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Part I: The Joyita uplift is a documented key to the central New Mexico late Virgilian and early Wolfcampian episode of erosion and accompanying deposition of clastic strata. Detailed studies of the lithologies and fusulinid faunas of the Pennsylvanian and Early Permian rocks confirm this uplift and the related unconformity. The present-day Joyita Hills (Los Canoncitos) is a complex Cenozoic horst on the east side of the Rio Grande graben in north-central Socorro County, New Mexico. Previous reports postulated a nearby uplift during late Desmoinesian, Missourian, and Virgilian time coexistence with the Penasco or southern Unconpahgre landmass.Recently (1963), Missourian fusulinids were identified from upper Pennsylvanian limestones in the Joyita Hills. Early Wolfcampian Bursum-facies arkosic limestone-conglomerates, derived from Pennsylvanian limestones and Precambrian granite gneiss of southern Joyita Hills area, unconformably truncate southwestward, in order, Missourian, Desmoinesian, Atokan, and Precambrian rocks. In southern Joyita Hills, Bursum strata abut against remnant hills of Precambrian granite gneiss. These hills were buried by basal Abo red beds which, adjacent to the hills, gradationally overlie Bursum purplish-green shales and limestones.Joyita Hills area, lying east of the Lucero Basin and southwest of the Estancia Basin, was a submarine platform with small, low islands during Atokan and Desmoinesian time, as attested by black Atokan shales and Desmoinesian arkosic limestone-pebble conglomerate. The thinness of remnant upper Pennsylvanian strata is believed due mainly to erosion during early Wolfcampian time, not owing to erosion during late Desmoinesian, Missourian, or early Virgilian times. As the early Wolfcampian Bursum facies, bearing a Schwagerina and Tricites fauna, is unconformably on Virgilian beds in many parts of central New Mexico, the Joyita uplift is a documented key to this late Virgilian and early Wolfcampian episode of erosion and of accompanying deposition of clastic strata.Structural features of Pennsylvanian age in north-central and south-central New Mexico appear to have been aligned roughly north-south. Major sediment traps in north-central New Mexico during Pennsylvanian time were the Rowe-Mora Basin( or Taos trough of Sutherland), in central New Mexico the Estancia Basin and Lucero Basin, and in south-central New Mexico the Orogrande Basin and San Mateo Basin. Source areas for these sediments were the Uncompahgre, Penasco, Pedernal, and Zuni uplifts. The Joyita uplift is on the east flank of the Lucero Basin and on the southwest margin of the Estancia Basin; its present-day elevated expression dates from late Tertiary time, but pre-Mesozoic strata are relatively thin in the Joyita Hills.Part II: Fusulinids occur in great abundance throughout the interval of Pennsylvanian sediments in the Joyita Hills. A new genus Parafusulinella is described with two new species, P. propria from the Joyita Hills, and P. mexicana from the Boca Grande Mountains of northwestern Mexico. Other new species described from the Joyita Hills include Plectofusulina rotunda, P. coelocamara, P. fusiformis, Beedeina joyitaensis, Wedekindellina elongata, W. alveolata, Triticites riograndensis, and T. liosepta. The stratigraphic occurrence of the fusulinids, their biozones and paleoecological significance have been discussed in Part I of this study. Additional discussion concerning stratigraphy, faunal assemblages, taxonomy, systematic descriptions, and phylogeny follows. All specimens and types are filed in the Texaco Inc. paleontological collections. |
