The stratigraphy of the Lower Cretaceous Speeton Clay Formation in a cored borehole off the coast of north-east England

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Abstract
SUMMARY: A fully cored stratigraphical borehole in the Southern North Sea Basin at 54°39′N, 0°14′E encountered a succession of Lower Cretaceous clays and mudstones, representing part of the Speeton Clay Formation of the Cromer Knoll Group, resting on Upper Jurassic Kimmeridge Clay. The Lower Cretaceous beds comprise a basal phosphatic pebble-bed (equivalent to bed E, the Coprolite Bed, at Speeton) overlain by c.90m of marine clays ranging from Ryazanian to Barremian (equivalent to beds D8 – LB6 at Speeton) and include seven thin bentonite horizons. The three uppermost bentonite horizons lie within the Valanginian to Hauterivian, an interval from which no bentonites have previously been recorded in the European area. Six of the seven bentonite horizons recorded in the borehole have now been recognised in the type section at Speeton, Yorkshire. The borehole succession yielded rich microfaunal assemblages, which have enabled a detailed correlation to be made with the beds of the type locality at Speeton. The sequence cored in the borehole demonstrates a remarkable similarity to the Speeton sequence, despite an 80-kilometre separation of the localities.

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