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
Résumé
9 Holocene earthquake history of the Central High Segment of the North Anatolian Fault is 10 examined here for the first time based on analysis of seismoturbidites within a 21-m-long piston 11 core recovered from the Kumburgaz Basin in the Sea of Marmara. The visual lithological 12 description combined with detailed grainsize analyses indicate that the deep basin hemipelagic 13 sediments are interrupted by 28 turbidite units during the last 6.1 cal kyrs BP. The turbidites 14 show strong segregation and a sharp boundary between a coarse basal part and overlying 15 homogenite as inferred from detailed sedimentological and geochemical data. Several 16 amalgamated turbidites are recognized by repeated fining upward sequences with no 17 intervening homogenite indicating multiple episodes of traction and deposition as a result of 18 various slope failures and turbidity currents. Each unit was possibly triggered by the same 19 earthquake event rupturing in the Sea of Marmara. The most common sedimentary feature is 20 the continuous parallel lamination that was presumably introduced by long lasting water 21 oscillations on suspended sediments due to the seiche effect. The establishment of geochemical 22 criteria and exclusive sedimentary processes distinguish earthquake triggered turbidites 23 (seismoturbidites) from other trigger factors. Moreover, such distinction allows us to evaluate 24 2 hydrodynamic sedimentary conditions and processes in the Kumburgaz Basin. The base of most 25 seismoturbidites are associated with a sharp increase in Mn concentration that can be explained 26 by a diagenetic enrichment of Mn at the oxic/anoxic interface of the sediments near the seafloor 27 prior to the deposition of the turbidite. An age-depth model of the studied core based on seven 28 AMS 14 C ages allows precise correlation between historical earthquakes and seismoturbidites 29 in the Kumburgaz Basin. At least the latest nine of them fit well with the previously recorded 30 major earthquake events between ca. ~500 cal yrs BP and 2.5 cal kyrs BP. 31
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