BLOOD HILL, BRAMFORD

H . B . M o t t r a m

North-west of Ipswich, in the parish of Bramford, is a partially dug away spur called Blood Hill. It is centred at Nat. Grid Ref. TL113 485. The northern pit area is owned by Suffolk County Council and the southern by Robert Cubitt Holdings Ltd. The pit was worked for chalk for over 100 yrs and although infilling commenced in 1977 chalk working only ceased in 1986.

The lowest deposit known at Blood Hill is the Upper Chalk. It is generally a jointed white chalk with layers of nodular flint. The Chalk is often directly overlain by till; see Fig. 1. This till is a tenaceous, structureless mud containing innumerable pea sized chalk fragments. The peripheral zones of the till body can be brown or pale grey but otherwise the mud is distinctly dark grey throughout. The almost black colouration is due to the high content of ground-up carbonaceous Kimmeridge Clay of Jurassic age. Boulders of the latter are found on rare occasions as are Kimmeridgian fossils such as the ammonites Pavlovia pallasioides and Rasenia involuta, ich-thyosaur vertebrae, and large shrimps. Other derived fossils include the oyster Gryphaea arcuata, the ammonite Kosmoceras compressum and the belemnites Cylindroteuthis puzosiana and Gonioteuthis quadrata. A belt of non-chalky sand may occur against or near to the western edge of the till (photos 14 & 15, McKeowan & Samuel, 1985). The sand is sometimes gravelly and vertically bedded. It is thought that the sand infilled a stream which had enlarged a shrinkage crack that formed during consolidation of the till.

The till described above occurs widely in East Anglia and it is known as the Lowestoft Till. In the Gipping Valley area, however, it is also referred to as the Blakenham Till (Rose et al, 1978; Allen, 1984 & 1988). It drapes the plateaux of the area and the abutting lower levels which possibly represent the edge of a valley/flood plain that was associated with the early Anglian out wash (Corton Sands, Sandy Lane Gravels etc). The till was amassed from the base of the Anglian ice sheet as a lodgement till, although Allen (1984) considers that a degree of slumping also occurred at Blood Hill and at similar locations. It is thought that the lodgement till was also deposited into a buried channel and that this till still lines the buried channel between Mason's Works and Blood Hill (Mottram & Huntley, 1984).

A river seems to have approximately followed the same route as the buried channel at Blood Hill. As the river flowed through Blood Hill it cut down into the till in the buried channel so that part of the western side of the buried channel here is no longer lined by till. It is suggested that glacial melt water, which may have already been flowing as a river, became dammed by ice or debris to the north of Blood Hill; perhaps at Gt. Blakenham. A large lake formed and, when the lake burst through, a torrent hurtled along with enormous erosive force and deeply incised the till below (the sediment load being deposited further downstream).

As the river assumed or resumed normal flow conditions, then sediment was laid down at Blood Hill. This sediment is a chalky sand and gravel with

Trans. Suffolk Nat. Soc. 27 (1991)

Trans. Suffolk Nat. Soc. 27 (1991)

BLOOD HILL, BRAMFORD 39

occasional cobbly beds. Derived fossils, usually Gryphaea arcuata and belemnites, may be found. This stratum is the Haughley Park Gravels. Chalk gravel is easily comminuted during river transport and so the high proportion of chalk gravel infers that the outwash had not travelled far from the ice sheet. Research in the area (Allen, 1984) has shown that the Haughley Park Gravels generally represent braided river sediments and that the exposures of this deposit at Blood Hill are of this nature. The limited information here on current flow directions provided by subsidiary channels and cross-bedding confirms an approximately southward flow.

Resting within the top of the Haughley Park Gravels, in one small area of Blood Hill, is a strip of banded brown till. This would have been formed by meltout from the upper surface of the ice near the ice front. It has been called the Blood Hill Till by Allen (1984) who proposed that it was subjected to mud flow prior to incorporation within the sands and gravels.

Folds and faults within the Haughley Park Gravels represent accomo-dative movements induced by melting of ice blocks, freezing and thawing of water in the sediment and differential consolidation of the underlying till.

A non-chalky red-brown material, ranging from clay to fine sand, thinly blankets the site. It commonly protrudes downwards in cryoturbation lobes and sometimes in deep hollows. When present directly above chalk the chalk has a weathered putty like nature. Although tubules and feint colour laminations are present in the red-brown material no sedimentary structure can be detected. The sediment is considered to have an aeolian origin and is often assumed to be of Devensian age (Perrin et al, 1974).

References

Allen, P. (ed). (1984). Field guide (revised edition, October 1984) to the Gipping and Waveney Valleys, Suffolk. May 1982. Quaternary Research Association. Cambridge.

Allen, P. (1988). Localities-Day 1, Great Blakenham. in Gibbard P. L. & Zalasiewicz J. A. (eds). (1988). 87.

Gibbard, P. L. & Zalasiewicz (eds). (1988). The Plio-Pleistocene of East Anglia. Field guide. Quaternary Research Association. Cambridge.

McKeowan, M. C. & Samuel, M. D. A. (1985). Regional study of the sand and gravel resources of Essex and South Suffolk. British Geol. Surv. Keyworth.

Mottram, H. B. & Huntley, S. L. (1984). The formation of sub-glacial buried channels in the Lower Gipping Valley. Trans. Suffolk Nat. Soc. 20, 70.

Perrin, R. M. S., Davies, H. & Fysh, M. D. (1974). Distribution of late Pleistocene aeolian deposits in eastern and southern England. Nature. 248, 320.

Rose, J., Allen, P. & Wymer, J. J. (1978). Weekend field meeting in south-east Suffolk. 15-17 October, 1976. Proc. Geol. Ass. 89, 81.

H. B. Mottram, 66 Glastonbury Close, Ipswich, IP2 9EE

Trans. Suffolk Nat. Soc. 27 (1991)