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The Lewis overthrust provides scientific insight into geologic processes happening in other parts of the world, like the Andes and the Himalaya Mountains.The onset of Cordilleran orogenesis began in the Middle Jurassic time, as a result of the breakup of Pangea and North American plate motion toward subduction zones at the western margin.This thrust and fold belt has a thin skinned geometry as indicated by the array of thrust faults that interleave and overlap along strike and cut across strata at low to moderate angle that flatten with depth, repeat the same Cambrian to Triassic stratigraphy from thrust sheet to thrust sheet, and merge into a common basal décollement, the Rocky Mountain basal décollement.The Rocky Mountain thrust and fold belt propagated from west to east, accommodating up to 200 km of horizontal shortening near the Canada and US border, and about 70 km in northern parts of BC and Montana.Specifically, personnel at Geochron Laboratories of Cambridge, Massachusetts, USA, performed the K-Ar dating for Austin et al. However, when they did, their website clearly stated in a footnote that their equipment could not accurately date rocks that are younger than about 2 million years old ("We cannot analyze samples expected to be younger than 2 M.
9), the K-Ar method cannot be used to date samples that are much younger than 6,000 years old (Dalrymple, 1991, p. A few thousand years are not enough time for 40Ar to accumulate in a sample at high enough concentrations to be detected and quantified.
I am interested in natural landscapes and the geologic processes responsible for their formation.
D., Yale University, 1964 My research is in the field of Quaternary Geology and Geomorphology.
This roadcut a few miles south of Cascade along I-15 illustrates one of the basic principles used by geologists to determine the relative ages of rocks. Determining relative ages of rocks is important, but where igneous rocks are found radiometric dating techniques can provide a more accurate age.
The horizontal layers are sandstones made up of sediment laid down near the coast of a shallow sea that was present here millions of years ago. Since the igneous rock cuts across the sandstone layers, geologists conclude that the sandstone was there first. cuts across another rock, then that which cuts across happened after the older rock was formed. The Ar 40/Ar 39 and K/Ar (potassium/argon) methods can be used for dating the type of igneous rock shown in the photo.