THE CONGLOMERATE MEMBER OF THE GOKCEOREN FORMATION, OREN BASIN, WESTERN TURKEY: ITS AGE, SEDIMENTOLOGY AND TECTONIC SIGNIFICANCE

Exposed along the northern margin of the Golf of Gökova in the vicinity of the town of Oren, western Turkey, is about 150 meters thick, cobble to boulder conglomerate composed mostly of the clasts of limestone, marble, and low grade (phyllite) metamorphic rocks of the Licyan nappes. We studied this conglomerate, in detail, in terms of its stratigraphy, sedimentalogy and tectonic significance. The conglomerate is generally poorly sorted and contains clasts up to 1 meter in diameter in its basal part. The clast size gets generally gets smaller upward where it contains sandstone lenses. The conglomerate unconformably overlies the marbles of the Licyan Nappes. The northern boundary of the conglomerate is a down to south normal fault system that was probably responsible for the deposition of the unit. Our preliminary interpretation is that this conglomerate is a submarine alluvial fan deposit. The conglomerate was mapped as part of the Gokceoren formation and assigned a Late Oligocene age by Gurer and Yilmaz (2002).

A recent geophysical study by Kurt, Demirbag and Kuscu (1999) shows the presence of a major down to the north fault, Datca fault, along the southern margin of the Golf of Gokova. The Datca fault has a large rollover anticline and antithetic faults associated with it. The fault controls the deposition in the Golf of Gokova and is assigned a Latest Miocene-Pliocene age. The fault system that controlled the deposition of the conglomerates of the Gokceoren formation strikes parallel to subparallel to Datca fault. Therefore, we interpret this fault system as the antithetic faults of the Datca fault. If this interpretation is correct, the Datca fault must be as old as Late Oligocene in age. This, in turn, suggests that the N-S extension in western Turkey was initiated in Late Oligocene.