Newly-observed post-Variscan extensional mini-basins: The key to the prospectivity of the under-explored platform areas

Thick Paleozoic successions are buried under the underexplored platform areas flanking the main North Sea depocentres. Here, we focus on the tectono-stratigraphy and prospectivity of the East Shetland Platform and Norwegian-Danish Basin, on the U.K. and Norwegian-Danish Continental Shelf respectively. These areas have been extensively covered with 3D broadband dual-sensor towed streamer (GeoStreamer®) seismic surveys, enabling improved imaging and play understanding. Although differences are apparent between the study areas (e.g., Zechstein salt thickness and mobility), they all underwent a similar post-Iapetus poly-phase tectonic evolution, and consist of alternations between Paleozoic highs with long-lasting hiatuses and post-Variscan intra-platform basins, with a near-complete succession and maximum sedimentary thickness of 5-7 seconds two-way-time. Numerous high effective porosity reservoir units are highlighted (including Devonian-Permian sandstones), and large Paleozoic structural traps are potentially present below intra-platform basins. Hydrocarbon charge occurs via lateral migration from Jurassic kitchens and/or vertical/lateral migration from deeper Devono-Carboniferous source intervals. Evidence of active hydrocarbon generation are present at even c. 100 km from the closest Jurassic source kitchen (e.g., seeps, pipes, shallow gas). This study argues that post-Variscan intra-platform basins play a crucial and often under-appreciated role in North Sea platform prospectivity, potentially enabling both Paleozoic source maturation and pre-Cretaceous trapping.