Tertiary ophiolite-related sedimentation in S.W. Turkey

Abstract

The Lycian Tauride mountains of S. W. Turkey comprise a central relatively autochthonous carbonate platform unit bordered by two allochthonous units, the Lycian Nappes to the west and the Antalya Complex to the east. From these allochthons thick sequences (`1,000 m) of clastic sedimentary rocks were shed during the Miocene into a basin floored by the subsided carbonate platform.

The Miocene sediments, exposed over ca. 2,500 km², have been mapped at 1:25,000 scale; several hundred sedimentary logs have been measured. Three new formations are recognised; the Kerner and Salir Formation of Lower Miocene age, and the Kasaba Formation of Middle to Upper Miocene age. Individual sedimentary facies are dominated by coarse grained ophiolite-derived sediments of which redeposited and sub aerial conglomerates and sandstones are the most widespread.

Along the western margin of the basin closest to the Lycian Nappe front, the Kerner Formation consists of conglomerates and sandstones deposited within a fan-delta. More distal sequences pass basinwares into small submarine fan systems. The overlying Kasaba Formation was deposited as an alluvial fan which prograded into a shallow sea. Proximal alluvial fan deposits consist of dominantly clast-supported massive conglomerates. These pass downslope into well defined conglomerate-sandstone-mudstone fining-upward units. Shallow marine shelf deposits are the lateral equivalents of this distal fan/braidplain succession. Small patch reefs were developed in the marine sequence during periods of reduced sediment supply.

In more central parts of the basin a thick (-800 m) sequence of redeposited bioclastic breccias was derived from a contemporaneous shallow water carbonate build-up. In the south, limestone conglomerates, calcareous sandstones and mudstones, deposited in a submarine fan environment document the uplift and sub aerial exposure of a large area of the older carbonate platform.

Along the eastern margin of the basin the Salir Formation mainly comprises conglomerates and sandstones deposited by sediment gravity flows on small submarine fans. Above is a conglomerate dominated sequence deposited on a fan-delta.

Palaeocurrents and downslope facies transitions demonstrate that the ophiolitic sediments of the Kemer Formation were derived from the Lycian Nappe ophiolitic unit to the west. Emplacement of this unit onto the carbonate platform in Lower Miocene times evidently resulted in irregular subsidence, with uplift and subaerial exposure of areas of older carbonate platform rocks. The western margin of the basin was progressively overthrust until the nappes finally came to rest in the Late Miocene. The regressive-upwards sedimentary sequence reflects both progressive basin infilling and Late Miocene lowering of sea level.

Along the eastern margin, palaeocurrent analysis and downslope facies transitions show that the Antalya Complex was emplaced from the east but only advanced a short distance beyond the eastern margin of the basin. This is consistent with strike-slip dominated emplacement of the Antalya Complex in contrast to the gravity driven emplacement of the far travelled Lycian Nappes. As the Lycian Nappes and Antalya Complex approached the basin from opposite directions their respective ophiolite units must have been derived from separate, or at least distinct, ocean basins to the north and south respectively, of the carbonate platform now flooring the Miocene basin between them. The wider plate-tectonic implications of this conclusion are investigated briefly.