Late Quaternary climatic events and sea-level changes recorded by turbidite activity, Dakar Canyon, NW Africa

Abstract

The relationship of sea-level changes and short-term climatic changes with turbidite deposition is poorly documented, although the mechanisms of gravity-driven sediment transport in submarine canyons during sea-level changes have been reported from many regions. This study focuses on the activity of the Dakar Canyon off southern Senegal in response to major glacial/interglacial sea-level shifts and variability in the NW-African continental climate. The sedimentary record from the canyon allows us to determine the timing of turbidite events and on the basis of XRF-scanning element data, we have identified the climate signal at a sub-millennial time scale from the surrounding hemipelagic sediments. Over the late Quaternary the highest frequency in turbidite activity in the Dakar Canyon is confined to major climatic terminations when remobilisation of sediments from the shelf was triggered by the eustatic sea-level rise. However, episodic turbidite events coincide with the timing of Heinrich events in the North Atlantic. During these times continental climate has changed rapidly, with evidence for higher dust supply over NW Africa which has fed turbidity currents. Increased aridity and enhanced wind strength in the southern Saharan–Sahelian zone may have provided a source for this dust.

Sediment transport and turbidite architecture in the submarine Dakar Canyon off Senegal, NW-Africa

“…Concurrently, a shelf record displayed distinct dust events during the last 5000 years, suggesting that during several short-lasting drought periods extraordinary increases in dust accumulation in the tributaries of the canyon provided the main trigger for these recurrent turbidites . Similar climate driven turbidite activity during the last 240 kyr is also observed in the Dakar Canyon (Pierau et al, 2010). An initial correlation of turbidite events in the Dakar Canyon and in the Timiris Canyon offshore the hyperarid Sahara showed that both canyons consistently revealed highest turbidite frequencies during late glacial to deglacial times and during Heinrich events.…”

“…2A). Additionally, core GeoB 9612-3, taken from the northern levee, serves as stratigraphic reference section and monitors shifts in hemipelagic background sedimentation (Pierau et al, 2010). Detailed structural and textural analyses of the turbidite sequences were determined using X-ray radiographies, taken from sediment slides of 1 cm thickness.…”

“…3). According to the analyses of the X-ray radiographs, these turbidites shows no erosional features and are interpreted as spill-over turbidites (Pierau et al, 2010). The GSD of the bulk hemipelagic sediment of core GeoB 9612-3 is dominated by the silt and clay fraction (Fig.…”

“…The age model of core GeoB 9612-3 and the correlation of GeoB 9614-1 and GeoB 9615-1 is presented in Pierau et al (2010) and only briefly summarised here. First, all turbidite deposits were cut out of the sections to remain a continuous hemipelagic sediment record (Fig.…”

“…The stratigraphic concept of Cores 9612-3, 9614-1 and 9615-1 is based on the correlation by their characteristic total reflectance pattern (Pierau et al, 2010). The sedimentary record of Core 9612-3 covers the past 240 kyr BP (Fig.…”