NOTES ON THE GEOLOGY OF THE COUNTRY AROUND INGHAM, NEAR BURY ST. EDMUNDS b y B. M .
FUNNELL.
T h i s account is primarily intended for the use of local naturalists and schools. T h e area is one of considerable complexity and uncertainty even for glacial deposits. Individual formations are both variable in character and patchy in distribution. Consequently some errors were made when the area was originally surveyed by H M Geological Survey. With this in mind, these notes have been prepared to illustrate particular present-day exposures rather than to give general accounts of the nature of each formation. Following this factual portion of the paper is a discussion ot the geological history and its relation to a current Pleistocene chronology.* T h e TOPOGRAPHY of the area is subdued, and the total ränge of relief is little more than 100 feet. T h e r e are two easily appreciated features to which attention may be drawn. lhe first is the high-level plateau of Boulder Clay which stands at about 170 175 feet O D. T h i s may be clearly seen on the road irom Elveden to Culford, where it crosses Weatherhill Heath The second is the main terrace in the Valley Gravel, which declines f r o m about 90 feet O . D . to 60 feet O.D., alongside the nver Lark (within the limits of our area). T h i s terrace is; well seen between Fornham All Saints and Hengrave, between West Stow and Icklingham, and at Cavenham Heath. T h e r e are other lesswell-marked features in the Valley Gravel, and the modern alluvium forms a lowest level abutting against older deposits, almost ubiquitously with a small step. A subsidiary point of interest (see Watt, 1955) is an exposure of stone stripes (evidence of one-time periglacial conditions), on the surface of the chalk at T h e t f o r d Heath, beside the road on the north side (N.G. 850795). (All grid references in this account refer to O.S., 1 : 63360, Sheet 136.) * T h e c u r r e n t c h r o n o l o g y a d o p t e d h e r e is t h a t b a s e d o n t h e s u c c e s s i o n o u t l i n e d b y B a d e n - P o w e l l (1948). T h e c o r r e l a t . o n vvith h e N o r t h E u r o p e a n c h r o n o l o g y s e t o u t b e l o w !S b a s e d o n W e s t (1954). The g e n e r a l l y a c c e p t e d A l p i n e e q u i v a l e n t s a r e p l a c e d in b r a c k e t s . Gipping Till H o x n e interglacial Lowestoft Till Corton Beds
^ , . , T = Great Interglacial Elster-Saale (Mindel-Riss)
baale
(K1SS
>
p r o b a b l y
Elster
<Mindel)
228
GEOLOGY OF THE COUNTRY AROUND INGHAM
C O M M E N T S ON T H E GENERAL N A T U R E O F T H E DEPOSITS, F O L L O W E D BY N O T E S ON T H E P R E S E N T DAY EXPOSURES, I N APPROXIMATE S T R A T I G R A P H I C A L ORDER The CHALK forms a basement to the Pleistocene deposits in the area, and, generally speaking, only outcrops on the sides of the larger Valleys. The thickness of the Chalk was shown by a deep bore at Culford which proved 556 feet of Chalk and Chalk Marl. This was underlain by 75.5 feet of Gault and Lower Greensand and, there being no other Mesozoic rocks present, the surface of the Palaeozoic rocks was met with at —530 feet O.D. (All boring records mentioned in this account are given in Woodland 1942.) There are few good exposures in the Chalk. 1924 and 1935.)
(See Hewitt
Exposure I , ROBERT'S BRIDGE. N.G. 775681. Derelict. The Chalk-with-flints is disturbed to the base of the section. Exposure II, WILLOWMERE S P I N N E Y . N.G. 896775. A good exposure of normal, white uncemented chalk, with sub-horizontal layers of flint nodules. There is also some tabular flint along inclined planes in the chalk, and marcasite nodules can be found. A Micraster coranguinum (Leske) collected near the base of the 30 - 40 foot section, indicates the presence of the " coranguinum" zone of the Upper Chalk. Inoceramus involutus J. de C. Sowerby also occurs. Theie are Solution pipes from the surface to depth of a few feet. The GRAVEL AND SAND formation is probably a complex of deposits resting on an irregulär surface of Chalk. Boring records are inadequate but confirm a geneial absence west and north-west of the outcrop seen on the map. The bulk of the deposit tends to lie in irregulär troughs, running both along the line of the Lark, and also east and north-east under West Stow, Ingham and Honington. Thicknesses are very variable ; they may in places approach 150 feet. The following characteristics of present exposures are general, but not ubiquitous:—chalk as pebbles or grains, angular or battered flint, false or irregulär bedding, many erratics of Mesozoic rocks, and an ochreous colour. The BOULDER CLAY of the district was originally mapped as one formation. However, F. J. Bennett (1884a) recognised a difference between the tills of different parts of the area. The first type,
GEOLOGY OF THE COUNTRY AROUND INGHAM
229
found towards the east and south, had a bluish-grey clay matrix,* with chalk and flint stones and " foreign " boulders. It was up to 100 feet thick. T h e second type, found towards the west and north, was a brown, sandy and very chalky tili containing flints of local origin. It was patchy in occurrence and only reached 25 feet in thickness. Recently (West & Donner, personal communication) east-flowing ice has been deduced at Rampart Field (XIII), and at Denham (just south of our area), from an analysis of the fabric of a tili corresponding to the description of the first type. A south-east flow has been deduced from a tili of the second type at Culford (XIV), and at Chalk Farm (just north of our area). A topographical guide to the limits of the two tills will be suggested later. There are sometimes difficulties in distinguishing them at exposures without recourse to an analysis of the fabric, because, in weathered form, both may be brownish. Boring records suggest that the' Boulder Clay (sensu lato) occurs at lower levels, and in greatest thickness, along the line of the troughs mentioned above, but there are exceptional thicknesses elsewhere. LOAMS, possibly representing interglacial conditions, are recorded " from underneath boulder clay " (Whitaker, etc. 1891, Bennett 1884b), in the district, but they have not been recently investigated. SUPRA-BOULDER CLAY GRAVELS occur at Ingham and Fornham. Exposures are now overgrown and the description (Whitaker, etc. 1891), in view of the duplicity of the Boulder Clay, is both ambiguous and inadequate. The VALLEY GRAVEL is probably a composite group of more or less terraced deposits. These deposits consist, in the main, of ochreous to fawn sands and gravels. The gravel, in addition to sub-angular flint, contains vein quartz, quartzite, and other siliceous pebbles such as chert. The quartz sand is often false-bedded. Palaeolithic implements are found in some places and mammalian bones have also been recovered. * Since this paper was prepared, Mr. J. L . Gilbert has kindly sent me the following note. " DĂźring March, 1942, I noticed that blue boulder clay had been dredged from the river Lark at Fornham St. Martin, between the lock and the mill. On examination it proved to be drived from the Kimmeridge Clay and was very fossiliferous. T h e fossils included Aptychus latus, Protocardium striatula (juvenile), Exogyra virgula, Exogyra nana, Lucina substriata, Oxytoma dorsetensis, Astarte extensa, Ostrea sp. (juvenile), Area sp., PhĂśladidea compressa, Entolium corneolum, Lingula ovalis, " Terebratula " (2 spp.), Isocrinus sp. (one ossicle), and a fragment of saurina bone. Phosphatic concretions and selenite (twin crystal) also occurred. (Identifications made with the assistance of Mr. A. G. Brighton.) "
230
GEOLOGY OF T H E COUNTRY AROUND
INGHAM
The following list of exposures is grouped according to the main formations found in each. GRAVEL
AND SAND,
AND BOULDER
CLAY
Exposure I I I , T A Y L O R ' S G R O V E N . G . 907753 Derelict. About 9 to 12 feet of horizontally-bedded shingle and sand. The flints are often sub-angular and are accompanied by a high proportion (almost 50 per cent.) of quartzites and quartz. T h e quartzites are of Bunter type and most are small (0.5 inches). T h e gravel shows a wide ränge of pebble-size and in this sense is badly graded. T h e top layers are festooned * Exposure
IV,
STANCHIL'S
FARM.
N . G . 810683.
A chalk floor appears to be overlain by about 3 feet of micaceous grey loam. There follow above about 20 feet of alternating sand or loam, and gravel; each alternation is 2 to 3 feet thick. Flints are sub-angular and sub-rounded, and there are other siliceous pebbles. Exposure V , E A S T F A R M . N . G . 874792. Derelict. About 12 feet of chalk-bearing flint gravel, and sand, festooned at the surface. Exposure VI, BARNHAM. N . G . 880793. Derelict. About 24 feet of chalk-bearing sand and flint gravel with a capping of flint boulders (up to 9 inches mean diameter) near the road ; elsewhere the surface layers are festooned. Exposure V l l a , B A R N H A M H E A T H . N . G . 885794 and 885797. Derelict. T h e old gravel pit near the spinney shows evidence of a chalk-bearing flint gravel. The other main workings are in yellow sands and flint gravel, with rough horizontal bedding, festooned at the surface. Exposure V I I I , L I T T L E L I V E R M E R E . N . G . 880727. Derelict and overgrown. Gravel near the top is large (stones up to 6 inches across) and at lower levels chalk pebbles may be found. Exposure IX, L I M E K I L N P L A N T A T I O N . N . G . 832716. Derelict but well expcsed. T h e lowest 10 feet consists of a coarse flint and chalk gravel, with battered sub-angular flints up to 2 feet across, and chalk cobbles up to 9 inches across. There are numerous erratics, including clay, cementstone and shelly limestone. T h e middle 4 feet consists of even-bedded sand, which is loamy in places. The uppermost 3 feet is again a coarse flint and chalk gravel, with maximum diameters of about 6 and 4 inches respectively. *Festooning in soils and uncemented deposits of gravel, etc., is a product of periglacial conditions.
GEOLOGY OF THE COUNTRY AROUND INGHAM Exposure X,
INGHAM FOLLY.
N.G.
231 848717.
A complex exposure about 25 to 30 feet deep. T h e lower levels consist of chalk-bearing flint gravels and sands. Overlying this is an extremely coarse, flint and erratic, boulder bed with boulders commonly 1 to 2 feet across and exceptionally a yard or so long. Large septaria, blocks of oolite, shelly limestone, etc. are common. Exposure X I , INGHAM.
N . G . 855713.
This exposure is being rapidly extended. At the time of t h t present survey there were two main features exposed. T h e r e was a layer of gravelly solifluxion deposit, which was about 6 feet thick at the uphill end and expanded to 12 feet at the downhill end, where it contained some brown chalky boulder clay. Secondly, the underlying chalk-bearing gravels and sands were seen to be decalcified in " Channels " . T h e decalcified product was dark, ferruginous and dull in appearance, and the bedding was obscure or steeply inclined parallel to the margins of the " Channels " . Near the edges of the decalcified portions fragments of corroded Ostrea (oyster) were found. Exposure X I I , FLEMPTON. N . G . 809695. Derelict. About 12 feet of coarse, yellow-brown, flint gravel with a crudely horizontal disposition. T h e flint is angular or subangular and up to 9 inches across ; it is accompanied by grits, quartzites and cherts. Festooning extends from the surface to a depth of 6 feet. E x p o s u r e X I I I , RAMPART FIELD.
N.G.
790720.
Derelict. T h i s is a complex exposure. A boulder clay (up to 15 feet thick) of chalk pebbles in a brown clay occurs in two Channels at the top of the west side of the quarry. A set of reversed faults, which cut the boulder clay and underlying gravel and sand, shows a general strike running north-south. T h e remainder of the exposure consists of a variety of false-bedded sands and gravels, all with a conspicuous content of chalk, and yielding numerous erratics including clay, oolite, Carbomferous limestone, Red Chalk, belemnites and oysters. At their thickest the gravels reach 30 feet, the lowest 10 feet of gravel being followed by 6 foot alternations of sand and gravel; gravel occurs at the surface on either side of the boulder clay. T h e gravels are considerably thinner on the east side of the workings, where chalk is seen near the surface. Exposure X I V , CULFORD. N . G . 826711. Derelict. About 20 feet of a sandy tili containing large flints and chalk pebbles. T h i s is an example of the second tili.
232
GEOLOGY OF THE COUNTRY AROUND INGHAM VALLEY
GRAVEL
Exposure V l l b , BARNHAM H E A T H . N . G . 885801. This exposure is mainly below water-level. T h e gravels form a terrace, and a loamy continuation of them overlaps on to other gravels mentioned under V l l a . T h e main bedding is horizontal but some of the sand is false-bedded. T h e gravel consists of flint, and resistant erratics. There is no festooning in the upper layers. It is at least 12 feet thick. Flint implements and bones have been found in these gravels ; those preserved in Ipswich Museum include " main Clactonian and Acheulian, and possibly even early Clactonian implements ". A few Levallois flakes have also been claimed. Exposure X V , FAKENHAM N O R T H . N . G . 906771. Derelict. Yellow to fawn, flint and resistant erratic gravel. At least 12 feet thick. Exposure XVI, W E S T S T O W . N . G . 820708. About 20 feet deep. At the base there is 6 feet of sand with sweeping false-bedding inclined south-south-east. T h e sand is well-graded and grey in colour. Overlying gravels show decreasing dips to the south-east as the surface is approached. At the surface the gravel is horizontal. T h e gravel consists in the main of flint, but there are also chert and quartzite, pebbles and a very little hard chalk is present in addition. There are irregularities in the gravels to a depth of about 6 feet, but a sand seam at 3 feet from the surface is only slightly undulose. DISCUSSION
OF
THE GEOLOGICAL T H E AREA
HISTORY
OF
T h e C H A L K is here regarded as a backcloth to the succession of Pleistocene events. Owing to the relative uniformity of conditions during the time when the Chalk was deposited more general accounts may be consulted for information on its zones, fauna, etc. (e.g. Chatwin 1954, Hewitt 1924, 1935.) There is a great amount of the GRAVEL AND S A N D formation exposed at present. Generally speaking these deposits were laid down on the dip slope of the Chalk cuesta, probably in large measure by outwash from the Lowestoft Till glacier (see later). T h e bedding and the high proportion of chalk in the deposits suggests that these are outwash materials, and the erratics at many exposures {e.g. V, VI, IX, X, XI, and probably X I I I ) point to association with the Lowestoft Till. It is likely, as indicated by the boring records, that the dip slope of the Chalk was diversfied by Valleys and that these were modified or exaggerated by the erosion accompanying the arrival of glacier ice. Thert is no evidence of shells comparable to those found on the Suffolk
GEOLOGY OF THE COUNTRY AROUND INGHAM
233
coast in the Corton Beds (which may be regarded as general time-equivalents), and the gravels, or rather boulder beds, are coarser than those underlying Lowestoft Till further east (e.g. the Sand and Gravel formation near Bungay). The lowest Pleistocene datum in the area, however, is the Lowestoft Till, and it is possible that Pleistocene stages, older than those parts of the Gravel and Sand which form its outwash, are represented. There is very little concrete evidence for these stages, but two things may be noticed in this connection. An outlier of so-called " Pebbly Gravel" is recorded at Stanton (Bennett 1884b). Secondly, certain of the exposures noted under Gravel and Sand above (e.g. III and IV) are typical with respect to the others, notably in the primary absence of chalk constituents, but also in the nature of the bedding. These facts are suggestive, but it is impossible to draw any coherent conclusions from them at present. The BOULDER CLAY, as previously indicated, exhibits two different facies. Bennett at first believed that the difference resulted from two separate glaciations. Later, howevei, he recanted, saying he had found the two types interbedded (Bennett 1884 a, and p.s.). It is suggested here that his first opinion was correct. Thefirsttype described above it is comparable in lithology to the Lowestoft Till (see Baden-Powell 1948). The determinations of direction offlowmentioned above are consistent with others made in the Lowestoft Till elsewhere (West and Donner, personal communication). At present this tili is preserved (a) in " buried Channels " at the margin of, and within the area covered by, the second tili, (b) at the surface beyond the present limits of the second tili, i.e., roughly south of Risby and Timworth. The evidence suggests that " buried Channels " are the product of sub-glacial excavation (see, for example, Boswell 1913, pp. 610 - 611), and in East Anglia they are frequently associated with boulder clay of Lowestoft Till type. Typically, but not always, they approximate to the courses of the present main Valleys. In our area they are proved by borings under both the Lark Valley and the depression running north-east through Culford, etc. As these excavations are not base-levelled they may be found at almost any level. The occurrence noac^d by Mr. Gilbert at Fornham St. Martin is of this type and ltis suggested that the Rampart Field exposure (XIII) also has something of this nature. The land surface of boulder clay to the south of Risby is distinctly undulating or rounded, and is usually above 200 feet O.D. This is in contrast with the plateau formed by the second tili, which will be mentioned later. We may be fairly confident that the deposition of thefirsttili was followed by an interglacial period corresponding to the Hoxne interglacial, whose deposits rest on Lowestoft Till at Hoxne (Baden-Powell 1948). There is little clear evidence from
234
GEOLOGY OF THE COUNTRY AROUND
INGHAM
interglacial deposits in our area however, but the L O A M S mentioned above are possibly interglacial. (See also Paterson 1937 and 1940, esp. 1940; Baden-Powell and Oakley 1952.) T h e second type of tili described above is very probably the same as the Gipping Till (see Baden-Powell 1948). T h e determinations of direction of flow mentioned above are consistent with those made elsewhere in the Gipping Till, including that given by the fabric of the Gipping Till overlying the Hoxne interglacial deposits (West and Donner, personal communication). At present the extent of this second tili is difficult to determine. T h e following suggestions may be offered as a guide to its extent: (a) it forms a characteristic plateau ; (b) it is podsolised in places, and profoundly altered to a gravelly sand in others (Watt 1940). These two characteristics are probably not independent. In our area there are large stretches such as Shravedell Heath, Berner's Heath, Weatherhill Heath, etc., where this tili underlies an almost dead-flat plateau at, or just below, 180 feet O.D. This plateau contrasts with the rounded topography of the Lowestoft Till south of Risby. T h i s is probably an expression of the different lithologies of the two tills. It could be argued that this topographical contrast is the result of different conditions of deposition. It seems more likely, depositional differences apart, that the Gipping Till plateau maintains its integrity because of its permeability, which permits the downward percolation of rainwater sufficient to preclude the extensive development of surface drainage. On the contrary, the clayey Lowestoft Till, with its low permeability, would induce surface run-off which would break up the topography even if it was originally deposited as a plateau. In connection with (b), it may be noticed that Bennett (1884) associated the occurrence of superficial sand in the area with the outcrop of this tili, suggesting that it might be derived either from sand and gravel or from weathering of the tili. T h e observations that this tili may be extensively podsolised, which were mentioned above, Support the second alternative. T h e extent of the superficial sand may be a guide to the previous extent of the tili, especially to the north and west. In brief then, there seems to be good confirmation that the Boulder Clay, mapped as one formation by H . M . Geological Survey, is in fact composed of two tills, produced by two glaciers, during different glacial periods separated by an interglacial period. T h e Lowestoft Till glacier flowed east over the entire area. T h e later Gipping Till glacier flowed south-east; one tongue extended at least as far as Ipswich (Baden-Powell 1948), but there is no clear evidence of it extending more than a very small distance due south of our area. There is a possibility that the SupraBoulder Clay Gravels may be glaciofluvial deposits associated with the Gipping Till, and some of the deposits mapped as Gravel and Sand may yet prove to be Gipping Till outwash.
GEOLOGY OF THE COUNTRY AROUND
INGHAM
235
It is difficult to formulate any presentable conclusions on the GRAVEL of the district because the evidence available is not conclusive and present exposures are poor. In the Lark Valley the main terrace feature declines from about 90 feet O.D. at Fornham All Saints, where the modern alluvium stands at about 80 feet O.D., to about 65 feet O.D. at Cavenham, where the modern alluvium stands at less than 50 feet O.D. T h e West Stow (XVI) exposure belongs to this terrace. Mammalian bones have been recorded from Flempton, and teeth and tusks of Elephas primigenius from Rampart Field (Whitaker 1891). T h e record of large blocks of basalt and hard sandstone at Flempton (Whitaker 1891) suggests that some of the deposits, at least, may have accumulated under periglacial conditions, but the relation of these deposits to the main terrace' feature in not known. Remnants of another terrace feature are found at a lower level, e.g., at just above 50 feet O.D., where the road to West Stow leaves the main Icklingham-Lackford road. VALLEY
In the Valley of the Little Ouse, Levallois implements have been claimed in situ at a depth cf about lOfeetintheBarnhamHeath gravels ( V l l l b ) . This is consistent with a post-Riss age fcr the gravels. T h e terrace in the gravels stands at just above 50 feet O.D., i.e. very little above the modern alluvium. ACKNOWLEDGMENTS I am very grateful for assistance from the Morley Bursary towards the cost of fieldwork. I am indebted to Professor W. B. R. King for a discussion of general aspects and to Messrs. R. G. West and J. Donner for numerous discussions and permission to incorporate unpublished Information. I also acknowledge permission to copy Geological Survey maps, granted by the Director of the Geological Survey. SELECTED
REFERENCES
Baden-Powell, D . W. F. 1948.
" T h e Chalky Boulder Clays of Norfolk and Suffolk", Geological Magazine, Vol. 85, pp. 279-96.
Baden-Powell, D . W. F. 1952. and Oakley, K . P.
" Report on Westley Skull Site ", Proc. Prehistoric Soc., N.S. Vol. X V I I I , Pt. 1, pp. 1-20.
Bennett, F . J.
1884a.
Proc. NorwichGeol. Soc. Vol. I, No. VII, pp. 242, 252-62, and postscript (see Whitaker, etc. 1891).
236
GEOLOGY OF THE COUNTRY AROUND
Bennett, F. J.
INGHAM
1884b. " T h e Geology of the country around Diss, Eye, Botesdale and Ixworth", Geol. Surv. Memoir (50 N.W.). Boswell, P. G. H. 1913. " Age of the Suffolk Valleys, with notes on the Buried Channels of D r i f t " , Q.J.G.S., Vol. LXIX, pp. 581-620, esp. pp. 610-611. Hewitt, D. H. 1924. " Notes on some Chalk sections in the district around Thetford, Norfolk ", Proceedings of the Geologists' Association, Vol. 35, pp. 220-244. 1935. " Further notes on the Chalk of Thetford District, Norfolk", Proceedings of the Geologists' Association, Vol. 46, pp. 18-37. Paterson, T . T. 1937. " Palaeolithic Succession : No. I. Bamham Sequence", Proc. Prehistoric Soc., N.S. Vol. III, Pt. 1, pp. 87-135. Paterson, T . T . 1940. " Palaeolithic Succession: No. and Fagg, B. E. B. II. T h e U. Brecklandian Acheul (Elveden) ", Proc. Prehistoric Soc., N.S. Vol. VI, Pt. 1, pp. 1-29. 1940. " Studies in the Ecology of BreckWatt, A. S. land IV ", Journal of Ecology, Vol. 28, p. 42 et seq. Watt, A. S. 1955. " Stone Stripes in Breckland, Norfolk", Geological Magazine, vol. xcii, pp. 173-4. 1891. " T h e Geology of Parts of CamWhitaker, W., bridgeshire and Suffolk",Geol. VVoodward, H.B. Surv. Memoir (51 N.E.). Jukes Brown, A.J., etc. Woodland, A. W. 1942 " Water Supply of Cambridge& Ipswich District, Pt. I I I and 1946. Pt. X, Geol. Surv. Wartime Pamphlet, No. 20. T h e following are recommended for schools, etc. :â&#x20AC;&#x201D; 1954. " East Anglia and adjoining Chatwin, C. P. areas", British Regional Geology, 3rd Edn. Himus, G. W. 1954. " Dictionary of Geology ", (R8), Penguin Books.
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INGHAM
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