Oncoidal Facies Across the Carboniferous-Permian Transition (Hadim Nappe, Southern Türkiye): Paleoenvironmental Implications and Correlations

Abstract

The cortoid and/or oncoid-bearing carbonates of the Girvanella Limestone Facies of the Hadim Nappe that were deposited during the early-middle Gzhelian-middle Asselian time interval are represented by a succession that laterally extends over dozens of kilometres and is up to 60 m thick. This facies is easily distinguishable from the facies above and below and is considered a significant sedimentological marker unit by its lithological properties (e.g., brownish-red colour and large oncoids). Eight microfacies types are recognised from the Girvanella Limestone Facies: cortoid grainstone/floatstone, cortoid-bioclastic grainstone/rudstone, cortoid-aggregate grainstone, bioclastic grainstone to packstone, oncolite packstone/rudstone, oncoid grainstone/floatstone, mudstone/wackestone, and algal fenestral bindstone that are indicative of moderate to high-energy shallow marine carbonate platform settings (e.g., sand shoals and bank zone and lagoon-peritidal zone). Oncoid-bearing facies across the Carboniferous-Permian transition in the Hadim Nappe show a well correlation with similar deposits from South China, Iran, Mexico, Carnic Alps (Austria), and Japan. This widespread and synchronised deposition of the oncoid-bearing facies corresponds to the major phase (Glacial period III) of the Late Palaeozoic Gondwana glaciation and global sea-level drop associated with this glaciation.