Permian deposits of the Southern Alps as product of initial alpidic taphrogenesis

Abstract

Sedimentological and morphotectonic investigations of Permian deposits between the Val Camonica and the Karawanken Mountains indicate the development of a complex rift-system which initiated the alpidic sedimentation phase. The extensive distribution of regoliths and palaeosoils at the base of the Permian deposits demonstrate the existence of a consolidated and subsequently truncated crust. The senile topography which prevailed at the beginning of the Permian had to be modified by fault movements to provide the erosional and transport energy required for the deposition of psephytes and other siliciclastica (scarp foot fans). The formation of syndepositional graben structures, diagnostic for an overall distentional regime, led to the development of three morphotectonic units. Commencing in the early Permian with fissure volcanism, a central, northeasterly trending rift developed. The western margin of it was modified by rift-parallel faulting the resulting trough serving as receptacle for lacustrine sediments. The area to the east of the central rift was separated by a pronounced graben shoulder, the eastern perimeter of which supported a marine carbonate platform. Rejuvenation of tectonism near the middle of the Permian established a new, east-southeast trending rift-branch and expelled the sea from the eastern basin. The ensuing fluviatile regimes, draining mainly in southerly to south-westerly directions resulted in a general equalisation of the landscape. In the late Permian, the eastern part of the area became inundated by a shallow, evaporitic sea, but fluviatile conditions prevailed in the west until the onset of the Triassic. Current directions indicate a south-westerly outlet path for these systems and thus the existence of another, presumably marine base level in that direction.