T284 Geology in the National Parks: Research, Mapping, Education, and Outreach II

Wednesday, 3 November 2010
1:30 PM - 5:30 PM
Room 405

PALEOGENE FAUNAS FROM THE KISHENEHN FORMATION IN AND AROUND GLACIER NATIONAL PARK

Paper number: T284-3
Program: Technical Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

The Kishenehn Formation is a thick sequence, up to about 3000 m, of Cenozoic non-marine sediments representing alluvial fan, fluvial, paludal, lacustrine, and other depositional environments. Exposures of the formation are relatively rare, and mostly occur along cut banks of the North and Middle forks of the Flathead River, which form the southern and western borders of Glacier National Park in northwestern Montana. Outcrops of the formation continue northward along the North Fork into adjacent British Columbia. During an episode of crustal extension from the middle Eocene to the early Miocene (49-20 Ma), extensional collapse of the Cordilleran fold-thrust belt resulted in evolution of the Kishenehn Basin as a depositional zone. The basin is unique among sedimentary basins of the western United States in that it contains a nearly complete paleontological and sedimentological record across the poorly constrained Eocene-Oligocene boundary.

Although the formation is for the most part sparsely fossiliferous, the specimens known, especially from some of the oil shales that preserve leaves, insects, and fishes, may be of the highest quality. Molluscan remains are relatively common and extremely diverse with over 55 taxa (35 terrestrial, 20 aquatic) in the North Fork region and 62 taxa (37 terrestrial, 25 aquatic) in the Middle Fork region. Analysis of their habitat preferences and δ18O values of bivalve and gastropod shell carbonate indicates that the record supports origin from a variety of altitudes. Reptilian and mammalian fossils tend to be fragmentary, but the diverse mammalian record provides a good base for biostratigraphy. Age range for the formation is based on both radiometric dating and these biostratigraphic correlations. The oldest deposits, containing mammalian taxa that range in size from tiny insectivores to immense titanotheres, are from middle Eocene exposures along the Middle Fork. Younger fossils, ranging through the Oligocene, have been found along the North Fork and its tributaries. Composition of the mammalian fauna from these localities indicates prevalence of environmental conditions different from those of similarly aged deposits to the south and east and greater similarities to localities farther north.