Sequence Stratigraphy as a “Concrete” Stratigraphic - SEPM Strata

A subaerial unconformity represents a significant gap in the stratigraphic record as
determined by its relationship to overlying (onlapping) and underlying (truncated) rocks.
As discussed by Barrell (1917), it is interpreted to be formed during base level fall by
subaerial erosional processes especially those connected to fluvial or chemical erosion.
In regards to its relation to time surfaces, it is an approximate time barrier and time
surfaces, for the most part, do not pass through it. In other words, almost all strata below
the surface are older than almost all those above. There are definitely exceptions to this
and these can be associated with migrating uplifts (Winker, 2002). Also, a small amount
fluvial strata overlying an SU may have been deposited during base level fall (Suter et al,
1987; Galloway and Sylvia, 2002; Blum and Aslan, 2006) and is thus older than some of
the down-dip strata below the unconformity).
As will be discussed below, a surface with all the above characteristics but with marine
strata above is best classed as an unconformable shoreline ravinement rather than a
subaerial unconformity. Importantly, the formation of a subaerial unconformity was
deduced in the Wheeler (1958) and Jervey (1988) models and it expands basinward
during base level fall. A subaerial unconformity meets all the criteria for a useful surface
in sequence stratigraphy. Although the surface has been given other names besides
subaerial unconformity such as lowstand unconformity (Schlager, 1992), regressive
surface of fluvial erosion (Plint and Nummedal, 2000) and fluvial entrenchment/incision
surface (Galloway and Sylvia, 2002), the term subaerial unconformity has the widest
acceptance and is the best one to use for this surface.
Regressive Surface of Marine Erosion (RSME)
This surface was first empirically recognized and named by Plint (1988). It is a sharp,
scoured surface which separates underlying offshore marine strata that coarsen and
shallow upwards from overlying shoreface strata that also coarsen and shallow upwards
(Fig. 9). Thus it lies within an overall regressive succession but can be considered as a
change in depositional trend from deposition to non-deposition. It most cases erosion
beneath the RSME is minor and localized and thus it can usually be considered a diastem
rather than an unconformity. However the potential for more substantial erosion exists
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