Provenance of the Tullock member of the Fort Union formation, Powder River Basin, Wyoming and Montana: Evidence for early Paleocene Laramide uplift

Journal Article · Fri Jan 01 00:00:00 EST 1993 · Mountain Geologist; (United States)

OSTI ID:6938343

Hansley, P L; Brown, J L ^[1]

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1. Geological Survey, Denver, CO (United States)

A petrologic and provenance study of the lower Paleocene Tullock Member of the Fort Union Formation in the Powder River Basin (PRB) indicates that Laramide uplifts to the west and south of the PRB were emergent and shedding detritus by early Paleocene time. This conclusion is based largely on the presence of abundant first-cycle carbonate clasts in the northwestern PRB and metamorphic and igneous clasts and labile heavy-mineral grains in the Tullock throughout the basin. The proximity and composition of the north end of the Bighorn uplift strongly suggest that is was the source for carbonate, igneous, and metamorphic rock fragments in northwestern Tullock outcrops. Lack of conglomeratic material in northwestern outcrops, however, indicates that the Bighorn uplift was not yet well developed and perhaps the Pryor Mountains uplift farther to the west was contributing some detritus. In the southern PRB, abundant labile heavy minerals and igneous rock fragments in the Tullock indicate that other uplifts to the west and south (i.e. Granite Mountains, Washakie, Owl Creek, and Laramie uplifts) had also started to rise by early Paleocene time. Paleocurrent directions show that Tullock streams flowed generally east-northeast across a gently sloping alluvial plain toward the retreating Cannonball sea, suggesting that the Black Hills were not yet emergent and, as a result, the basin had not fully developed. Our conclusions are supported by recent fission-track, palynological, and sedimentological studies that indicate that Laramide-style forland deformation in southwestern Montana began in late Cenomanian to Turonian time and migrated through central Wyoming to the Colorado Front Range by late Maastrichtian time. 37 refs., 8 figs., 3 tab.

• OSTI ID: 6938343
• Journal Information: Mountain Geologist; (United States), Vol. 30:1; ISSN 0027-254X
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
03 NATURAL GAS
POWDER RIVER BASIN
GEOLOGY
COAL DEPOSITS
NATURAL GAS DEPOSITS
PETROLOGY
SEDIMENTARY BASINS
WYOMING
DEVELOPED COUNTRIES
GEOLOGIC DEPOSITS
GEOLOGIC STRUCTURES
MINERAL RESOURCES
MONTANA
NORTH AMERICA
RESOURCES
USA
WATERSHEDS
011000* - Coal
Lignite
& Peat- Reserves
Geology
& Exploration
030200 - Natural Gas- Reserves
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& Exploration