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Chemostratigraphy of Upper Cretaceous Chalk Sequences in Norwegian-Danish Basin and North Sea Central Trough

Niels Oluf Jorgensen

Geochemical studies of subsurface sections and outcrops in the Upper Cretaceous chalk sequences from the Norwegian-Danish basin and the North Sea Central Trough have resulted in a detailed chemostratigraphy for these strata. The most applicable chemostratigraphic markers are based on the distribution of strontium, magnesium, manganese, the 13C/12C ratio, and the variations in the carbonate contents. It is demonstrated that the chemostratigraphic approach is valid at two levels: (1) a superior chemostratigraphy in which deep-sea cores from the Atlantic Ocean and sections from western Europe are correlated on the basis of significant geochemical anomalies and long-term variations most likely induced by oceanic geochemical cycles and sea level fluctuati ns; (2) a subordinate but detailed intrabasinal chemostratigraphic correlation which primarily reflects the physicochemical conditions in the depositional environment.

The Upper Cretaceous chemostratigraphy established in the Danish area allows a detailed correlation between relatively continuous chalk sequences in the Norwegian-Danish basin and the rather condensed and hiati-influenced sections in the oil fields of the North Sea. The results emphasize the applicability of chemostratigraphy in the subsurface exploration for hydrocarbon reservoirs in chalk.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.