James Dixon

The breakup unconformity of the Amerasia Basin, Arctic Ocean: Evidence from Arctic Canada

To delineate more closely the age and evolution of the Amerasia Basin of the Arctic Ocean, a breakup unconformity has been identified in sedimentary basins along the Canadian margin of the basin on the basis of one or more of the following criteria. (1) Strata underlying such an unconformity are cut by major normal faults which extend into the basement, whereas strata overlying the unconformity are relatively unfaulted. (2) A major decrease in subsidence rate in the marginal basins coincides with the time of breakup and the formation of the unconformity. (3) Volcanic rocks occur beneath the unconformity. The widespread late Albian-Cenomanian unconformity is interpreted to be the breakup unconformity and thus this time interval would coincide with the initiation of sea-floor spreading in the Amerasia Basin. Sea-floor spreading and the opening of the Amerasia Basin by the counterclockwise rotation of northern Alaska and adjacent northern Siberia away from the Canadian Arctic Islands are interpreted to have occurred during Late Cretaceous time and to have ceased near the Cretaceous-Tertiary boundary when the active plate margin switched to the site of the present Eurasia Basin.

Structure of the southeast margin of the Beaufort-Mackenzie basin, Arctic Canada, from crustal seismic-reflection data

New seismic-reflection profiles image the crustal structure of the Beaufort-Mackenzie basin and adjacent features near the Mackenzie Delta in northwestern Canada. The Mesozoic to Quaternary sediments are nearly 12 km thick under Richards Island at the edge of the Beaufort Sea and are bounded by listric normal faults on the south edge of the Beaufort-Mackenzie basin. These faults parallel features that are Proterozoic in age; this suggests that the older features controlled the younger. Thrust faults are identified from offsets in reflections from Proterozoic strata underlying the Campbell uplift. The age of the compression is not yet clearly established; it may be either Late Proterozoic or late Paleozoic. A Late Proterozoic age would imply that Precambrian compressional structures underlie much of northwestern Canada. A late Paleozoic age would imply that Ellesmerian (Devonian–Carboniferous) compressional structures are buried beneath the Arctic coastal plain from the Mackenzie River delta to the Parry Islands fold belt, some 1000 km to the northeast in the Arctic Archipelago. The base of the crust is imaged on the south end of the profile at approximately 39 km, whereas in the north it is inferred, from gravity modeling, to be at approximately 28 km.

Regional lithostratigraphic units in the Triassic Montney Formation of western Canada

The Montney Formation is a Lower Triassic, siliciclastic-dominant unit in the subsurface of west-central Alberta and northeast British Columbia (Fig. 1⇓). Throughout its area of occurrence it is underlain unconformably by either Permian or Carboniferous strata and overlain abruptly, and probably unconformably, by the Middle Triassic Doig Formation. Towards its eastern outcrop limit Jurassic strata truncate successively older Montney beds. Fig. 1. Location of study area and cross-section in Figure 3⇓. Although strata equivalent to the Montney in outcrop have been subdivided into a number of named members (see Davies et al., 1997, for a brief review), generally it has proven difficult to correlate the outcropping units into the subsurface. Only Barss et al. (1964) suggested such a correlation when they correlated the uppermost beds of the Montney Formation, which in the western parts of the basin have a distinct log signature, with Manko’s (1960) Black Shale member of the Sulphur Mountain Formation. However, as will be discussed later, this correlation is incorrect. Internal subdivision of the subsurface Montney Formation has only been attempted with any degree of consistency by Davies et al. (1997). The objective of this paper is to review the lithostratigraphic divisions of previous authors and offer an alternative and regionally consistent subdivision into informal members. The lithostratigraphic scheme presented herein resulted from the author compiling a series of regional cross-sections through the Montney Formation, but due to the size of such cross-sections they cannot be published in the journal format. ### Introduction Montney strata were formally defined in the subsurface of western Canada by Armitage (1962), in the Texaco NFA Buick Creek 6-26-87-21W6 well of northeast British Columbia, between log depths 5625 ft and 6500 ft (1714.5 and 1981.2 m respectively). In the type section, the Montney rests unconformably on Permian strata and is …

Using copulas for implementation of variable dependencies in petroleum resource assessment: Example from Beaufort-Mackenzie Basin, Canada

Petroleum resource potential modeling seeks to characterize undiscovered petroleum resources. This information from the modeling can contribute to a reduction in corporate risk while characterizing the commercial potential of the undiscovered resources. Such models consider different types of variable dependencies arising from geologic risk evaluation, volumetric calculation, and resource aggregation to higher geographic levels. Commonly, the available data are not sufficient to specify such variable correlations or interdependencies, particularly in frontier regions. It is also a challenge to formulate variable correlations in resource calculations because geologic variables have to be fit to a multivariate lognormal distribution or other specific multivariate distributions with an appropriate correlation structure. However, variable correlations are common among the geologic variables, and ignoring the interdependencies may lead to a serious bias in the resource potential estimation and the uncertainty range. Recent methodological developments in statistics indicate that the use of copulas permits more flexibility for the consideration and incorporation of variable interdependency, thus analogs can be introduced to problems where estimating correlation structures are impossible and wider choices of statistical distributions become available. This article proposes the use of copulas for handling variable dependency in petroleum resource assessment. The methods and procedures are illustrated using examples from a hypothetical data set and the crude oil resource appraisal of Tertiary clastic plays in Beaufort-Mackenzie Basin in Arctic Canada. Comparisons of crude oil resource estimates obtained using different correlation scenarios for these plays suggest that when positive correlations are used, the mean value of the oil resource is increased about 1.6 times that estimated, assuming a complete independence among the input variables.

Foraminiferal Biostratigraphy and Seismic Sequences: Examples from the Cenozoic of the Beaufort-Mackenzie Basin, Arctic Canada

Cenozoic strata of the Beaufort-Mackenzie Basin were deposited in a series of 9 sequences on the continental margin of Arctic Canada. Seismostratigraphic and biostratigraphic (foraminiferal) schemes for analyzing these strata have evolved concurrently. Integration of these two methods is illustrated from selected Eocene to Miocene sections referenced to a transgressive-regressive sequence model. Marginal marine foraminiferal assemblages from seismic topset facies are low in diversity, dominantly agglutinated (Portatrochammina, Jadammina, Labros pira, Textularia), and markedly different in successive sequences. Mid-shelf deltaic facies are also dominated by agglutinated genera (Bathysiphon, Haplophragmoides, Insculptarenulla, Recurvoides, Reticulophragmium). In contrast, foraminiferal assemblages from non-deltaic, outer shelf to upper slope facies (seismic topsets to foresets) are mostly calcareous benthic species. In continental-rise facies (seismic bottomset facies), agglutinated foraminifers are also abundant (Ammodiscus, Ammolagena, Bathysiphon, Cystammina, Glomospira, Haplophragmoides, Insculptarenulla, Reticulophragmium, Recurvoides, Reophax), but typically are long ranging. Lower slope to continental rise turbiditic deposits are mostly barren, except for reworked microfaunas. Faunal changes at sequence boundaries indicate the scope of tectono-oceanographic reorganization which generated each depositional episode. For example, major faunal changes encountered at sequence boundaries near the Eocene/Oligocene and Miocene/Pliocene boundaries reflect global-scale events.

A modification of Wittenberg's model for the deposition of thick sandstone bodies in the Triassic Doig Formation, Wembley area, west-central Alberta

The Middle Triassic Doig Formation of the Wembley area, in west-central Alberta, contains several north–south oriented, elongate, narrow, thick sandstone bodies encased in a predominantly shale succession. Downdip from the thick sandstone body and the enclosing shale-rich beds at Wembley is a succession of sandy siltstones (informally named the sandy siltstone unit). Published interpretations of these coarse clastic units include incised valley-fill, or the fill of contemporaneous growth-fault grabens for the elongate sandstone bodies, and healing-phase deposits (i.e. transgressive beds) for the sandy siltstone unit. A re-examination of the stratigraphic setting and contained facies suggests that the incised valley-fill model seems unlikely, based on the predominance of offshore and lower shoreface beds within the entire length of the elongate bodies, with little evidence for tidal influence or facies normally associated with such settings. Stratigraphic correlations indicate that the elongate bodies formed after deposition of the enclosing shale succession, hence contemporaneous growth faulting is unlikely. However, a slump event, followed by sediment fill is a possible alternative explanation. Correlations also indicate that the downdip sandy siltstone unit is a continuation of progradation that formed the younger shale-rich beds, located landward of the sandy siltstone unit, and are not transgressive deposits. The sandy character of these beds is interpreted to result from deposition during sea-level fall and lowstand, when a regressive surface of erosion formed on the shelf platform. Only the uppermost beds of the sandy siltstone unit can be considered transgressive.

A major unconformity at the base of the Upper Triassic Charlie Lake Formation in the Western Canada Sedimentary Basin

Abstract The Middle Triassic succession of the Western Canada Sedimentary Basin consists of a series of prograding offshore to shoreface sediment lenses of the Doig Formation, overlain by a widespread shoreface sandstone of the Halfway Formation, in turn overlain by lagoonal and supratidal deposits of the Upper Triassic Charlie Lake Formation. Two distinct erosion surfaces are present in the Halfway to lowermost Charlie Lake succession — within or at the base of the Halfway Formation, depending on geographic location, and at the base of the Charlie Lake Formation. Early studies interpreted the erosion surface associated with the Halfway Formation to be an unconformity. At least one author interpreted an unconformity at the base of the Charlie Lake Formation. Subsequently, a conformable facies interpretation became dominant, with the erosion surface associated with the Halfway Formation relegated to be the base of tidal channel deposits. In the conformable facies interpretation, the Doig to lowermost Charlie Lake succession consists of a series of prograding transgressive–regressive sequences. Recently the unconformity interpretation has been resurrected with regional correlations and facies analysis to support the interpretation. The distribution of facies and stratigraphic relationships do not fit the conformable facies interpretation particularly well and are better explained by the presence of a major unconformity. Of the two erosion surfaces in the Halfway to lower Charlie Lake succession, the one at the base of the Charlie Lake Formation is interpreted to be the unconformity, and the erosion surface associated with the Halfway Formation is interpreted to be a regressive surface of marine erosion.

A New Method for Recognizing Subsurface Hydrocarbon Seepage and Migration Using Altered Foraminifera from a Gas Chimney in the Beaufort-Mackenzie Basin

A new method for recognizing hydrocarbon seepage and migration in exploration wells is documented from the Immiugak A-06 exploration well that drilled through a hydrocarbon-related diagenetic zone (HRDZ). The HRDZ is seismically conspicuous as part of a gas chimney on a shale-cored anticline in the Tertiary of the Beaufort-Mackenzie Basin, Arctic Canada. The HRDZ contains classic diagenetic minerals, notably greigite (Fe3S4) and calcite with 34S and 13C values diagnostic of hydrocarbon-related, sulfate-reducing, microbial activity. The HRDZ also contains exceptionally preserved calcareous benthic foraminifera with conspicuous bitumen-filled chambers and agglutinated foraminifera with bitumen and diagenetic silica with bound particles. Silica was highly mobile within the seepage or migration system and was precipitated and dissolved extensively in the agglutinated foraminifera. Seismic profiles, resistivity anomalies, diagenetic minerals, and altered foraminifera all suggest that significant hydrocarbons migrated or seeped through sandy Oligocene and Miocene strata at the crest of a shale-cored anticline in response to late Miocene tectonism. Hydrocarbon-related diagenesis can be distinguished from standard burial diagenesis using the foraminiferal coloration index (FCI). Foraminiferal coloration within the HRDZ was controlled by silicification in a bitumen-rich environment. The FCI values in the HRDZ are much higher than predicted for normal burial and show abnormal variance caused by variable dissolution of foraminiferal silica. The FCI values from agglutinated foraminifera outside the HRDZ show a uniform linear trend increasing with depth. The extent of hydrocarbon-related diagenesis observed in foraminifera can be used to assess the relative magnitude of hydrocarbon seepage in the Beaufort-Mackenzie Basin and potentially other petroleum basins.

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 …