Fossils found in the Çalkaya Formation are basically the same as those found in the Yenimahalle Formation. In general, gastropod and bivalve fossils in The Aksu Basin is a sedimentary basin in southwestern Turkey, around the present-day Aksu River. Located at the intersection of several major tectonic systems, in the Isparta Angle, the Aksu Basin covers an area of some 2000 square kilometers. Together with the Köprü Çay Basin and the Manavgat Basin, the Aksu Basin forms part of the broader Antalya Basin. It forms a graben relative to the surround By the… By the Early Miocene, a "right-lateral transform fault plate boundary" had formed between the Cyprus Trench and the Isparta Angle. This led to the creation of "a hybrid, terrestrial-shallow marine accommodation space" on the eastern side of the Isparta Angle, where sediments from the Antalya Complex further east were deposited. In the Middle Miocene (c. 16-11 MYA), the Aksu Basin was formed as a graben cutting through the Karabayir platform. Meanwhile, the surrounding continental areas were being pushed upward; erosion from these areas provided a lot of sediment that was poured into the emerging Aksu Basin. According to Kaya, this was especially the case with the rapidly uplifting Antalya Complex to the east; it "provided the topographic gradient and gravitational potential energy for the necessary fluvial erosion and transport for sediment supply". Poisson et al. instead highlight the basin's northern and western margins, where a series of fan deltas at prehistoric river mouths left thick sediment deposits – for example, the present-day Kapıkaya and Kargı fan deltas. The Aksu and Karpuzçay Formations were deposited during this period in what Kaya describes as "fluvial, deltaic to beach environments". Coral reefs fringed the coastline. These reefs lay on a "warm, well-aerated shallow marine shelf" in the photic zone. The low species diversity – primarily colonies of Porites and Tarbaellastraea – may indicate a "stressed" environment. The shore was "medium-high wave energy-dominated", and the climate was temperate to subtropical. The presence of coral fossils among the fan delta deposits is likely from periods when sudden sea level increase left the deltas underwater. Traces of coral reefs at Kargı and Sütçüler have been dated to Late Tortonian times. Around 5.6 MYA, the Mediterranean region was hit by the Messinian salinity crisis. Sea levels dropped tremendously, and there was rapid erosion and desiccation. Growth of the fan deltas stopped as the receding coastline left the entire Aksu Basin on land. Deep gorges were carved in the areas that were now exposed as dry land. One of them, now a deep undersea canyon in the Gulf of Antalya, is still traceable in front of the present day Düden and Karaman river mouths. A similar canyon likely existed on the Aksu, but it has since been buried by Quaternary sedimentation on the marine shelf. Poisson et al. reconstructed the course of the Aksu River around the end of the Messinian (c. 5.3 MYA) this way: the river flowed through the Eskiköy Canyon, then "crossed the Antalya alluvial plain before joining the Antalya abyssal plain, through the actively cutting Antalya canyon". Poisson et al. also argued that the Gebiz Limestone was formed during the Messinian, implying that there was still at least a pocket of sea in the Aksu Basin even while the sea retreated. They characterize this environment as "very shallow marine", with coral reefs, which then gradually became more restricted as it gave way to land and eventually dried up completely. This characterization is disputed – Üner et al. instead describe the Gebiz Limestone as being deposited after sea levels rose again; Kaya attributes the Gebiz Limestone to the "latest Miocene-early Pliocene", describing it as being deposited by a NW-SE-oriented lake that formed during this period. According to Kaya's interpretation, the Aksu Basin was a "fluvial, fluvial-delta, beach setting" during the Middle Miocene (c. 16-11 MYA), then "a lacustrine and lagoon environment" by the end of the Miocene (i.e. c. 5.3 MYA). Then, during the early Pliocene (c. 5.3-3.6 MYA), there was a relatively brief (at least geologically speaking) period of tidal flat and very shallow marine conditions. Later, there was a "return to entirely terrestrial conditions", and deposition by the ancient Aksu River formed the Belkis Conglomerate during the Pleistocene period. The Antalya Tufa was formed by cold springs in the early Pleistocene. This deposition happened "after extensional faulting had largely ceased within the main Aksu Basin". Some depositional features about the Antalya Tufa, such as the lack of detrital material, indicate that the waters originated from springs instead of as run off from the surrounding mountains. In addition, "The location of the palaeo-Aksu River with its coarse sediment input might explain why tufa was not deposited further east". Extensive karst systems supplied large volumes of water that had been supersaturated with carbonates, from the carbonate geology in the nearby Taurus Mountains. These waters came from lakes further north (as much as 100 km away), as well as from a now-dry polje system further south at Kestel. A cluster of springs at Kırkgöz ("forty springs"), in the northwestern part of the Aksu Basin, was one of the main sources where these carbonated waters came to the surface, but other springs no doubt also existed. At this time, the Aksu plain would have been dominated by lakes and wetlands, with water depths ranging from centimeters to meters. In some local depressions, water may have been up to 20 m deep. Various small rivers and streams, no more than about 10 m wide, meandered across a relatively flat plain, "constantly reworking friable carbonate deposits through which they passed". At first, tufa deposition was probably restricted to small lakes, such as near Kırkgöz. On the basin's eastern margin, deposition was primarily