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Amoco Exploration and Production Company, P.O. Box 3092, Houston, TX 77253, USA
An integrated late Cretaceous calcareous microfossil framework for the southern Norwegian chalks is presented based on detailed study of 13 wells (many with core) and circum-North Sea outcrops, in addition to many cosmopolitan events recognized in reference sections in Tunisia, North America and Europe. Previous biozonations for the North Sea chalks: (1) lack the biostratigraphic resolution needed in production geology; (2) are largely founded on benthic foraminifera and acme events; (3) fail to recognize numerous stratigraphic discontinuities within the North Sea chalks; and (4) are poorly calibrated. Application of this new integrated framework cautions towards the use of certain acme and benthic foraminifera events as chronostratigraphic horizons both within the basin and from the basin into circum-North Sea outcrops. An additional complicating factor is palaeogeographic segregation between low and high latitudes, which intensified during the middle Campanian and became problematic within the North Sea basin itself during the late Maastrichtian. A final consideration is redeposition, which can lead to erroneous correlations between wells, but may also affect reservoir quality. Established North Sea biozonations have not recognized this primary palaeoenvironmental signal and massive redeposition across major lithostratigraphic units, which has resulted in the correlation of diachronous facies rather than isochronous horizons. This could lead to complications in operational applications, such as biosteering.
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  E.V. ESMERODE, H. LYKKE-ANDERSEN, and F. SURLYK Interaction between bottom currents and slope failure in the Late Cretaceous of the southern Danish Central Graben, North Sea Journal of the Geological Society, 2008; 165: 55 - 72. [Abstract] [Full Text] [PDF]
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