Fluvial‐aeolian interactions: Part I, modern systems

Abstract

Two modern fluvial‐aeolian depositional systems (Great Sand Dunes National Monument, Colorado and the Mojave River Wash, California) are remarkably similar in spite of different climates, sizes, fluvial sediment textures, and relative directions of aeolian and fluvial transport. Dune growth and migration, and deflation of blowouts create 8–10 m of local relief in unflooded aeolian landscapes. There are six prominent fluvial‐aeolian interactions. (1) Fluvial flow extends into the aeolian system until it is dammed by aeolian landforms; (2) interdune areas (overbank‐interdunes) upstream of aeolian dams, and alongside channels are flooded; (3) water erodes dunes alongside channels and interdunes; (4) flood waters deposit sediment in interdune areas; (5) fluvially derived groundwater floods interdunes (interdune‐playas); (6) wind erodes fluvial sediment and redeposits it in the aeolian system. Unique and characteristic sediments are deposited in overbank‐interdunes and in interdune‐playas, reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions. These fluvial‐aeolian interdune deposits are characterized by irregular, concave‐up bases and flat upper surfaces containing mudcracks or evaporite cement. Characteristic low‐relief surfaces form in aeolian systems as an effect of flooding. Fluvial deposits are resistant to aeolian deflation. Aeolian sand is preserved when flood sediments are deposited around the bases of the dunes. Thus repetitive fluvial and aeolian aggradation tends to be ‘stepwise’ as interdune floors are suddenly raised during floods. The effects of flooding should be easy to recognize in ancient aeolianites, even beyond the area covered with overbank muds.

Stratigraphic architecture of back-filled incised-valley systems: Pennsylvanian–Permian lower Cutler beds, Utah, USA

“…Aeolian interdunes composed exclusively of aeolian wind-ripple strata had dry substrates, whereas those composed of massive sandstone record episodes of short-lived flash flood events along interdune corridors (cf. Langford and Chan, 1989;1993;Bullard and Livingstone, 2002;Mountney and Jagger, 2004;Cain, 2009) in a style similar to that in many present-day dune fields (Lancaster, 1983;Langford, 1989; Wakefield and Mountney Tooth, 1999; Stanistreet and Stollhofen, 2002;Krapf et al, 2003;2005). These massive sandstone sets are of fluvial origin and are differentiated from similar sets of aeolian origin by virtue of their diagnostic red-brown colour, occurrences of rare intraformational rip-up clasts and, in some cases, increased mica content.…”

“…The laterally extensive, horizontal bounding surfaces that truncate these elements are deflationary supersurfaces (Loope, 1985;Mountney, 2012). These supersurfaces record an episode of dune-field destruction brought about by an upwind reduction in availability of sediment for aeolian transport, leading to downwind cannibalisation of the dune field to the level of the water table by winds that were undersaturated with respect to their potential sand carrying capacity (see Loope, 1985;Langford and Chan, 1988;1989).…”

“…Langford and Chan, 1988;1989;Stanistreet and Stollhofen, 2002;Mountney and Jagger, 2004), relatively few have examined tripartite styles of interaction involving coastal settings where aeolian, fluvial and shallow-marine processes all operated coevally (e.g. Simpson and Eriksson, 1993;Blakey et al, 1996).…”

Sedimentary paleoenvironments of the Toro Negro Formation (Neogene), Andean broken foreland, northwest Argentina.

“…El bajo porcentaje de matriz de estas areniscas como la alta porosidad y la buena selección son características de un origen eólico (Ahlbrandt, 1979;Goudie y Watson, 1981). Acumulaciones eólicas análogas en sistemas entrelazados actuales fueron estudiadas por Tripaldi y Limarino (2008) quienes las consideraron similares a los depósitos de interacción eólica-fluvial descritos por Langford (1989) y Langford y Chan (1989). Los 'sets' de 2 m de espesor corresponderían a dunas medianas o protodunas (Hunter, 1977).…”

Alluvial-eolian interaction in a Cambrian rift margin: the Pedra das Torrinhas and Pedra Pintada formations (Guaritas Group, RS)

“…Brookfield 1992, Kocurek 1996 with an increasing interest in the particularities of the interactions among both systems (e.g. Langford 1989, Langford and Chan 1989, Stanistreet and Stollhofen 2002, Paim and Scherer 2007, with descriptions of the resulting depositional architecture (e.g. Herries 1993, Fischer et al 2007).…”