The Sedimentology of a Braided River

Abstract

X 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 tuud 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 hetwren-har variation, and give a rand vector mean 22 degrees from the river trend. Bisectors of channel directional arcs (maximumand average ranges) approximate the river trend within 5 degrees.

Early post-rift depositional systems of the Central Atlantic: Lower and Middle Jurassic of the Essaouira-Agadir Basin, Morocco

“…The fining-upward conglomerates and sandstones are interpreted to represent cyclic channel deposits in a braided river environment (Williams and Rust, 1969;Miall, 1977Miall, , 1996Bridge, 2003). The erosive clast-supported conglomerates with horizontal stratification were deposited by bar migration (Rust, 1972).…”

Migrating bars influence the formation and dynamics of their peers in large sandy‐gravel bed rivers

“…Bridge (1993) discussed the difficulty in establishing hierarchies of bars and channels in rivers with complex morphological patterns. Different ordering schemes exist (Bristow, 1987; Williams & Rust, 1969) and are difficult to apply. It is specifically confusing to distinguish between second‐ and third‐order bars that could correspond to dissected segments of a first‐order bar (Bridge, 1993).…”

“…Different ordering schemes exist (Bristow, 1987;Williams & Rust, 1969) and are difficult to apply. It is specifically confusing to distinguish between second-and third-order bars that could correspond to dissected segments of a first-order bar (Bridge, 1993).…”

Reconstruction of the Late Miocene to Pliocene continental succession of Samos Island: Palaeoenvironmental implications for the Eastern Aegean domain

“…In these environments, the influence of fluvial streams is evidenced by the clast‐supported fabric and clast imbrication, the presence of trough cross‐bedding and the erosive base which suggest that both T2 conglomerates and T3 coarse‐grained sandstones were deposited by traction processes, possibly the migration of large, gravelly, transverse bars (Boulton et al, 2019; Miall, 1996; Smith, 1990). Williams and Rust (1969), Bridge (1993) or Chanvry et al (2018) interpreted such facies as deposited in a braided channel network associated with high discharge flooding events.…”