Miocene transgression in the central and eastern parts of the Sivas Basin (Central Anatolia, Turkey) and the Cenozoic palaeogeographical evolution

Abstract

International audienceWe present here a reappraisal of the tectonic setting, stratigraphy and palaeogeography of the central part of the Sivas Basin from Palaeocene to late Miocene. The Sivas Basin is located in the collision zone between the Pontides (southern Eurasia) and Anatolia (a continental block rifted from Gondwana). The basin overlies ophiolites that were obducted onto Anatolia from Tethys to the north. The Central Anatolian Crystalline Complex (CACC) experienced similar ophiolite obduction during Campanian time, followed by exhumation and thrusting onto previously emplaced units during Maastrichtian time. To the east, crustal extension related to exhumation of the CACC created grabens during the early Tertiary, including the Sivas Basin. The Sivas Basin underwent several tectonic events during Paleogene–Neogene. The basin fill varies, with several sub-basins, each being characterised by a distinctive sequence, especially during Oligocene and Miocene. Evaporite deposition in the central part of the basin during early Oligocene was followed by mid-late Oligocene fluvio-lacustrine deposition. The weight of overlying fluvial sediments triggered salt tectonics and salt diapir formation. Lacustrine layers that are interbedded within the fluviatile sediments have locally yielded charophytes of late Oligocene age. Emergent areas including the pre-existing Sivas Basin and neighbouring areas were then flooded from the east by a shallow sea, giving rise to a range of open-marine sub-basins, coralgal reef barriers and subsiding, restricted-marine sub-basins. Utilising new data from foraminifera, molluscs, corals and nannoplankton, the age of the marine transgression is reassessed as Aquitanian. Specifically, age-diagnostic nannoplankton assemblages of classical type occur at the base of the transgressive sequence. However, classical stratigraphic markers have not been found within the planktic foraminiferal assemblages, even in the open-marine settings. In the restricted-marine sediments, there are rich planktic foraminiferal assemblages of classical type but these are of little use in stratigraphy. In contrast, the gastropod fauna indicate a Burdigalian age. Sediment reworking in the restricted-marine environments precludes stratigraphic determination. In such environments, micro- and nano-organisms experienced atypical developmental conditions. The small benthic foraminifera and associated ostracod assemblages are good indicators of salinity which varied considerably within the restricted-marine sub-basins. Some of the corals within the coralgal reefs barriers are also dated as Aquitanian. A combination of the salt tectonics and the late Miocene north-westward-verging thrusting created the present basin complexity

Paleomagnetic constraints on the timing and distribution of Cenozoic rotations in Central and Eastern Anatolia

“…Salt mobility led to strong local deformation and the formation of mini-basins (Callot et al, 2014;Kergaravat et al, 2016;Pichat et al, 2016;Poisson et al, 2016;Ribes et al, 2015). In the west, upper Miocene to recent volcanic rocks are found close to the EFZ and its connection to the Sivas fold-andthrust belt (Cater et al, 1991;Poisson et al, 1996;Yilmaz and Yilmaz, 2006).…”

“…3 and 8), north of which rotations are variable but generally clockwise, rotating as much as ∼ 30 • in the central and northern part of the basin (Gürlevik, Ulaş, Sivas, Kemah localities). Explaining the variable clockwise rotations is not straightforward, but well-documented intense deformation in part associated with intense local salt tectonics (Kergaravat et al, 2016;Pichat et al, 2016;Poisson et al, 2016;Ribes et al, 2015) may provide an explanation. We note, however, that one Oligocene locality (Güllük) to the north of the DTFZ reveals the counterclockwise rotations characteristic of the area to its south.…”

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

“…In this area, Cenozoic units commenced with massive gypsum formed as a transitional level from the Eocene to Oligocene (Hafik Formation: Kurtman, 1973) and upward, it grades into Oligocene sediments displaying lateral and vertical facies changes and different environmental conditions. The study area is considered as the Eğribucak inner basin (sensu stricto mini basin: Ringenbach et al, 2013;Callot et al, 2014;Poisson et al, 2015;Ribes et al, 2015) because of limited extension of lithological units and an isolated character from the neighboring depositional systems within the Sivas Basin. The evaporites exposed in the Eğribucak succession have been determined in various environments attributed to different ages ranging from early Miocene to middle Miocene (Table 1).…”

“…The late Eocene regression-associated tectonic activity constrained the basin-range upliftings that divided the basin into subbasins such as Akçakışla-Düzyayla, Şarkışla-Celalli, and Akkışla-Altınyayla (Cater et al, 1991;Yılmaz and Yılmaz, 2006). The Eğribucak area was previously determined as a minibasin that resulted from salt tectonism or a diapir-bounded local basin (Ringenbach et al, 2013;Callot et al, 2014;Poisson et al, 2015;Ribes et al, 2015). Environmental and lithological correlations are very difficult to establish between these inner/minibasins due to their own depositional characters.…”

“…The evaporite is questionable within the red-siliciclastic succession. In the study of Poisson et al (2015) the origin of evaporites was accepted as terrestrial. Our findings are generally arguing with marine origin related to the initial phase of the Oligocene transgression towards a fluvial fan (Hayward, 1985).…”