Source area and tectonic control on alluvial-fan development in the Miocene Fohnsdorf intramontane basin, Austria
Michael Wagreich, Philipp E. Strauss, 2005. "Source area and tectonic control on alluvial-fan development in the Miocene Fohnsdorf intramontane basin, Austria", Alluvial Fans: Geomorphology, Sedimentology, Dynamics, A. M. Harvey, A. E. Mather, M. Stokes
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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 augengneiss- and 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.
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Alluvial fans are important sedimentary environments. They trap sediment delivered from mountain source areas, and exert an important control on the delivery of sediment to downstream environments, to axial drainages and to sedimentary basins. They preserve a sensitive record of environmental change within the mountain source areas. Alluvial fan geomorphology and sedimentology reflect not only drainage basin size and geology, but change in response to tectonic, climatic and base-level controls. One of the challenges facing alluvial fan research is to resolve how these gross controls are reflected in alluvial fan dynamics and to apply the results of studies of modern fan processes and Quaternary fans to the understanding of sedimentary sequences in the rock record. This volume includes papers based on up-to-date research, and focuses on three themes: alluvial fan processes, dynamics of Quaternary alluvial fans and fan sedimentary sequences. Linking the papers is an emphasis on the controls of fan geomorphology, sedimentology and dynamics. This provides a basis for integration between geomorphological and sedimentological approaches, and an understanding how fluvial systems respond to tectonic, climatic and base-level changes.