# Why some layers can be missing from the sequence in some outcrops?

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#### Explanation

Explain in detail...

#### Explanation:

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1
Feb 8, 2018

For a number of reasons

#### Explanation:

Let us take a marine (coastal) depositional sequence to make it simple.
A variation of sea level may produce a "iatus" that is a break in the sequence due to the fact that, for a given period, there was no sea to deposit any sediments.

A change of "facies", that is for a given period the coastal environment ceased to produce the specific depostits (the mutation of a river's course, a climatic change, volcanic traps...)

Tectonic "overthrust": after the deposition of a continuous series tectonic forces may displace an allogenous series and place it on top of the existing one.

Reverse faulting, which is equivalent to high angle overthrusts with similar effect.

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