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COPYRIGHT ·~ 1977 BY ELSEVIER SCIENTIFIC PUt3LISHING COMPANY , AMSTERDAM
PRII\TF~) IN THE NE.THEI=!LANDS
[.zr··· ·,·:l'flc£' Ret•il'!ws. l.J ,19171 1-6~
.:=· r:: .. \ wr SLIC'ntific Publishing Compan_,. Am:;terdam-Printt>d i·· the ~.-therlands
A Review of the Braided-River Depositional
Environment
Anr'.~r:w D. Miall
ABSTRACT
Miall. A.D .. 1977. A revtew \lf the braided-river depositional en\'ironment. Earth-Sci .
Rev , 13: 1-62 .
r..-•1eralized sedimenlation models have been developed from a review of more t~an
s1· · · •·l..'ent papf'rs on modern and ancient braided-stream deposits. Braided rivers con
si:-.: .,; .I ,;pries of bro'\d, shullow channf'ls and bars, with elevated areas activ£> only durin!>!
flood:;, 'ind dry islands. There are three m<Jin bar types ; longitudinal, comprising crudely
bedded grav ·I sheets; transversn to linguoid, consisting of sand or gravel and formed hy
downstream avalanche-face progradation; and point or sidP hars. formed by hedform
coalescence and chute and swale development in areas of low energy. Important sedi-
ment-forminll processes include bar formation, channel-tloor dune migration, low-water
accretion and overbank sedimentation.
Braided-stream deposits consist of up to three gravel facies, five sand facies and two
fine-grained facies. Vertical sequences recorded in modern and ancient deposits are of
se\'f':':\1 :ypes: tlood-, channel fill-, valley fill-, channei .-e-occupation-and point bar-cycles.
Sur.~. 11 these fine upward and could be confused with meandering-river sequences.
Fae1t>:-. ;t:;st-mblal!f'S and vertical sequences fall into four main classes, which are proposed
as sedimentation modei:. for the interpretation of ancient braided-river dtposits in the sur-
face and subsurface :
(1) Scott type: copsists mainly of longitudinal har gravels with sand lenses formed by
infill of channels and scour hollows durin~ low water.
(2) DonJek type: may be dominated oy sand or wave!; distinguisht-d by fining-upward
cycles caused by lateral point-bar accric'tion or vertical chann£>1 aggradation . Cycl£>s com-
monly are less t;lan 3m thick, but ~ycles up to 60 m may be present. representing valley-
fill ,p !l1Pnce1' Longitudinal anri li.lgUOid·bar deposits. channel-tloor dunt> deposits, bar-top
and ·' :prb:-.nk deposits all may i·e important.
; _; 1 Piacte type: characterhed by an abundance of !inguoid bar and d ~ne deposits
\planar and trough crossbeddin~). No well-developed cyclicity, probably owing to a lack
of topographic differentiaticn in the rivu (no evidence of deep, primary channels, aban·
doneJ areas or overbank areas).
(4) Bijou Creek type . consists of horizontally laminated sand plus subordin;ne
amounts of sand showing planar crossbedding and ripple mo..:ks. Formed during nash
floods and may be most typicaJ of ephemeral streams .
INTRODUCTION
Braided rivers and meandering rivers commonly are regm·deJ as the two
main river types in the geological literature. Meandering rivers, it is now
widely understood, form deposits primarily by the action of lateral accretion