The late Early Miocene Acıpayam piggy-back basin: Refining the last stages of Lycian nappe emplacement in SW Turkey

Abstract

Alluvial fan to shallow-marine sedimentation in the Acıpayam piggy-back basin took place in the hinterland zone of the SE-facing Lycian nappe stack and constrains the age and style of late-stage advance of these nappes. Syn-orogenic sedimentation commenced in Burdigalian time and is marked by coarse-grained alluvial fan deposits that directly overlie Mesozoic ophiolitic rocks. Palaeocurrent data obtained from these coarse-clastic units suggest a south-southeastward drainage. The succession fines upwards and passes into fluvial deposits that become increasingly enriched in carbonate clasts derived from tectonically deeper-seated nappes, suggesting progressive unroofening of the nappe pile. Upwards, the succession is transitional to a Late Burdigalian–Early Langhian marginal marine succession, consisting of off-shore fines with coal seams that overly both the coarse-clastic sediments and basement rocks. Clastic sedimentation ceased at the end of Early Langhian based on reef carbonates that cap the succession. Shallow-marine deposits and overlying reef carbonates confirm a marine transgression that has been reported from elsewhere in the Tauride Belt. Detailed sedimentology of the Acıpayam basin fill succession, its age and overall tectonic setting imply that during Burdigalian time the succession was deposited in a piggy-back basin, located in the hinterland zone of actively moving thrust sheets. We propose a model in which thick-skinned thrusting invoked inversion of early extensional faults in the autochthon and may explain the generation of large open folds with thick sedimentary sequences in their core. The formation of these large folds may have importantly influenced the frontal accretion such that active shortening moved into the hanging wall resulting in episodic nappe advanced of structurally higher nappes in a mode similar to thin-skin thrusting. The tectonosedimentary evolution of the Acıpayam piggy-back is strongly dependent on its position relative to the hinge of the large open fold. The absence of any compressional signatures in the basin fill succession indicates that these thrust translations ceased shortly after Aquitanian time. By Serravallian, the succession was interrupted and the region was uplifted to its present elevation, probably by gravitationally isostatic (orogenic) rebound of the nappe stack. After these episodes, tectonic extension predominated and the succession became dissected by nappe-front parallel normal faults that bound the present Çameli Basin.