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