Recent sedimentation on the shelf and upper slope in the Bay of Anamur, southern coast of Turkey

Abstract

Sedimentological studies, supported by Uniboom profiles and sonographs, of surface sediments from a part of the narrow southern shelf of Anatolia, indented by the head of a submarine canyon and partly covered by meadows of macrophytobenthos, revealed abrupt lateral and vertical variations in the Holocene sedimentary facies. These variations have essentially been controlled by the migration of depocentres, (palaeo-) topography of the shelf and an overall decrease in the rate of fluviatile sediment supply in the late Holocene. As sea level reached approximately its present position nearly 5 ka B.P., the bulk of the siliciclastic input began to be trapped in the inner shelf zone (< 30 m deep) and the course of the Sultançay river, the major source of sediment supply, migrated away from the head of the canyon towards the west. The deeper parts of the shelf began to be influenced by the open-sea water masses and currents, becoming a site with favourable ecological conditions for the colonization of the sea floor by macrophytobenthos, coralline algae and epibenthic macro and microbenthos. Semi-indurated relict sandy sediments composed of quartz and detrital metamorphic and carbonate grains are exposed at some localities on the deeper part of the shelf. At most places in the outer shelf zone, they are covered by a relatively thin veneer of surficial carbonate-rich sediments having a total carbonate content of 30–80%. Most of the terrigenous mud bypasses the shelf to be trapped in the canyon head, but transport of modern detrital sand and gravel does not take place across the shelf. This is because of the relative weakness of the onshore-offshore currents, the prevailing microtidal conditions and a belt of phytobenthos between 10 and 30 m which traps the sediments. The plants also create the ecological conditions favourable for biological carbonate production. However, some gravel- and sand-size relict sediments have been transported from the outer shelf into the canyon head by gravity-induced or cross-canyon currents. The “mudline” occurs at about the 100 m isobath, marking the deepest limit of effective bottom turbulence for the resuspension of silt and clay on the shelf.