Alluvial-lacustrine sedimentation and volcaniclastic deposition in an intracontinental tectonic graben: paleoenvironmental evolution of the Neogene Sinanpaşa Basin,west-central Turkey

This study reports on the Sinanpasa Basin, a typical example of the Miocene tectonic intracontinental grabens formed in West Anatolia, Turkey. The study reconstructs the paleoenvironmental and paleogeographic history of the graben based on a detailed sedimentological analysis of basin-fill deposits exposed mainly near the graben's northern and southern margins. The sedimentary paleoenvironments in the graben range from basin-margin alluvial fan systems and basin-axis fluvial distributary system to an intrabasinal shallow lake environment surrounded by peat-forming mires, changing from carbonate to more clayey, episodically evaporitic, and shifting its shorelines considerably. The spatial distribution and stratigraphic stacking of these paleoenvironments indicate the main controlling role of climatic changes and an asymmetrical "see-saw" tectonic subsidence of the graben floor. An important component of the sedimentation in the graben was volcanism, which probably commenced in the late Early Miocene and was related to the development of a local stratovolcano. Volcanic products - accumulated mainly at the graben's northern margin - include variously welded pyroclastic airfall and ground-surge tephra, vent-derived volcanic fluidization breccias, autoclastic lava flow breccias, and water-bearing lahars. The volcanic deposits made the intrabasinal lake struggle for accommodation space within the graben, while the ash tephra and related hydrothermal activity had a major impact on the lake water chemistry. B- and U-bearing evaporites formed episodically in drying lake areas, reaching economic thicknesses in several adjacent sister grabens. The Sinanpasa Basin is a representative example of the Miocene tectonic grabens of West Anatolia, and its sedimentation model suggested by the present study may serve as a tentative reference case for the region's numerous sister grabens, helping to understand their sedimentation conditions, environmental changes, and lithostratigraphic facies organization.