Norwich Crag Formation
Norwich Crag Formation | |
---|---|
Ma | |
Type | Geological formation |
Unit of | Crag Group |
Sub-units | Chillesford Sand member, Chillesford Clay Member, Easton Bavents Clay Member, Westleton Beds Member, Sidestrand Member |
Underlies | Wroxham Crag Formation, Kesgrave Catchment Subgroup, Mid Pleistocene glacigenic deposits |
Overlies | Red Crag Formation, Coralline Crag Formation |
Thickness | about 70 metres |
Lithology | |
Primary | Sand |
Other | Gravel, clay, silt |
Location | |
Region | East Anglia |
Country | United Kingdom |
Type section | |
Named for | Bramerton, Norwich |
Named by | Clement Reid |
Year defined | 1890 |
Coordinates | 52°12′53″N 1°24′58″E / 52.2147°N 1.4160°E |
The Norwich Crag Formation is a stratigraphic unit of the British Pleistocene Epoch. It is the second youngest unit of the Crag Group, a sequence of four geological formations spanning the Pliocene to Lower Pleistocene transition in East Anglia. It was deposited between approximately 2.4 and 1.8 million years ago, during the Gelasian Stage.
The Norwich Crag is a marginal
Norwich Crag fossil fauna and flora have been studied since the 19th century for information about environmental conditions during the early Pleistocene. They provide evidence for a general climatic cooling trend from the Pliocene to the Pleistocene.
History of research
The term Crag was first used in a geological sense by R.C. Taylor in 1823, a word commonly used in Suffolk to designate a deposit of fossil sea shells[1] or any shelly sand or gravel.[2]: 32
The Norwich Crag was first identified in the early 19th century as a predominantly marine geological formation, then thought to be of
Six lithostratigraphic members were recognised by the Geological Society of London:[13] the Chillesford Church Member (a basal deposit of marine sand, formerly the Chillesford Sand Member); the Chillesford Member (micaceous, silty clays overlying the Church Member, formerly the Chillesford Clay Member); the Creeting Member (micaceous, inter-tidal sands); the College Farm Member (silty clay of mud flats associated with the Creeting Member); the Easton Bavents Member (clay with sand laminae); the Westleton Member (flint-rich gravels overlying the Easton Bavents Member).
The type site of the Formation is at Bramerton Pits SSSI, near Norwich.[14]
The sedimentary record
The Norwich Crag Formation is a marginal facies of the thicker, much better developed sedimentary sequence in the southern North Sea basin. It outcrops in the eastern half of the counties of Norfolk and Suffolk, and is also represented in Essex and Hertfordshire.
The Norwich Crag comprises a widespread sheet of well sorted, fine- to medium-grained micaceous, glauconitic, locally shelly sands (e.g. the Chillesford Sand Member), with localized beds of laminated silty clays (particularly the Chillesford Clay and Easton Bavents Clay members) and well sorted fine to medium sands with beds of rounded flint gravels (notably the Westleton Beds Member). The pebbles are predominantly composed of flint, typically more than 95% local material, either chattermarked (beach-abraded) or angular or sub-angular flint; the remaining 5% is typically white vein quartz and white quartzite.[17] The heavy minerals in the sand-sized fraction of the sediment are characterised by high concentrations of garnet, amphibole and epidote, which suggests that the sands originated from eastern (continental) rather than western (British) fluvial sources.[18] The sandy sediments are near-shore marine deposits, with the clay members being estuarine or lagoonal,[12] and the flint gravels are also near-shore marine, interpreted as channel infills, the gravels having been reworked from gravel beach deposits.[19] These deposits represent environments fluctuating between marine transgressive and regressive episodes on the western margins of the North Sea basin.[20] The source of the distinctive flints, which are often rounded in the coarser sizes in the Westleton Beds Member, is as yet to be conclusively determined but it has been argued that the flints were obtained from local rather than distant Chalk .[21] Comparison with better preserved sedimentary sequences of similar age in the Netherlands has shown that the Norwich Crag sequence is highly incomplete.[22] Interpretation is hampered by difficulties with distinguishing major non-sequences from minor, local erosional discontinuities.[12]
For surface mapping purposes, the
The Westleton Member may be regarded as a sedimentologically coherent and a lithologically and stratigraphically consistent unit stretching from central Norfolk to the Suffolk coast.[25] Beds of fine-grained sediment may also serve as marker horizons in the Crag Basin. Considering the lithostratigraphy to include subsurface sediments evidence by borehole, Riches (2012) proposed three major units for the Basin; most recognisable where they are separated by regressive marine marker beds of silty clay, with the uppermost equated with the Chillesford Clay Member.[18]
Palaeogeography
Early Norwich Crag deposition in East Anglia took place within a topographical context established in the late Pliocene: an eastward dipping plain developed on Cretaceous Chalk interrupted by three SSW to NNE trending depressions partly filled with Red Crag sediments.
Tectonic context
Since its deposition, the Norwich Crag Formation has undergone tectonic uplift and tilting as part of regional processes operating on the margins of the North Sea basin.[17] The Chillesford Sand Member ranges in elevation from c.90 metres above sea level at Widdington, Essex, to its base at c.6 metres below sea level in the Aldeburgh-Sizewell area. There is therefore evidence for regional uplift of over 90 metres in western East Anglia and tilting towards the North Sea over the last two million years.[15][30] The uplift has, however, been uneven, with little change apparent in north-east Norfolk in the West Runton – Happisburgh area.[17]
Evidence for fluctuations in relative sea level in the Crag Basin during the Plio-Pleistocene have been attributed to a variety of mechanisms including glacio-isostatic adjustments, eustatic changes and basinal response to sedimentary loading.[25]
Fauna and flora
The fossil fauna and flora of the Norwich Crag have been studied since the early 19th century for
They provide evidence for a general climatic cooling trend from the Pliocene into the Pleistocene.[18] Three biostratigraphic stages have been identified based on fossil pollen assemblages: Thurnian, Antian/Bramertonian and Baventian/Pre-Pastonian a, representing a cold-warm-cold climatic sequence.[12] Comparison with the better preserved sedimentary sequence in the Netherlands and the North Sea suggests it is unlikely that this represents a single climatic cycle but rather a sequence of episodes represented in an incomplete sedimentary record.[32] The historic chronostratigraphic correlations and palaeoenvironmental interpretations based on biostratigraphy (local and continental) have been criticised as poorly defined and unreliable by Riches (2012).[18]As the Norwich Crag is a marine formation, the majority of fossils found in it are of marine origin; any terrestrial species were originally blown or washed into it from land, or derived from earlier deposits, particularly the Red Crag.[33] Vertebrate fossils tend to be concentrated in the basement bed[2][14][33] or in gravel lags.[34] Species of warm and cold substages are represented, sometimes mixed together; this may pose problems for palaeoecological interpretation.[22][35]
Mammals
Land mammal fauna
From a biostratigraphic point of view, the terrestrial mammal fauna of the Norwich Crag belongs to the Late
Vole fossils from the Norwich Crag contribute to the
Marine mammal fauna
Marine taxa from Easton Wood include
Birds
Very few avian fossils have been found in the Norwich Crag. Bones of
Reptiles and Amphibians
No reptile and amphibian fossils have yet been recorded from the Norwich Crag.[42]
Fish
Fossil marine fish from the Norwich Crag include genera Chrysophrys sp. (a
Molluscs
Molluscan fossils are abundant at certain horizons in the Norwich Crag. Historically, they have been used to construct palaeontological zonal schemes and to infer palaeoclimatic changes.[44] However they show evidence of considerable transportation, and consequent mixing of faunal assemblages from the earlier Red Crag Formation.[45] The use of molluscan fossils for climatic reconstruction has proved problematic. For instance species found together at several levels in the Ludham borehole notably Serripes groenlandicus (Greenland cockle) and Calyptraea chinensis (Chinese hat snail) have notably different climatic tolerances today (arctic and lusitanic respectively).[9] The presence of mixed arctic, boreal and lusitanic faunal elements at certain levels in the Ludham borehole give no indications of the climatic fluctuations evident from foraminiferal evidence.[35] The local variability of molluscan assemblages at similar horizons was noted by Reid as adding uncertainty to their use for biostratigraphic correlation.[14] However, molluscan fossils have proved most useful as indicators of water depth in marine facies.[35] Molluscan assemblages identified from Norwich Crag deposits represent a range of environments (inner sublittoral; open coast; tidal flat wadden; offshore sublittoral) and climatic conditions (boreal; low arctic; temperate).[45] Cold climate indicator species include Astarte borealis and Yoldia myalis from Baventian deposits at Covehithe.[22] Some species have distinct biostratigraphic value. The absence of Macoma balthica is considered to be an indicator distinguishing Norwich Crag molluscan assemblages from those of the later Wroxham Crag.[2][7][14] Fossil shells are scarce or absent in some horizons, which may be due to contemporaneous erosion or non-deposition or post-depositional calcium carbonate solution.[18]: 368
Plants
The most complete fossil record of plant life in the Norwich Crag is provided by evidence from the Ludham research borehole. Pollen analysis in association with foraminiferan evidence[7][10] allowed the identification of pollen assemblage biozones and consequent designation of five biostratigraphic stages, of which three (Thurnian, Antian and Baventian) are correlated with the Norwich Crag. The Thurnian was identified as a glacial stage with an oceanic heath type of vegetation; the Antian with temperate mixed coniferous / deciduous forest including Tsuga (hemlock) and Pterocarya (wingnut); the Baventian, a glacial stage more severe than the Thurnian, with the return of oceanic heath.[8][46] Further work on Norwich Crag sediments at Bramerton, Norfolk, allowed a Bramertonian stage to be identified, characterised by temperate forest with Quercus, Carpinus and Alnus. Correlation was made with the pollen assemblage from Chillesford.[47][48] Specimens of fossil wood have occasionally been found, for example pyritised pine and oak at Holton.[33]
Dinoflagellates
Foraminifers
Fossil foraminifera provide important evidence for climatic and environmental interpretation and stratigraphic correlation in the Norwich Crag. The Ludham borehole has provided the most complete foraminiferal record, and has allowed the designation of seven biozones.[7] Further biozones were identified at Bramerton and Easton Bavents, and assemblages identified at a number of other Norwich Crag sites, permitting correlation with the more complete sequence in the Netherlands.[10]
Dating and correlations
The Norwich Crag Formation was deposited during the
Eoliths and early humans
The discovery of chipped and flaked flints in the Norwich Crag and Red Crag basement beds in the late 19th and early 20th centuries was claimed as evidence for some of the earliest human settlement in Britain.[54] A typologically diagnostic form of 'eolithic' beak-shaped instrument was proposed by E Ray Lankester, the ‘rostro-carinate’, based upon a ‘Norwich Test Specimen’ flint found in the basal Norwich Crag at Colman's Pit, Whitlingham.[53] The human origin for these Crag specimens was refuted by FN Haward[55] on the basis of a systematic analysis of flint fracture patterns and geological context. The fractures were identified by Warren (1923) as caused by sub-soil pressure flaking.[56]
See also
References
- ^ Forby, F (1830). The Vocabulary of East Anglia. JB Nichols & Son, London, Volume I, p.81
- ^ a b c d e f g Woodward, HB (1881). The Geology of the Country around Norwich. Memoirs of the Geological Survey of the United Kingdom. London: HMSO.
- ^ Prestwich, J (1890). On the relation of the Westleton Beds or Pebbly sands of Suffolk to those of Norfolk and on their extension inland; with some observations on the period of the final elevation and denudation of the Weald and the Thames valley, etc. Part 1. Quarterly Journal of the Geological Society, vol.46, pp.84-119.
- ^ Reid, Clement (1882). The Geology of the Country around Cromer. Memoirs of the Geological Survey of the United Kingdom. London:HMSO, p.9.
- ^ Woodward, HB (1876). The Geology of England and Wales. Longmans, Green & Co, London; pp.286-291.
- ^ Harmer, FW 1900. The Pliocene Deposits of the East of England - Part II : The Crag of Essex (Waltonian) and its relations to that of Suffolk and Norfolk. Quarterly Journal of the Geological Society, vol.56; pp.705-744.
- ^ a b c d e Funnell, BM (1961). The Palaeogene and early Pleistocene of Norfolk. Transactions of the Norfolk and Norwich Naturalists’ Society, vol.19, pt.6, pp.340-364
- ^ a b West, RG (1962). Vegetational history of the Early Pleistocene of the Royal Society Borehole at Ludham, Norfolk. Proceedings of the Royal Society of London, B155, pp.437-453.
- ^ a b Norton, PEP (1967). Marine Molluscan Assemblages in the Early Pleistocene of Sidestrand, Bramerton and the Royal Society Borehole at Ludham, Norfolk. Philosophic Transactions of the Royal Society of London, Series B, vol.253, no.784.
- ^ ISBN 0 19 854414 6.
- ^ Zalasiewicz, JA & Mathers, SJ (1985). Lithostratigraphy of the Red and Norwich Crags of the Aldeburgh-Orford Area, south-east Suffolk. Geological Magazine, vol.122, pt.3; pp.287-296.
- ^ ISBN 9072869613.
- ISBN 1 86239 042 8.
- ^ a b c d e Reid, Clement (1890). The Pliocene Deposits of Britain Memoirs of the Geological Survey of the United Kingdom, London: HMSO
- ^ a b c Mathers, SJ & Zalasiewicz, JA (1988a). The Red Crag and Norwich Crag Formations of southern East Anglia. Proceedings of the Geologists’ Association vol.99, pt.4; pp.261-278
- ^ The BGS Lexicon of Named Rock Units. British Geological Survey. Online at http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=NCG. Accessed October 2017.
- ^ a b c d e f g h Rose, J (2007). Palaeogeography of Eastern England during the Early & Middle Pleistocene. In: Candy, I et al. The Quaternary of Northern East Anglia Field Guide. Quaternary Research Association, 2007.
- ^ a b c d e f g Riches, P (2012). The palaeoenvironmental and neotectonic history of the Early Pleistocene Crag basin in East Anglia. Ph.D thesis, Royal Holloway, University of London.
- ^ Mottram, HB, (2017). Tidal-inlets and gravel deposition during the late Norwich Crag (Lower Pleistocene) of north-eastern Suffolk, U.K. Proceedings of the Geologists’ Association 128; pp.547–557.
- ISBN 0 11 884543 8.
- ^ Mottram, HB, (2022). On the supply of clasts to the Westleton Beds: a review. Bulletin of the Geological Society of Norfolk 72; pp.11–28.
- ^ ISBN 0 412 44190 X.
- ISBN 978 085272 823 9.
- ^ Rose, J, Moorlock, BSP & Hamblin, RJO (2000). Lithostratigraphy and palaeoenvironments of the pre-Anglian sands and gravels of East Anglia. In: Lewis, SG, Whiteman, CA & Preece, RC (eds). The Quaternary of Norfolk and Suffolk Field Guide. Quaternary Research Association, 2000.
- ^ a b Sinclair, J (1999). Plio-Pleistocene relative sea-level changes in East Anglian: evidence from the Westleton Member and related deposits. Proceedings of the Geologists' Association 110, pp.149-162.
- ^ a b c Funnell, BM (1996). Plio-Pleistocene Palaeogeography of the Southern North Sea Basin (3.75 - 0.60 Ma). Quaternary Science Reviews, vol.15.
- ^ Kuhlmann, G (2004). High resolution stratigraphy and paleoenvironmental changes in the southern North Sea during the Neogene : an integrated study of Late Cenozoic marine deposits from the northern part of the Dutch offshore area. Geologica Ultraiectina, Vol.245
- ^ Funnell, BM (1987). Late Pliocene and Early Pleistocene stages of E Anglia and the adjacent North Sea. Quaternary Newsletter 52, June 1987
- ^ Hamblin, RJO, Moorlock, BSP, Booth, SJ, Jeffery, DH & Morigi, AN (1997). The Red Crag and Norwich Crag formations in eastern Suffolk. Proceedings of the Geologists’ Association, vol.1088, pp.11-23.
- ^ Mathers, SJ & Zalasiewicz, JA (1988). The Pliocene to early Middle Pleistocene of East Anglia. In: Gibbard, PL & Zalasiewicz (eds). Pliocene-Middle Pleistocene of East Anglia Field Guide. Quaternary Research Association, 1988.
- ^ ISBN 9072869613.
- ^ Gibbard, PL, Gibbard, West, RG, Zagwijn, WH, Balson, PS, Burger, AW, Funnell, BM, Jeffery, DH, de Jong, J, van Kolfschoten, T, Lister, AM, Meijer, T, Norton, PEP, Preece, RC, Rose, J, Stuart, AJ, Whiteman, CA and Zalasiewicz, JA. (1991). Early and early Middle Pleistocene correlations in the southern North Sea Basin. Quaternary Science reviews, vol.10, no.1.
- ^ a b c d e Spencer, HEPS (1970). A Contribution to the Geological History of Suffolk, Part 5 : The Early Pleistocene. The Crag Epochs and their Mammals. Transactions of the Suffolk Naturalists’ Society no.15, pt.4.
- ^ a b Richards, AE, Gibbard, PL and Pettitt, ME (1999). The sedimentology and palaeoecology of the Westleton Member of the Norwich Crag Formation (early Pleistocene) at Thorington, Suffolk, England. Geological Magazine vol.136, pt.4.
- ^ a b c Norton, PEP (1977). Marine Mollusca in the East Anglian pre-glacial Pleistocene. In: Shotton, FW (ed). British Quaternary Studies - Recent Advances. Clarendon Press, Oxford, 1977.
- ^ a b UK Fossils (undated). Easton Wood
- ^ a b c Mayhew, DF (2011). West European arvicolid evidence of intercontinental connections during the early Pleistocene. Quaternary International, vol.30.
- ^ Carreck, JN (1966). Microtine remains from the Norwich Crag (Lower Pleistocene) of Easton Bavents, Suffolk. Proceedings of the Geologists' Association, vol.77, pt. 4.
- ^ a b Mayhew, DF & Stuart, AJ (1986). Stratigraphic and taxonomic revision of the fossil vole remains (Rodentia, Microtinae) from the Lower Pleistocene of Eastern England. Philosophical Transactions of the Royal Society of London, B312, pp.431-485.
- ^ Mlikovsky, J (1995). Tertiary Avian Localities of the United Kingdom. Acta Universitatis Carolinae Geologica, vol.29, pp.759-771.
- ^ Dyke, GJ, Nudds, RL & Walker, CA (2007). The Pliocene Phoebastria (‘Diomedea’) anglica: Lydekker's English fossil albatross. Ibis vol.149, no.3, pp.626-631.
- ISBN 0 19 511232 6.
- ^ Newton, ET (1891). The Vertebrata of the Pliocene Deposits of Britain. Memoirs of the Geological Survey of the United Kingdom, London.
- ^ Harmer, FW 1902. A sketch of the later Tertiary history of East Anglia. Proceedings of the Geologists’ Association, vol.17.
- ^ ISSN 0261-3611.
- ^ West, RG, Funnell, BM, and Norton, PEP (1980). An Early Pleistocene cold marine episode in the North Sea: pollen and faunal assemblages at Covehithe, Suffolk, England. Boreas, vol.9.
- ^ Funnell, BM, Norton, PEP & West, RG (1979). The crag at Bramerton, near Norwich, Norfolk. Philosophical Transactions of the Royal Society of London, B, 287, 489-534.
- ^ West, RG (1980). Pleistocene Forest History in East Anglia. New Phytologist, 85
- ^ Riding, JB, Moorlock, SP, Jeffrey, DH & Hamblin, RJO (1997). Reworked and indigenous palynomorphs from the Norwich Crag Formation (Pleistocene) of eastern Suffolk: implications for provenance, palaeogeography and climate. Proceedings of the Geologists’ Association, vol. 108, pt.1.
- ^ ISBN 978 085272 823 9.
- ^ a b Maher, B & Hallam (2005). Palaeomagnetic correlation and dating of Plio/Pleistocene sediments at the southern margins of the North Sea Basin. Journal of Quaternary Science, vol.20, pt.1.
- ^ a b Kuhlmann, G et al (2006). Integrated chronostratigraphy of the Plio-Pleistocene interval and its relation to the regional stratigraphical stages in the southern North Sea region. Netherlands Journal of Geological Sciences, vol.85, pt.1.
- ^ a b Lankester, E Ray (1914). Description of the Test Specimen of the Rostro-carinate Industry found beneath the Norwich Crag. Occasional Papers no.4, Royal Anthropological Institute, London.
- ^ Reid Moir, J (1927). The Antiquity of Man in East Anglia. Cambridge University Press.
- ^ Haward, FN (1919). The origin of the 'Rostro-carinate Implements' and other Chipped Flints from the Basement Beds of East Anglia. Proceedings of the Prehistoric Society of East Anglia vol.3 pt.1 (1918-1919).
- ^ Warren, SH (1923). Sub-soil Pressure flaking. Proceedings of the Geologists' Association of London, vol.34.
Further reading
- Arthurton, RS, Booth, SJ, Morigi, AN, Abbott, MAW & Wood, CJ (1994). Geology of the country around Great Yarmouth. Memoir for 1:50,000 Geological Sheets 162. British Geological Survey, HMSO, London. ISBN 011 884491 1.
- Chatwin, CP (1954). East Anglia and adjoining areas (3rd Edition. British Regional Geology. London: HMSO.
- Cox, FC, Gallois, RW & Wood, CJ (1989). The geology of the country around Norwich. Memoir for 1:50,000 Geological Sheet 161. British Geological Survey. ISBN 011 884410 5.
- Dixon, RG (ed) (2012). A Celebration of Suffolk Geology. GeoSuffolk 10th Anniversary Volume. GeoSuffolk, Ipswich. ISBN 0 9508154 7 0.
- Mathers, SJ, Woods, MA & Smith, NJP (2002). Geology of the Ipswich District. Sheet Explanation of the geological map Sheet 207 Ipswich. British Geological Survey, Keyworth. ISBN 978 085272572 6.
- Mathers, SJ and Smith, NJP (2002). Geology of the Woodbridge & Felixstowe District. Sheet Explanation of the geological map Sheets 208 and 225 Woodbridge & Felixstowe. British Geological Survey, Keyworth. ISBN 0 85 272431 4.
- Moorlock, B, Hamblin, RJO, Booth, SJ & Morigi, AN (2000). Geology of the country around Lowestoft and Saxmundham. Memoir for 1:50,000 Geological Sheets 176 and 191. British Geological Survey, HMSO, London. ISBN 0 11 884543 8.
- Moorlock, BSP, Hamblin, RJO, Booth, SJ & Woods, MA (2002). Geology of the Mundesley and North Walsham District. A brief explanation of the geological map Sheet 132 Mundesley and Sheet 148 North Walsham. British Geological Survey, Keyworth. ISBN 0 85 272438 1.