Miocene sea-level changes in northernmost Anatolia: Sedimentary record of eustasy and tectonism at the peri-Pontide fringe of Eastern Paratethys

摘要

This study from the Central Pontide Miocene foredeep basin compares the local record of relative sea-level changes at the Turkish southern periphery of the Eastern Paratethys with the general Paratethyan eustatic history. Detailed sedimentary facies analysis is used to decipher high-resolution sequence stratigraphy of the basin-fill succession. The Tarkhanian-Chokrakian Sinop Formation overlies directly the pre-Cenozoic bedrock and consists of neritic to littoral, foreshore and barrier-lagoon deposits, which form transgressive-regressive parasequences with estimated time spans of ca. 60 to 700 ka. The overlying Konkian-Bessarabian Gelindk Formation occurs as the infill of fluvial valleys, up to ＞ 120 m deep, which were incised during the Karaganian and filled with deltaic to non-deltaic bayhead shoreline deposits passing up-valley into alluvium. The valley-fill deposits form parasequences with an estimated mean time span of ca. 300 ka, organized into a lower regressive and an upper transgressive set. These lst-order parasequences consist of smaller, 2nd-order parasequences with an estimated mean time span of ca. 5 ka. All the main mid-Miocene Paratethyan eustatic events are recognizable in the basin-fill successioa although their record appears to have been modulated by the local tectonism and high rate of post-orogenic sediment supply. The signal of 3rd-order eustatic cycles is recorded on a stratigraphic scale of parasequence sets. The lst-order parasequences are attributed to pulses of the basin subsidence, which was initially driven by the thrust loading of the collapsing Pontide orogen and later by the neotectonic inception of the strike-slip North Anatolian Fault System. The 2nd-order parasequences represent minor subsidence pulses and/or the Milankovitch eustatic cycles. The study shows how a comparative analysis of local sequence stratigraphy and eustatic sea-level record can serve to recognize the relative role of eustasy, tectonics and sediment supply in a sedimentary basin.