Seismic stratigraphy and late quaternary sediments in inner and mid-shelf areas of eastern Mersin Bay, northeastern Mediterranean Sea

Abstract

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 roughtly the Holocene and is characterized by parallel/divergent to sigmoidal reflection patterns above (Unit 1) and sigmoidal-obolique 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.