Abstract: Post-Jurassic Deformation of the Brae Area, South Viking Graben, UK

Branch J. Russell, Thomas A. Mazza, Kevin J. Dale

The Brae area (U.K. Blocks 16/3,16/7 and 16/8) lies roughly 75 km north of the Moray Firth basin/ Central Graben/ South Viking Graben intersection in the UK North Sea. 3-D seismic analysis reveals multiple phases of oblique contraction, thermal subsidence, and sediment compaction influenced post-Jurassic deformation of the Brae area. Kinematic analysis of Early Cretaceous contraction is the focus of this paper.

The Brae fields are located in Upper Jurassic sediments in hangingwall anticlines. Structural reconstructions and decompaction models indicate that mild Early Cretaceous contraction of the Brae area took place principally above reactivated NE-trending normal faults and NW-trending lateral ramps. The present structural closure of the Brae fields developed principally during Early Cretaceous contraction.

Additional contraction in the Brae area occurred during the late Paleocene-early Eocene. This deformation was restricted to the South Viking Graben/Fladen Ground Spur contact, along adjacent intragraben basement highs, and to the west. The western boundary fault zone, reactivated during Early Cretaceous contraction, was abandoned during the Paleocene in favor of lower-angle east-dipping footwall short-cut faults through the Fladen Ground Spur, which emerge further west.

Pre-Cretaceous structure, both Jurassic and Paleozoic, strongly influenced post-Jurassic contractional fabric development. Structural development was also affected by partial decoupling of Upper Jurassic and younger strata from Middle Jurassic and older strata along Callovian to Volgian shales.

Interpretation and integration of regional 2-D seismic lines in the South Viking Graben with the local 3-D data indicate that post-Jurassic contraction was not restricted to the Brae area.

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