Abstract: The Sedimentary Respojse to Uplift and Rifting Prior to Oceanic Spreading in the North Atlantic

Neil A. McMahon

The Mesozoic basins of the North Atlantic display a unique and economically significant clastic sedimentation history during the pre-, syn- and post-rift phases of oceanic formation. However, the controls on the temporal and spatial distribution of clastic supply has remained poorly constrained. Application of sequence stratigraphy to onshore exposure from continental Europe and subsurface data from the Grand Banks and Celtic Sea basins has allowed correlation of regional unconformities and maximum flooding surfaces. Biostratigraphic analysis of well logs and onshore exposures has allowed the major maximum flooding surfaces to be used in the construction of detailed chronostratigraphic diagrams which serve as a template for studying the Callovian to Aptian evolution of these areas. Th correlations constrain the dimensions of major unconformities in each basin and enabled them to be separated from localized unconformities using a knowledge of the tectonic history interpreted from seismic data and displayed on accurate plate reconstructions. Relationships drawn between the position of rifting in the North Atlantic and areas of erosion may be integrated with palaeogeographic maps to demonstrate that four regional unconformities (base Oxfordian, Kimmeridgian-Tithonian, Early Berriasian and Early Barremian) are traceable in the Mesozoic basins. The latter three unconformities are associated with volcanic emplacement and significant clastic pulses ahead of, or offset from, the sea-floor-spreading axis. Therefore, multiple or large thermal uplifts may have preceded the acti e rift and prepared the lithosphere for ocean formation. A knowledge of the effects of such uplifts is likely to have importance in understanding clastic reservoir distribution.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994