Quantification of source-to-sink transport time of turbidite sands from continental erosional to marine depositional environments

Turbidity currents are the final link of the sedimentary source-to-sink chain as they transport continental sediments to deep sea depocenters through underwater land sliding events. Their triggers are numerous: floods, storms, earthquakes, or simple destabilization of continental slope sediments due to overload. Turbidite sediments generally originate from widespread drainages, making them ideal targets for geological reconstructions integrated over large areas and are thus key sedimentary archives to track past, large-scale continental processes.

To interpret the information contained within turbidites, it is however crucial to correctly date them. In most studies, turbidites are considered as instantaneous deposits and dated using foraminifera of the over and underlying hemipelagic layers, and the absolute age of the sediments they transport is rarely constrained.

In this work, we bring new light on the age of the material remobilized by turbidity currents by using ¹⁴C on both foraminifera and vegetal debris contained in turbidites from three different cores of the Ogowé turbiditic system, western Africa. Two of these turbidites from two different cores are also investigated at higher resolution with 20 foraminifera samples and 38 vegetal debris samples (~1 sample every 5 cm vs. 1 sample/turbidite for the rest of the cores). The radiocarbon ages measured in the turbidites, when compared to the depositional ages of under- and overlying hemipelagic layers provide quantitative information on the total transportation time from the source to the depositional environments, including both the duration of transport on land, and the potential storage of the sediments onshore and offshore (on the continental margin). To compare these results to a smaller, highly-connected turbiditic system, we apply the same method to turbidite sands from the Var turbiditic system, southeast France. To compare these results we apply the same method to turbidite sands of the Var system in SW France. The Var drainage is smaller than that of the Ogowé, is affected by significant relief (maximum altitude of 2916 m) and steep slopes, and possesses no continental margin, creating a very efficient connection from continent to the deep sea.

Our results shed new light on the transport and residence time of turbidites which varies from 1 ka to 15 ka, on the residence time of sediments on the continental slopes or margins ranging from null to about 7 ka, and on the depositional sequences and mechanisms of turbidites. We are able to show that the transport time of sediments in such distal environments can vary on the order of 10 ka and is therefore important to constrain.