Collection 18651-PC, Little Flat Fm. Siltstone Member, Chesterfield Range (Carboniferous of the United States)

Where: Idaho (43.8° N, 111.7° W: paleocoordinates 0.7° S, 44.2° W)

• small collection-level geographic resolution

When: Quadratia zone, Siltstone Member (Little Flat Formation), Meramecian (343.0 - 335.5 Ma)

• The Mississippian rocks in the Chesterfield Range consist of Lodgepole limestone overlain by a 1900ft. limestone-sandstone sequence here designated the Chesterfield Range Group. The lower terrigenous part, about 965 ft. thick is the Little Flat Fm., it has a basal siltstone member, a middle sandstone member, and an upper sandy limestone member. The upper part of the Chesterfield Range Group, here named the Monroe Canyon Limestone is about 925 ft. thick and contains a lower massive member and a medial medium-bedded member, and an upper cherty member. The range stretches northwest from Soda Springs, Idaho. It is an eastern dipping block of Paleozoic strata irregularly overlapped by the Tertiary Salt Lake Fm.

Environment/lithology: siltstone

• The formation is mostly quartzose in the lower part, but contains carbonate cement and some limestone interbeds near the base. The lower 126ft. consists of pale red, pinkish weathering siltstone and fine-grained sandstone with two fine-grained cherty limestone units. This is the siltstone member. The overlying 551ft. of beds is fine-grained, calcareous quartz sandstone and quartzose limestone in relatively thin, platy beds. They make up the sandstone member. Limestone is more abundant in the upper part of the formation, which has been separated out as the sandy limestone member, 288ft. thick.

Primary reference: J. T. Dutro and W. J. Sando. 1963. New Mississippian Formations and Faunal Zones in Chesterfield Range, Portneuf Quadrangle Southeast Idaho. Bulletin of the American Association of Petroleum Geologists 47(11):1963-1986 [T. Olszewski/M. Gibson]more details

PaleoDB collection 12807: authorized by Tom Olszewski, entered by Melissa Gibson on 17.12.2001

Creative Commons license: CC BY (attribution)

Taxonomic list

• Also included is an Orthotetid brachiopod, indet. and Ostracodes, undet.
Show authors, comments, and common names
Stenolaemata
 Cryptostomata - Fenestellidae
Fenestella sp.
Fenestella sp. Lonsdale 1839
 Cryptostomata - Acanthocladiidae
Polypora ? sp.
Rhynchonellata
 Rhynchonellida - Leiorhynchidae
Leiorhynchus (cf. Leiorhynchus) carboniferum
 Spiriferida - Spiriferidae
Spirifer sp.
Spirifer sp. Sowerby 1818
Strophomenata
 Productida - Araksalosiidae
Quadratia (cf. Quadratia) hirsutiformis