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ABSTRACT: Cenozoic Stratigraphic Evolution, North Sea and Labrador Sea

F. M. Gradstein, W. A. Berggren, M. A. Kaminski, M. A. D'Lorio, A. C. Grant, S. Cloetingh, B. S. Mudford, C. M. Griffiths

We are studying Cenozoic correlation patterns, burial trends, and subsidence history of the Central North Sea, Labrador, and Orphan basins. Our objectives are (1) to detail intraregional mid-high latitude biozonations using noise filtering and probabilistic zonation techniques; (2) to detail paleobathymetric trends from basin margins to centers; (3) to apply this knowledge to model basin evolution, in the perspective of the evolving North Atlantic Ocean; (4) to evaluate causes for the occurrence of major hiatuses and rapid changes of subsidence; and (5) to relate rapid changes in sedimentation in the last few millions of years to model observed undercompaction trends.

Cenozoic microfossil assemblages in these basins are similar, related to similarities in sedimentary and paleoeceanographic conditions. In more basinal wells, flysch-type agglutinated foraminiferal assemblages occur, also known from Carpathians, Trinidad, and Moroccan foredeeps. Over 90% of agglutinated taxa are common between these basins, although local stratigraphic ranges vary sufficiently to rely on the concept of average ranges, rather than total ones for correlations. Cenozoic stratigraphic resolution in the North Sea and Labrador basins generally is in 3-5-Ma units, and paleobathymetric zonations define a minimum of five niches, from inner shelf to middle slope regimes. Significant hiatuses occurred in the late Eocene through the Miocene, particularly in northern Labrador and orthern North Sea.

Subsidence in the Labrador/Grand Banks passive margin half grabens was strongly influenced by Labrador Sea opening between anomalies 34 (Campanian) and 13 (early Oligocene), when subsidence exceeded sedimentation and bathyal conditions prevailed along the margin. Thermally induced subsidence in the central North Sea grabens was considerable in the late Paleocene, when the Norwegian Sea started to open. In both basins, a significant departure from the overall thermally driven subsidence is observed in the middle Miocene through Quaternary, when basinward sites experienced up to four times larger subsidence than basin edges. In fact, the latter experienced considerable uplift that may have escalated glaciation. Intraplate stress changes contributed to these tectonic trends.

A one-dimensional model of fluid pressure evolution indicates that the rapid North Sea Neogene shale sedimentation has led to compaction-driven overpressuring of a similar magnitude to that observed. Ice-induced loading may accentuate pressure trends, but its magnitude is subject to speculation.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990