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GEOREF RECORD

Evolution of a Permo-Triassic sedimentary melange, Grindstone Terrane, east-central Oregon; with Suppl. Data 91-21

Charles D. Blome and Merlynd K. Nestell
Evolution of a Permo-Triassic sedimentary melange, Grindstone Terrane, east-central Oregon; with Suppl. Data 91-21
Geological Society of America Bulletin (October 1991) 103 (10): 1280-1296

Abstract

The Grindstone terrane in east-central Oregon is one of the few areas in western North America where large blocks of unmetamorphosed Devonian, Mississippian, and Permian limestones are inter mixed with Permian and Lower Triassic radiolarian chert and Pennsylvanian?, Permian, and Triassic volcaniclastic rocks. Although originally described as parts of a coherent succession, we interpret the Grindstone rocks to be a sedimentary melange composed of Paleozoic limestone slide and slump blocks that became detached from a carbonate shelf fringing a volcanic knoll or edifice in Late Permian to Middle Triassic time and were intermixed with Permian and Triassic slope to basinal clastic and volcaniclastic rocks in a forearc basin setting. Paleogeographic affinities of the Grindstone limestone faunas and volcaniclastic debris in the limestone and clastic rocks all indicate deposition in proximity to an island-arc system near the North American craton. The Grindstone terrane deposits are unconformably overlain by Upper Triassic to Middle Jurassic sequences of the Izee terrane. Although lithologic and faunal differences indicate that the Grindstone and Izee terranes together represent a tectonic block separate from the adjacent Baker terrane, all three terranes were juxtaposed by Late Triassic or Early Jurassic time.We recommend reduction to informal status for the Coffee Creek (Mississippian), Spotted Ridge (Pennsylvanian?), and Coyote Butte (Permian) formations because (1) they cannot be mapped or traced beyond limited areas, and (2) these older rocks are chaotically inter-mixed with younger chert and volcaniclastic rocks. New biostratigraphic data indicate that the bulk of the Spotted Ridge volcaniclastic rocks represent a part of the Triassic Vester Formation of the Izee terrane.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 103
Serial Issue: 10
Title: Evolution of a Permo-Triassic sedimentary melange, Grindstone Terrane, east-central Oregon; with Suppl. Data 91-21
Affiliation: U. S. Geol. Surv., Denver, CO, United States
Pages: 1280-1296
Published: 199110
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 115
Accession Number: 1991-046413
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. block diags., geol. sketch map
N43°40'60" - N44°34'00", W121°07'00" - W119°40'00"
N43°57'00" - N44°58'60", W119°40'60" - W118°13'60"
N42°00'00" - N44°04'60", W119°55'00" - W118°10'00"
Secondary Affiliation: Univ. Tex. at Arlington, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1991
Program Name: USGSOPNon-USGS publications with USGS authors
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