Palynofloral association sequence stratigraphy of the Palaeocene Thanet Beds and equivalent sediments in eastern England

Abstract

Previous attempts to correlate the Thanetian sediments of East Anglia and Kent have provided a broad stratigraphic framework. Established dinoflagellate cyst zonation schemes can be used to subdivide the Late Palaeocene Thanet Beds and Ormesby Clay into two zones, based primarily on occurrences of Alisocysta margarita (Harland) Harland, 1979a, and Palaeoperidinium pyr pyrophorum (Ehrenberg) Sarjeant, 1967. This twofold subdivision does not provide a sufficient basis for correlation of Thanet Beds and Ormesby Clay sections. As an alternative in this study, palynofloral associations (e.g. the Areoligera cf. coronata-Inaperturopollenites hiatus association) are used as the basis for detailed stratigraphic correlation in which nine “association sequences” ( T1– T9) are defined. These association sequences are regarded as representing at least nine Thanet Beds and Ormesby Clay depositional units which onlap the Late Cretaceous Chalk erosion surface from the north and east. A depositional history is proposed indicating that the lower part of the Ormesby Clay corresponds to the lowstand systems tract of cycle TA2.1 of Haq et al. (1987), which is not represented in the Thanet Beds. Most of the Ormesby Clay and Thanet Beds was deposited as retrograding sequences during the transgressive systems tract of cycle TA2.1. Thin claystones with an offshore marine palynoflora at the top of the Ormesby Clay and Thanet Beds are regarded as deposits of the TA2.1 highstand systems tract and are restricted to the northeast of the study area.