Recent surficial shelf sediments of the Cilician Basin (Turkey), northeastern Mediterranean

Abstract

The continental shelf of Mersin Bay forms the northwestern margin of the Adana-Cilician Basin; it extends from the Göksu delta (in the southwest) to the Seyhan-Tarsus-Ceyhan delta (in the northeast) and is narrower and steeper in the southwest than in the northeast. Five depositional zones are recognised on the basis of the analysis of surficial sediments: (1) a “ Modern Terrigenous Prism”; extending from the coast to 50 m water depth; (2) a “ Shelly Zone” on the mid-shelf (50–100 m), characterised by an abundance of skeletal debris; (3 and 4) “ Prodeltaic Zones (I and II)” in the northeastern and southwestern parts of the shelf, where silty sediment from the major Seyhan-Tarsus and Göksu rivers, respectively, has been deposited; and (5) the “ Outer Shelf Zone”, extending from the 100-m contour to the shelf edge, characterised by clay-sized sediment and abundant remains of planktonic micro-organisms. Sediment appears to be reaching the shelf from two main sources: (i) a lateral supply from the coastal rivers between the two major deltas, which is being dispersed along the coast to form the “ Modern Terrigenous Prism” and is dominated by near-shore wave activity and wave-generated currents; and (ii) fine-grained sediment from the Seyhan-Tarsus rivers, transported along the shelf under the action of the cyclonic Mediterranean circulation. Some of the latter sediments settle to form the distal tongue of the Seyhan-Tarsus delta (Prodeltaic Zone I), whilst the remainder settles over part of the shelf to the southwest. The sediment supplied by the Göksu river is generally swept away to the southwest, by the southwesterly-flowing cyclonic Mediterranean Current and it influences the shelf only within its immediate vicinity to form Prodeltaic Zone II. The mid-shelf area (Shelly Zone), lying at water depths of between 50 and 100 m, receives some fine silt and clay. However, it is cloaked in a thin layer of skeletal debris, which is difficult to explain but may be partly of anthropogenic origin although this requires further investigation.