Aggradation

Aggradational Parasequence Set

Bedsets

Bounding Surfaces

Marine Flooding

Parasequence Set

Progradation

Progradational Parasequence Set

Retrogradation

Retrogradation Parasequence Set

Sequence

Stacking Patterns

Systems Tracts

Well-Log Seq-Strat

A relatively conformable succession of genetically related beds or bedsets (within a parasequence set) bounded by marine flooding surfaces or their correlative surfaces (Van Wagoner, at SEPM's 1985 Midyear Meeting). Patterns of the stacking of parasequence sets are used in conjunction with bounding surfaces and their position within a sequence to define systems tracts (Van Wagoner et al., 1988).

Thus a parasequence is commonly identified and seperated from other parasequences by flooding surfaces and is often characterized by a cycle of sediment that either coasens or fines upward. Thus the flooding surfaces are usually identified by abrupt and correlatable changes of the grain size of the sediments on either side of that flooding surface. This change in grain size is often caused by the abrupt changes in energy that are associated with the waves or currents of the sea transgressing across the sediment interface. These abrupt changes in grain size that bound a parasequence can be identified in well logs, outcrop and seismic and used to identify a parasequence cycle. Examples of these grain size changes can be seen in the parasequences of tidal flats, beaches, and deltas.