A parasequence is a fundamental concept of
sequence stratigraphy
Sequence stratigraphy is a branch of geology, specifically a branch of stratigraphy, that attempts to discern and understand historic geology through time by subdividing and linking sedimentary deposits into unconformity bounded units on a variety ...
. Parasequences are not directly related to
sequences.
Definition
A parasequence is defined as a genetically related succession of
bedsets that is bounded by
marine flooding surface Marine flooding surfaces are a fundamental concept in sequence stratigraphy, where they form the limiting surfaces of parasequences.
A marine flooding surfaces is defined as a sharp contact that separates overlying younger strata with deep-water ...
s (or their correlative surfaces) on top and at the bottom.
The succession is supposed to be relatively conformable in the sense that breaks in deposition within the parasequence are much shorter than the time of deposition of the parasequence itself.
Most parasequences show a shallowing upward,
which is sometimes also included into the definition.
Properties
Since parasequences are relatively conformable, so
Walther's law applies within a parasequence. This is not necessarily the case for transitions from one parasequence to another. They are also typically of the size of one up to tens of meters.
References
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[ {{Cite journal, last=Van Wagoner, first=JC, date=1988, title=An overview of the fundamentals of sequence stratigraphy and key definitions, language=en, publisher=Special Publications of SEPM ]
Sequence stratigraphy