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Lower-middle carboniferous boundary in central taurides, Turkey (Hadim area) : paleontological and sequence stratigraphic approach

Atakul, Ayşe
The aim is to delineate the effective boundary between Lower and Middle Carboniferous (mid-Carboniferous boundary) and to study the meter-scale cyclicity and foraminiferal evolution across a stratigraphic section comprising this boundary. In order to perform such a study, a 25,64 m stratigraphic section, which is mainly composed of carbonates has been measured in the Hadim region of the Central Taurides. In this study, calcareous foraminifers have been studied in the measured section. These foraminiferal assemblages contain 62 species. Based on these foraminifers, four biostratigraphic zones have been defined covering the interval from Upper Serpukhovian to Lower Bashkirian. These zones comprise in ascending order, the Eostaffella ex gr. ikensis ا E. postmosquensis Zone (Zapaltyubinsky Horizon ا Upper Serpukhovian), the Plectostaffella jakhensis ا P. bogdanovkensis Zone and the Millerella marblensis Zone (Bogdanovsky Horizon ا Lower Bashkirian) and the Semistaffella sp. Zone (Syuransky Horizon ا Lower Bashkirian). In order to construct the sequence stratigraphic framework, detailed microfacies studies were carried out and eleven different microfacies types were identified. Based on the stacking patterns of these microfacies, six main types of cycles, A-F, and ten subcycles are recognized. Twenty-three shallowing upward meter-scale cycles and three sequence boundaries have been determined in the studied section. The duration of cycles has been calculated as 2 my and cycle periodicities correspond to the Milankovitch eccentricity bant. Results of quantitative analysis of benthic foraminifera have been used to demonstrate the biological response to cyclicity. Eostaffellids, archaediscids, unilocular forms and irregularly coiled bilocular forms are the calcareous foraminiferal groups responding the meter-scale cycles.