Abstract: Structural Development of the Gediz and Buyuk Menderes Graben, Western Turkey: Effect of Basinward Migration of Faulting on Half-Graben Sedimentation

Harvey A. Cohen, Chris J. Dart, H. Serdar Akyuz, Aykut Barka

The Miocene to Recent Oediz and Buyuk Menderes graben developed upon metamorphic rocks of the Menderes Massif in response to N-S extension. The basins are asymmetric half-graben with dominant active extensional fault traces on their southern and northern margins, respectively. Extension was accommodated primarily by rigid body rotation of domino-type blocks 0.2-0.8 km wide on planar faults. In places, back-rotation on antithetic faults has produced basinward dipping strata. Early-formed antithetic faults have been rotated through the vertical, ruling out distributed vertical shear as a significant deformation mechanism. Faulting on the hangingwalls has produced at least 400 m relative uplift and locally derived coarse detritus. Average footwall sediment dips of 25 to 30° and aver ge synthetic fault dips of 45° yield estimates of beta between 1.3 and 1.4. Swaths of exhumed sediments up to 10 km wide on the footwall and hangingwall margins are fault-bounded. Divergent wedge geometries, unconformable relationships, and palaeocurrent orientations in the lowermost units indicate that exhumed sediments all post-date the onset of rifting. Faulting migrated basinward with time, resulting in uplift and cannibalization of the basin fill. This contributed towards the development of large footwall-derived alluvial fans that displace axial drainage across the modern graben floors toward the footwall margins. This contrasts with models of half-graben sedimentation in which axial systems are concentrated over the locus of maximum subsidence.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994