The Upper Cretaceous to Palaeogene Sedimentary History and Tectonic Evolution of the Bala Basin, Central Anatolia, Turkey

Abstract

The study area is situated on the northern extension of the Tuzgolu basin, (Central Anatolia) and contains Upper Cretaceous--Tertiary volcanic, clastic, and carbonate rocks with evaporites deposited on an ophiolitic melange basement, the Ankara Melange. The present structure of the area is the result of tectonism during late Alpine movements. The movements controlled the timing and conditions of sediment accumulation.

The Bala basin evolved on the northern continental margin of the Kirsehir block. A brief period of south dipping subduction, which originated a continental island arc, was followed by oblique subduction, transform fault and continent to continent collision stages. These determined the shape and depositional characteristics of the basin. This is supported by independent magnetic evidence which suggests a 90° anti-clock wise rotation of the Kirsehir block during the Upper Cretaceous--Eocene period.

Deposition of sediments occurred in two phases. The Upper Cretaceous--Middle Eocene phase contains seven formations, Four are believed to have been deposited in a deep marine environment by mass movements and turdidity currents sometimes forming submarine fans, and two are shallow marine to continental deposits. The seventh is composed mainly of Andean type calcalkaline volcanic rocks and their pyroclas-tics and was formed by subaerial lava flows. The formations reflect conditions of deposition in different parts of the basin and therefore some are the time equivalent of others. The Middle Eocene to probably Oligocene phase consists of two interfingering formations deposited in continental and marine environments of deposition.

Palaeocurrent and petrographic data suggest that during the first phase, the source area was to the southeast and formed by volcanic rocks of Sarikaya formation and Ankara Melange, while in the second phase sediments were derived