Sequence Stratigraphy as a “Concrete” Stratigraphic - SEPM Strata

definition of the maximum regressive surface as discussed above and the apparent
coincidence of the theoretical CC and the empirical MRS in deep basinal settings is not
unreasonable, as will be discussed in more detail later.
To us, the deductive correlative conformity, although it has theoretical appeal, is not a
bona fide sequence-stratigraphic surface because of the lack of any defining
characteristics which would allow such a surface to be recognized with any semblance of
scientific objectivity (i.e with empirical observations) in most data sets. We thus reject its
use as either a potential unit boundary or correlation framework surface in sequence
stratigraphy. As will be described later, it appears that the start of base level rise can in
many instances be approximated by the MRS and, given this, the CC would be redundant
in most cases.
Within-trend Facies Contact (WTFC)
Embry (2001, 2002) introduced the within-trend facies contact and this terminology has
been adopted by Catuneanu (2006). This surface is defined as a conformable or
diastemic contact between two distinct lithofacies and it occurs within a regressive or
transgressive succession. It does not represent a change in depositional trend and thus it is
a lithostratigraphic surface and not a sequence stratigraphic one. It forms most commonly
as facies prograde and retrograde in response to the interaction of base level changes and
sediment supply. In most cases it is a highly diachronous surface and time lines pass
through it at a high angle. As discussed by Embry et al (in press), there are a few
instances when such a contact has a low diachroniety. The contacts of an ash bed are the
classic example of this. The basal boundary of individual turbidite flows and storm
deposits can also have low diachroniety. However such specific contacts are of limited
areal extent, and, on a regional scale, the base of the first turbidite or storm deposit is
highly diachronous. Just as a magnetostratigraphic boundary would not be acceptable as a
biostratigraphic boundary, a lithostratigraphic contact is not acceptable as a sequence
stratigraphic contact. It is most important that within-trend facies contacts are not used to
bound sequence stratigraphic units. Any attempt to do so violates basic stratigraphic
principles.
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