Distribution of the Middle Ordovician Copenhagen formation and its trilobites in Nevada

Abstract

The Copenhagen Formation of central Nevada is composed of a basal sandstone (member A) and two calcareous siltstone and silty limestone members (members B and C). In areas north and south of Antelope Valley, member B of the formation is recognized, but the overlying member C is not recognized. To the east and southeast the supposedly older uppermost beds of the Antelope Valley Limestone are actually equivalent to the lower beds of member B. To the west in two thrust sequences of the Toquima Range, the Caesar Canyon Limestone of Kay and Crawford and an unnamed limestone are probably equivalent to the uppermost Copenhagen Formation. Species of 21 genera of trilobites are described from members B and C. Four additional taxa have not been identified below familial rank. The most evident change in trilobite assemblages takes place about 100 feet below the top of member C in the type locality around Antelope Valley; these highest trilobites suggest correlation with the Viola Limestone of Oklahoma. The trilobites from lower in member C indicate a Wilderness-Barneveld age.

Late Ordovician trilobites from the Taimyr Peninsula, Arctic Russia

“…Tripp's illustrations of R. abundans are very small, but they do show an oval glabellar outline on larger specimens like that of R. elegans. Raymondella nevadensis Ross & Shaw, 1972, from the Copenhagen Formation, Nevada, has a glabella similar to R. elegans, although its pygidial ribs are more transverse. An unnamed Raymondella sp.…”

Journal of Research of the U. S. Geological Survey, 1973, volume 1, issue 1

“…More specifically, as shown by figure 2, the modal field of the conglomerate clasts bears a close correspondence to the composite plot of modes for specimens from the granitic rocks of the Salinian block. The Salinian modal trend is unusual because it is more horizontal than the modal trend of most other granitic suites in the Cordilleran batholithic belt (Ross, 1972), which strengthens the case for correlation.…”

“…Such conditions are easily satisfied throughout much of the Cordilleran batholithic belt, but the nearest and most obvious source area is the Salinian block of the California Coast Ranges. The general basement rock types in the Salinian block (Ross, 1972) are similar to those in the clasts of the K-feldspar arkose facies. More specifically, as shown by figure 2, the modal field of the conglomerate clasts bears a close correspondence to the composite plot of modes for specimens from the granitic rocks of the Salinian block.…”

“…This tentative conclusion has resulted from study of basement rocks along the San Andreas fault by Ross (1970Ross ( , 1972 and study of the Cretaceous and Tertiary sedimentary rocks near Gualala by Wentworth (1966Wentworth ( , 1968, in the context of abundant evidence of large rightlateral slip on the San Andreas fault. The character of the Gualala conglomerates is thus a possible key to a Late Cretaceous tie across the San Andreas fault.…”

Systematics of Encrinuroides and Curriella (Trilobita), with a new Early Silurian encrinurine from the Mackenzie Mountains

“…Encrinuroides sp. of Ross and Shaw (1972) (from the Caradoc of Nevada) represents this clade in western North America. Encrinurus gibber Dean, 1979, from the Middle Ordovician of Newfoundland, might be related to this broadened Physemataspis group.…”