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National Geologic Map Database
Geologic Unit: Coal Creek
Map showing publication footprint
  • Usage in publication:
    • Coal Creek member
  • Modifications:
    • First used
    • Geochronologic dating
  • Dominant lithology:
    • Sandstone
    • Siltstone
    • Mudstone
    • Marl
    • Conglomerate
  • AAPG geologic province:
    • Montana folded belt
Publication:

Constenius, K.N., Dawson, M.R., Pierce, H.G., Walter, R.C., and Wilson, M.V., 1989, Reconnaissance paleontologic study of the Kishenehn Formation, northwestern Montana and southeastern British Columbia, IN French, D.E., and Grabb, R.F., eds., 1989 field conference guidebook; Montana centennial edition; geologic resources of Montana, Volume 1: Montana Geological Society Annual Field Conference, 1989, p. 189-203.


Summary:

Kishenehn Formation mapped in Kishenehn basin, a half-graben 95 mi long and 1-8 mi wide extending from Flathead, BC, CN south to north end Flathead Lake, Flathead Co, MT, Montana folded belt province. Consists of 3,000 ft (basin edges) to 11,000+ ft (basin center) of synorogenic deposits. Divided into informal members (ascending): 1) basal member recognized primarily on limonitic-staining, pressure-marked conglomerate clasts (of well-rounded Proterozoic and Paleozoic quartzites), and stratigraphic position, only in North Fork region, dominantly sandy conglomerate interbedded with pebbly sandstone, carbonaceous mudstone and coal 460 to 3,900 ft thick; 2) Coal Creek member (first used), a heterogeneous assemblage of sandstone, siltstone, mudstone, lignite, oil shale, marlstone, conglomerate 3,770-11,500+ ft thick known in Middle and North Fork areas; 3) Pinchot member (first used), red-brown, fine- and coarse-grained conglomerate with interbeds of red-brown and gray calcareous claystone and gray sandy conglomerate in Middle Fork area 660-4,900 ft thick. Coal Creek-Pinchot contact not exposed. A 33.2 +/-1.5 Ma fission track date obtained from fine-grained gray tephra as much as 8 in thick in middle of Coal Creek member. Fossils: leaves, gastropods, bivalves, insects, fish (listed) suggest age range of late Eocene to early Miocene, and sub-tropical to warm temperate climate. Shown as Oligocene age on geologic map.

Source: GNU records (USGS DDS-6; Denver GNULEX).


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