Page 147 - Sedimentology and Stratigraphy

134 Rivers and Alluvial Fans

Fig. 9.8 This large braided river has
moved laterally from right to left.

it is complete, but it is common for the top part to be channel and hence recognise individual channel-fill
eroded by the scour of a later channel. successions.
In regions where braided rivers repeatedly change
position on the alluvial plain, a broad, extensive
region of gravelly bar deposits many times wider 9.2.2 Mixed load (meandering) rivers
than the river channel will result. These braidplains
are found in areas with very wet climates or where In plan view the thalweg (9.1.2) in a river is not
there is little vegetation to stabilise the river banks straight even if the channel banks are straight and
(e.g. glacial outwash areas: 7.4.3). The succession parallel (Fig. 9.10): it will follow a sinuous path,
built up in this setting will consist of stacks of cross- moving from side to side along the length of the
stratified conglomerate, and it can be difficult to channel. In any part of the river the bank closest to
identify the scour surfaces that mark the base of a the thalweg has relatively fast flowing water against it

Fig. 9.9 Depositional architecture
of a braided river: lateral migration

of the channel and the abandon-
ment of bars leads to the build-up of

channel-fill successions.