Sedimentological and geochemical approaches for determination of the palaeoceanographic and palaeoclimatic conditions of Lower Cretaceous marine deposits in the eastern part of Sakarya Zone, NE Turkey

Abstract

Upper Jurassic–Lower Cretaceous carbonate successions are widely exposed throughout the Sakarya Zone, Northern Turkey. The carbonates are considered as invaluable archives of palaeoceanographic and palaeoclimatic conditions of Tethys Ocean. We, here, present new micropaleontological, microfacies, and stable isotope data (δ18O and δ13C) of Lower Cretaceous carbonate succession of the eastern part of Sakarya Zone, NE Turkey. The studied Lower Cretaceous carbonates are characterized by, from bottom to top, microfacies associations within Unit 1 and Unit 2 that were deposited in the Barremian–Albian. Unit 1 (Barremian–Aptian) is represented by the predominance of benthic foraminiferal associations and shallow marine organisms. Unit 1 shows alternations of different microfacies, including non-laminated mudstone (MF-1), autochthonous bioclastic-foraminiferal grainstone and packstone (MF-2) and intraclastic grainstone/packstone (MF-3). An abrupt palaeoenvironment change is represented by Unit 2 with deeper water microfacies associations consisting of dark grey limestones with chert nodules, mud-rich texture, reworked skeletal fragments, sponge spiculitics and a presence of the planktonic organism. Unit 2 (Albian) displays two different microfacies: reworked bioclastic packstone/wackestone microfacies (MF-4) and gradually overlying sponge spiculitic wackestone–mudstone (MF-5). The integration of microfacies and micropaleontological data implies that the Barremian–Albian interval represents the inner platform to the slope palaeoceanographic conditions revealing an overall transgressive trend, which is consistent with a significant rise in the sea level throughout Tethys margin during the Albian. The Albian sea-level rise is likely triggered by the sedimentary evolution of the basin due to the extensional tectonic regime in NE Turkey. Besides, the palaeo-temperatures are measured by the δ18O data that were obtained from well-preserved belemnite samples in Unit 2. Palaeotemperature analysis presents a range of 18.30–26.77 °C with an average of 23.13 °C during the Albian. Our palaeo-temperature data are conformable with the warm Cretaceous climatic conditions, which are recorded in the different parts of the Tethys margin. Therefore, this contribution provides the first insight into the palaeoclimatic conditions of the Tethys ocean for the eastern part of the Sakarya, NE Turkey.