Facies partitioning and stratal pattern in salt-controlled marine to continental mini-basins: Examples from the Late Oligocene to Early Miocene of the Sivas Basin, Turkey

Abstract

The Sivas Basin (Turkey) records a complex interaction between sedimentation, salt tectonics and regional shortening leading to the formation of numerous mini-basins. The segmentation into mini-basins was initiated during the Oligocene by the deposition of the fluvio-lacustrine Karayun Fm. This continental succession is overlain abruptly by an Oligo-Miocene shallow marine succession Karacaoren Fm, which comprises two main sub-environments: (i) mixed deltaic and carbonate ramp, (ii) coastal plain and lagoon. The Karacaoren Fm, forms a marine succession more than 1500 m thick that passes vertically upwards into a continental succession, the fluvial-dominated Benlikaya Fm. These two formations are the focus of the present study. During the period of marine sedimentation, the competing accumulation of carbonates and clastics is related not only to the topography inherited from salt tectonics, but also to relative sea-level variations expressed by two large-scale transgressive regressive cycles. We analyse these complex facies and stratal relationships to illustrate the modifications induced by salt tectonics. This study is based on extensive fieldwork and mapping making use of numerous measured stratigraphic sections and aerial photos over a large area comprising more than fifteen adjacent outcropping mini-basins. The aim of this study is to provide a detailed description of the stratigraphic relationships, correlations and sedimentary systems distribution in mini-basins during deposition of the Oligo-Miocene shallow marine and continental successions. We first clarify the vertical stratigraphic succession of the Oligo-Miocene marine and continental deposits and establish correlations between the studied mini-basins. These correlations then allow us to characterize and assess the local effects of salt withdrawal in relation to the regional forcings associated with flexural subsidence, tectonic shortening and relative sea-level changes. An improved understanding of the complex interactions of these variables provides a framework to distinguish the mechanisms that control facies distribution and stratal geometry in salt basins.