Paleoceanographic Approach to the Kimmeridge Clay Formation

R. G. Miller

The Upper Jurassic/Lower Cretaceous Kimmeridge Clay Formation (KCF) is northern Europe's premier source rock and can be understood using a new but relatively simple oceanographic model. This explains or accommodates most current observations about the KCF and its depositional environment and draws upon palaeogeographic, palaeoclimatic, geochemical, sedimentological, and palaeontological evidence.

Plate tectonic reconstruction shows a triangular epeiric basin joining the Boreal Ocean through a narrow northern seaway. The Tethyan Ocean forms the base at palaeolatitude 30°-35°N, with eastern Greenland (and America) and Scandinavia forming the other two sides. North-trending grabens and numerous islands define several subbasins. The net current flowed southward (the evidence ranges from ammonite distribution to southward-decreasing uranium concentrations) but was constricted by the narrow seaway. The Coriolis force probably diverted this flow southwestward, with only a sluggish flow southeastward over Britain and the North Sea basin. Evaporative brines (cf. Red Sea surface water, 21°C and 41 ^pmil salinity) formed in arid, shallow, southern embayments to sink and fi l the grabens, progressively moving northward and creating a stable stratified water column. Organic productivity was not high but preservation was exceptionally efficient. Organic preservation ceased suddenly and synchronously following oxygenation of the bottom water. This could have been achieved simply by reducing the temperature of the Boreal current. The resulting water inversion would be rapid and basinwide.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.