Stratigraphy, petrology, and provenance of Cenomanian to Turonian Frontier Formation near Lima, southwest Montana
The Frontier Formation in the study area is subdivided into three informal lithofacies, all of which were deposited in fluvial environments: a mixed clastic lower unit (1500 ft), a fine-grained medial unit (5000 ft), and a mixed clastic upper unit (800 ft). In the lower unit, sandstones contain as much as 50% total feldspar and volcanic rock fragments; conglomerates are rich in quartzite clasts derived from the Belt Supergroup and contain as much as 15% silicic volcanic and 2% limestone clasts. Mudstone, siltstone, shale, and coal are interbedded with the sandstones. The fine-grained medial unit contains nonvolcanic mudstones and siltstones and minor sandstones and pebble conglomerates rich in chert and limestone lithic detritus. The mixed clastic upper unit contains abundant porcellanite and bentonite; sandstone interbeds contain plagioclase and limestone lithic grains. Sources for Frontier detritus include Proterozoic, upper Paleozoic, and Mesozoic sedimentary and volcanic rocks to the south and west. The Frontier was deposited during a depositional cycle prior to development of the Laramide Blacktail-Snowcrest uplift. Exposures of the Frontier near Lima appear to be among the thickest in the region and were probably deposited near the axis of a foredeep in front of the advancing Cordilleran thrust belt.
- Research Organization:
- Geological Survey, Denver, CO (USA)
- OSTI ID:
- 6148164
- Report Number(s):
- CONF-890404-
- Journal Information:
- AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States), Vol. 73:3; Conference: AAPG annual convention with DPA/EMD Divisions and SEPM, San Antonio, TX, USA, 23 Apr 1989
- Country of Publication:
- United States
- Language:
- English
Similar Records
Correlation of Lower and Upper Cretaceous Blackleaf Formation, Lima Peaks area to eastern Pioneer Mountains, southwestern Montana foreland basin
Provenance and sediment-dispersal system in tectonically active rapidly evolving foreland basin, Western Interior
Related Subjects
MONTANA
PETROLEUM DEPOSITS
RESERVOIR ROCK
STRATIGRAPHY
COAL
CONGLOMERATES
GEOLOGIC FORMATIONS
LIMESTONE
SANDSTONES
SHALES
SILTSTONES
CARBONACEOUS MATERIALS
CARBONATE ROCKS
ENERGY SOURCES
FEDERAL REGION VIII
FOSSIL FUELS
FUELS
GEOLOGIC DEPOSITS
GEOLOGY
MATERIALS
MINERAL RESOURCES
NORTH AMERICA
RESOURCES
ROCKS
SEDIMENTARY ROCKS
USA
020200* - Petroleum- Reserves
Geology
& Exploration