A Contribution to the Geological History of Suffolk. Part 1

TRANSACTIONS A CONTRIBUTION TO THE GEOLOGICAL HISTORY OF SUFFOLK Part 1 SUMMARY OF THE GEOLOGICAL SEQUENCE HAROLD E . P . SPENCER,

F.G.S.

IN the British Isles there is as great a variety of geological formations as in any comparable area of the earth. T h e oldest fossiliferous strata, Cambrian, occurs in Ireland, Scotland, and Wales, with pre-Cambrian and Igneous also, bat in East Anglia such ancient rocks are very deeply buried below more recent formations.

Travelling from west to east one passes over successively newer formations, all of which are tilted eastward and each successively with later and less primitive forms of life represented by fossils (FIG. 1). T h e series thus traversed are Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, and Cretaceous. What is presumed to be Silurian limestone and which possibly represents the top of a buried mountain system has been reached in deep bores at Harwich, Sutton, and Weeley.

Similar tilting toward the North Sea occurs in Suffolk where in the western part of the county much of the chalk has been ploughed off by ice.

In south and east Suffolk there is a greater variety of postcretaceous deposits to be found than in any other such limited area in this country. Excepting only the upper part of the series the Eocene is representated by the Thanet and Reading beds, Oldhaven Sand, and London Clay. T h e Miocene is not known to have any surviving deposit but its former presence is indicated by derived fossils. Remnants only of the Pliocene Coralline Crag exist but the early Pleistocene Red and Norwich Crag sections are the best in Europe. T h e middle and upper Pleistocene are well represented by the series of glacial and interglacial beds which include the Cromer Forest bed series, the Cromer and Lowestoft tills, the Hoxnian interglacial beds, the Gipping tili and Ipswichian interglacial, and also deposits probably representing the last glaciation. Post glacial beds include accumulations of beach shingle, blown sand, and marsh deposits.

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The Pleistocene is popularly known as the " Ice Age " but the fact is that there was a series of very cold periods, the last four of which vvere originally known as Guntz, Mindel, Riss, and WĂźrm; now, however, local terms are applied in various regions like the term " Gipping tili " and " Ipswichian interglacial " used above.

It is important to note that at least six earlier glaciations have been recognized in southern Europe, one of which is the Donau which mav well have occurred in Pre-Crag times. The evidence for each as one goes back in time is successively scantier but there are indications of these cold periods in the Permian and Carboniferous epochs in other parts of the world.

Cretaceous The Cretaceous formation in Suffolk is represented by Chalk which is about 900 feet thick in the east and over 90% pure calcium carbonate. It is remarkably free from flints and fossils are not common. The chalk in the Gipping Valley consists of the zones of Actinocamax quadratus and Belemnitella mucronata, but at Great Blakenham excavations have reached the Marsupites zone. The uppermost Chalk in England is the zone of Ostrea lunata which is exposed on the foreshore at Trimingham, Norfolk ; this indicates that in Suffolk at least 250 feet has vanished, largely perhaps by the action of ice as is shown by the quantity of chalk in the chalky boulder clays deposited by retreating ice sheets.

The Marsupites chalk was formerly exposed at Monks Eleigh and lower zones occur to the west buried under glacial beds.

Chalk quarries exist at Claydon, Great and Little Blakenham, YVhitton, Coddenham and in the Sudbury district. The Bramford and Offton pits are now obscured. From Roman times onwards chalk was quarried and burned to produce lime to mix with sand for mortar with which to build town walls, Castles, monasteries and houses. Clav lump and wattle and daub cottages had to be protected by a coating of lime plaster. The industry was last in Operation at Bramford in about 1940 where whiting was also produced for vvhitewash and distemper manufacture.

Eocene—Thanet Bed When the chalk first emerged from beneath a retreating sea much vanished owing to the normal weathering processes, rain, etc., which wear down land surfaces, and by the action of rivers which bear the waste down to the sea where new deposits are formed and in turn emerge to become another land. No evidence of Post Cretaceous land exists in Suffolk and the base of the Eocene lies conformably on the Chalk consisting of a thin bed of oddly shaped flints forming the basement bed of the Thanet Sand. Many of the flints are stained green by Glauconite (hydrous Silicate of iron and potassium), to which mineral the dark colour of the Thanet

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Bed is due. The surface of many of the flints has an eroded appearance ; the term Bullhead Bed applied to this Stratum is derived from the shape of the flints.

The Thanet Bed is the lowest member of the Lower London Tertiaries which also include the Reading Sands and Clays and the London Clav. They extend from Hampshire to Norfolk, Alling the London Basin. Thanet Beds occur in the Sudbury area and in the Ipswich to Bramford region but are seldom exposed.

Reading Beds The Reading fluviatile sands and coloured plastic clays are next in the series, the latter are generally grey or green with crimson blotches due to the presence of Haematite, an oxide of iron, and have been used for brickmaking. These bricks are still made at Great Cornard brickyard. The deposits are not fossiliferous and were formerly exposed at the base of Hog Highland Cliff but are now hidden by the development of Cliff Quay, Ipswich. The sand was formerly worked at Bramford and Dales Road, Ipswich.

At Maidenhall, Ipswich, crimson blotched Reading sand was temporarily exposed in deep trenches ; the sand also contained fist-sized irregulär pieces of " race " (concretions of calcium carbonate). Large blocks of concretionary sandstone (" Sarsens ") occur in the Reading sand and these are similar to those used for the trilithons at Stonehenge, though smaller. Portions of Sarsens (the name being derived from Saracen), were used in the Gipping Valley as " saddle querns" on which corn was ground by a reciprocating motion by both Neolithic and Bronze age people.

Many Sarsens have been dredged from the bed of the Orwell, some of which bear Striae caused by the movement of ice over them while still embedded. Part of the rockery in the Lower Arboretum, Ipswich, is made up of Sarsens.

At Thorington Street, near Higham, Sarsens were common below the river gravels where the London Clay had been removed during the formation of the Stour Valley and many have been found in gravel workings. Professor P. H. G. Boswell, in the Ipswich Memoir of the Geological Survey, indicated a line from Bramford to Sudbury beyond which he believed that no sarsens occurred. Portions of broken sarsens have however been found in the Waveney Valley at Homersfield and Weybread and part of an unrolled one in the gravel workings at Blythburgh Heath.

These discoveries contributed to the confirmation of the inference that Eocene deposits had formerly extended further north than the text books indicate. Subsequently well borings in Norfolk, near Loddon, penetrated previously unrecorded London Clay.

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FIG. 1 Diagramatic section from Wales to Suffolk showing the eastward dip of the strata 1 Cambrian, 2 Ordovician, 3 Silurian, 4 Devonian, 5 Carboniferous, 6 Permian 7 Trias, 8 Jurassic, 8 Cretaceous, 10 Eocene, etc.

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FIG. 2 Ideal section through H o g Highland showing the remnant of O L D H A V E N Sand Height about 100 feet—not to scale.

GEOLOGICAL HISTORY

Hocmiqhland

Fig. 3

Fig. 4

Fig. 5

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202 Transactions of the Suffolk Naturalists', Vol. 13, Part 4 Oldhaven Bed An important section was exposed when the end of Hog Highland was dug away during the construction of the last section of Cliff Quay, Ipswich, when a hitherto unknown Suffolk deposit was revealed (FIG. 2). Underlying the London Clay was a dorne shaped section of grey sand, with sand filled borings of marine organisms in the Reading bed below. Scattered throughout the sand were slate coloured flint pebbles, teeth of sharks and crushed fragile shells. This is thought to be a remnant of the Oldhaven bed and another remnant was observed at Bobbit's Hole in Belstead Brook Valley. The late Professor P. G. H. Boswell disagreed with this interpretation but he did not see these temporary sections and the very marked unconformity below the London Clay. The basement bed of well rounded pebbles under the London Clay and doubtfully referred to the Blackheath Beds indubitably owes its formation to the destruction of the Oldhaven Sand.

In southern England thick beds of marine pebbles channelled into the Woolwich Beds are known as Blackheath Beds and are associated with buff or grey sands. Parts of the pebble beds are silicified, forming blocks of conglomerate (Puddingstone) like the Hertfordshire Puddingstone. Erratic blocks of this rock occur in glacial deposits from Essex to Norfolk and are more likely to have originated from local Eocene beds than to have been transported from the west by ice. This stone was used 2 , 0 0 0 years ago by early Iron Age man in East Anglia for their beehive-shaped rotary hand mills.

London Clay London Clay was formerly used for brickmaking from Sudbury to Bramford, whence to the north it is buried below Crag and glacial beds : its present boundary crosses the coast near Great Yarmouth. The former extension of the London Clay over Norfolk has been recently proved by its presence in a well boring.

This formation was probably laid down by great rivers like the Amazon and Mississippi, which annually carry vast amounts of silt to the sea. At this time the climate in the northern hemisphere was tropical to sub-tropical as is shown by the presence of fossil fruits of the Nipa Palm, now found living in southern Asia. There are also remains of turtles, fishes and of the teeth and vertebrae of sharks, while fossils of crabs and lobsters are common.

Branches of trees were swept out to sea, became waterlogged and sank to become stone-like, or be preserved by pyritisation.

One such tree, Cercidiphyllum spettceri, Brett, grew as far north as the present arctic circle and today has but two living relatives, one each in China and Japan. This species was discovered in a block of septaria on the Orwell shore by Bridge Wood, Nacton in 1927.

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The London Clay varies in texture and colour from a tough, bluish, jointed rock to a more sandy light brown clay. Sometimes it is greenish owing to the quantity of particles of pyrites therein, when it is unsuitable for brickmaking. Where the colour is brownish it is usually due to the oxidising action of percolating water which converts the iron Compounds into Limonite (hydrated oxide of iron). Crystals of Gypsum (calcium sulphate) frequently occur, sometimes they are minute and glisten in the sunlight but large groups of radiating crystals may be found.

Another formerly economic product of the London Clay was the colloidal limestone, or Septaria, formerly called Harwich Cement Stone because it was used during the 19th Century for the manufacture of Roman Cement. This industry died out as a result of the invention of Portland Cement. The rock was collected from the shores of the estuaries and dredged from the sea bed.

Blocks of it were first used as a building stone by the Romans and later by the Normans for Castles and churches, etc. Orford Castle was mainly constructed of it. The London Clay septaria occur as a Stratum about a foot thick and large slabs are exposed by the action of waves during stormy weather when there are also high tides. These slabs break up into angular blocks under the influence of the weather and are scattered along the foreshore of the Orwell and Stour estuaries. Unlike the septarian nodules in the Jurassic marine clays, which are usually bun-shaped, calcite veins are the exception rather than the rule. The septaria are so named because the nodules of colloidal limestone have the peculiar property of cracking internally leaving hollows, sometimes of a honeycomb pattern, in which crystaline calcite (calcium carbonate) forms. (These Jurassic septaria frequently occur in glacial clays.) The comparatively rare veins in London Clay septaria are generally in the form of pale green banded veins which are attractive when cut and polished. Formerly the pyritised wood washed from the clay by the tides of the Essex coast and along the estuaries was collected by the poor who were paid with brass tokens by the lords of the Manors of Frinton and Minster.

This was sold as a source of sulphur for the manufacture of sulphuric acid and iron sulphate. Copperas Bay, near Harwich, was so named because of this industry.

The surface of the London Clay is very uneven, varying from sea level to at least 100 feet O.D. (FIG. 3). It cannot be said if this is in part due to post Eocene modification by weathering during a terrestrial epoch but it is most probably due to erosion by the Miocene, Pliocene, and early Pleistocene Crag Seas. In some places the whole of the London Clay is missing, as at Gusford Hall, Belstead, and Bramford Chalk Pit. Proof of its former existence lies in the evidence of much weathered septaria at the base of the overlying Red Crag at the former site.

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In the Ipswich area deep Valleys have been formed by the action of the water from the springs which emerge from the base of the Red Crag. This erosion was probably rapid about three or four thousand years ago when the climate is believed to have been much wetter and the water table higher than at the present time.

The fact is that the settlement of the sites where Ipswich and Woodbridge now exist is entirely due to the presence at each place of an abundance of springs, the water of which now goes to waste in the sewers.

No evidence of the upper Eocene strata have been observed in the region and although negative evidence is not always conclusive, deposits may not have been laid down. The Eocene epoch represents the early part of the " Age of Mammals " of which only erratic fossils from the sub-Crag prove the earlier existence of Coryphodon*, Lophidonj, and Hyracotherium in East Anglia.

Hyracotherium is the ancestor of the old world horses.

Miocene The noted " Boxstone " molluscan fauna preserved in the Red Crag Basement Red represents the vanished Miocene marine epoch.

The Boxstones are rolled nodules of hard brown sandstone of which perhaps 20% contain remains of shells, or hollows from which shells have been removed in Solution. A much smaller proportion contain cetacean teeth or pieces of bone and a few have teeth of the giant shark, Carcharodon megalodon, which occur also in the sub-crag deposit. Carcharodon teeth occur in Miocene beds of Malta and North America. It may be inferred that the Boxstones represent the indurated portions of a marine sand containing remains of mollusca and marine mammals which extended over an unknown area of north-east Essex and south-east Suffolk and was completely destroyed by the Pliocene Coralline Crag Sea. The fossils were in turn derived from the Coralline Crag Basement Bed during the subsequent incursion of the Pleistocene Red Crag Sea. The Cetacean teeth, tympanic bones, etc., found as erratic fossils in the Red Crag Basement Bed have never been studied as a group, neither has any work been done to establish their origin, but it is suggested that their similarity to the teeth in the Boxstones implies that they may be of Miocene age.

With regard to remains of Miocene land mammals nothing is known in the Boxstones but incomplete teeth of the Mastodon, Tetrabelodon (Tetralophodori) angustidens, recently recognised by Dr. Miklos Kretzoi amongst Basement bed fossils, points to an earlier Miocene terrestrial epoch. A tooth of Prolagus from the Alderton Red Crag provides supporting evidence. It is a seldom recognised fact that existing geological formations are what has survived the destructive agencies of later ages. â&#x20AC;˘Coryphodonâ&#x20AC;&#x201D;peak tooth.

fLophidonâ&#x20AC;&#x201D;crest tooth.

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Pliocene

In Great Britain the Pliocene is represented by three remnants of a formerly extensive deposit of marine sand with large numbers of Polyzoan fossils and molluscan remains known as the Coralline Crag, or White Crag. T h e only remains of mammals fourid in the sands are Cetacean but teeth of Mastodonts and antler fragments of extinct forms of Axis Deer occur in the Basement Bed below the Crag. These represent remains of a land fauna derived from river and lake deposits of a Pliocene era destroyed by the Coralline Crag Sea. Similar remains of land animals have been found in Dove Holes, Derbyshire and are preserved in Manchester Museum.

The largest area of Coralline Crag extends northward from Butley Creek to Sizewell Bay where the outcrop is below the sea and Consolidated fragments are cast ashore during storms. Exposures exist at Aldeburgh, Orford, and Sudbourne. A smaller area is at Sutton and Ramsholt, with the most southerly and smallest at Tattingstone where little can now be Seen.

During the Pliocene marine epoch the climate was warm but it probably deteriorated toward the end of the period when evidently the sea level was lowered and a new land emerged on which new genera of mammals developed, the Mastodonts and Axis type of deer became extinct.

Early Pleistoceneâ&#x20AC;&#x201D;Red Crag

Fossil remains of elephants and horses from the Red Crag Basement Bed (also known as the " Nodule Bed " and the " Suffolk Bone Bed " ) suggest a terrestrial phase of the early Pleistocene which was destroyed by the subsequent incursion of the Red Crag Sea. Because of the presence of an abundance of phosphatic nodules ( " Coprolites " ) at the base of the Red Crag the deposit was extensively worked during the 19th Century in East Suffolk to provide the raw material for the infant artificial fertilizer industry at Ipswich, Bramford, and Stowmarket. The incredible number of fossil shells attracted the attention of collectors, just as postage stamps and coins do today, and many large collections of shells were formed. It is stränge that equal attention should not have been given to fossils of contemporary mammals of which all too few were collected and preserved. Fortunately it has been possible to remedy this in some measure in recent years. Most attention was given however to the incredible numbers of molluscan remains and although some derived mammalian fossils were described no special study was made of them as a group. As a result of this one-sided study the obvious major break between the Pliocene Coralline Crag and the early Pleistocene Red Crag was overlooked or ignored and the erroneous reference of all Crag deposits to the Pliocene was prolonged until the official revision of the Plio-Pleistocene boundary at the International Geological Congress in London in 1948.

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Pleistocene Erratic rocks and fossils from Yorkshire together with striated flints, etc., in the Red Crag Basement Bed have been put forward as proof of a pre-Crag glaciation to which agency the destruction of the pre-crag continent must in some measure be due. The theory of transport by floating ice is untenable as the molluscan fauna shows the sea of the earlier Red Crag to have been at least as warm as the present Mediterranean and, incidentally, it was at least 150 feet deeper than the North Sea today.

As the sea level rose the erosion of the sea cliffs must have been more rapid than at present, consequently fossils of the older beds found their way into the new deposit, the Basement Bed, and this accounts for the very miscellaneous series of erratic rocks and fossils in it. The Red Crag is comparably richer in fossils than any other East Anglian formation, but most are marine.

Relatively rare are the remains of the contemporary land mammals which occur in the Crag sands as distinct from the derived fossils in the Basement Bed. These constitute an almost completely new fauna replacing that which became extinct with the close of the Pliocene epoch. For the first time true elephants, horses with new genera and species of the deer family appeared the study of which was neglected until post war years. Members of the new fauna inevitably developed on a vanished land, partly destroyed perhaps by the action of ice, but mainly by the incursion of the Red Crag Sea which also largely destroyed the Coralline Crag and much of the London Clay.

The Red Crag, so far as is known, is the oldest of the series and is arbitrarily subdivided into the Waltonian zone of north-east Essex, the Newbournian zone between the Deben and Orwell Estuaries, and the Butleyan zone as far as Aldeburgh. In spite of all that has been written about this division the deposit poses many unsolved problems, some of which will be considered in a later chapter. Its correlation with the Villafranchian of Southern Europe has now been established through the contemporary mammals.

The Zones of the Crag series have been based on the percentage of living and extinct mollusca without regard to the contemporary mammalia which ränge in time from Pre-Crag times to the Cromer Forest Bed series, which may perhaps be deltaic deposits of the period. The Norwich Crag is assumed to be later in origin than the Red Crag. It extends northward from Aldeburgh to northern Norfolk where the last of the series is known as Weybourne Crag and is noted for the abundance of shells of Tellina bathica.

T. bathica is regarded as evidence of a cool climate, but on the chalk of the foreshore at low tide at Runton, embedded in a very ferruginous crag are numbers of large left-handed univalves

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which appear to be Neptunia contraria which is a warmth indicating species. It is possible that there are two crag beds of entirely different ages represented. Pollen analysis done by the Subdepartment of Quaternary Research at Cambridge has shown a cool period toward the close of the Crag series.

T h e Cromer Forest Bed Series is not fully understood but has been generally regarded as the First interglacial. T h e deposits rest on Crag and are buried below the Cromer Till, the oldest known British glacial clay. Part of the Series extend along the coast as far south as Kessingland and is exposed in the CortonHopton beach. Formerly bones, etc., of elephants, deer, etc., were collected and are preserved in Norwich Museum where they may be seen on request.

T h e post-Cromerian part of the Pleistocene is inaccurately known as the " Ice Age " though deposits of Till, etc., indicate a series of four glaciations. T h e earliest surviving Till is that so well exposed along the Cromer coast but its supposed extension inland is the Norwich Brickearth which is found as far south as Kessingland and Covehithe. Along the Corton coast a Stratum of sand, the Corton Bed, intervenes between the Tills of the Cromerian Glaciation and the Lowestoft Till (lower Chalky Boulder Clay). This controversial bed has been regarded as an interglacial formation but as the two Tills are generally regarded as the product of sea ice and land ice of the same Glaciation respectively it must represent an interstadial (temporary) warm phase.

Lowestoft Till Covers much of northern Suffolk as a continuous bed, but in the south, particularly around Ipswich it is patchy which proves that forces of denudation and erosion continued. T h e ice, which brought this Till, is responsible for cutting the 130 feet deep buried Channel below the Gipping valley from Bramford to Ipswich, but does not appear to reach the sea (FIG. 4). Following the retreat of the Lowestoft ice the climate improved and became very warm with elephant, rhinoceros, horses, red and fallow deer, etc. At Hoxne brickworks chipped flints were first recognized as implements of prehistoric man in 1795 and were found with remains of animals which were perhaps killed by the hunters. These were found in a silted up lake bed and artifacts with bones have also been found in old deposits of the Thames at Clacton, Essex. T h e Hoxne lake bed now forms part of the plateau with new Valleys formed on each side, eloquent evidence of great topographical changes (FIG. 5).

This warm period, called the Great Interglacial, was followed by the Gipping Glaciation, which like the preceding one extended as far south as the T h a m e s Valley. T h e Gipping Till although it came from the north is patchy in that direction and more widespread in the south where it forms the heavy agricultural

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soil. Once again discontinuity of a formerly continuous bed proves destructive agencies at work but as no major ice sheet is known to have come so far south, ice cannot have been one of them.

The Ipswichian interglacial followed the retreat of the Gipping ice and the evidence of the fossils indicate a Mediterranean type of climate. The discovery of lake beds in Belstead Brook Valley at Bobbitshole afforded means through pollen analysis of recording the changes in the flora during the first half for this interglacial, while finds of bones during the building of the railway (1840-50) and in subsequent excavations, provided ample evidence of its fauna. Other confirming evidence is from the Stour Valley at Stutton, Harkstead, and Sudbury and this may be called the Mammoth-Red Deer fauna. In the Waveney Valley as well as in the Gipping are bones and teeth indicating climatic deterioration for there is a Mammoth-Reindeer fauna heralding the last glaciation when, although no mass of ice hundreds of feet thick reached Suffolk much evidence of minor ice action from local accumulations has been observed on Valley slopes. The Bobbitshole Beds were cut through by a small Valley glacier and disturbance of soil on hill sides by freezing and thawing (solifluction) is ample evidence of cold conditions. With this glaciation the Mammoth and Woolly Rhinoceros became extinct and the Pleistocene epoch came to an end.

Stratigraphical Sequence in South and East Suffolk RECENT LAST GLACIATION

Alluvium ; Marine Beach Deposits ; Blown Sand.

Solifluction and Frost Crack phenomena.

Unbedded gravelly Tills containing sand boulders and Chalky Till erratics.

IPSWICHIAN Bobbit's Hole Lake deposits, Ipswich, also Bramford INTERGLACIAL Road gravels and Barham lower gravel.

So-called Orwell Forest Bed. Bobbit's Hole Loess GIPPING GLACIATION

Upper Chalky Boulder Clay (Gipping Till), contortion of deposits mainly in Valleys. This tili is variable, passing into clayey gravel and sometimes 80% chalk.

Varved clays or laminated Brickearths appear below and ?above Gipping Till.

Phase of severe erosion and denudation.

HOXNIAN INTERGLACIAL

LOWESTOFT GLACIATION

(last

phase)

INTERSTADIAL LOWESTOFT GLACIATION

(first

phase)

Hoxne Lake deposistâ&#x20AC;&#x201D;South Kirnham and Waldingfield Bedsâ&#x20AC;&#x201D;correlated with Clacton and Swanscombe.

Varved clays of Great Blakenham and Sudbury areas and laminated deposits of Buried Channel at Ipswich.

Chalky Jurassic (Lowestoft Till) and Chalky Oxfordian Boulder Clays. Excavation of Buried Channels.

Varved Clay of Boxford (and Marks Tey Brickvard, Essex).

Corton Marine sand.

Cromer Till and Norwich Brickearth.

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CROMERIAN

INTERGLACIAL

Cromer Forest Bed Series.

EARLIEST Red Crag, N o r w i c h Crag, Westleton M a r i n e Shingle, PLEISTOCENE Chillesford Beds.

Terrestrial phase—great erosion.

PLIOCENE MIOCENF

Coralline Crag.

Denudation of U p p e r Eocene ; deposition and erosion ; Terrestrial and M a r i n e phase ; Crag Boxstones.

EOCENE

Thanet

Bed ;

Reading Sands and Clays ;

Clay—lower p o r t i o n only.

CRETACEOUS

U p p e r Chalk.

London