Foraminiferal biostratigraphy and sequence stratigraphy across the mid-Carboniferous boundary in the Central Taurides, Turkey

Abstract

The Aladag Unit is one of the main tectonic units in the Tauride Belt, located in southern Turkey. It includes a continuous Paleozoic carbonate sequence encompassing the mid-Carboniferous boundary, with outcrops being especially well exposed in the Hadim region. The boundary succession lithology is mainly composed of carbonates with intercalated quartz arenitic sandstone layers. Based on foraminifers, four biostratigraphic zones have been defined in the interval from the Upper Serpukhovian to the Lower Bashkirian. These zones are, in ascending order: the Eostaffella ex gr. ikensis—E. postmosquensis Zone (Zapaltyubinsky Horizon, Upper Serpukhovian); the Plectostaffella jakhensis—P. bogdanovkensis Zone, and the Millerella marblensis Zone (Bogdanovsky Horizon, lower Bashkirian); and the Semistaffella sp. Zone (Syuransky Horizon, lower Bashkirian). The mid-Carboniferous boundary occurs between the Eostaffella ex gr. ikensis—E. postmosquensis Zone and the Plectostaffella jakhensis—P. bogdanovkensis Zone. Boundary beds are characterized by eight, repeatedly occurring microfacies types, namely: (1) coated crinoidal packstone; (2) coated bioclastic grainstone; (3) oolitic grainstone; (4) oolitic packstone-grainstone; (5) intraclastic grainstone; (6) mudstone-wackestone; (7) quartz-peloidal packstone; and 8) quartz arenitic sandstone. Based on microfacies stacking patterns, various types of shallowing-upward cycles have been recognized. Depositional sequences and sequence boundaries are correlatable with those described from North America and Russia and Carboniferous global sea-level curves. The duration of cycles has been estimated as 100 ky, suggesting that cycle periodicities correspond to the Milankovitch eccentricity band.