Changes

Individual channels split around numerous mid-channel islands or braid bars. During floods erosion occurs on the upstream ends and lateral sides of bars and eroded material is added to the downstream side of the bar. Because each channel has a different depth, lateral migration of the channel results in scour to differing depths. Multiple fining-upward cycles (which are commonly truncated) occur within the resulting sand body. Each fining-upward cycle (owing to deposition of a laterally migrating channel) is characterized by a scoured base and overlying sets of large-scale cross-bedding in which individual sets are up to 1 m thick ([[:file:M31F2.jpg|Figure1A]]). This lower sequence of large-scale cross-bedding can attain thicknesses of up to 7 m. Small-scale ripple bedding, scour and fill structures, organic trash, and clay layers are occasionally found.

Individual channels split around numerous mid-channel islands or braid bars. During floods erosion occurs on the upstream ends and lateral sides of bars and eroded material is added to the downstream side of the bar. Because each channel has a different depth, lateral migration of the channel results in scour to differing depths. Multiple fining-upward cycles (which are commonly truncated) occur within the resulting sand body. Each fining-upward cycle (owing to deposition of a laterally migrating channel) is characterized by a scoured base and overlying sets of large-scale cross-bedding in which individual sets are up to 1 m thick ([[:file:M31F2.jpg|Figure1A]]). This lower sequence of large-scale cross-bedding can attain thicknesses of up to 7 m. Small-scale ripple bedding, scour and fill structures, organic trash, and clay layers are occasionally found.

Overlying this unit is a zone displaying finer grain size and composed of lenticular-shaped units of large-scale cross-bedding (trough type) intercalated with zones of climbing ripple laminations, horizontal laminations, and ripple cross-bedding ([[:file:M31F2.jpg|Figure 1B]]). In some places small-scale laminations are present within certain zones. The uppermost unit of the fining-upward cycle displays horizontal laminations separating well-defined, near-horizontal sets of steeply dipping ripple-drift bedding ([[:file:M31F2.jpg|Figure 1C]]). Small-scale convolute laminations and burrowed sand and silt layers are common in the uppermost part of the unit. However, scouring by later migration of the channel often removes this upper burrowed section.

Overlying this unit is a zone displaying finer [[grain size]] and composed of lenticular-shaped units of large-scale cross-bedding (trough type) intercalated with zones of climbing ripple laminations, horizontal laminations, and ripple cross-bedding ([[:file:M31F2.jpg|Figure 1B]]). In some places small-scale laminations are present within certain zones. The uppermost unit of the fining-upward cycle displays horizontal laminations separating well-defined, near-horizontal sets of steeply dipping ripple-drift bedding ([[:file:M31F2.jpg|Figure 1C]]). Small-scale convolute laminations and burrowed sand and silt layers are common in the uppermost part of the unit. However, scouring by later migration of the channel often removes this upper burrowed section.

[[file:M31F3.jpg|thumb|300px|{{figure number|2}}Summary diagrams illustrating the major characteristics of braided channel deposits (letters on the vertical section refer to core or outcrop photographs).<ref name=Colemanandprior_1981 />]]

[[file:M31F3.jpg|thumb|300px|{{figure number|2}}Summary diagrams illustrating the major characteristics of braided channel deposits (letters on the vertical section refer to core or outcrop photographs).<ref name=Colemanandprior_1981 />]]