River Arch Research Articles

Winagami reflection sequence: Seismic evidence for postcollisional magmatism in the Proterozoic of western Canada

A recent Lithoprobe seismic-reflection transect in the Peace River arch region of the Western Canada sedimentary basin traverses continental crust that was assembled in a series of magmatic and collisional events during the interval 2.0–1.9 Ga. The seismic data reveal panels of dipping reflectivity at tectonic domain boundaries, but they are otherwise dominated by prominent, subhorizontal reflections that occur between 3.5 and 18.5 km depth over an area of at least 120 000 km 2 . These reflections, here named the Winagami reflection sequence, overlap several tectonic domains and are comparable in geometry, depth, and areal distribution to sills and discordant intrusive sheets imaged by previous seismic profiling in the Baltic shield and the Basin and Range province of the western United States. As many as five distinct reflections are present, some of which can be traced for more than 100 km. Contrasting reflection character in adjacent tectonic domains suggests an intrusive geometry controlled partly by the mechanical properties of the host rocks. Seismic modeling indicates that observed waveforms are consistent with reflections from tabular mafic bodies ∼70 m thick. The Winagami reflection sequence crosscuts the collisional fabric (ca. 1890 Ma), but the sequence is offset by a brittle fault with an estimated age of 1760 Ma. These timing constraints suggest that the Winagami reflection sequence is a previously unknown component of a regional magmatic event emplaced during a period of brittle indentation of the western Canadian shield by the Slave province.

Granite Wash Alluvial Fans, Fan-Deltas and Tidal Environments, Northwestern Alberta: Implications for Controls on Distribution of Devonian Clastic Wedges Associated with the Peace River Arch

Granite Wash Alluvial Fans, Fan-Deltas and Tidal Environments, Northwestern Alberta: Implications for Controls on Distribution of Devonian Clastic Wedges Associated with the Peace River Arch

Salmon River Arch revisited: new evidence for 1370 Ma rifting near the end of deposition in the Middle Proterozoic Belt basin

New U–Pb zircon dates on diabase, diorite, and migmatites within a large magmatic complex in east-central Idaho have refined the age and tectonic setting of the East Kootenay orogeny that affected the Belt basin ca. 1370 Ma. These data show that a large volume of mafic magma was injected into the basin in east-central Idaho and followed shortly thereafter by its own felsic differentiate and granitic plutons and metamorphism of the host sediments ca. 1370 Ma. These data show that the magmatic complex and associated gneisses in east-central Idaho are not pre-Belt basement, but contemporaneous in age with the Belt basin. Nd isotopic analysis of the magmatic rocks establishes that they are not derived from known Proterozoic or Archean basement terranes, but could have formed from the host Yellowjacket Formation or juvenile 1.7 Ga crust. Nd isotopic composition of gneisses and the Yellowjacket Formation are interpreted to support previous correlations between these rocks and the Belt Supergroup. Metamorphic barometry on 1370 Ma migmatites intercalated with the magmatic complex constrain the metamorphism to pressures of 450 MPa (14 km) initially and show that pressure increased to 650 MPa (20 km) before the end of metamorphism, which is consistent with magma intrusion into the bottom of the basin, followed by basin subsidence and sediment loading. We postulate that the East Kootenay orogeny is a pulse of bimodal magmatism, basin rifting, and renewed subsidence and sedimentation that shortly preceded the end of deposition in the Belt basin.

Detrital zircon reference for Cambrian to Triassic miogeoclinal strata of western North America

U-Pb analyses of 656 single zircon grains from Cambrian to Triassic miogeoclinal strata provide a latitudinal and temporal reference for the ages of grains that accumulated along the western margin of North America. Comparisons between this detrital zircon reference and the ages of grains in potentially displaced terranes outboard (west) of the miogeocline should help establish when the terranes first arrived in sedimentary proximity to western North America. North-south variations in the ages of grains in Cambrian and Devonian to Triassic strata, which reflect the north-south changes in the age of cratonal rocks near the margin, should also help place constraints on a terrane's paleolatitude during these time periods. The technique cannot be used to determine paleolatitude during Ordovician time, however, because miogeoclinal strata from northern Canada to northern Mexico are dominated by grains shed from the Peace River arch (northwestern Canada).

3-D velocity structure from simultaneous traveltime inversion of in-line seismic data along intersecting profiles

A method for simultaneously inverting in-line seismic-traveltime data recorded along a network of intersecting linear profiles is presented. Consistency of the models at the intersection points is assured and permits 3-D structural and velocity variations to be inferred by interpolation between the profiles. Common model parameters are used at the intersection points, thereby minimizing the number of independent model parameters and maximizing the degree of constraint of each 2-D model. The method has two main applications: (1) to obtain the most constrained set of 2-D models for each profile if subsequent 3-D modelling is not possible, and (2) to provide a 3-D starting model for subsequent 3-D modelling if there is sufficient azimuthal data coverage. Some ideal line geometries are suggested, but the method is applicable to any set of two or more lines with one or more intersection point. A new interpretation of crustal seismic data from the Peace River Arch region of the Western Canada Sedimentary Basin, consisting of four profiles, is presented using the simultaneous-inversion method for both refracted and reflected arrivals. The results are generally consistent with a previous interpretation of the data in which each profile was modelled independently of the others using 2-D forward modelling. However, the models obtained by inversion contain less lateral heterogeneity that more accurately reflects the resolution limits of the data. This illustrates the need to reconsider data that have only been analysed by forward modelling.

A 3-D Physical Modelling Approach to Fault Identification, Peace River Arch, Alberta, Canada: Implications for Reef Development: ABSTRACT

A 3-D Physical Modelling Approach to Fault Identification, Peace River Arch, Alberta, Canada: Implications for Reef Development: ABSTRACT

Dolomitization and Porosity Development in the Middle and Upper Wabamun Group, Southeast Peace River Arch, Alberta, Canada

Dolomitization and fracturing are critical to porosity development in most Wabamun Group reservoirs in the southern part of the Peace River arch. Cores from Peoria, Normandville, and Eaglesham fields and adjacent areas were examined to determine the relationship between depositional facies, dolomitization, fracturing, and porosity. Three-dimensional (3-D) seismic data indicate that most upper Wabamun dolomites are coincident with mound-like structural highs at the top of the Wabamun, with structural relief due largely to differential compaction between dolomite and adjacent limestone. The dolomite bodies generally are small, only 100-300 m across, which makes 3-D seismic data very helpful in Wabamun exploration. When this depositional/diagenetic model for dolomitization w s integrated into 3-D seismic interpretations, Canadian OccidentaPs discovery rate in the Wabamun increased from approximately 25 to 80%. Dolomitization and porosity are laterally quite variable in the Wabamun with the 200-250-m Wabamun section changing laterally from porous dolomite to nonporous limestone in less than 1 km (sometimes as little as 150 m). Two generations of replacive dolomite were identified, early near-surface and late hydrothermal. The early dolomite is facies, fabric, and mineralogy selective with some burrow fills and aragonitic mollusks being preferentially dolomitized in dolomitic limestones. Complete dolomitization is common in unfossiliferous carbonates (mudstones and peloid wackestones and packstones), which are interpreted as being deposited on paleotopographic highs and dolomitized by seawater or slightly evaporated seawater during shallow burial. Most fracturing occurred after early, repla ive dolomitization. Late hydrothermal dolomitization was not strictly facies or fabric selective. Features associated with hydrothermal dolomites include vugs, fractures, collapse breccias, white dolomite cement, anhydrite, and coarse calcite cement, although anhydrite and coarse calcite cement precipitated distinctly after hydrothermal dolomitization. Late dolomitization, karst-like dissolution and collapse apparently were localized near the margins of the early dolomites where adjacent limestones were dolomitized or dissolved. Dissolution of calcite in partially dolomitized limestones resulted in geopetal accumulations of dolomite rhombs (porous sucrosic dolomite) in some fractures and burrow fills. Hydrothermal fluids apparently moved updip through the underlying Winterburn and/or Leduc formations, an then upward through porous, early dolomites in the Wabamun, causing dolomitization of adjacent limestones and karst-like dissolution. Stable oxygen isotope ratios of the dolomites are quite variable (^dgr18O ranges from -2.0 to -11.4^pmil, PDB), supporting multiple stages of dolomitization during progressive burial.

Apatite fission track paleothermometry of the peace river arch region, Western Canada sedimentary basin

Apatite fission track paleothermometry of the peace river arch region, Western Canada sedimentary basin

Patterns of Burial-and Tectonically Controlled Dolomitization in an Upper Devonian Fringing-reef Complex: Leduc Formation, Peace River Arch Area, Alberta, Canada

ABSTRACT Cumulative patterns of dolomitization in a subsurface Upper Devonian carbonate platform in the Peace River Arch area, Alberta, are related to progressive burial ( 1 km) fracturing focused basin-derived fluids along subvertical structural conduits and into adjacent permeable strata. In the Early Mississippian ( 3 wt % Fe) dolomite in the platform, heralding increased Fe mobilization during burial diagenesis. A negative shift in 18O values, -6.5 to -15, is associated with successive fracture-related dolomites, and is interpreted to reflect an increase in fluid temperatures. Fracture-related flow was probably rapid; petrographic and isotopic signatures of fracture-related dolomitization can be traced 300 m upsection from the Leduc Formation.

Dolomitization and Porosity Development in the Wabamun (Devonian), Peace River Arch, Alberta

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Regional-Scale Porosity and Permeability Variations, Peace River Arch Area, Alberta, Canada (1)

This study examines the large-scale variability of porosity and permeability of the sedimentary rocks in the Phanerozoic succession in the Alberta part of the Peace River arch area of the Western Canada sedimentary basin. The study is based on about 450,000 core analyses at approximately 22,000 wells in an area of more than 165,000 km{2}. Plug-scale porosity and permeability values are scaled up to the well scale by hydrostratigraphic unit, resulting in two sets of about 16,000 values each for porosity and permeability, unevenly distributed both areally and with depth. The permeability frequency distributions are lognormal for most of the units or parts of the units. The regional-scale variability of porosity and permeability is quite high, between 1 and 38% for porosity, and 0.001 md and 3 d for permeability. The clastic units of the foreland basin exhibit a relatively high correlation between permeability and porosity. Several areal trends and patterns are identified for groups of hydrostratigraphic units, patterns that change gradually from one group to another. It is hypothesized that the observed variability is caused by the dominance of the Peace River arch, carbonate deposition, or compaction at various times throughout the evolution of the basin. Based on the predominant controlling factor, the geological history can be divided into four periods: arch influence during the Early to Middle Devonian, reefal carbonate-deposition influence during the Middle to Late Devonian, passive margin influence during the Late Devonian to Middle Jurassic, and orog nic influence since the Middle Jurassic.

Oil/Source Correlations of Devonian and Mississippian Reservoired Oils in the Peace River Arch Area of the Western Canada Basin

Oil/Source Correlations of Devonian and Mississippian Reservoired Oils in the Peace River Arch Area of the Western Canada Basin

Present and Past Geothermal Regimes and Source Rock Maturation, Peace River Arch Area, Canada (1)

Present and past geothermal regimes in the Peace River arch area in the Western Canada sedimentary basin were studied using stratigraphic, hydrogeological, geothermal, and geochemical data from about 22,000 wells drilled in the area. The analysis of the main characteristics of heat flow and of the flow of formation waters showed that conduction is the main mechanism for the transport of the terrestrial heat to the surface. The regional-scale distribution of the integral geothermal gradient (from the base to the top of the sedimentary column) shows a north-northwest increase from 25 degrees C/km to more than 35 degrees C/km, caused by increased heat flow of crustal origin. Some local anomalies superimposed over this trend are related to variable radiogenic heat production n the basement. The thermal history was reconstructed for the last 70 m.y. since the Laramide orogeny, during which maximum burial was attained. The paleoheat flow was lower than at present, with a warming trend since the Late Cretaceous or the Tertiary. The reason for this warming trend is not examined in this paper. Analysis of the level of maturation of the source rocks showed that the Upper Cretaceous rocks are generally immature, the Lower Cretaceous rocks are in the oil window, the Jurassic to Mississippian rocks are in various stages of oil and gas generation, and the Devonian source rocks are generally overmature. The maturation history shows that the Paleozoic source rocks entered the oil window during the Late Cretaceous and early Tertiary, whereas the Cretaceous rocks matured during the post-Eocene regional uplift.

Thermal History of the Peace River Arch Region, Western Canada Sedimentary Basin: Constraints from Apatite Fission Track Data

Thermal History of the Peace River Arch Region, Western Canada Sedimentary Basin: Constraints from Apatite Fission Track Data

Foraminifera of the middle to upper Albian transition (Lower Cretaceous), northeastern British Columbia

Throughout Alberta and Saskatchewan, the upper Albian Substage lies unconformably on subjacent beds. However, on the Peace River in northeastern British Columbia, 32 km below Hudson Hope, a silty shale outcrop shows uninterrupted marine deposition across the Middle–Upper Albian substage boundary. An arenaceous foraminiferal fauna of 21 genera and 57 sub-generic taxa is illustrated from this outcrop of the Hasler Shale. The collections come from above the previously illustrated microfauna of the Stelckiceras liardense Zone and below the occurrence of Haplophragmoides gigas gigas and provide a spectrum of transitional faunules spanning the middle–upper Albian boundary. The corresponding boundary of the Ammobaculites wenonahae Subzone of the Gaudryina nanushukensis Zone with the overlying Haplophragmoides uniorbis Subzone (new) at the base of the Haplophragmoides gigas Zone is defined at 73 m above the top of the Cadotte Sandstone by the disappearance of A. wenonahae. Genera within the upper part of the A. wenonahae Subzone and the H. uniorbis Subzone include Bathysiphon, Saccammina, Pelosina, Hippocrepina, Psammosphaera, Thuramminoides, Ammodiscus, Miliammina, Psamminopelta, Reophax, Scherochorella, Haplophragmoides, Ammobaculites, Bulbophragmium, Ammobaculoides, Textulariopsis, Pseudobolivina, Trochammina, Gravellina, Eggerella, and Verneuilinoides. Two new species and two new subspecies are established, viz. Ammobaculites kokei, Trochammina bredini, Haplophragmoides gigas Cushman pregigas, and Reophax deckeri Tappan sliteri. Species originally described from the upper Albian of Wyoming, such as Haplophragmoides uniorbis Eicher, originated out of boreal stock, as they are recognized within the middle Albian upper A. wenonahae Subzone north of the Peace River Arch. On the Peace River, the passage from middle Albian to upper Albian is marked by water depth at or below wave base, but regression is reflected at the substage boundary by the sharp reduction in variety of taxa.

Geothermal Regime and Maturation in the Peace River Arch Area, Canada

A comprehensive approach was used in the study of geothermal regime and maturation in the Peace River arch area, western Canada, with the purpose of evaluating the potential for hydrocarbon resources. The present-day geothermal regime was determined based on bottom hole temperature, thermal conductivity, and radiogenic heat production data. Hydrogeological studies show that the heat transfer in the region is dominated by thermal conduction. Since the study area is relatively undisturbed and there are no large-scale changes in the thermal conductivity of sediments, the regional distribution of the geothermal gradient is controlled by the heat flow from the crystalline basement. The temperature distribution is controlled in addition by the thickness and thermal conductivity of the sediments. The good control on the present-day geothermal regime allows a good evaluation of thermal maturation and calibration of models for thermal history reconstruction. A thermal inverse method, in which the paleoheat flux is estimated by optimization of the calculated to the measured vitrinite reflectance data, was used to reconstruct the thermal history of the area. The paleoheat flow in most of the region shows a warming-up trend with geological time. The paleoheat flow values on the arch were relatively higher than those off themore » arch, supporting the proposed rifting origin of the arch. Two regional thermal maturation trends are present for most of the source rocks in the area, one increasing from northeast toward the disturbed belt and another increasing from north to south. Both of these trends reflect the structural control of the regional thermal maturation.« less

A case study of migration from the West Canada Basin

Abstract A regional model for hydrocarbon charge in the West Canada Basin is presented. Three discrete ‘hydrocarbon cells’: Devonian, Mississippian-Neocomian and mid Upper Cretaceous (Post-Mannville) host petroleum which was indigenously generated from five major source rocks. Source depositional environment and Columbian-Laramide basin geometry control this pattern. On a regional scale, lateral carrier bed migration dominates basin plumbing, with the mid Cretaceous Mannville Group (oil sands) acting as the ultimate gathering point for subcropping source-carrier systems. At a play-specific level, an example of significant local vertical migration within the gas phase is presented to explain charge of Permo-Carboniferous sands in the Peace River Arch area.

Multiple Phase Fracture and Fault-Controlled Burial Dolomitization, Upper Devonian Wabamun Group, Alberta

ABSTRACT Recent data from the subsurface Tangent, Eaglesham and Normandville fields, located east of the Peace River Arch in northern Alberta, indicate that these Wabamun Group subtidal carbonates have undergone a complex diagenetic history related to multiple stages of fracturing and faulting. Burial dolomitization, which generated mainly matrix dolomites, was responsible for the development of porous reservoir rocks which are spatially highly variable. Primary porosity was reduced by marine and early burial diagenesis, which formed micrite, syntaxial overgrowths, granular, blocky and coarse fracture-filling calcite cements. Minor amounts of microdolomite and floating dolomite rhombs formed during shallow burial. Further porosity reduction by mechanical compaction and cementation, except for minor dissolution, and initial fracturing, resulted in predominantly tight limestones. Matrix dolomitization is associated with the second, most extensive phase of fracturing, which greatly increased both the porosity and permeability of the tightly cemented Wabamun limestones. Dolostones, which comprise 85% matrix dolomite, are the principal reservoir rock but have highly variable porosity. Large dissolution cavities developed locally after formation of the matrix dolomites. The third phase of fracturing crosscuts the matrix dolomites. In the Tangent field, these fractures locally form irregular cavity systems which are partly filled with finely crystalline and saddle dolomites. These fine-crystalline dolomites probably represent dolomite silt and sand derived from brecciation of the earlier matrix dolomite during faulting. Renewed faulting was responsible for rotation of breccia clasts. Saddle dolomite was precipitated during at least two phases, on the sides and undersides of some clasts, and in fractures. Late-stage bladed anhydrites and fracture-filling coarse calcites precipitated during hydrocarbon generation, presumably in the Late Cretaceous, except locally where source rocks may have been heated by ascending hot brines. The timing of dolomitization and fracturing is difficult to determine. Early fractures most likely occurred in the Late Devonian to Early Carboniferous during early burial and mechanical compaction. The second phase of fracturing probably occurred during the Mississippian to Pennsylvanian when the Normandville and Dunvegan faults underwent movement during the foundering of the Peace River Arch. The third phase of fracturing is linked to the more rapid subsidence and burial by the Cretaceous and Early Tertiary clastic wedge, which presumably reactivated some of the earlier faults. The combined stratigraphic, petrophysical and geochemical data support the following interpretations. 1) Early dolomite rhombs and patches resulted from the movement of seawater through semi-lithified sediment near the sediment-water interface or during early compaction. 2) Matrix dolomites formed at temperatures of between 40 and 65°C and depths of about 500 to 1500 m. Probable fluid sources for matrix dolomites were Devonian brines buried with these and underlying sediments and expelled by mechanical compaction, possibly aided by seismic pumping, along stage II fracture-fault conduits. 3) Sucrosic, saddle and reworked dolomites postdate stage III fractures and occurred during deep burial. Most saddle dolomites formed at temperatures around 100°C, but a few formed near 200dC. These dolomites formed from warm, highly saline, basin brines and/or from hot brines that ascended along fractures and faults and other stratigraphic conduits from deeper parts of the basin and/or the crystalline basement.

Regional Maps of the Albian Peace River and Lower Shaftesbury Formations on The Peace River Arch, Northwestern Alberta and Northeastern British Columbia

ABSTRACT Regional isopach maps of the Albian Peace River Formation and lower Shaftesbury Formation in northeastern British Columbia and northwestern Alberta indicate that the penecontemporaneously subsiding Peace River Arch affected sedimentation and erosional patterns of the mapped units. The Cadotte and Paddy members are characterized by abrupt superposed and thick northern depositional edges representing paleoshorelines that trended northeast-southwest. An elongate east-west, isopach depression in the Cadotte Member across Twps. 69, 70 and 71 is interpreted as representing an incised valley, resulting from erosion of previously deposited sediments of the Cadotte Member. In the southeast part of the map area, the Cadotte Member appears to have been erosionally removed. Superposition of modern drainage networks on the paleo-drainage network shows remarkable coincidence, suggesting an underlying structural control. RESUME Des cartes isopaques regionales des formations Peace River et Shaftesbury inferieure (Albien) dans le nord-est de la Colombie britannique et le nord-ouest de l'Alberta indiquent que l'arche de Peace River qui s'affaissa penecontemporainement eut un effet sur les schemes de sedimentation et d'erosion des unites cartographiees. Les membres Cadotte et Paddy sont caracterises par des limites de sedimentation septentrionales abruptes superposees et epaisses, qui representent d'anciennes lignes de rivage orientees nord-est\sud-ouest. Une depression dans l'isopaque du membre Cadotte est allongee est-ouest a travers les Twps. 69, 70 et 71, et est interpretee comme representant une vallee encaissee, qui est le resultat de l'erosion de sediments du membre Cadotte. Dans la partie sud-est de la region cartographiee, le membre Cadotte semble avoir ete enleve par l'erosion. La superposition des reseaux de drainage modernes sur l'ancien fait ressortir une coincidence remarquable, suggerant ainsi un controle structural sous-jacent. Traduit par Marc Charest

Upper Proterozoic to Middle Cambrian History of the Peace River Arch: Evidence from the Rocky Mountains

ABSTRACT The stratigraphic record exposed in the Rocky Mountains provides important information on the early uplift history of the Peace River Arch that is unavailable from the subsurface. Thickness and facies changes in Upper Proterozoic, Lower Cambrian and Middle Cambrian strata show that the arch was a positive tectonic feature from the latest Upper Proterozoic (sub-Gog Group) through Middle Cambrian. No evidence of a two-sided arch was found in the Upper Proterozoic Windermere Supergroup: the High is not the Cordilleran expression of the Peace River Arch, but part of a more proximal facies of the Windermere Supergroup that extends from what subsequently became the south margin of the Arch to well north of the Arch area (58°N). In the Rocky Mountains the south margin of the Arch follows important transverse, basement-involved structure(s) that formed during Late Proterozoic (Windermere) rifting. Similar structures may extend into the subsurface where they could have been reactivated during episodic tectonism associated with the uplift and subsidence of the Peace River Arch. During the Cambrian, the south margin of the Arch was a fundamental tectonic feature and the stratigraphic changes associated with this feature subsequently caused the formation of anomalous east-west trending faults and folds during the Cretaceous-Eocene deformation that formed the Rocky Mountains. RESUME Le registre stratigraphique expose dans les montagnes Rocheuses fournissent une importante information sur l'histoire du soulevement de l'arche de Peace River vers son commencement qui n'est pas disponible des donnees de subsurface. Les changements d'epaisseur et de facies dans les couches du Proterozoique inferieur et du Cambrien inferieur et moyen, demontrent que l'arche etait une particularite tectonique positive a partir de la fin du Proterozoique superieur (groupe sous-Gog) et a travers le Cambrien moyen. Aucune preuve d'une arche a deux cotes ne fut trouvee dans le supergroupe Windermere du Proterozoique superieur: la crete Mt. Vreeland n'est pas l'expression cordillerienne de l'arche de Peace River, mais fait partie d'un facies plus proximal du supergroupe Windermere qui s'etend de ce qui devint par la suite la limite sud de l'arche, jusqu'a bien au nord de la region de l'arche (58°N). Dans les montagnes Rocheuses la limite sud de l'arche suit une importante ou d'importantes structures transversales impliquant le socle et qui se formerent durant la creation de rifts du Proterozoique superieur (Windemere). Des structures semblables pourraient se prolonger dans la subsurface ou elles pourraient avoir ete reactivees durant des episodes de tectonisme associes au soulevemant et a la subsidence de l'arche de Peace River. Durant le Cambrien, la marge sud de l'arche etait une particularite tectonique fondamentale et les changements stratigraphiques associes a cette particularite furent par la suite la cause de failles et de plis anormaux, orientes est-ouest, durant la deformation Cretace-Eocene qui produisit les montagnes Rocheuses. Traduit par Marc Charest