Gemlik Körfezi'nin (Marmara denizi) geç kuvaterner stratigrafisi ve morfotektoniği

Gulf of Gemlik is an east-west oriented marine inlet with a maximum depth of 113 m in the south-eastern part of the Sea of Marmara. It is located on the middle branch of the North Anatolian Fault Zone (NAFZ). In this study, the Quaternary paleoceanographic evolution and morphotectonics of the Gemlik Gulf are investigated using high resolution seismic, bathymetric and core stratigraphic data obtained during the various cruises of R/V Urania. The studied Core M13-08 was recovered from a depth of 73.5 m from the northern shelf of Gemlik Gulf during RV Urania 2013 expedition. The 6.70 m long core was analyzed for magnetic susceptibility (MS) using Multi Sensor Core Logger (MSCL) and dated using Accelerator Mass Spectrometry (AMS) radiocarbon analysis. According to 14C dates and fossil content, Core M13-08 covers the last 12.6 uncalibrated ka BP (all radiocarbon ages in this thesis are in uncalibrated 14C years), and includes two litho-stratigraphic units: an upper marine unit (Unit L1) and the lower lacustrine-deltaic unit (Unit L2). As a result of seismic to core correlation, Unit L1 and L2 correspond to seismic stratigraphic units S1 and S2. In Core M13-08, Unit L2 consists of dark gray, well-sorted medium sand, with fresh to brackish water bivalves and high MS due to high concentrations of magnetic minerals. The upper-most part of the Unit L2 is composed of gray, well-sorted sand with normal grading that is well consistent with the decreasing MS value towards to the boundary between Unit L2 to L1. This stratigraphic boundary is associated with an unconformity surface that separate the lacustrine to marine units in the studied core. The marine unit L1 is a green mud with marine fossils (bivalves and foraminifera) showing a fining upward sequence. The highest MS value in Unit L1 is associated with a thin layer consisting brownish green banded clay and the overlaying dark to light brown green clayey mud. As a result of detailed seismic stratigraphic analysis, four main seismic stratigraphic units have been differentiated in the seismic profiles from the Gemlik Gulf. We called these stratigraphic units in the profiles as units S4, S3, S2, and S1 from the bottom to top. The youngest lowstand unconformity surface is represented by reflector surface (marked as red) that is a shelf-crossing unconformity characterized by subtle erosional truncation of the underlying older units in shallow (<-75 m) part of the Gulf. Ages of the seismic stratigraphic can be estimated by core-to-seismic correlations, using radiocarbon chronology of Core M13-08 and previously published chronostratigraphic information of Core GE-124 from the eastern part of the Gulf. Unit S1 is characterized by horizontal and continuous, acoustically strong internal reflectors. It extensively covers the younger units. The base of the Unit S1 separates the upper marine and the lower lacustrine sediments in the Gemlik Gulf. This unit was deposited during the last 10.6 ka BP Unit S2 is a bedded mud drape with acoustically moderate to low internal reflectors in the basin (>-75 m) and progradational clinoforms with acoustically stronger internal reflectors on the shelf-edge, where the prograding nature of this unit implies regressive deposition. The unit is truncated by the main unconformity surface in the profiles. This unit was deposited during 13.9-10.6 ka BP. Unit S3 includes highly-reflective, conformable and moderately continuous internal reflectors. On the shelf, Unit S3 consists of clinoforms and deltaic foresets with acoustically strong internal reflectors. The unit characterizes a deltaic system located on eastern and northern shelf margins of the Gulf. In the deep basin (> ~ -75 m), Unit S3 shows transition to horizontal and parallel-bedded sediments. This unit was deposited during 15.8-13.9 ka BP. Unit S4 is the oldest sedimentary unit recorded in the high resolution seismic profiles. On the western part of the gulf, this unit consists of highly-reflective parallel bedded internal reflectors. Towards the eastern part of the basin, where the gulf begins to deepen below -75 m, Unit S4 comprises mound-shaped sediments with wavy internal reflectors that are truncated or separated by erosional gullies formed on a reflector (marked as blue on the interpreted seismic lines). This unit is older than 15.8 ka BP. Using the high resolution seismic profiles and the updated bathymetric map, we produced a new fault map of the Gulf. This map shows that the main active faults in the area are roughly E-W oriented İmralı, Gemlik, Kocadere, Gençali dextral transform faults. The Armutlu, Kocadere and Gemlik faults have a clear normal component with a maximum vertical offset of 6.2 m, 8.53 and 6.97 m, respectively. The fault geometry suggests that the deep Burgaz Basin of the Gemlik Gulf has evolved as a pull-apart basin between the Armutlu and Kocadere transform faults. The transpression by the Gemlik and Western Faults resulted in the Gemlik Uplift (Rise) in the east the Gemlik sill in the west of Gemlik Gulf. The core and seismic stratigraphic analyses show that the Gulf was a lacustrine environment prior to 10.6 ka BP, with lacustrine shelf-edge delta developments in the north and east during 15.8-13.9 ka BP. There was lowering of the lake level and erosion during part of the Bølling-Allerød and Younger Dryas, which was followed by the marine transgression at 10.6 ka BP, about one thousand years later than the first entry of Mediterranean waters in the Sea of Marmara. The reason for the 1 ka delay is the -55 m sill to the west of the Gemlik Gulf. It is recommended that this study is extended to the west of the Gulf, using similar techniques of multi-beam bathymetric mapping, high resolution seismic reflection profiling and core analysis. The seismic reflection data is especially needed for the near shore areas along the southern shoreline of Gemlik Gulf.