Diatomaceous oozes of the Middle Caspian Sea

Ten cores taken by a gravity corer from an area 5 × 5 km in size at the foot of the western slope of the Derbent Basin recovered uniform sections composed of variegated clotted diatomaceous oozes and soft gray clays with hydrotroilite-enriched spots, lenses, and laminae, the abundance of which increases downward. The diatom assemblages indicate a strongly freshened basin, which was replaced in the Holocene (Novocaspian time) by the brackish-water and then present-day saline sea. The grain-size composition of the sediments was determined by the gravitational deposition of suspended particles and by the near-bottom currents. The latter likely promoted the concentration of diatom frustules and accumulation of diatomaceous oozes.