Abstract

The KuÅŸçular formation (early Paleocene) around Baskil and Keban (ElaziÄŸ) in the Eastern Taurids represents alluvial fan and playa lake facies that were deposited in an intermontane foreland basin. The formation with a total thickness of up to 585 m consists of seven lithofacies of massive conglomerates, stratified conglomerates, massive sandstones, stratified sandstones, red mudstones, nodular gypsiferous mudstones and stratified gypsum. These lithofacies are represented by deposits of alluvial fan lithofacies assemblage (inner, medial and outer fan lithofacies assemblage) and dry mud flat-saline playa lake lithofacies assemblage. The northern part of the basin which is the source region for the deposition of alluvial fan deposits is surrounded by highly elevated topography. Therefore, distribution of alluvial fans to the basin and transport of the sediments were from the source region to the north. At the beginning of deposition, fan deposits show a lateral distribution from the margin to the centre of basin (from proximal to distal). Distal deposits reaching the centre of basin and gypsiferous playa lake deposits at the centre are in lateral and vertical transition. In the proceeding periods, due to intense tectonism, uplift and rejuvenation of sediment supply from the source, middle and proximal fan deposits advanced to the centre of basin where they covered the deposits of initiation period. Thus, a megasequence with grain-size coarsening upward developed in the basin. The soft-sediment deformation structures (for example slump folds), which are commonly observed in playa and distal fan deposits of this sequence indicate that seismicity was quite active in the early Paleocene. This seismic activity may have resulted from activity along the Pertek thrust fault that controls the basin to the north. The Ergani-ElaziÄŸ-Malatya-Elbistan branch of the Neotethys Ocean started to close due to northward directed subduction in the upper Cretaceous and at the end of this period the ElaziÄŸ magmatic arc collided with the Keban continental plate. In association with the compressional tectonic regime resulting from this collision, the Keban metamorphics were thrusted southward onto the ElaziÄŸ magmatics along the Pertek thrust fault. The KuÅŸçular formation is composed of synorogenic-syntectonic sediments that were deposited in a tectonically-controlled, rapidly-filled intermontane basin in front of this thrust fault. This sequence with a grain size coarsening upward indicates the presence of a progradational alluvial fan and rapidly-filling, tectonic-controlled basin which is seismically active.

Key words: Alluvial fan, KuÅŸçular formation, Eastern Turkey, intermontane foreland basin.