cross-stratification. In some places, the sediment's grain size increases significantly as it goes towards upper layers, getting coarser and eventually giving way to conglomerate. Glover and Robertson interpreted the Çalkaya Formation as "a combination of the Pliocene Alakilise and Eskiköy Formations", but Kaya interpreted it as a separate formation since there is "no observable direct contact between them". The presence of pebbles "bored by sponges and marine bivalves" led Glover and Robertson to conclude that the Çalkaya Formation, like the Yenimahalle Formation below it, was marine in origin. Fossils found in the Çalkaya include foraminifera, ostracods, and "abundant" bivalve and gastropod mollusks. These are similar to the Yenimahalle Formation, and the Çalkaya Formation has been dated to the Pliocene or Upper Pliocene. Tufa deposits The southwestern boundary of the Aksu Basin is marked by a 30 km by 40 km area of tufa and travertine deposits. This area includes the city of Antalya as well as an undersea portion submerged beneath the Gulf of Antalya. The deposits get progressively thicker towards the west — from 30 m thick in the east to 250 m thick in the west. No absolute age is given for these deposits, but they lie conformably on top of the Çalkaya Formation. The lowermost tufa deposits are made of "clay-rich microcrystalline carbonates, containing gastropod and algal fossils". Two sets of "conjugate oblique-slip faults" run northwest-southeast and northeast-southwest along the length of the entire formation. These deposits were formed by cold springs in the early Pleistocene. Belkis Conglomerate The youngest unit in the Aksu Basin is the Belkis Conglomerate, which only has visible outcroppings in the basin's southern part, in the Yenimahalle-Çalkaya sub-basin. It lies unconformably on top of the Yenimahalle and Karpuzçay Formations. In composition, the Belkis Conglomerate is similar to the conglomerate portions of the Yenimahalle Formation. It is "highly heterogenous and composed mainly of clasts of Cretaceous limestone, serpentinite, and chert in a poorly sorted sandstone-siltstone matrix". The ancient city of Aspendos was built on top of the Belkis Conglomerate, and its stone structures were originally quarried from here. The Belkis Conglomerate is Pleistocene in origin, described as "fluvial terraces", and formed by "deposition in fluvial floodplains and channels along the ancestral Aksu River, together with regional uplift". Specifically middle Pleistocene. Other features Eskiköy canyon The Eskiköy canyon, about 50 km north of Antalya, is from the pre-Pliocene. The canyon had its origins in