Gravity Deposits in Deep Sea Fans and on Continental Slopes, Black Sea

M. K. Ivanov, A. I. Konyukhov

Gravity deposits are very widely distributed in the deep Black Sea basin. The main volume of such deposits is located on the lower continental slopes and continental rises, where deep-sea fans extend. The Danube submarine fan and Rioni-Inguri system of fans are the largest of them.

The Danube fan has a classical structure. It is clearly expressed in the bottom relief and traced by reflection profiles for more than 200 km. The fan body is levee valley, which splits in a mid-fan area into numerous meandering distributaries. The fan consists of gravity and hemipelagic deposits. These are mainly turbidites of various compositions. Channels are filled with grain-flow deposits (sand), debris-flow deposits (sandy clay with shells), and slides from valley walls (mud, sapropelic mud). Levees in upper and mid-fan areas are formed by specific turbidite sequences: mudstone crumbs in the base, thinly laminated silt and clays in the middle, blue mud on the top. Hemipelagic sediments increase noticeably on outer slopes of the levees. In the Pleistocene sequence these are mud; n the Holocene, sapropelic mud and coccolith-diatom ooze. Distal turbidites are widespread in the lower fan areas. In the base of each cycle is a thin sand-silt layer with unclear graded bedding; the upper part is represented by mud. Reflection profiles demonstrate an ancient fan system with buried channels and levees. Configurations of these bodies are very similar to those of the modern fans.

The sedimentary lens on the sea floor opposite the mouths of submarine canyons of the Rioni, Inguri, Kodori, Supsa, and Chorokh Rivers was formed by overlapped modern and ancient fans. The Inguri and Rioni produced a practically single submarine fan, the largest in this area. It is rather well expressed morphologically and traced by reflection profiles for more than 100 km. In its lower part it overlays a number of small fans. The Rioni-Inguri fan is smaller than the Danube, but the whole system of overlapped fans occupies an area of about 17,000 km², being more than 3 km thick. The composition and structure of sediments in this deep-sea system change sharply, depending on the geomorphological position.

The large slumps and slides are widespread on the continental slope and rise of the Black Sea basin. Sometimes they are immersed into hemipelagic mud or turbidites. The size and distribution of such bodies depend on structure and tectonic activity of the continental margin.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.