Tectonic-sedimentary development of the Upper Cretaceous-Middle Eocene K?r?kkale Basin, Central Anatolia, Turkey

Central Anatolia, Turkey, lies in the Alpine-Himalayan orogenic belt and is one of the world’s best localities to study the tectonic-sedimentary processes involved in an ancient continental collision zone. In this area, a strand of northern Neotethys subducted northwards under the Eurasian (Pontide) margin in Late Cretaceous-Early Cenozoic time. Subduction generated ophiolites, magmatic arcs, accretionary prisms and accretionary forearc-type sedimentary basins, now preserved in a wide E-W-trending suture zone which is exposed throughout Central Turkey. However, there is still debate on the timing and mechanism of subduction and continental collision.

In order to reconstruct the tectonic history of the region, we have gathered and synthesised new sedimentary, structural and geochemical field data. One approach is to study the sedimentology, stratigraphy and provenance of a series of Upper Cretaceous-Middle Eocene syn-tectonic basins which are located at the southern margin of the Eurasian margin. The best example is the K?r?kkale Basin, situated ~60 km east of Ankara. This basin developed on a mainly Late Cretaceous subduction-accretion complex and the margin of a Mesozoic microcontinent to the south of a volcanic arc. Basin deposition began with deep-marine Campanian volcaniclastic sediments (750 m) which pass upwards into Maastrichtian calciturbidites (500 m). These sediments represent arc magmatism and the erosion of a shallow-marine carbonate platform to the north. Above come Palaeocene deep-water siliciclastic turbidites (500-800 m) and thin (30 m) units of detached limestone blocks and debris flows which record the erosion of a subduction- accretion complex and an associated coralgal carbonate platform to the north. During Early to Middle Eocene time, shelf-type shallow-water limestones (50 m) and terrigenous siliciclastic sediments (200-300 m) were deposited, typically unconformably on crystalline basement rocks in a shallow-marine deltaic-type setting.

These new data can be used to test and develop current models of Late Cretaceous subduction processes in this region, where existing models point to either: 1) a stationary, north-dipping subduction zone which was active beneath the Eurasian margin and generated continental margin magmatism or; 2) a north-dipping subduction zone which was active beneath the Eurasian margin and subsequently migrated (rolled back) southwards triggering intra-oceanic arc magmatism. Based on the oceanic provenance of basin-fill sediments during subduction, the evidence presented here is consistent with option 2.