Sequence Stratigraphy as a “Concrete” Stratigraphic - SEPM Strata

others will be experiencing base level rise(normal regression). Thus the “start of forced
regression” occurs at many different times during an interval of base level fall and the
reason for this is that the shoreline along its extent occupies areas with markedly different
rates of subsidence. In fact, forced regression may not even occur during some times of
base level fall when the subaerial unconformity never extends beyond the coastal plain.
Plint and Nummedal (2000) and Catuneanu (2006) characterize the BSFR as the
clinoform representing the start of offlap along a given transect perpendicular to the
shoreline. Because offlap (forced regression) will begin at very different times along a
shoreline, there will be many such clinoforms developed parallel to depositional strike.
Notably such theoretical time surfaces were never recognized or even considered to be
present in the stratigraphic record until the Jervey Model was published and thus have no
empirical roots.
Unfortunately, it is impossible to recognize “the first clinoform associated with offlap” in
almost every conceivable geological setting. Such a time surface has no observable
characteristics which allow it to be recognized with any semblance of scientific
objectivity. It occurs within a succession of coarsening-upward strata and no
sedimentological variation or change in grain size trend, which might mark the surface
occurs in the succession (Fig. 11). This lack of objective criteria for the recognition of
such a surface over most of the basin has been noted by Posamentier and Allen (1999),
Plint and Nummedal (2000) and Catuneanu (2006) among others. Posamentier and Allen
(1999, p.90) state “it exists only as a chronohorizon, .. precise identification .. can be
limited”. Plint and Nummedal (2000, p. 5) note that such a time surface is “difficult or
impossible to recognize in outcrops or well logs”. Catuneanu (2006, p.129) admits “the
basal surface of forced regression .. has no physical expression in a conformable
succession of shallow water deposits”. Thus it is widely accepted that the BSFR is a
theoretical surface (or set of surfaces) which has no physical attributes to allow its
objective recognition in well exposed sections or in core.
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