Genesis of the Pliocene conglomerate: Kütahya and Eskişehir—central west Anatolia, Turkey

Abstract

Agate formation in the Pliocene conglomerates is found as nodules in the central western part of Anatolia and is unique in terms of sepiolite replacement. Therefore, the geology, mineralogy, and genesis of agate nodules in polymictic conglomerates from Yazlıca in the Kütahya region are presented in this study. Furthermore, the properties of Yazlıca agate are compared to Dereyalak agate formed in Pliocene conglomerates from the Eskişehir region. Yazlıca agate nodules are formed from three to 30 cm in diameter and have mainly four different colors with a zoned appearance. XRD analyses show that chalcedony is the main silica mineral constituting agates in this region. The existence of sepiolite in agates was detected using XRD analysis in this research. DTA analysis also confirmed endothermic peaks at approximately 724°C and 737°C followed by exothermic peaks at approximately 800°C and 830°C, further indicating that sepiolite exists in Yazlıca agates. Dereyalak dendritic agate nodules were formed in the same period (Pliocene) so the Yazlıca agate formation was compared to the Dereyalak agate formation. This research concluded that both agate occurrences were formed through sepiolite replacement via low-temperature, silica-rich hydrothermal solutions within fracture systems.