Grain size and clay mineralogy of Late Quaternary sediments on a tectonically active shelf, the southern Sea of Marmara: clues to hydrographic, tectonic and climatic evolution

Abstract

The clay mineral content and grain size composition of sediments obtained from 29 cores (up to 350 cm in length) on the southern Marmara shelves have been analysed in order to determine the effects of climatic, neotectonic and hydrodynamic changes on the distribution pattern of Holocene sediments in this sea. Grain size data revealed the occurrence of three types of core characterized respectively by fine-grained (rich in sill and clay), coarse-grained (rich in sand and gravel) and fine- to coarse-grained sediments. Clay mineral assemblages are dominated by smectite (22-86%), illite (11-70%) and kaolinite (2-46%) with traces of chlorite. The distribution pattern of the clay minerals in most of the cores reveals upward-increasing smectite and decreasing illite contents, accompanied by an upward increase in crystallinity index for smectite. Analysis of high-resolution seismic profiles and sedimentation rates suggests that the coarser-grained sediments are relict deposits. formed under shallower water-higher energy conditions at some time during the latest Pleistocene-Early Holocene. With the beginning of marine transgression during the Early Holocene up to the present, deeper water/lower energy conditions have prevailed, characterized by finer-grained sedimentation and increased deposition of smectite with increased crystallinity. Copyright (C) 1999 John Wiley & Sons, Ltd.