Sea-level changes and related depositional environments on the southern Marmara shelf

Abstract

Petrographic data obtained from 182 surface sediment samples together with the available bathymetric data are used to investigate the effects of the last major sea-level changes on shelf evolution in the southern Sea of Marmara. Grain-size analysis reveals the presence of at least three belts or zones which are rich in coarse-grained (sand and gravel) sediments. These coarse-grained belts which are up to 45 km long, 15 km wide, show up to 20 m of relief and are presently found at 40–80 m (average 60 m) water depths. Based on microscopic examination and residual analysis, the sediments from these belts are interpreted as indicators of high-energy shallow waters where detrital siliciclastics, with some benthic contribution, accumulated. The presence of a 62–65 m deep sill in the Çanakkale Strait and the consideration of sea-level curves would suggest that the Marmara shelves must have been subaerially exposed down to −65 m water depths for about 10,000 yrs (22,000–12,000 yrs B.P.), sufficient time to modify former shelf topographies and form such bottom relief. While difficult to date, we believe that coarse-grained belts found on the southern Marmara shelf must be relict (i.e., former shorelines, beaches) and their formation is largely related to low stands of sea-level during the Late Pleistocene regression and early Holocene transgression. However, the available high-resolution seismic profiling data suggest that the neotectonism in this seismically active Sea of Marmara plays an important role to explain the raise of these older shorelines to their present levels on the sea-floor.