Biostratigraphic and Sedimentological Studies of Natural Gas-Bearing Triassic Strata in the Halfway River Map Area, NE British Columbia (NTS 94B)
- Jim Mortensen, J-P Zonneveld and Martyn Golding

The British Columbia portion of the Western Canadian Sedimentary Basin (WCSB) is far less developed than the Alberta portion. In the past decade this area has experienced tremendous growth, particularly in natural-gas exploration. Despite this fact many parts of northeastern British Columbia remain significantly under explored due to difficulties in accessibility and a lack of available infrastructure. Triassic clastic strata in this region are among British Columbia's most important reservoir intervals, hosting approximately 37% of British Columbia's conventional gas reserves. The nature and depositional setting of the Triassic succession in northeastern BC, however, have received relatively limited study.

Recent investigations of Triassic strata farther to the northwest in Yukon Territory has demonstrated that Early and early Middle Triassic units did not accumulate as an easterly derived off-shelf deposit as had previously been thought, but rather formed in a foreland basin setting east of a collisional orogen that developed along the western margin of Ancestral North America in latest Permian time, when the Yukon-Tanana Terrane collided with and began to override the continental margin. Overlying Late Middle and Late Triassic clastic strata in this area appear to represent an overlap sequence that was deposited across both the western edge of Ancestral North America and the collisional orogen to the west. There are hints that a similar tectonic scenario occurred during the deposition of economically important, gas-bearing Triassic strata farther south in northeastern BC. If correct, this would have important implications for the stratigraphic framework of the Triassic units in this area, and for the nature and disposition of potential source and reservoir units.

The proponents of this study are carrying out a one-year biostratigraphic and provenance study of the Triassic section in the Halfway River map area in northeastern BC. This work is being done in conjunction with a geological mapping project that is currently underway in the area by the Oil and Gas Division of the BC Minisry of Energy, Mines and Petroleum Resources. The main objectives of the study are to provide a much-improved biochronology for the Triassic section in this area, and to evaluate the proposed two-stage depositional model for the deposition of this package.

Technical Articles
2012: "Biostratigraphy and sedimentary provenance of Lower and Middle Triassic natural-gas--bearing rocks in northeastern British Columbia: progress report"
- Summary of Activities 2011, Report 2012-1 p. 97-114 (pdf, 5.8 MB)

2011: "Stratigraphic correlation and sedimentary provenance of Triassic natural gas–bearing rocks in northeastern British Columbia: correlation from outcrop to the subsurface"
- Summary of Activities 2010, Report 2011-1 p. 229-239 (pdf, 4.0 MB)

2010: "Biostratigraphic and sedimentological studies of natural gas-bearing Triassic strata in the Halfway River map area (NTS 094/B), northeastern British Columbia: progress report"
- Summary of Activities 2009, Report 2010-1 p. 249-258 (pdf, 4.4 MB)

Theses
Ph.D. Thesis - Martyn Golding
Biostratigraphy and sedimentology of Triassic hydrocarbon-bearing rocks in northeastern British Columbia - University of British Columbia, 2008 - Available digitally through UBC (pdf, 12 MB)

Abstract: The Triassic Montney and Doig formations in the subsurface of northeastern British Columbia are important hydrocarbon reserves for the province. However the age and tectonic setting of these formations, and their outcrop equivalents (Grayling, Toad and Liard formations), are poorly constrained. The collection of conodont and detrital zircon samples from outcrop sections, and from core taken from subsurface hydrocarbon wells, has allowed the biostratigraphy of these formations to be improved, and the tectonic setting to be inferred. The study of new conodont samples, together with re-examination of existing collections, has led to the recognition of more than thirty new species and morphotypes within the Anisian (Middle Triassic) of British Columbia. These new taxa have in turn allowed the recognition of 11 new faunal assemblages that further refine the conodont biostratigraphic scale for the Anisian of British Columbia. Conodont biostratigraphy of the Montney and Doig formations in the subsurface has allowed correlation of these formations with those of surface sections, and also for the first time provided an age for the boundary between them. The boundary is recognised to be diachronous, and it is oldest in the centre of the study area. The basal Doig Formation is condensed, and shows most condensation at the edges of the study area. Both observations imply the presence of palaeo-highs to the west as well as to the east during the Triassic. This conclusion is supported by detrital zircon geochronology, which demonstrates the presence of sediment derived from the Arctic and from the pericratonic Yukon-Tanana terrane in the Triassic rocks of northeastern British Columbia. Previous hypotheses of Permo-Triassic accretion of this terrane onto the North American margin (the Klondike Orogeny) are supported by this study, and the Triassic sediments of northeastern British Columbia are interpreted to have been deposited in the foreland basin of this orogeny. 

 


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