Geology and Hydrocarbon Potential, United Kingdom Sector, Western Approaches Basin: ABSTRACT

Abstract

The Western Approaches basin covers an area of approximately 20,000 mi2 (52,000 km2) and lies along the median line between the British and French sectors of the northwest European continental shelf. About 40% of the basin lies within United Kingdom designated waters. Seismic coverage of this area is extensive, but only four deep holes have been drilled. The basin was initiated toward the end of the Carboniferous and then underwent rapid fault-controlled subsidence, accumulating a thick succession of Permo-Triassic red beds and evaporites. Marine conditions became widely established during the Rhaetic and Early Jurassic but block faulting and uplift then led to widespread erosion, with the result that Jurassic and Lower Cretaceous sediments are now largely confined to the deeper parts of the basin. These vertical crustal movements were the result of Atlantic rifting and appear to have been accompanied by strike-slip faulting and localized volcanism. A marine transgression tentatively dated as Barremian/Aptian marked the end of rifting activity and is visible on seismic records as a conspicuous angular unconformity. The basin then unde went gradual subsidence throughout the Late Cretaceous and early Tertiary until Alpine compressional movements led to further uplift and erosion. Several different structural trapping mechanisms have been identified and potential reservoirs exist in the Permo-Triassic and Jurassic to Lower Cretaceous intervals. Rhaetic and Lower Jurassic claystones have source potential, and maturation studies, though not conclusive, suggest that locally they will be mature for hydrocarbon generation. The timing of migration and the effectiveness of seals remain speculative due to lack of stratigraphic information. End_of_Article - Last_Page 615------------