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Controls on Sedimentation of a Fluvial System: the Case of Salt Related Mini-basins (Sivas, Turkey).

Abstract

Understanding the influence of salt tectonics on fluvial or marine sedimentary successions and the associated stratal geometry as well, is fundamental for hydrocarbon exploration and reservoir prediction in mini-basins. However, a limited number of mini-basins provinces have been described, especially with fluvial dominated infill. Most of the published papers refer to the three following classical examples: the Paradox Basin (USA), the PriCaspian basin (Kazakhstan), and the German and North Sea Permo-triassic basins. A spectacular outcrop analogue, recently re-interpreted, is the mini-basin province of the Sivas basin (Central Anatolian plateau, Turkey). The Sivas basin is an elongated Oligo-Miocene basin showing numerous mini-basins separated by evaporites structures such as welds and diapirs of various shapes. The mini-basins can be precisely mapped with aerial photos and fieldwork and these record a variability of fluvial dominated facies constituting the infill of the basins. Our work focuses on six of the mini-basins entirely exposed, which present a 1km to 2.5km sedimentary pile of continental sediment unconformably capped by a transgression. The infill of these mini-basins began during the late Oligocene over an older basal salt layer, with (1) a playa-lake system deposited under arid climatic conditions (sheet-flood and evaporites), followed by (2) a braided fluvial system occurring during a humid period (Karayün Fm), (3) then a lacustrine system that is finally capped by (4) shallow marine deposits (Karacaören Fm.) during the Early Miocene. The abrupt facies changes bounding stratigraphic units are related to base level changes in relation with regional climatic events modified locally by salt tectonics. Climatic-driven and regional tectonics (basin-wide events) variations modify the rate and style of sediment supply and the regional subsidence, but all this events are recorded in a coeval manner by the fluvial system in each mini-basin. In contrast, the salt tectonic modify locally sedimentary record and associated stratal pattern within each mini-basin.