Sedimentology and mineralogy of surficial bottom deposits from the Aegean–Çanakkale–Marmara transition (Eastern Mediterranean): effects of marine and terrestrial factors

Abstract

Abstract Grain size, carbonate and XRD-mineral data of surficial shelf sediments from 113 stations in the Aegean–Marmara-transition revealed the presence of three distinctive sectors which were controlled by the changing morphologic, hydrodynamic, benthic and terrigenous conditions that lasted during the late Quaternary. The northeastern Aegean Sea forms the western sector of the study area. This region shows several bank-and ridge-like bottom features at 60–70 m water depths which are widely capped with sand and gravel (up to 93%) of both biogenic (>30% CaCO 3 ) and terrigenous ( 3 ) origin. The low abundances of fine-grained materials (1–24% mud) in this biogenic belt are probably in response to higher current velocities in the sea and to low fluvial discharges from the adjacent land masses. Biogenic materials consist of a large variety of calcareous remains of benthic organisms, which are partly cemented by carbonate. It is hypothesized that this biogenic belt, at least in part, is a relict feature. Canakkale Strait is the central sector of the study area and its bottom is covered largely by terrigenous sand and gravel ( 3 ). The coarse-grained nature of the sea floor of Canakkale Strait can be explained by the prevailing high current velocities. Western Marmara Sea is the eastern sector of the study area where the local major rivers supply a great part of the terrigenous materials and the prevailing low current velocities favour fine grained materials’ deposition here ( 3 ; up to 99% mud). Calcite (mainly Mg-calcite; 5–92%), quartz (3–72%), feldspars (mainly plagioclase; 7–56%) and micas are the major bulk minerals in the sediments. Except for Mg-calcite which is mainly derived from calcareous biogenic components, bulk minerals reflect a terrigenous source from the adjacent land masses. In particular, the overall lower qtz/fsp ratios in the study area (0.4–1.2) showed significant increases (i.e. enrichment of quartz relative to feldspars; qtz/fsp: 1.2–2.4) in the inner biogenic belt of the northern Aegean Sea where older or relic (early Holocene) sediments are suspected to occur. If so, these values can be used as an indicator for long duration of lowstands of sea level and associated intense current and wave activities. 17 A-expandable smectite (23–84%), illite (12–43%) and kaolinite (6–38%) determined in the less than 2 μm of the sediment are the major clay minerals. Higher abundances of smectite relative to illite and kaolinite found in sediments particularly off the mouths of rivers, Karamenderes, Gonen and Biga and off the Gokceada and Bozcaada Islands reflect mainly local sources for the clay minerals studied. The higher smectite/illite ratios of abundances are largely attributed to the weathered volcanic rocks which are widely distributed on the surrounding land masses. However, the prevailing current and wind patterns seem to be important factors controlling clay mineral distribution in marine sediments of this study.