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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
(Begin page 1967)
AAPG Bulletin, V.
Nonmarine
sequence
stratigraphy: Updip
expression of
sequence
boundaries and systems tracts in a high-resolution
framework, Cenomanian Dunvegan Formation, Alberta foreland basin,
Canada
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A. Guy Plint,1
Paul J. McCarthy,2 Ubiratan F.
Faccini3
1Department of Earth Sciences, University
of Western Ontario, London, Ontario, Canada, N6A 5B7; email: [email protected]
2Department of Geology and Geophysics, and Geophysical
Institute, University of Alaska, Fairbanks, Alaska, 99775-5780;
email: [email protected]
3Universidade do Vale do Rio dos Sinos-UNISINOS, Geologia-Centro
7 Av Unisinos 950, Sao Leopoldo-RS, Brasil, 93022-000; email:
[email protected]
AUTHORS
Guy Plint received a B.Sc. degree from the University of Reading in 1977 and a D.Phil. from the University of Oxford in 1981. After postdoctoral fellowships at the University of New Brunswick (1981-1984) and McMaster University (1984-1986), he joined the faculty at the University of Western Ontario. His current research interests include sedimentology and high-resolution stratigraphy in the Cretaceous of the Western Canada basin and in the Oriente Basin of Ecuador, in an effort to understand controls on cyclic sedimentation.
Paul McCarthy received B.Sc. and M.Sc.
degrees from the University of Western Ontario and a Ph.D. from
the University of Guelph, Canada. From 1996 to 1999 he was a postdoctoral
fellow at the University of Western Ontario. Since June 1999 he
has been an assistant professor of geology at the University of
Alaska, Fairbanks. His current research interests include paleopedology,
fluvial sedimentology, and nonmarine sequence
stratigraphy of
Paleozoic and Mesozoic alluvial deposits in Alaska, western Canada,
and Nova Scotia.
Ubiratan F. Faccini is currently an associate
professor at Universidade do Vale do Rio dos Santos (UNISINOS),
Brazil. He received his B.Sc. (1983) and M.Sc. (1990) degrees
in geology from Universidade Federal do Rio Grande do Sul. Presently
he is concluding his Ph.D. thesis at that university. His research
focuses on sedimentology and application of sequence
stratigraphic
concepts to nonmarine deposits, with particular interest in the
Permian and Triassic red beds of the Parana basin, Brazil.
ACKNOWLEDGMENTS
This project began in 1984 during a postdoctoral
study by Plint, under the supervision of Roger Walker-little did
we realize what a monster we had tackled! The results reported
here build on 15 seasons of field work and many years of well
-
log
correlation. We thank Joyia Chakungal, Steve Donaldson, Patrick
Elliott, Yuanxian Hu, Sid Leggett, Matthew Lumsdon, Dany Martinioni,
Chantale McIntosh, Jennifer McKay, Joanna Moore, Annemarie Plint,
Julie Sanders, David Uličn¦, and Jennifer Wadsworth
for unstinting field assistance at different stages of the project.
We are very grateful to the Natural Sciences and Engineering Research
Council of Canada for long-term support through four grant cycles,
and we also thank Amoco Canada, Canadian Hunter Exploration Ltd.,
Home Oil Ltd., Husky Oil Operations Ltd., Pan Canadian Petroleum
Ltd., Petro-Canada Ltd., Wascana Energy Inc., and Union Pacific
Resources Inc. for additional generous support. Faccini thanks
UNISINOS for granting leave to pursue work on the Dunvegan Formation
and the Brazilian Government (FAPERGS and CAPES) for supporting
his work on nonmarine
sequence
stratigraphy in Canada and Brazil.
Janok Bhattacharya kindly supplied copies of the working cross
sections from his Ph.D. research, thereby saving us many months
of correlation, and Margot McMechan provided palinspastic restoration
of our Foothills outcrop sections. David Mercer photographed all
the drawings. Informal reviews by Nick Christie-Blick, Mike Leeder,
Andrew Miall, and Chris Paola stimulated some serious rethinking,
although we stress that our interpretations do not necessarily
reflect the views of these colleagues. We appreciate formal reviews
by Mike Blum, Ashton Embry, and Lesli Wood who did much to broaden
our thinking and weed out logical and terminological inconsistencies.
Responsibility for remaining errors and omissions remains with
us.
ABSTRACT
Ten allomembers, labeled J-A, have been
mapped in the deltaic Dunvegan Formation using 2340 wells and
63 outcrop sections. Each allomember spans about 200 k.y., is
bounded by regional transgressive surfaces, and consists of 3-10
component shingles, apparently of autogenic origin. Allomembers
H-E are discussed in this article. Their internal stacking patterns
and bounding surfaces permit interpretation as depositional sequences.
Sequences H-F have a sigmoidal-prismatic geometry, downlap to
the southeast, and thin northwest onto the coastal plain. No differential
thickening exists toward the orogen in the southwest. In contrast,
sequence
E thickens markedly toward the northwest. The tabular
geometry of sequences H-F suggests accommodation was controlled
by sea level change, whereas the wedge geometry of
sequence
E
suggests significant tectonic tilting. Subaerial unconformities
that bound valleys and extend onto adjacent interfluve paleosols
can be traced 120-330 km updip into outcrop. The base of each
sequence
is characterized by shoreline backstep of 80-150 km.
Transgressive and highstand shingles in each
sequence
comprise
marine deltaic deposits that pass landward into coastal plain
strata. Falling-stage shingles offlap seaward with little or no
nonmarine equivalents updip, whereas lowstand shingles show renewed
coastal onlap. In outcrop, three nonmarine systems tracts are
recognized: (1) A channel-dominated, low-accommodation systems
tract fills valleys up to 35 m deep and is equivalent to the early
transgressive systems tract. (Begin page 1968) (2) A lacustrine-dominated,
high-accommodation systems tract comprises mudstone enclosing
ribbon channel sandstones, blankets interfluves, and forms the
bulk of each
sequence
. It is equivalent to late transgressive
and early highstand systems tracts. (3) A paleosol-dominated,
low-accommodation systems tract occupies the upper part of each
sequence
and is capped by the
sequence
boundary. It is equivalent
to the late highstand systems tract.
Sequence
-bounding interfluve
paleosols represent tens of thousands of years of pedogenesis
related to slow aggradation, followed by fluvial entrenchment
and clastic bypass, and represent the late highstand, falling-stage,
lowstand, and early transgressive systems tracts. Coastal plain
deposits record only part (perhaps <50%) of the time represented
by each
sequence
. Updip sediment bypass promoted falling-stage
delta progradation, characterized by offlap. These observations
imply that, in this example, the subaerial
sequence
boundary and
fluvial valleys formed initially in updip areas and expanded progressively
seaward.
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