Sedimentary record of mid-Miocene seismotectonic activity in the Sinop Peninsula, north-central Turkey

Authors: AYHAN ILGAR

Abstract: The middle Miocene shallow-marine siliciclastic succession in the Sinop Peninsula, north-central Turkey, bears a well-preserved sedimentary record of syndepositional deformation associated with the buried escarpment of an oblique-slip dextral reverse fault and attributed to seismotectonic activity. The deposition occurred in a marginal trough at the edge of a tectonically inverted retroarc foreland basin of the Central Pontides. The synsedimentary deformation involved contemporaneous shoreface deposits and their consolidated, weakly cemented littoral substrate. Deformation features include neptunian dykes, convolute stratification, plumose transposition structure, injection dykes, diapirs, and large sandstone blocks dislodged from the fault escarpment. The genetic sequence of deformation structures deciphered from the outcrop section indicates 3 main episodes of seismotectonic activity associated with the fault and separated by renewed sediment accumulation. The first episode formed a surface rupture equal to about a third of the total minimum vertical displacement, estimated at \sim5.5 m, with a detachment of a large sandstone block from the fault scarp. The second episode is inferred to have involved at least 2 closely consecutive earthquakes, which caused partial liquefaction and fluidization of footwall sediment. The last episode of fault activity caused detachment of an even larger sandstone block and was followed by abrupt basin subsidence, possibly accompanied by a minor tsunami. The seismotectonic events postdated the Pontide orogen and are considered to represent an early phase of neotectonic activity in the north-central Turkey, heralding the development of the North Anatolian Fault Zone. Similar deformation features associated with fault escarpments are potentially common in the stratigraphic record, but may have been lumped with fault breccias or talus deposits and escaped recognition. The study offers detailed sedimentological criteria for the recognition of syndepositional seismotectonic activity.

Keywords: Northern Anatolia, Central Pontides, marginal trough, fault, synsedimentary deformation, neotectonics

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