Toward the Formalization of Sequence Stratigraphy

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By: IWGSS (Octavian Catumeanu, the author of Principles of sequence stratigraphy, 2006)

Abstract

Sequence stratigraphy is a modern and hugely popular approach of integrated stratigraphic
analysis, and yet it is the only type of stratigraphy that is not standardized in international
stratigraphic codes. This paradox is explained by the existence of several competing models, and
by the dissemination of confusing or even conflicting terminology. The key to the formal
inclusion of sequence stratigraphy within the array of stratigraphic disciplines is the recognition
of what are core aspects versus those of lesser significance, and an appreciation that the approach
to standardization has to be entirely unbiased. With at least five different sequence stratigraphic
models currently in use, the main task is to find what they have in common, and formalize those
core aspects that everybody can accept, recognizing what is trivial and may be left to the
discretion of the practicing geologist.

It is well-established that all sequence stratigraphic models have merits and pitfalls, and that
success in their application may vary with the case study; otherwise, a single universal model
would have emerged by now. The approach to standardization proposed here is to promote those
concepts that can be accepted by all, and thus retain flexibility in the application of the sequence
stratigraphic method. This approach is in line with the way allostratigraphy is standardized in the
North American Stratigraphic Code and in the International Stratigraphic Guide. After including
the discontinuity/unconformity-bounded units of allostratigraphy in the Code and Guide,
formalizing the concept of ‘sequence’ as a unit bounded by unconformities or their correlative
conformities is the next logical step, long overdue. Once the ‘sequence’ is formalized as a
generic concept, one can take a step further and list the various types of sequences, by defining
what surfaces are selected as sequence boundaries in each case. Because no one model may
provide the optimum approach for all circumstances, trying to define what specific surfaces of
sequence stratigraphy should receive the formal status of ‘sequence boundary’ is not practical,
and will never provide an acceptable solution for all groups. Furthermore, depending on location
within the basin, each sequence stratigraphic surface may be ‘practical’ (i.e., easy to map) in
some depositional systems and ‘impractical’ (i.e., difficult to map) in others. Similarly, the
mappability of various sequence stratigraphic surfaces also depends on the type of data (e.g.,
outcrop vs. well-log vs. seismic) available for analysis. This paper strives to identify the common
ground between the various sequence stratigraphic ‘schools’, and assesses what is reasonable to
standardize at this point in international stratigraphic codes or guides.