Sequence Stratigraphy as a “Concrete” Stratigraphic - SEPM Strata

time surface at the start of base level fall for the correlative conformity (Jervey, 1992,
Posamentier and Allen, 1999). Such a sequence was divided into three systems tracts
(LST, TST and HST) (Fig. 7). The other sequence model used the entire subaerial
unconformity and the time surface at the start of base level rise (Hunt and Tucker, 1992;
Plint and Nummedal, 2000) for its boundary. As previously described, this sequence
model had four systems tracts (LST, TST, HST, FRST) (Fig.6). These two models
basically represent a revised Type 1 model and a revised Type 2 model although few
workers actually recognize this clear correspondence.
An added source of confusion with the model of Hunt and Tucker (1992) is that the
forced regressive systems tract (FRST) is also referred to as falling stage systems tract
(FSST) (Nummedal et al, 1993; Plint and Nummedal, 2000). Making a bad situation
worse, this systems tract was later called the regressive systems tract by Naish and Kamp
(1997). The Naish and Kamp (1997) proposal is a fine example of thoughtless
nomenclature because, not only were there already two different names for the exact
same unit, the term regressive systems tract was already in use for an entirely different
type of sequence unit (Embry and Johannessen, 1992). Fortunately, the doubly
problematic nomenclature of Naish and Kamp (1997) has been ignored by most workers.
Given these two distinctly different ways of delineating the boundaries for sequences and
systems tracts through model-driven sequence stratigraphy, it is not surprising there was,
and continues to be, considerable confusion and miscommunication in sequence
stratigraphy. However, the occurrence of two overlapping but different ways of defining
a sequence and its component systems tracts was not the only problem for the modeldriven
approach. As discussed below, model-driven methods and terminology suffer from
a far more serious problem – the impossibility of being able to recognize some of the
proposed, model-driven, bounding surfaces in an objective, scientific fashion. This
critical problem is discussed in detail when the surfaces of sequence stratigraphy are
described and evaluated and the different options for defining a sequence boundary are
examined.
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