image: ripple marks on quartzite bed
Ripple marks are the primary
sedimentary structures which are formed before the formation of sedimentary rocks.
These structures are formed between
the sediment deposition and the rock formation.
Generally ripple marks are formed by
the action of water or by the action of wind.
So on the basis of their medium of
formation they may be eolian or aqueous.
Ripple marks are formed at the bottom
of the water body by the action of water or may be at the surface by the wind.
On the basis of the flow of the current,
ripple marks are of two types:
1)
Oscillation ripples:
It consists of sharp crests and board
troughs.
Crests are convex upward whereas
troughs are convex downwards.
The sharp crest points towards the
younger beds, whereas the broad troughs points to older beds.
It is formed in the stagnant water
bodies.
Whenever the wave disturbs the upper
surface of the water body, the particles at the bottom are also disturbed.
Then the particle moves along the
flow of the current forming the primary marks on the sediments as a oscillation
ripple marks.
By knowing the direction of crests
and troughs, the direction of bed can be determined.
2)
Current ripples:
Both crests and troughs are rounded.
It is generally characterized by
gentle current slope towards upward direction and steeper current flow towards
downward.
These ripples are developed when the
current either water or wind moves across the particles.
Determining bed direction by ripples:
For example: when the crest of the
ripple marks present on the bed at certain angle points upward to the left then
the bed is right-side-up.
But if the same crest points downward
to the right then the bed is overturned as the crest always points towards the
younging direction.
Awesome!!! Thanks for the lesson!!😊 🙏 😊
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