Southern Alberta Plains Research Articles

Stratigraphic architecture of the Belly River Group (Campanian, Cretaceous) in the plains of southern Alberta: Revisions and updates to an existing model and implications for correlating dinosaur-rich strata.

The Upper Cretaceous (Campanian) Belly River Group (BRG) of southern Alberta has a complex internal stratigraphic architecture derived from differential geometries of its component formations that resulted from regionalized tectonic influences and shifting source areas. A full understanding of BRG architecture has been compromised heretofore by a limited understanding of subsurface data in southwestern- and southeastern-most Alberta. In this study outcrop exposures throughout southern Alberta are tied to reference well logs and subsurface cross-sections allowing a more precise understanding of BRG architecture and how it relates to well-known vertebrate fossil producing areas. Modifications to an existing stratigraphic model of the BRG show that the Oldman and the Dinosaur Park formations have reciprocal north-to-south wedge-shaped geometries and a diachronous contact that become prominently expressed south of Twp 12. The updated model also demonstrates that the Oldman Formation thickens stratigraphically up-section to the south, and that the Foremost-Oldman contact is, essentially, a datum across much of southern Alberta. Identification of the Oldman Formation in the subsurface remains based on its relatively high gamma-ray response in mudstone successions, but it is also recognized that many of its sandstones exhibit relatively low gamma-ray responses like those in underlying and overlying formations. Nomenclature and subdivisions of the Oldman Formation are revised to accommodate this updated understanding, and modifications are also made to the definition of the Judith River-Belly River discontinuity, a newly recognized surface that marks the onset of accommodation and eustatic rise in sea-level in the northern Western Interior Basin at ~76.3 Ma.

The “Judith River−Belly River problem” revisited (Montana-Alberta-Saskatchewan): New perspectives on the correlation of Campanian dinosaur-bearing strata based on a revised stratigraphic model updated with CA-ID-TIMS U-Pb geochronology

Terrestrial strata of the Judith River−Belly River wedge, widely exposed in the plains of north-central Montana, southern Alberta, and southwestern Saskatchewan, were pivotal in early stratigraphic investigations of the Western Interior of North America and are renowned to this day for their spectacular preservation of Late Cretaceous fossils, most notably dinosaurs. Correlation of the Judith River Formation in Montana with the Foremost, Oldman, and Dinosaur Park Formations (= Belly River Group) in Canada has been challenging for a variety of reasons, including lithostratigraphic complexities, legacy bentonite ages of limited comparability, and distinctly different stratigraphic models on opposite sides of the international border. An updated model calibrated with U-Pb zircon ages provides an improved framework for stratigraphic analysis. New geochronology indicates that the Oldman−Dinosaur Park discontinuity in Dinosaur Provincial Park correlates in age with the mid-Judith discontinuity in the Judith River Formation in Montana, which is interpreted as an expansion surface linked to a major pulse of accommodation and onset of the Bearpaw transgression at ca. 76.3 Ma. The regionally expressed shift in alluvial facies marking the mid-Judith discontinuity can be traced in well logs from Montana to southern Canada, where it loses distinction and transitions to a subsurface signature typical of the Oldman−Dinosaur Park discontinuity, which in turn can be traced north to Dinosaur Provincial Park and beyond. Across this expanse, both discontinuities parallel the Eagle/Milk River shoulder at approximately the same stratigraphic height, confirming their chronostratigraphic significance. These findings have clear implications for regional correlation and the evolution of alluvial depositional systems in a foreland basin setting, and they afford an opportunity to evaluate existing interpretations and advance understanding of the stratigraphy and paleontology of the Judith River−Belly River wedge. The term “Judith River−Belly River discontinuity” should be used henceforth to refer to the chronostratigraphically significant stratal discontinuity that subdivides the Judith River−Belly River wedge throughout the plains of north-central Montana, southern Alberta, and southwestern Saskatchewan.

Controls on accommodation during the early-middle Campanian in southern Alberta, western Canada foreland system

The Western Canada Sedimentary Basin is a retroarc foreland system produced by thrust sheet loading in the Canadian Cordillera and resultant flexural displacement of the lithosphere east of the orogenic front. Theoretical models of flexural tectonism and dynamic loading have long been used to predict the effects of these controls on the creation/destruction of accommodation in retroarc foreland settings, however, few field studies have attempted to evaluate their relative contributions for a given point in geologic time. As key regional drivers of subsidence/uplift and implicitly, relative sea level rise and fall, flexural tectonism and dynamic loading impart unique signatures (subsidence geometries) which can be discerned via the spatial and temporal analysis of event-significant surfaces preserved in the geologic record. We use magnetostratigraphy to constrain the timing of a major marine incursion (transgressive phase of the second-order Campanian Claggett Cycle, which spanned ∼8 Myr in its entirety) at three locations in the southern Alberta plains where the onset of this transgression is marked by a widespread ravinement surface. A chronostratigraphic framework is presented which includes new empirical ages for stratigraphic units above and below this key surface, informally termed the Milk River ‘shoulder’. The framework provides a basis for determining the earliest extents of the Claggett (Pakowki/Lea Park) sea in southern Alberta, and for characterization of its subsequent expansion during the early-middle Campanian. Although commonly depicted as a simple, westward-expanding seaway, we observe that the initial expansion of the Claggett sea in southern Alberta was more complicated and proceeded in multiple directions through time, prior to maximum transgression and the ensuing second-order regression. We interpret the Claggett sea as restricted to the Alberta foredeep at ∼82.0 Ma, before inundating a paleotopographic high associated with a prominent basement feature in southernmost Alberta (Sweetgrass Arch) at ∼81.0 Ma, likely establishing a connection with the Claggett sea in northern Montana. As relative sea level continued to rise, the sea reached the Rocky Mountain foothills in the west while also advancing more than 100 km eastward into the forebulge region during peak transgression (∼80.0 Ma). With this history established, we ascertain the overriding cause for the Claggett transgression was dynamic subsidence because (1) the magnitude, direction, and timing of relative sea level rise and the associated expansion of the Claggett sea fits published dynamic subsidence models for the Campanian of North America, and (2) several hundred metres of marine sediments are preserved on the early-middle Campanian forebulge, requiring accommodation which cannot be explained by widely accepted flexural models or eustatic estimates.

Age, Correlation, and Lithostratigraphic Revision of the Upper Cretaceous (Campanian) Judith River Formation in Its Type Area (North-Central Montana), with a Comparison of Low- and High-Accommodation Alluvial Records

AbstractDespite long-standing significance in the annals of North American stratigraphy and paleontology, key aspects of the Upper Cretaceous Judith River Formation remain poorly understood. We re-evaluate Judith River stratigraphy and propose new reference sections that both document the range of lithologies present in the type area in north-central Montana and reveal dramatic changes in facies architecture, fossil content, and rock accumulation rates that can be mapped throughout the type area and into the plains of southern Alberta and Saskatchewan. One section spans the basal contact of the Judith River Formation with marine shales of the underlying Claggett Formation. This contact, which lies along the base of the Parkman Sandstone Member of the Judith River Formation, is erosional and consistent with an episode of forced regression, contrary to previous descriptions. A second reference section spans the entire Judith River Formation. This complete section hosts a lithologic discontinuity, herein ref...

A revised stratigraphy and depositional history for the Horseshoe Canyon Formation (Upper Cretaceous), southern Alberta plains

The Upper Cretaceous paralic to nonmarine Horseshoe Canyon Formation (HCFm) of southern Alberta is divided into seven mappable members: Strathmore, Drumheller, Horsethief, Morrin, Tolman, Carbon, and Whitemud (bottom to top). This subdivision, based on combined outcrop and subsurface analyses, reflects lithostratigraphic variations related to changes in sea level (previously recognized) and newly documented changes in climate, volcanism, and orogenesis in an evolving foreland basin. Million-year-scale cycles of orogenesis resulted in changes in sediment supply and rates of subsidence in the basin and are interpreted in the context of a simple, two-phase foreland-basin sequence stratigraphic model: (i) overthrust loading resulting in reduced rates of sediment supply and subsidence in the most distal portions of the Alberta foredeep (our field area); (ii) tectonic quiescence leading to increased rates of sediment supply and subsidence during proximal-foredeep rebound. During the first ∼2.5 Ma of its history (Strathmore and Drumheller members), the HCFm was tectonically and climatically “stable”, and depositional style and stratigraphic architecture were influenced by vertical aggradation and modest progradation of shorelines. During the remaining ∼4.5 Ma (Horsethief, Morrin, Tolman, Carbon, and Whitemud members), there were more complex and frequent changes in climate, volcanism, orogenesis, landscape weathering, and soil formation. Understanding this previously unrecognized complexity is critical for correctly assessing hydrocarbon resource distributions and biostratigraphic and taphonomic patterns.

Crustal geometry and tectonic evolution of the Archean crystalline basement beneath the southern Alberta Plains, from new seismic reflection and potential-field studies

Deep seismic reflection profiling of the southern Alberta crystalline basement, namely the Archean Medicine Hat block (MHB), has revealed that the crust is characterized by west- and southwest-dipping reflection fabrics, a layered lower crust, and geometric cutoffs that are interpreted to be remnants of a complex tectonic history. Upper to middle crustal dipping reflections are interpreted to be associated with Archean rocks drilled below the Western Canada Sedimentary Basin and their geometry is consistent with east- and northeast-verging imbrication. Layered lower crustal reflections of the MHB are interpreted as Early Proterozoic delaminated Loverna block crust and injected mafic material, based on geometric relationships, xenolith dating, and gravity modelling. The reflection Moho is diffuse below the MHB at ~15 s two-way time (~47 km). This is similar to estimates based on adjacent seismic refraction data and is up to ~8 km deeper than regions north of the MHB. The MHB crust is interpreted to have undergone two episodes of crustal deformation in the Precambrian: (1) Late Archean formation of the MHB crust by continental collision of two Archean domains along a crustal-scale ramp; and (2) Early Proterozoic crustal shortening associated with the formation of the Vulcan structure, the delamination of the Loverna block crust, and postcollisional injection of mafic melts beneath the MHB crust. Radiometric dating of lower crustal xenoliths suggests a significant Early Proterozoic thermal event in the deep crust beneath the MHB that is coeval with orogenic activity in the Trans-Hudson Orogen and the East Alberta Orogen.

Crustal geometry and tectonic evolution of the Archean crystalline basement beneath the southern Alberta Plains, from new seismic reflection and potential-field studies

Crustal geometry and tectonic evolution of the Archean crystalline basement beneath the southern Alberta Plains, from new seismic reflection and potential-field studies

Relationship between thermal maturation gradients, geothermal gradients and estimates of the thickness of the eroded foreland section, southern Alberta Plains, Canada

Analysis of post-Laramide (Tertiary) uplift and erosion in the southern Alberta Plains indicates that the greatest erosion occurred in regions where the youngest stratigraphic units are preserved. This is consistent with geological structure and the few preserved stratigraphic constraints on erosional history. Throughout this region, erosion is pervasive and the uplift history is commonly constrained by coalification data. The analysis of coalification, erosion and paleogeothermics are interrelated and knowledge of them is important to understand hydrocarbon generation and tectonic history. Several independent attempts to analyse coalification, erosion and paleogeothermics in this area have given different results. The most striking differences are those between estimates derived from the analysis of well profile coalification gradient and those determined using a commonly accepted relationship between the amount of eroded section and the equilibrium moisture content of near-surface coals. The match between present and paleogeothermal gradient fields is better when the latter technique is used. Correlation is expected between the late orogenic and present geothermal gradient fields because the hydrodynamically controlled advective heat flow pattern that now dominates geothermal gradients in the Mesozoic and Tertiary Foreland succession was initiated by the growth of topography in the west throughout Cordilleran orogeny. Well profile coalification gradients have significant, though commonly unacknowledged, uncertainties. These uncertainties are propagated in erosion and paleogeothermal gradient calculations. Ideally the relationship between erosion estimates using well profile coalification gradients and near surface coal properties can be compared. Unfortunately, the uncertainties in well profile coalification gradients prevent this.

Brooks Aqueduct

The Brooks Aqueduct is a very large elevated flume commissioned in 1914 by the Canadian Pacific Railway (CPR) to carry water at the rate of 25.5 m3/s over a valley 3.2 km wide and 20 m deep. Construction of the aqueduct permitted the irrigation of a 50 000 ha block of land within a region now known as the Eastern Irrigation District in southern Alberta. The flume is 6.5 m wide and 2.5 m deep with a curved cross section. It is supported by 1030 columns. A 3000 mm diameter inverted syphon near the outlet of the flume permitted the crossing of the CPR main line through the valley. All components of the aqueduct, including the shell of the flume, columns, syphon, and inlet and outlet structures, were constructed of reinforced concrete. The Brooks Aqueduct was abandoned in 1979 with the completion of its earth-fill replacement. Except for a 122 m section, removed to permit the construction of a county road, the old aqueduct still stands. It serves to remind us of the significant engineering accomplishments of the pioneer civil engineers who helped to realize ambitions to irrigate the vast plains of southern Alberta at the turn of the century. On May 28, 1988, the Brooks Aqueduct was named a National Historic Civil Engineering Site by the Canadian Society for Civil Engineering. Key words: Brooks Aqueduct, history.

Fossil seed cuticles from the Upper Cretaceous Whitemud beds of Alberta and Saskatchewan, Canada

Abundant fossil cuticles are associated with megaspores in the Upper Cretaceous Whitemud beds of the southern Alberta plains and in the Whitemud Formation of the Cypress Hills. Form genera Spermatites Miner and Costatheca (Dijkstra) Hall are emended, and the new genus Carpotheca is described. The three genera are differentiated by shape and orientation of cuticular cells. Ten new species of seed cuticles are described. The affinity of Spermatites with the extant genus Juncus L. is reaffirmed, and it is suggested that Costatheca may be related to extant species of Butomus L. In the Whitemud, Costatheca is more abundant in the Alberta plains, whereas Spermatites and Carpotheca are better represented in the Cypress Hills. The fossil microfloral assemblage indicates that these beds were deposited in a continental, fluviatile to lacustrine environment, having a subtropical climate, in agreement with previous sedimentological, isotopic, and palynological investigations.

Continental Lower Cretaceous Stratigraphy, Sweetgrass Arch Area, Southern Alberta and Northern Montana: ABSTRACT

An integrated regional scheme of lithostratigraphic nomenclature is proposed to encompass the Lower Cretaceous strata on both sides of the international border. The Blairmore Group, defined in the southern Alberta Foothills, is extended to encompass the entire Sweetgrass arch area. The informal Cut Bank sandstone member of northern Montana is raised to formation status and extended into southern Alberta. The Cut Bank Formation is correlated with the Cadomin Conglomerate of the Alberta Foothills. The Mannville Group formerly was extended to the Lower Cretaceous continental strata of the southern Alberta plains. This name is now restricted to strata occurring north and east of the Sweetgrass arch area which resemble the type Mannville. The Kootenai Formation (Group?) nomenclature, formerly used in Montana, is discarded because of continued confusion with the older, formally defined Kootenay Group of the Alberta Foothills. Most of the informal members defined in various oil fields should be confined strictly to the areas in which they are defined. The present configuration of the Sweetgrass arch is the product of Late Cretaceous-Early Tertiary Laramide deformation, but the presence of a paleotectonic high coinciding with the present arch trend can be documented from the early Paleozoic. Sedimentation and erosional patterns were greatly affected by the ancestral arch and produced marked stratigraphic variations End_Page 579------------------------------ around it resulting in independent Canadian and American schemes of stratigraphic nomenclature being proposed. End_of_Article - Last_Page 580------------

Mckean Complex Subsistence and Hunting Strategies in the Southern Alberta Plains

(1978). Mckean Complex Subsistence and Hunting Strategies in the Southern Alberta Plains. Plains Anthropologist: Vol. 23, No. 82, pp. 175-193.

Coulee Alignment and the Wind in Southern Alberta, Canada

Study of the distinctive pattern of alignment and geographical distribution of more than 250 coulees in the plains of southern Alberta shows that (1) the coulees in question have a mean orientation of N. 70° E., and (2) their spatial distribution is not ubiquitous but rather displays a concentration in the area from Lethbridge west to the Rocky Mountain front. Several possible hypotheses of origin of the aligned coulees are considered, including subsurface structural control, the role of regional slope, the effect of lithologic differences, and wind action. Action of postglacial wind, operating to initiate surface furrows (by wind-driven snow or rain) that were enlarged by running water, accounts for the three outstanding characteristics of the aligned coulees: (1) their preferred orientation of N. 70° E., which approximates the mean direction of the strongest chinook winds in the southern Alberta plains; (2) their geographical distribution, which coincides with that part of the region experiencing the most pronounced chinooks; and (3) their almost exclusive location on windward topographic surfaces. No other hypothesis of origin is known that can satisfactorily explain all of these observed facts.

Geographical Distribution of Post-Glacial Slumping in Southern Alberta

Study of more than 100 post-glacial landslides of the slump variety in the plains of southern Alberta reveals that a remarkably high proportion (87%) has occurred on slopes of northerly, northeasterly, easterly, and southeasterly aspect. While lithologic and engineering properties of the Upper Cretaceous sediments and Pleistocene glacial mantle of this area undoubtedly have conditioned the geological behavior of the earth materials affected, it is here contended that microclimatic factors favoring the accumulation and retention of snow on slopes of particular exposure, or aspect, have more strongly controlled the geographical distribution of the observed slumps. Reasons for and consequences of microclimatic control are discussed.

Radiometric Dating of the Bearpaw Sea: ABSTRACT

Sampling of the bentonites included in the Upper Cretaceous Bearpaw formation of southern Alberta and adjacent areas has provided material for a geochronological investigation of this marine sequence of strata. K-Ar dating of biotite and sanidine included in the bentonites has indicated that the Bearpaw sea invaded most of the southern Alberta Plains 72-73 million years ago. The transgression of the sea was probably rapid and the base of the formation may be isochronous over most of the area, with the possible exception of areas in southern Saskatchewan and northern Montana where the sea might have transgressed somewhat earlier. The regressive upper boundary of the Bearpaw formation is set at 68 million years in the westernmost plains and at 66 million years farther east n the Cypress Hills region. The geochronological picture is compatible with the paleogeography of the Bearpaw. The bentonites intercalated with the normal sediments represent ashfalls produced by relatively remote volcanic eruptions. Study of the phenocrysts in the sand-size fraction, provided that contamination by detrital material has been negligible, has indicated that most of the bentonites are remarkably uniform in petrologic type and are dominantly andesitic. A source area is suggested in the eastern Cordilleran belt of northern Montana, where strong volcanism throughout most of the Late Cretaceous accompanied the gradual emplacement of the Boulder batholith. The andesitic nature of the Bearpaw bentonites is compatible with granodioritic magmatism in the postulated source area. End_of_Article - Last_Page 525------------

Tectonics of Plains of Southern Alberta: ABSTRACT

Structures having two different origins are present. One is associated with the Sweetgrass intrusives and may have developed in two stages, beginning with the early Laramide. Later crustal movements were the result of adjustment following the removal of a large block of sediments known as the Cypress prism during the late Tertiary. Such structures are relatively superficial. The area is glaciated, outcrops are sparse, and additional information must come from drilling. New subsurface data will be of interest only if it is considered in the light of the knowledge that such structures do exist on the plains. End_of_Article - Last_Page 788------------

Mississippian Stratigraphy of Southern Alberta Plains: ABSTRACT

The Mississippian sediments of Southern Alberta Plains region, known only from the subsurface, are described as to lithology, thickness, rock units, their correlation with adjacent areas, and history of deposition. The section thins from west to east due to post-Paleozoic erosion and to less degree by reason of depositional thinning. In the extreme western part of the map area, there remains approximately 1,400 feet which is one-third of the total Mississippian measured in the mountains. The rock units and member names defined and introduced by Douglas in 1953 and the more recently emended subdivisions and new names being proposed by the Mississippian Committee for the Foothills area in the vicinity of Turner Valley oil field are defined, for adjacent Plains region, in Shell-Anglo Pine Creek well. The formation names, Bakken, Banff, Pekisko, Shunda, Turner Valley, and Lower Mount Head, are used for this general area. It is further proposed to introduce the name Elkton for the commercial gas zone of the Elkton well. This zone is regarded as correlative of the Crystalline and Lower Porous of Turner Valley field usage. The correlation of these rock units is illustrated on cross sections from the Pine Creek well to the northeast, toward the Big Valley fields, southeast to Saskatchewan and south to Kevin-Sunburst area in Montana. The Banff of Pine Creek well is correlated with the Mc+Mb2 (Lodgepole) of the Kevin End_Page 419------------------------------ Sunburst area; the Pekisko and Shunda plus Elkton member of the Turner Valley with Mb1 (Mission Canyon); and the upper part of the Turner Valley with the Ma unit. The typical lithological units of the Bakken formation of Montana and the Dakotas are present in the southeastern part of the map area. The formation thins to near zero toward the west as a depositional edge due to epeirogenic movements prior to Mississippian deposition. To the north, the lower black shale only is present as a distinguishable rock unit and the name Exshaw is applicable. The upper part of the formation changes to gray shale that is not readily distinguished from the overlying Banff shale. End_of_Article - Last_Page 420------------

Useful Blairmore Microfossil Zone in Central and Southern Alberta, Canada

The Lower Cretaceous of the central and southern Alberta plains and the central foothills area contains a rich assemblage of ostracodes and charophytes. This zone is useful in correlating stratigraphic sections from the foothills to the plains area and can also be used as a mappable horizon in the oil fields. Twenty-three of the most commonly occurring species belonging to ten genera are figured and described.

Marine Jurassic Formations of Southern Alberta Plains

The Jurassic sediments of the Southern Alberta Plains, known only from subsurface work, are described as to lithology, thickness, distribution, stratigraphic relationships, and geologic history. The three-fold subdivision of the Ellis group into Swift formation, Rierdon formation, and Sawtooth formation, established in Montana, is recognizable and applicable in Alberta. A major unconformity between the Jurassic beds and the underlying Paleozoic limestone influences the distribution of the Sawtooth formation. Late Jurassic or early Cretaceous erosion truncating the Jurassic formations from south to north has determined the present extent and northern boundaries of these formations in Southern Alberta.

Stratigraphy of Plains of Southern Alberta. A Symposium. Alberta Society Petroleum Geologists and the American Association of Petroleum Geologists

<i>Stratigraphy of Plains of Southern Alberta. A Symposium</i>. Alberta Society Petroleum Geologists and the American Association of Petroleum Geologists