Holocene sedimentation in the tectonically active Tekirdağ Basin, western Marmara Sea, Turkey

Abstract

The effects of various depositional conditions and active tectonics on the late Holocene sedimentation in the Tekirdağ Basin, west of the Marmara Sea were investigated in 11 gravity cores and on 3 seismic profiles, representing shelf to slope to deep-basin floor environments. Except for the two coarser-grained (avg. 60% sand and gravel) and calcareous (avg. 25% CaCO3) shelf cores, sediments in the slope and basin floor cores constitute low calcareous (avg. 12% CaCO3) and terrigenous mud (>90% silt and clay). The occurrences of relatively higher total organic carbon contents in sediments from the southern slope (1.14–1.38%) compared to that from the northern slope (0.37–1.2%) indicate significant input from the southern rivers. The presence of silty–sandy laminations within the mud matrix of the cores and chaotic and mounded reflection configurations on the seismic profiles from the slope and basin floor environments all suggest the effects of gravity mass movements of sediments (slides, slumps, turbidites) most likely due to seismotectonic events (earthquakes). However, it was difficult to establish a basin-wide correlation between the historical earthquake events in the region and the positions of silty–sandy laminations in dated deep-sea sediment cores due to complicated other events, such as repeated river run off and floods, increased sediment load and slope failure. The water contents of sediments from the basin floor (avg. 10–30%) are significantly lower than those from the slope sediments (avg. 32–46%). The former can be explained by the influences of synsedimentation with tectonics and compaction between the North and South Boundary Sub-faults of the NAF system, whereas the latter shows fluidization of slope sediments during sliding and slumping. Radiocarbon-dated base sections from three cores revealed that sediment deposition at these sites commenced about 4700 BP when the late Holocene depositional conditions changed from the formation of “Upper Sapropels” to the present state. The increases of organic carbon contents at or near the base sections of the cores support this contention.