Stratigraphy and geologic history of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming

Abstract

PLATE 1. Columnar sections showing Madison Limestone-Amsden Formation contact relations in central and western Wyoming and south-cenrtral Montana.

Pelecypoda and Rostroconchia of the Amsden Formation (Mississippian and Pennsylvanian) of Wyoming

“…The lithology and biostratigraphy of the Amsden is discussed by Sando, Gordon, and Dutro (1974). In considering the distribution of the fossil faunas within this formation, its transgressive nature must be borne in mind.…”

“…The Amsden collections have been given numbers from 1 to 160 for the purpose of simplification; full descriptions are given in Sando, Gordon, and Dutro (1974). A checklist of the pelecypod and rostroconchian collections is given in table 4.…”

Journal of Research of the U. S. Geological Survey, 1974, volume 2, issue 5

“…The angular character of the fragment and its occurrence near a breccia-filled solution cavity suggests that it is a residual block that was washed into a nearby sinkhole during erosion of the Madison. This occurrence is reminiscent of the residual fossiliferous chert fragments overlying the Redwall Limestone and in solution cavities in the upper part of the Redwall in northern Arizona (Sando, 1963(Sando, , 1969, where the chert fragments contain some corals that do not occur in the main body of the Redwall and represent strata that were removed during post-Redwall erosion.…”

“…In east-central Nevada, the Prospect Mountain Quartzite is generally considered to be entirely Early Cambrian in age (Kellogg, 1963;Drewes, 1967;Fritz, 1968;Whitebread, 1969;Hose and Blake, 1970), although the Stella Lake Quartzite (or unit H), which is here included in the Prospect Mountain Quartzite, was considered to be Precambrian in age by Misch and Hazzard (1962) and Woodward (1963 The Madison Limestone, a widespread sequence of Mississippian carbonate rocks in Montana, Idaho, Wyoming, and Utah, has long been known to be separated from superjacent formations by a widespread regional unconformity, but the time span of the hiatus represented by this discontinuity has been evaluated only recently. Zonation of the Madison and superjacent beds by means of foraminifers, corals, and brachiopods (Sando, Mamet, and Dutro, 1969;Sando, Gordon, and Dutro, 1975) led to the conclusion that the time interval not represented by sedimentary deposits varies considerably in magnitude in different parts of the northern Cordilleran region and has a maximum span of nearly three provincial series of the Mississippian ( fig. 1).…”

Mississippian and Pennsylvanian stratigraphy in southwest Montana and adjacent Idaho

“…3). It represents a shallow-water, probably lagoonal, embayment marking the initiation of cycle III eastward transgression of the Cordilleran sea onto the cratonic karst plain during post-Mission Canyon time (see Dutro, 1975, andSando, 1976).…”