Seismic architecture and sedimentation in northwest Spitsbergen fjords

Abstract

Acoustic records from several Spitsbergern fjords yield a characteristic sedimentary architecture. Subaqueous fans (1–3° surface slope), fed by tidewater glacier-derived sediments, are particularly well developed. An upper fan has been built on an underlying fan in response to a shift in the position of the tidewater glacier sediment source. The sequence of tidewater glacier fluctuations and sedimentation since the Late Weichselian, interpreted from seismic records, comprises the following: (1) Deposition of an acoustically transparent unit, interpreted as either basal till deposited during Late Weichselian glaciation or a glacimarine unit formed during early, rapid ice retreat. (2) Ice retreat up fjords by about 9000–10,000 yrs B.P. (3) Deposition of a lower fan complex over several thousand years, and slow infilling of bedrock-controlled basins in more ice distal locations. (4) Ice readvance to 2–3 km beyond modern ice margins, linked to Little Ice Age climatic deterioration from the 13–14th century. Overriding of part of the lower fan complex, inducing deformation. (5) Deposition of Little Ice Age submarine terminal moraines and basal till by readvancing glaciers. Deposition of the upper fan during 500 yr Little Ice Age ice advance. (6) Retreat of tidewater glacier termini to their present positions since Little Ice Age termination at the end of the 19th century. Deposition of a thin veneer of sediment inside the Little Ice Age submarine moraines as glacier retreat takes place.