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.