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Brian R. Rust

Bio: Brian R. Rust is an academic researcher from University of Ottawa. The author has contributed to research in topics: Pennsylvanian & Fluvial. The author has an hindex of 23, co-authored 37 publications receiving 2681 citations.

Papers
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01 Jan 1977
TL;DR: In this paper, Braided alluvial deposits are characterized by three lithotypes: gravel-, sand-dominant, and silt-dominating, and the coarser components of the cycle are interpreted as deposits of an active braided tract; grain size decreases as the tract aggrades and becomes inactive.
Abstract: Braided alluvial deposits form in rivers and on alluvial fans and plains, and comprise three lithotypes: gravel-, sand- and silt-dominant. The gravel lithotype is characterised by framework-supported gravel, which in proximal deposits is mainly horizontally bedded and imbricate, occurring together with matrix-supported (debris flow) gravel in alluvial fan deposits. Horizontally bedded gravel accumulates on longitudinal bars, which are thought to originate as primary bedforms of high stage flow. Distal gravel deposits are characterised by cycles in which trough cross-bedded framework-supported gravel fines upwards to sand (commonly trough cross-stratified) and massive to laminated mud. The coarser components of the cycle are interpreted as deposits of an active braided tract; grain size decreases as the tract aggrades and becomes inactive. Proximal sandy braided deposits typically lack mud in primary layers, but it is abundant as intraclasts on erosion surfaces. Horizontally stratified, low-angle (<10°) stratified, and trough cross-stratified sand are also abundant, in vertically and laterally variable successions. Distal sandy braided deposits commonly have fining-upward cycles, lateral continuity, and a significant primary mud content. They are transitional to deposits of meandering systems. Silty braided deposits are typically traction- rather than suspension-laid, and lack association with coarser channel sediments. They are rare today, because most fine-grained alluvium accumulates on floodplains of meandering systems, for which vegetation is an important stabilising component. Terrestrial vegetation was essentially absent before Late Paleozoic times, when braided alluvium, including the silt-dominant type was widespread, particularly on alluvial plains of humid regions.

408 citations

Journal ArticleDOI
TL;DR: In this article, a straight, four-mile tract of the Donjek River, Yukon, Canada is braided throughout, discharging about 50,000 cfs in flood.
Abstract: A straight, four-mile tract of the Donjek River, Yukon, Canada is braided throughout, discharging about 50,000 cfs in flood. The active part of the tract shows upper regime flow in the main channels, and lacks vegetation. Higher, older levels are former river courses, partly or completely vegetated, with continuous flow (principally lower regime) only in the main channels. Comparing channel (width:depth) and topographic indices, the younger surfaces are more strongly dissected because of active channel cutting, whereas channels on older levels are subject to infilling. The sediments vary from clays to coarse gravels; most are poorly sorted. CM plots permit division into three main groups: silt and mud of low energy environments such as abandoned channels, gravel of high energy channel-bar complexes, and a variable intermediate group which fills channels under medium-energy conditions. Seven facies are distinguished on textural, floral, and sedimentary structural characteristics. Facies relations are mostly gradational within channels, commonly fining upwards. They are more complex between channels, and invariably erosional. The origin and directional significance of hierarchical orders of sedimentary structures were studied. Six hundred and sixty measurements of small-scale structures (mostly ripples) show moderate within-bar and between-bar variation, and give a grand vector mean 22 degrees from the river trend. Bisectors of channel directional arcs (maximum and average ranges) approximate the river trend within 5 degrees.

378 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the Donjek, a proglacial braided river with a coarse heterogeneous bedload ranging from −7 to +8 φ.
Abstract: The Donjek is a proglacial braided river with a coarse heterogeneous bedload ranging from −7 to +8 φ. The three reaches studied comprise, in downstream order, a zig-zag reach formed by the interaction of the river and tributary fans, a straight reach, and a meandering reach, all with internal braids. The straight to meandering junction is unusual in that slope and discharge both increase. The dominant bed-forms are longitudinal gravel bars, which migrate only during flood. Their internal structure is poorly defined horizontal bedding, which suggests that gravel deposition takes place on the upper bar surfaces, rather than on foreset slopes at the downstream margins. At lower stage sand accumulates in wedge-shaped units lateral to the bars, with internal high-angle cross-stratification and ripple cross-lamination; other sedimentary structures are rare. A simple facies model can be constructed on the basis of two trends: a proximal-distal trend, and an active-stable trend. Both result in the increased abundance of fine-grained sediment. Random directional measurements give good estimates of the river trend from small-scale structures (mainly ripples) and from channels, the latter giving the closest approximation. The variability of ripple orientation always exceeds that of channels. Both increase in the meandering reach, although the divergence of the vector mean from the river trend is not significantly greater than in the straight reach.

307 citations

01 Jan 1977
TL;DR: In this paper, a new classification of alluvial channel systems is proposed, based on the braiding parameter: the number of braids per mean meander wavelength, braids being defined by the mid-line of the channels surrounding each braid bar.
Abstract: A new classification of alluvial channel systems is proposed, based on the braiding parameter: the number of braids per mean meander wavelength, braids being defined by the mid-line of the channels surrounding each braid bar. Single-channel and multi-channel systems are defined as having braiding parameters less than and more than one, respectively. Channel systems are further divided into low-and high-sinuosity categories at the boundary 1.5, giving four types, of which single-channel high-sinuosity (meandering) and multi-channel low-sinuosity (braided) are by far the most common. The other two types are much less abundant: single-channel low-sinuosity (straight), and multi-channel high-sinuosity (anastomosing). The classification can be applied to ancient alluvial deposits through an understanding of the processes that relate channel morphologies to their resulting sedimentary suites. As the processes are imperfectly understood, so the application to paleochannels is imprecise. However, it can be made satisfactorily in most cases, provided maximum use is made of the channel-process information in alluvial sedimentary models.

243 citations

Journal ArticleDOI
TL;DR: In the Cooper and Diamantina Rivers, Lake Eyre Basin, Australia, a significant amount of sand-sized mud is transported as pedogenic aggregates by modern rivers as discussed by the authors, and the conditions required for formation of pedogenic mud aggregates are abundant clay containing at least minor swelling clay, and a climate with at least seasonally hot dry periods.
Abstract: Abundant sand-sized mud aggregates in the Cooper and Diamantina Rivers, Lake Eyre Basin, Australia are attributed to bedload transport of aggregates formed in deeply-cracked floodplain soils. The conditions required for formation of pedogenic mud aggregates are: (i) abundant clay containing at least minor swelling clay, and (ii) a climate with at least seasonally hot dry periods. The worldwide distribution of these soils (Vertisols) suggests that a significant amount of mud is transported as pedogenic aggregates by modern rivers. Ancient analogues in which mud aggregates and Vertisol profiles have been recognized are the Jurassic East Berlin Formation (Connecticut, USA) and the Carboniferous Maringouin Formation (New Brunswick and Nova Scotia, Canada). The dominant red mudstones of these formations are interpreted as mainly bedload sediments deposited by sheet floods in semi-arid palaeoclimates. The Triassic Hawkesbury Sandstone (NSW, Australia) also contains sand-sized mudstone aggregates, thought to be pedogenic, but its paleosol and other facies point to formation in a wetter palaeoclimate. The indications are that bedload transport of mud as pedogenic aggregates was as significant a process in ancient rivers as it is at present.

156 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, the authors proposed a new method of analysis for fluvial facies, which subdivides fluvic deposits into local suites consisting of one or more of a set of eight basic three-dimensional architectural elements.

1,804 citations

Journal ArticleDOI
TL;DR: A review of more than sixty recent papers on modern and ancient braided-stream deposits can be found in this article, where several sedimentation models have been developed from a review of recent work.

1,755 citations

01 Jan 1977
TL;DR: In this paper, a new model, the Trollheim type, is proposed to include gravelly deposits characterized by abundant debris flows, and the South Saskatchewan type is proposed for sand dominated cyclic deposits.
Abstract: This article serves as an introduction to the papers dealing with braided river deposits in this volume. A lithofacies code erected earlier by the writer is expanded to include matrix-supported gravel, low-angle cross stratified sand, erosion surfaces with intraclast conglomerates, and massive mud deposits. The four vertical profile models erected by the writer are expanded to six. A new model, the “Trollheim type” is proposed, to include gravelly deposits characterized by abundant debris flows. The Donjek sequence type is restricted to gravel-dominated cyclic deposits and a new model, the “South Saskatchewan type”, is erected for sand dominated cyclic deposits. The Scott, Platte and Bijou Creek models remain essentially unchanged.

1,290 citations

Journal ArticleDOI
TL;DR: In this paper, the relation between a stream's ability to entrain and transport sediment and the erosional resistance of floodplain alluvium that forms the channel boundary provides the basis for a genetic classification of floodplains.

952 citations

Journal ArticleDOI
TL;DR: In this article, the authors present a literature dataset that represents more than 1500 bedrock and Quaternary fluvial bodies for which width (W) and thickness (T) are recorded.
Abstract: The three-dimensional geometry of fluvial channel bodies and valley fills has received much less attention than their internal structure, despite the fact that many subsurface analyses draw upon the geometry of suitable fluvial analogues. Although channel-body geometry has been widely linked to base-level change and accommodation, few studies have evaluated the influence of local geomorphic controls. To remedy these deficiencies, we review the terminology for describing channel-body geometry, and present a literature dataset that represents more than 1500 bedrock and Quaternary fluvial bodies for which width (W) and thickness (T) are recorded. Twelve types of channel bodies and valley fills are distinguished based on their geomorphic setting, geometry, and internal structure, and log-log plots of W against T are presented for each type. Narrow and broad ribbons (W/T 1000, respectively) are distinguished. The dataset allows an informed selection of analogues for subsurface applications, and spreadsheets and graphs can be downloaded from a data repository. Mobile-channel belts are mainly the deposits of braided and low-sinuosity rivers, which may exceed 1 km in composite thickness and 1300 km in width. Their overwhelming dominance throughout geological time reflects their link to tectonic activity, exhumation events, and high sediment supply. Some deposits that rest on flat-lying bedrock unconformities cover areas > 70,000 km2. In contrast, meandering river bodies in the dataset are < 38 m thick and < 15 km wide, and the organized flow conditions necessary for their development may have been unusual. They do not appear to have built basin-scale deposits. Fixed channels and poorly channelized systems are divided into distributary systems (channels on megafans, deltas, and distal alluvial fans, and in crevasse systems and avulsion deposits), through-going rivers, and channels in eolian settings. Because width/maximum depth of many modern alluvial channels is between 5 and 15, these bodies probably record an initial aspect ratio followed by modest widening prior to filling or avulsion. The narrow form (W/T typically < 15) commonly reflects bank resistance and rapid filling, although some are associated with base-level rise. Exceptionally narrow bodies (W/T locally < 1) may additionally reflect unusually deep incision, compactional thickening, filling by mass-flow deposits, balanced aggradation of natural levees and channels, thawing of frozen substrates, and channel reoccupation. Valley fills rest on older bedrock or represent a brief hiatus within marine and alluvial successions. Many bedrock valley fills have W/T < 20 due to deep incision along tectonic lineaments and stacking along faults. Within marine and alluvial strata, upper Paleozoic valley fills appear larger than Mesozoic examples, possibly reflecting the influence of large glacioeustatic fluctuations in the Paleozoic. Valley fills in sub-glacial and proglacial settings are relatively narrow (W/T as low as 2.5) due to incision from catastrophic meltwater flows. The overlap in dimensions between channel bodies and valley fills, as identified by the original authors, suggests that many braided and meandering channel bodies in the rock record occupy paleovalleys. Modeling has emphasized the importance of avulsion frequency, sedimentation rate, and the ratio of channel belt and floodplain width in determining channel-body connectedness. Although these controls strongly influence mobile channel belts, they are less effective in fixed-channel systems, for which many database examples testify to the influence of local geomorphic factors that include bank strength and channel aggradation. The dataset contains few examples of highly connected suites of fixed-channel bodies, despite their abundance in many formations. Whereas accommodation is paramount for preservation, its influence is mediated through geomorphic factors, thus complicating inferences about base-level controls.

633 citations