Tectonic history of Sweetgrass Arch, Montana and Alberta-key to finding new hydrocarbons

Conference · Wed May 01 04:00:00 EDT 1985 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:6170473

The Sweetgrass arch of northwestern Montana and southern Alberta is a major ancient structural feature. Initial anticlinal emplacement occurred during the early Paleozoic and was parallel with the cratonic margin. Strong uplift followed by peneplanation occurred during the Late Jurassic and basal Cretaceous during the westward drifting of the North American plate following the breakup of Pangea. During Cretaceous and early Tertiary times, the Sweetgrass arch was quiescent, but was rejuvenated in mid to late Tertiary, upwarped by a basement flexure to its present structural configuration: a 200 mi (322 km) long, north-plunging anticline showing 10,000 ft (350 m) of structural relief. Midway down its plunge, the anticline is offset 30 mi (48 km) by a right-lateral transcurrent fault. During Late Cretaceous and early Tertiary, plutonic uplifts were emplaced on the east flank, forming traps for oil then migrating updip from the Williston and Alberta basins. Oil and gas accumulated in Mississippian, Jurassic, and basal Cretaceous reservoirs in structural and stratigraphic traps around these plutonic uplifts. Subsequent late Tertiary doming of the Sweetgrass arch tilted the earlier structural traps and drained them, resulting in remigration of much of the oil and gas to the crest of the arch. The tilting failed to destroy many of the stratigraphic traps. As a result, down the flanks of the Sweetgrass arch are many frozen stratigraphic traps including Cut Bank field, the largest single-pay stratigraphic trap in the north Rockies. On the crest are large structure accumulations of remigrated oil at Kevin Sunburst and Pondera. Evidence of remigration is recorded by live oil show tracks in the reservoirs and remnant gas caps throughout the area of earlier accumulations. A potential exists for finding new frozen traps on the flanks and remigrated oil accumulations on or near the crest of the Sweetgrass arch.

• Research Organization: Infinity Oil Co., Billings, MT
• OSTI ID: 6170473
• Report Number(s): CONF-8506201-
• Conference Information: Journal Name: Am. Assoc. Pet. Geol., Bull.; (United States) Journal Volume: 69:5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
03 NATURAL GAS
030200 -- Natural Gas-- Reserves
Geology
& Exploration
ALBERTA
ANTICLINES
CANADA
CENOZOIC ERA
CRETACEOUS PERIOD
EXPLORATION
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GEOLOGIC TRAPS
JURASSIC PERIOD
MESOZOIC ERA
MINERAL RESOURCES
MONTANA
NATURAL GAS DEPOSITS
NORTH AMERICA
PETROLEUM DEPOSITS
RESOURCES
TECTONICS
TERTIARY PERIOD
USA