Detrital zircon geochronology of Pliocene deltaic sediments in the Marmara region (Turkey): Implication for sedimentary provenance and morphotectonic evolution

Abstract

: The İstanbul Pliocene deposits consist of an alternation of sand, clay, and coal in the northern part of İstanbul that characterizes a delta plain deposit on the southern coastal line of the Black Sea. The Pliocene sediments, which are located conformably on the fluvial sediments consisting of coarse clastics, are about 80 meters thick and outcrop as isolated patches in Şile in the east of the İstanbul Strait (Bosphorus) and Kısırkaya in the west. The U/Pb detrital zircon ages obtained from the sands of Kısırkaya and Şile region showed that the Pliocene deposits contain Proterozoic (2396 ± 72 – 542.4 ± 7.9 Ma), Paleozoic (540 ± 12 – 258.9 ± 5.2 Ma), Mesozoic (248.8 ± 4.4 – 71.8 ± 1.2 Ma), and Cenozoic (63 ± 1.8 – 22.18 ± 0.95 Ma) zircons derived from a piedmont plateau. Presence of the youngest Oligocene–early Miocene zircons (22.18 ± 0.95 – 31.1 ± 1.2 Ma) reveals that the source of this succession may be the Northwest Anatolia and/or northern Aegean region where magmatic rocks of the same age crop out. In addition to the zircon data in the sandy deposits, trace element geochemistry also shows that the drainage basin of the Pliocene rivers transporting clastics to the basin is located in the southwestern region of İstanbul and flowed into the Black Sea before the formation of the Marmara Sea. These rivers would have been blocked in the early Quaternary by the Marmara Sea depression, which was formed by extensional faults, the product of an approximately N–S extensional tectonic regime in the region. This tectonic regime caused the rapid uplifting of the İstanbul region and the Istranca Mountains in the north of the Marmara, and the eroded flattened areas called the Bursa–Balıkesir plateau in the south, in the form of horsts. Subsequently, before the North Anatolian fault reached the region, it formed deformation structures under the effect of dextral shear in a wide zone in the Marmara region. This tectonic regime was ended when the North Anatolian fault reached and cut the Marmara Sea region in the Latest Quaternary.