June 2011

On Friday 17th June....

Chris Stevenson will present:

Title:
The flows that left no trace: investigating channelised large-volume turbidity currents that bypassed sediment without eroding the seafloor

Abstract:

Submarine channels are the main conduits for sediment transport in the ocean, from continental shelf to abyssal plain. Individual flow events can transport >100 km³ of sediment and deposit across vast areas of seafloor; these flows are therefore responsible for some of the largest sediment accumulations on Earth. Seafloor gradient exerts a major control on the ability of sediment flows to erode/bypass and transport sediment. In particular, recent work off Northwest Africa has highlighted the influence of seafloor gradient on turbidity currents passing through deep-water channels (e.g. Wynn et al., in press). We build upon these recent studies by utilizing a spatially extensive core correlation framework across the Madeira Distributary Channel System, offshore Northwest Africa. These shallow channels (~20 m deep) extend for over 700 km and connect two large basins that form part of the extensive Moroccan Turbidite System. Over the last 400 ka this system has been host to some of the largest gravity flows ever recorded on Earth, with run out distances exceeding 2000 km and volumes >150 km³. Excellent core control, coupled with a robust geochemical and chronostratigraphic framework, enables individual flow events to be documented in both down-flow and across-flow directions.