The search for onshore analogues for the offshore Upper Cretaceous Chalk of the North Sea

Abstract

Suitable onshore analogues for offshore wind-farm turbine foundations in the Chalk of the North Sea would be invaluable. Such foundations require examples of near surface weathering illustrating both glacial and periglacial Quaternary processes as well as lithology and tectonic structure of the Chalk. From the Cenomanian to Early Campanian, the coast of East Yorkshire illustrates hard, high density, glacially eroded chalks similar to those found immediately offshore. Higher in the Campanian offshore East Yorkshire, younger, low density chalks, not present onshore, have been found (the Westermost Rough Member). In contrast, north Norfolk and its coastal cliffs provide examples of soft, high porosity, part glacially and part periglacially weathered chalks. Complex sedimentary structures seen in offshore seismic sections are similar to those on the French coast of the Pays de Caux. These coastal sections are compared with results from offshore wind farm ground investigations. Seismic sections illustrate Quaternary channels cutting into the Chalk and a landscape of hills and valleys similar to the onshore Wolds. High resolution 2D digital seismic sections, combined with cored boreholes, provide the evidence for applying the detailed Chalk lithostratigraphy to the offshore southern North Sea and illustrate the relationship between tectonic structure and sedimentation in the Chalk. The map for the offshore extension of Chalk provinces is revised, with Transitional Province lithologies typical of the Chiltern Hills and East Anglia, extending north-eastwards from Norfolk into the Dowsing Fault zone. Geotechnical properties are related to the buried offshore Chalk landscape as well as to Chalk lithostratigraphy.