Abstract Two major facies are represented: one predominantly carbonate and the other with a higher proportion of non-carbonate clastics. The lower two-thirds of the former consists mainly of small and large reef bodies and reef detrital beds which can not easily be correlated regionally. The clastic sequence on the other hand offers an opportunity of regional faunal correlation in spite of detailed changes in facies. The dolomitic siIts tones of the Ghost River formation lie below undoubted Devonian over much of the region and are of uncertain age. In the clastic sequence they are overlain in turn by dark, coarse-grained dolomites of the lower, and the black argillaceous limestones of the upper Flume formation; black calcareous and non-calcareous shales of the Perdrix formation; interbedded shales and limestones with some small algal and coral reefs of the Mount Hawk formation; silty and sandy dolomites, limestones, and mudstones of the Alexo formation; massive crystalline limestones and dolomites of the Morro member and thin-bedded dolomites, dolomitic breccias and cherty limestones of the Costigan member of the Palliser formation. Seven rhynchonellid zones are recognized in this sequence, each with a characteristic fauna. Several are distinguishable in well cores from the plains to the east and most of them may be traced in the northern outcrop regions of the Mackenzie River basin. Of the zone fossils, two species and one subspecies are new and, with one additional rhynchonellid species, are described in the appendix.

Abstract Deposition of the Sauk megasequence of northwestern Canada, from Peace River in British Columbia (north of lat. 56°N) to the Beaufort Sea in the Northwest Territories and Yukon Territory (lat. ∼70°N), occurred along a complex segment of the rifted western margin of Laurentia. This synthesis describes the stratigraphy, depositional history, tectonic setting, and resource potential associated with the development of the Cambrian-Ordovician great American carbonate bank. There have been few detailed studies of the Sauk megasequence in these remote areas of Canada, and much information on platform and equivalent facies remains at a reconnaissance scale. Platform rocks occur as relatively flat-lying strata of the Interior Platform that thin eastward onto the Canadian shield and correlate westward to strata within the deformed belt of the Canadian Cordillera. It is generally accepted that the Sauk megasequence was deposited along the subsiding rifted margin of Laurentia because facies pass from shallow-marine settings to deeper water slope and basinal settings from east to west. Abrupt facies changes, thickness changes, and intercalated volcanic rocks in most successions suggest a setting more complex than a simple passive margin during the development of the Cambrian-Ordovician great American carbonate bank. During Sauk megasequence deposition, positive and negative tectonic features controlled deposition along the continental margin and are represented by distinct present-day physiographic regions. The northern Rocky Mountains region lies between 56 and 60°N and is included in this summary because its geologic history is more similar to regions to the north, instead of to the southern Cordillera. North of 60°N latitude, five main regions span the vast northern Canadian mainland sedimentary basin: Beaufort-Mackenzie, Interior Plains, Mackenzie Arc, Northern Yukon, and Selwyn-Cordillera. The lower Paleozoic succession is poorly known in the “Beaufort-Mackenzie Basin,” a term that typically refers only to uppermost Cretaceous to Holocene Mackenzie Delta sediments. The northern Rocky Mountains region lies north of Peace-Athabasca arch. The arch was a positive area and forms the southern limit to the Macdonald platform and the Kechika trough, a graben system that flanked the platform to the west. The Kechika trough accumulated mainly shallow-water siliciclastic sediments until the Late Cambrian, and Sauk I and II super-sequences are characterized by complex facies changes. Carbonate deposition was prominent in the Middle Cambrian when bioherms developed on tilted fault blocks in the western part of the Kechika trough. The uppermost Cambrian–Ordovician Sauk III stratigraphy records deposition during postrift passive-margin thermal subsidence; however, during the middle Sauk III supersequence, a distinct east-to-west platform-to-basin setting evolved in response to renewed extension along the margin. The Interior Plains region lies mainly in the Northwest Territories and contains a subsurface record of the Mackenzie platform. In the Cambrian, the area was an epicontinental marine basin consisting of several depocenters that opened to the south and were segmented by positive high elements such as the Mackenzie arch. Lower and Middle Cambrian units are siliciclastic dominated and discontinuous because of the extent of paleogeographic highs. Extensive Sauk III platform carbonates of the Mackenzie platform were deposited beginning in the latest Cambrian. The Mackenzie Arc region is the eastern part of the foreland belt in Yukon and the Northwest Territories. It offers a more continuous stratigraphic record compared with the Interior Plains, but abrupt facies changes from north to south suggest phases of extension. The region contains deformed strata of the Mackenzie platform, the Mackenzie arch, and the eastern part of Selwyn Basin, which extended into the platform as Misty Creek embayment. The Sauk I supersequence is siliciclastic dominated, and carbonates are present only in distal slope settings. Sauk II and III supersequences are carbonate dominated, representing expansion of the Macdonald platform across the Mackenzie arch. Prominent slope facies in the Sauk II and III supersequences suggest an abrupt platform-to-basin setting that also accumulated submarine volcanics during phases of extension. The Selwyn-Cordilleran region extends from southwestern Yukon and northeastern British Columbia to the international border with Alaska. It is an area of deformed incompetent strata that were deposited in the Selwyn Basin, west of the Mackenzie Arc. The region contains autochthonous North American strata east of the Tintina Fault, and parautochthonous and al-lochthonous terranes west of the fault. One parautochthonous terrane thought to be a displaced slice of the North American margin is the Cassiar terrane or Cassiar platform. The Sauk mega-sequence of Selwyn Basin is generally similar to that of the Mackenzie Arc region, although the Sauk I and II supersequences contain additional units of distal basinal siliciclastic facies. The northern Yukon region contains several mountain belts and intermontane basins or lowlands that contain a succession with overall similarities to the North American Sauk mega-sequence, although the record is poorly understood in this remote area. The main tectonic element is a broad area of platform carbonates, the Yukon stable block, which is bordered to the east by the Richardson trough and to the south by the Selwyn Basin. The lower Sauk I supersequence is absent because of uplift of the Ogilvie arch. Block faulting influenced a mostly siliciclastic-dominated Sauk II supersequence, although deposition of carbonate resumed during deposition of the upper Sauk II supersequence and persisted throughout the Sauk III supersequence deposition. Sauk megasequence carbonates that may have been part of the great American carbonate bank underwent abrupt lateral facies changes indicative of syndepositional extension during the Early to Middle Cambrian, and again in the Middle Ordovician. These tectonic complexities, coupled with the lack of detailed studies, preclude a comprehensive sequence-stratigraphic analysis and determination of relative or eustatic sea level changes. The base of the Sauk megasequence is a prominent sub-Cambrian unconformity in most regions; however, eastward (toward the craton), this surface represents a merger of several unconformities, and westward (basinward), various Cambrian units overlie Proterozoic rocks. The base of the Tippecanoe megasequence, although muted and less clear in thicker shelf and offshelf successions, lies in the Middle or Upper Ordovician. The Sauk I supersequence is dominated by shallow-water siliciclastic deposits, many of which are localized in extent, with rare carbonate in distal settings such as the Selwyn Basin. Carbonate units of the middle to upper Sauk I supersequence were most likely deposited basinward of a carbonate platform. The best record of Sauk II carbonate deposition occurs along the margins of the Selwyn Basin or is represented bynarrow tracts associated with block faulting. The basal parts of the Sauk III supersequence are poorly known, but significant Upper Cambrian terrigenous siliciclastic rocks in some regions suggest a phase of uplift. The Sauk III supersequence is otherwise characterized by widespread deposition of carbonate platform and equivalent slope and basin deposits at the edge of platforms during widespread transgression and continued margin subsidence. The vast area of northwestern Canada has both hydrocarbon and mineral resource potential in rocks of the Sauk megasequence, although exploration is limited by remoteness and lack of infrastructure. Early Paleozoic intracratonic and platform-to-basin settings of the margin accumulated both potential source and reservoir rocks for fluid hydrocarbons. The Colville Hills area of the Interior Plains region has the most significant discovery of gas and some condensate within Cambrian strata. This basal Cambrian siliciclastic play potentially exists across the Interior Plains. Porous reservoir facies of Cambrian–Ordovician platform carbonates constitute another potential play, and abundant source rocks are present within equivalent basinal facies. Although mountainous regions have little hydrocarbon potential because of their geologic history, some Cambrian–Ordovician rocks host mineralized zones, particularly in the Selwyn-Cordillera region such as the metallogenic belt of Zn-Pb-Ag sedimentary exhalative deposits of the Anvil district along the western margin of the Selwyn Basin.

Abstract The Taglu gas field, discovered in 1971, is located near the outer fringe of the Mackenzie River delta, in the south-central part of the Beaufort Tertiary basin. Four wells and available seismic lines currently define about 12 sq mi (31 km 2 ) of productive area within a structural closure. The gas occurs in lower Tertiary sandstone reservoirs on the updip edge of a rotated down-to-basin fault block. The basin is filled by a deltaic clastic sequence of sandstone and shale; deposition, which prograded northward, began in Late Cretaceous time and is continuing today at the shelf edge. The southeast margin of the basin lies along the Tuk Peninsula. There, the Tertiary sediments prograded across a linear block-faulted hinge line formed of Lower Cretaceous transgressive sandstone and shale sequences overlying Paleozoic and older beds. Within the Lower Cretaceous beds, complex faulting and reservoir distribution control the hydrocarbon “play” that has yielded oil at Atkinson and gas at Parsons Lake. The southwest margin of the basin lies along the locally designated “West coastal plain” (Yukon or Arctic coastal plain) where a thick Jurassic—Lower Cretaceous sedimentary section accumulated in front of a rising mountain belt. Only a small portion of the Tertiary-Cretaceous basin extends onto the onshore part of this southwest margin. Offshore, the younger strata thicken abruptly into Mackenzie Bay and the Beaufort Sea. During Tertiary time, the rapidly deposited, prograded sediments in the basin became involved in a partly gravity-induced, detached style of structural deformation. This deformation, which contrasts with the high-angle, basement-involved block faulting of the margins, has created diapirlike, shale-cored structures and growth faults. The association of these structures with prospective reservoir sequences has resulted in the style of hydrocarbon accumulation represented by the Taglu gas field. Associated with sedimentation and deformation of this type is the phenomenon of overpressure, which has been encountered in most wells in the Mackenzie River delta. It is caused by undercompaction of fine-grained impermeable sediments, whereby pore waters are unable to escape and must support part of the weight of overburden. Organic material within the Beaufort Tertiary strata has a predominantly terrestrial character. This fact, combined with low maturation levels, probably accounts for the predominance of gas and condensate discovered to date in the Beaufort Tertiary basin. In the Taglu field, gas is produced from multiple sandstone reservoirs, probably of Eocene age, in a 1,700-ft (518 m) stratigraphic delta-front sequence below 7,700 ft (2,347 m). Gas columns of up to 1,700 ft (518 m) fill the closure almost to the spillpoint. The gas is usually wet and consists of 91-96 percent methane and 4-9 percent heavy hydrocarbons (C 2+ ), with no hydrogen sulfide. Wet-gas reserves are estimated to be in excess of 3 Tcf. About 75 percent of the Taglu gas reservoirs consists of beach and stream-mouth bar sandstones; distributary-channel sandstones make up approximately 15 percent and shoreface sandstones about 10 percent. Net sandstone thicknesses in the wells range from about 450 to 600 ft (135-185 m). The abundant, organic-rich, delta-front shales interbedded with the reservoir sandstones are the most likely source of the hydrocarbons. Therefore, a relatively small drainage area is required. An immature woody material, possibly with some biodegradation, is indicated as the hydrocarbon source by the relatively high aromatic content of the associated condensates. The condensates have API gravities ranging from 33 to 48°, and a very low sulfur content. Oil gravities range from 17 to 32° API. Pour points range from +45ºF (+7.22ºC) in a paraffinic oil to –55ºF (–48.33ºC) in a naphthenic oil. The low gravity and pour point of some of the oils may be due to biodegradation which removed paraffins by bacterial action.

Abstract Cretaceous rocks extend through the mid-continent from northern Yukon Territory and District of Mackenzie southward along Mackenzie and Rocky Mountains and eastward across the Plains of Alberta, Saskatchewan, and Manitoba to the Canadian Shield. They underlie Mackenzie Delta and Plains in the District of Mackenzie. Exposures of Cretaceous rocks are found in the southern Plains along many of the major river systems. One of the celebrated localities is at Dinosaur Park, southeastern Alberta, designated a World Heritage Site. Elsewhere in the Plains, Cretaceous rocks are mainly covered by Pleistocene drift, except in the Cypress Hills and along the Manitoba Escarpment on the eastern side of the basin. Many investigations of Cretaceous rocks have been carried out over a period of more than 125 years. Studies of oil sands, heavy oil areas, and coal-bearing areas, regional and economic studies, and detailed surface and subsurface studies have contributed to understanding the history of these rocks. More than 100 000 boreholes have been drilled in the southern part of the Western Canada Basin. Well control is relatively sparse in the District of Mackenzie where, too, outcrops are lacking in large areas. Drilling in the Eagle Plains, Mackenzie Delta, and along the Mackenzie Valley has provided much needed data. Recent coal exploration in the foothills and mountains of British Columbia and in the Plains of Alberta and Saskatchewan has contributed greatly to the overall knowledge of the Cretaceous rocks.