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INGHAM – THE GEOLOGY REVEALED BY THREE SITES OFF THE BURY–THETFORD ROAD HOWARD MOTTRAM Introduction There have been various stages in the exploitation of aggregates and the subsequent infilling of sites on the northern side of the village of Ingham. The original Geology Sheet Memoir (Whitaker et al., 1891) described some sections just off the southeastern corner of Figure 1 and Simon Lewis, 1993, described a shallow excavation, accessed from the Culford Road, that was 400m to the west of the north-western corner of Figure 1. These small exposures will not be discussed. The focus of this article will be the 3 larger sites that were accessed from the A134 (Bury-Thetford Rd). These are shown on Figure 1 and will be described as; 1- Western Area. This is a roughly elliptical site lying immediately to the east of woodland known as the Folly. The site is centred around TL848717 and was used for waste disposal by Hales. 2-Central Area. A pit effectively bounded by two north-south aligned tracks, it was dug out by D.G.W. Aitkens and subsequently landfilled by Suffolk County Council. This is centred around TL853716. 3-Eastern Area. Continuing eastwards from the latter site towards the Bury Rd there have been further workings, centred around TL856716. These have been carried out by Ingham Hardcore Company Ltd, TJ & WM Cardy, and Culford Waste Ltd and are now in the aftercare stage of restoration.
Figure 1. Ingham - Site Locations and chalk topography
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The geological strata encountered are set out below in Table 1. TABLE 1 OUTLINE OF GEOLOGICAL STRATA Myrs OLD
STRATA
0.45
Glacial Till (Lowestoft Till) – sediment previously trapped within the ice at the base of the Anglian ice-sheet and left when the ice melted Glacial Sand & Gravel – deposited by rivers of melt water that drained away from the front of the Anglian icesheet
0.9 ?
90
EVIDENCED BY dark brown, silty clay with numerous small to medium gravel sized fragments of chalk
pale coloured, wide range of sizes (cobble to silt) usually mixed together (ie poorly sorted), flint pebbles still angular, often has chalk particles, some Jurassic fossils
Ingham Sand & Gravel 0 – deposited by the large Bytham/Ingham River
orange-brown to yellow brown, well sorted, half of the pebbles are well rounded and quartzose (mainly quartzite, some vein quartz), half of the pebbles are of sub-angular flint, not chalky here
Lewes Nodular Chalk Formation – an accumulation 9 of the protective coats of minute marine algae
mainly soft white chalks, occasional hard chalk at the shallow depths seen here the chalks usually show that they have been weathered by later geological periods to a breccia (shattered into small fragments) or to a putty like material
Western Area Several years after the Hales’ site had been infilled, it was investigated by the Water Research Centre (WRc) and between 1974 and 1990 over 30 boreholes were drilled (for a full list of WRc work at this site, see Fleet et al., 1994). From its investigations, the WRc confirmed that the general surface of the Chalk here slopes approximately south-south-westwards. This is in keeping with published plots of the Chalk surface (Harvey, 1973 and IGS, 1981). On a local scale, the WRc work showed that there are distinct valley-like and headland-like undulations of the Chalk surface. The surface can vary considerably over short distances so that plots of the contours of the Chalk surface have to be generalised. Figure 1 shows my interpretation of the Chalk surface which is similar to those that were drawn by the WRc. The WRc work also showed that the relationship of the Glacial Sand & Gravel to the Glacial Till is not uniform: Glacial Sand & Gravel occurs on top of, underneath, around and within Till. Central Area The Aitkens’ pit commenced parallel to the westernmost of two north-south aligned tracks and Glacial Sand & Gravel was excavated from a gentle depression that bottomed out in the irregular Chalk surface between +37 and +30m OD. I joined SCC in 1978 and by the time I had the opportunity to visit the site, much of the geology in this area had been covered up. Fortunately, BGS photos taken in 1977 (ref P212115P212117 and P212135) can now be seen on-line, each with a short narrative, and they Trans. Suffolk Nat. Soc. 52 (2016)
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give a good indication of what was here and they typify how difficult it has often been to find good exposures at the Ingham sites. From 1978 to 1979 excavation then progressed somewhat eastwards, essentially following the aggregate around the contours of the land where it outcropped from below a cover of Till. This resulted in a sinuous steep sided trench some 20 to 50m wide. The IGS examined the new exposures in 1978 and, from the north-western part of this trench Tim Lawson described a “typical section” (Bristow, 1990), the location of which is transposed onto Figure 2 as “Recorded 1978”. Although quartzose pebbles were noted in some beds of sand and gravel, these pebbles were not common and Lawson confirmed that this was Glacial Sand & Gravel. BGS photos from 1978 (ref P212226-212233) illustrate the geology from this part of the site. Along part of the south-western/southern side of the trench, the Chalk was exposed as a steep face and it included a hard nodular band which was probably a bed known as the Chalk Rock. Sand and gravel was banked up against the steep face of the Chalk and showed that the sand and gravel occupied a structure cut down into the Chalk. In 1981 the IGS’s Martin Clarke and Clive Auton noted that in part of the northern face, which is also indicated on Figure 2, that the sand and gravel was the quartzose Ingham Sand & Gravel. They recorded these sands and gravels as blanketing the Chalk in that northern face. In the bottom of the excavated trench they recorded this sand and gravel as sometimes penetrating the Chalk in solution bowls and pipes but they also recorded Glacial Sand & Gravel and Till infilling solution pipes (Clarke & Auton, 1982), see BGS photos from 1981 (ref P212950-212958). The Quaternary Research Association (QRA) meeting visited here in 1982 at which time it was also noted that there was faulting in the Ingham Sand & Gravel. As the faults
Figure 2. Ingham - Excavation, channels and chalk at various dates
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were not accompanied by folding, it is unlikely that the faults were caused by the bulldozer like forward pushing movement of the ice-sheet. It is therefore likely that the faults were caused by the sand and gravel subsiding. A shallow scoop of Glacial Sand & Gravel that only partly penetrated the Till was noted by the IGS. This may well have extended from the “old gravel pit” shown on the 25 inch OS map surveyed in 1883 but which had gone by the time of the 1903 survey. If so, then the shallow feature was probably a shallow channel or depression that was orientated east-north-east to south-south-west here. In 1984 the eastern half of the northern edge was stripped back. It could be seen that Glacial Sand & Gravel had cut down through the Till and into the underlying Ingham Sand & Gravel but whether the Glacial Sand & Gravel cut through the entire thickness of the Ingham Sand & Gravel and into the Chalk was not discernible. However, it was clear that this incision was the eastern edge of a glacial channel and, in the short length then exposed, it was aligned north-north-west to south-south east, see Figure 2. Mineral exploitation continued and in the south-eastern corner of this excavation it followed the aggregate down even deeper. This was not simply an extension of the cutting, it was in a steeply sided hole, see Figure 2. The deep hole was excavated to about 50m across, although borehole evidence indicates that the feature is probably wider than this. For safety reasons the Suffolk County Council (SCC) surveyors never measured the final depth, simply indicating that it was below +27m OD. I don’t know of a comprehensive record of its stratigraphy but I noted that the infilling strata were not a chaotic jumble but were quite orderly with bedding planes dipping steeply down in an approximately southerly direction. The strata varied in composition from beds of cobbles to beds of chalky sand. SCC finished its landfilling in 1988 leaving the Aitkens’ workings in only a small area in the south-eastern corner around the deep hole which itself was then backfilled. By the time that the QRA revisited Suffolk in 1991, exposures in the Central Area had effectively gone. Eastern Area This commenced as an extension of the area around the deep hole. Overall the Eastern Area workings were shallower than the workings in the Central Area had been. This was partly due to planning restrictions rather than aggregate depths. Ashamedly I only visited once. It was in 1994 and the detailed relationships of the strata were poorly exposed. The surface of the Chalk was hummocky and the Ingham Sand & Gravel occupied solution hollows no more than 3m across. The Glacial Sand & Gravel was mainly composed of chalky sand but, when present, the pebbles in it were small sized. Foresets in the gravel and sand beds dipped down to the east. Till was also present and there were infilled frost wedges in the Glacial Sand and Gravel. However, Simon Lewis and Dave Bridgland had examined the site a few years earlier and in their account they also refer to the particularly deep hole that straddled the Eastern and Central Areas (Lewis & Bridgland, 1991). They noted that the faults in the Ingham Sand & Gravel do not continue up into the Glacial Till. From trial pits in the field north of the site they recognised that Glacial Sand and Gravel infilled several Trans. Suffolk Nat. Soc. 52 (2016)
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channels and within the pit they identified the western edge of a deep channel that was slightly sinuous with an overall orientation here of north-east to south west, see Figure 2. This channel cut steeply through the Ingham Sand & Gravel and into the underlying Chalk at the site. Discussion - weathering and erosion of the chalk in-situ During the Cenozoic (Tertiary) Period the Chalk would have been variously eroded and weathered by the sea and rivers. Perhaps some 200m thickness was stripped away as the surface was re-sculpted. Subsequent erosion by the Bytham/ Ingham River and the Anglian ice-sheet and outwash processes would have created new features sometimes obliterating the Caenozoic ones and sometimes preserving them beneath new sediments. Chalk dissolves very slowly, mostly as the result of cold, mildly acidic rainfall and peaty groundwaters. This can result in underground tunnels and caverns that suddenly reveal themselves when an area of a field, part of a road or a house collapses. Clive Edmonds (Edmonds, 1983) indicated that there are some 5–10 solution features per 100km2 in this region. I have previously described sink holes in the Chalk in the parish of Lackford, some 7–8 km south-west of Ingham (Mottram, 1991), and a recent renaissance of Paterson’s research by Richard West (West, 2016) sets out numerous solution features in the Suffolk-Cambridgeshire Brecklands. It should therefore be no surprise that solution features occur at Ingham. Several solution pipes were observed in the Central Area at Ingham (Clarke & Auton, 1984), some filled with Ingham Sand & Gravel and some with Glacial Sand & Gravel and Till. If the solution pipes were open at their tops, i.e. sink holes, then when the Bytham/ Ingham River or the glacial meltwaters flowed over the sink holes they would have been filled directly in an organised and concordant way. This was not the case. The IGS showed that the Ingham Sand & Gravel sometimes sagged down over solution pipes. Only the lower beds were seen as being affected in this way which indicated that each disturbance event was relatively small and could be accommodated or dissipated within the lower beds. This could have occurred when; a. The sand and gravel was not frozen and sand grains and pebbles crept or gently slumped down into the cavities. b. The sand and gravel was frozen and slowly bent down towards the cavities under the weight of overlying materials. This would not have been as effective in filling narrow, relatively deep cavities and would have needed to be supplemented when the frozen material melted. Two scenarios spring to mind:a.
The solution pipes were open topped cavities that formed slowly and were progressively infilled by the overlying Ingham Sand & Gravel.
b.
The solution pipes had roofs that collapsed and, even if collapse was catastrophic, the cavities were only large enough to cause some local disturbance of the overlying Ingham Sand & Gravel and not large enough to have caused widespread chaotic collapse.
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The Ingham Sand & Gravel in the Central and Eastern Sites exhibited faults, structures that also appeared to be related to subsidence here. For brittle fracture to have occurred in sand and gravel then the Ingham Sand & Gravel must have been frozen. It was noted that the faults run through the entire thickness of the Ingham Sand & Gravel but do not continue up into the Glacial Till and on this basis it was established that the subsidence had finished before the Till was emplaced (Lewis & Bridgland, 1984). The Till is closely associated with the Glacial Sand & Gravel and so subsidence also seems to have finished before the Glacial Sand & Gravel was deposited. Considering the infilling with Glacial deposits. The infilling is irregular and in the Till the orientation of pebbles and banding was sometimes almost vertical, indicating that the Glacial deposits were not laid down into voids directly from rivers or ice-sheets but that they also collapsed into the voids. These collapses and infills must have been later than the collapses and infills relating to the Ingham Sand & Gravel. The overall evidence in respect of solution features suggests that subsidence of them occurred during different periods and resulted in different infilling strata and styles of disruption. Given the propensity for solution features to occur in this area of Suffolk, the deeply excavated hole referred to earlier struck me as being a large cavity. Because of their notoriety we tend to think that large cavities would have undergone sudden chaotic collapse but Tony Waltham and Peter Fookes showed that large cavities can fail in less dramatic ways (Waltham & Fookes, 1993). Therefore, the orderly infill observed here was quite in keeping with a large cavity. The deeply excavated hole was traversed by a steeply sided channel of Glacial Sand & Gravel. Particularly on the basis of the steepness, it was suggested that the channel was formed by water flowing under high pressure below the ice-sheet (subglacial meltwater) rather water draining away from the melting front of the ice-sheet (Lewis & Bridgland, 1991). Sub-glacial channels often have very irregular bases and a deep depression would have been quite compatible with this. There is now a lack of opportunity to clarify the origin and infill of the deep hole but the chances are that a sub-glacial stream exploited a large solution feature. Discussion - Solution of eroded chalk That solution has taken place within the Chalk bedrock raises the question as to whether solution has also taken place in derived chalky material in the overlying deposits. There is plenty of evidence of chalky material within the Anglian Glacial Sand & Gravel, and the Till, but this is not replicated by the Ingham Sand & Gravel. At Ingham, the Ingham Sand & Gravel is totally devoid of chalky material but at Timworth, 2.4km to the south, some chalky material was found (Lewis & Bridgland, 1991). Chalk material has also been found at other sites representing younger (topographically lower) terraces of the Bytham/Ingham River. Even so, the ratios of chalk material to flint material were still much less than those in the Glacial deposits of the area. At face value this evidence suggests that that there had been widespread dissolution of chalk material from the Ingham Sand & Gravel before the Anglian
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Glacial period. However, the paucity of chalky material is also thought to be in part due to the Bytham/Ingham River having obtained some of its sediment by reworking older deposits of chalk free flint gravels. References Clarke, M. R. & Auton, C. A. (1984). 15. Ingham TL 851715. p71-72. In Allen, P. ed. Field guide to the Gipping and Waveney valleys, 7-9 May 1982. Quat. Res. Assoc. Edmonds, C. E. (1983). Towards the prediction of subsidence risk upon the Chalk outcrop. Q. J. Eng. Geol. London 16: 261–266. Fleet, M., Young, C.P., Blakey, N.C. & Lewin, K. (1994). Landfill Monitoring Investigations at the Ingham Landfill Sites: 1974–1992. (CWM/052/92), Department of the Environment. Harvey, B. I. (1973). Records of wells in the area around Bury St Edmunds: inventory for one-inch geological sheet 189, new series. Inst. Geol. Sci./ Brit. Geol. Surv. Lewis, S. G., (1993). The status of the Wolstonian glaciation in the English Midlands and East Anglia. Unpublished Ph.D. Thesis, University of London. Lewis, S. G. & Bridgland, D. R. (1991). Ingham (TL 855715) and Timworth (TL853692), Suffolk. p71–83. In Lewis, S. G., Whiteman, C. A. & Bridgland, D. R. (eds) (1991) Central East Anglia and the Fen Basin. Field Guide. Quat. Res. Assoc. Mottram, H. B. (1994). The Geology of Hall Heath, Lackford. Trans. Suff. Nat. Soc. 30: 48–50. IGS (1981). Hydrogeological map of Southern East Anglia (1:125 000) - Sheet 2. Crag and Lower Greensand: geological structure. Brit. Geol. Surv. Waltham, A. C. & Fookes, P. G. (2003). Engineering classification of karst ground conditions. Q. J. Eng. Geol. London, 36: 101–118. West, R. G. (2016). T. T. Paterson’s contributions to Breckland Pleistocene geology in the 1930s: a tribute and commentary. https://issuu.com/suffolknaturalistssociety/ docs/paterson Whitaker, W., Woodward, H. B., Bennett, F. J., Skertchly, B. J. & Jukes-Brown, A. J. (1891). The geology of parts of Cambridgeshire and of Suffolk (Ely, Mildenhall, Thetford) (Explanation of Sheet 51 N.E. with part of 51 N.W.) Mem. Geol. Surv. GB.
H. B. Mottram The Warren, Duckamere, Bramford, Ipswich IP8 4AH
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