Middle and upper Cambrian platform evolution and paleogeography, northwestern Montana, northern Idaho, and northeastern Washington

Conference · Sat Aug 01 04:00:00 EDT 1987 · AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

OSTI ID:5906807

Bush, J H; Hayden, L L

In western Montana, three Middle and Late Cambrian correlative Grand Cycles commence with inner detrital basal half cycles overlain by middle carbonate half cycles. Each half cycle represents up to one formation with the Park to Pilgrim, shale to carbonate transition, an example of one complete cycle. As with other regions of the Cambrian Cordilleran shelf, cycle components are closely related to paleogeographic position, producing differences that make correlation across depositional belts difficult. However, combined lithologic paleontologic, and cyclic correlations from southwestern Montana to isolated outcrops in northwestern Montana, northern Idaho, and northeastern Washington outline platform evolution and paleogeography. Early Middle Cambrian ramp deposition occurred with non-tectonic highs (Montania) in northwestern Montana and possible distally steepened ramps in northern Idaho. After eastward transgression, upward-shallowing Middle Cambrian carbonates formed algal-peritidal complexes that extended from central Montana to northeastern Washington. These complexes were influenced by clastic influx from central Idaho (Lemhi arch .), but they completely covered Montania and separated an eastern intrashale basin from the outer ramp. During the Late Cambrian, below wave base distal ramp carbonate deposition returned to northern Idaho and northeastern Washington. However, the distal ramp was separated from the intrashelf basin until Early Ordovician by the still existent but less extensive peritidal complexes. The ramp that developed over portions of the three states differed considerably from the cratonic margin in southern British Columbia, described by Aitken in 1966 and 1978, as a stationary accretionary rim on its seaward side persisting from Middle Cambrian to Middle Ordovician time.

• Research Organization: Univ. of Idaho, Moscow
• OSTI ID: 5906807
• Report Number(s): CONF-870915-
• Conference Information: Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Journal Volume: 71:8
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
& Exploration
CAMBRIAN PERIOD
CARBONATE ROCKS
DEPOSITION
FEDERAL REGION VIII
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
IDAHO
MONTANA
NORTH AMERICA
ORDOVICIAN PERIOD
PALEOZOIC ERA
ROCKS
SEDIMENTARY ROCKS
TECTONICS
USA
WASHINGTON