ABSTRACT

Spectacular coastal cliff exposures in an early Cretaceous deltaic succession near Kvalvågen in eastern Spitsbergen, Norwegian Arctic, show a variety of styles of gravity-driven deformation and resedimentation associated with delta-front progradation and instability. The large-scale collapse involved a distributary-channel sand unit, some 20 m thick, and the underlying delta slope/prodelta shaly heterolithics. The deformation was essentially brittle, whereby large blocks of the delta-front succession slid and rotated. Its gross style involved two large cuspate tear-away scars, at least 1-1.5 km wide and 50-60 m deep, separated by narrow remnant buttresses of in-situ strata. The basement in the region was tectonically active, and the delta-front failure was most likely seismically triggered.

Initial infill of the collapse scars involved slumps and debris-flows, derived from scar walls and, locally, from the sliding blocks themselves. These deposits partly smoothed the local topography created by the slide blocks. This early infill was followed by deposition of thin, mainly muddy turbidites, probably shed from the scar walls by small localized failure. Renewal of fluvial supply of sand led to the main infill of the scar depressions. This stage involved effluent-generated turbidites (heterolithic), and increasingly sandier turbidites and liquefied sandflows derived from unstable, oversteepened distributary mouthbars. The mouth-bar systems eventually achieved stability and prograded across the infilled scars. They were affected by periodic storm-wave attack and sudden increases of water depth. The scar infill at that stage was subject to minor growth faulting, possibly related to new seismic tremors.

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