Sarah J. Davies¹, Nancye H. Dawers², Aileen E. McLeod³, John R. Underhill³

(1) The University of Leicester, Leicester, United Kingdom
(2) Tulane University, New Orleans, LA
(3) The University of Edinburgh, Edinburgh, United Kingdom

ABSTRACT: Reassessing the Importance of Early Syn-Rift Extension for Facies Distribution and Stratal Architecture: Insights from the North Sea Hydrocarbon Province

This study addresses the complex relationship between extensional fault population evolution and patterns of early syn-rift sedimentation. We have used 3D seismic and well data to examine the early syn-rift Tarbert Formation along the Middle-Late Jurassic Brent-Statfjord fault array, in the northern North Sea basin. The Tarbert Formation is of variable thickness across our study area, and thickness variations define a number of 1-5 km wide depocentres bounded by normal faults. Divergent reflections indicate that the faults were active during deposition. Many of these faults became inactive during later Heather Formation times, whereas others remain active and later link, forming the Brent-Statfjord array. The preservation of the Tarbert Formation in footwall and hangingwall locations demonstrates that, during the earliest syn-rift, the rate of deposition balanced the rate of fault-controlled subsidence. Local space generated by hangingwall subsidence was superimposed upon accommodation generated by a sea-level rise. In early Tarbert Formation times, transgression across the pre-rift coastal plain produced lagoons and bays, which became increasingly marine. In part of our study area, shallow marine sediments are erosionally truncated by fluvial deposition constrained by a fault growth monocline. We illustrate that stratal architecture and facies distribution of early sedimentation is strongly influenced by the active short-lived faults. Local depocentres adjacent to fault displacement maxima focussed channel stacking and allowed the aggradation of thick shoreface successions. These depocentres formed early in the rift phase are not necessarily related to Late Jurassic-Early Cretaceous depocentres developed along the major linked normal fault systems of the North Sea.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado