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Abstract: Sequence Stratigraphy and Quantitative Palynology: An Integrated Approach for the Recognition and Hierarchization of Time Significant Surfaces of the Brent Delta

Alain Lejay, Dominique Pourtoy, Francoise Vannier, Jean Gerard, Remi Eschard

The Brent Group is divided into informal lithostratigraphic Formations related to specific groups of environments first interpreted in the Brent field. Boundaries are diachronous, related to the migration of formations through time depending on regional relative accommodation space variations.

Integration of quantitative palynology and sequence stratigraphy allows to identify and hierarchize a number of regional isochronous surfaces and time intervals. Transgressive and Maximum Flooding Surfaces are identified from the sedimentological analysis of facies and succession of environments. Quantitative palynology identifies a number of palyno-events, mainly based on variations of abundances of palynomorphs and defines "time guides" at local/regional scales. The integration of both techniques as time indicators has been applied in the reconstruction of the Brent delta geometry in the Norwegian sector.

In the northern part of the Brent Delta, 5 reliable time intervals were regionally recognized. These are bounded by TS and MFS and constrained by at least 8 main palyno-events of regional/semi-regional significance. In the southern part, a number of 9 reliable time intervals were recognized, bounded by 4 main palyno-events.

The result is the definition of a chronostratigraphic scheme and the correlations at the regional scale for the whole Brent Group. The Brent Group is deposited during a complete large scale, regressive-transgressive cycle comprising Rannoch, Etive, Lower Ness (regressive part) and, Upper Ness Tarbert Formations (transgressive part). The Heather Formation, as prodelta offshore shales, belongs to both parts of the cycle. An initial basal transgressive wedge is recorded in the North-Eastern margin of the Viking Graben (the Oseberg fan-delta Formation).

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France