Temperate, meteoric diagenesis of Pliocene skeletal carbonates from eastern England

Abstract

The Crags of eastern England include marine skeletal carbonates which were deposited and lithified under temperate conditions. The Coralline Crag (Pliocene), in particular, exhibits a variety of carbonate cement types which indicate exposure to meteoric groundwaters during a regressive episode. The Coralline Crag has been divided into an upper division of dominantly well sorted skeletal calcarenites and calcirudites and a lower, poorly sorted silty calcarenite division. ‘Dogtooth’ sparcement and rudimentary syntaxial cement overgrowths on echinoderm fragments are characteristic of the sediments of the upper division, which has undergone extensive aragonite dissolution. This division is consequently relatively evenly cemented. In the underlying sediments aragonite dissolution has not occurred and the sediments have remained largely uncemented, with cement restricted to irregular patches where growth of intra- and inter-particle equant spar has effectively eliminated porosity. In contrast with the upper leached sediments, syntaxial echinoderm overgrowths show a greater development but only where interference from surrounding sediment and sparry cement was absent. The elongate shape of the Coralline Crag outcrop may be the result of preferential cementation of the upper, coarser, well sorted calcarenites originally deposited as an elongate sediment body, possibly as an offshore sandbank.