Abstract:

The Late Pleistocene-Holocene evolution of the Adapazarı Basin was investigated using the stratigraphy, geometry, and absoluteluminescence dating of the 4-step fluvial terrace staircases of the Sakarya River. The results revealed that the fluvial cycle was primarily related to relative sea level changes of the Black Sea. The initiation of deposition and the abandonment ages of the terraces indicated relative high stands during marine isotope stage (MIS) 5a (~84-72 ka), 3 (40-30 ka), and 1 (9 ka-recent). The erosional periods in between the terrace steps reflected the response of the Sakarya River to the significantly low stands of the sea. The spatiotemporal position of the high terraces (T4 and T3) yielded an average of 0.78 ± 0.03 mm/year, and uniform and aseismic rock uplift rate for the NW part of the Anatolian Plate bounded by the North Anatolian Fault, which ruptured during the 1999 İzmit earthquake. The lower terrace (T1) was previously used to determine the horizontal slip rate of the Sapanca-Akyazı segment of the earthquake rupture and reported as 16.7 + 3.6/-2.5 mm/year. Further displacement measurements from the surfaces of T2 and T1 yielded a vertical slip rate of 1.49 ± 0.2 mm/year, calculated for the Late Holocene. Extrapolation of these 2 vertical rates to the south and north of the fault zone, in time and space, used in conjunction with the stratigraphy and geometry of the Adapazarı Basin, provided an estimation constraining the timing of the initiation of the fault to 450 ± 50 ka and the total thickness of the basin to ~1100 m.

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