Holocene sedimentation patterns and bedforms in the wave-current-dominated nearshore waters of eastern Mersin Bay (eastern Mediterranean)

Abstract

The distribution and bedforms of Holocene sediments in relatively high energy, wave-dominated nearshore waters of the eastern Mersin Bay (eastern Mediterranean) were investigated by high resolution seismic profiles, sidescan sonar records and surface sediment samples. High-resolution seismic reflection profiles show that the sedimentary column consists of two main sequences separated by a mid-reflector (R), showing irregular and erosional surface features, which is interpreted as the Late Pleistocene/Holocene boundary. The upper sequence which is seen as parallel to slightly divergent reflection configurations in a sheet-like to wedge-shaped geometry, approximates to Holocene deposits reaching up to 10 m in thickness about 2 km seaward of the shoreline, with a slight tendency to increase offshore. Seismic data indicate that the unconformity between the late glacial subaerial surface and the overlying post-glacial transgressive deposits occurs at depths of 1–10 m below the seafloor. Holocene sedimentation rates are estimated to be 10–100 cm per 1000 yr. Typical ridge-furrow systems cutting into beachrocks are apparently products of mechanical erosion at very shallow water depths. The lower seismic sequence underlying the reflector R may represent pre-Holocene deposits and is characterized by complex stratified reflection patterns, commonly showing hummocky to mounded and chaotic cut-and-fill facies. Sidescan sonar records indicate prominent features of these nearshore areas such as gravel waves between sand patches and beachrocks: The former are thought to have been produced as a result of the interaction of waves and currents on the sediment surface with an apparently westerly migration direction for sand, whereas the latter were formed during the lowstand of sea level in the Late Holocene. Muddy sand is the dominant sediment type in the nearshore waters of Mersin Bay (in depths less than 15 m) with local sand and gravel patches and beachrock outcrops.