Quaternary and Late Tertiary of Montana: Climate, Glaciation, Stratigraphy, and Vertebrate Fossils
QUATERNARY AND LATE TERTIARY OF MONTANA: CLIMATE, GLACIATION, STRATIGRAPHY, AND VERTEBRATE FOSSILS Larry N. Smith,1 Christopher L. Hill,2 and Jon Reiten3 1Department of Geological Engineering, Montana Tech, Butte, Montana 2Department of Geosciences and Department of Anthropology, Boise State University, Idaho 3Montana Bureau of Mines and Geology, Billings, Montana 1. INTRODUCTION by incision on timescales of <10 ka to ~2 Ma. Much of the response can be associated with Quaternary cli- The landscape of Montana displays the Quaternary mate changes, whereas tectonic tilting and uplift may record of multiple glaciations in the mountainous areas, be locally signifi cant. incursion of two continental ice sheets from the north and northeast, and stream incision in both the glaciated The landscape of Montana is a result of mountain and unglaciated terrain. Both mountain and continental and continental glaciation, fl uvial incision and sta- glaciers covered about one-third of the State during the bility, and hillslope retreat. The Quaternary geologic last glaciation, between about 21 ka* and 14 ka. Ages of history, deposits, and landforms of Montana were glacial advances into the State during the last glaciation dominated by glaciation in the mountains of western are sparse, but suggest that the continental glacier in and central Montana and across the northern part of the eastern part of the State may have advanced earlier the central and eastern Plains (fi gs. 1, 2). Fundamental and retreated later than in western Montana.* The pre- to the landscape were the valley glaciers and ice caps last glacial Quaternary stratigraphy of the intermontane in the western mountains and Yellowstone, and the valleys is less well known.
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