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

The stratigraphy of the uppermost levels of the Menderes Massif is controversial and within its details lie vital constraints to the tectonic evolution of south-western Turkey. Our primary study was carried out in four reference areas along the southern and eastern Menderes Massif. These areas lie in the upper part of the Menderes metamorphic cover and have a clear stratigraphic relationship and contain datable fossils. The first one, in the Akbük±Milas area, is located south-east of Bafa Lake where the Milas, then Kõzõlag AE aç and Kazõklõ formations are well exposed. There, the Milas formation grades upwards into the Kõzõlag AE aç formation. The contact between the Kõzõla-g AE aç and the overlying Kazõklõ formation is not clearly seen but is interpreted as an unconformity. The Milas and Kõzõlag AE aç formations are also found north of Mug AE la, in the region of Yatag AE an and Kavaklõdere. In these areas, the Milas formation consists of schists and conformably overlying platform-type, emery and rudist-bearing marbles. Rudists form the main palaeontological data from which a Santonian±Campa-nian age is indicated. The Kõzõlag AE aç formation is characterized by reddish±greyish pelagic marbles with marly-pelitic interlayers and coarsening up debris flow deposits. Pelagic marbles within the formation contain planktonic foraminifera and nanoplankton of late Campanian to late Maastrichtian age. The Kazõklõ formation is of flysch type and includes carbonate blocks.

A schist sequence of the central Menderes Massif, in which lenses of fossiliferous marbles are found, is observed in the southern flank of the Aydın Mountain, north of Köşk (Aydın), around Egrikavak village. These rocks have been considered as Permo-Carboniferous in age and are included in the Göktepe Formation of earlier studies. However, some rudist species are described from thickly bedded gray marbles that have a concordant contact with the overlying schist sequence. Although the rudists have been metamorphosed, it is observed that some contain fossils are well enough preserved to determine the following rudist fauna: Hippurites lapeirousei (GOLDFUSS), Hippurites nabresinensis FUTTERER, Hippurites cf. colliciatus WOODWARD. This rudist fauna dates the schist sequence as SantonianCampanian. The schist sequence is overlain by a thick tectonostratigraphic pile of orthogneiss which has been interpreted as the Pan-African metamorphic core of the Menderes Massif. A widespread cataclastic and mylonitic zone is present between the underlying rudist-bearing marbles and the structurally overlying orthogneiss sequence. The existing kinematic studies in the footwall and hangingwall of this tectonic contact reveal two different phases of deformations, a contractional phase followed by an extensional phase. During the contractional event, which occurred at 36 Ma, the orthogneiss sequence was thrust faulted northwards over the schist sequence. This thrust fault was later reactivated as a low-angle normal fault beneath a supradetachment sedimentary basin of Early-Middle Miocene age. The fossil discoveries of this study and the existing kinematic studies reveal that a new structural model for the central Menderes Massif in which the tectonometamorphic units form a major southward closing recumbent fold needs to be reviewed.

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