Embry, Ashton F.1
(1) Geological Survey of Canada, Calgary, AB
ABSTRACT: Third Generation (3G) Sequence Stratigraphy
Sequence stratigraphy has been continually evolving since Larry Sloss proposed it in
1949. First generation (1G) sequence stratigraphy consisted of the recognition of
unconformity-bounded sequences. Unfortunately this resulted in nomenclatural chaos because
each time an unconformity disappeared a new set of sequences had to be designated.
Second generation (2G) sequence stratigraphy began in 1977 with the publication of papers by Exxon researchers. This methodology resolved the problem of nomenclatural chaos by extending the sequence boundary basinward along a “correlative conformity”. This allowed sequences recognized on the basin margins to be extended over a basin without any nomenclatural change. Further refinements included the recognition of other sequence stratigraphic surfaces and the subdivision of a sequence into systems tracts. This methodology suffered from the application of non-actualistic concepts such as instantaneous base level fall and from the use of invisible time surfaces and highly diachronous, facies contacts for boundaries. These practices resulted in erroneous interpretations of facies relationships and in an unacceptable amount of subjectivity in boundary delineation.
Third generation (3G) sequence stratigraphy maintains the main components of the former methodologies and avoids the pitfalls that have limited their usefulness. In 3G sequence stratigraphy subaerial unconformities and maximum regressive surfaces are used as sequence boundaries and a sequence is subdivided into a transgressive systems tract and a regressive systems tract by a maximum flooding surface. This objective methodology elevates sequence stratigraphy to a rigorous scientific discipline that marries inductive observations with theoretical deductions of stratigraphic development during base level change.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.