Late Ordovician paleogeography of central Idaho and its tectonic implications

Conference · Fri Feb 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5171174

Measures, E A ^[1]

---

1. Univ. of Idaho, Moscow (United States)

The Late Ordovician (Cincinnatian, Ashgill) paleogeography of central Idaho has been weakly constrained in the past. Previously, this area was treated as a simple extension of the miogeocline-eugeocline paleogeography defined from units in the Great Basin (Nevada and Utah). Detailed analysis of the Upper Ordovician Fish Haven Dolomite enables a more refined paleogeographic interpretation to be made at this time. The Fish Haven Dolomite (260 m or 800 ft, average thickness) of central Idaho is composed of 16 different carbonate facies which can be grouped into three sequences; facies within each sequence are depositionally related. Overall, the facies and sequences indicate that a carbonate ramp formed in central Idaho outboard of the craton and a hinge zone, within a subsiding area of the miogeocline. Shallow subtidal ramp deposits were probably deposited in approximately 30 m (100 ft.), or less, of water depth. During this time interval, open ocean, anoxic bottom waters extended up into deep ;subtidal regions (60 m or 200 ft). This information indicates that the Late Ordovician carbonate ramp underwent backstepping at its outermost portion resulting n drowning of the western ramp and eventual migration of transitional facies deposits (Roberts Mountains Formation) over miogeoclinal deposits. Tectonics played an active part in the deposition of the Fish Haven Dolomite in the miogeocline of central Idaho. The ultimate cause of the tectonism is not known at this time, but could be related to changes in the rate of sea-floor spreading, active structures within the continental margin, proximity of the Ordovician Klamath Mountains island arc Terrane, or unknown processes.

• OSTI ID: 5171174
• Report Number(s): CONF-9103128-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:2; Conference: American Association of Petroleum Geologists (AAPG)/Society of Economics, Paleontolgists, and Mineralogists (SEPM)/Society of Exploration Geophysicists (SEG)/Society of Professional Well Log Analysts (SPWLA) Pacific Section annual meeting, Bakersfield, CA (United States), 6-8 Mar 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CARBONATE ROCKS
DEPOSITION
IDAHO
SEDIMENTARY BASINS
GEOLOGIC HISTORY
STRATIGRAPHY
TECTONICS
GEOLOGIC FORMATIONS
LITHOLOGY
ORDOVICIAN PERIOD
DEVELOPED COUNTRIES
FEDERAL REGION X
GEOLOGIC AGES
GEOLOGIC STRUCTURES
GEOLOGY
NORTH AMERICA
PALEOZOIC ERA
ROCKS
SEDIMENTARY ROCKS
USA
580000* - Geosciences