Controls on the Lower Cretaceous Carbonate Habitats of the South Porcupine and Goban Spur Basins, Offshore Ireland

摘要

Exploration drilling together with 2D seismic data suggests the presence of an extensive Lower Cretaceous carbonate depositional province in the South Porcupine and Goban Spur Basins, offshore southwest of Ireland. Interpreted environments of deposition range from large scale carbonate shelf development through platform margin to isolated offshore carbonate build-ups. During the Late Jurassic to Early Cretaceous period, these basins underwent a phase of normal detachment faulting and regional subsidence associated with high degrees of lithospheric extension. This phase of tectonic activity is interpreted to have exerted a primary regional control on carbonate development in two ways: rapid development of accomodation space limited the influence of clastic sediment input in basin margin depocentres; and the rotated, up-standing footwall crests of normal fault blocks provided intra-basinal bathymetric shoals for carbonate colonisation. Locally, both eustatic and isostatic changes are interpreted to have controlled carbonate deposition, providing a linkage from macro-scale stress fields to micro-scale reservoir architecture. Trophic conditions such as paleo-latitude, ocean circulation and wind direction appear to have exerted a secondary influence on carbonate development. These Lower Cretaceous carbonate sequences can be correlated with world class petroleum reservoirs which span the northern hemisphere from the Middle East to the Gulf of Mexico. Such carbonate systems could form the basis of an important paradigm shift away from the traditional Mesozoic clastic-dominated play systems of the Atlantic Margin in the future exploration of these emerging frontier deepwater basins.