SEISMIC STRATIGRAPHY AND LATE QUATERNARY SEDIMENTS IN INNER AND MID-SHELF AREAS OF EASTERN MERSIN BAY, NORTHEASTERN MEDITERRANEAN-SEA

High-resolution shallow-seismic reflection (Uniboom) profiles obtained in inner and mid-shelf areas of eastern Mersin Bay (Turkey, northeastern Mediterranean) show that the sedimentary column comprises two major and distinct lithological sequences (C and B) separated by a reflector (R) which is interpreted as the pre-Holocene surface. The upper sedimentary sequence (C) is thought to represent roughly the Holocene and is characterized by parallel/divergent to sigmoidal reflection patterns above (Unit 1) and sigmoidal-oblique to disrupted, wavy and hummocky reflection configurations below (Unit 2). This may reflect changes in relative sea level and or depositional conditions during the earlier and later stages of Holocene. The Holocene sequence (C) reaches a maximum thickness of approximately 35 m about 500-600 m seaward of the mouth of Seyhan River and thins in all directions away from this point. Adjacent shelf areas are characterized by thinner (10-15 m thick) depositional sequences. Holocene sediment accumulation rates range from 1 to 3.5 m/ka. The lower sedimentary sequence, B, is marked by chaotic reflection configurations and is interpreted as having formed largely during the Plio-Pleistocene. The top of this sequence displays various channel/onlap fills with parallel to oblique reflectors. This record may represent the pre-Holocene surfaces produced by subaerial, fluvial erosion of the pre-existing shelf. At least two or three orders of strong. continuous reflectors similar to Late Pleistocene/Holocene unconformities are observed within sequence B, and the repetitive pattern of the interfaces indicates cyclic sedimentation due to climatic fluctuations and oscillating sea-level changes. mostly in the Pleistocene. Lithological logs from numerous soil borings on the adjacent coast suggest a significant increase in the thickness of the Plio-Quaternary sequences. from a few metres on the alluvial fan-delta systems west of Mersin to a few hundred metres on the fluvial plain-delta system east of Mersin. Climatic and sediment-discharge fluctuations and coastal morphology controlled the temporal and spatial distributions of Late Pleistocene and Holocene sediments in eastern Mersin Bay.