Late Cenozoic evolution of the upper Bjørnøya Fan, western Barents Sea margin: A seismic sequence stratigraphic analysis

Abstract

The Bjørnøya Fan is located at the SW Barents Sea continental margin and consists of a succession of glaciomarine sediments up to 3.5-4 km in thickness. The evolution of the Bjørnøya Fan is closely related to the history of the Plio-Pleistocene northern hemisphere glaciations. In the present master thesis, the seismic stratigraphy of the Bjørnøya Fan was divided into three major glaciomarine units (GI-GIII), seven megasequences (MS1- MS7) and 28 sequences (S1- S28). Relative chronology of the identified seismic sequences was done and their approximate ages constrained, based on published ages of the seven megasequences. The seismic sequences are repeated through the whole Bjørnøya Fan. Each seismic sequence may hypothetically represent one glacial cycle. One individual glacial cycle is interpreted to be related to the advance of a glacier ice sheet to the continental shelf edge, followed by retreat, glacioeustatic sea level rise and deposition of interglacial mud or clay, before the next advance of glacial ice sheet of the new glaciation. Variations in depositional processes resulted in shifts in depocenters through time. These changes reflect the evolution of the glaciomarine depositional environment in time and space. Within the Bjørnøya Fan, three stages of development can be marked, correlated to the three glaciomarine units GI-III. The three units represent three stages influenced by the northern hemisphere glaciations and their effect on the development of the SW Barents Sea continental shelf. The first stage is correlated to the initiation of glaciations in the Barents Sea continental shelf and represents a transition from pre-glacial to glacigenic sedimentation. The second stage, initiated at ~ 1.5 Ma ago, is characterized by distinct prograding clinoforms that are correlated to the onset of repeated major ice sheet expansion to the shelf edge. In the third stage, depositional conditions changed to be characterized by glacigenic debris flows that were sourced from a common and homogenous part of the upper part of the Bjønøya Fan. The Bjørnøya Fan appears to have been repeatedly affected by altogether 28 glacial events, some of which may represent stadials, represented by the 28 seismic sequences. It seems that the glacial history at several sites of the NE Atlantic margin is similar, revealing successions of about 30 possible glacial sequences or depositional units, representing glacial IV cycles. The maximum number of glacial cycles can vary from place to place due to a number of factors, such as geological setting that influenced the effect of glaciations and preservation potential of glacigenic deposits on the continental shelf basins. In the present study the correlation between Iceland, the Mid-Norwegian continental shelf and the SW Barents Sea continental shelves were examined.