The Sustut Group within the study area is a nonmarine succession of fine to coarse grained elastics, deposited in an alluvial fan environment. Regionally, the Sustut Group is divisible into the Tango Creek and Brothers Peak Formations. In the study area, the two formations are entirely Late Cretaceous (Campanian to Maastrichtian) in age, based on palynological evidence.
In the southern Sustut Basin, only the uppermost 400 m of the Tatlatui Member of the Tango Creek Formation is exposed. Sediments of the Tatlatui Member are divided into fine and coarse grained lithofacies. The fine grained lithofacies is composed of interbedded mudstone, siltstone and fine grained sandstone, which is interpreted as an alluvial plain deposit. Pebble conglomerate interbedded with coarse to medium grained sandstone comprise the coarse grained lithofacies which is considered to be a braided river deposit.
The Brothers Peak Formation comprises 1 000 m of diverse elastics and tuffs, which are divisible into the lower and upper Laslui Member, and the overlying Spatsizi Member. The lower Laslui Member conformably overlies the Tatlatui Member of the Tango Creek Formation, and is characterized by several fining upwards sequences of cobble conglomerate to medium grained sandstone, attributed to deposition by high energy braided streams in the mid-fan region of an alluvial fan complex. Sediments of the upper Laslui Member are divided into a fine grained lithofacies consisting of mudstone, interbedded with lesser amounts of siltstone, fine grained sandstone and tuff beds, and a coarse grained lithofacies composed of orthoconglomerate, paracong1omerate and coarse grained sandstone. The fine grained lithofacies comprises the majority of the sequence and is interpreted as an alluvial plain deposit. Coarse grained sediments of the upper Laslui Member were likely deposited during stages of high water discharge, by major distributaries, sheetfloods and debris flows. The Spatsizi Member is gradational from the upper Laslui Member and is composed of sandstone/mudstone sequences interpreted as sandy braided stream deposits of an alluvial plain.
Detrital components of the Tango Creek and Brothers Peak sandstones are mainly chert, quartz, plagioclase and volcanic rock fragments. Paleocurrent measurements and provenance considerations suggest source terranes were located to the east during Tango Creek deposition, and to the west during Brothers Peak deposition. In the southern Sustut Basin, the Tango Creek Formation documents uplift and erosion in the Omineca Belt and Paleozoic rock units, following accretion of the first composite terrane (terrane I) to the North American Margin. The Brothers Peak Formation is considered a result of local uplift and volcanic activity, accompanying the accretion of a second composite terrane (terrane II). / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/24854 |
| Date | January 1985 |
| Creators | McKenzie, Kathleen Jane |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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