Differential effects of base-level, tectonic setting and climatic change on Quaternary alluvial fans in the northern Great Basin, Nevada, USA
Adrian M. Harvey, 2005. "Differential effects of base-level, tectonic setting and climatic change on Quaternary alluvial fans in the northern Great Basin, Nevada, USA", Alluvial Fans: Geomorphology, Sedimentology, Dynamics, A. M. Harvey, A. E. Mather, M. Stokes
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Mountain-front alluvial fans in the northern Great Basin were affected by interactions between the tectonic setting, late Quaternary climatic changes and climatically induced base-level changes through fluctuations in pluvial lake levels. Four fan groups were studied on the margins of and near pluvial Lake Lahontan with varying geology and tectonic settings. All fans were affected by climatically led variations in sediment supply, but only those on steep mountain fronts adjacent to deep lakes were affected by base-level changes during lake desiccation.
Relationships between fan segments and dated lake shorelines, augmented by soil and desert pavement characteristics, have enabled fan segments older and younger than the lake highstands to be identified. Major periods of fan aggradation occurred prior to the last glacial maximum and during the Holocene, with little or no fan deposition occurring during and after the last glacial maximum, at the time of high lake levels. The interactions between tectonics, climate and base-level change have produced distinctive fan geometric relationships between older and younger fan segments, also expressed in the morphometric properties of the fans. Tectonics primarily influence the fan setting, particularly the accommodation space, and interact with sediment supply rates partly related to source-area geology. The climatic signal is present in all four groups of fans, but is modified locally by a base-level signal only where deep pluvial lakes abutted to relatively high levels on fans on relatively steep mountain fronts.
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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.