The Mesozoic evolution of the southern North Atlantic region and its relationship to basin development in the south Porcupine Basin, offshore Ireland

Abstract

Abstract The Mesozoic history of a number of Atlantic borderland sedimentary basins can be related to the early opening history of the southern North Atlantic Ocean. Regional tectonic controls such as plate motion vectors and the pre-existing tectonic grain had an important role in basin development and are expressed as local tectonostratigraphic events. The evolving palaeogeographies for the region are demonstrated in a series of maps based on computer-generated plate reconstructions. The Porcupine Basin, centrally located in the study area, lay close to the intersection of three plate boundaries that separated Eurasia from North America and controlled opening of the Bay of Biscay. The south Porcupine Basin, where there is relatively poor data control, is considered in the context of broader platetectonic controls, which were also responsible for the development of contiguous and better understood basins during Mesozoic time. This approach provides new insight into the structural evolution and likely facies development in the south Porcupine Basin, allowing broad inferences for petroleum prospectivity to be made. Initial Permo-Triassic fault-controlled extension led to continental deposition, which, if associated with aeolian and/or fluvial reservoir rocks, will mostly be too deep to be prospective. Thermal subsidence during Early Jurassic time was associated with flooding and fine-grained clastic deposition with anticipated moderate source rock potential. Regional uplift of the northern Porcupine area during Mid-Jurassic time forced shorelines and shelves southwards and the south Porcupine Basin could contain good reservoir quality sandstones and possible waxy deltaic-type source rocks of this age. In Late Jurassic time, major crustal extension took place with potential for reservoir and source rocks in locally expanded footwall successions. Further extensional faulting occurred in earliest Cretaceous (Neocomian) time with further synrift plays possible at this level. Growth of the Porcupine Median Volcanic Ridge is attributed to Barremian-Aptian time and related to continuing extension associated with a northwesterly arm of a triple junction positioned to the south of the Porcupine area. Strong subsidence of the basin centre during this time will have a significant impact on source rock maturation and flank trap geometries in the south Porcupine Basin.