ARE THE EAST-WEST TRENDING GRABENS OF THE WESTERN ANATOLIA EXTENDED TERRANE, TURKEY, SYMMETRICAL STRUCTURAL FEATURES?

The Western Anatolia Extended Terrane, Turkey, contains two main east-west trending extensional basins that were formed during the Cenozoic extension in the region. They are named as Alasehir (Gediz) and Buyuk Menderes Grabens (BMG). The two grabens usually considered as symmetrical structures formed in Early Miocene and developed by similar structural processes; they were considered as supradetachment basins developed along the north and south-dipping detachment surfaces respectively.

During this investigation, seven depth-converted 2-D seismic reflection profiles and well log data from one well are used to delineate the geometry of the subsurface structural features and the Cenozoic stratigraphy of the eastern part of the BMG. Depth converted seismic profiles indicate ~2100 meters (m) thick Early Miocene to recent sedimentary rock units in the BMG. The south-dipping normal fault along the northern margin of the BMG has been active probably since Miocene. The Miocene to Pliocene sedimentary units show thickness variations along the N-S cross-sections constructed based on the structural interpretation of the seismic data. The Neogene units are thickest in the center of the graben, and illustrate a wedge-shaped geometry towards the north and south-dipping graben bounding faults flanking the graben. Due to this geometry, syn-sedimentary extension in the graben has not formed a rollover structure and associate extensional folds and faults.

The subsurface structural geometry of the BMG contrasts with the structural geometry of the Miocene to recent sedimentary units in the Alasehir Graben (AG) which contains a thicker (3000 m) sedimentary succession, a rollover structure. Although the AG and BMG may have started to form simultaneously in Early Miocene time during the Cenozoic extensional phase in the region, they do not contain symmetrical structural features. The BMG may have developed as a rift basin while the AG formed as a supradetachment basin.