Sediment dispersal from source to shelf on an active continental margin, S. Turkey

Abstract

Provenance and sediment dispersal has been investigated in the eastern part of the southern Turkish coast and its adjacent continental shelf. The physiographic and geological setting make this area especially interesting for the study of post-orogenic (Molasse-type) sedimentation. The siliciclastic fractions of river, beach and shelf-surface sediments were examined. Grain-size frequency and statistical analyses showed that the sands of these environments can be distinguished by their textural parameters. The sediments are rich in heavy minerals such as olivine, pyroxenes, amphiboles and opaques. Combined light- and heavy-mineral data indicate that the siliciclastic detritus was derived largely from the ultramafic suites of the ophiolite complexes exposed in the hinterland. The mineral spectra of the river sands and the heavy-mineral provinces delineated along the coast faithfully reflect the various petrographic units of the source area. In the coastal region a northeasterly longshore current plays an important role in the sediment dispersal. Two types of surface sediments are present on the shelf: A fine-grained, mineralogically fairly homogeneous and a medium grained. The latter is thought to be the deltaic deposits of the ancestral Seyhan and Ceyhan rivers during the low sea-level stages of the Quaternary, probably indicating the position of the coastline at that time. The distribution patterns of the principal heavy minerals indicate the major point-sources of sediment supply onto the shelf and reveal intensive mixing and sorting processes. As a result, the mineral distribution along depositional strike is homogeneous whilst down-dip, well-defined, grain-size-related mineral zones have developed.