Northeast British Columbia Research Articles

Geology of northeast British Columbia and northwest Alberta: diamonds, shallow gas, gravel, and glaciersThis article introduces a selection of papers published in this Special Issue on the theme Geology of northeastern British Columbia and northwestern Alberta: diamonds, shallow gas, gravel, and glaciers.

This special issue reports on some of the results of a multi-disciplinary research program conducted in the Boreal Plains of northwest Alberta and northeast British Columbia. Several innovative approaches to conducting geoscientific research in this remote drift-covered region are presented, including geochemical analysis of bentonites for evaluating kimberlite potential, the use of electromagnetic surveys for mapping buried aggregate deposits, and paleo-topographic mapping techniques to define buried channels. Results of the program include the discovery of several large aggregate deposits, the first kimberlite indicator minerals in northeast British Columbia, a significant sphalerite dispersal train in northwest Alberta, the first documented report of kimberlite-sourced bentonites, and numerous previously unknown interglacial sites. Together these papers provide a greatly enhanced understanding of the glacial history, Quaternary stratigraphy, and kimberlite geology of northwest Alberta and northeast British Columbia and provide an improved framework for resource exploration in the region.

Quaternary stratigraphy and glacial history of the Peace River valley, northeast British ColumbiaThis article is one of a selection of papers published in this Special Issue on the theme Geology of northeastern British Columbia and northwestern Alberta: diamonds, shallow gas, gravel, and glaciers.

Two Cordilleran and three Laurentide glacial advances are recorded in Quaternary sediments and landforms in the Peace River valley, northeast British Columbia. The advances are inferred from fluvial gravels, glaciolacustrine sediments, and tills within nested paleovalleys excavated during three interglaciations and from the distribution of granitoid clasts derived from the Canadian Shield. Till of the last (Late Wisconsinan) Laurentide glaciation occurs at the surface, except where it is overlain by postglacial sediments. The advance that deposited this till was the most extensive in the study area, and the only advance definitively recognized in western Alberta south of the study area. Late Wisconsinan Cordilleran till has not been found in the study area, but Cordilleran and Laurentide ice may have coalesced briefly during the last glaciation. Support for this supposition is provided by the inferred deflection of Laurentide flutings to the southeast by Cordilleran ice. The earliest Laurentide advance may have been the least extensive of the three Laurentide events recognized in the study area. Erratics attributed to this advance occur only east of the Halfway River – Beatton River drainage divide.

Mapping Quaternary paleovalleys and drift thickness using petrophysical logs, northeast British Columbia, Fontas map sheet, NTS 94IThis article is one of a selection of papers published in this Special Issue on the theme Geology of northeastern British Columbia and northwestern Alberta: diamonds, shallow gas, gravel, and glaciers.

The relatively subdued topography of British Columbia’s northern interior plains does not reflect the irregular, buried bedrock surface. Many areas have been deeply incised by preglacial rivers that have subsequently filled with a succession of Quaternary sediments. In this study, oil and gas petrophysical logs, drill chip samples, water well logs, and surficial and bedrock outcrop maps were used to model the bedrock topography of the Fontas map sheet (NTS 94I). The modelled data produced several depressions that are interpreted to be paleovalleys incised into the soft Cretaceous shale of the Fort St. John Group. Understanding the geometry, thickness, and stratigraphy of the drift has considerable safety and resource management implications as artesian aquifers and natural gas were encountered in the drift during oil and gas well drilling. Four major paleovalleys are suggested. The most dominant paleovalley (Kotcho–Hoffard Paleovalley) is located south of the Etsho Plateau and trends west-southwest across the map area. A second depression occurs within the loop of the Hay River and may be a tributary of the Kotcho–Hoffard Paleovalley that links with the Rainbow Paleovalley in Alberta. A third paleovalley is mapped south of the Sahtaneh River (Kyklo Creek Paleovalley) and is either a tributary to, or crosscuts the Kotcho–Hoffard Paleovalley. The Niteal Creek Paleovalley is located between the Fontas and Sikanni Chief rivers. Its geometry is speculative as there are sparse data, but it may be a tributary of the Kotcho–Hoffard Paleovalley.

AMS-dated late Pleistocene taiga vole (Rodentia: Microtus xanthognathus) from northeast British Columbia, Canada: a cautionary lesson in chronologyThis article is one of a selection of papers published in this Special Issue on the themeGeology of northeastern British Columbia and northwestern Alberta: diamonds, shallow gas, gravel, and glaciers.

Dissected colluvial sediments on a Peace River terrace at Bear Flat, northeast British Columbia enclosed a late Pleistocene micromammalian faunule. The fossil remains, including a few loosely articulated skulls and mandibles, were dominated by taiga voles ( Microtus xanthognathus ). The Bear Flat site constitutes the second fossil occurrence in the region of this elusive species, which is unknown in British Columbia in historic times. The late Pleistocene age, determined by accelerator mass spectrometry directly on taiga vole bone collagen, is consistent with the ages of widespread taiga vole records peripheral to the Laurentide ice sheet in western, mid-western, and eastern North America. The presence of allo-chronous remains within a comprehensively dated sedimentary sequence provides a cautionary note about straightforward acceptance of relative stratigraphic dating.

Quaternary stratigraphy of the Prophet River, northeastern British ColumbiaThis article is one of a selection of papers published in this Special Issue on the theme Geology of northeastern British Columbia and northwestern Alberta: diamonds, shallow gas, gravel, and glaciers.

Exposures in the Prophet River valley in northeast British Columbia provide a unique glimpse into the Quaternary history of the northwest Canadian Boreal Plains. The region shows evidence of Late Wisconsinan Laurentide glaciation in the form of widespread till, containing abundant erratic clasts derived from the Canadian Shield. Vertical sections along the Prophet River expose non-glacial and advance glacial sediments below this till. Pre-Late Wisconsinan non-glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites. Macrofossils within horizontally laminated organic-rich black clay and silt indicate deposition on the floodplain of the paleo-Prophet River within an oxbow lake. The climate during deposition is interpreted to be similar to present, supporting a dominantly spruce forest. Wood obtained from eight sites provided non-finite radiocarbon ages, and one sample provided an age of 49 300 ± 2000 BP, which is also considered non-finite. Glaciolacustrine clays and silts, deposited during impoundment of eastward-flowing drainage by the advance of the Laurentide Ice Sheet (LIS) in the Late Wisconsinan, overlie the non-glacial sediments throughout the valley. A blanket of clast-poor, clay-rich till up to 20 m thick, and deposited by the LIS, drapes the glaciolacustrine sediments. Since deglaciation, the Prophet River has incised the valley and formed fluvial terraces at different levels above the modern river.

The cumulative effects of resource development on biodiversity and ecological integrity in the Peace-Moberly region of Northeast British Columbia, Canada

Rapid acceleration of industrial development in north-eastern British Columbia is currently occurring without a comprehensive assessment of the effects it will have on ecological or cultural systems. The cumulative effects of past development are already being felt within the Treaty 8 First Nations of the region but these effects have not been quantified from a landscape point of view. Using habitat modeling and GIS analysis the effects of 35 years of agricultural and industrial development on forest biodiversity and ecological integrity were investigated for a 410,000 ha landscape in north-eastern British Columbia. The study identified a significant increase in area impacted by developments which lead to a shift in landscape structure and significant change in forest biodiversity. Forest fragmentation and habitat loss has resulted in an increase in open, early seral and edge habitats at the expense of contiguous mature forests. The change in landscape structure resulted in a significant increase in species richness as generalist and early seral species responded positively to increases in these habitats. A significant increase in brown-headed cowbird parasitism risk was also detected. Changes in landscape structure, reduction in habitat for 22% of modeled species, increase parasitism and predation risk due to fragmentation, and increased access have resulted in a cumulative effect of recent resource development on ecological integrity that is both additive and synergistic. The propose acceleration of future development will increase the risk to maintaining the biodiversity and ecological integrity in the Peace-Moberly region of British Columbia.

Stratigraphic relationships of the Triassic Halfway Formation in the Western Canada Sedimentary Basin

Although the lithostratigraphic definition of the Middle Triassic Halfway Formation at the type section is quite precise and should be a clear guide to identifying the formation, there has been some confusion in its usage in the Western Canada Sedimentary Basin (WCSB). Some of the problems were identified by Dixon (2005) and schematically illustrated in his figure 6 but his work focused more on the identification of an unconformity rather than on nomenclatural problems. A lithostratigaphic unit is a mappable, usually contiguous, lithological body, which may or may not have chronological significance. The Halfway Formation fits this definition, for the most part, but depending on how you interpret stratigraphic relationships within the Middle to lowermost Upper Triassic succession, there are significant chronostratigraphic implications about the position of strata commonly identified as Halfway Formation. After studying the Triassic in the WCSB for a number of years (Dixon, 2002a, b, 2004, 2005, 2007, 2008) I believe some light can be shed on the problem and it is the intent of this brief note to attempt some clarification by illustrating the stratigraphic relationships in the Doig to lower Charlie Lake succession and show that strata identified lithostratigraphically as Halfway Formation can be chronostratigraphically very different in various parts of the basin. ### Definition of Halfway Formation Hunt and Ratcliffe (1959) defined the Middle Triassic Halfway Formation from the Southern Production No. B-14-1 well, located at 1-12-84-23W6 in northeast British Columbia (Fig. 1⇓), between log depths 5000 and 5148 ft (equivalent to 1523.5 and 1567.9 m in the re-entered 2/1-12-84-23W6 well). In the type well the Halfway Formation is defined as the predominantly sandstone interval underlain by thinly interbedded mudstone, siltstone, and sandstone of the Doig Formation, and overlain by thinly to thickly interbedded mudstone, dolostone, anhydrite, and sandstone of the Charlie Lake …

Regional facies trends in the lowermost beds of the Upper Triassic Charlie Lake Formation, in the subsurface of Western Canada

Abstract Regionally extensive core coverage in beds of the lowermost Upper Triassic Charlie Lake Formation — between the A marker and underlying Middle Triassic Halfway or Doig beds — in the subsurface of west-central Alberta and adjacent northeast British Columbia facilitate the interpretation of a regional depositional setting. Three broad facies assemblages are identified: 1) red beds; 2) grey beds; and 3) sandstone beds. These three assemblages occur in geographically restricted areas. The red-bed assemblage occurs mostly along the eastern margin of the basin and is interpreted as predominantly intertidal to supratidal, sabkha deposits. The grey-bed assemblage is present between the red-bed and western sandstone assemblages and consists of predominantly intertidal to shallow subtidal beds deposited in a lagoon. Sandstones occur in two locations; in the west they are part of a linear belt, and at the second location they are associated with a local paleogeographic feature, the Beatton High, located within the grey-bed assemblage north of Fort St. John, in northeast British Columbia. The western sandstones are deposits of a barrier-island complex, whereas the sandstones associated with the Beatton High are local tidal channel and fan-delta deposits sourced from the Beatton High. The west-to-east facies changes and north-northwest alignment of the facies define a western, sandy barrier-island complex behind which (to the east) was a lagoon with sabkha deposits at its eastern margin. In the lagoon, a mixture of siliciclastics, carbonates and evaporites were deposited.

Middle Turonian dinosaur paleoenvironments in the Upper Cretaceous Kaskapau Formation, northeast British Columbia

The Kaskapau Formation is a mudstone-dominated wedge up to 950 m thick that spans late Cenomanian to middle Turonian time. The formation has a prominent wedge geometry and was deposited in the foredeep of the Western Canada Foreland Basin. In outcrop in northeast British Columbia, nearshore sandstones are locally well developed and include rare wedges of nonmarine strata. On Quality Creek, near Tumbler Ridge, 11 m of nonmarine strata contain abundant dinosaur tracks and the first in situ dinosaur bone reported from British Columbia. This site, at a paleolatitude of about 67°N, preserves a rare glimpse of Turonian terrestrial environments during global eustatic highstand. Three main dinosaur habitats are recognized: strandplain and beach-ridge; freshwater lake; and brackish lagoon. Back-beach sandstone has a relief of about 2.5 m, interpreted as beach ridges; sandy coals containing abundant dinosaur tracks represent inter-ridge slough deposits. Overlying lake deposits comprising laminated muds with freshwater molluscs grade up into rooted muddy siltstone and locally, dinoturbated sandstone. Lake deposits are capped by lagoonal mudstone with abundant brackish-water molluscs, locally including a dinosaur-trampled oyster bioherm. The upper parts of sandy lagoonal deltas are pervasively dinoturbated. Sandstone filling a tidal channel contains logs, oyster shells, and bones of dinosaurs, turtles, and crocodiles, as well as fish scales. The lagoonal succession is erosively overlain by offshore sandy mudstones. Various lines of evidence suggest that the mean annual temperature at this sea-level location was about 14 °C, with a cold-month mean no less than 5.5 °C. The high-latitude location implies a significant period of winter darkness, and correspondingly diminished plant productivity.

Numerical modeling of hydrothermal fluid flow coupled with mass transport: An example from the Devonian Wabamun Group, northeast British Columbia, Canada

Several researchers have suggested that upward and lateral hydrothermal fluid flow was responsible for dolomitization of various Devonian and Mississippian reservoirs in the Western Canada Sedimentary Basin (WCSB) based on sedimentological, geochemical and diagenetic evidence. In this study, a numerical model was applied to investigate hydrothermal fluid flow in the Wabamun Group, Parkland field, northeastern British Columbia, Canada. Our numerical results indicate that faults play the most critical role in controlling hydrothermal fluid flow. They provide a pathway connecting the basement of the basin and overlying sedimentary layers. Upwelling fluid flow via faults may bring reactants and heat from underlying strata to shallow formations for diagenetic reactions (e.g. dolomitization and/or chertification) or forming ore deposits. Salinity distribution of formation water, permeability configuration of host rock and regional fluid flow are also important factors affecting hot and brine fluid flow and accompanying heat and mass distribution.

Acid-gas injection at West Stoddart, British Columbia: An analogue for the detailed hydrogeological characterization of a CO 2 sequestration site

Geological sequestration of CO 2 is an option for significantly reducing emissions into the atmosphere. Various hydrocarbon companies in western Canada are currently injecting acid-gas (CO 2 and H 2S) into deep subsurface formations. At West Stoddart, in northeast British Columbia, acid-gas has been injected since 1998 at 1600 m depth into sandstones of the Triassic Halfway Formation, which forms a regional aquifer. A comprehensive subsurface characterization was conducted of the regional and local-scale geology, reservoir characteristics, mineralogy, in situ fluid properties, and hydrogeology. Preliminary results from geochemical and numerical multi-phase flow modelling suggest that the majority of the injected acid-gas will dissolve in the formation water and remain within a radius of a few kilometres of the injection well. The experience with the acid-gas injection at West Stoddart and other operations in the Alberta Basin has shown that the process of large-scale CO 2-injection into deep aquifers is technically feasible.

Airborne Electromagnetic Mapping for Buried Quaternary Sands and Gravels in Northeast British Columbia, Canada

An airborne electromagnetic (AEM) survey using the Fugro RESOLVE™ system was conducted over a known, buried sand and gravel deposit in northeast British Columbia, Canada to determine its effectiveness for mapping similar deposits in the area. The rarity of gravel deposits in this region provides a significant economic constraint for developing oil and gas infrastructure. Topographic relief is minimal and the area is overlain by organic materials, clay-rich tills, and glaciolacustrine sediments. Traditional exploration methods, such as airphoto interpretation, are therefore ineffective for locating these buried deposits. The buried deposit appears as a resistivity high on the apparent resistivity maps, particularly the [Formula: see text] map. The resistivity high covers a larger area than that defined initially by test pitting. Trenching within this extended zone verified the presence of sand and gravel. Other resistive features in the region were identified by the survey and one of these was confirmed by recent test pitting to be a large sand and gravel occurrence. No surface indications of sand and gravel were evident over any of these occurrences. The cross sections indicated these sand and gravel occurrences have resistivity values greater than [Formula: see text], often greater than [Formula: see text], whereas the surrounding till has resistivity values between 5 and [Formula: see text]. The airborne survey proved to be a highly successful method of locating sand and gravel deposits in this area of British Columbia that could be widely used in other plains regions with similar geological settings.

A new type section for the Upper Triassic Siphon Member, Charlie Lake Formation, in northeast British Columbia

The Upper Triassic Charlie Lake Formation of the Western Canada Sedimentary Basin contains a number of named members. One such unit is the Siphon Member, first used in a publication by Hess (1968). His work was a series of regional cross-sections and descriptions of Upper Triassic strata in northeast British Columbia. In this publication he introduced a number of informal and named members, however, in many instances he did not properly define the members or designate type sections, including the Siphon Member. Many of Hess’ (1968) stratigraphic units were identified in the Fort St John area of northeast British Columbia (map-sheet 94A). McAdam (1979) identified and correlated the Siphon Member in a manner similar to Hess, but also failed to designate a type section. This lack of a type section was remedied by Rowley (in Glass, 1990), who designated the 2-18-84-19W6 well (see Fig. 1⇓ for location) as the type section, between log depths 4411 and 4416 ft (1344.5–1346 m). Fig. 1. Location maps: a) location of study area, b) location of cross-section in Figure 2⇓. (Figures 2⇓ to 4⇓⇓ following end of article.) The Siphon Member presents some problems with how the member has been used and correlated by those in the petroleum industry and in published material. On Hess’ (1968) cross-sections it is very obvious the Siphon Member has two very distinct gamma-ray log signatures. In the eastern wells, the log signature is …

Postglacial record of diatom assemblage changes related to climate in an alpine lake in the northern Rocky Mountains, Canada

We relate changes in diatom assemblages to Holocene climate since ca. 10 300 cal. years BP at a small (4 ha), alkaline, alpine tundra lake in the Rocky Mountains of northeast British Columbia. A complex of small benthic Fragilaria-type taxa generally dominated the fossil diatom communities reflecting shallow, alkaline, and likely low light conditions resulting from minerogenic turbidity or extensive ice cover throughout the Holocene. Shifts in diatom assemblages occurred with changes in local vegetation, inferred from pollen and stomate records, and shifts in charcoal-inferred fire frequency (e.g., lowering of tree line and reduced fire frequency (approx. 7500 cal. years BP) and establishment of modern alpine tundra (approx. 3500 cal. years BP). Importantly, striking changes in diatom communities (e.g., during the mid-Holocene (approx. 5500 to approx. 3500 cal. years BP) and Medieval Warm Period (approx. AD 800 to approx. AD 1250)) occurred without evidence of vegetation shifts. During these times, diverse periphytic diatoms dominated suggesting improved benthic habitat availability with longer growing seasons and probably reduced alkalinity and turbidity with warmer- and wetter-than-present climates. Diatom analysis from this alpine lake provides a sensitive record of climate-related limnological responses, but also refines our previous understanding of Holocene climate changes in the northern Rocky Mountains inferred from terrestrial-based paleoecological records.Key words: alkalinity, alpine lakes, climate change, diatoms, Holocene, paleolimnology.

A Completion Solution for the Paddy Reservoir in Northeast British Columbia: A Case Study

Abstract The Paddy reservoir, located near the Foothills of the Rocky Mountains in northeast British Columbia, Canada, is a fluvioestuarine valley-filled sandstone that has moderate to high permeability. Evidence of tectonic stress has been observed during hydraulic fracture treatments in the form of excessive wellbore friction and net pressures. Historically, attempts to fracture-stimulate these wells has been difficult due to the inability to generate sufficient fracture width necessary for proppant placement. This paper presents a completion solution for the Paddy reservoir in northeast British Columbia that enabled successful placement of propped fracture treatments. Pressure response of past fracture treatments were analysed to understand the cause of past failures, and to quantify the influence of tectonicallyinduced stress. A recommended completion solution is presented which includes orientated perforating to reduce near-wellbore friction and a process for designing fracture treatments to enable successful placement of proppant. Field examples of the new completion technique are presented which show that near-wellbore friction was reduced by 50%, and that up to four times the amount of proppant was placed in the formation compared to previous treatments. Pressure match simulation results from the fracture treatments are also presented. Geologic Summary The Paddy Member forms the upper portion of the Peace River Formation and is distributed over the Peace River area of northwest Alberta and northeast British Columbia. It is underlain by dominantly coarse-grained shoreface deposits of the Cadotte Member and overlain by marine shales of the Shaftesbury Formation. The Paddy Member is made up of thinly bedded sandstones and shales with occasional thin coals. In the study area, the Paddy is approximately 40 m thick. Reservoir quality, incised valley sandstones located in the upper part of the unit are up to 18 m thick. They are dominantly fine to medium and occasionally coarse grained, fairly quartz-rich sandstones with 10 - 30% chert and other lithic grains. Beds are from centimetre to metre scale in thickness and show small to large-scale trough cross lamination. Where bedding thickness is reduced, millimetre scale wavy shale laminae are common and are often incorporated into stylolitic concentrations, which greatly reduce vertical permeability. The cleaner sandstones were probably deposited under fluvial conditions with some tidal influence where thin shale laminae are common. The dominant cement in these sandstones is quartz, which substantially occludes intergranular porosity in the study area. Small amounts of carbonate cements also occur but are rarely volumetrically important. In addition to intergranular porosity, a significant amount of microporosity has been generated through the dissolution of detrital grains, primarily chert. The abundance of microporosity in these sandstones, together with low water saturations indicated by wireline log analysis, may be the origin of the widely held concern that the Paddy reservoir is susceptible to formation damage through water blocking. Core from the study area indicates that porosity in the Paddy reservoir ranges up to 20%, with associated permeability to air at minimal confining pressure of several hundred millidarcies. A minimum porosity cutoff for pay is taken at approximately 8 - 9%, which is typically associated with 1 md permeability.

Magnetotelluric response and geoelectric structure of the Great Slave Lake shear zone

The Great Slave Lake shear zone (GSLsz) is a northeast-trending 25-km-wide dextral continental transform fault from the foothills of the Rocky Mountains in northeast British Columbia to the southeast side of Great Slave Lake. Based on its magnetic expression the GSLsz can be correlated for at least 1300 km, mostly in the subsurface. Magnetotelluric (MT) soundings were made at 60 sites in the southwest part of the Northwest Territories, Canada, along the LITHOPROBE Slave–Northern Cordillera Lithospheric Evolution (SNORCLE) Transect Corridors 1 and 1A, in the Summer and Autumn of 1996. Of these, 15 sites were along Corridor 1A which crossed the GSLsz, the Great Bear magmatic arc and Hay River terrane to the northwest of the shear zone, and the Buffalo Head terrane to the southeast. The primary objective of the Corridor 1A deployments was to image the structure of the GSLsz. Analysis of MT data indicates that along the Corridor 1A the resistivity structure is approximately 1D at shallow depth (<1 km) corresponding to Phanerozoic sedimentary rocks, 2D in the upper to mid crust with a strike ∼N30°E, and approximately 2D in the lower crust to lithospheric mantle with a strike of ∼N60°E. The direction in the upper crust is interpreted to represent the local-scale (<50 km) horizontal strike of the GSLsz whereas the direction in the mantle is parallel to the larger-scale strike of the GSLsz. 2D inversions of the MT data reveal that the GSLsz forms a crustal-scale resistive zone (>5000 Ωm) that is spatially correlated with a magnetic low. The GSLsz comprises greenschist to granulite facies mylonites. Its high resistivity is interpreted to be due to the resistive nature of the granitic protolith of the mylonites and that mylonites are dominated by rocks deformed in the ductile regime. To the northwest of GSLsz the MT profile reveals crustal conductors beneath the Great Bear magmatic arc and Hay River terrane. The enhanced conductivity occurring beneath the Great Bear magmatic arc is interpreted to be caused by electronic conduction within deformed and metamorphosed rocks of the Hottah terrane or the Coronation Supergroup. The MT results also reveal a mantle conductor beneath the margin of the Hottah terrane and Great Bear magmatic arc that is interpreted to be associated with the subduction of oceanic lithosphere. A second mantle conductor to the southeast is truncated at the GSLsz suggesting an older source for the enhanced conductivity and that the GSLsz includes significant strike–slip motion of sub-crustal lithosphere.

Isotopic provenance of the lower Muskwa assemblage (Mesoproterozoic, Rocky Mountains, British Columbia): new clues to correlation and source areas

The Proterozoic Muskwa assemblage is a thick (6 km) sequence of essentially unmetamorphosed, predominantly fine-grained siliciclastic and carbonate strata carried within thrust sheets of the Canadian Rocky Mountains of northeast British Columbia. It is inferred to be widespread in the subsurface of the autochthon to the east on the basis of seismic reflection profiles. The age and stratigraphic affinities of this succession are uncertain, although it is known to be older than 779 Ma based on the age of cross-cutting dikes. We report U-Pb SHRIMP ages for detrital zircons from four sandstone units and Sm-Nd data for interbedded shales that refine stratigraphic ages and correlation. The provenance characteristics of the Muskwa assemblage offer another piece in the puzzle of correctly assembling Rodinia. 207Pb/ 206Pb ages determined by SHRIMP analysis of 94 detrital zircon grains from four sandstone units range from ca. 3075–1766 Ma with a pronounced concentration of ages at ca. 1850 Ma and a paucity of grains in the interval 1920–2000 Ma. The youngest, most concordant analysis constrains the maximum age of the Muskwa assemblage to 1766±14 Ma (99.5% concordant). Sm-Nd analysis of associated mudrocks result in a range of ε Nd values that overlap with western Canadian Shield sources but result in T DM model ages of 2.30–2.45 and 2.18–2.33 Ga, using Goldstein et al. (1984) or DePaolo (1981) models, respectively. The pattern of U-Pb ages is similar to that of the western Canadian Shield but precludes a significant contribution from Proterozoic orogens in the northwest Canadian Shield, specifically the Thelon, Taltson and Calderian phase of Wopmay orogen. The abundance of grains with young ages (1850–1770 Ma) implies derivation from similarly aged rocks of the Rimbey granite belt, Hearne Province and possibly the internides of the TransHudson Orogen. The provenance characteristics of the Muskwa are compatible with sediment derived from unroofing and erosion of the orogenic topography formed by the collisional shortening of the Hearne Province during terminal assembly of the Canadian Shield ca. 1.8 Ga. The provenance characteristics of the Muskwa assemblage are distinct from those considered typical of Succession B strata, which are characterized by detrital zircons and Sm-Nd signatures derived from the Grenville Province of eastern North America. Hence, the Muskwa assemblage is assigned to Succession A, although it cannot be demonstrated which, if any, of the Succession A successions in western Canada are direct correlatives. Regional considerations suggest that the most likely correlation is with cratonic sand sheets of the Amundsen, Thelon and Athabasca basins that developed immediately after assembly of the core of Laurentia.

Reply to Discussion: Vreeland Diamictites - Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British Columbia

Hoffman et al. (1998b) developed a modified ‘snowball’ Earth hypothesis to explain the association of Neoproterozoic low-latitude glaciation with the deposition of “cap carbonate” rocks bearing highly depleted carbon isotopic values. According to this hypothesis, a runaway albedo feedback caused the world’s oceans to freeze for millions of years. During this time interval, the continental ice cover was thought to have become thin and patchy because of the virtual elimination of the hydrological cycle (Kirschvink, 1992; Hoffman et al., 1998b). The Vreeland diamictites record vigorous erosion by an extensive ice sheet at or near the pressure melting point (McMechan, 2000). Their deposition and that of several other thick (>800 m) Neoproterozoic glaciogenic deposits, including the Mineral Fork diamictites in Utah (Christie-Blick, 1983), Rapitan diamictites in northwestern Canada (Yeo, 1981), the Sturtian diamictites in South Australia (Young and Gostin, 1989), the Hangeerqiaoke diamictites in northwest China (Wang et al., 1981), the Port Askaig diamictites in southwest Scotland (Spencer, 1971), and the Chuos diamictites in northwest Namibia (Hoffman et al., 1998a), show that substantial areas of vigorous contential glaciation occurred in the Neoproterozic. The existence of these deposits is incompatible with the hypothesized thin and patchy continental ice cover of the ‘snowball’ Earth model (Christie-Blick et al., 1999; McMechan, 2000). Rather than taking the sedimentary record as evidence of warmer climates and partially open oceans, Hoffman (in Hoffman and Schrag, …

Vreeland Diamictites - Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British Columbia

Vreeland Diamictites - Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British Columbia

Vreeland Diamictites - Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British Columbia

Research Article| September 01, 2000 Vreeland Diamictites – Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British Columbia* M.E. McMechan M.E. McMechan Geological Survey of Canada, 3303 - 33rd St. NW, Calgary, AB, T2L 2A7 Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2000) 48 (3): 246–261. https://doi.org/10.2113/48.3.246 Article history received: 09 Dec 1999 accepted: 27 Apr 2000 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation M.E. McMechan; Vreeland Diamictites – Neoproterozoic glaciogenic slope deposits, Rocky Mountains, northeast British Columbia. Bulletin of Canadian Petroleum Geology 2000;; 48 (3): 246–261. doi: https://doi.org/10.2113/48.3.246 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Neoproterozoic diamictites of the Vreeland Formation exposed in the Snake Indian and Wapiti Pass thrust sheets of the central Rocky Mountains, northeast British Columbia, form a thick (350 to 2000 m) glaciogenic deposit within the passive margin succession of the Windermere Supergroup. They are the deposits of the younger worldwide episode of Neoproterozoic glaciation. Diamictites were deposited as laterally extensive sheets in a mid slope setting with minimal sediment reworking or transport by bottom currents. In the Wapiti Pass thrust sheet, the absence of dropstones and lone-stones, in facies-equivalent and interbedded fine-grained strata, indicates there was little, if any, ice rafting during sedimentation. Diamictites are the deposits of unconfined debris flows derived from the slumping of glacial deposits near the shelf-slope break. In the Snake Indian thrust sheet, dropstones and lonestones indicate ice rafting. Diamictites formed from both unconfined debris flows and the “rain-out” of ice-rafted and sediment plume material. Deposition of thick diamictites in the Mount Vreeland area was probably localized by syndepositional, west-side-down normal fault(s).Diamictites contain abundant extrabasinal (felsic and basic intrusive, volcanic, quartzite) and intrabasinal (argillite, sandstone, carbonate) clasts. They record a major source of material entering the Windermere depositional basin distinct from the basinal turbidite system of the southern Cordillera. The high volumes of glaciogenic sediment and large extrabasinal clasts indicate the transportation of massive amounts of material to the shelf-slope break by glaciers and glacial processes. Their deposition appears to be incompatible with the snowball Earth model for Neoproterozoic glaciation, with its thin patchy continental ice cover and the virtual elimination of the hydrological cycle.Locally, the diamictites are overlain by a thin deep-water limestone (cap carbonate). Olistoliths of plafformal carbonates in the immediately overlying argillite indicate deposition of postglacial (cap) carbonates on the shelf to the east, continued deposition in a slope environment in the study area, and continued instability and fault-related uplift of the shelf edge. Detailed mapping of the southwest flank of Ice Mountain shows that carbonate olistoliths, rather than a carbonate platform, overlie the diamictites. No evidence was found of penetrative deformation, uplift or erosion of diamictites during the Neoproterozoic to support a previous interpretation of the Neoproterozoic “Vreeland High”. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.