Lower Miocene Alluvial Deposits of the Požeška Mt. (Pannonian Basin, Northern Croatia): Cycles, Megacycles and Tectonic Implications

In the area of the present Požeška Mt. braided alluvial fans were formed during the Early Miocene above the subsiding Cretaceous-Palaeogene basement. Due to autocyclic processes, i.e. lateral migration of flows due to vertical aggradation of longitudinal bars, or migration of the main trench, small-scale fining-upward cycles were formed. The complete succession of the alluvial deposits is composed of two fining-upward megacycles, which are the consequence of allocyclic influences, i.e. the pulsating character of synsedimentary tectonics. Megacycles were developed parallel to backstepping of the front of the fault scarp towards the mountain massif, caused by normal faulting along the active margin of an extensional basin. This kind of depositional style indicates that the Sava fault operated as a normal fault at the beginning of its life during the Early Miocene, probably the Ottnangian.