Physical stratigraphy of Swift-Morrison and Kootenai-Colorado depositional sequences in the Late Jurassic-Early Cretaceous overfilled backarc and foreland basins, western Montana

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5021058

Meyers, J H ^[1]; O'Malley, P J ^[2]

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1. Winona State Univ., MN (United States). Dept. of Geology
2. Indiana Univ., Bloomington, IN (United States). Dept. of Geosciences

Late Jurassic-Early Cretaceous sedimentation in western Montana includes two depositional sequences. The older sequence (Swift-Morrison Formations) was deposited in the Sundance foreland basin and ensuing Morrison back-arc basin. The younger sequence (Kootenal Formation-Colorado Group) was deposited in the overfilled early Rocky Mountain foreland basin. Swift strata record coastal onlap and marine progradation over a dissected structural complex (Belt Island) and include a laterally restricted basal conglomerate (0--4 m-thick) representing estuarine paleovalley fill, and an overlying pervasive 16--25 m-thick upward-fining sandstone body dominated by tidal features. To the south, the sandstone body is conformably overlain by distal alluvial-fan and coastal-plain green mudstone, interbedded thin micritic limestone, and red mudstone of the lower and middle Morrison Formation. Morrison red mudstones contain thin sheet sandstones and sparse thick lenticular sandstones, representing northeastward dispersal of detritus in a mud-dominated distal alluvial fan. Northward, the Morrison thins and is mostly green and gray mudstone with thin interbedded sheet sandstone and rare intraformational-pebble-bearing ribbon sandstone. To the south, Kootenai rocks unconformably overlie the Morrison Formation and include a thick basal sandstone deposited in northeast-flowing truck rivers whose courses were controlled by subtle structural topography developed along reactivated basement faults. In the Great Falls area this sandstone (K1-Cutbank of Foster, 1992) may represent distributary channels in a prograding fluvial-dominated delta in the Sunburst sea. Overlying mudstones and thick nodular limestones (K2) represent alluvial-plain sedimentation and paleosol development. Thin shallow-marine sandstone (K3-Sunburst) caps the fluvial-deltaic sequence in the Great Falls area.

• OSTI ID: 5021058
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
BROWN COAL
CARBONACEOUS MATERIALS
COAL
CRETACEOUS PERIOD
DEPOSITION
DEVELOPED COUNTRIES
ENERGY SOURCES
FOSSIL FUELS
FUELS
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC STRUCTURES
GEOLOGY
JURASSIC PERIOD
LIGNITE
MATERIALS
MESOZOIC ERA
MONTANA
NORTH AMERICA
PETROLOGY
ROCKS
SEDIMENTARY BASINS
SEDIMENTARY ROCKS
STRATIGRAPHY
USA