New Mexico Geology最新文献

{"title":"Chronology of colluvial apron deposition within Canada del Buey, Pajarito Plateau, New Mexico","authors":"K. Lepper, K. Crowell, C. Wilson","doi":"10.58799/nmg-v33n1.3","DOIUrl":"https://doi.org/10.58799/nmg-v33n1.3","url":null,"abstract":"This investigation uses optically stimulated luminescence (OSL) dating to examine the chronology of colluvial apron development and to help constrain long-term process rates within the mesa and canyon systems of the Pajarito Plateau in north-central New Mexico. In addition to ages, the OSL data provide insight into the dynamic interactions of surface processes within the mesa and canyon systems. Our results can be interpreted to suggest that foot-slope deposits within Canada del Buey represent a complex interplay of depositional processes in which eolian inputs from outside of the Pajarito Plateau play a role. Depositional ages, both on the mesa top and in foot slopes, record episodic inputs to the system in the late Pleistocene, middle Holocene, and late Holocene. These periods correlate well to eolian activity and significant climatic events in the Southern Plains and desert Southwest.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2011-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174580","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 Late Cretaceous oyster Cameleolopha bellaplicata (Shumard 1860), guide fossil to middle Turonian strata in New Mexico","authors":"S. Hook, W. A. Cobban","doi":"10.58799/nmg-v33n3.67","DOIUrl":"https://doi.org/10.58799/nmg-v33n3.67","url":null,"abstract":"Cameleolopha bellaplicata (Shumard 1860) is an easily recognized fossil oyster that occurs abundantly in sandy strata in Arizona, Colorado, New Mexico, Utah, and Texas, where it is restricted to the middle Turonian ammonite zones of Prionocyclus hyatti and P. macombi. It is a distinctive, medium-sized, plano-convex, ribbed oyster that has an undulating or zigzag margin and a small to nonexistent attachment scar; it occurs in great numbers, usually as original shells. In central New Mexico, C. bellaplicata is an excellent guide fossil to the Fite Ranch Sandstone Member of the Tres Hermanos Formation, which was deposited as nearshore sands during the second major transgression of the Late Cretaceous seaway in the state. Since 1965 Cameleolopha bellaplicata has been split, erroneously, into two chronological subspecies: a supposedly older, more coarsely ribbed form, C. bellaplicata novamexicana (Kauffman), that was thought to be restricted to the middle part of the Prionocyclus hyatti Zone, and a younger, more delicately sculptured form, C. bellaplicata bellaplicata (Shumard), that ranges into the overlying P. macombi Zone. Although the two subspecies have type localities in Socorro County, New Mexico, and Grayson County, Texas, respectively, their supposed chronostratigraphic relationship could not be established at either type locality because the two supposed subspecies do not occur together at either type locality. Presumably, this chronostratigraphic relationship was established in Huerfano County, Colorado, where the ranges of the two morphotypes were interpreted to lie one above the other within the P. hyatti Zone and with no zone of overlap. However, the chronological separation of the morphotypes by ammonite zone was based on a misidentification of the prionocyclid ammonite that occurs with the holotype of Cameleolopha bellaplicata novamexicana. Initially, only fragments of large individual prionocyclids were found; they were identified as Prionocyclus hyatti. Recent collections of ammonites from the type area of C. b. novamexicana contain small diameter internal molds that are unequivocally the younger P. macombi, rather than the older P. hyatti; associated fauna includes Inoceramus dimidius White, which substantiates assignment of the holotype of C. b. novamexicana to the younger P. macombi Zone. With the index ammonite identified correctly, there is no chronostratigraphic basis for the subspecies separation. A reinterpretation of the original morphometric data shows that the presumed differences between the subspecies are subtle and represent normal species variation. Beginning in the late 1940s, strata that are now included in the Tres Hermanos Formation in New Mexico and Arizona were correlated with and included in the stratigraphically higher Gallup Sandstone. In the late 1970s, collections of Cameleolopha bellaplicata and its descendant C. lugubris from the Zuni and Acoma Basins in west and west-central New Mexico were instrumental i","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2011-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71175107","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":"A rare, large artesian subaqueous spring in the upper Rio Grande","authors":"P. Bauer, P. Johnson","doi":"10.58799/nmg-v32n1.26","DOIUrl":"https://doi.org/10.58799/nmg-v32n1.26","url":null,"abstract":"","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174705","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 Holocene record of fire and erosion in the southern Sacramento Mountains and its relation to climate","authors":"G. Meyer, J. Frechette","doi":"10.58799/nmg-v32n1.19","DOIUrl":"https://doi.org/10.58799/nmg-v32n1.19","url":null,"abstract":"As highlighted in this issue’s Gallery of Geology on page 24, large, severe wildfires have become part of the New Mexico late spring and early summer experience in the last few decades. Such fires have considerable relevance to geomorphologists, as erosion rates in mountainous landscapes are often dramatically increased in the several years after severe fires. Erosion and sediment transport often take place during major debris flows and flash floods (Fig. 1). These events are most commonly triggered by intense thunderstorm rainfall, as in New Mexico’s summer monsoon, and very rapid runoff from slopes devoid of vegetation or forest litter. Although water-repellent soils formed by fire effects are often cited as the primary cause of increased runoff, the creation of extensive bare, smooth soil surfaces alone is more than sufficient— for example, consider the erosion that would occur on a plowed, smooth farm field at slope angles of 15–30° or more! The extreme flows that are generated can entrain huge volumes of sediment as they course down slopes and channels. Events of this nature affected a number of small, steep drainages in the Sacramento Mountains southeast of Cloudcroft after the 2002 Penasco fire. Large quantities of mudto boulder-sized sediment may be deposited on alluvial fans along the valley margins, and in some cases deep gullies are also cut in the fans. Major damage to roads, buildings, and property resulted in several locations in the Penasco fire area, as valleyside alluvial fans are common sites for residential and other development. Along with their importance in understanding geologic hazards and watershed impacts, sediments deposited on alluvial fans by postfire debris flows and floods also provide a means of assessing the timing and spatial distribution of past forest fires, and relations between fire and climate, in particular episodes of severe drought. These sediments are often rich in charcoal fragments from the burned area, which allows radiocarbon dating of fire-related sedimentation events thousands of years into the past, providing an important supplement to the more commonly available tree-ring fire histories. Tree-ring dating has provided a wealth of information on low-severity surface fires that scar trees, but leave them living. Such fires swept through the understory of many southwestern forests every few years to a few decades before European settlement and intensified grazing, logging, and fire suppression in the late 1800s (e.g., Brown et al. 2001). However, tree-ring fire-scar records extend back about 500 yrs at most, and do not provide data on severe fires that kill large stands of trees. Standdestroying fires can be dated via the ages of living trees that germinated after fire, but this reveals the last such fire only, and again is limited to about the last 500 yrs. Therefore, alluvial sediments can greatly extend fire histories, albeit with greater uncertainty in ages. Climatic change on time scales of a th","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174894","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":"Cretaceous stratigraphy, paleontology, petrography. Depositional environments, and cycle stratigraphy at Cerro de Cristo Rey, Dona Ana County, New Mexico","authors":"S. Lucas, K. Krainer, J. Spielmann, K. Durney","doi":"10.58799/nmg-v32n4.103","DOIUrl":"https://doi.org/10.58799/nmg-v32n4.103","url":null,"abstract":"Cretaceous marine and nonmarine strata of late Albian–middle Cenomanian age are exposed around the Cerro de Cristo Rey uplift in southern Doña Ana County, New Mexico. These strata comprise a section approximately 350 m thick and are assigned to the (ascending order) Finlay, Del Norte, Smeltertown, Muleros, Mesilla Valley, Mojado (=“Anapra”), Del Rio, Buda, and Mancos (=“Boquillas”) Formations. Macrofossils and microfossils from these strata indicate that the Finlay, Del Norte, Smeltertown, Muleros, and Mesilla Valley Formations are of late Albian age, whereas the Del Rio, Buda, and Mancos Formations are of Cenomanian age. The base of the Cenomanian is most likely at a trangressive surface within the uppermost Mojado Formation. The late Albian (Manuaniceras powelli Zone) to early Cenomanian (Neophlycticeras hyatti Zone) sedimentary succession at Cerro de Cristo Rey consists of alternating fossiliferous limestone, shale with limestone and sandstone intercalations, and sandstone. Muddy limestone types are commonly wavy to nodular and represent deposits of an open-marine shelf environment below wave base. Intercalated coquina beds rich in mollusc shells are interpreted as storm layers. Shale was deposited in an open-shelf environment below or near wave base during periods of increased siliciclastic influx. Intercalated thin limestone and sandstone beds are inferred to be storm layers. The siliciclastic Mojado Formation is a regressive-transgressive succession formed in depositional environments ranging from lower shoreface to upper shoreface and even fluvial, again overlain by shallow-marine siliciclastics. Although the Washita Group section at Cerro de Cristo Rey is much thicker and displays some differences in facies, the succession shows similar transgressive and regressive trends compared to the Washita Group of north Texas. Thus, we recognize eight unconformity-bounded depositional cycles in the Cretaceous section at Cerro de Cristo Rey, the upper Finlay Formation (youngest cycle of the Fredericksburg Group), lower Mancos Formation (base of Greenhorn cycle), and six Washita Group cycles: WA1 = Del Norte Formation, WA2 = Smeltertown Formation, WA3 = Muleros Formation, WA4 = most of Mesilla Valley Formation, WA5 = uppermost Mesilla Valley Formation and most of Mojado Formation, and WA6 = uppermost Mojado and Del Rio and Buda Formations. The persistence of cycles from the tectonically passive, openmarine margin of the Gulf of Mexico into the tectonically active Chihuahua trough suggests that regional if not global eustasy, not local tectonism, drove late Early to early Late Cretaceous sedimentation at Cerro de Cristo Rey. Introduction Cerro de Cristo Rey is a prominent peak in Doña Ana County, New Mexico, just north of the U.S.–Mexican border and just west of the city of El Paso, Texas (Fig. 1). The mountain was long referred to as the Cerro de Muleros, but was renamed Cerro de Cristo Rey (“Sierra” de Cristo Rey of Hook 2008 and Cobban et al. 2008,","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174508","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":"Interannual variablity of wildfires and summer precipitation in the Southwest","authors":"D. Gutzler, Laura J. Van Alst","doi":"10.58799/nmg-v32n1.22","DOIUrl":"https://doi.org/10.58799/nmg-v32n1.22","url":null,"abstract":"As described in the accompanying Gallery of Geology article, springtime is wildfire season in the Southwest. The table of recent fires in New Mexico on page 25 is dominated by events in May and June. Hot, dry, windy conditions in the spring promote wildfire development. Drought conditions make some years more fire prone than others, and long-term climatic changes in temperature and precipitation affect the general fire regime in the Southwest (Meyer and Frechette, this issue). The onset of the North American monsoon, usually around the beginning of July, brings higher humidity and intermittent rainfall, dampening grass and dry fuel and generally marking the end of the fire season (and the acceleration of plant growth that provides fuel for the next year's fire season). It is also possible that wildfires affect the regional climate, although this connection is harder to quantify. Large fires inject large quantities of soot and smoke high into the atmosphere. Winds then blow these particulates across the Southwest, so the impact of locally injected particulates can spread far beyond the source. Other sources of particulates, such as widespread air pollution, have been shown to block sunlight and depress precipitation. A study of the South Asian monsoon showed that black carbon soot associated with air pollution decreases the radiative heating of the surface, thereby altering atmospheric stability and largescale temperature gradients that drive monsoon circulations (Ramanathan et al. 2005). Compared to the South Asian brown cloud, southwestern wildfires in most years generate much smaller quantities of particulates that remain airborne for a shorter period of time. However the timing of the southwestern fire season in late spring is potentially just right to affect the onset of the monsoon. The onset date is highly correlated with total seasonal precipitation, such that late onset is usually a precursor of low total summer rainfall (Higgins et al. 1997). We describe here a preliminary assessment of the hypothesis that large spring wildfires could depress monsoonal precipitation, by comparing a 25-yr time series of acreage burned in southwestern wildfires in June with the subsequent precipitation observed in July and August (Van Alst 2009). Data","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174543","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":"Rhyolites and associated deposits of the Valles - Toledo caldera complex","authors":"J. Gardner, F. Goff, S. Kelley, E. Jacobs","doi":"10.58799/nmg-v32n1.3","DOIUrl":"https://doi.org/10.58799/nmg-v32n1.3","url":null,"abstract":"Several decades of focused studies on the Valles–Toledo caldera complex and the Jemez Mountains in northern New Mexico have brought about new understanding of the relations of stratigraphic units that record the complex’s evolution. We present here a revision of the formal stratigraphic nomenclature for the Quaternary Tewa Group, an established stratigraphic unit that includes the volcanic and volcaniclastic deposits of the caldera complex. We propose 11 completely new units of member rank, with descriptions of lithology, contact relations, distribution, and type areas. These new members are parts of the Bandelier Tuff, Cerro Toledo, and Valles Rhyolite Formations, and serve to depict the magmatic and geomorphic evolution of the area during and following each of two major caldera-forming episodes. With results from mapping efforts in the Jemez Mountains revealing the broad implications and interrelations of some established units, we redefine one formation (Cerro Toledo Rhyolite) and demote three formal members (El Cajete, Battleship Rock, and Banco Bonito) to bed or flow rank. Because it has been shown repeatedly in published works that one formation (Cerro Rubio Quartz Latite) was originally defined based on erroneous relations, we propose its formal abandonment. Additionally, we propose formal abandonment of one established member (Valle Grande Member of the Valles Rhyolite) because of lack of utility and widespread disuse. Our proposed revisions embody the practices of geologic mappers, and serve to better clarify relations of volcanic and volcaniclastic rocks through the evolution of the Valles–Toledo caldera complex. The new formal stratigraphy that we propose will provide a flexible but robust framework for on-going and future research in the Valles–Toledo caldera complex.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174784","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":"Gallery of Geology - Dripping Springs fire","authors":"J. Love","doi":"10.58799/nmg-v32n1.24","DOIUrl":"https://doi.org/10.58799/nmg-v32n1.24","url":null,"abstract":"","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174688","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":"Flemingostrea elegans, n. sp.: guide fossil to marine, lower Coniacian (Upper Cretaceous) strata of central New Mexico","authors":"S. Hook","doi":"10.58799/nmg-v32n2.35","DOIUrl":"https://doi.org/10.58799/nmg-v32n2.35","url":null,"abstract":"The marine oyster Flemingostrea elegans, n. sp., appears suddenly in lower Coniacian (Upper Cretaceous) strata of central New Mexico. It has no immediate ancestor in the Western Interior of the United States and has not been found anywhere outside central New Mexico. Flemingostrea elegans occurs in nearshore sandstones in the Mulatto Tongue of the Mancos Shale in Socorro County and the Gallup Sandstone of Lincoln County. This medium-sized oyster, with its distinctive terebratuloid fold, is an excellent guide fossil to the lower Coniacian, and is a great aid in distinguishing the Mulatto Tongue from other tongues of the Mancos Shale in Socorro County and in differentiating Coniacian from Turonian sandstones in Lincoln County. It occurs in great numbers, often as articulated shells, and is easily distinguished from all other Turonian through Coniacian oyster species by the fold in its lower valve. Its presence above coal beds in the lower part of the Crevasse Canyon Formation provides definitive evidence for a third cycle of transgression/regression of the western shoreline of the Late Cretaceous Seaway as far south in New Mexico as central Socorro County. The Santonian dwarf species, Flemingostrea nanus (Johnson 1903), known only from Santa Fe County, New Mexico, is redescribed and illustrated. Flemingostrea nanus, F. elegans, n. sp., and the upper Cenomanian F. prudentia (White 1877) are the only species of Flemingostrea known from the Western Interior. Ostrea elegantula Newberry 1876, which has been confused in the literature with F. elegans, n. sp., should be considered formally as a nomen oblitum (a forgotten name) and not used again. Ostrea elegantula was named but not described or illustrated by J. S. Newberry in his geological report of Captain J. N. Macomb’s 1859 San Juan exploring expedition. F. B. Meek, who wrote the paleontological report on the Cretaceous fossils collected on that expedition, did not describe, illustrate, or mention it. Newberry’s type specimens were illustrated in 1883 by C. A. White, again without description. Attempts to recover Newberry’s type locality along the Canadian River, Colfax County, New Mexico, were unsuccessful.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2010-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71174917","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":"New sites of 3.1-Ma pumice beds in axial fluvial strata of the Camp Rice and Palomas formations, southern Rio Grande rift","authors":"G. Mack, N. Dunbar, R. Foster","doi":"10.58799/nmg-v31n2.31","DOIUrl":"https://doi.org/10.58799/nmg-v31n2.31","url":null,"abstract":"Newly discovered pumice beds in axial-fluvial strata of the Pliocene–lower Pleistocene Camp Rice and Palomas Formations in the southern Rio Grande rift are geochemically correlated to a previously dated 3.1-Ma pumice bed at Hatch Siphon. The Lucero pumice in the Dona Ana Mountains is 1–1.5 m thick and consists of granule- and pebble-sized pumice intercalated with fluvial sand, whereas the Mud Springs pumice along the southeastern flank of the Mud Springs Mountains is 10 cm thick and is composed of sand-sized pumice. Samples from all three sites consist of vesicular, rhyolitic glass fragments and are compositionally identical, particularly with respect to Fe, Ca, and Mn, suggesting derivation from the same 3.1-Ma volcanic eruption. The composition and age of this erupted material is consistent with derivation from the Grants Ridge area, south of Mt. Taylor, implying transport to the ancestral Rio Grande via the Rio Puerco drainage system. If the correlation is correct, the Lucero pumice, along with a bed of 1.6-Ma pumice and the constructional top of the Camp Rice Formation (~0.8 Ma), provide chronologic constraints on the rate of onlap of the northwestern Dona Ana Mountains by axial-fluvial sediment of the Camp Rice Formation. From 3.1 to 1.6 Ma, the sediment accumulation rate was 46.7 m/ Ma, and the lateral rate of eastward onlap was 2 km/Ma. The corresponding values diminished to 18.8 m/Ma and 0.89 km/Ma, respectively, from 1.6 to 0.8 Ma, perhaps due to activity on the Jornada fault, which borders the northern Dona Ana Mountains. If the correlation between the Mud Springs pumice and 3.1-Ma Hatch Siphon pumice is correct, then the Mud Springs pumice provides a reliable chronologic marker within the Palomas Formation that can be compared to existing biostratigraphic data from the same region. The 3.1-Ma Mud Springs pumice is located within the stratigraphic range of the vertebrate collection of Lucas and Oakes (1986) and is consistent with their interpretation of the fauna as medial Blancan in age (~3 Ma). In contrast, the vertebrate collection of Repenning and May (1986), which has been interpreted as very early Blancan II in age (~4.5 Ma), seems anomalously old, given the fact that it is only ~20 m beneath the Mud Springs pumice.","PeriodicalId":35824,"journal":{"name":"New Mexico Geology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2009-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"71173986","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}