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Published online by the Canadian Society of Petroleum
Geologists, October, 2009. The document can be accessed
at http://www.cspg.org

Suggested reference is:
Embry, A.F., 2009, Practical Sequence Stratigraphy. Canadian
Society of Petroleum Geologists, Online at www.cspg.org, 79 p.

The fifteen chapters were originally published as separate
articles in fifteen issues of the CSPG monthly publication, The
Reservoir, May, 2008 – September, 2009.

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38

clastic strata (e.g., Hunt and Tucker, 1992; Plint
and Nummedal, 2000; Mellere and Steel, 2000;
Coe, 2003; Catuneanu, 2006, and very many
others). The obvious pitfall in using the base
of submarine fan deposits as an equivalent
of a BSFR is that it is highly unlikely the first
gravity flow deposits will coincide, or even
be remotely close to coinciding, with the
start of base-level fall. Turbidite deposition
can be initiated any time during fall and, in
many cases, does not occur at any time during
fall (Catuneanu, 2006). The same logic applies
to the use of the highly diachronous, basal
contact of a shallow marine deposit for a
BSFR (e.g., Burchette and Wright, 1992). Such
a facies contact forms throughout the entire
interval of fall as the shallow water facies
progrades basinward over deeper water
facies. A serious problem of trying to equate
a BSFR with inappropriate materialbased
surfaces as discussed above is that such a
pract ice can result in mis leading and
erroneous interpretations of depositional
history.

Given the above arguments, a BSFR is best
seen as a purely deductive construct (i.e.,
hypothet ica l surface) which has no
characteristic physical attributes to allow its
recognition in well exposed strata, in core,
and on almost all seismic lines. Despite these
issues, the BSFR has been proposed as both
a sequence boundary (Posamentier and Allen,
1999) and a systems tract boundary (Hunt
and Tucker, 1992; Plint and Nummedal, 2000;
Catuneanu, 2006). The pract ica l i ty of
employing a “cryptic”, time-based surface as
a unit boundary wi l l be discussed in
forthcoming articles that look at how
sequence stratigraphic units are defined.

Correlative Conformity (CC)Correlative Conformity (CC)Correlative Conformity (CC)Correlative Conformity (CC)Correlative Conformity (CC)
Hunt and Tucker (1992, p. 6) characterized a
correlat ive conformity, as “truly a
chronostratigraphic surface” equivalent to
the depositional surface (clinoform) at the
end of base-level fall (i.e., start base-level
rise). It represents the sea floor at the
moment in time when base-level fall gives
way to base-level rise. Like the BSFR, a CC is
model-dependent and had not been
described as a distinct surface before the
Jervey (1988) model for explaining the origin
and geometries of sequence stratigraphic
surfaces was published. Hunt and Tucker
(1992) did not provide any specific criteria
which would allow the recognition of a CC
except in areas of submarine fan deposition.
Hel land-Hansen and Gjelberg (1994),
Helland-Hansen and Martinsen (1996), and
Catuneanu (2006) have elaborated on this
surface and advocated for its use in sequence
stratigraphic classification.

From a theoretical point of view, the CC
joins the basinward end of the subaerial

unconformity (SU) in a ramp setting for the
slow initial rise model (described in part 7
of this series) (F igure 8.3, page 37) .
Basinward, it occurs within a coarsening-
upward succession situated between the MFS
below and the MRS above. In a ramp setting
for the fast initial rise model, the CC will be
truncated at the end of the unconformable
shoreline ravinement (SR-U) (Figure 8.2,
page 36). In a shelf / slope / basin model,
where an SOS develops, and for either slow
or fast initial base-level rise, the CC will
theoretically occur in a succession of basinal
turbidites and will onlap the SOS (Figure 8.4,
page 37).

To my knowledge, no one has ever published
any observable criteria for recognizing the
correlative conformity over most of a basin.
This is not surpris ing g iven that no
sedimentary break or change in
sedimentation style or trend occurs over
much of the marine area at the start of base-
level rise, especially when base-level rises
slowly at the start (Figure 8.3, page 37).

This lack of observable characteristics is
recognized by Catuneanu (2006, p. 122) who
states “The main problem relates to the
difficulty of recognizing it in most outcrop
sect ions, core or wirel ine logs.” As
Catuneanu (2006) explains, the correlative
conformity “develops within a conformable
prograding package (coarsening upward
trends below and above); lacking any
lithofacies and grading contrasts”. The main
problem associated with the correlative
conformity is also enunciated by Plint and
Nummedal (2000, p. 5) who succinctly state
“From a practical point of view, this marine
surface will be difficult to impossible to
identify.”

Catuneanu (2006) and Catuneanu et al. (in
press) suggest that seismic data offer the
best opportunity to identify and correlate a
CC. A CC can be approximated by a
basinward seismic reflector which joins with
a more landward reflector that encompasses
the SU and / or the SR-U. Catuneanu (2006)
interprets such a seismic-based CC in his
Figure 4.17. As shown in Figure 8.2 (page
36), the MRS and the CC will theoretically
a lmost coincide when the start of
transgression occurs very soon after start
of base- level r ise and perhaps more
important ly, the MRS adjoins to the
basinward end of the unconformity. In this
case the seismic ref lector which
encompasses a theoretical CC will also
encompass a material-based MRS. The
question remains if a seismically recognized,
time-based CC for a ramp setting is in
actuality a material-based MRS. I suspect it is
in most, if not all cases, but we need studies
involving core and seismic to resolve the

question of whether or not a CC is a real
surface which has physical properties that
can generate a seismic reflector. The other
material-based surface which is sometimes
labeled as a CC on seismic is the slope onlap
surface (SOS). The reason for such a
portrayal is shown in Figure 8.4 (page 37),
which i l lustrates that the landward
termination of the SOS adjoins the basinward
termination of the basin flank unconformity
(SU or SU / SR-U). Thus the same seismic
reflector that encompasses the SU / SR-U on
the basin flank encompasses the SOS farther
basinward.

Hunt and Tucker (1992) suggested that the
change from a coarsening-upward succession
of turbidites to a fining-upward succession
might approximate such a boundary and this
has theoretical support (Catuneanu, 2006).
However, the material-based maximum
regressive surface would also be placed at
such a horizon of change in depositional trend
(coarsening trend changing to a fining trend).
Notably, Catuneanu (2006) and Catuneanu
et al. (in press) would not put the time-based
MRS at this horizon, but rather would place
it strat igraphical ly higher at an often
unrecognizable (“cryptic”) horizon within
shaly turbidites. The position of this horizon
depends on a specific sequence stratigraphic
model.

This significant difference in the placement
of the MRS in deep water strata highlights
the essential difference between the two
approaches to surface defin it ion. The
material-based approach uses an MRS with
defined, observable criteria whereas the
time-based approach uses a theoretical,
model-dependent, indefinite horizon for the
MRS.

In summary, the correlative conformity,
although it has theoretical appeal, is a time-
based, sequence-stratigraphic surface lacking
defining characteristics which would allow
such a surface to be recognized with
reasonable scientific objectivity (i.e., with
empirical observations) in most data sets.
Despite these formidable problems, the CC
has been proposed as both a sequence and
systems tract boundary (Hunt and Tucker,
1992; Plint and Nummedal, 2000; Catuneanu,
2006). The practicality of such usage will be
discussed in future articles in this series.

With this article, all the various specific types
of sequence stratigraphic surfaces which have
been recognized / proposed, including both
material-based ones and time-based ones,
have been described. Such surfaces provide
the means for defining a variety of specific
types of sequence stratigraphic units.
Material-based sequence stratigraphic units
are defined by various combinations of

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39

bounding, material-based surfaces. Timebased
sequence stratigraphic units employ the
time-based surfaces discussed above, in
addition to material-based surfaces, for
defining unit boundaries. The existence of
both material-based units and time-based
units has been a major source of confusion
for those wanting to employ sequence
stratigraphic units in their studies and to
communicate their findings. In the next
article, I will describe and evaluate the
pract ica l i ty of the di f ferent types of
sequences, both material-based and time
based, which have been proposed for use. In
subsequent articles, I’ll tackle systems tracts,
followed by parasequences.

ReferencesReferencesReferencesReferencesReferences
Burchette, T. and Wright, V.P. 1992. Carbonate ramp
depositional deposits. Sedimentary Geology, v.79,
p. 3-57.

Catuneanu, O. 2006. Principles of Sequence
Stratigraphy. Elsevier, New York, 375 p.

Catuneanu, O. et al. In press . Towards the
Standardization of Sequence Stratigraphy. Earth
Science Reviews.

Coe, A. (ed.) 2003. The sedimentary record of
sea-level change. Cambridge University Press,
New York, 287 p.

Cross, T. 1991. High resolution stratigraphic
correlation from the perspective of base level
cycles and sediment accommodation. In:
Unconformity related hydrocarbon exploration
and accumulation in clastic and carbonate
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Mountain Association of Geologists, p. 28-41.

Embry, A.F. 1995. Sequence boundaries and
sequence hierarchies: problems and proposals.
In: Sequence stratigraphy on the northwest
European margin. R. J. Steel, F. L. Felt, E.P.
Johannessen, and C. Mathieu (eds.). NPF Special
Publication 5, p. 1-11.

Embr y, A .F. 2008a. Pract ica l Sequence
Stratigraphy IV: The Material-based Surfaces of
Sequence Stratigraphy, Part 1: Subaerial
Unconformity and Regressive Surface of Marine
Erosion. Canadian Society of Petroleum Geologists,
The Reservoir, v. 35, issue 8, p 37-41.

Embr y, A .F. 2008b. Pract ica l Sequence
Stratigraphy VI: The Material-based Surfaces of
Sequence Stratigraphy, Part 3: Maximum Flooding
Surface and Slope Onlap Surface. Canadian
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35, issue 10, p 36-41.

Helland-Hansen, W. and Gjelberg, J. 1994.
Conceptual basis and variability in sequence
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Helland-Hansen W. and Martinsen, O.J. 1996.
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Hunt , D. and Tucker, M. 1992. Stranded
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Jervey, M. 1988. Quantitative geological modeling
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approach. C. Wilgus, B.S. Hastings, C.G. Kendall,
H.W. Posamentier, C.A. Ross, and J.C.Van Wagoner
(eds.). SEPM Special Publication 42, p.47-69.

MacNeil, A. and Jones , B. 2005. Sequence
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Mellere, D. and Steel, R. 2000. Style contrast
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central Wyoming (Hatfield Member of the
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Plint, A. and Nummedal, D. 2000. The falling stage
systems tract: recognition and importance in
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responses to forced regressions. D. Hunt, and R.
Gawthorpe (eds.). Geological Society of London,
Special Publication 172, p.1-17.

Posamentier, H. 2001. Sequence stratigraphy:
Balancing the theoretical and the pragmatic
(abstract). Canadian Society of Petroleum
Geologists, The Reservoir, v. 28, issue 11, p. 14.

Posamentier, H. and Allen, G. 1999. Siliciclastic
sequence strat igraphy � concepts and
applications. SEPM Concepts in Sedimentology
and Paleontology, no. 7, 210 p.

Posamentier, H., Allen, G., James, D., and Tesson, M.
1992. Forced regress ion in a sequence
stratigraphic framework: concepts, examples and
exploration significance. AAPG Bulletin, v. 76, p.
1687-1709.

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provide a top seal. Similar fairways of porous,
nearshore sandstone can sometimes be
delineated for TSTs and, in this case, the
sandstone will often pinchout landward due
to onlap onto a shoreline ravinement. Such
sandstone is usually well sealed by overlying
shale and siltstone that were deposited as
transgression progressed.

There can be no doubt that the proper
interpretation of depositional facies is critical
for successful explorat ion. The same
sentiment applies to the surfaces of sequence
stratigraphy and an incorrect interpretation
of a given surface can lead to misdirected
exploration. Often only mechanical logs are
available for a sequence interpretation and
in this situation an unconformable shoreline
ravinement can be easily be mistaken for a
maximum regressive surface and viceversa.
On a gamma log, both surfaces are drawn at
the change from a shal low marine,
coarsening-upward succession (RST) to a
shallow marine, fining-upward one (TST). If
the underly ing coarsening-upward
succession terminates in shaly, mid-shelf
sandstone, the explorat ionist would
naturally want to locate potentially porous,
shoreface sandstone in that RST. If the surface
encountered in the control point is a
maximum regress ive surface, then a
shoreface sandstone unit would occur
landward of the control well. However, if
the surface is an unconformable shoreline
ravinement then the shoreface sandstone
unit would occur basinward of the control
well, in exactly the opposite direction as was
dictated by the MRS interpretation. As
illustrated by this example, the correct
interpretation of sequence stratigraphic
surfaces is critical for exploration success.

Concluding RemarksConcluding RemarksConcluding RemarksConcluding RemarksConcluding Remarks
This article wraps up the Practical Sequence
Stratigraphy series, which has covered the
main topics of sequence strat igraphy
including historical development, the
surfaces of sequence stratigraphy, the linkage
between base level and sequence
stratigraphic surfaces, the units of sequence
stratigraphy, and more general topics of
sequence hierarchies, correlation, and
sequence boundary origin.

Sequence stratigraphic analysis is a core
methodology in petroleum exploration. If it
is applied in an objective, pragmatic manner
with the use of a material-based surfaces
and units, it can greatly enhance petroleum
exploration and exploitation. The method
involves:

• Identification of sequence stratigraphic
surfaces in a succession,

• Correlation of the surfaces over the
study area,

• Determination of the facies
distribution within the sequence
stratigraphic framework,

• Interpretation of the depositional
history of the succession in terms of
tectonic and/or eustatic base-level
changes,

• Construction of facies maps at both
the approximate time of maximum
regressive and the approximate time
of maximum transgression for each
sequence.

With the adoption of this methodology,
sequence stratigraphy becomes a valuable
addition to the explorationist’s tool kit.

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