EARLY SUBMARINE LITHIFICATION IN THE RED CHALK AND LOWER CHALK OF EASTERN ENGLAND: A BACTERIAL CONTROL MODEL AND ITS IMPLICATIONS

Publisher Website
Google Scholar
Abstract
SUMMARY: Early submarine lithifications are common in the Albian and Cenomanian Red Chalk and Lower Chalk of eastern England. They have developed generally in shallow water sediments deposited relatively slowly in the aphotic zone of the Chalk sea. Five varieties of early lithification are described and interpreted in detail. The lithification has occurred during the intrinsic diagenesis of the sediment ranging from very close to the water/sediment interface to some metres below. It has been caused by the precipitation of a ferroan calcite cement (2940–8900 ppm Fe 2+ ) under anaerobic alkaline conditions. The preservation of aragonitic fossils indicates that sources from within the sediment and the external reservoir of sea water supplied the necessary Ca 2+ and CO 3 2− . Indirect evidence suggests that (1) bacterial ammonification and sulphate-reduction have effected the precipitation of the ferroan calcite cement, and (2) porewater temperature, depositional rates, and the content of aragonite and organic matter in the sediment were important factors in controlling the development of early lithification. The importance or the bacterial mechanism as a general lithification process in the aphotic marine environment is discussed.