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NGMDB
Geologic Unit: Portneuf
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Map showing publication footprint
  • Usage in publication:
    • Portneuf limestone*
  • Modifications:
    • Named
  • Dominant lithology:
    • Limestone
  • AAPG geologic province:
    • Snake River basin
Publication: Summary:

Named as the upper formation of the Thaynes group (rank raised) for exposures at the head of Portneuf River in Bingham Co., ID in the Snake River basin. No type locality designated. Overlies the newly named Fort Hall formation, upper formation of the Thaynes group. Underlies the Ankareh sandstone. Consists of about 1,500 ft of siliceous, cherty, gray to yellow limestone. Bedding is massive. Has rounded, elongated nodules and streaks of chert. Silicified fossils. Portneuf fauna described by Girty. Is fairly resistant to erosion. Forms low, broad ridges and sloping interfluvial areas. Assigned to the Lower Triassic. Stratigraphic table.

Source: GNU records (USGS DDS-6; Denver GNULEX).

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Portneuf limestone*
  • Modifications:
    • Revised
    • Overview
  • AAPG geologic province:
    • Snake River basin
Publication: Summary:

Assigned as the upper formation of the Thaynes group. Overlies Fort Hall formation, middle formation of the Thaynes. Upper contact revised in that Portneuf unconformably underlies the newly named Timothy sandstone. Rocks assigned to the Timothy in this report were designated Ankareh sandstone in earlier reports. Stratigraphic table. History of nomenclature chart. Mapped (geologic map) in the eastern part of the study area in Ts 2-4 S, Rs 37 and 38 E, Bingham Co., ID in the Snake River basin. Consists of massive, siliceous, cherty, gray to yellowish limestone. Forms low broad ridges and sloping interfluve areas. Estimated to be about 1,500 ft thick. In the Lanes Creek, Freedom, and Montpelier quads. to the east, a redbed member 200 to 1,000 ft thick occurs in the middle of the Portneuf. The redbeds are red shales and sandstones. Numerous fossils (gastropods, brachiopods, pelecypods, scaphopods, echinoids) found. Assigned to the Lower Triassic.

Source: GNU records (USGS DDS-6; Denver GNULEX).

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Portneuf limestone*
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Snake River basin
Publication: Summary:

Mapped (geologic map) as the upper formation of the Thaynes group in the quads., Bingham Co., ID in the Snake River basin. Distribution is irregular. Is usually bounded by faults. Consists of massive, siliceous and cherty, gray to yellow limestone. Chert occurs as rounded, elongated nodules and in streaks. Is fossiliferous (terabratuloids, echinoid spines, brachiopods, gastropods, cephalopods, scaphopods). Locally includes interbedded red sandstone and shale. Estimated to be 1,500 ft thick, though accurate thickness not obtainable because of structural complexities. Assigned to the Lower Triassic.

Source: GNU records (USGS DDS-6; Denver GNULEX).

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Portneuf limestone member*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Snake River basin
    • Wasatch uplift
Publication: Summary:

Is one of seven members assigned to the Thaynes formation. Formerly assigned formation rank as part of the Thaynes group. Is 1,730 ft thick at Fort Hall, Bingham Co., ID in the Snake River basin and 1,170 ft thick at Sheep Creek, Caribou Co, ID on the Wasatch uplift. A 440 ft thick redbed tongue, newly named Lanes tongue of the Ankareh formation separates the Portneuf into an upper and lower part. Overlies the sandstone and limestone unit of the Thaynes. Underlies Timothy sandstone member of Thaynes. Block diagram. Cross section. Correlation chart. Assigned to the Lower Triassic.

Source: GNU records (USGS DDS-6; Denver GNULEX).

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Portneuf Limestone Member*
  • Modifications:
    • Overview
  • AAPG geologic province:
    • Wasatch uplift
Publication: Summary:

As a member of Thaynes Formation is divisible into two mapped parts that are separated by the Lanes Tongue of the Ankareh Formation in the eastern part of the quad., Caribou Co., ID on the Wasatch uplift. The lower part of the Portneuf overlies the informally designated nodular siltstone member of the Thaynes. The lower part is 300-400 ft thick and consists of gray, finely crystalline, massive, cliff-forming, fossiliferous limestone and minor amounts of gray, fine grained sandstone and siltstone. The upper part beneath the Timothy Sandstone Member of the Thaynes consists of 250 to 300 ft of dark gray, microcrystalline, laminated, platy limestone interbedded with green shale, and fine grained sandstone that are overlain in sequence by: 1.) gray, finely crystalline, thin- to thick-bedded, commonly ledge-forming limestone that has small nodules of gray chert, and a few thin interbeds of gray sandstone, siltstone and shale, and 2.) gray to brown, fine- to medium-grained, thin- to medium-bedded, locally ripple marked sandstone interbedded with gray shale and siltstone. Early Triassic age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

NGMDB
Map showing publication footprint
  • Usage in publication:
    • Portneuf Limestone Member*
  • Modifications:
    • Revised
  • AAPG geologic province:
    • Snake River basin
Publication: Summary:

Revised in that Portneuf Limestone Member of the Thaynes Formation overlies Fort Hall Member (reduced in stratigraphic rank) of the Thaynes, and underlies Timothy Sandstone (formerly the upper member of the Thaynes). Timothy removed from Thaynes because of its "nonmarine origin". Portneuf is a gray to brown, thin- to thick-bedded, dense, gray-weathering, cherty limestone. Chert occurs as nodules and as discontinuous layers. Is 1,500 to 1,730 ft thick. Assigned to the Lower Triassic.

Source: GNU records (USGS DDS-6; Denver GNULEX).

NGMDB
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For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).

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