Sedimentological and geochemical evidence for seismoturbidite generation in the Kumburgaz Basin, Sea of Marmara: Implications for earthquake recurrence along the Central High Segment of the North Anatolian Fault

Holocene earthquake history of the Central High Segment of the North Anatolian Fault is examined here for the first time based on analysis of seismoturbidites within a 21-m-long piston core recovered from the Kumburgaz Basin in the Sea of Marmara. The visual lithological description combined with detailed grainsize analyses indicate that the deep basin hemipelagic sediments are interrupted by 28 turbidite units during the last 6.1 cal kyrs BP. The turbidites show strong segregation and a sharp boundary between a coarse basal part and overlying homogenite as inferred from detailed sedimentological and geochemical data. Several amalgamated turbidites are recognized by repeated fining upward sequences with no intervening homogenite indicating multiple episodes of traction and deposition as a result of various slope failures and turbidity currents. Each amalgamated unit was possibly triggered by the same earthquake event rupturing in the Sea of Marmara. The most common sedimentary feature is the continuous parallel lamination that was presumably introduced by long lasting water oscillations on suspended sediments due to the seiche effect. The establishment of geochemical criteria and exclusive sedimentary processes distinguish earthquake triggered turbidites (seismoturbidites) from other trigger factors. Moreover, such distinction allows us to evaluate hydrodynamic sedimentary conditions and processes in the Kumburgaz Basin. The base of most seismoturbidites are associated with a sharp increase in Mn concentration that can be explained by a diagenetic enrichment of Mn at the oxic/anoxic interface of the sediments near the seafloor prior to the deposition of the turbidite. An age-depth model of the studied core based on seven AMS ¹⁴C ages allows correlation between historical earthquakes and seismoturbidites in the Kumburgaz Basin. At least the latest nine of them fit well with the previously recorded major earthquake events between ca. ~500 cal yrs BP and 2.5 cal kyrs BP.