The upper part of the Carstone and the Hunstanton Red Chalk (Albian) of the Hunstanton Cliff, Norfolk

Abstract

In northwest Norfolk, the Gault Formation passes from clays into sands at the top of the Carstone Formation and red and sandy, pebbly, limestones of the Hunstanton Red Chalk Formation, well exposed in the sea cliffs at Hunstanton. The Carstone at Hunstanton can be divided into two Members, separated by a marked erosion surface. The Lower Carstone is of early Aptian age at its base, but is otherwise unfossiliferous. The top of the Upper Carstone is of Middle Albian, Hoplites spathi Subzone age and passes lithologically into the basal beds (C) of the Hunstanton Red Chalk. Barely a metre in total thickness, the Hunstanton Red Chalk includes sediments of several Subzones of the Middle and Upper Albian within the three units comprising the Formation. The basal unit (C) is of Hoplites spathi Subzone age. The middle unit (B) has a complex depositional and erosional history. In the more northern part of the section, bedded pebbly limestone of late Anahoplites intermedius Subzone (Middle Albian) age rests on unit C. These are overlain non-sequentially in part of the section, by bedded concretionary limestones with interstitial marl of late Dipoloceras cristatum Subzone and early Hysleroceras orbignyi Subzone (Upper Albian) age. Strong post-formational current scour produced a boulder bed from these limestones which, in the southern part of the section, rests directly on unit C. The basal part of the upper unit (A) is of Hysteroceras varicosum Subzone age, followed in turn by sediments of Callihoplites auritus Subzone and Stoliczkaia dispar Zone age.