa 20

fabrilcognizable

anioni dita o [DÌ

Graindlone

Pale cycle caps Marmotada limestone Pale mostre

Progoionio

Bounditone

sumber

ef obervatone

The frequency of depositional fabric observed in thin scetions of'limestone and dolomite of the Pale and the Marmolada. Boundstone clearly prevails, the higher percentage of grainstone at the Marmolada probably a sampling elfoct caused by the limited thickness of the investigated interval. Most sucrosic dolomite preserves 1 relict Fig.

of the depositional texture

Marmolada limestone (Pian dei Fiacconi,

=Ad)

fracturest

porosityi Micriic crusts =—————121%4>m_1@@"@—@ saddie dolomite 8 dolomite

Mombs=

foraminiters®®

microproblematica, sponges, corals em bivalvesi crinoid ossiclesa dasycladacean algaeB

pisoidsi

Intraciastsi blocky calcite) microcrystalline and fibrous cement radiolarians

fractures

Pale, all limestone samples (dolomite <50%,

139)

porosity

NOME Tmm__———r—@e_y@——

saddle dolomite dolomite mombs

piSolds em Intraciasts È volcanic graîns foraminifersI Microproblematica, sponges, corals Bivalves crinoid ossicies

|pere E

dasyciadacan algae Micrito

blocky calcita

quartz, chert 1 OPaques microcrystalline and fibrous cement |

O raw data MI

The quantitativi correeted for dolomite.

Fig.

composition

of limestone

data corrected for dolomite percentage

from

the Pale and the Marmolada, showing the raw data and data

boundstone fabric which can grade grainstone 7). The the thin scale section packstone (Fig. or

into

relict fabric of dolomite, recognizable in all cyele cap dolomite and the majority of sucrosic dolomite thin sections, document similar depositional fabric a

(PI.

5).

Limestone is composed of two major components, namely cement and micritic crusts (Fig. 8). The micritic crusts occur layers, aggregate grains, intraclasts and oncoids and show clotted-peloidal fabric composed small (5-20 jim) crystals with many irregularly distributed spaces occupied by slightly turbid to transparent, microcrystalline c: cite spar. This is the typical “structure grumeleuse' of Caviux (1935). Entrapped foraminifers, rare volcanic glass and quartz grains, Occasionally remnants of microproblematica are preserved resembling bushy bacteria colonies (PI. 4). AIl microproblematica and metazoan remains are volumetrically negligible. Calcite cement shows continuos development from microerystalline to drusy or fibrous in millimetre size pore spaces. Both cement types were, Fibrous cement therefore, counted as one class. typically shows sweeping extinction under crossed polars, can show millimetre thick layering parallel to pore walls and grows centripedally into pore spaces. Fibrous cement occasionally recrystallized to a mosaic of anhedral blocky calcite crystals. Cement the micritie crusts. Blocky is nearly as abundant calcite shows a similar continuous development from fibrous or drusy calcite and typically fills the larger pore spaces, but is volumetrically very unimportant (ca. 5%). Ferroan cements identified by staining are extremely rare and restricted to singular examples of fibrous calcite in cyele cap dolomite and blocky dolomite as pore fill in sucrosic dolomite, and were not counted separately There no significant difference composition between the limestone of the Pale and those of the Marmolada. Micrite restricted to beds above the progradational interval of the Pale and makes up a total of ca. 6% all thin sections. Dolomite consists of a mosaic of anhedral crystals, which have typical sizes of 50-250 um, are thin transparent can show generally unzoned Relict a around zone turbid core. structures of fi. brous cements are now replaced by a mosaic of clear dolomite crystals. distinuished Cyele cap dolomite and ankerite from limestone the complete absence of shells, and from sucrosic dolomite în the crystal size, um. Pisolites are relatively more common. Relict structures of fibrous cements, now a mosaic of clear

are

5-50

dolomite crystals in size similar to those of suerofracture and pore sic dolomite, are common Remnants bacteria of (Rivwfilling cement (PI. 4), laria and Schizothrix types) are preserved as mic-

fills

ritic structures whose tubular voids are filled with microerystalline dolomite. Dolomitic limestone dolomite-limestone transitions consists of euhedral to anhedral, unzoned dolomite rhomboedra in allochems, preferably in the micritic crusts (PI. 6). The distribution of dolomite rhombs ranges from random within to concentrations at the edges of allochems. A conspicuous and consistent feature that dolomite rhombohedra in contact with fibrous calcite cement are not cuhedral but have serrated contacts. Some rhombs have a core forming pore space. Saddle dolomite occurrences at the Pale are limited a few samples, all from the vicinity of volcanic dikes and from the circular breccia of Pale di San Lucano. At the Marmolada, saddle dolomite can occur along with blocky calcite in pore spaces not completely filled by fibrous calcite. AII bed parallel contacts between different mineralogies are digitate stylolites with amplitudes of several millimetres to centimetres. Stylolites are less common in limestone than dolomite. Of 174 sections thin limestone, 26 (15%) contain one or. several subhorizonal stylolites with an amplitude of >—5 mm. Thin sections the Marmolada limestone show stylolites at all. In 172 dolomite thin sections of the Pale, 69 (40%) contain stylolites with this minimum amplitude. Cemented fractures make up ca. 1% of the rock volume. They cons mos ly of anhedral dolomite crystals or fibrous and blocky calcite and range width from less than mm {0 a centimetre. The fractures normally have sharp, parallel contacts with the matrix of the host rock, but are difficult to identify in dolomite, Calcite filled fractures are absent in dolomite. virtually absent in limeOpen pore spaces few 9). stone (Fig. samples contain a low Only percentage of residual primary porosity resulting from incomplete cementation by fibrous blocky calcite. None of the limestone thin sections show evidence for porosity caused by dissolution. Point count porosities range from 0 in most cases to 35% in a singular sample of fibrous calcite. The average lîmestone porosity is 1%, By contrast, dolomite shows intererystalline pore spaces as residues of primary porosity. The crystal faces are euhedral and not modified by dissolution. addition, a network of tubular pores, ca. 10pm diameter, with a dark rim occurs in many dolomite samples (PI. 7), including partially silicified portions

are

Sabre rcognizabie

Dore i 24

Poe

Là

Graîngtone

number

100

observatone

limestone and dolomite of the Pale and frequency of depositional fabric observed in thin sections the Marmolada. Boundstone clearly prevails, the higher percentage of grainstone at the Marmolada is probably a sampling effect caused by the limited thickness of the investigated interval. Most sucrosic dolomite preserves a refiet. of the depositional texture.

Fig.

The

Marmolada limestone (Pian dei Fiacconi,

nda)

fracturesi

porosityi mieritie crusts saddie ciolomite #

dolomite hombs: foraminifers@

microproblematica, spong6s, corals Bivalvesi rinaldi ossicles®i

dasyoladacean

algo

pisol Intraciast:

blocky calcite)

[

microcrystalline and fibrous cement radiolarians

Pale, all limestone samples (dolomite <50%,

fractures

n=198)

porosity Br

micritle crusts

saddie dolomite

dimo pompe PISAICS mr microproblematica,

Intraciasts sl volcanie gralns foraminifers

corals sponges, valves tinoke ossicles dasyeladacean algao

mmictit blocky calcite

quartz, chert Opaques microcrystalline and fibrous cementi

È)

O raw data

Il data corrected for dolomite percentage The quantitative composition of limestone from the Pale and the corrected for dolomite.

Fig.

Marmolada, showing

the raw data and data

is 1,00000

0,10000

porosity (%)

01000011

—__

——

limestone «horizontal sample (n=40) (Marmolada) +vertical sample (n=39)

dolomite (n=10)

(Pale di San Lucano)

30 25

Pale and Marmolada

sucrosic dolomite and limestone (n=285)

» cycle cap dolomite (n=30)

€

”

oe ar è epitto ms 50

“i

100

dolomite %

Cross-plot of'the petrophysically determined porosities and permeabilities (A) from the limestones of the Marmolada and dolomite from the Pale. The cross-plot porosities and dolomite percentage (13) determined from thin ion point counts in good agreement with the petrophysically meusured porosities, but high porosities dolomite (ca. >10%) are rtefacts caused by micromolds from recent boring organisms. Fig. 9.

dolomite interfingering with basinal limestone, and one case blocky and fibrous calcite. This type of porosity typically increases towards the edge of the samples. AII pore spaces in limestone and doJomite are microscopically unconnected. Practically all porosity >2% occurs în dolomitic limestone and dolomite, whereby the dolomitic limestones show virtually no porosity in the calcareous portions. Conspicuous forms of neomorphism in

spar micritization or neomorphic spar have not been observed. This does not mean that recrystallization did not occur (Bamunst 1971), but the degree cannot quantified by optical petrography. It is not relevant for the purpose this study to what extent the microcrystalline calcite spar of the micritic erusts a product of neomorphie alteration ora primary cement.

20 Dolomite stoichiometry

3.4.

“The mol% MgCO, of 23 analysed

dolomites average 49% (range between 48,5 and 50%, only one analysis provided 45 mol%). 95 percent of the analysed dolomites are thus nearly stoichiometrie.

Vitrinite reflectance

3.5.

The analysis of organic material has provided Rm values ranging from 0,49% 1,54%. The lowest value is based on only 25 measured points, and 0,54% a more reliable value for the minimum The highest values were obtained from 1). (Table the base of the platform Valle di San Lucano.

3.6

Porosity, pressures

permeability

and

capillary

Petrophysical determination of porosity confirms the low thin section porosities (Fig. 9). Vertical and horizontal permeabilites of limestone show no systematie difference, nor do permesbillites covary with porosity. Dolomite porosity from thin sections can be substantially higher than porosity determined by petrophysical measurement. Porosities are randomly distributed. The distribution of pore throat radii calculated from capillary pressure measurements is very similar for limestone and dolomite, most occurring in the range from 0,1 to um (Fig. 10). The largest pore throats are somewhat larger in dolomite than in limestone, which is no surprise given the general differences in crystal size. The distribution function of the resulting permeabilities shows that permeability is reduced virtually 0 when pore throat size falls below 0,5 um, and that only the volumetrically subordinate, largest pore throats contribute to permeability. 1

3.7.

Geochemical data

Because

of the sampling method applied, the rethe

values of limestone

miccomprise both and ritie particles microcrystalline spar. These valported

ues are, therefore, strictly speaking average values of ivo different constituents. Fibrous cemeni values

are treated separately. The available literature data from the Latemar were included Table 2 for cominconsistent parison. Although the data coverage for the 3 platforms, a number systematic relationevident ships are (Fig. 11). For Pale, the range of is identical in limestone, calcite cemeni, and sucrosic dolomite:

in is of

the

050

ankerîte, but average ankerite is somewhat heavier invariant over the entire than dolomite. The range 12). thickness The most negative doplatform (Fig. in dolomite breccia pipes (Fig. lomite values occur 1.3%o heavier than dolomite 13). Average 2""C limestone and shows almost exclusively positive values, whereas limestone matrix can reach 4,8% A distinet negative excursion of limestone 2/C is ‘observed around the marker bed of the Pale di San

Lucano

(Fig. 14).

Detailed analysis of 20 limestone-dolomite transitions confirm that dolomite 2‘C consistentiy heavier than limestone (Table 3). This is different for 2!*O, which is in most but not all cases heavier in dolomite. A weak correlation with sample evident, where cm-spaced analyses result in tance between dolomite and negligible differences limestone. In the progradational interval the Pale di San Lucano, where closely spaced data are avail1,69%o. able, the difference of the averages AII 3 platforms show similar 2%O values for limestone, but values heavier than about -4% lacking at the Latemar (and the Marmolada). Average dolomite is heavier at the Pale than at the Latemar. The average limestone is >2%a heavier at Marmolada and the Latemar. At the Latemar, the average difference between dolomite and lime0,4%o, the Marmolada has not enough dostone lomite data. The #Sr/**Sr values show a considerable range, irrespective of the mineralogy, and most data fall outside, but are relatively close to, the Middle Trial. (2003). assic seawater composition of Kortk Limestone and dolomite can be radiogenic, depleted or normal marine. At the dolomite-limestone transitions, dolomite and limestone can, but do not always, show values differing up to 0,0003 at the metre scale. Sr/*Sr ratios of the Marmolada limestone and cement are higher than those of the Pale. Strontium concentrations of limestone and cement are somewhat higher than of dolomite, and cycle cap dolomite contaîns insignificantly more Sr than dolomite. Cross-plots of the measured sucrosic 'Sr/6Sr values versus other parameters (Sr concentration, 2°C and 260, Mn, Fe, stoichiometry) lack covariance. This holds for the data as a whole and split into the different facies (Fig. 15). Other element concentrations are similar in all platforms, but Fe enriched the Latemar dolomite. Mn shows a the Pale. higher average

are

d!C

100

iimestone — porosity 0,5%

permeabilty 0.0002 mD

(bar)

poemi, porosity 4,49% ou

permeability 0,014 mD

A 08

saturation (fraction)

function

—

distribution

0001

0010

0100 pore

limestone dolomite

permeabilty imestone

—

permeabllity dolomite

1,000

throat radius (um)

Fig. 10. The capillary pressure curves for limestone and dolomite show similar pressure/saturation relationships (A), which are transformed into distribution functions of the pore throat radii (B). The related permeability distribution shows that nearly all permeability is effective in the largest pore radi, which make up enly a minor proportion of the pore radii present in the rock. Originally reported psia pressures were recalculated bar.

Discussion 4.1

Porosity and permeability evolution

Related to the question guiding this study, porosities and permeabilites and their distribution are parameters which allow first estimate of fluid Now properties of a rock. The thin section data indicate that porosities are randomly distributed in the plat-

form, and that limestone is essentialiy a tight rock lacking porosity and permeability. These properties were acquired early in the diagenetic history. The intimate association of the micritic crusts and microcrystalline and fibrous cement has (not necessarily, but possibly, genetic) parallels in travertine, Where a tight rock originate at the water-sediment interface (PrxTECOSt 2005). Fibrous cement is

can

4190 tive. PDBI È

Pale

ssucrosio dolomite elimestone = cycle cap dolomite x ankerite calcite cement

n=606

2180 [ievs.

PDB]

4 Latemar (Carmichael et al, 2008)

n=239

41°

etmestone 1 dolomite

Srl

SLA

gti 2)

dolomite calcite cement

as 11.

nel

Fig.

« imestone

Cross-plots of 2"C and 2%0 from 3 different platforms.

also surficial in origin, easily demonstrable by the tepees onlapped by bedded limestone. Il the blocky calcite were considered a “deeper” cement and its volume added limestone porosity, porosities would only come close those of suerosie dolomite, and near surface limestone permenbilities would not have been significantly higher than those measured. The porosities in dolomite are partly due to the channel type microporosity, a statement which can only be supported qualitatively because porosity burial

types were not distinguished during point counting. This poretype an artefact, most likely not caused by diagenesis but recent boring organisms (fungi, bacteria). Il it were caused by leaching from flowing fluids, the euhedral crystals facing pore spaces în the same samples would be difficult 10 explain. it were molds of Triassic bacteria, theîr presence blocky fibrous calcite would implausible. If this outerop effect substracted, dolomite becomes tight rock with properties similar the limestone. It is important to note here that this, probably re-

and

= thin

section porosiy (%} to ‘s

ede

s00

«limestone (n: Ladomee

tal

20 0.90)

«dolomite (n=243) Limestone (1-47)

Lemon

40 (£PDB)

SOT

oro o

loto (248)

orer8=

io ozoso0

o70ss

0700

3 È

124) corte Limestone

n-11)

Lcamentins2)

Fig. 12. Variability of porosity and geochemical parameters of'the Pale as funtion of their stratigraphic position. The vertical axis is the number of model layers and shows the relative stratigraphic position of the measured parameters Marine Sr isotope signal (blue bar) after Korte et al, (2003). Data from the progradational interval (Fig. 14) are excluded.

Vallon delle Lede

Milletomanti

Pradidali

%PDB

III dolomite breccia «db

+0 mineralogy

Fig.

13.

XRD

-mineralogy and stable isotope data

of the continuousty sampled sections (10m intervals) of the 3

for locations see Fig. AII sections consist of nearly 100% dolomite, and the breccias show conspicuously low 20. Whereas 2UC displays a trend towards lighter values upward, è""O shows no trend. Depth scali tion (metres above sea level) and corresponds approximately to stratigraphie thickness due to the low

Pale di San Martino,

structural dip.

cent, alteration ofthe rock had obvious effect on the geochemical signal, because there is no covariance of dolomite porosity with oxygen (Fig. 16), carbon and strontium isotope signals. It is unelear whether the higher porosities in Latemar dolomite than in limestone are due a similar effect, because no petrography was provided by CarMicHAFI. et al. (2008). The relict fabric of the sucrosic dolomites suggest that the transformation of limestone dolomite affected a precursor rock with composisimilar tion and properties the measured dolomite and permeabilities, which correspond to porosities those of limestone minus blocky cement. The petrographic relationships between dolomite and fibrous cement the dolomite-limestone tranno

into

sition can be interpreted in two different ways. The fibrous cement is fact younger that rst option than dolomite. This would mean that dolomite forfibrous calmation occurred before cementation cite, and, given the volume of fibrous cement, that the limestone had much higher permeability than the dolomite. This is not very likely because of the common fibrous cement relict structures în dolomite. More likely, the corrosion of dolomite is the result of recrystallization of the fibrous cement the expense of dolomite. Calcite cement probably stabilized later than dolomite, which is also evidenced by the somewhat higher temperatures measured in Latemar calcite (Ferky et al., 2011).

in by

* Î

(m)

so depth

A) 5

soli”

li n

” “

dolomite (n=50) «limestone (n=36)

thin section porosiy (%)

£ —

« dolomite (n=176) +

limestone and cal. cite cement (n=76]

TO.» dolomite (n=176)

59 -* Imestone and

Pai

cal-

cite coment (0-76),

4 2 3'0 (PDB)

n so so

to 9 10 30 50

mi_—_—__, 0.7073 0.7074 0,7075 0,7076 0,7077

O,7O78

0.7079

0,708

0,7081

87811868, Fig.

14.

Variability of porosity and

Marine Sr isotope

cochemical parameters of the progradational interval of Pale di San Lucano.

ignal (blue bar) after KORTE et al. (2003).

200

100 Sr

00m)

300

400

ebasinal (n=3) elimestonie Pale (n=14)

acyele caps Pale (n=10}

e sucrosio dolomite Pale (n=32) scoment Pale (n=4) a Marmolada limestone e cement Marmolada

oro

ara cron

Pale

E ozoso

8 orore

* cycle cap dolomite

orta o7o68

ss sos

—

“

sucrosie dolomite (n=22)

molto CAGO

ovose oro88

Pale sucrosic dolomite (n=29)

307004

71/068;

dan

È orore

czor

orosei 0

Fig.

15.

Cross-plots of$

100

Fe,

2000 Ma

(ppm)

3000

4000

isotopes and other measured parameters show the lack of covariances.

42 Main arguments against fluid flow

only is it impossible to synthesize dolomite under near surface conditions, but dolomite has also never been produced experimentally by Mowing potentially reactive brines through compact limestone. is trivial but not generally acknowledged that past fiuid flow cannot be demonstrated, but Not

for

only evidence or against it can be extracted from static rock properties. Best evidence for flow are rock properties, or gradients. systematic changes Relative to the dolomite problem, such evidence is absent in general and in the study area in particular. In spite of the tight rock properties, however, it is difficult to prove that fluid Now through such rock is impossible. Fluid flow is strongly dependent on

în cement. Even

a non-water wet situation and with nanoscale permeability pathways unrelated to depositional texture, it is not understandable why the cement systematically excluded from partial dolomitization flowing fluids were respensible. The second major argument against fluid flow limestone. Vertical is provided by the geometries limestone corridor residues are not predicted by any dolomitization model currently used, whether ît is reflux of saline brines, geothermal convection, seawater-freshwater mixing, compactional or hydrothermal fluids (PurseR et al. 1994 and WiLson al. 1990, for cartoons of different hydrologic models).

(%)

porosity

section

thin

30 (%:PDB) of dolomite oxygen isotopes and

Cross-plot porosity determined lacking covariance. Fig.

16.

from thin sections

shows the

the capillary properties of the rock. Although high percentage pore throat radii are close to the thickness of the immovable water films around grains (Morrow 1991), flow could have been possible in a neutrally wet or non-water wet situation. A chemical reaction with the host rock, however, would probably be inhibited because of the decreasing element concentration the boundary layer under these circumstances (cf. Wepier,1997). Non-water wet conditions can best explain the displacive cement crusts of the tepees, which would require high pressure differentials to move fluids through a thin film in a water wet situation (Bamtugsi 1971). Wettability, not only of of carbonates, is a problemati is inconsistent, subject (o changes issuc, because and cannot be measured in-situ (c.g. CHILINGARIAN et al. 1996). Wettability issues are not normally included in diagenetio studies of carbonate rocks. Homogeneous dolomite with heterogeneous porosity distribution is difficult to explain by fluid flow. The main arguments against fluid flow. however, come from the petrography at the dolomitelimestone transitions. If flowing fluids were responsible for the transformation of limestone into dolomite, the dolomite should either grow system atically from fractures, bedding planes or other potentially high permeability “channels” into the host rock, from the pore spaces into the matrix. A gradient should develop, because large amounts of fluid have to pass the unreacted matrix, too. AII this is not observed. AII thin sections of dolomitie limestone show that dolomite is restricted to the matrix, only in largely dolomiti samples dolomite also occurs

of dolomite

Alternative origin

43.

The alternative to fluid flow that the Mg was Two contained primarily in the rock. options exis The is that dolomite is a primary precipitate, Which unlikely because of the experimental failof synthesis, and the fibrous cement crystals, îts ure which are unknown dolomite polymorphs. The seeond, more likely, is that dolomite is a product of

first

mineral transformation.

The alternative is a dolomite precursor consisting of very high Mg calcite. The dominant role of bacteria is al plausible (Monty unproven 1995). In the analysed carbonates, demonstrable bacteria play a vanishingly small role, but the exact genesis ofthe platform carbonates is not relevant for this study. Mg calcite is stable in scawater but thermodynamically unstable (Ramvast 1971). Modem natural high-Mg calcite normally does not exceed ca. 30 mol% MgCO, and is usually substantially below this value, but Mg calcite with >50 mol% MECO, has been synthesized at ambient conditions (Giover & Steri, 1967). Itis generally accepted that high-Mg calcite stabilizes into calcite (Barnugst 1971). This should be no different in extremely high-Mg calcite, but rethe modem. mostly quires an open system such highly porous and permeable and often unconsolidated, sediments, from which this diagenetic rule is derived. How element concentrations were modified în the primarily tight Triassic carbonates during surficial diagenesis, and how much if any Mg was lost, is unstudied. Itis trivial that the Mg remains in rock if'ît cannot escape because ol'a tight matrix and a tight overburden In principle, the proposed origin of dolomite includes a simple isochemical recrystallization, lar the model proposed by Nasiletal. (2011) from the study of recent corraline red algae. The crystal system remains trigonal, only the crystal class a

but

sim

in changes from orthorhombic to rhombohedral, hexagonal îs

for ankerite. This type of dolomite formation

compaction process, beits effeet a (chemical) with the density increase from cause it is associated dolomite (2,84-2.86), and either a in

calcite (2.71) to

volume reduction or a porosity increase by about

6%.

the precursor calIt were pure coincidence te had an average of exactly 49 mol% M2CO,, minmeasured from stoichiometry, at the time had it eral transformation. If recrystallization would create calcite lenses in dolomite, such as in

less,

cycle cap dolomites with fibrous calcite cements, which suggests that some cement held less Mg however, 100% the matrix. The rule dolomite without calcite inclusions and is more îndicative of >50 mol% My most cases. Excess Mg could have been lost via fractures, e.g. în coml nation with compaction (see below). Mineralogical inhomogeneities were obviously equalized by mithe isocroscale redistribution, clearly reflected lated dolomite crystals in dolomitic limestone, aragonitie shells replaced by dolomite crystals, and by the equilibrated geochemical signal, but the exact al. 2009) is process (“diagenetie filter”, Giscuer some

than

unknown. When

from

and at which depihs the transformation

calcite to dolomite occurred is unconstrained

field

relationships. It is possible that the ci se tallization temperatures of Ferry et al. (2011) typical, but untested for the Pale. Formation of doTomite would then be a subsurface, “burial”, phenomenon. This includes the cycle cap dolomite. Although it is widely believed that fabric preservation such as thatseen in the cyele caps indicates syndepositional dolomitization, evidence for this lacking. Crystal sizes (or matching assumption mineralogica! boundaries displaced by the early fibrous calcite, i. c., geometrical data), and reworked their transformaclasts do not evidence the time tion into dolomite or ankerite. Limestone preservation as corridors could simresult of efficient escape of Mg from the ply be same depositional mineralogy in fracture zones, or limestone was primarily basically free of Mg. Both role. The secondary los effects may have played of material, particularly of Sr, but probably also of and Mn, limestone favours the first option. from

are

the

4.4.

Vitrinite reflectance

interpretation ol'isotope data needs to consider the maximum temperatures (o which the studied formations were exposed. Vitrinite reflecA reasonable

tance

data provide independent estimates, which are

otherwise usually inferred from oxygen isotope data or circumstantial evidence. The temperature obtained from vitrinite reflectance is dependent on the rate ofheating and increases with the rate (BURNIIAM & Swrrnry 1989). Because neither the rate, the exact age nor the origin (simple geothermal heating or magmatic heating) of the temperatures are known, only minimum and maximum values can be calculated from analyses of the study area. The Rm data indicate minimum temperatures of about 90° for the base and top of the platform, but in the area of the long sections minimum temperature for the base of about 130? obiaîn for the platform base, and a minimum temperature of 70-100* for the middle part of the platform (Vallon delle Lede, Tab. 1) The resulting minimum temperature difference ca, 30° for halfthe platform thickness. In the Pale di least San Lucano, the temperature difference was 35° for the whole platform thickness.

the

4.5 Isotopes

isotope signal of the Ti

platforms is the with to question of respect highly problematic different mineralogies. The first the controls on the question to be clarified îs the potential modification of the isotope signature due to resetting, In a rock with 1% porosity and stagnant porefluids, the water/rock ratio is 0,01, which would effectively preclude any modification of oxygen. carbon or strontium isotopes (Baynex & Hanson 1990). According which is the to Banner & Hanson, resetting most susceptible t0 resetting, would require fluidi rock ratios >0,1. Resetting of oxygen isotopes could have occurred only in the most porous carbonates analyzed under stagnant pore water conditions. The indilacking covariance between porosity and did that this not occur. cates This suggests that dolomite 050 în fact records whereby “origithe original precursor calcite nal” refers to the diagenetie stage from which on no exchange was possible due to the porosity-perfluid meability evolution. This is not necessarily the true depositional signal acquired at the sediment-water interface, but rather diagenctic, albeit “early”, signal ofevolved pore waters. In particular, the low Sr concentrations in limestone are incompatible with a depositional signal, which is normally significantiy higher in marine carbonate (Bamm:rst 1971). The loss must have occurred în near surface settings, because there are no Sr-rich minerals in any of the The

of 00,

2“

20,

platforms or adjacent rocks. closed system, temperasuch Itis clear that

ture would have no effect on isotopes. This means that fluid 2°0 cannot determined from clumped because in this case was isotope thermometry, is It not set by temperature. no surprise that over the entire platform thickness of the Pale, where temperature difference was at least 35°, no 2!"0 trend visible. By contrast, NC shows a trend of upward decreasing values which is compatible with the trend of the marine signal in the Middle Triassie, but the marine baseline is poorly defined (Kortr et

al.

2005).

In terms of dolomite and limestone origin, the stable isotope signal problematic. lrrespective of the origin of dolomite, average limestone should be it (re)erystallized lighter in both 2"C and 250 from the same fluids. Similar fractionation factors have been proposed for 2*O of replacement dolocalcite as mite (Lanp, 1980) and 'O enrichment the mol% of MECO, (JMENLZ-Lorrz et a function al. 2004; 3-6%0). ca. 0.6%o heavier Aragonite &'"O than pure calcite, reducing the difference relative to high-Mg calcite by up to a third with respect to calcite. Fractionation of in calcite with SOmol% MBCO, should result in enrichment of ca. 1,2% relative to pure calcite, and aragonite should be 1,8%o heavier than calcite (Rusinson & Clayca. ron 1969), sothat the difference between aragonite and a coeval high-Mg calcite containing 50 mol% MgCO, should be 0,6%. Dolomite interpreted as result of fluid flow is normally considered to have inherited the carbon signal from the precursor rather than the fluid, an assumption which is unsupported by data, because a high water/rock ratio would also modify the carbon signal (Banner & Hanson 1990) The relationships predicted by fractionation experiments are only partly observed in the isotopes, and they are inconsistent when different platforms are regarded. Whereas the difference in dC (doJomite-limestone) of the Pale is almost exactly the amount a 50% difference in Mg mol% predicted by theory suggesting primarily different polymorphs (high-Mg calcite and calcite, respectively), the 20 averages are nearly identica! suggesting the same very similar Mg-content of the precursor. This overlap of "O appears typical, not only în the Dolomites (e.g. Mountioy & AMTHOR 1994; Mirirr & For, 1994). The necessary difference of >3% în fact observed in some beds of the Pale, but the to negamajority of transitions shows much tive differences (Table 3). This suggests that fractionation alone cannot account for the differences in a"0. Fluids of different composition must be conlered as a possibility, particularly at the Latemar, where the negative difference would suggest that

for

less

limestone was enriched in Mg relative to dolomite, an implausible scenario if fractionation alone were

the reason for the

è0 signal

Marmolada and Latemar have significantly heav-

ier 0"C than the Pale. This cannot be the expression is of a purely marine signal of calcite, because

unlikely that seawater had different compositions in a small sedimentary basin. As for d!0, polymorph differences contamination need be considered. that the consisted mainItis possible wo platforms ly of aragonite because of the conspicuous cement botryoids (Aissaovi, 1985) and that the aragonite 0"C signal was completely preserved, but the dif. Terence ca. 0,4%o higher than the calcite-aragonite fractionation. Because the vicinity of the volcanic centres, these platforms could have been influeneed by magmatic CO, (Pentecost, 2005), and the difference between the Pale and the Latemar may be unrelated to polymorph differences. lt is someWhat surprising that în recent geochemical studies of the Latemar the potential influence of magmatism on the isotope signal not even discussed, but environmental effects considered only atmospheric (Curisr et al., 2012). Whereas the problem of fractionation during mineral formation relatively well established, litile is known about the reverse effect, the modification of isotope signals during the loss of elements such as Mg and Sr during diagenesis of superficialIy tight carbonate. Possibly the incorporation heavy an only partly reversible reaction. The isotopes similar Sr concentrations in limestone and dolomite poînt into this direction. The selective, mineral specific and platform specific shift of'isotopes, therefore, remains problematic. Based on isotopes it cannot be decided whether limestone was always different modified by deposited as a polymorph (early) diagenesis to escape transformation into do-

lomite.

4.6

Chemical compaction

The range of interpretations of isotope data is fiurther complicated by the possible contamination of marine signal by compactional fluids. Chemical compaction played in dolomite greater its limestone, but or, more likely, precursor than

the

role

the amount is not quantified yet, Compaction also played a role in the strata below the platforms, and mass ‘balance problem. The disposes an enormoi solved material has to be removed by Îluids, with a fluid-rock ratio of >8000 (Saranicz & Davisoy, 2005). Removal of dissolved material requires flow paths, which can only have been (he fractures, s

fluids, and a hydraulic gradient. Seawater is readily available during deposition, but would not rise against gravity through the platforms. The required gradient could have been provided by artesian freshwaters, a not totally exotic possibility if the present synelinal configuration of the Dolomites is considered. Artesian waters would, however, have a freshwater signal plus that of the dissolved (marine) carbonates explaining the strongly negative of the breccias and, possibly, the negative shift of the Latemar dolomite. Dissolution ad recyeling would explain why all Sr ratios except for one lic between the Permian minimum the Lower Triassic maximum (KorTE et al., 2003). Lacking covariance and the tight rock fabric indicate carly diagenetic contamination of the platforms. Mg-reeycling also would cause dolomite geometries mimicking hydrothermal christmas trees (Davis & 2006) such in the Latemar, because could have caused local anomalies of high-Mg calcite at the sediment-water interface in otherwise calcitie (or aragonitic) platforms constituting anomalies themselves. The breccia pipes are geometrically and, therefore, probably genetically linked to dolomite, which can be demonstrated at least for the Latemar (CarMicnaLL et al., 2008), but are probably fluid escape structures mostly unrelated to magmatism or elevated temperatures. This also explains why the Latemar dolomite d"0 shifted to negative values relative to Latemar limestone. Latemar dolomite is apparently related t0 escape structures, and provides geometrical evidence that the Latemar limestone formed as a primarily Mg-poor carbonate polymorph. This is less certain for the Pale.

and

Sur,

Conclusions

ing loss of Mg, Sr and other elements. In contrast to dolomite, limestone occurs in structurally defined corridors. Transformation into dolomite was either impeded bythe primarily low or absent Mg content. or the Mg and other elements efficiently escaped in fracture zones before other carbonates were fransformed to dolomite. The dolomite problem is a problem caused by inappropriate models, including possibly the present one, not an enigma of natural sciences. false

Acknowledgments thank C.-D. Satiler for the XRD analyses, Ralf Littke

(Aachen) analyzed the organic-rich roeks and provided ihe vitrinite reflocance data. Andrcas Weller and Wolfgang Deb(Clausthal) determined the porositîes and permeabilites from plug sampes, Kurt Mengel (Clausthal) provided the REA

sett

lor dolomiie stoîchiometry, Corc-Laboratories measured and evaluated the capillary: pressure survos. Rob Ellam (Glasgow) provided che Sr isotope analyses, Mike Isuaks (Reading) and Andreas Pack (Gottingen) the stable isotopes. Roxar provided free research licenses of the modelling software IRAP-RMS. Frank Sandbagen organized the manufacture ol the thin section point count device, and Felix and XRD data

(Aberdeen)

Blendinger compiled a PC programme to make it operarional Raîner Miller provided editorial support. The support of all'in: dividuals and organizations is gratefully acknowledyed.

References

its

Aissaoui, D.M. (1985): Botryoidal aragonite and diagenesis.Sedimentology, 32: 345-361. Banner, 1.L. & Hanson, GN. (1990) Calculation of simultaneous isotopic and trace element variations during waler-rock interaction with application carbonate diagenesis.Geochim. mochim. Acta, 54, 3123-3137. Bamiuast, R.G.C. (1971): Carbonate sediments and their diagenesis.620 p.; Amsterdam (Elsevier), A. BoseLiNI, (1989): storia geologica delle Dolomiti- 148 p.; Grafiche Lema di Maniago, Pordenone. Buannax, A. K. & Sweenty, 1. (1989) A chemical kinetic model of vitrinite maturation and reflectance.- Geochim. Cosmochim. Acta 53: 2649-

Dolomite ofthe Triassic Pale is a typical platfrom a calcareous precurwhich tight rock when transformed sor, dolomite. Negligible porosities and permeabilities were acquired during surficial diagenesis. Dolomitization by fluid flow through such rock is unthat the Mg was in the rock likely. The alternative before transformation into dolomite, suggesting a high-Mg mol%MgCO,) calcite precursor. Isotope data allow a wide range possible interpretations, and significance equivocal. Recycling of compactional material, artesian freshwater and magmatic CO, could have played a significant role during deposition, in a addition t0 mineral specific fractionations and their potential reversal durform dolomite. It formed

was

its

(50

their

2657.

Carmicari,

Fury, LM. & MeDornoLGH, (2008): Formation of replacement dolomite in the Latemar carbonate buildup, DoloField relations, mites, northem Italy: part and geochemistrx- Am, mineralogy, Sci., 308: 851-884. L.M (2008): Formation Carmicnati, SK. & of replacement dolomite in the Latemar carbonate buildup, Dolomites, northern Italy: part 2 SK.,

WE.

Fay,

Origin of'the dolomitizing fluid and the amount and duration of fluid flow.- Am. I. Sci., 308: 885-904.

CastigLioni, B. (1939): Il gruppo delle Pale di San Martino e le valli limitrofe Memorie dell’ Istituto di Geologia e Mineralogia Università di Padova, 17: 1-110. Caviux, L. (1935): Les roches sedimentaires de France. 463 Paris (Masson). Cimincarian, G. V., Mazzuno, SJ. & Riekk, H.H. (1992): Carbonate Reservoir Characterization: A Geologic-Engineering Analysis 994 p.; Amsterdam (Elsevier), N., Immenzausrr, A., Amour, F., MUTTI, M., Paestoy, R., Winiriaxe, FE, PETERIANSE. A., Ecrnmore, S.0, Duyn, PA. & Agar, S.M. (2012): Triassic Latemar cycle tops = subacrial exposure of platform carbonates under tropical arid climate. Sedimentary Geol., doi:10.1016/j. sedgeo.2012.02.008 CraicH, H. (1957): Isotope standards for carbon and oxygen correction factors for the analysis of carbon dioxide- Geochim. Cosmochim. Acta, 12:133-149. Davis, G.R. & Swi, L.B. Jr. (2006): Structuraliy controlled hydrothermal dolomite reservoir facies: an overview.- Am. Assoc. Petr. Geol. Bull,

pi;

Cris,

90:

1641-1690.

(1962); Classification of carbonate rocks according to depositional textures Am. Assoc. Petrol. Geol. Mem., 1: 108-121 Ferry, J.M., Passev, B.H., VasconceLos, C, & Ener, JM. (2011): Formation of dolomite at 40 80 °C in the Latemar carbonate buildup, DoJomites Italy, from clumped isotope thermom39: 571-574. etry— Geology, Giscier, E., Swarr, PK. & Lomanno, A.I. (2009): Stable isotopes ofcarbon and oxygen in modern

sediments of carbonate platforms, barrier reef, atolls and ramps: patterns and implications. Spec. Publs Int. Ass. Sedimentol., 41 61-74, Giove, E.D. & Sirvet, R.E. (1967): Synthesis of magnesian calcites— Geochim. Cosmachim, 31:

600-603.

Goroknov L., Semigitatoy, M., Baskakov A., Kurvavin, E, MeLniIKOv, N, SocHnava, A., & TurcHexko, T. (1985): Sr isotopic composition in Riphean, Vendian and Lower Cambrian carbonates from Siberia (translated from the original Russian). Stratigraphy and Geological Correlation,

3: 1-28.

Jneniz-Lorrz, C.,

Rowankk,

C.S., Hucwias,

F.1.,

Onvoro, H. & Casato, E. (2004): Oxygen isotope

var-

fractionation in synthetic

magnesian

7107-712: Lawn, L.S. (1980): The isotopie and trace element geochemistry of dolomite: the state ofthe art. 73:

DunkAW, R.I.

Acta,

calcite. Geochim. Cosmochim. Acta, 68: 33673377 Jivievez-Lorez, C., Romantik & Canauiero, E. (2006): Carbon in synisotope fractionation thetic magnesian calcite— Geochim. et Cosmochim. Acta, 70: 1163-1171 Kaczmarek SE. & Sitey, D.F: (2011): On the evolution of dolomite stoichiometry and cation order during high-temperature synthesis experiments: an alternative model for the geochemical evolution natural dolomites. Sedimentary Geology, doi:10.1016/j.sedgeo.2011.07.003 Kixe, P.B. (1948): Geology of the southern Guadalupe Mountains, Texas U.S. Geol. Survey Prof. Paper, 215: 183p. Korte, C., Kozux, HLW., Brrekscien P. & Vezza, (2003): Strontium isotope evolution of Late Permian and Triassic seawater- Geochim, Cosmochim. Acta, 67: 47-62. Koxir, C., Kozur, H.W. & Viuzer, (2005): 25C and 20 values Triassic brachiopods and carbonate rocks as proxies for coeval seawater and palacotemperature.— Palacogeography, Palacoclimatology, Palacoecology, 226: 287- 306. Krovcti T.E. & Hurtey PM. (1968): Strontium iation and whole-rock isochron studies, Grenville Province Ontario Geophys. Res.,

SEPM

Spec. Publ., 28: 87-110.

Lawn, L.S. (1985):

The

origin oTmassive dolomite—

Geol. Education, 33: 112-125. Leowarpi, P. (1968): Le Dolomiti. 1.

Geologia dei Monti tra Isarco e Piave 1071 p.; Mantrini Rovereto. Lirrke, R., Urat, T.L., Urtmann, AK. & Risvanis, F. (2012): Reflectance of dispersed vitrinite Palacozoic rocks with and without cleavage: Impliions for burîal and thermal history modeling in the Devonian of Rursee area, northern Rhenish Massif, Germany. Intem. J. Coal Geology 89: 41-50. Macnet, F.G. (2004); Concepts and models of dolomitization: a critical reappraisal.- Geol. Soc. London, 7-63 Publ., JK. & Fork, R.L. (1994): Petrographic, Miur, geochemical and structural constrainis on the timing and distribution of postlithification dolomite in the Rhaetian Protoro (,.Caleare nero”) of Portovenere area, La Spezia, Italy. Spec Publs. Int. Ass. Sediment., 24: 187-202. Mossisovics, E.V. (1879): Die Dolomit-Riffe von Sùdtiro] und Venetien— 552 p.; Wien, (Hélder). in

Spec.

235:

8: Monty, C.L. (1995): Mud mounds: their origin and evolution

Spec. Publ. Int. Ass. Sediment., 23:

Sdap.

Morrow, N.R. (1991): Interfacial phenomena

in pe-

troleum recovery. 449p.; New York (Dekker), Mountioy, E.W. & Amruor, J.E. (1994); Has burial dolomitization come age? Some answers from the Westem Canada Sedimentary Basin.Sediment., 24: 203-229. Spec. Publs. Int. Nas, M.C., TrorzscH, U., Oppyke, B.N., Trarrorp LM., Russei, B.D & Kunr, DI. (2011): First discovery of dolomite and magnesite in living coralline algae and its geobiological im3331-3340. plications.- Biogeosciences, Prvemmcost, A. (2005): Travertine. 445p.; Berlin, (Springer). Purckii, W.R(1949): Capillary Pressures - their measurement using mereury and the caleulation of permeability therefrom.- Trans. AIME, 186: 39 - 48. Purser, B.H., Tucker, M.E. & Zexoer, H.H. (1994): Problems, progress and future research concerning dolomites and dolomitization— Spec. Publ. Intern. Assoc. Sediment., 21: 3-20.

Ass.

Rusrsson, M. & CLavion, R.N. (1969); Carbon-13

fractionation between aragonite and calcite.Geochim, Cosmochim. Acta 33: 997-1002. Sararicz, M. & Davisox, (2005): Pressure soluchalk.- AAPG Bulletin, 89; 383-401. tion flow through ScuemecGer, A.E. (1957): Physics Toronto Press), porous media. (University of Swansov, B.F. (1981): A Simple Correlation Between Permeabilities and Mercury Capillary I.

Pressures.-

Petrol.

Techn.,

December 1981

2498 - 2504.

Wepitk, G. (1997): Lehrbuch der physikalischen

Chemie— 1070 p.; Weinheim (VCH). Wirsox, EN. Harp, LA. & Prius, OM. (1990): Dolomitization front geometry, Muid flow pattem, and the origin of massive dolomite: the Triassic Latemar buildup, northern Italy. Am. J. Sci., 290: 741-796 Zaxenri, D. (1987): Le piattaforme carbonatiche triassiche delle Pale di San Martino (Dolomiti). Memorie delle Scienze Geologiche Padova 39:

73-83.

39011481

pasano9

1ex puo pue

amionzi

jonpoxd

1a) asso

soada

LbS+

=Ogj@ ‘69/0:

xe *2'0-=

1LL0L'0=1S9gl!8/9

=Og,?

GUOISAU

*40G-=OgiP SUOISAUI

seuepunoq

0g?

I=0g1 auuoop ojiogeo

ANLUOIOP

199L0L'0=189919,9

*R99'0=0g10

ure/6 shOIgU

PAAIESSIA

Buipuodsa1109

UONISUEN

LIA

139

paio Cura

pue

ue SI

ankerite 3130=

0,40%0

3190--1,20% 8751P®51-0,7074440

limestone 8781/068r=0,7076510

2190

ankerite 8781/8681=0,7074220

Plate 3. Mineralogical transitions and their geochemical signal. (A) a bedding parallel transition with an undularing boundary between limestone and dolomite, (B) is a lateral transition within one bed.scale is 2m long, . In both cases, all measured isotope values are different for limestone and ankerite.

°%L6'L-

°K0S'S-=Ogj?

unum

=Ogj0 pelly

XIMELI

SpioA

AUojeo

°%€0'0-

°%£2'0-

Arewid sNOIgI}

BUOJSAUUI]

aJiuiojop

=Og1@

open

SIILIO]OP

CUI

EONEWA|GOIdO

AUOJOO

PLLIOJSUEN

MYIS-U!

LIU

fracture

=Og,@

Plate S. Preservation of fabric in dolomite. (A) Preservation fabric also common sucrosic dolomite, here a transition between boundstone and graînstone, with relict fabric of fibrous cement (white) and residual primary porosity of 10,5%. Pose spaces are partly occluded by ferroan dolomite (pink staîn). Thin section, scamned, Pale di

San Lucano. (B) typically compo: cap dolomite ne with perfect preservation the fabric. The primary voids and a subvertical fracture are largely filled with fibrous cemeni, which are now a mosaie of Cycle

anhedral dolomite crystals and suggest a calcitie precursor. Thin section, scanned, Pale di San Lucano.

Plate 6. Thin section micrograph of dolomitic limestone, in which isolated, cuhedral dolomite erystals occur erystals. At the contact with cement, the dolomite rhombs show a serrated boundary, probably caused by recrystallization of calcite later than dolomite crystal formation. The relationships between dolomite and limestone matrix the matrix in are typical, dolomite is mostly confined dolomitie limestone. Hollow dolomite rhombi may point a non-stoichiometrie core.

the boundstone matrix surrounded by equani calcite

Plate 7. stone.

type microporosity in dolomite (blue) is responsible for the higher porosities in dolonrte than in Itis probably caused by recent boring organisms (Tungi, bacteria) perferring dolomite to limestone.

Channel

Table LL Vitrinite refiectance data of the Pale, for locations see Figure

[sample P6 LP8

[Rm] [sid. dev. _|081__]007

0,82_

[0,08

[on P600__]049

[on 0,044

P603A

[0,073 [0,141

[0.76

P6oB_(0,73

[T[C]

|n_

90-160 710-130

P6OSC

[0,64

10,123

[0.71

[0,109

|50

(P324 P326 P608

[0,564

P255 b256 P316

3 (Colle

(0,069

[0,11

D 12

6 (Poni)

[1,579

[0,163

[1,329

0,247

__]|50

0,709

[0.19

152

_,0,013

[50

0,278

[0.5

50m above base platform

Brunet)

4 (Velo della Madonna) 5 (Sass Maor)

_|SI

{Peis_(122

Pighera __|2 (Vallon delle Lede)

[0.158,50 |ozsa_

[top platform

—_|67

P603D

[0,563 [0.94 _liss

stratigraphic position

location (Fig. 2)

[120-170_|1 outside map of Fig.2

50__|120-170_]800m due N of Monte

[59

fees

|94_

_[90-160__[7(Cimon della Pala)

(Monte Feltraio) (Chiesa di San Lucano) |130-210_[10 (base Vallon delle Lede) |140-215 ‘155-220

above

ca, 50m

above base

P618_

P606_

|1,15

nenumber Terange

per sample of analyzed particles obtained by heating rate of 1%m.a. (minimum) and 1000%m.a, (maximum)

of temperatures

platform

10m below base platform _[20mbelow base platform

[1,58

(BursHnAM & SWEENEY, 1989)

base platform 100m above base platform basin, ca.100m above base basinal limestone

___[200m

_| ]

10m below base plattorm__]

— Table 2. Average properties of carbonate rocks from 3 different platforms.

n is]t = [re ce

li(setras lorale i [n fr sa far asa Viarmolada

Tatemar

mr E ea fan e rn II a as I

Pe e PO Foe: pronao

nota

i ge

re om

sei

tassa

ru Lee

"024 271

nt Re reco

vede

CORTI eros oO

TRI

ue das

Ji ar | ca

n tota — Timestone.

sO tLo0e)

Sedie

cigni

Sinti Fonni

A Zoom

caTo E Caen

290201

3%0 (POR)

SR—

int

480 28

[0707544

oroTesI

O.TOT8ZE2

ww SIA

220

minor

reported

ra pas

led ie fato dan

TRI L

soa sa DTOTITA,

—

ces

fs he

Tai

oa ber

col rai

[5.06

a24

ainsi no,

A tea msm

253,82

pesi

—+

sith <10% dolomits and alc, respoctively

t roported Carmichael et > toa number olanalyses for elements facies dolomie iter data under sueosic dolomite and cycle includes

* stable isotope data refer samples all dna for he Latemar from Carmichael

24%

e la a

[o.ro7887a

2 re >

castoro

si lan si

crm ha ces 8 fasi n < co 8950 (RePDB)

TEST

3 x

ar Ae casse

——S09%

]

Jsp zz 1101600

199

fan

E È

tate

eso ino) a

tar

er sr dat

Jan

182

a. (2008)

caps

al.

(2008) is 3 for both dolomite and limone:

content

sn reported

Table 3. Isotope data rom 20 limestone-dolomite transitions. number and

text Fig. î

2 3

[tansition [ope

[range of

dolomite! ankerite 1%]

dB 2__B

cal) |__[>o PDB] 2

AGNO (dol

AGC (do cal)

[3%

PDB] 03

ea BIS

7 &

10 (PL4A)

1a 15

IT IE

‘6

22 IS

2_IT 2

sample

|spacing [m]

0,0003822

oo [0,

3__

[max

1000

d__vRR

(dol-cal)

0,0002070

2_Js

3 FSrFSr

0-10 [0-75 0-100

0100

odi 00001190 0,02 0,0000750 0,02

[002

0-10

0,0000260 0,01

1002

S=on polished surface of hand specimen, T=from thin seetion Range of dolomite/ankerite %: numbers n iralies are estimates, others from XRD analyses ‘A=difference between samples with highest and lowest dolomite/ankerite% numbers in bold italics for A3'O (%o PDB) values > minimum fractionation factor (3%e) for coprecipitation

lausthaler eowissenschaften Geoforschung 2013 Beitràge aus der Geologie und Palziontologie

Clausthaler Geowissenschaften

—

735

Clausthal-Zellerfeld 2013

Geoforschung 2013 —

Beitràge aus der Geologie und Paliiontologie

Herausgeber: Institut ftir Geologie und Palaiontologie, TU Clausthal

mit Beitràgen von Babak Aghababalou, Alberto Bertini, Wolfgang Blendinger, Carsten Brauckmann, Elke Gròning, Gerhard Hahn, Stephanie Lohmeyer, Edwin Meissner und Peter Miller