ABSTRACT: Structural and Stratigraphic Evolution of the Celtic Sea Basins, Offshore Ireland

ROWELL, PHILIP, University of Texas at Austin, Austin, TX

The Celtic Sea basins developed as a series of discrete multirift stage intracratonic basins near the western margin of the European plate within the tectonic framework of Pangea breakup and the staged opening of the North Atlantic.

The Caledonian and Variscan orogenies each imprinted unique structural grains on the area and the intersecting pattern of these tectonic lineaments provided the structural framework for the subsequent rifting phases in the Triassic, Late Jurassic, and Early Cretaceous. The northeasterly oriented Caledonian structural trend dominates the overall orientation of the basins, but in detail the more easterly oriented Variscan overprint played a major role in differentiating the subbasins and their subsequent structural and stratigraphic evolution.

Detailed study within the largest basin in the area, the North Celtic Sea Basin, using an extensive well and seismic database, indicates that the mode of reactivation of pre-existing lines of structural weakness is dependent on the orientation of maximum tensional stress relative to these lineaments. The Triassic and Late Jurassic northeast-southwest tensional stress vector reactivated Caledonian lineaments as half-graben boundary faults and Variscan lineaments as transfer zones. Resultant fault geometries were thus relatively simple. On the other hand, the Early Cretaceous tensional stress vector was oriented more northeast-southwest oblique to the preferred directions of failure and the resulting fault patterns were much more complex. Subsequent right-lateral strike-slip deformation related to the Alpine orogeny reactivated both Caledonian and Variscan trends.

Synrift sediments form a significant part of the overall basin fill. The spatial distribution of depositional systems within these sediments is controlled by the underlying tectonic framework.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)