Depositional stages of the Eğribucak inner basin (terrestrial to marine evaporite and carbonate) from the Sivas Basin (Central Anatolia, Turkey)

Abstract

The Sivas Cenozoic Basin and coeval Central Anatolian basins such as Çankırı and Tuz Gölü are characterized by both marine and terrestrial sediments ranging in age from the Eocene to early Miocene. The evaporite regime here generally appeared during the late stage of Eocene transgression and persisted through the Oligocene time. However, marine-induced Oligocene evaporites are less known because of less paleontological evidence and regional tectonics and salt diapirism that mostly caused the destruction of their original stratigraphic positions. The Eğribucak area studied here, located about 25 km southeast of Sivas , provides a well-stratified key section to shed light on the depositional history of the Oligocene marine evaporite (coastal lagoon or sabkha complex) and other associated carbonate and siliciclastic units. The Eğribucak succession has a thickness of approximately 400 m and rests on thick fluviatile sediments commencing with red beds (mudstone, sandstone, and gravelly sandstone), and upwards, terrestrial gypsums are present within the red units as thin beds that are overlain by thick marine gypsum beds with rhythmical alternations of gray and green colored sandstone- marly limestone and limestone. The limestones alternating with the thick gypsum beds are rich in benthic foraminifers yielding a Rupelian-Chattian age. At the top of the section evaporites disappeared and lagoon-type limestone turned into thick platform carbonate dated as Oligocene-early Miocene. The Eğribucak succession shows a wide variety of depositional environments ranging from terrestrial to restricted marine to open marine from bottom to top. The short periods of the lithological alternations from siliciclastic to carbonate and evaporite indicate that the evaporite environment was not consistent through the Oligocene period. This would be formed as a marginal evaporite environment, presumably a coastal lagoon/sabkha affected by seasonal variations with arid and humid periods as well as eustatic sea-level changes. The Oligocene transgression culminated in the area with the deposition of platform-type carbonates and it continued during the early Miocene.

The Sivas Cenozoic Basin and coeval Central Anatolian basins such as Çankırı and Tuz Gölü are characterized by both marine and terrestrial sediments ranging in age from the Eocene to early Miocene. The evaporite regime here generally appeared during the late stage of Eocene transgression and persisted through the Oligocene time. However, marine-induced Oligocene evaporites are less known because of less paleontological evidence and regional tectonics and salt diapirism that mostly caused the destruction of their original stratigraphic positions. The Eğribucak area studied here, located about 25 km southeast of Sivas , provides a well-stratified key section to shed light on the depositional history of the Oligocene marine evaporite (coastal lagoon or sabkha complex) and other associated carbonate and siliciclastic units. The Eğribucak succession has a thickness of approximately 400 m and rests on thick fluviatile sediments commencing with red beds (mudstone, sandstone, and gravelly sandstone), and upwards, terrestrial gypsums are present within the red units as thin beds that are overlain by thick marine gypsum beds with rhythmical alternations of gray and green colored sandstone- marly limestone and limestone. The limestones alternating with the thick gypsum beds are rich in benthic foraminifers yielding a Rupelian-Chattian age. At the top of the section evaporites disappeared and lagoon-type limestone turned into thick platform carbonate dated as Oligocene-early Miocene. The Eğribucak succession shows a wide variety of depositional environments ranging from terrestrial to restricted marine to open marine from bottom to top. The short periods of the lithological alternations from siliciclastic to carbonate and evaporite indicate that the evaporite environment was not consistent through the Oligocene period. This would be formed as a marginal evaporite environment, presumably a coastal lagoon/sabkha affected by seasonal variations with arid and humid periods as well as eustatic sea-level changes. The Oligocene transgression culminated in the area with the deposition of platform-type carbonates and it continued during the early Miocene.