Yellowstone Ash in Montana скачать в хорошем качестве

Yellowstone Ash in Montana

This video covers Miocene (17 to 4.5 Ma) stream deposits of the ancestral Missouri River in southwest Montana. The deposits, named the Sixmile Creek Formation, help us to understand the importance of the track of the Yellowstone hot spot on the evolution of this drainage. Starting 17 million years ago with the outbreak of the hot spot near the collective borders of Nevada, Idaho and Oregon, thermal bulging of the crust generated the ancestral Missouri River, flowing to the northeast down extensional valleys or grabens formed by the bulging and stretching of the brittle crust. The drainage collected stream-deposited ash from caldera-forming eruptions of the hot spot, as well as distinctive far-traveled chert and quartzite gravel and locally-derived alluvial fan deposits. The ash can be found as far north as Hudson Bay! Our research shows that the ash was likely deposited during caldera-forming eruptions that breached the walls of existing calderas, releasing ashy lahars or sediment-laden outburst floods down the Missouri River. As the plate moved over the stationary hot spot to the southwest, it arrived at its present location a few million years ago, resulting in a collapse of the thermally-bulged crust left behind, forming northwest-trending basins and ranges. The development of this topography, the drainage system we see today, caused the termination of the ancestral northeast-flowing pathways of the Missouri River, raising the old deposits into many of the northwest-trending mountain ranges in southwest Montana. This video is focussed on spectacular exposures in the Sweetwater Range near the East Fork of Blacktail Deer Creek. I will not provide specific location data, since this area is highly sensitive, not only due to the fragility of the rocks, but the many bird species who nest here during the spring and early summer. An adventurous person has enough information to be able to visit the deposits, and so I ask that you tread lightly if you do so. There is a PowerPoint presentation on this YouTube site that goes into the details of this story, and I can share a PDF copy of a recent research article (Thomas and Sears, 2020) upon request. Thank you...Rob