Biostratigraphic Calibration and Sequence Stratigraphic Interpretation of the North Sea Upper Jurassic: Implications for the Spatial and Temporal Correlation of Clastic Reservoirs

Richard A.P. Hesketh, Dept. of Geology & Geophysics, The University of Edinburgh, Grant Institute, King's Buildings, West Mains Road, Edinburgh, EH9 3JW, United Kingdom, phone: 00 44 131 650 5917, fax: 00 44 131 668 3184, rhesketh@glg.ed.ac.uk and John R. Underhill, Department of Geology and Geophysics, The University of Edinburgh, Grant Institute, Kings Buildings, West Mains Road, Edinburgh, EH9 3JW, United Kingdom.

Sequence stratigraphic correlations within the highly prospective Upper Jurassic sequence of the North Sea are based primarily on biostratigraphic data derived from the study of palynological assemblages. Although these have classically been calibrated to the standard sub-Boreal ammonite zonation, the apparent discovery of anomalous ammonite and dinoflagellate cyst ("dinocyst") assemblages within the Outer Moray Firth (the western arm of the North Sea Rift System) has cast doubt upon the validity of this approach. The implications of these reported anomalies become most obvious when the conflicting biostratigraphic schemes are applied to lithostratigraphic sections from the existing offshore dataset. Palynological and ammonite-based datings conflict to such an extent that they provide correlations which are inaccurate to the tune of not just tens, but hundreds of feet. The aim of this paper is to report the results of an extensive study which integrates the macrofaunas and microfloras from well data (ditch cutting, core and sidewall core samples, as well as ammonites extracted from cored sections) with those derived from strategic field exposures. The resultant new ammonite-dinocyst correlations enable the construction of a robust biostratigraphic template for the Upper Jurassic succession in the North Sea. The integrated stratigraphic scheme provides the first unified and consistent tool for improved understanding of temporal and spatial controls on Upper Jurassic reservoirs in this part of the basin.

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