Geophysical log characterization of the Flamborough Chalk Formation (Late Cretaceous, Santonian – Early Campanian), East Yorkshire, UK: implications for understanding the onshore and offshore occurrence of the Late Campanian Rowe Chalk Formation

Abstract

Whilst borehole geophysical log profiles have been matched with formational subdivisions for large parts of the Chalk Group in Lincolnshire and Yorkshire, characterization of the youngest and thickest part of the outcropping succession, represented by the marl-rich and largely flint-free Flamborough Chalk Formation, has been hindered by lack of cored and geophysically logged boreholes. In the absence of optimal primary data, a stratigraphical interpretation of geophysical logs in the Flamborough Chalk has been developed by comparison of logs from deep hydrocarbons boreholes (penetrating more than 260 m of Flamborough Chalk) beneath Holderness (East Yorkshire) with generalized patterns of outcrop stratigraphy. This approach reveals geophysical log patterns that are consistent with lithology and thickness variations seen at outcrop, compatible with core and geophysical data for a deep borehole in the Flamborough Chalk at Carnaby (near Bridlington), and traceable northwards and westwards towards the margin of the Flamborough Chalk outcrop. These interpretations, and comparisons with geophysically logged offshore successions, suggest the presence of Flamborough Chalk beneath Holderness that is younger (?Late Campanian) than anything seen at outcrop, and, with the exception of possible ex-situ chalk rafts of glacial origin, cast doubt on the likely subsurface onshore extent of typically flint-rich Rowe Chalk Formation.