or faulted against them. The Eskiköy Formation primarily consists of sandy conglomerate and sandstone, with interspersed layers of mudstone. The conglomerate is "poorly sorted with mostly rounded pebbles and clasts of Jurassic micritic limestone, and Triassic chert and basaltic rocks". The formation's maximum depth is estimated at approximately 300 m. Akay et al interpreted the Eskiköy Formation as a lateral equivalent of the Gebiz Limestone, meaning that they date from the same time. Fossils found in the Eskiköy Formation's marl include several species of planktonic foraminifera: Orbulina, Biorbulina, Globigerinoides (multiple species: trilobus, obliquus extremus, obliquus s.s., bollii, emeisi, and aperture), and Globigerinita incrusta. Based on these planktonic foraminifera fossils, Poisson et al dated the formation to the Upper Miocene, which is consistent with Akay et al's interpretation. Yenimahalle Formation The Yenimahalle Formation is best exposed in two areas: around Yenimahalle in the southwestern part of the Aksu River valley, and around Gebiz in the east. It lies conformably on top of the Gebiz and Eskiköy Formations; i.e. they are not separated by an unconformity. The Çalkaya Formation sits on top of it. Around the village of Dorumlar, the Yenimahalle Formation is overlain by the Belkis Conglomerate, with an unconformity between them. The total thickness of the Yenimahalle Formation is about 250 m. The Yenimahalle Formation is made up of "blue-grey siltstone with embedded sandstone and graded gravelstone". There is also conglomerate included in the formation's upper layers. Characteristic features of the Yenimahalle formation include "low-angle cross-bedding and lamination, trough cross-bedding, ripple lamination, fining upwards sand channels, and gravel/conglomerate lenses". In some places, sandstone concretions are common. The presence of "Margaritae and Punctulate zones" in lower parts of the formation near Gebiz indicate that the formation can be dated to the Lower Pliocene. A number of fossilized bivalve and gastropod mollusk shells have been found in the Yenimahalle Formation, including Acanthocardia, Ostrea, Cerastoderma edule, Paphia, Dentalis, Gibbula, Fusinus, and Pectens. Glover and Robertson interpreted the Yenimahalle Formation as "the product of a shallow marine environment". Çalkaya Formation The Çalkaya Formation rests on top of the Yenimahalle Formation and consists of marly siltstone, sandstone, and conglomerate. Its lower part is similar in composition to the upper part of the Yenimahalle Formation. Siltstone layers in the Çalkaya Formation are interspersed with coal seams measuring 25-30 cm in thickness. Common features of the Çalkaya Formation include "low-angle cross-bedding, through cross-bedding, ripple lamination, and hummocky