Gas-charged late quaternary sediments in Strait of Çanakkale (Dardanelles)
Bedri Alpar, Hüseyin Yüce, Ertuğrul Doğan
Istanbul University, Institute of Marine Sciences and Management, 34470 Vefa, Istanbul, TURKEY
Department of Navigation, Hydrography and Oceanography, 81647 Çubuklu, Istanbul, TURKEY
The nature of bottom sediments in the Strait of Çanakkale (Dardanelles) depends on the interaction of the channel geometry and flow conditions. The sand-size sediments are found in narrow parts of the strait’s channel where high-energy conditions prevail. Such high-energy flow sections of the channel include the narrows of Çanakkale and Nara. Sand and silty sand are also distributed in narrow bands along both shores of the channel. Terrigenous mud is the major sediment type covering deeper and wider parts of the strait channel where bottom currents are relatively weak. Shallow seismic profiling shows the presence of two main seismic sedimentary sequences in the Dardanelles; late Quaternary sediments and acoustic basement. These are separated by an erosional truncation surface. The late Quaternary sediments consists of at least three sediment sub-units. These sub-units can be interpreted as Holocene posttransgression marine deposits (A1), basinward-prograding deltaic sediments deposited during the Würm glaciation (A2), and basal transgressive marine sediments (A3), possibly Tyrrhenian age. The acoustic basement is formed from the Miocene shallow marine clastic sediments distributed widely on both sides of the strait. The lower two sub-units of the late Quaternary sediments are locally gas-charged in the wider parts of the straits channel. The origin of the gas is not adequately known: it could have heen formed by fermantation reactions during the early diagenesis of sub-unit A3. The channel of the strait appears to be fault controlled with the faults being generally parallel to the coast. Some faults are still active and cut the late Quaternary sediments.
Keywords: Dardanelles, gas-charged sediments, bottom sediments, shallow seismic