What can cause a gap in the rock record

 The gaps in the rock are known as discontinuities that are basically caused by erosion. The unconformities in the rock is mainly caused by the erosion that represent the irregular line on the surface of the rock. The layer of each rock create a gap between the upper and the lower layer.  

Sometimes, the process of the over thrust can cause the gap on the surface of the rocks as the layer of the rock are set one over the another in the geological rock records.

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