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

Abstract

This study reports on the Sinanpaşa Basin, a typical example of the Miocene tectonic intracontinental grabens formed inWest Anatolia, Turkey. The study reconstructs the paleoenvironmental and paleogeographic history of the graben based on a detailedsedimentological analysis of basin-fill deposits exposed mainly near the graben’s northern and southern margins. The sedimentarypaleoenvironments in the graben range from basin-margin alluvial fan systems and basin-axis fluvial distributary system to anintrabasinal shallow lake environment surrounded by peat-forming mires, changing from carbonate to more clayey, episodicallyevaporitic, and shifting its shorelines considerably. The spatial distribution and stratigraphic stacking of these paleoenvironmentsindicate the main controlling role of climatic changes and an asymmetrical “see-saw” tectonic subsidence of the graben floor. Animportant component of the sedimentation in the graben was volcanism, which probably commenced in the late Early Miocene andwas 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 lavaflow breccias, and water-bearing lahars. The volcanic deposits made the intrabasinal lake struggle for accommodation space withinthe graben, while the ash tephra and related hydrothermal activity had a major impact on the lake water chemistry. B- and U-bearingevaporites formed episodically in drying lake areas, reaching economic thicknesses in several adjacent sister grabens. The SinanpaşaBasin is a representative example of the Miocene tectonic grabens of West Anatolia, and its sedimentation model suggested by thepresent study may serve as a tentative reference case for the region’s numerous sister grabens, helping to understand their sedimentationconditions, environmental changes, and lithostratigraphic facies organization.