In geology, a sequence is a stratigraphic unit which is bounded by an unconformity at the top and at the bottom.
[1] In a more rigorous and general way, a sequence is defined as a "relatively conformable [...], genetically related succession of strata bounded by unconformities or their correlative surfaces"[2] Special cases of sequences include type 1 sequences and type 2 sequences.
[3] A related concept are parasequences.
Contrary to their name they are not smaller sequences.
This article about stratigraphy is a stub.