Paleocene deep-marine sandstone plays in the Siri Canyon, offshore Denmark–southern Norway

Abstract

The Paleocene Siri Canyon extends for more than 120 km from the Stavanger Platform to the Tail End Graben along the Danish–Norwegian North Sea boundary. Initial formation of the canyon system took place in the Early Paleocene (Danian) and was related to major, submarine sliding in the uppermost chalk section caused by uplift of the Scandinavian hinterlands. The trend of the canyon partly follows salt structures along the southern edge of the Norwegian–Danish Basin (part of the Northern Zechstein Basin). The canyon fill consists of deep-marine, highly glauconitic sandstones interbedded with hemipelagic and turbidite marls and mudstones. As for many Paleocene deep-marine sandstones in the North Sea, the sandstones of the Siri Canyon are massive and blocky. Frequent occurrence of injected sandstone sills/dykes, injection breccias, as well as erosion and associated rip-down clasts along the upper boundaries of in situ sandstones, indicate thorough, post-depositional modification. Fluidization is, thus, likely to be the main reason for the general scarcity of primary sedimentary structures and massive appearance of the sandstones. All sandstones are basically free of detrital clays and most likely formed from non-cohesive, concentrated density flows probably developed as turbidity currents. The sand flows were confined by the canyon and the depositional pattern indicates a complex interaction of turbidity currents, salt-induced seafloor topography and differential compaction. Release of sandy flows was probably caused by seismic shocks resulting in a collapse of unstable shelf sands concentrated on the Stavanger Platform. Transport distances of the sands were up to 120 km and thereby contrast with many Paleocene submarine sandstones in the North Sea. The deep-marine play in the Siri Canyon relies on long distance migration of hydrocarbons, up to 75 km from mature Jurassic source rocks in the Central Graben. This was facilitated by the elongate and confined geometry of the sandstones forming a well-connected system for updip migration.