These meetings were organised jointly with the Geological Society of Norfolk. They were led by Bob Markham and benefited greatly from the helpful input of the other participants.
The aim of the field day was to examine the Pleistocene succession in the huge Great Blakenham chalk and clay pits. Already in use as a land-fill site, access will be severely restricted in the future and the sections soon lost forever; it is a shame therefore, that only six people attended. Detailed descriptions of this section are given by Allen (1984, 1988), and excellent papers by Green & McGregor (1999), Rose et al (1999), Rose et al (2000) and Rose (2000) give up-to-date discussion.
We started at the top of the succession by looking at the Lowestoft Formation tills, of Anglian age. Of particular interest was the wide range of erratic types; several different ammonites, belemnites, oysters and Gryphaea were found, as well as a variety of rock types, including Spilsby Sandstone and Kimmeridge Clay. Earlier workers identified two main distinct till types ('Lowestoft' and 'Gipping') on the basis of colour. However, both tills seem to have been formed under similar conditions and, although granulometric data shows some variation, which may account for the colour differences, classic fabric and clast analyses have demonstrated that they probably represent facies variations of one lodgement till sheet. A variety of glaciotectonic disturbances of the underlying beds, including thrusts and deflected convolutions, indicate that ice sheet movement was from the north-west.
The underlying Palaeosols Layer comprises primarily the Valley Farm Rubified Sol Lessivé, where a concentration of clay and haematitic iron suggests an illuvial soil horizon and pedogenic origin in a temperate environment. Subsequent periglacial processes have deformed this to give an ' arctic structure'
The Kesgrave Sand and Gravel, on which the palaeosol is formed, is now interpreted as part of a Pastonian terrace of the former course of the Thames. They comprise nearly 4m of yellowish, flint/quartz/quartzite-rich sands and gravels. Sedimentary structures in the lower part of the unit indicate fluviatile transport from the southwest.
The stratigraphic position of the Creeting Sands, c.11 m thick, has also long been a problem, and certain aspects of its interpretation remain enigmatic. They are clean white unfossiliferous well-sorted fine and medium grained micaceous sands. Well-developed small and medium scale ripple bedding is characteristic, with flaser bedding and channelling quite evident. The interpretation is of tidal estuarine conditions, maybe beach, sandflat or nearshore deposits, although there is a wide variation of palaeocurrent directions (rather than the bi-polar distribution expected from a tidal environment). The sands are correlated with the Chillesford Beds, possibly Bramertonian in age. The composition of gravel stringers again suggests derivation from a proto - Thames drainage system. The College Farm Silty Clay beds towards the top of the Sands contain a Pinus woodland vegetation with areas of heathland, and is interpreted as a possible high tidal flat deposit.
Underlying the Creeting Sands is the so-called "Red Crag Basement Bed", commonly c.30cm thick. This is a red sandy conglomerate cemented by iron oxide, comprising flint pebbles with abundant phosphatic nodules and containing sharks teeth and bone fragments. Correlation with the base of the Red Crag is based upon general similarities, though there are significant differences between this deposit and, for example, the Battisford pebble bed or basal phosphatic pebble beds in the Red Crag itself.
The Basement Bed rests upon Gonioteuthis granulata chalk at Great Blakenham, and, further to the east, upon the London Tertiary series. The Chalk received only a cursory examination, mainly because it was getting rather late in the afternoon.
The warm, hazy and muggy day encouraged 17 people to attend- an excellent number! The exposure was good, as would be expected from this eroding coastline, although beach sand did cover much of the foreshore. However, we were able to see the main features of c.l.4m of Baventian clays at the base of the cliff and on the upper foreshore, including much bioturbation (including U-shaped ?Arenicola tubes) and some of the desiccation cracks interpreted as the drying out of sediments in the inter-tidal zone. Some of the very friable mollusc fauna was also found in the discontinuous shell seams, particularly Macoma calcarea. The mollusc fauna is listed and discussed by Long ( 1974 ). The macro- and micro-faunas both indicate cold water conditions and support the pollen evidence - the Boreal pollen assemblages indicate grass heath with sparse woodland, probably only able to grow in sheltered places. It may well have been the case that conditions were cold enough for sea-ice to have been present. The section is only 3km north of Easton Bavents, where the type section of Baventian cold stage is displayed.
The overlying sands and gravels of the Westleton Beds, c.2m thick, are described and discussed in the classic paper by Hey (1967) and also by Mottram (1989), Mathers & Zalasiewicz (1996), Sinclair (1999) and many others in the recent literature. We discussed them at length and benefited greatly from Howard Mottram's detailed knowledge of the geology of these beds. It is thought that the Westleton Beds accumulated as a coastal shingle plain comparable to Dungeness today, or possibly in a tidal inlet and barrier island complex, in a temperate phase, possibly the Pastonian. The sedimentary structures were thus of great interest as evidence of environmental conditions and palaeo-geography. Above them lies c.4m of Kesgrave Formation (see above), the fluviatile deposits of the ancestral River Thames, which was not examined in detail.
This was a joint meeting with the Essex Local Group of the Geologists' Association and the Essex Rock and Mineral Society to study two outcrops of the Coralline and Red Crags. 14 attended. The number of easily accessible and well-exposed inland Crag pits is slowly decreasing as more and more become overgrown through neglect or disuse. These pits, two of the more frequented by Crag enthusiasts, display a number of interesting features.
Buckenay Farm, near Alderton
This "island" is an inlier of Red Crag, which forms a topographical high, surrounded by reclaimed Holocene salt marsh nearly lkm to the east of the former cliff line. The pit is described in Gibbard & Zalasiewicz (1988) and further details of the structures and faunas are given by Dixon (2001).
The Red Crag sediments show a number of structures. Most obvious are megaripples between 1 - 2 m high, but also channel bedded units and small and medium scale ripples. The ripples commonly show excellent examples of shell avalanche and imbrication structures. The foresets tend to be coarse and shelly sand, while bottomsets are often finer grained. Mud drapes can be seen in places, associated with small scale ripples and other silty partings. The interpretation is of fairly shallow water, around 5 - 8m, with current directions generally towards the west-south-west, with tidal currents superimposed upon this.
The mollusc faunas predominantly represent shell gravels. The faunal composition changes from a Venerupis-Glycimeris assemblage with significant frequencies of Aloidis lower in the sequence to a Spisula shell gravel with a large frequency of Mytilus in the upper part. This vertical (ie. temporal) change is accompanied by significant changes in other species, for example the increase in Macoma spp, Mya and Cardium angustatum; and the decrease in Astarte spp, Venus ovata and Cardita corbis. Certain horizons, for example in the south face, are characterised by very numerous thin, irregular vertical endogenetic agglutinated tubes, up to 7cm long, occasionally composed of ovoid fecal pellets, possibly belonging to an amphipod or small worm; this trace fossil is also characteristic of parts of the upper Red Crag on a regional scale.
A similar sequence of structures and faunas is identifiable in the upper part of the Red Crag over much of the area between the Deben and Butley rivers and the vertical changes support the view (seen regionally) of a shallowing sea towards the close of Red Crag times (Dixon, 1979).
Sutton Knoll
This locality (=Rockhall Wood of some authors) has been studied for over 160 years, long known as an island of Coralline Crag during Red Crag sea times, with its Coralline Crag cliffs and blocks 'buried' in Red Crag. The classic description was by Prestwich (1871), some of the figures of which were reproduced by Boswell (1928), but more recent descriptions have been by Balson & Long (1988) and Balson et al (1990); Wood (2000) reproduces two of Prestwich's diagrams and Balson et al (1993) describe the stratigraphy of the Coralline Crag as a whole.
The best Coralline Crag exposure is found on the northern side of the 'island'. The lower beds are shelly silty sands with evident bioturbation and an abundant fauna of molluscs, particularly bivalves, and bryozoans. Some horizons have been calcite-cemented to form a hard limestone. The upper horizons are shelly sands, from which aragonite has been removed by post-depositional solution processes to be re-precipitated as calcite cement to form a soft limestone (the "Bryozoan Rock Bed" of some authors, so often used as a building stone locally). Occasional solution pipes can be seen extending down from the surface. The sands exhibit well-developed cross-bedding and are interpreted as a tidal sand ridge in relatively shallow water migrating in a generally south-west direction.
The abutting and unconformable Red Crag is best seen on the east face of the 'island', but is much overgrown. It contains much derived Coralline Crag fauna, and even pebbles of that Crag encrusted with Red Crag barnacles, indicating that the Coralline Crag had already been cemented prior to the deposition of the Red Crag. Nevertheless, collecting yields an abundant fauna, including the little sea urchin Echinocyamus pusillus.
Roger Dixon
Further reading
Allen, P. 1984. Field guide (Revised edition, October 1984) to the Gipping and Waveney Valleys, Suffolk, May 1982. Quaternary Research Association: Cambridge.
Allen, P. 1988. In: Gibbard, P.L. & Zalasiewicz, J.A. Op. Cit.
Balson, P.S., Mathers, S.I. & Zalasiewicz, J.A. 1993. The lithostratigraphy of the Coralline Crag (Pliocene) of Suffolk. Proceedings of the Geologists' Association 104,59-70.
Balson, P.S., Humphreys, B. & Zalasiewicz, J.A. 1990. Field Guide No.3: Coralline and Red Crags of EastAnglia. 13th International Sedimentological Congress. U.K.
Balson, P.S. & Long, P.E. 1988. In: Gibbard, P.L. & Zalasiewicz, J.A. Op Cit.
Boswell, P.G.H. 1928. The Geology of the country around Woodbridge, Felixstowe and Orford. Memoir of the Geological Survey of England and Wales. H.M.S.O.
Dixon, R.G. 1979. Sedimentary facies in the Red Crag (Lower Pleistocene, East Anglia). Proceedings of the Geologists' Association 90,117-132.
Dixon, R.G. 2001. Report of Society Field Meetings. Bull. Geol. Soc. Norfolk 51, 117-126.
Gibbard, P.L. & Zalasiewicz, J.A. (eds.) 1988. Pliocene -Middle Pleistocene of East Anglia Field Guide. Quaternary Research Association: Cambridge.
Green, C. P. & McGregor, D.F.M. 1999. Pre-Anglian gravel deposits of the River Thames and its tributaries between Goring and Cromer. Proceedings of the Geologists' Association 110, 117-132.
Hey, R. W. 1967. The Westleton Beds Reconsidered. Proceedings of the Geologists' Association 78, 427-445.
Lewis, S.G., Whiteman, C.A. & Preece, R.C. (eds) 2000. The Quaternary of Norfolk and Suffolk: Field Guide. Quaternary Research Association, London.
Long, P.E. 1974. Norwich Crag at Covehithe, Suffolk. Transactions of the Suffolk Naturalists' Society 16, 199-208.
Mathers, S. & Zalasiewicz, J. 1996. A gravel beach-rip channel system: the Westleton Beds (Pleistocene) of Suffolk, England. Proceedings of the Geologists' Association 107,57-67.
Mottram, H.B. 1989. The Upper Caenozoic sequences around Long Row, Covehithe. Transactions of the Suffolk Naturalists' Society 25, 86-91.
Prestwich, J. 1871. On the structure of the Crag-beds of Suffolk and Norfolk with some observations on the organic remains. Part ll: The Red Crag of Essex and Suffolk. Quarterly Journal of the Geological Society of London 27, 325-356.
Rose, J. 2000. Pre-glacial Quaternary processes and events in Norfolk: a review sketch. In: Dixon, R.G. (ed.) The Geological Society of Norfolk Jubilee Volume. 66-75.
Rose, J., Whiteman, C.A., Allen, P. & Kemp, R.A. 1999. The Kesgrave Sands and Gravels: 'pre-glacial' Quaternary deposits of the River Thames in East Anglia and the Thames valley. Proceedings of the Geologists' Association 110, 93-116.
Rose, J., Moorlock, B.S.P. & Hamblin, R.J.O. 2000. In: Lewis, S.G., Whiteman, C.A. & Preece, R.C. Op. Cit.
Sinclair, J.M. 1999. Plio-Pleistocene relative sea-level changes in East Anglia: evidence from the Westleton Member and related deposits. Procedings of the Geologists' Association 110,149-162.
Wood, A.M. 2000. The stone tapestries of the Red Crag. In: Dixon, R.G. (ed): The Geological Society of Norfolk Jubilee Volume 41-49.
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