View source for Earth:Norwich Crag Formation

{{Infobox rockunit
| name           = Norwich Crag Formation
| period         = Pleistocene
| age             = {{fossil range|2.4|1.8}}
| image          = Easton Wood cliffs, Covehithe, Suffolk.jpg
| caption=Easton Wood cliffs, Covehithe, Suffolk
| imagesize      = 
| type           = [[Earth:Geological formation|Geological formation]]
| prilithology   = Sand
| otherlithology = [[Earth:Gravel|Gravel]], [[Earth:Clay|Clay]], [[Earth:Silt|Silt]]
| unitof         = [[Earth:Crag Group|Crag Group]]
| subunits       = Chillesford Sand member, Chillesford Clay Member, Easton Bavents Clay Member, Westleton Beds Member, Sidestrand Member
| underlies      = 
| overlies       = 
| thickness      = 
| area           = 
| map            = 
| map_caption    =

<!----Location---->
| location 
| coordinates    = 
| region         = East Anglia
| country        = UK
| extent         =

<!--Type section--->
| namedfor       = Bramerton, Norwich
| namedby        = Clement Reid
| year_ts        = 1890
| location_ts    = <!--Place,mountain,...-->
| coordinates_ts = {{coord|52.2147|1.4160|display=inline,title}}
| paleocoordinates_ts = 
| region_ts      = <!--Region of type section-->
| country_ts     = <!--Country of type section-->
| thickness_ts   = <!--Thickness at type section-->
}}

The '''Norwich Crag Formation''' is a stratigraphic unit of the British [[Earth:Pleistocene|Pleistocene]] Epoch. It is the second youngest unit of the [[Earth:Crag Group|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 [[Earth:Facies|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.  It was deposited in a near-shore environment, and comprises a range of sands, silty clays and flint-rich gravels representing various [[Earth:Marine transgression|transgressive]] and [[Earth:Marine regression|regressive]] marine episodes. It rests in some places on the [[Earth:Red Crag Formation|Red Crag Formation]] and in others unconformably on Coralline Crag, Palaeogene formations and [[Earth:Chalk Group|Chalk Group]] bedrock. It is overlain by the Wroxham Crag Formation, and unconformably by the Kesgrave Catchment Subgroup and Mid Pleistocene glacigenic deposits.

Norwich Crag [[Biology:Fossil|fossil]] [[Earth:Fauna|fauna]] and [[Earth:Flora|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 is commonly used in Suffolk to designate a deposit of fossil sea shells or any shelly sand or gravel. It was first used in a geological sense by R.C. Taylor in 1823.<ref name=''Forby_1830''>Forby, F (1830). ''The Vocabulary of East Anglia''. JB Nichols & Son, London.</ref><ref name=''Woodward_1881''/>

[[File:Burgh Kiln quarry geological exposure, Norfolk, UK.jpg|thumb|right|300px|Geological section at Burgh Kiln quarry, Norfolk (Reid 1890).]]
The Norwich Crag was first identified in the early 19th century as a predominantly marine geological formation, then thought to be of Pliocene age, outcropping from Aldeburgh to the valley of the River Bure. It was variously termed the Mammaliferous Crag (Charlesworth 1836), Norwich Crag (Lyell 1839), Norfolk Crag (Phillips 1863) and Upper Crag (Godwin-Austen 1868).<ref name=''Woodward_1881''>Woodward, HB (1881). ''The Geology of the Country around Norwich''. Memoirs of the Geological Survey of the United Kingdom.</ref> Five [[Earth:Horizon (geology)|horizons]] were initially recognised: the Mammaliferous Stone-Bed; the Fluvio-marine Crag; the Chillesford Crag; the Chillesford Clay; the Bure Valley Crag, including the Westleton Beds.<ref name=''Woodward_1881''/> Additional units were identified in the Norwich Crag Series, the Weybourne Crag<ref name=''Prestwich_1890''>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.</ref><ref name=''Reid_1882''>Reid, C (1882). ''The Geology of the Country around Cromer''. Memoirs of the Geological Survey of the United Kingdom; p.9.</ref> and the Bure Valley Beds.<ref name=''Woodward_1876''>Woodward, HB (1876). ''The Geology of England and Wales''. Longmans, Green & Co, London; pp.286-291.</ref>  This stratigraphy was later formalised by FW Harmer, who grouped them all into an Icenian faunal zone of the Pliocene.<ref name=''Harmer_1900''>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 Soc, vol.56; p.721.</ref> Research into sediments from the [[Earth:Ludham Borehole|Ludham research borehole]] (1959) allowed a sequence of vegetational and faunal episodes to be recognised in the Norwich Crag, based on fossil [[Biology:Foraminifera|foraminifera]], pollen and mollusca.<ref name=''Funnell_1961''>Funnell, BM (1961). ''The Palaeogene and early Pleistocene of Norfolk''. Transactions of the Norfolk and Norwich Naturalists’ Society, vol.19, pt.6</ref><ref name=''West_1962''>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.</ref><ref name=''Norton_1967''>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.</ref> A revised lithostratigraphical and biostratigraphical framework was published by Funnell and West (1977).<ref name=''Funnell&West_1977''>Funnell, BM & West, RG (1977). ''Preglacial Pleistocene deposits of East Anglia''. In: Shotton, FW (ed). ''British Quaternary Studies: recent advances''. Oxford University Press, 1977. {{ISBN|0 19 854414 6}}.</ref> Research into the lithostratigraphy of the Norwich Crag was carried out by the British Geological Survey between 1975 and 2006 as part of work to remap the geology of Norfolk and Suffolk; new techniques allowed improved understanding of local detail,<ref name=''Zalasiewicz&Mathers_1985''>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.</ref> and it became possible to distinguish the Norwich Crag from the succeeding Wroxham Crag (now subsuming the Weybourne Crag and Bure Valley Beds). Following international revisions to the Pliocene/Pleistocene boundary, the Norwich Crag is now placed in the Lower Pleistocene.<ref name=''Gibbardetal_1998''>Gibbard, PL, Zalasiewicz, JA & Mathers, SJ (1998). ''Stratigraphy of the marine Plio-Pleistocene crag deposits of East Anglia''. In: van Kolfschoten, T and Gibbard, PL (eds): ''The Dawn of the Quaternary - proceedings of the SEQS-EuroMam Symposium : Kerkrade, 16–21 June 1996''. Netherlands Institute of Applied Geoscience, 1998; pp.239-262. {{ISBN|9072869613}}.</ref>

Six lithostratigraphic members were recognised by the Geological Society of London<ref name=''Bowened_1999''>Bowen, DQ (ed) (1999). ''A revised correlation of Quaternary deposits in the British Isles''. Special Report no.23, The Geological Society, p.22. {{ISBN|1 86239 042 8}}.</ref>: 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 infilling tidal inlets<ref>Mottram, H.B., 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 (2017) 547–557.</ref> overlying the Easton Bavents Member).

The [[Social:Type site|type site]] of the Formation is at Bramerton Pits SSSI, near Norwich.<ref name=''Reid_1890''>Reid, C (1890). ''The Pliocene Deposits of Britain''. Memoirs of the Geological Survey of the United Kingdom, London.</ref>

==The sedimentary record==
[[Image:Westleton Beds on Westleton Heath, Suffolk.jpg|thumb|right|300px|Flint gravels of the Westleton Member exposed in an old quarry on Westleton Heath, Suffolk, UK; thought to have been largely deposited in tidal inlets younger than the Baventian cold stage.]]
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.<ref name=''Gibbardetal_1998''/><ref name=''Mathers&Zal_1988a''>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</ref>. Geological field relationships show that it rests with discontinuity on the [[Earth:Red Crag Formation|Red Crag Formation]] and oversteps in other places onto the Coralline Crag, the Palaeogene formations and [[Earth:Chalk Group|Chalk Group]] bedrock. It is overlain disconformably by the Wroxham Crag Formation, and unconformably by the Kesgrave Catchment Subgroup and Mid Pleistocene glacigenic deposits<ref name=''BGSLexicon''>''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.</ref>. 

The Norwich Crag comprises a widespread sheet of well sorted, fine- to medium-grained [[Chemistry:Mica|mica]]ceous, [[Chemistry:Glauconite|glauconitic]], locally shelly sands (eg 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 [[Earth:Flint|flint]], typically more than 95% local material, either chattermarked (beach-abraded) or angular or sub-angular flint; the remaining 5% is typically white vein [[Chemistry:Quartz|quartz]] and white [[Earth:Quartzite|quartzite]].<ref name=''Rose_2007''>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.</ref> The [[Earth:Heavy mineral|heavy mineral]]s in the sand-sized fraction of the sediment are characterised by high concentrations of [[Chemistry:Garnet|garnet]], [[Chemistry:Amphibole|amphibole]] and [[Chemistry:Epidote|epidote]], which suggests that the sands originated from eastern (continental) rather than western (British) fluvial sources.<ref name=''Riches_2012''>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.</ref>  The sandy sediments are near-shore marine deposits, with the clay members being estuarine or lagoonal<ref name=''Gibbardetal_1998''/> and the flint gravels also being near-shore marine deposits<ref>Mottram, H.B. 2012.The Norwich Crag geology of the country around Westleton. 251-258. in Dixon, R. (ed). A celebration of Suffolk geology. GeoSuffolk. {{ISBN|0-9508154-7-0}}</ref>. These deposits represent environments fluctuating between marine transgressive and regressive episodes on the western margins of the North Sea basin.<ref name=''Moorlocketal_2000''>Moorlock, BSP, 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. {{ISBN|0 11 884543 8}}.</ref> Comparison with better preserved sedimentary sequences of similar age in the Netherlands has shown that the Norwich Crag sequence is highly incomplete.<ref name=''Jones&Keen_1993''>Jones, RL & Keen, DH (1993). ''Pleistocene Environments of the British Isles''. Chapman & Hall. {{ISBN|0 412 44190 X}}.</ref> Interpretation is hampered by difficulties with distinguishing major non-sequences from minor, local erosional discontinuities.<ref name=''Gibbardetal_1998''/>

For surface mapping purposes, the British Geological Survey has recognised five members: the Chillesford Sand, Chillesford Clay, Easton Bavents Clay, Westleton Beds and Sidestrand Members.<ref name=''Leeetal_2015''>Lee, J. R.; Woods, M. A.; Moorlock, B. S. P., eds. (2015). ''British Regional Geology: East Anglia (5th ed.)''. British Geological Survey. {{ISBN|978 085272 823 9}}.</ref> The uppermost beds of the Crag Group (formerly the Bure Valley Beds and Weybourne Crag) are now attributed to the Wroxham Crag Formation, based on their high proportion of fluvially-derived, far-travelled lithological components.<ref name=''Roseetal_2000''>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.</ref>

Considering the lithostratigraphy to include subsurface sediments, Riches (2012) proposed three major units for the Crag Basin; most recognisable where they are separated by regressive marker beds of silty clay, with the uppermost equated with the Chillesford Clay Member.<ref name=''Riches_2012''/>

==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<ref name=''Funnell_1961''/>. It is conjectured that at c.2.4 million years BP the North Sea coastline lay across east Norfolk and east Suffolk, with a continuation eastwards to Holland; there were local embayments in the areas of Stalham, Bungay and Stradbroke.<ref name=''Rose_2007''/><ref name=''Funnell_1996''>Funnell, BM (1996). ''Plio-Pleistocene Palaeogeography of the Southern North Sea Basin (3.75 - 0.60 Ma)''. Quaternary Science Reviews, vol.15.</ref> The North Sea was a [[Earth:Bight (geography)|bight]] at this time, with its southern margin defined by the chalk hills of the Weald-Artois anticline where the Strait of Dover is now located.<ref name=''Kuhlmann_2004''>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</ref> There is evidence for later marine transgression and extension of the sea as far west as the Stansted area of Essex, associated with deposition of the Chillesford Sand Member during a period of high sea levels around two million years ago<ref name=''Mathers&Zal_1988a''/><ref name=''Funnell_1987''>Funnell, BM (1987). ''Late Pliocene and Early Pleistocene stages of E Anglia and the adjacent North Sea''. Quaternary Newsletter 52, June 1987</ref> correlated with the Antian/Bramertonian Stage. This was followed by marine regression during the Baventian/Pre-Pastonian a Stage.<ref name=''Gibbardetal_1998''/> Evidence for major rivers, the Bytham and Proto-Thames, draining into the Crag Basin at this time is represented by far-travelled material found in estuarine deposits in eastern Suffolk, the Easton Bavents Clay and Chillesford Clay Members.<ref name=''Hamblinetal_1997''>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.</ref> The coastline shifted north-eastwards to a position in north-east Norfolk by about 1.75 million years BP.<ref name=''Funnell_1996''/>  This later period is associated with deposition of the Wroxham Crag Formation and marked fluvial input by the Proto-Thames, Bytham River and Ancaster River systems.<ref name=''Rose_2007''/>

==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.<ref name=''Rose_2007''/> 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.<ref name=''Mathers&Zal_1988a''/><ref name=''Mathers&Zal_1988b''>Mathers, SJ & Zalasiewicz, JA (1988). ''The Pliocene to early Middle Pleistocene of East Anglia''. In: Gibbard, PL & Zalasiwicz (eds). ''Pliocene-Middle Pleistocene of East Anglia Field Guide''. Quaternary Research Association, 1988.</ref> The uplift has, however, been uneven, with little change apparent in north-east Norfolk in the West Runton – Happisburgh area.<ref name=''Rose_2007''/>

==Fauna and flora==
The fossil fauna and flora of the Norwich Crag have been studied since the early 19th century for [[Earth:Biostratigraphy|biostratigraphic]] and palaeoclimatic interpretation. Taxa used include plants, molluscs, foraminifers, mammals and [[Biology:Dinoflagellate|dinoflagellate]]s.<ref name=''Jones&Keen_1993''/><ref name=''Head_1998''>Head, MJ (1988). ''Marine environmental change in the Pliocene and early Pleistocene of eastern England: the dinoflagellate evidence reviewed''. In: van Kolfschoten, T and Gibbard, PL (eds): ''The Dawn of the Quaternary - proceedings of the SEQS-EuroMam Symposium : Kerkrade, 16–21 June 1996''. Netherlands Institute of Applied Geoscience, 1998. {{ISBN|9072869613}}.</ref>
They provide evidence for a general climatic cooling trend from the Pliocene into the [[Earth:Pleistocene|Pleistocene]].<ref name=''Riches_2012''/> 
Three biostratigraphic stages have been identified based on fossil pollen assemblages: Thurnian, [[Earth:Bramertonian Stage|Antian/Bramertonian]] and [[Earth:Pre-Pastonian Stage|Baventian/Pre-Pastonian a]], representing a cold-warm-cold climatic sequence.<ref name=''Gibbardetal_1998''/> 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.<ref name=''Gibbardetal_1991''>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.</ref> The historic chronostratigraphic correlations and palaeoenvironmental interpretations based on biostratigraphy (local and continental) have been criticised as poorly defined and unreliable by Riches (2012).<ref name=''Riches_2012''/>

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 [[Earth:Red Crag Formation|Red Crag]].<ref name=''Spencer_1970''>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.</ref> Vertebrate fossils tend to be concentrated in the basement bed<ref name=''Woodward_1881''/><ref name=''Reid_1890''/><ref name=''Spencer_1970''/> or in gravel lags.<ref name=''Richardsetal_1999''>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.</ref> Species of warm and cold substages are represented, sometimes mixed together; this may pose problems for palaeoecological interpretation.<ref name=''Jones&Keen_1993''/><ref name=''Norton_1977''>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.</ref>

=== Mammals ===
====Land mammal fauna====
[[File:Newton 1891, plate 2.jpg|thumb|right|300px| ''Phoca'' (seal) humerus & ''Trichecus'' (walrus) femur fragments, figured in Newton 1891, plate 2.]]
From a biostratigraphic point of view, the terrestrial mammal fauna of the Norwich Crag belongs to the Late Villafranchian European Land Mammal Age and is correlated with [[Earth:European land mammal age|European Neogene Mammal Zone]] MN17.  The richest and best-preserved assemblage is found in deposits of Antian/Bramertonian age at Easton Wood, Covehithe. Taxa collected from this site include proboscideans ''[[Biology:Mammuthus meridionalis|Mammuthus meridionalis]]'' and '' [[Biology:Anancus|Anancus arvernensis]]'', horse ''Equus robustus'', deer '' [[Biology:Eucladoceros|Eucladoceros falconeri]]'' and '' [[Biology:Eucladoceros|Eucladoceros sedgwicki]]'', gazelle '' [[Biology:Gazella borbonica|Gazella anglica]]'', beaver ''[[Biology:Trogontherium|Trogontherium]]'' sp., wolf '' [[Biology:Canis etruscus|Canis etruscus]]'', voles ''Mimomys pliocaenicus'', ''Mimomys reidi'' and  ''Mimomys tigliensis'', and lemming ''Lemmus kowalskii''.<ref name=''UKfossils_EastonWood''> UK Fossils (undated). ''Easton Wood''  [https://ukfossils.co.uk/2005/07/07/easton-wood/]</ref><ref name=''Mayhew_2011''>Mayhew, DF (2011). ''West European arvicolid evidence of intercontinental connections during the early Pleistocene''. Quaternary International, vol.30.</ref><ref name=''Carreck_1996''>Carreck, JN (1966). ''Microtine remains from the Norwich Crag (Lower Pleistocene) of Easton Bavents, Suffolk''. Proceedings of the Geologists' Association, vol.77, pt. 4.</ref>.
Bramerton has yielded [[Biology:Holotype|holotypes]] of the extinct otter ''Enhydra reevei'' and the gazelle '' [[Biology:Gazella borbonica|Gazella daviesii]]''<ref name=''Riches_2012''/>. The whole skeleton of a [[Biology:Mastodon|mastodon]] is reported to have been found in the basal Stone Bed resting on Chalk at Horstead in 1820<ref name=''Woodward_1881''/>. 

Vole fossils from the Norwich Crag contribute to the ‘vole clock’ used for biostratigraphic zonation of Pliocene and Pleistocene sediments<ref name=''Mayhew&Stuart_1986''/>. For instance, ''Mimomys pliocaenicus'' is a biozonal species for European Neogene Mammal Zone MN17<ref name=''Mayhew_2011''/>. Bramerton has yielded the most primitive microtine rodent assemblage known from the British Isles<ref name=''Mayhew&Stuart_1986''>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.</ref>.

====Marine mammal fauna====
Marine taxa from Easton Wood include ''[[Biology:Orca|Orca]]'' and walrus ''Alachatherium cretsii''<ref name=''UKfossils_EastonWood''/> . Short-beaked common dolphin ''Delphinus delphis'' and indeterminate whale bones are recorded from Holton and Thorington<ref name=''Spencer_1970''/><ref name=''Richardsetal_1999''/>.

=== Birds ===

Very few avian fossils have been found in the Norwich Crag. Bones of ''common guillemot'', ''little auk'' and various indeterminate seabird bones have been recorded from Aldeby, Chillesford, Easton Bavents and Yarn Hill.<ref name=''Reid_1890''/><ref name=''Spencer_1970''/><ref name=''Mlikovsky_1995''>Mlikovsky, J (1995). ''Tertiary Avian Localities of the United Kingdom''. Acta Universitatis Carolinae Geologica, vol.29, pp.759-771.</ref>. The albatross ''Phoebastria anglica'' has been recorded from Easton Wood, Covehithe.<ref name=''Dykeetal_2007''>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.</ref>

=== Reptiles and Amphibians ===

No [[Biology:Reptile|reptile]] and [[Biology:Amphibian|amphibian]] fossils have yet been recorded from the Norwich Crag.<ref name=''Holman_1998''>Holman, JA (1998). ''Pleistocene Amphibians and Reptiles in Britain and Europe''. Oxford University Press. {{ISBN|0 19 511232 6}}.</ref>

=== Fish ===

Fossil marine fish from the Norwich Crag include genera ''Chrysophrys'' sp. (a [[Biology:Australasian snapper|snapper]]) and ''Acipenser'' ([[Biology:Sturgeon|sturgeon]]), and species ''Platax woodwardii'' (a batfish), ''Gadus morhua'' (Atlantic cod) and ''Raja clavata'' (thornback ray).<ref name=''Newton_1891''>Newton, ET (1891). ''The Vertebrata of the Pliocene Deposits of Britain''. Memoirs of the Geological Survey of the United Kingdom, London.</ref> Teeth of the freshwater fish ''Esox lucius'' (northern pike) have been found at Bramerton.<ref name=''Woodward_1881''/>

=== 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.<ref name=''Harmer_1902''>Harmer, FW 1902. ''A sketch of the later Tertiary history of East Anglia''. Proceedings of the Geologists’ Association, vol.17.</ref> However they show evidence of considerable transportation, and consequent mixing of faunal assemblages from the earlier Red Crag Formation.<ref name=''Long&Cambridge_1988''>Long, PE & Cambridge, PG (1988). ''Crag Mollusca: an overview''. In: Gibbard, PL & Zalasiewicz, JA (eds). ''Pliocene-Middle Pleistocene of East Anglia Field Guide''. Quaternary Research Association, 1988. {{ISSN|0261-3611}}.</ref> The use of molluscan fossils for climatic reconstruction has proved problematic. For instance species found together at several levels in the Ludham borehole notably ''[[Biology:Serripes groenlandicus|Serripes groenlandicus]]'' (Greenland cockle) and ''[[Biology:Calyptraea chinensis|Calyptraea chinensis]]'' (Chinese hat snail) have notably different climatic tolerances today (arctic and lusitanic respectively).<ref name=''Norton_1967''/> 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.<ref name=''Norton_1977''/> The local variability of molluscan assemblages at similar horizons was noted by Reid as adding uncertainty to their use for biostratigraphic correlation.<ref name=''Reid_1890''/> However, molluscan fossils have proved most useful as indicators of water depth in marine facies.<ref name=''Norton_1977''/>
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).<ref name=''Long&Cambridge_1988''/> Cold climate indicator species include ''[[Biology:Astarte borealis|Astarte borealis]]'' and ''[[Biology:Yoldia myalis|Yoldia myalis]]'' from Baventian deposits at Covehithe.<ref name=''Jones&Keen_1993''/> Some species have distinct biostratigraphic value. The absence of ''[[Biology:Limecola balthica|Macoma balthica]]'' is considered to be an indicator distinguishing Norwich Crag molluscan assemblages from those of the later Wroxham Crag.<ref name=''Woodward_1881''/><ref name=''Funnell_1961''/><ref name=''Reid_1890''/> Fossil shells are scarce or absent in some horizons, which may be due to due to contemporaneous erosion or non-deposition or post-depositional [[Chemistry:Calcium carbonate|calcium carbonate]] solution.<ref name=''Riches_2012''/>{{rp|368}}

=== Plants ===

[[File:Pterocarya fraxinifolia (Caucasian wingnut), Norwich, UK.jpg|thumb|right|300px|A specimen of ''[[Biology:Pterocarya fraxinifolia|Pterocarya fraxinifolia]]'' (Caucasian wingnut) in St George's churchyard, Tombland, Norwich – a species native to the area 2 million years ago.]]
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<ref name=''Funnell_1961''/><ref name=''Funnell&West_1977''/> 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 [[Earth:Bramertonian Stage|Antian]] with temperate mixed coniferous / deciduous forest including ''[[Biology:Tsuga|Tsuga]]'' (hemlock) and ''[[Biology:Pterocarya|Pterocarya]]'' (wingnut); the [[Earth:Pre-Pastonian Stage|Baventian]], a glacial stage more severe than the Thurnian, with the return of oceanic heath.<ref name=''West_1962''/><ref name=''West&Norton_1980''>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.</ref> Further work on Norwich Crag sediments at Bramerton, Norfolk, allowed a [[Earth:Bramertonian Stage|Bramertonian]] stage to be identified, characterised by temperate forest with ''[[Biology:Oak|Quercus]]'', ''[[Biology:Hornbeam|Carpinus]]'' and ''[[Biology:Alder|Alnus]]''. Correlation was made with the pollen assemblage from Chillesford.<ref name=''Funnelletal_1979''>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.</ref><ref name=''West_1980''>West, RG (1980). Pleistocene Forest History in East Anglia. New Phytologist, 85</ref> Specimens of fossil wood have occasionally been found, for example [[Chemistry:Pyrite#Pyritised fossils|pyritised]] [[Biology:Pine|pine]] and [[Biology:Oak|oak]] at Holton.<ref name=''Spencer_1970''/>

=== Dinoflagellates ===

Dinoflagellate fossil assemblages have been used in the Norwich Crag as indicators of palaeoclimatic conditions,<ref name=''Head_1998''/> although evidence for reworking of earlier dinocysts suggests caution in interpretation.<ref name=''Ridingetal_1997''>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.</ref>

=== Foraminifers ===

Fossil [[Biology:Foraminifera|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.<ref name=''Funnell_1961''/> 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.<ref name=''Funnell&West_1977''/>

==Dating and correlations==
The Norwich Crag Formation was deposited during the Gelasian Stage of the [[Earth:Pleistocene|Pleistocene]], between about 2.4 and 1.8 million years ago<ref name=''Mathers&Hamblin_2015''>Mathers, SJ & Hamblin, RJO (2015). ''Late Pliocene and Pleistocene Marine Deposits''. In: Lee, JR; Woods, MA; Moorlock, BSP, eds. ''British Regional Geology: East Anglia (5th Edition)''. British Geological Survey; fig.46. {{ISBN|978 085272 823 9}}.</ref>. The evidence from fossil plants, mammals, molluscs, foraminifers and dinoflagellates has been used to make [[Earth:Biostratigraphy|biostratigraphic]] correlations between [[Earth:Chronostratigraphy|chronostratigraphic]] Stages recognised in East Anglia and the more complete sequence on the Continent. Wider correlation is made with Marine Isotope Stages (MIS) and [[Earth:Magnetostratigraphy|magnetostratigraphy]], despite uncertainties in interpretation<ref name=''Maher&Hallam_2005''>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.</ref><ref name=''Mayhew_2011''/>. It has been noted by Riches (2012) that pollen and foraminiferan assemblages are not age diagnostic, and may not alone be sufficient to sustain reliable stratigraphy<ref name=''Riches_2012''/>. The Thurnian Stage has been variously correlated with Stage Tiglian A or Tiglian B in the Netherlands; the [[Earth:Bramertonian Stage|Antian/Bramertonian]] with Tiglian C1-3 or C1-4b; the [[Earth:Pre-Pastonian Stage|Baventian/Pre-Pastonian a]] with Tiglian C1-4b or C-4c<ref name=''Rose_2007''/><ref name=''Funnell_1996''/><ref name=''Kuhlmannetal_2006''/><ref name=''Head_1998''/>. This timespan is correlated with MIS 81 to 68<Ref name=''Rose_2007''/> or MIS 95 to 71<ref name=''Kuhlmannetal_2006''>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.</ref>, covering a time period of between 2.44 and 1.8 million years before present in the Matuyama Chron<ref name=''Mathers&Hamblin_2015''>Mathers, SJ & Hamblin, RJO (2015). ''Late Pliocene and Pleistocene Marine Deposits''. In: Lee, JR; Woods, MA; Moorlock, BSP, eds. ''British Regional Geology: East Anglia (5th Edition)''. British Geological Survey; fig.46. {{ISBN|978 085272 823 9}}.</ref>, corresponding to the magnetostratigraphic interval between the Reunion Sub-chron and the top of the Olduvai Sub-chron<ref name=''Rose_2007''/><ref name=''Maher&Hallam_2005''/>.

==Eoliths and early humans==
[[File:Lankester 1914, plate 3c.jpg|thumb|right|300px| An annotated picture of the Norwich Test Specimen, figured in Lankester 1914, Plate 3.]]
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.<ref name=''ReidMoir_1927''>Reid Moir, J 1927. ''The Antiquity of Man in East Anglia''. Cambridge University Press.</ref> A typologically diagnostic form of [[Earth:Eolith|'eolithic']] beak-shaped instrument was proposed by [[Biography:Ray Lankester|E Ray Lankester]], the ‘rostro-carinate’, based upon a ‘Norwich Test Specimen’ flint found in the basal Norwich Crag at Colman’s Pit, Whitlingham.<ref name=''Lankester_1914''>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.</ref> The human origin for these Crag specimens was refuted by FN Haward<ref name=''Haward_1919''>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).</ref> 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.<ref name=''Warren_1923''>Warren, SH (1923). ''Sub-soil Pressure flaking''. Proceedings of the Geologists' Association of London, vol.34.</ref>

==See also==
* [[Earth:Geologic time scale|Geologic time scale]]
* Geology of England
* Geology of the North Sea
* [[Earth:Ludham Borehole|Ludham Borehole]]
* [[Earth:Quaternary|Quaternary]]
* [[Earth:Pleistocene|Pleistocene]]
* Palaeontology

== References ==
{{reflist|30em}}

==Further reading==
{{refbegin}}
*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}}.
*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}}.
{{refend}}

==External links==
* [http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=NCG BGS Stratigraphic Lexicon: Norwich Crag Formation]
* [http://www.norfolkgeology.co.uk/ Geological Society of Norfolk ]
* [http://www.geoessex.org.uk/ GeoEssex]
* [http://geosuffolk.co.uk/ GeoSuffolk ]
* [https://sites.google.com/site/norfolkgeodiversity/ Norfolk Geodiversity Partnership] 
* [http://www.qra.org.uk Quaternary Research Association]

[[Category:Biostratigraphy]]
[[Category:Pleistocene]]
[[Category:Pleistocene animals]]
[[Category:Pleistocene life]]
[[Category:Quaternary]]
[[Category:Quaternary life]]

{{Sourceattribution|Norwich Crag Formation}}