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Mesozoic Epicontinental, Flyschoid and Molassoid Depositional Phases of Yukon’s North Slope
The Jurassic and Cretaceous sedimentary record of Yukon’s north slope consists of discrete, successive, epicontinental, flyschoid and molassoid elastic phases. Each is characterized by its facies associations, thickness variability, sandstone petrography, and inferred tectonic setting.
During the Jurassic and Early Cretaceous, until the Albian Stage, epicontinental marine sandstone and mudstone were evenly deposited over a large area of northern Yukon. Widespread deltaic lobes and sand-bar complexes suggest that the sea was generally shallow. Typically, the sandstones are nearly pure quartz and contain less than 5% chert or feldspar. Their mineral maturity, as well as facies trends and paleocurrent structures, indicate derivation from the craton to the southeast.
Restructuring of the tectonic framework in early Albian time resulted in a marine trough which received 15,000 feet (4600 metres) of shale, siltstone, turbiditic sandstone, and conglomerate from a rising western highland. The trough axis runs from the Arctic coast southward through the headwaters of Blow and Bell Rivers. This flyschoid clastic wedge rapidly becomes thinner toward the east where phosphatic iron carbonate accumulated on a restricted shelf. The flyschoid elastics are very immature and extremely variable in composition. Some sandstones are enriched in chert, others in andesitic or slaty fragments. The trough was deformed and uplifted in the early Upper Cretaceous, leaving restricted hypersaline basins near Mackenzie Delta.
In Maestrichtian time rejuvenated highlands shed detritus northward, resulting in 7,000 feet (2150 metres) of molassoid alluvial, deltaic, littoral and marine deposits of sandstone, conglomerate, mudstone and coal under the present coastal plain. The sandstones are relatively uniform in composition and contain quartz, chert and feldspar, as well as sedimentary, metamorphic and volcanic lithoclasts.
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