The early-mid Quaternary development of the Bjørnøyrenna Trough Mouth Fan reconstructed from 3D-seismic data

Abstract

The early-mid Quaternary development of the Bjørnøyrenna Trough Mouth Fan is studied using 3D seismic data. The stratigraphy is divided into three seismic units; unit A (oldest) to C and is correlated to previously established stratigraphic frameworks in the Barents Sea. The reflection configuration and the geometry of the units, in combination with geophysical attribute analysis form the basis for reconstructing the early development of the Bjørnøyrenna Trough Mouth Fan and the impact alongslope and downslope sedimentation have on the fan evolution.

The early stages of Quaternary development of the margin is characterized by downslope mass movements such as slides, debris flows and turbidity currents (unit A). These deposits are related to the intensification of the Northern Hemisphere glaciations, and they were most likely sourced from grounded glaciers reaching the shelf break. Proglacial sediments deposited here were remobilized downslope, resulting in the development of a thick sediment fan along the western margin prograding in a southwestern direction, into the deep sea.

The seismic facies and external form at the lower part of unit B and C are interpreted to represent buried contourite drifts. The drifts began accumulating on the lower slope and they were most likely initiated by north-flowing alongslope currents similar to the present day West Spitsbergen Current. The drifts suggest a change in depositional environment from the underlying units, with limited influence from glacial processes which allowed for alongslope sedimentation to dominate. Both of the drifts (unit B and C) were later buried by downslope mass movements such as debris flows during a glaciomarine environment caused by re-advancement of ice-sheets. The depocenters within unit A to C are migrating from southwest (unit A) to northwest (unit C) in the study area, and these changes in margin build-out direction are most likely related to varying input from the Svalbard-Barents Sea Ice-sheet and the Fennoscandian Ice-Sheet during margin progradation.

This study shows alternating alongslope accumulating contourites building up the continental slope and downslope accumulating deposits from debris flows building out the slope (i.e. margin progradation). Combined, this show that both alongslope and downslope sedimentation play an important role in the evolution of glaciated margins, and it is critical to carefully map out and understand both of these main margin-building processes when reconstructing margin development and doing source to sink studies.