The palaeoenvironmental and neotectonic history of the Early Pleistocene Crag basin in East Anglia

Peter Riches

Research output: ThesisDoctoral Thesis

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A palaeoenvironmental history and correlation of the deep Crag sequence in East Anglia is presented in terms of processes rather than purely biostratigraphic concepts. A critical review of the historic correlations and palaeoenvironmental interpretations of the Crag demonstrates that the biostratigraphical interpretations include weak assumptions that led to a poorly defined and unreliable paradigm.

The base of the Crag surface was mapped and revealed NE-SW trending ridges and troughs, formed largely by Pre-Crag fluvial erosion, that cross an easterly dipping surface bounded to the north by the uplift associated with the Dowsing-Hewett Fault Zone and to the south by the Ipswich-Felixstowe high.

The lithologies and sedimentology of key sites at the margin of the basin around Norwich are described and combined with a comprehensive review of borehole data, across the basin, including gamma-ray logs, to propose a new lithostratigraphical model of the Crag basin. Three lithostratigraphic units, separated by silty clay marker beds, have been defined and the upper marker bed equates with the Chillesford Clay Member. The heavy mineral assemblages indicate the sediments were derived predominantly from the east and were deposited in shallow coastal to inter-tidal environments on the southern North Sea basin margin. The Crag sediments progressively onlapped the margins of the basin and infilled an accommodation space that increased eastwards as the basin subsided. The top of the Crag sequence is a polygenetic erosional surface beneath the Westleton Beds, or the Wroxham Crag, or fluvial sands and gravels, or glaciofluvial and glacial deposits. A distinctive quartzose gravel in the Norwich area has been interpreted as evidence for an early, eastward flowing River Bytham to the north of its later route through Suffolk.

Syndepositional subsidence also occurred in the southwest (Stradbroke Trough) area and differential movement of basement blocks occurred during the Early and Middle Pleistocene, particularly on the NE-SW Framlingham Chalk ridge across East Suffolk. The base of the Crag has also been tilted by much later regional uplift in the west and southwest.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • Rose, Jim, Supervisor, External person
  • Schreve, Danielle, Advisor
Award date1 Jan 2013
Publication statusUnpublished - 2012

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