Source area and tectonic control on alluvial-fan development in the Miocene Fohnsdorf intramontane basin, Austria

Middle Miocene alluvial fans in the intramontane Fohnsdorf Basin of the Eastern Alps originated along normal faults and linked strike-slip faults in a continental half-graben setting. The fans display considerable facies differences. Debris flows of the Rachau fan are characterized by a sandy matrix and large boulders, whereas debris flows of the Apfelberg fan are characterized by higher silt and clay content and smaller clasts. Key control of debris-flow facies is the lithology contrast in the fan source areas. Sand, pebbles and large outsized boulders originated predominantly from the resistant augengneissand amphibolite-dominated hinterland of the Rachau fan, whereas a significant higher proportion of mud and silt and smaller boulders have been derived from the Apfelberg fan catchment, which was dominated by mica schists and marble. From: HARVEY, A.M., MATHER, A.E. & STOKES, M. (eds) 2005. Alluvial Fans: Geomorphology, Sedimentology, Dynamics. Geological Society, London, Special Publications, 251, 207–216. 0305–8719/05/$15 © The Geological Society of