Geology of the Chama Basin最新文献

{"title":"Mesozoic stratigraphy of the Chama Basin. Second-day road log from Ghost Ranch to Tierra Amarilla and Chama","authors":"S. Lucas, A. Heckert, K. Zeigler, Donald E. Owen, A. Hunt","doi":"10.56577/ffc-56.39","DOIUrl":"https://doi.org/10.56577/ffc-56.39","url":null,"abstract":"","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"107 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121441691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Age of the Cretaceous Menefee Formation, Gallina Hogback, Rio Arriba County, New Mexico","authors":"S. Lucas, J. Spielmann, D. R. Braman, B. Brister, L. Peters","doi":"10.56577/ffc-56.231","DOIUrl":"https://doi.org/10.56577/ffc-56.231","url":null,"abstract":"A BSTRACT . —At the Gallina hogback on the eastern edge of the San Juan Basin, the Menefee Formation is ~180 m thick. It consists of trough crossbedded and thinly laminated sandstone beds, between which are mudstone, coal and coaly mudstone beds. Previous age interpretations of the Menefee have been based on the ammonite biostratigraphy of the underlying and overlying strata. An Ar/Ar age of 78.22±0.26 Ma of an ash bed high in the Menefee section indicates a middle Campanian age, but is not consistent with previously published radioisotopically-calibrated ammonite biostratigraphy. Also, we report a pollen assemblage collected from throughout the Menefee section at that Gallina hogback that indicates an age of late Santonian to early Campanian). We conclude that the the Menefee Formation at the Gallina hogback is best assigned an early Campanian age, about 81 Ma, but that uncertainty remains in assigning a precise age until the discrepancies between ammonite biostratigraphy, palynostratigraphy and radioisotopic dating are fully resolved.","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117268041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Pennsylvanian section at Chaves Box, Rio Arriba County, New Mexico","authors":"S. Lucas, B. Kues, K. Zeigler, K. Krainer, G. Spencer","doi":"10.56577/ffc-56.129","DOIUrl":"https://doi.org/10.56577/ffc-56.129","url":null,"abstract":"—At Chaves Box, southeast of Chama (T29N, R4E, Rio Arriba County), a 130-m-thick section of Pennsylvanian strata crops out between Proterozoic quartzite and the Upper Triassic Chinle Group. These strata can be assigned to a lower interval A of quartzose sandstone and an upper interval B of arkosic sandstone and marine limestone. The marine limestone yields a moderately diverse but poorly preserved normal-marine invertebrate fossil assemblage that consists of 11 species of brachiopods, of which Composita subtilita and Anthracospirifer cf. curvilateralis chavezae are by far the most abundant; an unidentified hexactinellid sponge; crinoid fragments, bryozoans, including Prismopora; the gastropod Retispira tenuilineata; the bivalves Aviculopecten, Myalina and Polidevcia; and rare trilobites. The fusulinids Beedeina haworthi (Beede) and Wedekindellina euthysepta (Henbest) indicate a middle Desmoinesian age, as do the brachiopods. The Pennsylvanian section at Chaves Box can be assigned to the Hermosa Group, probably as a clastic facies equivalent to part of the Paradox Formation. The Pennsylvanian strata at Chaves Box document the changeover from quartzose deposition during final erosion and collapse of the San Luis uplift to initial deposition of arkosic clastics shed from the Uncompahgre uplift. This event, which occurred across the early-middle Desmoinesian boundary, is accompanied by a major regional marine transgression that extended marine deposition as far north and east as Chaves Box. FIGURE 1. Location map and geologic map (after Muehlberger, 1968) of Chaves Box in northern New Mexico. 130 LUCAS, KUES, ZEIGLER, AND KRAINER crystalline quartz is rare. Detrital feldspars and rock fragments are lacking. Accessory minerals are zircon and tourmaline. The matrix is stained dark brown–black by iron hydroxides and hematite. Petrographic sample 3 (Figs. 2, 3A) is a coarse-grained, moderately sorted, angular to subangular arkosic arenite composed of abundant monocrystalline quartz, many polycrystalline quartz grains and detrital feldspars. Most feldspars appear fresh (unaltered) and are broken in-situ. Untwinned potassium feldspars, perthitic feldspars, microcline and rare polysynthetic plagioclases are present. Rock fragments are rare and consist of feldspar and quartz. The sandstone also contains a few detrital micas (biotite and muscovite) and chert grains. The pore space is filled with reddish-brown matrix. Locally, detrital quartz grains display authigenic overgrowths. We also examined two characteristic limestone samples. Petrographic sample 4 (Fig. 3E-F) is a bioclastic wackestone composed of gray, bioturbated micritic matrix that contains relatively few bioclasts, including large fragments (up to several cm) of bryozoans, bivalves, brachiopods, fusulinid tests, small gastropods, echinoderm fragments (partly silicified), echinoderm spines, ostracods, very rare smaller foraminifers and abundant calcified spicules. Petrographic sample 5 (Fig. 3D) i","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125198788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Mosasaur Prognathodon from the Upper Cretaceous Lewis Shale near Durango, Colorado and distribution of Prognathodon in North America","authors":"S. Lucas, T. Ikejiri, Heather Maisch, T. Joyce, G. Gianniny","doi":"10.56577/ffc-56.389","DOIUrl":"https://doi.org/10.56577/ffc-56.389","url":null,"abstract":"—We document an incomplete skeleton of the mosasaur Prognathodon overtoni (Williston) from the middle part of the Lewis Shale southwest of Durango, Colorado. The locality’s stratigraphic position below the Huerfanito Bentonite Bed and associated ammonites of the zone of Baculites perplexus Cobban indicate that the mosasaur is of middle Campanian age. In North America, Prognathodon has a remarkably long (essentially all of the Campanian-Maastrichtian) and geographically broad (west to east coasts) distribution. Prognathodon was a large, deep water predator of the Late Cretaceous seas.","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123882079","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Insights into the petroleum geology and stratigraphy of the Dakota interval (Cretaceous) in the San Juan Basin, northwestern New Mexico and southwestern Colorado","authors":"C. F. Head, Donald E. Owen","doi":"10.56577/ffc-56.434","DOIUrl":"https://doi.org/10.56577/ffc-56.434","url":null,"abstract":"—Highlights of an integrated study to evaluate the original and remaining Dakota gas resources in the San Juan Basin are presented. Dakota (Cretaceous) reservoirs contain a major stratigraphic gas accumulation with cumulative production of more than 6 TCF, and include braided and meandering fluvial, deltaic, shoreface, and shelf-ridge sandstones in seven distinct reservoir units. Data from 85 measured sections, 32 core descriptions, and 7,000 wells were integrated to construct a regional stratigraphic framework that correlates outcrops with the subsurface over the entire San Juan Basin. In addition, a 3,300-well digital log database was constructed to compute the petrophysical parameters and volumetric potential of each reservoir. Integration of these datasets and the resulting maps provides methods for determining the significance of various depositional trends, reservoir characteristics, and trapping mechanisms for gas production. Volumetric original gas-in-place and recovery factor maps closely approximate geologic and production trends, providing a basis for additional exploration and development opportunities. FIGURE 1. Dakota resource assessment workflow and primary study components. 435 INSIGHTS INTO THE PETOLEUM GEOLOGY OF THE DAKOTA INTERVAL in the Dakota producing interval has led to confusion, especially where exploration and production occurs in the Burro Canyon, but production is reported as from the Dakota producing interval. The Dakota contains several sandstone beds separated by shales. For at least 50 years, San Juan Basin subsurface geologists have informally lettered these Dakota interval sandstones from the top down as they were encountered in drilling. This practice has been inconsistent and confusing because Dakota sandstone beds wedge out and merge within the basin and different geologists and companies have used the letters differently, especially in separate parts of the basin. Table 1 lists the inconsistent usage of lettered beds from all published papers in which this nomenclature has been used. Formal lithostratigraphic member names have been defined from outcrops around the San Juan Basin by Owen (1966), Landis et al (1973), Aubry (1988), and Owen and Owen (2005, in this guidebook). Only recently have some subsurface geologists (for example, Owen and Head, 2001) begun to correlate the formal outcrop members of the Dakota into the subsurface to replace the numbered sandstones. Table 2 lists these formal members and those of adjacent formations. Note that the informal “Dakota main body” of previous usage has been formally named as the White Rock Mesa Member of the Dakota Sandstone (Owen and Owen, 2005, this guidebook). Key surfaces used in sequence-stratigraphic analysis, (Figure 2) especially marine-flooding surfaces and sequence-bounding unconformities, are also recognizable on outcrops, and well logs and can be used to define stratigraphic units. In the Dakota producing interval, many of these surfaces coincide with ","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"27 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121207994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Review of Upper Triassic stratigraphy and biostratigraphy in the Chama Basin, northern New Mexico","authors":"S. Lucas, K. Zeigler, A. Heckert, A. Hunt","doi":"10.56577/ffc-56.170","DOIUrl":"https://doi.org/10.56577/ffc-56.170","url":null,"abstract":"Articles are printed or decorated with thermoplastic color by an offset process, by melting the thermoplastic color in a screen, applying the melted thermoplastic color by the screen to a transfer member which is at a temperature below the melting temperature of the thermoplastic color, adhesively coating the surface of the article to be printed or decorated, and then transferring the color from the transfer member to the adhesively coated article surface.","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"154 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115178813","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The microvertebrate fauna of the Upper Triassic (Revueltian) Snyder Quarry, north-central New Mexico","authors":"A. Heckert, H. Jenkins","doi":"10.56577/ffc-56.319","DOIUrl":"https://doi.org/10.56577/ffc-56.319","url":null,"abstract":"—The Snyder quarry is a well-documented assemblage of Late Triassic invertebrates and vertebrates from the Painted Desert Member of the Upper Triassic Petrified Forest Formation in the Chama Basin, north-central New Mexico. The presence of Revueltian index taxa, including the aetosaurs Typothorax coccinarum and Desmatosuchus chamaensis and the phytosaur Pseudopalatus buceros, demonstrate that the Snyder quarry is of Revueltian (early-mid Norian) age. Screenwashing matrix from the primary bonebed at the Snyder quarry yielded a moderately diverse assemblage of microvertebrates, some of which were not represented in the macrovertebrate fauna. Microvertebrate fossils from the Snyder quarry are mostly scales and bone fragments—complete teeth are unusually rare. New records include a tooth of the hybodontoid shark Lonchidion and numerous scales of a palaeoniscid fish tentatively assigned to aff. Turseodus. The microvertebrate assemblage differs somewhat from the known macrovertebrate assemblage, and includes many more osteichthyan fossils. Osteichthyans dominate the microvertebrate fauna, and include semionotids, redfieldiids, palaeoniscoids, and indeterminate sarcopterygians. Osteichthyans are largely represented by scales, with the exception of the indeterminate sarcopterygians and actinopterygians, represented by fragments of dentigerous toothplates, fossils previously assigned to “colobodontids.” The microvertebrate tetrapod fauna represented by teeth includes metoposaurid amphibians, juvenile (?) phytosaurs (?), probable dinosaurs, aetosaurs and other diverse, unidentified archosauromorphs. Many of the vertebrae appear to pertain to small archosauromorphs. The microvertebrate assemblage is unusual in that recovered vertebrae and other non-cranial elements greatly outnumber intact teeth, which normally dominate Chinle microvertebrate assemblages. We interpret this as additional support for the hypothesis of a catastrophic origin for the Snyder quarry vertebrate assemblage, as more typical Chinle Group microvertebrate assemblages are attritional deposits in which teeth greatly outnumber vertebrae.","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"57 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125675562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stratigraphy and correlation of the Permo-Carboniferous Cutler Group, Chama Basin, New Mexico","authors":"S. Lucas, K. Krainer","doi":"10.56577/ffc-56.145","DOIUrl":"https://doi.org/10.56577/ffc-56.145","url":null,"abstract":"—Nonmarine siliciclastic red beds at the base of the Phanerozoic section across most of the Chama Basin of northern New Mexico are assigned to the Pennsylvanian-Permian Cutler Group. These strata are here divided into two mappable lithostratigraphic units, the El Cobre Canyon and overlying Arroyo del Agua formations. The El Cobre Canyon Formation is up to 500 m of brown siltstone, sandstone and extraformational conglomerate of an ephemeral braided stream environment that overlies Proterozoic basement in the subsurface and is conformably overlain by the Arroyo del Agua Formation. Siltstone beds of the El Cobre Canyon Formation contain numerous rhizoliths and comprise relatively thin, slope-forming units between multistoried sandstone beds that are arkosic, micaceous, coarse grained and trough crossbedded. The Arroyo del Agua Formation is up to 120 m of orange siltstone, sandstone and minor intraformational and extraformational conglomerate of a braided to anastomosed stream depositional environment. The siltstones are thick, slope-forming units with abundant calcrete nodules between thin sandstone sheets that are arkosic and trough crossbedded. In the Chama Basin, the De Chelly Sandstone (= Meseta Blanca Member of the Yeso Formation) locally overlies the Arroyo del Agua Formation, but at most outcrops the Upper Triassic Chinle Group rests unconformably (some slight angularity is evident) on the Arroyo del Agua Formation. Megafossil plants, palynomorphs and fossil vertebrates indicate the El Cobre Canyon Formation is of Late Pennsylvanian-Early Permian (early Wolfcampian) age. Sparse fossil vertebrates indicate the Arroyo del Agua Formation is of late Wolfcampian age. Correlation of Cutler Group strata southward to Jemez Springs suggests that the Abo Formation is equivalent to the upper part of the El Cobre Canyon Formation and the entire Arroyo del Agua Formation. The lower part of the El Cobre Canyon Formation in the Chama Basin is correlative to mixed marine-nonmarine strata of the upper “Madera Group” at Jemez Springs. FIGURE 1. Index map showing distribution of Cutler Group outcrops in the Chama Basin and location of type sections of El Cobre Canyon and Arroyo del Agua formations. 146 LUCAS AND KRAINER In 1874, E. D. Cope traveled through part of the Chama Basin, observing Cutler Group strata along the Rio Gallinas. Like Newberry, he (Cope, 1875) also considered these red beds to be of Triassic age, primarily because Cope found Late Triassic fossils of unionid bivalves and reptiles in the upper part of the red bed succession (Petrified Forest Formation of Chinle Group of current usage: Lucas et al., 2003). Fossils subsequently collected by David Baldwin from the lower part of the red bed succession convinced Cope (1881; also see Marsh, 1878) of their Permian age. Williston and Case (1912, 1913; also see Huene, 1911) described the Cutler Group red beds in El Cobre Canyon and in the Rio Puerco valley. They applied no lithostratigraphic names to ","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"16 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126079581","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mineral deposits in Rio Arriba County, New Mexico","authors":"V. McLemore, Gretchen K. Hoffman","doi":"10.56577/ffc-56.445","DOIUrl":"https://doi.org/10.56577/ffc-56.445","url":null,"abstract":"—More than $40 million worth of mineral production has come from 14 types of deposits in 19 mining districts in Rio Arriba County. Three of these districts (Nacimiento, Jemez pumice, No Agua) are considered significant deposits for copper, silver, and pumice, although known large deposits are in adjacent counties (Taos, Sandoval). However, the presence of these significant deposits and the potential for discovery of additional metals resources in the Bromide No. 2 and Hopewell districts in Rio Arriba County should encourage exploration in the county. Despite the presence of remaining resources of feldspar, mica, niobium, rare-earth elements, and beryllium, it is unlikely that the pegmatites in the Petaca and Ojo Caliente districts will ever produce again because of small size and grade. Only the Menefee Formation coal at shallow depths has limited economic significance in the Moreno coal field, where preliminary estimates indicate demonstrated resources at a depth of 61 m are 8 million short tons. Currently only aggregate pits (sand and gravel, scoria, pumice) are active and production of aggregate (sand and gravel, pumice, and scoria) is likely to continue in the future. FIGURE 1. Mining districts in Rio Arriba and adjacent Counties, New Mexico. 446 MCLEMORE AND HOFFMAN provisions to obtain private ownership of federal land containing valuable mineral resources. The act was subsequently amended in 1870 and 1872 and in the years since. The mining act further encouraged mining and prospecting in Rio Arriba County and elsewhere in New Mexico and the mining boom of 1870-1890 began. Many districts in Rio Arriba County began to open up and production began as the Apache Indian threat was subdued (Table 1). The telegraph and then the railroad improved conditions in the area as mining continued to flourish. New metallurgical techniques were developed. Times were exciting for the miner in the late 1800s as metal prices soared. The 1870s and 1880s saw growth in mining in many districts in Rio Arriba County. Silver became important in 1870-1880s in many districts. In 1890 the Sherman Silver Act was passed which increased the price and demand for silver. However, it was short lived. The Sherman Silver Act was repealed in 1893 and most TABLE 1. Mining districts in Rio Arriba County, New Mexico. Names of mining districts are after File and Nothrop (1966) wherever practical, but many districts have been combined and added. Commodity symbols are defined in Appendix 1. District identification number is from the New Mexico Mines Database (McLemore et al., 2005). Estimated value of production is in original cumulative dollars and includes all commodities in the district, except aggregate (sand and gravel) and crushed and dimension stone. Production data complied from Lindgren et al. (1910), Anderson (1957), U. S. Geological Survey and Bureau of Mines Mineral Yearbooks (1900-1993), and Energy, Minerals and Natural Resources Department (1986-2003). Types of deposits","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128384950","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Late Hemphillian (Late Miocene) vertebrate fauna from the Black Mesa Quarry, Chamita Formation, Rio Arriba County, New Mexico","authors":"G. Morgan, D. Koning, S. Lucas, G. Spencer","doi":"10.56577/ffc-56.408","DOIUrl":"https://doi.org/10.56577/ffc-56.408","url":null,"abstract":"—The Black Mesa Quarry contains a newly discovered vertebrate fauna of late Miocene (late Hemphillian) age from the Chamita Formation near Lyden, Rio Arriba County, northern New Mexico. This fauna is derived from the Cuarteles Member stratigraphically high in the Chamita Formation. The site is only 10-16 m below the overlying Pliocene Servilleta Basalt and is in a relatively intact landslide block on the eastern slope of Black Mesa. Eight taxa of mammals are currently known from the Black Mesa Quarry: the puma-sized cat Pseudaelurus cf. P. hibbardi, the one-toed horse Dinohippus interpolatus, the giant camel Megatylopus cf. M. matthewi, the llama-like camel Hemiauchenia cf. H. vera, an unidentified antilocaprid, the rabbit Hypolagus cf. H. gidleyi, a smaller unidentified rabbit, and a small unidentified murid rodent. Further work at the Black Mesa Quarry, together with additional screenwashing for microvertebrates, will certainly add to the faunal list. The Black Mesa mammals, in particular D. interpolatus, M. matthewi, and H. gidleyi, are similar to the well known late Hemphillian faunas from the San Juan Quarry and Rak Camel Quarries. These other quarries also occur in the Chamita Formation about 7 km to the southwest. Several 40Ar/39Ar radioisotopic dates on tephras indicate that the San Juan Quarry and Rak Camel Quarries are between 6.8 and 7.0 Ma. The Black Mesa fauna is either time-equivalent to or somewhat younger than the San Juan Quarry fauna and Rak Camel Quarries fauna (5.9-6.8 Ma), but is older than latest Hemphillian (~5 Ma) faunas such as Walnut Canyon in southwestern New Mexico. FIGURE 1. Index map showing the location of upper Hemphillian fossil sites in the Chamita Formation, including the Black Mesa Quarry, Española basin, Rio Arriba County, northern New Mexico. 1. Chamita Formation type section; 2. San Juan Quarry and Rak Camel Quarries; 3. Black Mesa Quarry; 4. Lyden Quarry. 409 LATE HEMPHILLIAN VERTEBRATE FAUNA FROM THE BLACK MESA QUARRY species of large mammals in the fauna, a medium-sized felid, a small camelid, and an antilocaprid, are represented by only one or several fossils. Based on the discovery of several leporid teeth and postcranial elements on the surface of the quarry, we screenwashed a small sample (~100 kg) of sediment and have recovered additional specimens of rabbits, as well as small rodents. The Black Mesa Quarry fauna is certain to increase as we are planning further prospecting, excavating, and screenwashing, as well as prospecting in nearby exposures of the Chamita Formation. We follow Tedford et al. (2004) in using the biochronology of the Hemphillian (late Miocene and earliest Pliocene, 4.9-9.0 Ma) North American land-mammal “age” (NALMA). Other abbreviations used are: AMNH (American Museum of Natural History) and NMMNH (New Mexico Museum of Natural History). Tooth positions are abbreviated as follows: upper teeth are designated by upper case letters followed by a number giving the tooth position (e.g","PeriodicalId":345302,"journal":{"name":"Geology of the Chama Basin","volume":"28 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1900-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129352956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}