Geochemistry of the Upper Cretaceous - Miocene strata in the Tekman-Karayazi Basin (Turkey): Tectonic processes, sedimentation patterns, and the source rock quality along the northern branch of the Neo-Tethys Basins and northeastern Arabian plate

Tekman-Karayazi Basin (TKB) is one of the Eastern Anatolia basins which is located in the south of the Izmir-Ankara-Erzincan Suture Zone and is characterized by sedimentary units ranging in age from Upper Cretaceous to Pliocene. The basin began to form in Upper Cretaceous (Maastrichtian) in a tectonic depression, which over time evolved into a collisional foreland basin. While the Jurassic and Cretaceous Oceanic Anoxic Event (OAE) rocks were preserved in the NE of the Arabian Plate (SW of Iran), they are represented by an ophiolitic me & PRIME;lange which was formed as a result of the closure of the northern branch in the TKB and other basins on the Anatolian microplate. Four tectono-sedimentary phases are recognized over the ophiolitic me & PRIME;lange: Phase I (Maastrichtian-Paleocene (?), after obduction) is comprised of submarine fan deposits. Phase II (Paleocene -Lower Eocene, obduction phase) is characterized by major changes in gradually depositional environments in the TKB (clastics-nummulitic limestone), and continental to ramp carbonate to slope facies in others (e.g., Yakacik-Orhaniye, Haymana-Polatli). Phase III (Middle - Upper Eocene, ongoing collision phase) shows the development of tur-biditic and continental facies show that both TKB and/or the coeval basins have poor source rock potential. Phase IV (Oligo-Miocene, ending collision) represents from eastern to central in eastern Anatolian basins alluvial-fluvial to lacustrine and marine units during Oligocene - Miocene, respectively. The geochemical correlation between the bitumen extracted from sandstone sample and the Agcakoca shales suggests that this formation can be considered as the corresponding source rock unit; however, according to the Tmax values (364-444 degrees C, mean: 428 degrees C), this formation is mostly immature, a scenario supported by the dry wells in the region. The regional volcanic activities triggered in Miocene by continent-continent collision seems to have provided the heat which, in turn, caused the thermal cracking of kerogen in Agcakoca shales and locally induced petroleum expulsion. Mixing with the underground water on its way to reach a reservoir rock, the generated oil formed the oil seep. Therefore, we propose that a speculative Mescitli-Hanes,duzu (?) petroleum system may exist in this basin. We suggest that the combination of factors such as the asymmetric closure of the Tethys Ocean and the escape tectonics of the Anatolian Plate gave rise to the deposition of Paleocene to Miocene organic matter-rich shales in the NE of the Arabian plate, whereas uplift, antecedent topography, and the global paleo-climatic events disturbed the favorable conditions and caused the studied basins to lack the aforementioned generative source units.