Reconstruction of a Late Jurassic-Early Cretaceous carbonate platform margin with composite biostratigraphy and microfacies analysis (western Sakarya Zone, Turkey): Paleogeographic and tectonic implications

During Late Jurassic-Early Cretaceous the Pontides were the site of a wide carbonate platform facing the Tethys ocean in the south. In the western Pontides the Upper Jurassic-Lower Cretaceous shallow marine carbonates abut the Tethyan İzmir-Ankara suture with no evidence for platform margin deposits. The Sivrihisar klippe 50 km south of the İzmir-Ankara suture preserves a record of the missing platform margin. In the Upper Jurassic-Lower Cretaceous carbonates exposed in this Sivrihisar klippe, two coeval but dissimilar rock packages, separated by a thrust fault, have been detected. The lower succession is composed of Kimmeridgian-Valanginian slope to basin deposits. Within these carbonates the following biozones are defined: Globuligerina oxfordiana - Mohlerina basiliensis Zone (Kimmeridgian), Saccocoma Zone (lower Tithonian), Protopeneroplis ultragranulata Zone (upper Tithonian), Crassicollaria Zone (massutiana Subzone - uppermost Tithonian), Calpionella Zone (alpina, Remaniella, elliptica Subzones - lower Berriasian), Calpionellopsis Zone (simplex, oblonga Subzones - upper Berriasian) and Calpionellites Zone (darderi Subzone - lower Valanginian). These slope to basin deposits are overthrust from north to south by Kimmeridgian shallow marine carbonates. Within this unit Labyrinthina mirabilis - Protopeneroplis striata Zone (Kimmeridgian) is recognized. Based on the distribution of microfacies types and fossil assemblages, a Kimmeridgian-Valanginian depositional model is proposed for the western Sakarya Zone Carbonate Platform (SCP). The position of the studied sections with respect to the SCP, biofacies and microfacies associations suggest that the studied basin and slope deposits represent the remnants of the southern margin and slope of this carbonate platform largely truncated by erosion. The slope and basinal carbonates overthrusted by the coeval shallow marine deposits in a region situated to the south of the main İzmir-Ankara suture indicates an important imbrication and shortening related to the closure of the Tethys ocean.