Late Quaternary contourites and glaciomarine sedimentation in the Fram Strait

Abstract

Two sites in the eastern Fram Strait, the Vestnesa Ridge and the Yermak Plateau, have been surveyed and sampled providing a depositional record over the last glacial‐interglacial cycle. The Fram Strait is the only deep‐water connection from the Arctic Ocean to the North Atlantic and contains a marine sediment record of both high latitude thermohaline flow and ice sheet interaction. On the Vestnesa Ridge, the western Svalbard margin, a sediment drift was identified in 1226 m of water. Gravity and multicores from the crest of the drift recovered turbidites and contourites. 14C dating indicates an age range of 8287 to 26 900 years BP (Early Holocene to Late Weichselian). The Yermak Plateau is characterized by slope sediments in 961 m of water. Gravity and multicores recovered contourites and hemipelagites. 14C ages were between 8615 and 46 437 years BP (Early Holocene to mid‐Weichselian). Downcore dinoflagellate cyst analyses from both sites provide a record of changing surface water conditions since the mid‐Weichselian, suggesting variable sea ice extent, productivity and polynyas present even during the Last Glacial Maximum. Four layers of ice‐rafted debris were also identified and correlated within the cores. These events occurred ca at 9, 24 to 25, 26 to 27 and 43 ka, asynchronous with Heinrich layers in the wider north‐east Atlantic and here interpreted as reflecting instability in the Svalbard/Barents Ice sheet and the northward advection of warm Atlantic water during the Late Weichselian. The activity of the ancestral West Spitsbergen Current is interpreted using mean sortable silt records from the cores. On the Vestnesa Ridge drift the modern mass accumulation rate, calculated using excess 210Pb, is 0·076 g cm−2 year−1. On the Yermak Plateau slope the modern mass accumulation rate is 0·053 g cm−2 year−1.

Gas hydrate and free gas detection using seismic quality factor estimates from high-resolution P-cable 3D seismic data

“…Major factors that play a crucial role are lithology, fluid type, and structural features (Walsh, 1966;Johnston et al, 1979;Toksöz et al, 1979;Winkler et al, 1979;Spencer, 1979;Toksöz and Johnston, 1981;Winkler and Nur, 1982;Murphy et al, 1986;Pointer et al, 2000;Parra et al, 2002;Prasad and Nur, 2003;Behura, 2009). The exact details of the sedimentary environment of the study area are not well known, but it is believed to be composed of smoothly deposited layers of contourite deposits (Eiken and Hinz, 1993;Howe et al, 2008). Under such geologic settings, the major factors that can prominently change the intrinsic attenuation property of a medium are changes in fluid type and fluid saturation.…”

“…The contourite drift is in close proximity to the Molloy and the Knipovich slow-spreading oceanic ridges, and it is located between the Molloy and the Spitsbergen transform faults (e.g., Ritzmann et al, 2004). The Vestnesa Ridge consists of three main stratigraphic sequences named according to their correlation with ocean drilling program sites at the Yermak Plateau (YP) (Eiken and Hinz, 1993): The oldest unit (YP1) is of Miocene age and consists dominantly of syn-rift deposits directly lying over the oceanic crust (Eiken and Hinz, 1993;Ritzmann et al, 2004); the middle sequence (YP2) consists of sediments deposited by migrating contour currents; and, finally, the youngest sequence (YP3), is dominated by margin-parallel contour currents and by glacigenic debris flow deposits (Howe et al, 2008).…”

The Kongsfjorden Channel System offshore NW Svalbard: downslope sedimentary processes in a contour-current-dominated setting

“…b Regional setting of the study area. SBF Sjubrebanken Fan Contourite-drift deposition dominated the overall sedimentary environment in the eastern Fram Strait since at least 11 Ma and numerous sediment drifts have been identified on the continental slope off western Svalbard, mainly at water depths exceeding 1200 m [7,21,23,24,41,57,61]. However, multiple escarpments north of the study area provide evidence of repeated downslope sediment transport ( [10,50]).…”

“…It is composed of a more than 2-kmthick sediment sequence mainly dominated by contourite drifts (e.g. [7,23]). However, the upper part of the sediment column on the eastern Vestnesa Ridge is composed of prograding sequences reflecting enhanced sediment supply from Svalbard during glaciations [7].…”

“…Contourite drifts along the margins and within the adjacent deep sea suggest that bottom currents flowing parallel to the slopes can dominate the long-term sedimentation at local to regional scales (e.g. [7,21,23,33,36,56,57]). However, gullies, channels and canyons provide evidence of repeated and focused downslope processes leading to erosion and slope incision over time.…”