Dynamics of slow suspension flows on the Black Sea abyssal plain

Abstract

This paper aims to develop a theoretical hydromechanical model designed to explain slow motion of thin sediment suspension layer over the Black Sea abyssal plain. The suspension flows are regarded as a new lateral deep sea sediment transport mechanism differing from turbidity currents and other gravity flows in minor mass scale and velocity. The suspension can flow as a heavy liquid denser than the surrounding clear sea water if its upper surface has an inclination to the horizontal plane. Estimated kinematic viscosity coefficient of the suspension is about 3·10−4 m2/sec. Laboratory measurements showed that the suspension has properties of a viscous incompressible fluid. Its motion can be described by the Navier-Stokes equations if the suspension density is less than 1.32 g/cm3. According to box corer and multicorer sampling, a suspension layer, up to 20 cm thick, exists above the sediment surface on the Eastern Black Sea abyssal plain. It can move over the abyssal plain as a near-bottom gravity driven suspension current, several tens of centimeters thick or less, with velocities from several meters up to several kilometers per day, depositing a millimeter-scale terrigenous mud lamina on the way. Our study was focused on the Eastern Black Sea basin where the flat slightly inclined abyssal plain provides favorable conditions for suspension flows motion and lateral deposition of laminated sequences from these flows out of turbidite sequences which dominate in the. Western basin with the Danube turbidite system. Rather weak near-bottom suspension flows are generated here on the shelf from rather small Caucasian rivers discharge plumes and move downslope to the abyssal plane through numerous submarine canyons.