Category:Holostratigraphy of the Chalk Group

M A Woods

Contributors: I P Wilkinson (Foraminiferal biostratigraphy) and J B Riding (Palynology)

Summary

This is an interactive document providing detailed geological information on the Chalk Group of the UK. Links within the document allow the user to access information at the level of detail that is most appropriate. Emphasis is placed on the integration of geological data from the Chalk Group in different parts of the UK and from a range of disciplines, to provide a detailed, high-resolution stratigraphical framework (Holostratigraphy) for correlation.

Introduction

The Chalk Group, ranging from the Cenomanian (Late Cretaceous) to Danian (earliest Paleocene), predominantly comprises yellow white, very fine-grained and very pure, microporous limestones. The lower part is typically more argillaceous and usually flint-free, but flints form conspicuous bands in the higher part of the Group. The Chalk has an extensive outcrop across southern (where typical chalk is soft) and eastern England (where, north of the Wash, the chalks are generally harder than in the south). The Chalk also occurs beneath the Palaeogene basalts in Northern Ireland, where it has been hydrothermally altered to form the strongly indurated Ulster White Limestone. In parts of southern England the composite thickness of the Chalk reaches nearly 500 m. In north Norfolk the c. 450 m thick succession recorded in a borehole at Trunch [TG 2933 3455] is the most stratigraphically complete onshore in the UK. Elsewhere in the UK the thickness of the Chalk Group has been greatly reduced by stratigraphical condensation and/or early Palaeogene erosion; in south-east Devon the Lower Chalk is strongly condensed and much of the higher part has been removed by erosion, so that the total preserved thickness is just over 100 m. Offshore the Chalk Group occurs extensively in the southern, central and northern North Sea, where its thickness locally exceeds 900 m over rift structures.

The Chalk Group is the principal aquifer in southern England, and many civil engineering projects impinge upon it. It is also a major source of lime for agriculture and cement manufacture.