Trans-Pecos Texas Research Articles

Geochemical evolution of the REE-enriched Cave Peak porphyry Mo-deposit, Trans-Pecos Texas, USA

The Cave Peak deposit is a rift-related, breccia-hosted, fluorine-rich porphyry molybdenum deposit that is enriched in Nb, REE, and other critical minerals. Cave Peak is the easternmost member of a northwest-trending group of Paleogene intrusions in the Diablo Plateau along with the Marble Canyon stock, an unmineralized, petrogenetically related, compositionally zoned mafic alkaline pluton. The Cave Peak intrusions show within-plate geochemical affinity and is the product of a highly differentiated magma series. Curvilinear trends in Harker variation and trace element diagrams record magma differentiation from mafic to intermediate (44–69 wt% SiO2) to felsic (70–76 wt% SiO2) compositions at Marble Canyon and Cave Peak, respectively. Quartz syenite and monzonite from the Marble Canyon stock yielded zircon UPb ages of 36.2 ± 0.15 Ma and 36.1 ± 0.09 Ma, respectively. The youngest major intrusion at Cave Peak, an alkali feldspar granite porphyry, has a zircon UPb age of 34.8 ± 0.4 Ma, supporting that these intrusions represent a magma differentiation trend. The δ98Mo of Cave Peak molybdenites range between −0.39 ± 0.06 ‰ and + 0.52 ± 0.06 ‰ with a total Mo isotope range of 0.91 ‰. Cave Peak samples predominantly fractionated towards heavier δ98Mo. The Cave Peak data are distinctly heavier than data obtained from the nearby subduction-related Red Hills porphyry Cu deposit which has δ98Mo values of −0.25‰ to −0.51‰.

New specimens of middle Eocene omomyines (Primates, Omomyoidea) from the Uinta Basin of Utah and the Tornillo Basin of Texas, with clarification of the generic status of Ourayia, Mytonius, and Diablomomys

In the middle Eocene, multiple lineages of North American omomyoids independently evolved body masses greater than 500 g. Most of these large-bodied omomyoids are known from small sample sizes, which has contributed to a lack of consensus regarding their alpha taxonomy. Here, we describe new Uintan omomyine specimens from the Uinta Basin of Utah and the Tornillo Basin of Texas. These new samples expand the hypodigms of Diablomomys dalquesti, Mytonius hopsoni, and Ourayia uintensis, and favor the recognition of new species of Mytonius and Ourayia based on specimens from the Tornillo Basin. These samples support the recognition of Diablomomys as a valid genus distinct from Omomys, Ourayia as a valid genus distinct from Macrotarsius, and Mytonius as a valid genus distinct from Ourayia. Although Diablomomys and Omomys co-occur in the late Uintan of the Tornillo Basin, Ourayia and Mytonius are time-successive taxa with a wide distribution across multiple Laramide basins. The data presented here reinforce the conclusion that the Uintan was a time period in which omomyines diversified to include a large number of taxa with body masses above Kay's threshold and frugivorous–folivorous diets. These data also provide evidence that North American primate faunas exhibited a shifting pattern of regional endemism during the middle Eocene. By the early Uintan, primate faunas from Southern California were already quite distinct from primate faunas of the central Rocky Mountains or Trans-Pecos Texas. By the late Uintan, primate faunas in all three regions demonstrated greater provincialism, with Trans-Pecos Texas and Southern California both exhibiting a large number of endemic primate taxa and sharing only a single primate genus (Macrotarsius) in common. This increase in primate endemism across the Uintan may be tied to changes in paleohabitats associated with the larger trend toward decreasing temperatures from the Early Eocene Climatic Optimum to the Eocene/Oligocene transition.

Reproductively Viable Population of American Black Bears (Ursus americanus) in Lowland Chihuahuan Desert Habitat of Trans-Pecos Texas

Reproductively Viable Population of American Black Bears (Ursus americanus) in Lowland Chihuahuan Desert Habitat of Trans-Pecos Texas

Geochemical evolution of the Paradise Mountain Caldera complex, Davis Mountains: Implications for the tectonic and magmatic evolution of Trans-Pecos Texas and adjacent Mexico

The Paradise Mountain Caldera (~20 × 14 km), located west of Fort Davis, Texas, produced two major ignimbrite/lava complexes at ~36.2 and 35.9 Ma. The older unit (Fort Davis Tuff) is composed of rheomorphic tuff and overlying chemically similar lava. The younger unit (Wild Cherry Tuff) forms thick intracaldera deposits and an outflow sheet that spread over an estimated 2000 km2. Near the caldera, the two ignimbrites are separated by trachytic lava of the Mount Locke Formation. The 5-km diameter Point of Rocks intrusion, which crops out within the eastern margin of the caldera, may have fed the Mount Locke flows. Wild Cherry Tuff is overlain by silicic lava (Casket Mountain Formation, ~35.8 Ma), with which is shares chemical similarities. Intracaldera Wild Cherry Tuff was intruded by silicic intrusions and locally intensively silicified and kaolinized. In a revision of stratigraphic nomenclature, we assign all of the above volcanic units to a Barrel Springs Group.Collectively, the above units form a series ranging from trachyte to alkali rhyolite. Glomeroporphyritic trachyte of Mount Locke lavas represents silicic melt incompletely segregated from more mafic material within a source magma chamber. Variation between Mount Locke Formation trachyte and Fort Davis Tuff rhyolite can be modelled by fractionation of a mineral assemblage of plagioclase, clinopyroxene, FeTi oxides, and apatite; variation within the two major tuff units can be modelled almost exclusively by alkali feldspar. Central eruption within the caldera produced intracaldera tuff more evolved than most of its outflow. Alkali rhyolite of the Wild Cherry Tuff and Casket Mountain lavas, although similar in major element chemistry and mineralogy, show wide variation in incompatible trace elements, suggesting that evolution of silicic magmas in terms of major element chemistry had reached an impasse due to fractionation of a mineral assemblage whose bulk composition was similar to that of parental rhyolite.Paradise Mountain units represent a transition from alkalic magmatism in northeastern Trans-Pecos Texas to metaluminous to peraluminous magmatism in southwestern Trans-Pecos Texas and adjacent Mexico. Over a span of 10 Ma, silicic magmatism terminated southwestward over this region at a rate of about 24 km/Ma. This termination may reflect continued foundering of a sinking Farallon slab and associated asthenospheric mantle upwelling. Mafic magma derived by melting of lithospheric mantle formed plutons that, through filter pressing of silicic magma from crystalline mush, generated silicic melts. The transition across the Trans Pecos region from alkalic to metaluminous magmatism may have resulted through preferential modification of lithospheric mantle along the easternmost extent of Laramide subduction.

Polymerus americanus (Reuter) (Hemiptera: Miridae): Distribution, First Host Records, and Seasonality

Polymerus americanus (Reuter) is a mirine plant bug that has been seldom collected since its original description from Texas in 1876. Additional localities in Texas are recorded, and collection data are given for three previous records from Mexico (Coahuila, Hidalgo, and Nuevo León). Records from the eastern United States, and most western records other than West Texas, are considered probable misidentifications of other mainly dark species of the genus; the record from New Mexico requires verification. Nymphs and adults were observed in ornamental plantings of autumn sage (Salvia greggii Gray; Lamiaceae) at seven locales in Trans-Pecos Texas (Brewster, Jeff Davis, Pecos, and Presidio counties). Second through fifth instars and adults of a first generation were present in mid-April; late instars of another generation were found in late September and mid-October. The discovery of autumn sage as a host of P. americanus was facilitated by the plant's extensive use as an ornamental in the arid Southwest. The previous lack of bionomic information on the mirid is attributed mainly to the difficulty of finding native populations of autumn sage, a plant that grows in remote canyons and on mountain slopes in limited areas of West Texas and northern Mexico. Botanical information on autumn sage, including the history of its propagation, is provided.

Geochronology of the middle Eocene Purple Bench Locality (Devil’s Graveyard Formation), Trans-Pecos Texas, USA

Geochronology of the middle Eocene Purple Bench Locality (Devil’s Graveyard Formation), Trans-Pecos Texas, USA

Paleontology and Geology of the Badwater Creek Area, Central Wyoming. Part 21. Natrona, a New Genus of Rodent, Family Sciuravidae (Mammalia)

A new small sciuravid rodent, Natrona natronensis, new genus and species, from Uintan and Duchesnean deposits in the Wagon Bed Formation at the Hendry Ranch locality in central Wyoming exhibits some morphological parallelism in the structure of its P4 to the M1 of the more derived cricetid rodents. Other occurrences of this new lineage may be from the Eocene of Trans-Pecos Texas and Lac Pelletier, Saskatchewan, Canada.

Phylogeography and taxonomic revision of Nelson’s pocket mouse (Chaetodipus nelsoni)

AbstractChaetodipus nelsoni occurs on rocky substrates across the Mexican Altiplano. We investigated phylogeographic diversity within the species using morphologic, karyotypic, and molecular data. Data from nuclear (AFLP) and mitochondrial DNA support three distinct genetic groups with minimal substructuring coincident with biogeographic barriers previously identified in the Chihuahuan Desert and drainage basins of the Altiplano. We examined the morphological and karyotypic data in light of the molecular data. The results support recognition of three species within the currently accepted widespread C. nelsoni: 1) C. nelsoni restricted to a distribution centered on the El Salado River Basin; 2) elevation of C. n. collis to species, with two subspecies: one centered on Trans-Pecos Texas, the other on the Mapimí Basin (new subspecies); and 3) recognition of a new species, C. durangae, centered on the Nazas Basin and upper Río Mezquital drainage.

An unusual ‘shovel-billed’ dinosaur with trophic specializations from the early Campanian of Trans-Pecos Texas, and the ancestral hadrosaurian crest

We describe a new genus and species of hadrosaurid dinosaur, Aquilarhinus palimentus, from the lower shale member of the Aguja Formation (lower Campanian) of Big Bend National Park, south-western Texas. This species is characterized by several autapomorphies of the facial skeleton and mandible, including a crest composed of broadly arched nasals. Notably, the symphyseal processes of the dentary are elongated and reflected dorsally, causing the dentaries to meet with a ‘W’-shaped anterior profile. A hypothesized shovel-shaped ‘bill’, associated with widening of the skull, in A. palimentus might have been used in shovelling out and scooping up semiaquatic vegetation. This animal is otherwise superficially similar to kritosaurins like Gryposaurus but differs in the retention of key plesiomorphic character states in the maxilla and jugal. Phylogenetic analysis reveals Aquilarhinus to be a non-saurolophid hadrosaurid allied to Latirhinus from the late Campanian of Mexico, which bears a similar broadly arched nasal. The recognition of this lineage adds to the diversity of non-saurolophid hadrosaurids and points to the existence of a hitherto unknown diversity of ‘duck-billed’ dinosaurs outside of the saurolophine-lambeosaurine radiation. Cranial crests were ancestral for early hadrosaurids and evolved before the saurolophid radiation. Ancestrally, crests were ‘solid’, and consisted of arched nasals. These were retained among kritosaurins and subsequently modified into the diverse crest morphologies observed among derived saurolophines. Lambeosaurine ‘hollow-crested’ crest morphology departed from the ancestral, ‘solid-crested’ pre-saurolophid condition early following the origin of that clade.http://www.zoobank.org/urn:lsid:zoobank.org:pub:F7CE1BE7-1A76-4628-8510-93C37A1A807E

FIRST RECORD OF THE AMERICAN BLACK BEAR (URSUS AMERICANUS) FROM THE CHINATI MOUNTAINS OF WESTERN TEXAS

As part of an ongoing, large-scale project to monitor mammalian diversity, we set camera traps at four localities in Chinati Mountains State Natural Area, Presidio County, Texas. On 7 June and 3 and 7 July 2017, one of the cameras captured images of a subadult American black bear (Ursus americanus). The photo-verified individual represents the first account of the American black bear in the Chinati Mountains of western Texas. This record documents the species in an area spatially separated from other black bear populations in the region and supports the mainland–island metapopulation recolonization concept previously proposed for the American black bear in northern Mexico and Trans-Pecos Texas.

Generation of alkalic flood rhyolite: Insights from evolution of the Paisano volcano, Davis mountains, Trans-Pecos Texas, U.S.A.

Extensive silicic lava (flood rhyolite) constitutes part of the mid –Tertiary Paisano Volcano shield. This lava, borderline peralkaline quartz trachyte/rhyolite, forms part of a sequence of peralkaline rhyolite – quartz trachyte – trachyte produced as eruptions tapped deeper portions of underlying plutons. Flood rhyolite lava extended as far as 20 km from dikes of the eruptive center of the volcano, creating flows as thick as 100 m.Flood rhyolite was nearly aphyric to sparsely porphyritic, relatively hot (~911 °C) and erupted over a topographically subdued region, forming two lobes that extended north-northeast and southeast from a highland of previously-erupted rhyolite domes. Flood rhyolite extrusion followed eruption of a local ignimbrite, which filled valleys, flattening topography. Successive silicic flows off-lapped each other away from the volcano. Flood rhyolite eruption was followed by a second eruptive sequence that contained coarsely-porphyritic mafic trachyte lava.Silicic lava was most-likely generated by filter pressing from mush zones of mafic plutons. Glomeroporphyritic trachytes of the volcano are mixed rocks, silicic lava incompletely segregated from entrained fragments of mafic plutons. Continued evolution of quartz trachyte/low-silica rhyolite to peralkaline rhyolite was dominated by fractionation of alkali feldspar.

Ronald L. Ives Southwest Bibliography

Ronald L. Ives Southwest Bibliography Bill Broyles (bio) This list encompasses selected Ives's Southwest publications and a few others cited in the text. The full bibliography and most of the articles are available at the Arizona Historical Society in Tucson. The numbers at left are his own, showing the sequence in which they were published and the folder he fled it in. Missing numbers indicate it was on a diverse topic such as electronics, glaciers, photography, or folk tales. By his count he had 646 technical publications and drafts and 232 miscellaneous publications (M-series), as he called them. The format is the one he used. His first technical article was "Determination of the Relative Volumes of Two Combining Streams from Their Temperatures" in Science (1932, 76: 323), done at age 23. "The Southwest" is roughly used to include Arizona, Utah, Colorado, New Mexico, Texas, southern California, and northwestern Mexico. And like father, like son: An acquaintance of Ronald's father, J. E. Spiegelthal, noted that when Herbert E. Ives placed his own papers in the Smithsonian, he not only file-carded "everything he ever wrote" but he also "had a reprint of everything he had published" (Arizona Historical Society, Tucson, Ives Collection, MS-0983, box 24, Correspondence N-U, 1936–1981). [End Page 425] 3. Excursionando en los Pinacates, La Montana (Mexico, D.F.), April, 1934, 11, 12, et seq. 6. Recent Volcanism in Northwestern Mexico, Pan-American Geologist, 63, 1934, 335–338. 10. Geologic Verification of a Papago Legend, Masterkey (Los Angeles), 9, 1935, 160–161. 11. Infra-Red Photography for the Amateur, Camera, 51, 1935, 316– 320. 13. The Bolas de Plata Discovery of 1736, Rocks and Minerals, 10, 1935, 183–184. 15. Melchior Díaz, The Forgotten Explorer, Hispanic-American Hist. Rev., 16, 1936, 86–90. 16. A Trinchera near Quitovaquita, Sonora, Amer. Anthropologist, 38, 1936, 86–89. 17. Some Papago Migrations in the Sonoyta Valley, Masterkey, 10, 1936, 161–167. 18. The Radium Mining Area of Southwestern Colorado, Rocks and Minerals, 11, 1936, 223–234. 19. Desert Floods in the Sonoyta Valley, Amer. Jour. Science, 32, 1936, 349–360. 20. Mukuntuweap Canyon, Trail and Timberline, #221, 1937, 34–36. 35. Sedelmayr's Relacion of 1746, Bur. Amer. Ethnology, Bull. 123, 1939, 99–117. 44. Report of the Bishop of Durango on Conditions in Northwestern Mexico in 1745, Hispanic-American Historical Review, 19, 1939, 314–317. 45. Infra-red Photography as an Aid in Ecological Surveys, Ecology, 20, 1939, 433–439. 48. The Origin of Some Polished Stone Artifacts, Amer. Antiquity, 6, 1940, 70–73. 61. The Mitre Peak Area, Trans-Pecos Texas, Amer. Journal Science, 239, 1941, 339–353. 62. Designations of Locations on Maps and Photographs, Science, 93, 1941, 523. 65. The Origin of the Sonoyta Townsite, Sonora, Mexico, Amer. Antiquity, 7, 1941, 20–28. 67. The Monster of Quitovac, Masterkey, 15, 1941, 195–199. 71. The Copper Boulderwhip, Rocks and Minerals, 16, 1941, 455–458. 73. The Discovery of Pinacate Volcano, Sci. Mo., 54, 1942, 230–238. 93. Sunset Shadow Bands, Jour. Opt. Soc. Amer., 35, 1945, 736–738. [End Page 426] 122. Desert Ripples, Amer. Jour. Sci., 244, 1946, 492–501. 123. Ancient Trails in the Dugway Area, Utah, Masterkey, 20, 1946, 113–124. 129. Manje's Description of Casa Grande, Masterkey, 20, 1946, 148–151. 136. Glaciation in the Desert Ranges, Utah, Jour. Geol., 54, 1946, 335. 146. The Rediscovery of Cup Butte, Sci. Mo., 64, 1947, 33–41. 150. Dugway Tales, Western Folklore, 6 (1), 1947, 53–58. 152. Two Nahuatlan Terms from Northwestern Sonora, Int. Jour. Amer. Ling., 13, 1947, 119. 156. Behavior of Dust Devils, Bull. Amer. Met. Soc., 28, 1947, 168–175. 159. Reconnaissance of the Zion Hinterland, Geog. Rev., 27, 1947, 618–638. 166. Plunge Pools, Potholes, and Related Structures, Rocks and Minerals, 23, 1948, 3–10. 168. The Skull Valley Area, Utah, Rocks and Minerals, 23, 1948, 195–204. 169. The Camelback Caves, Rocks and Minerals, 23, 1948, 291–299. 170. Sonoran Mission Languages in 1730, Masterkey, 22, 1948, 93–96. 171. Latitude Determination without a Sextant, School Sci. and Math., 48, 1948, 441–445. 172. The Geodes of Oputo, Rocks and Minerals, 23...

Petrogenesis of Heavy Rare Earth Element Enriched Rhyolite: Source and Magmatic Evolution of the Round Top Laccolith, Trans-Pecos, Texas

The Round Top rhyolite located in Trans-Pecos Texas is enriched in Be, F, Li, Nb, Rb, Sn, Th, U, Y, Zr, and rare earth elements (REEs). REE-bearing minerals are mainly ubiquitous nano-scale accessory phases throughout the groundmass, incorporated in synchysite-group minerals, xenotime-(Y), Y- and Ce-rich fluorite, and zircon. The rhyolite is peraluminous, high-silica, alkaline (not peralkaline), with elevated heavy rare earth element concentrations and anonymously negative Eu values. Pervasive spongy groundmass and recrystallization textures are consistent with the elevated and remobilized Zr, Th, and Y + HREE (heavy rare earth element) concentrations and a high field strength element (HFSE) soluble, sub-alkalic, F-rich, magmatic system. REE-bearing minerals are present as late-magmatic, interstitial phases and attributed with closed-system, post-magmatic, hydrothermal alteration. Petrogenetic modeling provides scenarios that explain the geochemical evolution and REE complexing behavior in evolved rhyolite magmas, and determines possible source compositions and evolution. Trace element models suggest a system typical of having extensive magmatic differentiation. The resulting rhyolite magma is indicative of a silica-rich magmatic system enriched in H2O, Li, and/or F that could be considered transitional between pure silicate melt and hydrothermal fluid, where fluorine-ligand complexing was prevalent through late magmatic cooling and crystallization processes. Thorough differentiation and high fluorine activity contributed to the late stage crystallization of REE-bearing minerals in the Round Top rhyolite.

Rare Earth Elements (REE) Deposits Associated with Great Plain Margin Deposits (Alkaline-Related), Southwestern United States and Eastern Mexico

W.G. Lindgren in 1933 first noted that a belt of alkaline-igneous rocks extends along the eastern edge of the Rocky Mountains and Basin and Range provinces from Alaska and British Columbia southward into New Mexico, Trans-Pecos Texas, and eastern Mexico and that these rocks contain relatively large quantities of important commodities such as, gold, fluorine, zirconium, rare earth elements (REE), tellurium, gallium, and other critical elements. In New Mexico, these deposits were called Great Plain Margin (GPM) deposits, because this north-south belt of alkaline-igneous rocks roughly coincides with crustal thickening along the margin between the Great Plains physiographic province with the Basin and Range (including the Rio Grande rift) and Rocky Mountains physiographic provinces, which extends into Trans-Pecos Texas and eastern Mexico. Since 1996, only minor exploration and development of these deposits in New Mexico, Texas, and eastern Mexico has occurred because of low commodity prices, permitting issues, and environmental concerns. However, as the current demand for gold and critical elements, such as REE and tellurium has increased, new exploration programs have encouraged additional research on the geology of these deposits. The lack of abundant quartz in these systems results in these deposits being less resistant to erosion, being covered, and not as well exposed as other types of quartz-rich deposits, therefore additional undiscovered alkaline-related gold and REE deposits are likely in these areas. Deposits of Th-REE-fluorite (±U, Nb) epithermal veins and breccias are found in the several GPM districts, but typically do not contain significant gold, although trace amounts of gold are found in most GPM districts. Gold-rich deposits in these districts tend to have moderate to low REE and anomalously high tungsten and sporadic amounts of tellurium. Carbonatites are only found in New Mexico and Mexico. The diversity of igneous rocks, including alkaline-igneous rocks, and associated mineral deposits along this boundary suggests that this region is characterized by highly fractionated and differentiated, multiple pulses of mantle-derived magmas evolving to lower crustal magmas related to the subduction of the Farallon plate. The differences in incompatible trace elements, including REE and beryllium, between the different granitic to rhyolite rocks are likely related to either differences in the crustal rocks that were assimilated during magmatic differentiation or by potential minor contamination from crustal sources and/or magma mixing. Deep-seated fracture systems or crustal lineaments apparently channeled the magmas and hydrothermal fluids. Once magmas and metal-rich fluids reached shallow levels, the distribution and style of these intrusions, as well as the resulting associated mineral deposits were controlled by local structures and associated igneous rock compositions.

The Boquillas Formation of the Big Bend National Park, Texas, USA, a reference Cenomanian through Santonian (Upper Cretaceous) carbonate succession at the southern end of the Western Interior Seaway

Abstract The upper lower Cenomanian through middle Santonian (Upper Cretaceous) of the Boquillas Formation in the Big Bend Region of Trans-Pecos Texas consists of a marine carbonate succession deposited at the southern end of the Western Interior Seaway. The Boquillas Formation, subdivided into the lower, c. 78 m thick limestone-shale Ernst Member, and the upper, c. 132 m thick limestone/chalk/marl San Vicente Member, was deposited in a shallow shelf open marine environment at the junction between the Western Interior Seaway and the western margins of the Tethys Basin. Biogeographically, the area was closely tied with the southern Western Interior Seaway. The richly fossiliferous upper Turonian, Coniacian and lower Santonian parts of the Boquillas Formation are particularly promising for multistratigraphic studies.

Basement control of alkalic flood rhyolite magmatism of the Davis Mountains volcanic field, Trans-Pecos Texas, U.S.A.

Voluminous silicic lava flows, erupted ~37.4Ma from widespread centers within the Davis Mountains Volcanic Field (DMVF), covered approximately 10,000km2 with an initial volume as great as 1000km3. Lava flows form three major stratigraphic units: the Star Mountain Rhyolite (minimum 220km3) of the eastern Davis Mountains and adjacent Barilla Mountains, the Crossen Formation (~75km3) of the southern Davis Mountains, and the Bracks Rhyolite (~75km3) of the Rim Rock region west of the Davis Mountains proper. Similar extensive rhyolite lava also occurs in slightly younger units (Adobe Canyon Rhyolite, ~125km3, 37.1Ma), Sheep Pasture Formation (~125km3, ~36Ma) and, less voluminously, in the Paisano central volcano (~36.9Ma) and younger units in the Davis Mountains. Individual lava flows from these units formed fields as extensive as 55km and 300-m-thick.Flood rhyolite lavas of the Davis Mountains are marginally peralkaline quartz trachyte to low-silica rhyolite. Phenocrysts include alkali feldspar, clinopyroxene, FeTi oxides, and apatite, and, rarely, fayalite, as well as zircon in less peralkaline units. Many Star Mountain flows may be assigned to one of four geochemical groupings. Temperatures were moderately high, ranging from ~911 to 860°C in quartz trachyte and low silica rhyolite. We suggest that flood rhyolite magma evolved from trachyte magma by filter pressing processes, and trachyte from mafic magma in deeper seated plutons.The Davis Mountains segment of Trans-Pecos Texas overlies Grenville basement and is separated from the older Southern Granite and Rhyolite Province to the north by the Grenville Front, and from the younger Coahuila terrane to the south by the Ouachita Front. We suggest that basement structure strongly influenced the timing and nature of Trans-Pecos magmatism, probably in varying degrees of impeding the ascent of mantle-derived mafic magmas, which were produced by upwelling of asthenospheric mantle above the foundered Farallon slab. Basalt was able to penetrate Coahuila crust in the Big Bend region. Thicker Grenville crust under the Davis Mountains retarded ascent of mafic magmas, allowing mafic plutons to differentiate into silicic magma that was eventually erupted as flood lava. North of the Grenville Front, magmatism was further delayed and thicker, older crust there may have helped concentrate magmatism under the Davis Mountain region. Only after the onset of Basin and Range faulting was true basalt erupted over much of the Trans Pecos.

Embodiment, Transformation and Ideology in the Rock Art of Trans-Pecos Texas

Present in the Trans-Pecos rock art of west Texas are many motifs intelligible within hunter-gatherer ontological frameworks. These motifs—including human figures missing heads and limbs, figures with disproportionately large eyes, polymelia and pilo-erection—are concerned with somatic transformations and distortions experienced in altered states of consciousness. Ethnographic analogies also demonstrate that other Trans-Pecos features—smearing, rubbing and chipping of pigment and incorporation of natural inequalities of the rock surfaces into images—are evidence of kinetic experiences or embodied processes, including the important interaction with the ‘veil’ that separates one tier of the cosmos from others. By exploring the related concepts of embodiment, somatic transformation and process within non-Western ontologies, I offer a unified but multi-component explanation for the meanings and motivations behind several Trans-Pecos rock-art motifs. I also address the consumption of rock art in west Texas—how it was viewed and used by the original artists and subsequent viewers to shape, maintain and challenge ideologies and identities.

Kinematic Evolution of the Eastern Chalk Draw Fault during Basin and Range Extension: Evaluating the Role Played by Preexisting Structural Fabrics in Along-Strike Displacement Patterns

Basin and Range extensional structures in Trans-Pecos Texas have been interpreted to be strongly influenced by preexisting structures, including igneous centers in the Big Bend region. These igneous centers are interpreted to have deflected propagating faults, as they are rheologically strong relative to the surrounding rocks. We conducted detailed field mapping and analysis of fracture and fault data along the eastern segment of the Chalk Draw Fault in Big Bend National Park to evaluate its kinematic evolution and interaction with Paleogene plutons. Our primary results document the following key relationships: (1) the Rosillos Laccolith and other Paleogene plutons in the study area are pervasively fractured, dominantly by northwest-striking mode I fractures, which generally do not extend into adjacent sedimentary rock sequences; (2) throw on the eastern Chalk Draw Fault is strongly asymmetric, decreasing rapidly as it enters the Rosillos Laccolith; and (3) analysis of fault-slip data in the region documents dominantly N 52° E–directed regional extension along the northwest-striking segment of the Chalk Draw Fault and secondary structures. We interpret these relationships to indicate that the Rosillos Laccolith developed pervasive mode I fractures with a dominant northwest-southeast orientation during cooling under Basin and Range extensional stresses but that this occurred prior to extensional faulting within the region. We suggest that the highly fractured nature of the Rosillos Laccolith resulted in it being rheologically weaker than the surrounding Cretaceous sedimentary rocks, which resulted in (1) hindering southward propagation of the Chalk Draw Fault by dissipating stress at the fault tip within the highly fractured laccolith and (2) the strongly asymmetric distribution of slip due to a strong rheological contrast during fault propagation.

Geochronological and taxonomic revisions of the middle Eocene Whistler Squat Quarry (Devil's Graveyard Formation, Texas) and implications for the early Uintan in Trans-Pecos Texas.

The Whistler Squat Quarry (TMM 41372) of the lower Devil’s Graveyard Formation in Trans-Pecos Texas is a middle Eocene fossil locality attributed to Uintan biochronological zone Ui1b. Specimens from the Whistler Squat Quarry were collected immediately above a volcanic tuff with prior K/Ar ages ranging from ∼47–50 Ma and below a tuff previously dated to ∼44 Ma. New 40Ar/39Ar analyses of both of the original tuff samples provide statistically indistinguishable ages of 44.88±0.04 Ma for the lower tuff and 45.04±0.10 Ma for the upper tuff. These dates are compatible with magnetically reversed sediments at the site attributable to C20r (43.505–45.942 Ma) and a stratigraphic position above a basalt dated to 46.80 Ma. Our reanalysis of mammalian specimens from the Whistler Squat Quarry and a stratigraphically equivalent locality significantly revises their faunal lists, confirms the early Uintan designation for the sites, and highlights several biogeographic and biochronological differences when compared to stratotypes in the Bridger and Uinta Formations. Previous suggestions of regional endemism in the early Uintan are supported by the recognition of six endemic taxa (26% of mammalian taxa) from the Whistler Squat Quarry alone, including three new taxa. The revised faunal list for the Whistler Squat Quarry also extends the biostratigraphic ranges of nine non-endemic mammalian taxa to Ui1b.

Eastern Fox Squirrel (Sciurus Niger): New Threat to Pecan Orchards in Far West Texas

We report the first records of the eastern fox squirrel (Sciurus niger) in Trans-Pecos Texas. Sciurus niger is widely established in pecan orchards in the Lower El Paso Valley of the Rio Grande, El Paso County. Expansion of this population to other pecan-growing regions along the Rio Grande in New Mexico is possible. Research is needed on both the extent of damage caused by S. niger to pecan production and the control methods in this situation. We recommend a goal of complete eradication of S. niger from this region. Sciurus niger should be delisted as a game species in El Paso County, Texas, and throughout New Mexico, where there are no native populations of the species.