Tectonic Significance of Lower Cretaceous Gravels, Southern Canadian Rockies: Quantitative Models of Basin Development

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PIs will study the paleotopographic, subsidence and source area development history of the Upper Jurassic to Lower Cretaceous foreland stratigraphic sequence along the southern part of the Columbian orogenic belt in Canada and adjacent parts of Montana. The Columbian/Sevier belt, which marks the culmination of Late Mesozoic orogency in the Norther American Cordillera, is generally continuous along its length and overall is similar in structural style, timing and stratigraphic development of the adjacent foreland basin. Both regions contain Upper Jurassic, mud-dominated fluvial deposits with easterly paleoflow; comparatively widespread Lower Cretaceous chert-pebble grave; and a regional sub-Cretaceous unconformity separating the two units. The two regions differ, however, in the details of distribution and paleoflow directions within these units. In addition, the interpretation of tectonic driving forces differ between the two belts with collisions primarily responsible for the Columbian belt and magmatic activity apparently generating the Sevier belt. By quantitatively analyzing the southern Columbian foreland sequence and comparing these data to our previous study of the Sevier foreland sequence we will determine if the sequences record a similar evolutionary history. If so, then can two different mechanisms active in the Columbian and Sevier belts produce the same stratigraphic record? If not, then how do two very different thrust belt driving mechanisms produce such grossly similar stratigraphic packages and where does the transition lie between the two orogenic belts?