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Geology Group Field Meetings Report For 2001

Introduction

This account describes those field meetings that were held in Suffolk and Essex and were organised jointly with the Geological Society of Norfolk. They were led by Bob Markham. The field meeting ‘Box-stone Bonanza’ was cancelled because of the disastrous foot-and-mouth disease epidemic.

The Industrial Geology of Ipswich Docks Thursday 28 June. This was an evening walk around the dock area at Ipswich led by Bob Markham. 12 people attended on a fine and sunny, if slightly chilly evening. The meeting benefited enormously from the numerous contributions made by some of the attending participants.

The docks have a fascinating history and at one time were the largest enclosed area of water of its kind in the country. They were developed from 1837 onwards and completed in 1841/2. The new Customs House, with its white (?Cambridge Gault) bricks is dated 1845. The port flourished during Victorian times and up to the First World War; enlargements to the wet dock were completed in 1881. The present dockscape has remained remarkably unchanged since about 1890.

The geological and geomorphological setting of the docks was described, with reference to the sub-Tertiary palaeosurface, at c.–117 ft. OD, more recent infilled hollows and buried channels, and the origin of the Orwell Valley. The huge mammilated Sarsen stones, assumed to be from the Reading Beds, on the footpath just west of Stoke Bridge were examined and their origin as possible Miocene duricrusts discussed. These were dredged from the river during work on a flood protection scheme in 1975.

The building stones were described as the walk proceeded and included flint, sandstones, granites, Caen stone and many more; particular attention was paid to four large millstones of indeterminate origin set into the wall on the south side of Key Street, and some excellent current bedding displayed in sandstone paving slabs. Raw material imports were also discussed: coal from Newcastle, iron from Spain, Niedermendig lava from the Rhineland, rock salt from Cheshire, alum, Fullers Earth, pipeclays, slates, roadstone, asphalt, paving and setts, oil and much else. Some of the street names bear witness to these imports eg. Salthouse St. and Coprolite St. (probably the only street with this name in Britain, named after the phosphatic nodules from the Red Crag and the basis of the chemical fertiliser industry). The dockside was naturally the focus for many import-related manufacturing processes, such as iron works, brick-yards and gas works. The Flint Wharf was so called because of the imported flints used in F. Ransome’s Artificial Stone Works.

(I am most grateful to Bob Markham for allowing me to use freely his notes in the writing of this report).

The Sudbury Area Saturday 4 August Nine people attended this meeting on a bright and sunny day (apart from one lunch-time shower) to examine the stratigraphy of the Sudbury area. At one time there were many working Chalk and clay pits in the area and, even 30

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years ago, outcrops were quite good. This is not the case now! We visited 5 former pits – Lower Alexandra Brickworks (now housing estate), Railway Chalk Pit (housing), Great Cornard Brickworks (overgrown), Brundon Lane (much infilled) and the Victoria Pit (housing). However, sufficient was exposed to be able to gain an excellent overview of the succession in this interesting and often neglected area.

The Marsupites zone Chalk forms the bottom of the sequence. It is soft and marly here, with relatively few flints. It is overlain unconformably by the Lower London Tertiaries – the area lies just south of the NW limit of these beds, and just on the limit of London Clay. The Bull Head Beds, with the ‘devils dung’ flint pebbles and glauconitic clayey greensand, mark the base of the Tertiaries, followed by up to 4 m of brownish Thanet Beds sands. These are overlapped by 3 m of Reading Beds – brown mottled clays and subordinate sands, which exhibit cross-bedding and are somewhat impersistent and interdigitated.

The still enigmatic ‘Red Crag’ (6 m max) lies unconformably on Tertiaries or Chalk, forming remnant outliers and marking the western limit of the formation. It comprises ferruginous, rusty sands, cross-bedded in part, with ironstone bands, which occasionally contain the casts of shells and therefore indicate that decalcification has taken place. There is a basal pebble bed containing phosphatic nodules, rolled Tertiary clay pebbles, bone and teeth; shells are rarely found, and are rolled, broken and weathered – a list is given by Boswell (1929, p27), suggesting ‘Waltonian’ age.

The overlying Pleistocene caused much comment. Historically this area once showed “the finest inland sections of Drift in the kingdom” (Boswell 1929), with Chalky Boulder Clay passing down into bedded silts, often much contorted, and deposits of sands, silts and brickearth. At Brundon Lane are 210,000 year-old inter-glacial cross-bedded river terrace gravels containing abundant Gryphaea and belemnites, and with a well documented mammal fauna, which includes elephant, ‘elk’, bear, horse and deer. Several pieces of bone were found by participants. The site has also yielded Lower Palaeolithic flakes. There was discussion of buried channels and their morphology, the origin and development of river systems, ‘pre-diversionary’ drainage and the proto-Thames.

Pakefield Saturday 15 September Eight members attended this meeting on a sunny September day at Pakefield. After a briefing by Bob Markham, illustrated with the use of Blake’s 1884 Geological Survey section (produced by RD), the party descended from the caravan park 1 km north of Kessingland onto the beach. After several decades of cover by slipped material, exposures of the cliff section have been quite good for the last five years due to renewed coastal erosion along this stretch of coastline.

The group walked northwards, examining first the Anglian Jurassic-rich Chalky Boulder Clay. Several ammonites, belemnites, Gryphaea, septaria and fragments of bituminous Kimmeridge Clay (prompting discussion of Norfolk’s oil industry) were found in this sticky till.

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The underlying Corton Beds were also clearly exposed. These sands, c.8 m in thickness, are interpreted as distal proglacial outwash deposits, formed

to the south of the Scandinavian ice sheets about 440,000 years BP. They

are moderately well-sorted, fine to medium-grained pale yellow sands with

occasional pebbles, and exhibit well-developed medium and small-scale

cross bedding, with climbing ripples and ripple drift of particular interest.

Current directions indicate flow generally to the south, away from the ice

sheet. The lowest beds seen were those traditionally attributed to the Cromer

Forest Bed – a sequence of compressed muds and laminated silty clays, some of which contain much woody material and from which a significant mammal fauna is recorded, including lion, mammoth, deer, hippopotamus and bison (Stuart & Lister 2000). Part of the sequence, a well-developed Rootlet Bed, is interpreted as an over-bank, floodplain alluvial deposit and pollen analyses suggest deposition in a warm, temperate phase in the early Middle Pleistocene. Lunch was taken at Crazy Mary’s Hole (Lighthouse Gap), before proceeding a further 200 metres further north to examine some curious and unidentifiable vertical burrow systems from the Forest Bed Formation. The party then retraced its steps, further inspecting the section.

East Mersea Saturday 13 October Thirteen people attended this meeting in Essex on a beautiful sunny day to visit a classic Quaternary SSSI. While gathered in the car park, John Llewellyn-Jones, Natural History Curator at the West Mersea Museum, exhibited a tooth of Elephas antiquus, which had been found at this site and is to be displayed at the museum. Excellent descriptions and discussion of the section can be found in Bridgland et al. (1995).

Commencing at Cudmore Grove, at the eastern end of the section, we examined first the flinty Mersea Island Gravel, interpreted as a cold pre-Ipswichian proto-Thames-Medway deposit. Of particular interest was the small and medium scale cross bedding seen in some of the more sandy beds, indicating current directions generally towards the south-west, and the convolutions seen in a silty layer, which may have resulted from post-depositional dewatering.

Underlying the gravels are the temperate Hoxnian Cudmore Grove channel deposits. The channel is cut deeply into the London clay, extending some 11 m below OD, and is infilled with a sequence of silts and clays. The lower channel beds contain abundant Hydrobia and Cerastoderma, indicating brackish, estuarine or intertidal conditions. These were clearly exposed on the upper foreshore, revealed as the tide receded. The overlying sediments contain freshwater shells and an impressive assemblage of vertebrates, including voles, shrews, beaver, monkey and tortoise (Bridgland et al., 1988). Organic silty clays, containing wood fragments, make up the upper part of the sequence.

The London Clay is exposed in the central part of the cliff section and overmuch of the foreshore. It is a sticky blue-grey clay, weathering to a rusty

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brown. No fossils were found, but several pieces of pyritised wood were found on the shore.

The western part of the section is marked by a second channel cut into the London Clay and containing the Restaurant Gravels, proto-Blackwater fluvial deposits of temperate Ipswichian age. The gravels contain higher percentages of quartz and quartzite than the Cudmore Grove Gravels, and freshwater molluscs and mammals including hippopotamus, rhinoceros and elephant. ‘Brickearth’ sand and silt overlie the gravels, but the large amount of talus and overgrowth meant outcrop was poor.

Finally, at the saltings adjacent to the Cosway Holiday Home Park, the party inspected some recent salt-marsh deposits with root beds. This prompted discussion of the dating of recent sediments by animal and plant introductions into Britain.

Further Reading Boswell, P. G. H. 1929. The Geology of the Country around Sudbury (Suffolk).

Memoir of the Geological Survey of England & Wales, H.M.S.O. London. Bridgland, D. R., Allen, P. & Haggart, B. A. (eds) 1995. The Quaternary of

the Lower Reaches of the Thames. Field Guide, Quaternary Research Association, Durham.

Bridgland, D. R., Allen, P., Currant, A. P., Gibbard, P. L., Lister, A. M., Preece, R. C., Robinson, J. E., Stuart, A. J. & Sutcliffe, A. J. 1988. Report of Geologists’ Association Field Meeting in north-east Essex, May 22nd–24th, 1987. Proceedings of the Geologists’ Association 99: 315–333.

Stuart, A. J. & Lister, A. M. 2000. In: Lewis, S. G., Whiteman, C. A. & Preece, R.C. (eds), The Quaternary of Norfolk and Suffolk: Field Guide, 219–223. Quaternary Research Association: Cambridge.

Roger Dixon The White House, 7 Chapel Street, Woodbridge, Suffolk IP12 4NF