Abstract Along continental margins with rapid sedimentation, overpressure may build up in porous and compressible sediments. Large-scale release of such overpressure has major implications for fluid migration and slope stability. Here, we study if the widespread crater-mound-shaped structures in the subsurface along the mid-Norwegian continental margin are caused by overpressure that accumulated within high-compressibility oozes sealed by low-permeability glacial muds. We interpret 56 000 km 2 of 3D and 150 000 km 2 of 2D-cubed seismic data in the Norwegian Sea, combining horizon picking, well ties and seismic geomorphological analyses of the crater-mound landforms. Along the mid-Norwegian margin, the base of the glacially influenced sediments abruptly deepens to form 28 craters with typical depths of c. 100 m, areal extents of up to 5130 km 2 and volumes of up to 820 km 3 . Mounds are observed in the vicinity of the craters at several stratigraphic levels above the craters. We present a new model for the formation of the craters and mounds where the mounds consist of remobilized oozes evacuated from the craters. In our model, repeated and overpressure-driven sediment failure is interpreted to cause the crater-mound structures, as opposed to erosive megaslides. Seismic geomorphological analyses suggest that ooze remobilization occurred as an abrupt energetic and extrusive process. The results also suggest that rapidly deposited, low-permeability and low-porosity glacial sediments seal overpressure that originated from fluids being expelled from the underlying high-permeability and high-compressibility biosiliceous oozes.

Abstract The southern Tuaheni Landslide Complex (TLC) at the Hikurangi subduction margin displays distinctive morphological features along its distribution over the Tuaheni slope offshore Gisborne, New Zealand. We here present first analyses of a gravity core transect that systematically samples surficial sediments from the source area to the toe of this landslide complex, thus providing important new insight into shallow lithological variation in the slide complex. Geophysical and geochemical core logs and core descriptions form the basis for a characterization of representative sediment successions that are indicative of the respective slope segment of recovery. Our results show that the lithology of surficial sediments varies significantly along the length of the landslide complex. Depending on the slope segment observed, this variation includes post-Last Glacial Maximum (LGM) outer-shelf sediments, and hemipelagic drape and near-surface reworked debris avalanche deposits, as well as multiple intercalated thinner turbidites and tephra layers at the distal end of the profile. Lithological downslope variability suggests ongoing mass transport events through the late Holocene that were likely to have been limited to small mud-turbidite flows. Integration with acoustic sub-bottom imagery reveals the presence of multiple stacked mass-transport deposits at depth, contrasting with previous interpretations of a single parent failure.