The Colorado River is the terrestrial part of a continental scale sediment routing system that has been evolving and carving the landscape of western North America for at least six million years. This study aims to test models of the geological evolution of the Colorado River in particular and the more general drainage history of the SW US. Several possible routes are proposed for the ancestral Colorado River prior to its integration across the Colorado Plateau and incision of the Grand Canyon. Palynological samples from prodelta deposits of the palaeo-Colorado River delta in the Salton Trough produced reworked pollen and dinoflagellate cysts from the river catchment. These provide strong evidence that the Colorado River was fully integrated across the Colorado Plateau during the early Pliocene, supporting heavy mineral data and U-Pb detrital zircon ages. Detrital zircon U-Pb dating provides accurate information for the source of sediment in the basins. Comparison with known ages of zircons in sedimentary units of the Colorado Plateau as well as local basement rocks in the basinal regions has identified two populations of zircons in the deltaic sediments: one from local Mesozoic plutonic basement and a second from Colorado Plateau stratigraphy. The data support recent work on the timing of integration of the river through the Grand Canyon, proving that the 5.33 Ma Colorado River that fed into the Salton Trough was integrated across the Colorado Plateau at that time and that there had already been a degree of incision of the Grand Canyon. A literature review shows how uplift of the Colorado Plateau and development of the San Andreas transform boundary had significant consequences for evolution of the Colorado River. The San Andreas Fault in southern California is responsible for the dextral lateral migration of the Los Angeles Basin and Salton Trough (both on the Pacific Plate) at least from Middle Eocene through Present. The Colorado River, which drains much of the western part of the North American Plate, crossed this major strike-slip plate boundary prior to deposition of the main part of its sedimentary load. The delta of the Colorado is in the v northern Gulf of California at the present day, but palaeo-reconstructions of lateral displacement along the fault show that the Salton Trough lay adjacent to the point where the Colorado River crossed from the North American Plate (at about 5.33 Ma). It is also possible that at about 18 Ma, at the time of fault initiation, the Los Angeles Basin was at the same point. The study uses heavy mineral analysis (HMA) and associated techniques to test the hypothesis that an ancestral Colorado River supplied sediment both to the Los Angeles Basin and the Salton Trough. Analysis of HMA data suggests a broadly similar source for some of the sediment in the two basins, and for the modern river. The data also indicate changes in the catchment area, suggesting that the Colorado River became fully integrated across the Colorado Plateau by the early Pliocene.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:606443 |
| Date | January 2013 |
| Creators | Robinson, Paula J. |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=211121 |
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