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