Middle Cenozoic freshwater ostracoda from Northeastern Nevada

• F.M. Swain ^{[1] [2]}
  1. [1] University of Delaware

     University of Delaware

     Estados Unidos

     
  2. [2] University of Minnesota

     University of Minnesota

     City of Minneapolis, Estados Unidos

     
• Localización: Revista española de micropaleontología, ISSN 0556-655X, Vol. 18, Nº. 2, 1986, págs. 181-227
• Idioma: inglés
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• Resumen

  • Forty-two species and subspecies of freshwater Ostracoda are described from six localities in Middle Cenozoic, mainly Miocene, but perhaps also including Oligocene, rocks of northeastern Nevada. Seventeen of the species and subspecies are new, six species were described previously, and nineteen species are given affinitive assignment or are left in open nomenclature.

    The new species and subspecies are: Eucypris ornatoides elongata , n. subsp., E. microreticulata, n. sp., E. bobcatensis, n. sp., Cypricercus palisandensis, n. sp., C. toanoensis, n. sp., C. hunterensis, n. sp., C. elegantulus, n. sp., C.? sacramentoensis, n. sp., Bradycypris? medicinecreekensis, n. sp., Hemicyprinotus simplex, n. sp., Pactolocypris suborbicularis attenuatus, n. subsp., P. laevus, n. sp., P. cancellatus pronodosus, n. subsp., Paracypridopsis curta, n. sp., Candoniella pinecreekensis, n. sp., Ilyocypris thousandspringensis, n. sp., and Limnicytheropteron winecupensis, n. sp.

    The rocks from which the Ostracoda were obtained represented the Humboldt Formation as revised by Smith and Ketner (1976), a sequence comprising lacustrine, fluvial, ash, tuff, conglomerate, sandstone, claystone and limestone of mainly early Neogene age in northeastern Nevada, which, on the outcrop, exceeds 2500 feet (762 m) in thickness, but is probably much thicker in the subsurface. The ostracodes appear to represent mesotrophic to early eutrophic lake environments in which species of Cypridinae predominated over other types of ostracodes.

    The upper part of the Humboldt Formation in the area studied is typified by Pactolocypris laevus, n. sp. Cyprideis, n. sp., found also in the Salt Lake Group of southern Idaho, also occurs in the upper part of the Humboldt. The middle part of the Humboldt is represented in descending order by Cypricercus toanoensis, n. sp., C. hunterensis, n. sp., Pactolocypris suborbicularis attenuatus, n. subsp., Eucypris ornatoides elongata, n. subsp., Eucypris microreticulata, n. sp., and Heterocypris blairensis Swain and Wagoner. The lower part of the Humboldt is represented by Pactolocypris suborbicularis, n. sp., P. biprojectus Swain, which also occur in the Esmeralda Formation of western Nevada, and perhaps by Cypricercus palisadensis, n. sp., and Hemicyprinotus? simplex, n. sp.

    Additional collections are discussed from the Hay Ranch Formation (Pliocene), Elko County, the North Creek Formation (Oligo-Miocene?) White Pine County, and from the presumed Indian Well Formation (Oligocene?), Eureka County, Nevada.