Ordovician brachiopods, trilobites, and stratigraphy in eastern and central Nevada

Abstract

Trilobites, brachiopods, bryozoans, corals, ostracodes, and conodonts collected from seven Ordovician stratigraphic sections in Nevada have been tabulated and range in age from early Canadian to Barneveld.The 79 species described here represent 24 genera of brachiopods and 34 genera of trilobites ; two genera are new.Collation of the fossil assemblages, their stratigraphic positions, and their geographic distribution leads to several conclusions, some of which are: 1.The trilobites of the great bioherm at Meiklejohn Peak, near Beatty, Nev., of the Table Head Formation, Newfoundland, Canada, and from Lower Head, Newfoundland, Canada, are correlated with the OrthidieUa zone (Whiterock Stage) of east and central Nevada and with the Ort1iam~bonites minuseulus beds and older beds at Ikes Canyon, Toquima Range, Nev.These beds are earliest Whiterock or latest Canadian.2. The PaUiseria zone (Whiterock Stage) is correlative for the most part with the lower AnomalortJiis zone (Whiterock Stage), the RJiysostropJiia zone is correlative with the upper AnomalortJiis zone, and the upper AnomalortJiis zone is probably of Ashby ?-Po,rterfield age.3. The highest limestone of the Pogonip Group in east and central Nevada is probably of Porterfleld age, correlative with the lower part of the Copenhagen Formation of the Monitor Range.4. Differences in fossil assemblages previously interpreted as temporal are considered to have resulted from differences in facie,s. 5.At Ikes Canyon, Toquima Range, Nev., an unnamed limestone above the Pogonip Group and below the Silurian Roberts Mountains Formation is the lateral equivalent of the Ordovician Hanson Creek and Copenhagen (highest part) Formations ; this unit has been mapped previously as the Silurian Diana Limestone of Kay and Crawford (1964).6.An unconformity at Lone Mountain, west of Eureka, Nev., represents much of the upper part of the Antelope Valley Limestone and all the lower part of the Copenhagen Formation, approximately 700 feet of strata is believed to be missing.