James Dietrich

Crustal structure and tectonics of the southeastern Beaufort Sea continental margin

The structure of the southeast margin of the Canada Basin is synthesized from seismic reflection and refraction profiles in the southern Beaufort Sea and Mackenzie Delta, interpreted in conjunction with potential field data and the exploration seismic data base. The present margin was formed in the Jura-Cretaceous and comprises a complex pattern of rifted and transform faulted crustal segments. Thinning in the upper crust is bounded by the Eskimo Lakes Fault Zone (ELFZ), a series of extensional listric normal faults, and is controlled by preexisting structures. Lower crustal thinning and the transition to oceanic crust occurs outboard of the ELFZ. A thick (up to 16 km) Late Jurassic and younger synrift and postrift sedimentary succession overlies oceanic crust in the eastern part of the Canadian Beaufort Sea and thinned continental crust between the Mackenzie Delta and Alaska. Tertiary faulting in the sedimentary basin appears to be related to the crustal structure. Present-day seismicity in the southern Beaufort Sea is essentially limited to the area underlain by oceanic crust. Abrupt along-strike changes in crustal affinity and degree of thinning allow the recognition of a NW-trending transform fault. Regional gravity data, dominated by a series of coastline parallel highs, are used to extrapolate crustal features to the northeast along the Canadian polar continental margin. It is inferred that the Canadian polar margin consists of a number of 250-to-350-km-long stretched crustal segments separated by possible fracture zones. The orientation of the analogous tranform fault identified in the southeastern Beaufort Sea offers the possibility of kinematic constraints on models of ocean floor development within Canada 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.

Seismic Characterization of the Structural Front of Southern Quebec Appalachians

ABSTRACT Interpretation of recent industry seismic reflection data provides important insights into the structural style of the southern Quebec Appalachians structural front, south of Drummondville. Especially, the occurrence of thrusts propagating west of the mapped limit of the parautochthonous domain is widely documented. Extensive decollement planes dominate the structural style east of the Aston Fault and define the soles of tectonic slices stacked into hinterland-dipping duplexes. The Chambly-Fortierville Syncline and Logans Line are not imaged seismically. Growth faults were active since the deposition of the Potsdam Group and at least until the deposition of Trenton Group. Normal faults also extend into the overlying molasse and flysch units and antithetic faults are more common than previously documented. Normal faults are crosscut by Appalachian thrusts.

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 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.