Large Distributive Fluvial Systems: Characteristics, Distribution, and Controls on Development

Abstract

An analysis of remotely sensed imagery reveals that fluvial planform geometries within aggrading continental areas are dominated by distributive fluvial systems (DFSs). We documented the gradient, length, apex location, planform, termination type, and tectonic and climatic setting of 415 examples of fluvial systems which in planform display a radial, distributive channel pattern and have an apex-toe distance . 30 km (large DFSs). The longest of these DFSs is 704 km in length, with the majority (72%) ranging between 30 and 100 km in length. Gradients on individual systems range from 0.00003 (0.0018u) to 0.02656 (1.5u). Six planform types are recognized, those with: (1) a single braided channel that bifurcates downstream into braided and/or straight channels, (2) a single dominant braided channel, (3) a single dominant braided channel which becomes sinuous downstream often bifurcating, (4) a single dominant sinuous channel, (5) a single sinuous channel that bifurcates downstream into smaller sinuous channels, and (6) multiple sinuous channels. Of the studied examples 58% occur within exorheic basins and 42% in endorheic basins, with seven different termination types recognized. In many examples, channel planform changes downstream from a distributive pattern to a contributory pattern. In others, channels terminate at an axial fluvial system, at the coast, in eolian dune fields, playa lakes, permanent lakes, or wetlands. Large DFSs and their catchments are developed in all climatic regimes, including drylands, tropical, subtropical, continental, and polar climates. Large DFSs occur in all tectonic settings, including extensional, compressional, strike-slip, and cratonic tectonic regimes.General trends and relationships between the different studied parameters can be observed, leading to a broad understanding of the main controls on large DFS development. All of the planform types occur in all tectonic settings and all climate zones. Braided planforms dominate all tectonic settings, but particularly compressional regimes. High-gradient braided systems tend to be associated with areas of high relief and are well developed in dryland climates where discharge is inferred to be intermittent in comparison to tropical climates. Large DFSs with sinuous planforms do occur in dryland climates but tend to predominate in wetter, more tropical climates where discharge is more constant and the fluvial systems can distribute bedload more efficiently. Sinuous systems also tend to have significantly lower gradients than braided systems. Although these general observations can be made, there are significant variations from these trends, which are inferred to be controlled by variations in (1) discharge related to climate and (2) sediment supply, which is a function of climate, catchment size, catchment lithology, and catchment relief.Large DFS length is controlled by the available horizontal accommodation space, which in turn is strongly related to tectonic setting. The longest DFSs occur in peripheral foreland basins and cratonic se...

Fluvial geomorphic elements in modern sedimentary basins and their potential preservation in the rock record: A review

“…2H). Swamps and wetlands associated with DFS or 170 tributive fluvial systems were included in the DFS or tributive system, though we recognize that 171 wetlands may significantly affect facies locally (Hartley et al, 2010b Tandon and Sinha, 210 2007; Latrubesse, 2015). We also observed that the arrangement of fluvial geomorphic elements to be 211 consistent with the distributions described by DeCelles and Cavazza (1999) in most sedimentary basins 212 around the world (Fig.3).…”

“…Rivers on these large DFS tend to enter the 345 sedimentary basin as broad, braided channel belts. Down-DFS, many of the channel belts diminish in 346 width, caused by infiltration, bifurcation, or evaporation, becoming single-thread channels with higher 347 sinuosity Hartley et al, 2010b;Weissmann et al, 2011). For example, the Bermejo River 348…”

“…Studies of continental geomorphology outside these sedimentary basins may be 85 useful for understanding channel-scale depositional processes and upstream catchment contribution to 86 sediment supply and stream discharge. However, these will not further the understanding of 87 sedimentary basin-scale processes and overall geometries of deposits responsible for sedimentary basin 88 fill and evolution (Hartley et al, 2010b). 89…”

“…The term, DFS,wasdefined as 'the deposit of a fluvial system which in planform displays a radial 112 distributive channel pattern' (Hartley et al, 2010b, P. 168, emphasis added). In 2010 (Hartley et al 113 2010a,b; Weissmann et al, 2010), we proposed the DFS term in order to encompassfluvial and 114 alluvialdistributive landforms at all scales.…”

“…We specifically did not use the 128 term distributary, as this implies that coeval flow exists in several channels (Neuendorf et al, 2005). Not 129 all channel belts are coevally active on the DFS (Hartley et al, 2010b), nor is it possible to evaluate 130 whether channels were coeval from the rock record. 131…”