The study of the large-scale three-dimensional arrangement of sedimentary strata, and
the factors that influence the geometry of these sedimentary
packages. Sequences are defined as groups of strata that are
bounded above and below by identifiable surfaces that are
at least partly unconformities. Many sequence boundaries
show up well in seismic reflection profiles, enabling their
identification in deeply buried rock packages. Sequence
stratigraphy differs from classical stratigraphy in that it
groups together different sedimentary facies and depositional
environments that were deposited in the same time
interval, whereas classical stratigraphy would separate
these units into different formations. By analyzing the
three-dimensional shape of time-equivalent packages, the
depositional geometry and factors that influenced the deposition
are more easily identified. Some of the major factors
that control the shape of depositional sequences include
global sea-level changes, local tectonic or thermal subsidence
or uplift, sediment supply, and differential biologic
responses to subsidence in different climate conditions. For
instance, carbonate reefs may be expected to keep pace
with subsidence in tropic climates, but to be absent in temperate
or polar climates. The techniques of sequence
stratigraphy are widely used by sedimentologists and tectonicists
in the petroleum industry to understand regional
controls on sedimentation, and to correlate sequences of
similar age worldwide.
See also PASSIVE MARGIN; STRATIGRAPHY.
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