Neogene sedimentary evolution and biostratigraphy of the Kasaba and Aksu-Gebiz basins in the eastern Mediterranean: Insights from paleontology and Sr isotope stratigraphy

The Kaş-Kasaba and Aksu-Gebiz basins are two important Neogene basins in the Eastern Mediterranean, flanking the Gulf of Antalya in southwestern Anatolia. Comprehensive studies involving sedimentology, paleontology, and Sr isotopes have offered valuable insights into the sedimentary characteristics and depositional environments of these basins during the Neogene period. In the west, the Kasaba Basin features an early to middle Miocene carbonate-clastic succession that developed on the Late Cretaceous Beydağları autochthon, overlain by Paleocene-Eocene neritic carbonates. In contrast, the Aksu-Gebiz Basin in the east presents a transgressive sequence of middle Miocene to Pliocene clastics and carbonates, which developed on different basement units, including the Mesozoic metamorphosed carbonates and the Antalya Complex in the west. Biostratigraphic studies in the Kasaba (Kaş) region revealed 9 genera and 23 species of planktonic foraminifera in the Kasaba Formation, and 12 genera and 29 species in the Sinekçi Fm., marking the lower boundary of the Orbulina suturalis Lineage Subzone (MMi5a) of the middle Miocene. Similarly, in the Gebiz (Aksu) region, the planktonic foraminifera indicate the lower boundary of the MMi12a Globigerinoides obliquus extremus-Globorotalia suterae Interval Subzone of the late Miocene. Benthic foraminifera indicative of shelf environments were identified in both regions. Whole-rock strontium isotope chemostratigraphy revealed ages ranging from 14.3 to 23.7 Ma based on ⁸⁷Sr/⁸⁶Sr ratios from three key samples. Overall, studies in the Kasaba Basin suggest a lower to middle Miocene age with shallow marine environments, consistent with Serravallian to Langhian periods. In the Aksu-Gebiz Basin, detailed investigations of the Karpuzçay Formation identified a mid-Tortonian age. This age, combined with sedimentological and structural data, provides insights into the basin's tectonic evolution and flexural effects. Planktonic and benthic foraminifera within the sequence reflect inner shelf environments throughout. The strontium isotope analysis of samples from the Aksu-Gebiz Basin revealed significant variations in ⁸⁷Sr/⁸⁶Sr ratios, with ages ranging from the Tortonian (9.0 Ma) to the Messinian (5.3 Ma). By integrating biostratigraphy and whole-rock Sr isotope stratigraphy, this study refines the Neogene chronological framework of the Kasaba and Aksu-Gebiz Basins, providing new insights into the Eastern Mediterranean's geological history. These findings also improve stratigraphic correlations with adjacent basins, offering a more comprehensive regional context.