A braided river system in Iceland.
Stephen Lewis
Stephen Lewis
A braided river system in Iceland.
Braided River Systems
Braided River Systems have played a critical role in determining the way in which the sediments were deposited and the characteristics of the Millstone Grit that constitutes the rock blocks, tors and outcrops visible at Brimham.
Dr Roman Soltan
A detailed study of the rocks at Brimham shows that there are a number of specific characteristics that together provide very strong evidence that a braided river systm was responsible for the nature of the deposition of the sediments, particularly those that make up the tor features.
These are:-
1
Sediments are coarse-grained
2
Abundance of planar cross-bedding
3
Cross-bedding shows predominantly down-current dipping
4
Numerous in-channel bars and in-channel fill deposits
5
Lateral accretion and fill composed of sandy not fine grained facies
Characteristic No. 1
Coarse-grained
Many rocks show larger exposed quartz pebbles in distinctive layers.
Characteristic No. 2
Planar cross-bedding
Cross-bedding planes are common and visible on numerous rocks.
Characteristic No. 3
Down-current dipping
The bedding planes are at an angle to the horizontal.
Characteristic No. 4
In-channel bars
Complex bedding planes are an indication of the sediment flows being altered by the presence of snady bars within the river channels.
Characteristic No. 5
Lateral accretion
Indicative of the build up of sediment layers just above and below the sand bars.
Coarse grained
Normal flow conditions.
Flood and high energy flow conditions.
Post-flood, sorting completed.
Cross-bedding
Sediment builds up on the upstream side, the stross side, driven up the slope by the river current.
The current pusshes the sediment that has built up over the top of the slope and down the down-stream slope, the lee side.
The process is repeated and the down-stream layers build up.
Down current dipping
IIn-channel bars
Lateral accretion..
