Chapter 21 Flashcards
What are the oldest parts of Laurentia?
The oldest parts of Laurentia are the Slave and Superior Provinces. Both have rocks that are in the order of 4 Ga.
he five main geological regions of Canada are shown on Figure A. Name the regions A through E.
The regions A through E are A-the Cordilleran Fold Belt, B-the Western Canada Sedimentary Basin, C-the Canadian Shield, D-the Innuitian Fold Belt, and E-the Appalachian Fold Belt.
Which ancient continent collided with North America to form the Innuitian fold belt, and when did that take place?
Pearya collided with North America to form the Innuitian fold belt during the Devonian.
Explain why the ancient sedimentary rocks of the Athabasca and Thelon Basins are generally unmetamorphosed and undeformed.
The ancient sedimentary rocks of the Athabasca and Thelon Basins were deposited on the stable Canadian Shield and were never involved in tectonic processes; nor were they buried deeply enough to be metamorphosed.
Explain why ultramafic intrusions, like those of the Muskox Intrusion, are relatively common in Archean rocks, but rare in Phanerozoic rocks.
Ultramafic magma has to be very hot to be liquid, and while Earth’s interior was hot enough during the Archean, it is no longer hot enough.
Why are Cambrian marine organisms are so well preserved in the rocks of the Burgess Shale of British Columbia.
There are several reasons why the preservation is so good in the Burgess Shale: the rock is very fine grained so details are well defined; the dead organisms accumulated in a lifeless anoxic basin so they were not oxidized, scavenged, or broken down by bacteria while they were being fossilized; although some of the surrounding rocks are weakly metamorphosed, the Burgess Shale was protected from squeezing by adjacent strong limestone.
The Prairie Evaporite Formation overlies marine carbonate rocks of the Winnipegosis Formation and is overlain in turn by marine carbonate rocks of the Dawson Bay Formation. What type of changes might have led to the accumulation of evaporites during this period of marine deposition?
The Western Canada Sedimentary Basin was filled with marine water during pre-Prairie Evaporite times and Winnipegosis carbonate was deposited. It slowly dried out to produce the evaporite beds, but was later re-filled, leading to the deposition of Dawson Bay carbonate. The isolation of the basin during Prairie Evaporite times might have been due to a drop in sea level or tectonic uplift. A change to a dryer climate may also have been a factor.
What features of the Intermontane Superterrane have been used to indicate that these rocks formed south of the equator?
The rocks of the Intermontane Superterrane have fossils that are indicative of southern hemisphere deposition, and also have magnetic inclinations that imply an origin south of the equator.
What is the connection between terrane accretion on the west coast and the relatively rapid accumulation of sediments within the WCSB?
Terrane accretion on the west coast led to formation of the Rocky Mountains. The rapid erosion of these mountains provided a source for accumulation of sediments within the WCSB.
Why is the WCSB considered to be a foreland basin during the Mesozoic?
The western edge of the WCSB was pushed down by the mass of the Rocky Mountains toward the end of the Mesozoic, and thus can be thought of as a foreland basin.
The four main terranes of the Intermontane Superterrane are Cache Creek, Quesnel, Stikine, and Yukon-Tanana. Referring to Figure 21.4.2, determine the order in which these terranes are likely to have reached North America.
The likely order is Yukon-Tanana, Quesnel, Cache Creek, and Stikine, although it is also possible that these terranes were assembled as one unit prior to reaching North America.
The presence of Nanaimo Group sedimentary rocks far inland and at relatively high elevations on Vancouver Island is attributed to the accretion of the Pacific Rim and Crescent Terranes. What is the likely connection?
Nanaimo Group sedimentary rocks were forced inland and up to relatively high elevations on Vancouver Island when the accretion of the Pacific Rim and Crescent Terranes pushed Vancouver Island closer to the mainland.
The presence of Nanaimo Group sedimentary rocks far inland and at relatively high elevations on Vancouver Island is attributed to the accretion of the Pacific Rim and Crescent Terranes. What is the likely connection?
The Paskapoo Formation becomes thinner toward the northeast because the foreland basin gets shallower in that direction, and also because the source of the sediments is the Rocky Mountains, situated along the southeastern edge of the basin.
