Differential subsidence driving the formation of mounded stratigraphy in deep-water sediments; Palaeocene, central North Sea

Deep-water Palaeocene strata of the East Central Graben, UK North Sea, are characterised by elongate depressions and elevations parallel with the palaeotransport direction and with underlying structural lineaments. Palaeozoic and mesozoic faults underlying the basin were briefly re-activated during the Palaeocene, affecting the seabed topography in the form of gentle folding, faulting and slope instability. Two types of mounded features formed in response to the tectonically induced seabed structuration: (i) deformational mounded morphology, a product of syndepositional faulting and mass wasting, (ii) non-deformational mounded morphology, interpreted to result from changing flow dynamics as flows travelled over the deformed sea floor, accentuating the structural topography by means of localised erosion and deposition. This study shows how differential subsidence acted as the ultimate control behind a range of processes leading to mounded stratigraphy. The models of the origin of the mounded morphologies are novel in the context of the North-Sea Palaeocene and have implications for the prediction of lithology in mounded basinal deposits, in the North Sea and elsewhere.