Three-dimensional (3-D) seismic imaging of conduits and radial faults associated with hydrothermal vent complexes (Vøring Basin, Offshore Norway)

Here, we document a suite of radial faults associated with hydrothermal vent complexes in the Vøring Basin, offshore Norway. These complexes have pyramid-shaped, cylindrical- and conical-shaped conduits, with a dome-, or eye-shaped morphology at their summit, intruding on Paleogene sedimentary rocks. Hydrothermal vents are intimate with the tips of magmatic sills that were emplaced at depths ranging between 1800 and 5800 ms Two Way Travel Time (TWTT). At shallower depths of 1800 to 3000 ms TWTT and intermediate depths of 3000 to 5000 ms TWWT, magmatic sills regularly intersect the lower parts of the vent conduits, which are characterized here as pipes. An important parameter that is used to characterize the morphology of a hydrothermal vent conduit is the width of the conduit, which is defined as the longest axis marking the extent of the vents' conduit within the surrounding host-rock strata. Our findings reveal that radial faults are commonly associated with the summits of hydrothermal vents, implying the existence of local stress fields around the vents, where the maximum compressive stress is radial and minimum stress is circumferential, which overrides the regional stress field and indicate variable stress regimes as opposed to tectonic faults. Importantly, circumferential stretching due to catastrophic plumbing of hydrothermal fluids, differential compaction and intensive fracturing enabled the polygonal faults to realign in a radial pattern resulting in the formation of radial faults at the vent summit. As a corollary of this work, we hypothesize that pyramid-shaped hydrothermal conduits are possibly markers of protracted sill emplacement in sedimentary basins

Glacial, fluvial and contour-current-derived sedimentation along the northern North Sea margin through the Quaternary

The thick sequence of Quaternary sediments preserved within the northern North Sea contains important information about the glacial history, palaeo-oceanographic conditions and slope stability of this region during the last 2.6 million years. The interplay between glacial, fluvial and contouritic processes can be determined from seismic stratigraphic studies. Here, seismic horizon, attribute and geomorphological interpretations of an extensive 2D seismic dataset (∼100,000 km2) and two 3D seismic cubes (∼18,400 km2) are integrated with lithological data from eight exploration wells to map sandy sedimentary units. Mapping of seismic horizons and facies reveals that, in addition to prograding glacial sediments derived from the Norwegian mainland, the Quaternary succession includes wedge-shaped units with prograding internal clinoforms building out from the East Shetland Platform, relatively flat-lying units of acoustically stratified sediments within the central northern North Sea, and aggrading to prograding units with low-amplitude internal reflections on the continental slope. The lowermost unit of Quaternary sediment is interpreted as an ∼800 km3 earliest Pleistocene (∼2.6 Ma) turbidite-contourite deposit, in which turbidites derived from a fluvial delta building out from the East Shetland Platform transition seaward into aggrading to prograding sediments of the Shetland Drift. The wedge-shaped units are intercalated with glacigenic sediments in the central northern North Sea, showing that the East Shetland Platform was a major source area for the delivery of coarse-grained sediments during the Early Pleistocene (∼2.6–0.8 Ma). The distribution of units of aggrading to prograding geometries suggests that contourites continued to develop on the continental slope, including on the North Sea trough-mouth fan, throughout the Quaternary. These interpretations constrain a new model for the Quaternary evolution of the northern North Sea that reconciles the development of the eastern and western sides of this margin, and shows the importance of fluvial-deltaic and contouritic sedimentation during periods of reduced glacigenic sediment input. Our model also provides a high-resolution analogue for the sedimentary architectures and seismic facies that can be produced by the interplay of down-slope and along-slope processes on other continental margins

Glacial seismic geomorphology and Plio-Pleistocene ice sheet history offshore NW Europe

Plio-Pleistocene records of ice-rafted detritus suggest northwest European ice sheets regularly reached coastlines. However, these records provide limited insight on the frequency, extent, and dynamics of ice sheets delivering the detritus. Three-dimensional reflection seismic data of the northwest European glaciated margin have previously documented buried landforms that inform us on these uncertainties. This paper reviews and combines these existing records with new seismic geomorphological observations to catalogue landform occurrence along the European glaciated margin and considers how they relate to ice sheet history. The compilation shows Early Pleistocene ice sheets regularly advanced across the continental shelves. Early Pleistocene sea level reconstructions demonstrate lower magnitude fluctuations compared to the Middle-Late Pleistocene, and more extensive/frequent Early Pleistocene glaciation provides a possible mismatch with sea level reconstructions. This evidence is discussed with global records of glaciation to consider possible impacts on our wider understanding of Plio-Pleistocene climate changes, in particular how well Early Pleistocene sea level records capture ice sheet volume changes. Resolving such issues relies on how well landforms are dated, whether they can be correlated with other proxy datasets, and how accurately these proxies reconstruct the magnitudes of past climatic changes. Many questions about Pleistocene glaciation in Europe and elsewhere remain.<br/