The Sea of Marmara: a plate boundary sea in an escape tectonic regime

Abstract The Sea of Marmara is dissected by two major fault systems. The first consists of two east-west-striking, transtensional boundary faults and a number of secondary faults subparallel to them. The second is made up of NE-SW-trending, subvertical strike-slips and their conjugates oriented NW-SE that offset the first system. These fault systems segment the deep Marmara Sea into 5 blocks that are either rhomboidal, lazy-Z or wedge-shaped. Three of these blocks may be interpreted as pull-apart basins characterized by transtension, while the other two (sill areas) which separate the basins are transpressional push-up structures. The blocks are subjected to rapid, episodic subsidence, but they also undergo pervasive vertical motions and possible rotations relative to one another. The sedimentary column above the acoustic basement mapped within the Sea of Marmara can be divided into 3 seismic units: a folded and truncated pre-transform unit and two syn-transform units. The lower, thick syn-transform unit exhibits 3 distinct seismic facies: a well-stratified basin-fill facies cut by subvertical growth faults, a push-up facies with a contorted or chaotic internal configuration and a slump facies. The observed neotectonic and sedimentary regimes result from compressional movement between Eurasia and Africa, which has led to major dextral transform movements along the North Anatolian Fault Zone (“escape” tectonics), and from the fact that this fault zone splinters into two overlapping, right-stepping, oblique master faults at the eastern and western border of the Sea of Marmara respectively.

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