Fluvial Systems in Desiccating Endorheic Basins

Abstract

Endorheic basins are basins of internal drainage with no direct hydrological connection to the marine environment. In relatively humid settings, the depositional environments of the basin will be dominated by a basin centre lake, but if the climate is more arid, fluvial systems will be important depositional mechanisms, along with ephemeral lake, alluvial plain and aeolian reworking. Rivers in desiccating basins show a decrease in discharge down-flow because the loss of water by evaporation and soak-away exceeds the input to the system. One of the features of internal drainage is that all sediment supplied is deposited in the basin. Therefore, base level will be determined by the balance between sediment supply and basin subsidence. If sediment supply exceeds subsidence, the river channels will not deeply incise into the alluvial plain of the medial and distal parts of the system, and overbank flow in the distal areas will result in a high proportion of thin sheets of sand and mud deposited by unconfined flow. The depositional gradient will be very low (and may effectively be horizontal over much of the fluvial depositional tract), and a rising base level may also cause the rivers to back-fill the feeder valleys in the proximal areas. Avulsion and lateral migration of the channels across the alluvial plain result in a fan-shaped body of sediment being built up as the rivers distribute sediment, a geomorphological form referred to as a fluvial distributary system. However, the conditions for forming a fluvial distributary system are sensitive to climate, and with an increase in water supply, the basin-centre lake may become perennial: as the rivers will be feeding into a standing body of water, the distal part of the fluvial depositional system is therefore a delta. Lake deltas and fluvial distributary systems can hence be considered as members of a spectrum of depositional settings determined by climate. This continuum of processes and environments can be extended to include aeolian facies, which will dominate if conditions in an endorheic basin are too arid for a perennial fluvial system to form.

Architecture of an Oligocene fluvial ribbon sandstone in the Ebro Basin, North-eastern Spain

“…Fluvial ribbon sandstone bodies in the southern Ebro Basin share important likenesses in geo-metry and sedimentary structures to analogous bodies in northern parts of the Ebro Basin (e.g. Nichols, 2007) as well as in other basins (e.g. Stear, 1983;Smith, 1995;Gibling & Rust, 2006;King, 2008), suggesting common genetic features.…”

Catchment lithology as a major control on alluvial megafan development, Kohrud Mountain range, central Iran

“…The incised channel of the Soh fan is relatively deep, long and sinuous, while for the Zefreh fan it is shallow, short and braided. In drylands, sediment supply determines the shape of megafan channel networks and while sinuous channels develop in areas with low rate of sediment supply, braided type channels are characteristic of high sediment supply (Nichols, ; Hartley et al , ). Moreover, channel aggradation or incision controls the location of intersection point.…”

“…They are also distinguished from small debris cone and normal alluvial fans (piedmont and mountain front fans, mostly <10 km in length) by the presence of floodplain areas and absence of sediment gravity flows (see also Blair and McPherson, for a discussion of alluvial fan classification). Other terms that have been used to describe alluvial megafans include fluvial fans (Collinson, ; Horton and DeCelles, ); stream‐dominated alluvial fans (Weissman et al , ), and distributive fluvial systems (Nichols, ; Hartley et al , ; Weissmann et al , ). Although alluvial megafans are clearly related to emergence of a large mountain river onto a low‐relief alluvial plain, their stratigraphic evolution depends on variables such as source catchment characteristics, water discharge, sediment flux and subsidence rate, factors that are ultimately controlled by tectonic, climate and geomorphic processes (Gupta, ; Horton and DeCelles, ; Leier et al , ; Quigley et al , ; Goswami et al , ).…”

Dietary specificity and overlap in endorheic river fishes: How do native and nonnative species compare?

“…However, many rivers in arid or semi‐arid climates occur in dry, landlocked watersheds. These rivers, termed endorheic, generally have low species richness due to high levels of perturbation affecting the hydrologically closed systems (Nichols, 2007; Sigler & Sigler, 1987). Endorheic rivers also tend to be highly vulnerable to successful invasions as a result of their isolated nature, similar to highly vulnerable island systems (Sax & Brown, 2000).…”