Early Tertiary structural inversion in the Stord Basin, Norwegian North Sea

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Abstract
The Stord Basin is an east-sloping extensional basin that lies to the east of the Viking Graben in Norwegian waters of the northern North Sea. The basin formed by extension with normal faulting beginning in Triassic time and continuing episodically into the Middle and Late Jurassic. Seismic reflection profiles show that the normal faults which affect the sedimentary section are steeply dipping and approximately planar. Some of these faults were reactivated in the early Tertiary. This reactivation reversed earlier-accumulated normal displacement and created relative structural highs out of previous structural lows. The most obvious evidence of fault reactivation and structural inversion is the presence of hanging-wall folds that parallel the strike of reactivated faults. The inverted structures of the Stord Basin are part of a widespread field of early Tertiary inverted structures in north-west Europe. We suggest that these structures formed in response to horizontal compression that resulted from the interaction of stress fields set up by Alpine continent-continent collision and the early opening history of the North Atlantic Ocean.