Structural Mapping and Modelling of the Sub

Structural Mapping and Modelling of the Sub-Cretaceous Unconformity
and Delineation of Subcropping Formations, West-Central Alberta
Jesse T. Peterson
Kelsey E. MacCormack
Alberta Geological Survey
402, Twin Atria Building
4999-98 Avenue
Edmonton, AB
www.ags.gov.ab.ca
Stratigraphy
Structural Elevation
The sub-Cretaceous unconformity is an important
regional surface across the Alberta Basin, which
represents a significant period of nondeposition
and erosion initiated after the deposition of Upper
Jurassic / Lower Cretaceous sediments of the
first foreland basin clastic wedge. This major
unconformity surface also separates much of
the basin into two distinct depositional settings:
a lower passive margin and an upper foreland
basin. Structural modelling of the sub-Cretaceous
unconformity and zero-edge delineation of
subcropping formations are an integral part of a
larger project at the Alberta Geological Survey
(AGS) to create a provincial-scale 3D geological
model of the subsurface in Alberta.
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Pembina
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The results of this study were compared with a
previous unconformity surface generated using
pick data from numerous sources of varying quality,
revealing an overall improvement in the surface
prediction and enhanced identification of erosional
features associated with the sub-Cretaceous
unconformity.
Modelling of the unconformity surface will continue
across the province and will be a major component
of the provincial-scale 3D geological model of the
subsurface in Alberta.
Acknowledgements
The authors thank R. Elgr and J. Weiss for
cartography and GIS work.
MESOZOIC
ELLERSLIE
ROCK CREEK
POKER CHIP
NORDEGG
201
323
DEBOLT
SHUNDA
RUNDLE
MISSISSIPPIAN
OSTRACOD
BEDS
PEKISKO
BANFF
EXSHAW
WABAMUN
359
•Structural elevation of the sub-Cretaceous unconformity surface ranges from
−2642 metres above sea level in the southwest to −82 metres above sea level
in the northeast.
•Paleotopography is delineated by removing the dominant trend surface
to highlight the paleodrainage network formed on the sub-Cretaceous
unconformity.
•The overall dip of the surface is to the southwest, with a gradient of ~6 m/km in
the northeast quadrant and ~14 m/km in the southwest quadrant, highlighting
the effect of the proximity to the deformation front on regional structure.
•Relative elevations vary from −124 m to 140 m.
•Smaller-scale variability seen in the eastern half of the study area is due to
erosion of Paleozoic strata.
WABAMUN
•A Jurassic-aged topographic high, known as the Pembina Highlands, is found
in the central part of the study area with the Fox Creek Escarpment and the
Spirit River Valley to the west, and the Edmonton Valley to the east.
•Tributaries draining the Pembina Highlands are approximately perpendicular to
the main paleovalleys.
•The Wainwright Highlands appear in the northeast, formed of Paleozoic strata.
Wainwright
Highlands
a)
N
e
y
•An oblique view of
the sub-Cretaceous
unconformity surface
(Vert. Exag. = 100×).
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ve
Pembina Highlands
Vert. Vert.
Exag.Exag.
= 30x= 30x
N
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Va
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me
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sca y
kE
le
ree r Val
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xC
Fo t Riv
i
8. Results were cross-validated
using the ‘eroded tops’ data to
confirm
the
location
of
subcropping units.
ir
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6. Once the sub-Cretaceous unconformity surface was modelled, the
‘un-eroded tops’ picks (n = 6334) were modelled to evaluate where
the top of each stratigraphic unit intersects with the sub-Cretaceous
unconformity surface.
n
Study Area
Vert. Exag. = 30x
Pembina
Highlands
(Jur)
7. Each stratigraphic unit top was geostatistically modelled independently using a 500 m grid node
spacing and then integrated into a geocellular model using Petrel 2013 to define the geological
relationships between units. The stratigraphic unit surfaces were truncated by the sub-Cretaceous
unconformity surface to identify the subcrop geometry for each unit.
Cant, D.J. and Abrahamson, B. (1996): Regional distribution and
internal stratigraphy of the Lower Mannville; Bulletin of Canadian
Petroleum Geology, v. 44, p. 508–529.
Leckie, D.A. (2009): Geomorphology of the basinwide subCretaceous unconformity, Western Canada Foreland Basin; 2009
CSPG CSEG CWLS Convention abstract, p.131, URL <http://
www.geoconvention.org/archives/2009abstracts/022.pdf> [June
2014].
Losert, J. (1986): Jurassic Rock Creek Member in the subsurface of
the Edson area (west-central Alberta); Alberta Research Council,
Alberta Geological Survey, Open File Report 1986-03, 39 p., URL
<http://ags.gov.ab.ca/publications/abstracts/OFR_1986_03.html>
[June 2014].
Losert, J. (1990): The Jurassic-Cretaceous boundary units and
associated hydrocarbon pools in the Niton Field, west-central
Alberta; Alberta Research Council, Alberta Geological Survey,
Open File Report 1990-01, 41 p., URL <http://ags.gov.ab.ca/
publications/abstracts/OFR_1990_01.html> [June 2014].
Poulton, T.P., Tittemore, J. and Dolby, G. (1990): Jurassic strata of
northwestern (and west-central) Alberta and northeastern British
Columbia; Bulletin of Canadian Petroleum Geology, v. 38A, p.
159–175.
Vert. Exag. = 50x
b)
Asgar-Deen, M., Riediger, C. and Hall, R. (2004): The Gordondale
Member: designation of a new member in the Fernie Formation
to replace the informal “Nordegg Member” nomenclature of
the subsurface of west-central Alberta; Bulletin of Canadian
Petroleum Geology, v. 52, p. 201–214.
Marion, D.J. (1984): The Middle Jurassic Rock Creek Member and
associated units in the subsurface of west-central Alberta; in The
Mesozoic of Middle North America, D.F. Stott and D.J. Glass
(ed.), Canadian Society of Petroleum Geologists, Memoir 9, p.
319–343.
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a ll e
nV
nto
mo
N
N
Subcropping Stratigraphic Units
Paleogeography
5. The trend surface
residuals provide a
representation of the
paleotopography.
Ri
Fox
Cree
kE
sca
rp
m
en
t
4. Remove trend from the
modelled sub-Cretaceous
unconformity surface grid
using the raster calculator.
3. Model the sub-Cretaceous
unconformity surface using a
500 m grid cell spacing.
i r it
2. Evaluate trend (a) and
geostatistically
model
residual data values (b).
Sp
exploratory data analysis
on the ‘eroded tops’
dataset (n = 4192).
TRIASSIC
PERMIAN
PENNSYLVANIAN
DEVONIAN
Modelling Overview
1. Analyze and perform
CARBONIFEROUS
PALEOZOIC
•Erosion associated with the sub-Cretaceous unconformity affected stratigraphic units
ranging from the Upper Jurassic / Lower Cretaceous Nikanassin Formation to the
Upper Devonian Wabamun Group.
CADOMIN
FERNIE
JURASSIC
•Unconformity surface has variable topography.
GETHING
NIKANASSIN
UPPER SHALE
145
UPPER
•Not all formations in the stratigraphic framework are eroded by the sub-Cretaceous
unconformity (e.g., the Permian and Triassic).
STRATIGRAPHY
MANNVILLE
CRETACEOUS
LOWER
PERIOD
BULLHEAD
ERA
•Varying depositional settings, changing structural regimes, and numerous
unconformities led to a complex arrangement of formation extents in the subsurface.
Age in Millions
of Years
References
Ed
The study area covers NTS map sheets 83G, 83F,
83J, and 83K. The southwest limit of the study
area is defined by the approximate limit of main
Cordilleran deformation. Geophysical wireline
logs for over 4100 wells were reviewed to identify
the depth of the unconformity, the corresponding
subcropping formation, and other stratigraphic units
found below the unconformity surface. Select cores
from each subcropping formation were viewed to
validate log responses at the unconformity surface.
on
ont
Methods
Wainwright
Highlands
Edm
Initial modelling of the sub-Cretaceous unconformity
surface was completed using data from a variety of
sources with inconsistent pick criteria, resulting in a
variable-quality dataset with a clustered distribution.
Data filtering techniques were applied to identify
and remove potential outliers and anomalous
data. However, this procedure increased the
potential of removing good data that accurately
characterized areas of increased complexity. These
dataset characteristics resulted in higher levels of
uncertainty and reduced confidence in the initial
unconformity surface. Therefore, the data for this
crucial surface were re-evaluated and picked in a
consistent manner based on logs and core, using
an intelligent sampling configuration to optimize
data coverage. This resulted in a higher-confidence
surface model that was able to more accurately
characterize the true geological complexity.
Conclusions
Paleotopography
e nt
m
p
r
a
c
s
E
k
Fox Cree
Introduction
Red Earth
Highlands
(Miss/Dev)
Wainwright
Highlands
(Dev)
Poulton, T.P., Christopher, J.E., Hayes, B.J.R., Losert, J., Tittemore,
J. and Gilchrist, R.D. (1994): Jurassic and lowermost Cretaceous
strata of the Western Canada Sedimentary Basin; in Geological
atlas of the Western Canada Sedimentary Basin, G.D Mossop
and I. Shetsen (comp.), Canadian Society of Petroleum
Geologists and Alberta Research Council, p. 297–316.
• Paleotopography of the
unconformity surface corresponds
to features seen in Early
Cretaceous paleogeography.
•Stratigraphic units subcropping at the sub-Cretaceous unconformity in the
study area include, in descending stratigraphic order, the Nikanassin, Fernie,
Debolt, Pekisko, Shunda, Banff, Exshaw, and Wabamun.
Richards, B.C., Barclay, J.E., Bryan, D, Hartling, A., Henderson,
C.M. and Hinds, R.C. (1994): Carboniferous strata of the Western
Canada Sedimentary Basin; in Geological atlas of the Western
Canada Sedimentary Basin, G.D Mossop and I. Shetsen (comp.),
Canadian Society of Petroleum Geologists and Alberta Research
Council, p. 221–250.
Smith, D.G. (1994): Paleogeographic evolution of the Western
Canada foreland basin; in Geological atlas of the Western
Canada Sedimentary Basin, G.D Mossop and I. Shetsen (comp.),
Canadian Society of Petroleum Geologists and Alberta Research
Council, p. 277–296.