Organic-rich transitional facies in silled basins: Response to sea-level change

Abstract

High-resolution profiles of organic carbon, {delta}{sup 13}C{sub org}, sulfur, {delta}{sup 38}S, and some trace elements in cores from two silled basins, Kau Bay (Indonesia) and the Black Sea, allow division of the sedimentary record into three distinct units, representing a Pleistocene fresh-water-brackish water facies (unit 3), a Holocene transitional facies (unit 2), and a modern fully marine facies (unit 1). The geochemical characteristics of these units are strikingly similar for both basins. The sediments form unit 3 are characterized by the predominance of terrestrial organic matter, Mo and U concentrations at crustal abundance, and positive {delta}{sup 34}S values. The transitional sediments (unit 2) are strongly enriched in marine organic matter and Mo, V, and U and have intermediate {delta} {sup 34}S values. Sediments from the modern marine facies (unit 1) are moderately organic-carbon rich and slightly enriched in Mo and U and have negative {delta}{sup 34}S values. The organic-carbon-rich sediments from unit 2 were formed by increased production during the transition from the Pleistocene isolated fresh-water-brackish water environment to the modern open-marine facies. This temporarily higher productivity was caused by displacement of nutrients from the deep water into the euphotic zone, owing to the gradual infilling by marine waters.