Early Submarine Lithification in the Red Chalk and Lower Chalk of Eastern England: A Bacterial Control Model and Its Implications

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.

Secular variation in Late Cretaceous carbon isotopes: a new δ13C carbonate reference curve for the Cenomanian–Campanian (99.6–70.6 Ma)

“…Section details have been provided by Hill (1888), Jeans (1973Jeans ( , 1980, Paul et al (1994b), Gale (1995), Mitchell (1995Mitchell ( , 1996, Mitchell, Paul & Gale (1996) and Mortimore, Wood & Gallois (2001). A highresolution carbon-isotope stratigraphy of the Upper Albian-basal Turonian has been documented by Mitchell and co-workers (references above); the stratigraphic and δ 13 C data presented here are those of Mitchell, Paul & Gale (1996, fig.…”

“…Kennedy, 1969;Jeans, 1980) and France (Gale, 1995;Amédro & Robaszynski, 1999), Germany (the Middle Cenomanian Event of Ernst, Schmid & Siebertz, 1983;Meyer, 1990), and the Crimea (Marcinowski, 1980;Gale, Hancock & Kennedy, 1999).…”

Regional hardening of Upper Cretaceous Chalk in eastern England, UK: trace element and stable isotope patterns in the Upper Cenomanian and Turonian Chalk and their significance

“…The Louth Member (6-8 m thick in eastern England, 16 m thick at Dover) is a laterally continuous unit of white fine-grained chalk which can be traced from Speeton on the Yorkshire coast and throughout much of southern England. It lies between the base of the Variegated Beds/Plenus Marls and the underlying Nettleton Chalk Member (Jeans 1980) fig. 4), or in eastern England where it is within the Ferriby Formation (Lower to Upper Cenomanian).…”

“…It is divided into two by the laterally continuous marly Variegated Beds. The lower unit, Unit A, consists of normal hard chalk that shows no obvious field evidence of early lithification as defined by Jeans (1980). Its base marks the appearance of hard chalk as a continuous facies whereas in the underlying part of the Ferriby Formation occasional beds of this chalk type may occur but are interbedded with chalk and marl showing evidence of early lithification.…”

“…The top of Unit A is the sub-Plenus erosion surface, which defines both the base of the Variegated Beds and the Welton Formation. The upper unit, Unit B, includes the upper part of the Flixton Member of Jeans (1980), the Melbourn Rock Member of Jeans et al (1991, fig. 12) and some of the overlying chalk (Text- fig.…”