Evolution of a high-latitude sediment drift inside a glacially-carved trough based on high-resolution seismic stratigraphy (Kveithola, NW Barents Sea)
Monday, 14 December 2015
Poster Hall (Moscone South)
Kveithola is a glacially-carved, E-W trending trough located in the NW Barents Sea. A set of confined sediment drifts (the “Kveithola Drift”) is located in the inner part of the trough. We provide for the first time a detailed morphological, seismostratigraphic, lithological and sedimentological insight into this sediment drift. The PARASOUND data show that the drift is mainly well-stratified, characterized by sub-parallel reflections of moderate to high amplitude and good lateral continuity. The reflectors show an abrupt pinch-out on the northern edge where a distinct moat is present, and a gradual tapering to the south. Internally we identify the base of the drift and four internal horizons, which we correlate throughout the drift. Two units display high amplitude reflectors, marked lensoidal character and restricted lateral extent, suggesting a relatively larger contribution of gravity processes to the drift growth. Facies typical for contourite deposition are found in the sediment cores, with strongly bioturbated sediments and abundant silty/sandy mottles that contain shell fragments. These characteristics suggest a strong control by a bottom current flowing along the moat on the northern edge of the drift. Brine-enriched shelf water (BSW) produced during winter and flowing westward in the moat, is suggested to be responsible for the genesis of the Kveithola Drift. The formation of BSW is inferred to have started around 13 cal. ka BP, the onset of drift deposition, suggesting that conditions leading to atmospheric cooling of the surface waters and/or the presence of coastal polynyas and wind have persisted on the western Barents Shelf since that time. The units which formed under a larger influence of gravity processes (dated to the Younger Dryas and to 8.9-8.2 cal ka BP) indicate that bottom current activity was reduced during these two climatically colder periods, possibly due to expanded grounded and sea ice cover over the Barents Sea.