WITHJACK, M. O., Mobil Technology Company, Dallas,TX, and INGEBRIGTSEN, M., Mobil Exploration Norway, Inc., Stavanger, Norway

Abstract: Basement-Involved and Detached Extensional Structures: Examples from the Norwegian Sea

We have used regional and 3D seismic data, well data, and the results of scaled physical models to define the structural history of the Norwegian Sea. Our work suggests that two factors profoundly influenced the structural development and hydrocarbon potential of the area: the magnitude of crustal extension during the Early Cretaceous and the absence/presence of an Upper Triassic evaporitic package.

Rifting occurred throughout the Voring Basin, Halten Terrace, and Trondelag Platform during the Early Cretaceous. In the Voring Basin, the magnitude of extension was large. Massive, tilted fault blocks formed within the continental crust, and the crust thinned and subsided substantially.

In the Halten Terrace and Trondelag Platform, the magnitude of extension was less. Highangle, west-dipping normal faults developed within the continental crust and the overlying Paleozoic and Mesozoic strata. Deformation styles differed above an Upper Triassic package composed of interbedded salt and clastic sedimentary rocks.This shallow deformation, distributed in zones up to ten kilometers wide, included broad monoclines above deep-seated normal faults (i.e., extensional forced folds) and detached horsts, grabens, and tilted fault blocks near the footwall hinges of the monoclines. The detached normal faults flattened within the evaporitic package. Generally, the evaporitic package is thin above the footwalls of the deepseated normal faults and thick beneath the footwalls of the detached normal faults. Deformation patterns in the Halten Terrace and Trondelag Platform closely resemble those in scaled physical models with one or two ductile layers.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England