Rocky Mountain Foothills Research Articles

Passive-Roof Duplexes Under the Rocky Mountain Foreland Basin, Alberta (1)

Seismic reflection data in the Central Alberta Foothills near Edson reveal the presence of small passive-roof duplexes in Upper Cretaceous rocks within the otherwise undeformed foreland basin, as much as 40 km northeast of the mountain front monocline. The tops and bottoms of the duplexes are defined by backthrusts and sole thrusts, which follow bedding planes within Upper Cretaceous strata. Overlying the structures is an essentially uncontracted 1.8-km-thick section of Upper Cretaceous and Tertiary rocks, which is passively uplifted over the thickened duplexes. The underlying autochthonous sequence of Mesozoic and Paleozoic rocks exhibits some minor folding but is also uncontracted. Our interpretation extends both the upper and lower detachments of the widely accepted triangle-zone model more than 30 km farther under the foreland basin than has previously been supposed. The seismic data illustrate relatively clearly the form of the leading edge of the last phase of Rocky Mountain thrusting. We expect that similar features will be observed elsewhere in the Rocky Mountain foothills and, probably, at other mountain fronts worldwide.

Styles of Deformation in the Rocky Mountain Foothills and Front Ranges, Alberta, Canada

Styles of Deformation in the Rocky Mountain Foothills and Front Ranges, Alberta, Canada

Use of Computer-Aided Cross-Section Construction to Validate Seismic Interpretations: An Example from the Turner Valley-Quirk Creek Area of the Canadian Rocky Mountain Foothills

Use of Computer-Aided Cross-Section Construction to Validate Seismic Interpretations: An Example from the Turner Valley-Quirk Creek Area of the Canadian Rocky Mountain Foothills

Organic maturity in the western Canada sedimentary basin

Organic maturity of strata in the Western Canada Sedimentary Basin has been investigated in numerous studies using petrological, chemical and physical methods. Compilation of these data has facilitated a regional analysis of the maturity patterns and maturation history. Variation in maturity patterns can be divided into three levels; basin wide (1st order), regional (2nd order) and local (3rd order). First order variations are manifested by an overall increase in maturity of strata of the same age from east to west from the Plains to the Rocky Mountain Foothills and Front Ranges in response to progressively deeper burial and higher paleo-geothermal gradients. Superimposed on this first order (basinal scale) variation in maturity are second and third order variations which reflect local differences in depth of burial, conductive and advective heat transport or effects of thrust faulting. Maturity gradients in the axis of the basin are low, averaging 0.10 log% R omax/km, whereas in the Front Ranges and Foothills the gradients are substantially greater (average 0.25 log% R omax/km. Variations in maturity gradients reflect lower paleo-geothermal gradients resulting from rapid sediment loading and subsequent unloading in the Plains, and higher conductive heat transport in the deformed belt. The main component of maturity of most Phanerozoic strata occurred during deep burial under Upper Cretaceous and/or Paleogene molasse in foredeeps developed in response to crustal loading during the easterly migration of the foreland fold and thrust belt. As a result of the west to east propagation of deformation during the Laramide Orogeny, deep burial, maturation, hydrocarbon generation and uplift occurred earlier in the foreland belt (Late Cretaceous) than in the Plains to the east where the main component of maturity and hydrocarbon generation occurred as late as Eocene. In the Plains, because of the low maturity gradients, a thick succession of strata currently is within the oil window. In the deformed belt however, higher maturity gradients have resulted in a thinner succession of strata within the oil window. In response to higher paleo-geothermal gradients, strata in the deformed belt matured more quickly leading to more rapid hydrocarbon generation and migration than areas to the east. In the southern part of the Cordillera a significant component of maturation post-dates structural deformation of the strata whereas in northeastern British Columbia and adjacent parts of Alberta, maturity primarily pre-dates structural deformation. Data from some deep bore holes and surface samples in the southern part of the Cordillera provide evidence for maturity post-dating or accompanying emplacement of major overthrust sheets (tectonic burial). In most areas however, there is no clear evidence for the timing of maturity relative to faulting or evidence of frictional heating. The maturity gradients and levels of maturity of surface and near surface strata in the western Plains and Rocky Mountain Foothills indicate that a succession (several kilometres) of Paleogene strata were deposited in these regions (foredeep) and subsequently eroded in response to post-Laramide uplift.

Coal composition and facies variation in Gates Formation (Falher equivalent) seams, Rocky Mountain Foothills, northeastern British Columbia

Coal composition and facies variation in Gates Formation (Falher equivalent) seams, Rocky Mountain Foothills, northeastern British Columbia

Stratigraphy, Structural Geology, and Hydrocarbon Habitat in the Southern Canadian Rocky Mountain Foothills Belt

The Southern Canadian Rocky Mountain Foothills belt of south-western Alberta forms the easternmost subdivision of the Cordilleran region at this latitude. This structural zone is approximately 40 km wide and extends 440 km north-northwest from the US border to the North Saskatchewan River. It is characterized at the surface by deformed Mesozoic strata with isolated inliers of Paleozoic carbonates. The Foothills belt and adjacent plains and Front Ranges structural provices share a common Phonerozoic stratigraphy. This is comprised of 1 to 2 km of platformal Paleozoic carbonates and minor clastics which are blanketed by predominantly clastic Mesozoic and earliest Tertiary strata of a comparable to somewhat greater thickness that are related to Cordilleran orogenesis and erosion. Middle Proterozoic sedimentary rocks are carried in Front Range structures such as the Lewis thrust sheet, but only close to the US border. The major reservoirs in the Foothills belt occur in the Mississippian Turner Valley and Livingstone Formations and in the upper Devonian Paliser Formation. Traps are formed within structural imbrications by juxtaposition of reservoir units against tight footwall strata with lateral spillpoints controlling the extent of hydrocarbon accumulations. Producing fields are characterized by multipool structural stacks and are well illustrated by themore » Waterton and Jumping Pound West fields. The basal Mississippian Exshaw Formation is beleived to be the source for oil and gas in the region. Recoverable sales gas reserves in producing fields range over several orders of magnitude from 3.0 tcf down to 50 bcf. Considerable condensate, NGLs and sulfur complement their sales gas streams.« less

A palaeoenvironmental study of Fairfax Lake, a small lake situated in the rocky mountain foothills of west-central Alberta

Fairfax Lake is a small, oligotrophic to mesotrophic headwater lake situated in the Foothills of the Rocky Mountains of west-central Alberta (Latitude 52° 58′ N; Longitude 116° 34′ W). Through acquisition of a sediment core, and analyses of the diatoms, chrysophyte stomatocysts, pollen and sedimentary pigments, including myxoxanthophyll and oscillaxanthin, a palaeoenvironmental history of the lake has been determined. The sedimentary record spans ca. 13 200 years. An open tree-less vegetation existed in the region ca. 13 200–ca. 11 600 years BP. Maximum oscillaxanthin and myxoxanthophyll concentrations, hence the largest blue-green algal populations, occurred during the same interval. With increasing temperature pioneering parkland vegetation appeared ca. 11 600 years BP but was replaced ca. 10 100 years BP by spruce forest. Pine appeared ca. 7800 years BP and this marked the development of the present day montane boreal forest. Diatoms were not found until ca. 11 255 years BP. Benthic taxa dominated but by ca. 10 100 years BP planktonic taxa had become more prominent. Lake levels are interpreted as having risen, and the lake water was probably more transparent. Maximum chlorophyll and total carotenoid concentrations occur ca. 11 255 to ca. 7000 years BP corresponding to the warm early to mid-Holocene period. Lake nutrient levels appear to have been higher prior to ca. 7000 years BP, and the lake has changed from being eutrophic during the early Holocene to its present status as an oligotrophic to mesotrophic lake. Subtle hydrological changes have also occurred in the catchment as water levels do not appear to have remained constant.

Regional coalification of lower cretaceous coal-bearing strata, Rocky Mountain Foothills and Foreland, British Columbia and adjacent parts of Alberta, Canada

The regional coalification pattern of Lower Cretaceous strata in parts of the Canadian Foothills Belt and adjacent foreland has been determined by vitrinite reflectance measurements. The present study focusses on two coal-bearing sequences, i.e., Bluesky-Gething and Gates Formations, both of which contain coal resources of economic interest. Bluesky-Gething Formation. The vitrinite reflectances ( R max) range from 0.76% (high-volatile A bituminous coal) to 2.55% (semianthracite). ASTM rank maps for the study area indicate high-volatile A bituminous coal to low-volatile bituminous coal ranks for localities in the Inner Foothills, where seams of sufficient thickness occur at or near surface. These ranks place many of the Gething coals in a rank range suitable for the production of metallurgical coal. Vertical rank changes within the Bluesky-Gething Formation follow first-order regression lines. Factors influencing the rate of increase of R max per depth interval (coalification gradient) include present and paleogeothermal gradients, the rank level under investigation, conductivities of host rocks, thickness of coal seams and possibly locally increased heat flows by groundwater movements. Calibrated time-depth (burial) curves for the Lower Cretaceous Bluesky-Gething Formation suggest that the regional coalification pattern for the top of the formation results largely from variations in the depth and/or duration of burial beneath Maastrichtian-Tertiary foredeep deposits. Local variations in paleogeothermal gradients modified the overall pattern. Coalification increases from west to east across the Foothills occurred largely because of diachronous Laramide deformation that resulted in an eastward increase in duration and depth of burial. Maximum coalification occurs near the eastern limit of deformation. Coal rank decreases farther east as a consequence of eastward thinning of the Late Cretaceous-Tertiary sedimentary wedge. Rank also decreases significantly along strike because of northward thinning of the Maastrichtian-Tertiary section. Locally, northward thinning is enhanced by the north-side-up reactivation of old basement structures associated with the Peace River Arch/Embayment. The coalification pattern is more complicated from the base of the Bluesky-Gething Formation because thickness changes in the Lower Cretaceous Bluesky-Gething interval locally have a greater effect on the rank than does the regional change in thickness of Maastrichtian-Tertiary sedimentary wedge. Gates Formation. Detailed rank studies on laterally continuous coal beds of the Gates Formation showed that coalification levels were established before folding and thrusting started. Isoreflectance lines of the beds run parallel to the bedding of the folded strata. Seams collected from various thrust sheets do not in general show significant changes in vitrinite reflectances from one thrust sheet to the other. Many of the coals of the Gates Formation were found to have biaxial negative reflectance indicatrices. Orientation of R max is in all cases parallel or subparallel to the macroscopic fold axes which indicates preferential orientation of the aromatic lamellae of the coals in the direction of minimum compressive stress. It is suggested that the occurrence of biaxial negative coals is related to a tectonic stress field that existed during the later stages of burial.

A geographic information system for prediction of design flood hydrographs

A geographic information system (GIS) supporting a flood hydrograph prediction software package is described. The hydrograph prediction method is based on the convolution of excess rainfall with a synthetic unit hydrograph, derived by the Soil Conservation Service runoff curve number and a regional dimensionless unit hydrograph method, respectively. The GIS uses a raster method to store the following data: land use and land cover, soil type, rainfall intensity–frequency–duration statistics, runoff curve numbers (CN), regional dimensionless unit hydrograph, and regional lag-time relationship. The GIS has also the capability of computing a number of watershed and hydrologic parameters required for predictions, such as a watershed average rainfall and CN value, area, centroid, stream length, etc. Most of the data for such computations are input from a digitizer. Substantial time and cost savings are possible once the data base has been created. Application of the system is illustrated by an example of predicting flood frequency curves for selected watersheds in Alberta's Rocky Mountain foothills. Key words: geographic information system, flood hydrograph, curve number, hydrologic simulation, flood frequency.

Triassic oils and potential Mesozoic source rocks, Peace River Arch area, Western Canada Basin

Triassic oils and their potential Mesozoic source rocks in the Peace River Arch region (Western Canada Basin) have been examined using various analytical techniques. Triassic oils are divided into two groups, 1 and 2, on the basis of biomarker composition. Triassic outcrop samples from the Rocky Mountain Foothills are mature to overmature, and contain Type II/III organic matter with TOC's ranging from 0.1 to 15.0 wt% and HI values up to 445. Subsurface core samples from the Triassic Montney Formation are mature to overmature with TOC's (rarely) up to 2.8 wt% and HI values up to 398. The Triassic Doig Formation has good to excellent source potential and moderate to high maturity, with TOC values over 5.0 wt% and HI values commonly in excess of 300. The Jurassic “Nordegg Member” ranges from early mature to overmature, with TOC's as high as 23.5 wt% and HI values greater than 600 where maturity is low. Oil-source rock correlations are established, based on biomarker signatures, between the Group 1 oils and the Doig Formation. Group 2 oil was sourced by the “Nordegg Member”

Distribution and Movements of Female Mule Deer in the Rocky Mountain Foothills

Suivi par radiopistage de 27 femelles adultes de Odocoileus hemionus dans les collines du piemont des Rocheuses au colorado de 1982 a 1985 afin de determiner leurs deplacements saisonniers et les aires de deplacement hivernales

Computation of refraction static corrections using first‐break traveltime differences

Differences in first‐arrival traveltimes between adjacent records in multifold reflection surveys can be used to compute the depth and velocity structure of near‐surface layers. The procedure uses the redundancy of first‐break data in multifold surveys to enable a statistically reliable refraction analysis to be undertaken for either end‐on or split‐spread recording geometries. The traveltime differences as a function of source‐receiver offset provide a direct indication of the number of refractors present, with each refractor being defined by an offset range with a constant time difference. For each refractor, the time‐difference value at a common receiver from two shotpoints is used to partition the intercept time into the delay time at each shotpoint. This procedure is repeated until the delay times at all shotpoints and for all refractors have been computed. Refractor depths and velocities are evaluated from this suite of delay times. A surface‐consistent static correction to a selected datum level is then calculated at each surface station, using a replacement velocity equal to that of the deepest refractor. In a case history from the Canadian Rocky Mountain foothills, short‐ and intermediate‐wavelength weathering static anomalies were resolved successfully. Elevation and weathering static corrections of up to 40 ms were computed, with an estimated error of less than ±3 ms.

Performance validation of the Gueymard sky radiance model

Abstract The Gueymard model of short‐wave sky radiance has been validated against sky radiance date measured in the Rocky Mountain foothills of Alberta. Except for sky points within the circumsolar region in clear skies and for low sun positions in near overcast skies the model performs as well as other current sky radiance models.

Regional coalification pattern of Lower Cretaceous coal-bearing strata, rocky mountain foothills and foreland, Canada — implications for future exploration

The regional coalification pattern of Lower Cretaceous strata in parts of the Canadian Foothills Belt and adjacent foreland has been determined by vitrinite reflectance measurements. The present study focusses on two coal-bearing sequences, Bluesky-Gething and Gates Formation, both of which contain coal resources of economic interest. The vitrinite reflectances ( R max) in the Bluesky-Gething Formation range from 0.76% (high-volatile A bituminous) to 2.55% (semianthracite). Rank changes from top to the base of Bluesky-Gething Formation follow 1st-order regression lines. Factors influencing the rate of increase of R max per depth interval (coalification gradient) include paleogeothermal gradients, the rank level under investigation, conductivities of host rocks, and thicknesses of coal seams. Time-depth (burial) curves for the Lower Cretaceous Bluesky-Gething Formation suggest that the regional coalification pattern for the top of the formation results largerly from variations in the depth and/or duration of burial beneath Maastrichtian-Tertiary foredeep deposits. Coalification largerly predates deformation. The coalification pattern is more complicated for the base of the Bluesky-Gething Formation because thickness changes in the Lower Cretaceous Bluesky-Gething interval locally have a greater effect on the rank than does the regional change in the thickness of Maastrichtian-Tertiary sedimentary wedge. Detailed rank studies on laterally continuous coal seams of the Gates Formation showed that coalification levels were largerly established before folding and thrusting started. Isoreflectance lines of the beds run parallel to the bedding of the folded strata. Seams collected from various thrust sheets exposed at surface do not, in general, show significant changes in vitrinite reflectances from one thrust sheet to another. Many of the coals of the Gates Formation were found to have biaxial negative reflectance in dicatrices. Orientation of R max is in all cases parallel of subparallel to the mactroscopic fold axes indicating preferential orientation of the aromatic lamellae in the coals in the direction of minimum compressive stress. It is suggested that the occurrence of biaxial negative coals is related to a tectonic stress field that existed during the later stages of burial and subsequent deformation.

Sedimentological and palynological evidence of regional climatic changes in the Campanian to Paleocene sediments of the Rocky Mountain Foothills, Canada

Evidence of paleoclimatic variations in the upper Campanian to lower Paleocene post-Wapiabi sequence of strata is visible both laterally between the central and southern Foothills, and vertically in the stratigraphic record. These differences are expressed by the distribution of climatically sensitive sediments, i.e. coal and caliche, and associated palynological assemblages within floodplain facies, as well as by changes in the style of fluvial channels. The interpretation of a semi-arid environment for mature caliche paleosols is supported by the impoverished character of the associated palynological assemblages, both in terms of diversity and the number of specimens recovered, and by the conspicuous presence of Classopollis. The lateral extent of the semiarid floodplain facies and associated broad and mobile channel deposits is limited to the southern part of the basin. No signs of a caliche facies have been found in the post-Wapiabi strata of the central Foothills. Instead, some of the floodplain deposits associated with meandering streams in this part of the basin contain numerous, thick, coal-bearing intervals. The relative climatic differences between the more humid central part and the drier southern part of the basin prevailed throughout the entire post-Wapiabi interval. As this cannot be satisfactorily explained by the position of the sea shore or by orographic influences alone, there was probably another external factor. This could have been the pattern of atmospheric circulation, such as that responsible for the present-day climatic differences existing between the southern and central Foothills. Semiarid floodplain facies occur at two levels in the stratigraphic column of the southern Foothills (in the late Campanian, Belly River Formation and in the upper Maastrichtian to lower Paleocene, Willow Creek Formation). They correspond to regressive episodes of the epicontinental seaway. Intervening between these semiarid floodplain facies are the marine shales of the Bearpaw Formation and, both overlying and underlying them, thin coal beds. These represent recurrent periods of swamp growth and peat accumulation in back-barrier environments (lagoon-fill and supratidal marsh respectively). Because of the proximity of these swamps to the sea shore it is difficult to assess the influence of climate on the relative humidity of these settings on strictly sedimentological grounds. However, the terrestrial components of the palynological assemblages recovered from these marginal-marine settings and correlative lacustrine sediments (containing fresh-water stromatolites but no coal) in the central Foothills are in sharp contrast with the impoverished assemblages known from the caliche facies. The former are prolific, diverse, and contain a number of triprojectate pollen species, which indicate a relatively humid climate during the latest Campanian time.

An Analysis of Wind Fluctuation Statistics Collected under Stable Atmospheric Conditions at Three Sites in Alberta, Canada

Abstract Wind fluctuation data collected under stable atmospheric conditions at two prairie sites and a site located near the Rocky Mountain foothills have been analyzed. Results of the analysis show a marked tendency for horizontal fluctuation angles to vary inversely with wind speed. In contrast, vertical fluctuation angles tended to be invariant with wind speed. Atmospheric turbulence was much greater at the foothills site than at the prairie sites. This was mainly due to the fact that standard donations of vertical wind angles were almost twice as great. Standard deviations of horizontal fluctuation angles were only about 20% greater.

Modelling-tracer study for risk assessment of a proposed sour gas facility

As an integral part of a risk assessment of a sour gas pipeline proposed for a recreational area in the Rocky Mountain foothills, the dispersion of hydrogen sulphide was assessed using meteorological monitoring, tracer gas concentration measurement and a complex terrain diffusion model. Sulphur hexafluoride was released into the nocturnal drainage winds of two valleys in the eastern slopes of the Alberta Rockies southwest of Calgary. The resulting concentrations were measured at several points on transects at various distances from the source. The NUVAL version of the dispersion model IMPACT (Integrated Model for Plumes and Atmospherics in Complex Terrain) was site tuned using the measured concentrations and concurrent meteorological data. Relative mean absolute errors of 24-50% were obtained. The Gaussian model (PLUMES) with modified stability classes gave relative mean absolute errors of 42-64% in predicting transect maxima. Dilution rates were found to be much larger than would be experienced under similar conditions over flat terrain.

Evolution of the triangle zone in the Rocky Mountain Foothills near Coalspur, central Alberta

A triangle zone, which commonly occurs along the external margin of a foreland thrust and fold belt with a buried thrust front, is underlain by a subhorizontal, blind, foreland-verging thrust that ends against a foreland-dipping, hinterland-verging thrust. These contemporaneous thrusts, active towards the end of orogenesis, enclose an intercutaneous wedge that moved towards the foreland. During orogenesis, a triangle zone evolves through periodic replacement of faults bounding the active wedge. Replacements occur in cycles during each of which a lower fault tends to be replaced by one in a lower stratigraphic horizon, an upper fault by one farther away from the foreland. Each cycle ends with the lower fault moving to a younger horizon where it joins a new, more external upper fault.Near Coalspur, the triangle zone exposes the remnants of several wedges involving Upper Cretaceous and Paleocene molasse. Most of these wedges developed during the last cycle but one and have a combined displacement of about 5 km. Within this cycle, the younger the wedge, the older the strata at its extremity. The upper fault of each wedge cuts the lower fault of the preceding wedge. The upper fault of one of the wedges has a lateral ramp.

Lithologically Discordant Resistivity and IP Anomalies Associated With Hydrocarbons in the Rocky Mountain Foothills of Alberta Canada

The foothills of the Rocky Mountains in Alberta Canada contain several producing gas fields which are located in traps formed by the intense thrust faulting which characterizes this zone. The gas is found in Mississipian (Lower Carboniferous) rocks and the depth of the reservoirs lies in the range 3 to 6 km, with the depth being greater as the front of the Rocky Mountains is approached. The outcropping rocks of the area are Cretaceous sandstones and shales of marine and continental origin.

Comparative Age of Grassland and Steppe East and West of the Northern Rocky Mountain

Given the taxonomic and biogeographic differences between dominant species in grasslands of the Great Plains and the palouse grasslands and steppe of the Pacific Northwest, it seems likely that the two biomes have had separate origins. Fossil leaf and seed floras and pollen data from east and west of the Rocky Mountain cordillera and pollen data from the cordillera area suggest that three distinct floristic provinces were in existence by the beginning of mid-Miocene (Barstovian) time. Montane conifer forest poor in genera typified the Rocky Mountain foothills and nearby basins, while mixed conifer-deciduous hardwood forest and Taxodium swamps rich in woody genera occurred in the Columbia Basin. On the Great Plains the Kilgore flora (Barstovian of Nebraska) indicates deciduous open forest and prairie dominated by species of eastern and southern affinities. Younger Neogene floras in the Pacific Northwest suggest that steppe and local grassland were beginning to be important in the Pliocene of the Pacific Northwest, while grasslands and open forest became widespread on the Great Plains somewhat earlier (late Miocene or Clarendonian-Hemphillian time). The persistence of mixed conifer and broad-leaved forest on the Columbia Plateaus suggests that this area was open to the west through about 8 Ma. Due to the increasing height of the Cascade Range and/or regional upwarping, the rain shadow east of the Cascades became increasingly effective after the Clarendonian. Many of the terrestrial herbaceous groups and some shrub taxa of xeric environments reported here from a variety of sites are unknown in the Paleogene and may have evolved during the Neogene. According to the regional pollen record, terrestrial herbs become more diverse in the late Neogene. Recent fossil evidence has helped substantiate that the grasslands and steppe west of the Continental Divide in the Columbia Basin area are about three million years (Ma) old, about ten million years younger than similar vegetation types east of the Divide in the Rocky Mountain foothills and in the Great Plains. Biogeographic differences between the two areas are reflected in species composition and in the dominant habits of grasses. Some climatic differences between 'east' and 'west' exist, but they do not seem sufficient to account for the vegetation contrasts. We propose that an examination of the Late Cenozoic history (Miocene to present) of the northern Rocky Mountains may help illuminate the nature of origins of the grassland and steppe east and west of the Divide. The region to the west of the Rocky Mountains, the Columbia Plateaus3, is endowed with some of the finest and best-documented Miocene leaf floras in North America, while the region to the east, the Rocky Mountain foothills and the Great Plains, have Mio-Pliocene deposits for which pollen, leaf, and seed data are now available. To understand the history of grassland and steppe development, be