Differential effects of base-level, tectonic setting and climatic change on Quaternary alluvial fans in the northern Great Basin, Nevada, USA

Abstract

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 baselevel 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.Many studies have demonstrated how the geomorphology of alluvial fans reflects interactions between three sets

Experimental alluvial fans: Advances in understanding of fan dynamics and processes

“…downstream, either in relation to distal fluvial systems or to sedimentary basin environments (Harvey, 2005).…”

Dryland Alluvial Fans

“…Furthermore, increasing knowledge of Quaternary environments in the American deserts (Grayson, 1993;Enzel, Wells and Lancaster, 2003), particularly in relation to the basin-centre pluvial lakes (e.g. Wesnowsky, 1998, 1999), has enabled research into fan-lake relationships to focus on Quaternary fan dynamics Wells, 1994, 2003;Ritter, Miller and Husek-Wulforst, 2000;Harvey, Wigand and Wells, 1999;Harvey, 2005;Garcia and Stokes, 2006). Dry-region alluvial fans occur in all the major dryland mountain regions of the world.…”

“…Nanson, Chen and Price, 1995;Enzel, Wells and Lancaster, 2003;Al Farraj and Harvey, 2004). Interaction with lacustrine sediments, and particularly with dated lacustrine shorelines of pluvial lakes, does, especially in the Basin and Range area of the USA, provide the basis for calibrating relatively dated fan surfaces with a known Quaternary chronology (see Wells, 1994, 2003;Wesnowsky, 1998, 1999;Harvey, Wigand and Wells, 1999;Ritter, Miller and Husek-Wulforst, 2000;Harvey, 2005;Garcia and Stokes, 2006).…”

A numerical modelling and experimental study of flow width dynamics on alluvial fans

“…Previous studies of alluvial fans have demonstrated that these landforms afford considerable potential to contribute to this debate, not least because their limited extent (length) may promote relatively rapid and complex response to both internal and external perturbations (Hooke and Dorn, 1992;Harvey, 2002a;Viseras et al, 2003). Fieldbased interpretation of fan morphology and stratigraphy has often emphasized the role of external environmental forcing (Ritter et al, 1995;Whipple and Trayler, 1996;Harvey, 2002b;Hartley et al, 2005;Harvey, 2005). For example, Figure 1 shows a heavily entrenched tributary fan in the Avoca Valley, South Island, New Zealand, which could be interpreted to reflect a para-glacial decline in sediment supply (cf.…”