Cerro Toledo Research Articles

Ascogrammitis lehnertii (Polypodiaceae): A New and Dominant Understory-Species from a Diverse Community of Grammitid Ferns in the Andes of Ecuador

In the scope of pantropical studies aimed at understanding how the diversity of grammitid ferns (Polypodiaceae) has evolved and is maintained, we studied a diverse grammitid community in treeline elfin forests in eight study plots of 400 m2 each at 3200 m on Cerro Toledo, Loja, southern Ecuador. We recorded a total of 7986 individuals of 16 grammitid species. Ascogrammitis lehnertii is here described as a new species.We also recorded Mycopteris leucosticta, a species previously believed to be restricted to the Choco region of Ecuador. We found that the grammitid species were segregated by habitat into trunk-base and trunk specialists, which suggests that species coexistence in these diverse epiphytic communities is at least partly linked to habitat segregation. Ascogrammitis lehnertii and M. leucosticta were the second and third most abundant species, respectively, and both were mostly trunk-base species. The new species A. lehnertii differs from its congeners by the combination of its relatively broad lamina, (2-)3–4 cmwide, fertile leaves bearing 2mmlong reddish setae in and near the sori, and by bearing proliferous roots from which new plants emerge. Phylogenetic analyses of atps, rbcL, rps4, trnG-trnR, andtrnL-trnF DNA molecular sequences, using maximum likelihood, place A. lehnertii as sister to A. cuencana with strong support. Despite previous intensive collection efforts in Loja for the past 30 yr, all but one of the collections of this new species were made in the last three years. The discovery of A. lehnertii and the new record of M. leucosticta highlight the patchy distribution of some species in the Andes and the value of surveying habitats that potentially host unrecognized plant diversity. In order to facilitate further discovery, we provide a key to all species of Ascogrammitis.

El Paso Phase Obsidian Procurement in Southern New Mexico: Implications for Jornada Mogollon Regional Interaction and Exchange

Archaeologists rarely discuss obsidian procurement for the Jornada Mogollon region, but studies indicate groups overwhelmingly used obsidian that can be collected from Rio Grande gravels in southern New Mexico. Obsidian artifacts from two El Paso phase sites, Cottonwood Spring Pueblo and Madera Quemada Pueblo, were sourced using EDXRF spectrometry to determine: (1) is there evidence for non-Rio Grande gravel obsidian use, (2) is there a difference between the sites, and (3) how do these sourcing results compare with contemporaneous sites in the Casas Grandes area? This study has implications for regional interaction and exchange as the results validate the high frequency of Cerro Toledo Rhyolite obsidian in assemblages, but non-Rio Grande gravel sources were also used including Mule Creek projectile points. People at both sites used similar sources, with a few noted exceptions. Furthermore, groups in the Jornada Mogollon and Casas Grandes regions utilized dramatically different sources.

Volcanism and sedimentation along the western margin of the Rio Grande rift between caldera-forming eruptions of the Jemez Mountains volcanic field, north-central New Mexico, USA

The Cerro Toledo Formation (CTF), a series of intracaldera rhyolitic dome complexes and their associated extracaldera tephras and epiclastic sedimentary deposits, records the dynamic interplay between volcanic, tectonic, and geomorphic processes that were occurring along the western margin of the Rio Grande rift between major caldera-forming eruptions of the Bandelier Tuff 1.65–1.26Ma. The Alamo Canyon and Pueblo Canyon Members differ significantly despite deposition within a few kilometers of each other on the Pajarito Plateau. These differences highlight spatial distinctions in vent sources, eruptive styles, and depositional environments along the eastern side of the Jemez Mountains volcanic field during this ca. 400,000year interval. Intercalated pyroclastic fall deposits and sandstones of the Pueblo Canyon Member reflect deposition with a basin. Thick Alamo Canyon Member deposits of block-and-ash-flow tuff and pyroclastic fall deposits fill a paleovalley carved into coarse grained sedimentary units reflecting deposition along the mountain front. Chemistry and ages of glass from fall deposits together with clast lithologies of sedimentary units, allow correlation of outcrops, subsurface units, and sources. Dates on pyroclastic fall deposits from Alamo Canyon record deep incision into the underlying Otowi Member in the southern part of the Pajarito Plateau within 100k.y. of the Toledo caldera-forming eruption. Reconstruction of the CTF surface shows that this period of rapid incision was followed by aggradation where sediments largely filled pre-existing paleocanyons. Complex sequences within the upper portion of the Otowi Member in outcrop and in the subsurface record changes in the style of eruptive activity during the waning stages of the Toledo caldera-forming eruption.

Silicate Melt Inclusion Evidence for Extreme Pre-eruptive Enrichment and Post-eruptive Depletion of Lithium in Silicic Volcanic Rocks of the Western United States: Implications for the Origin of Lithium-Rich Brines

To evaluate whether anatectic and/or highly fractionated lithophile element-enriched rhyolite tuffs deposited in arid lacustrine basins lose enough lithium during eruption, lithification, and weathering to generate significant Li brine resources, pre-eruptive melt compositions, preserved in inclusions, and the magnitude of post-eruptive Li depletions, evident in host rhyolites, were documented at six sites in the western United States. Each rhyolite is a member of the bimodal basalt-rhyolite assemblage associated with extensional tectonics that produced the Basin and Range province and Rio Grande rift, an evolving pattern of closed drainage basins, and geothermal energy or mineral resources. Results from the 0.8 Ma Bishop tuff (geothermal) in California, 1.3 to 1.6 Ma Cerro Toledo and Upper Bandelier tephra (geothermal) and 27.9 Ma Taylor Creek rhyolite (Sn) in New Mexico, 21.7 Ma Spor Mountain tuff (Be, U, F) and 24.6 Ma Pine Grove tuff (Mo) in Utah, and 27.6 Ma Hideaway Park tuff (Mo) in Colorado support the following conclusions. Melt inclusions in quartz phenocrysts from rhyolite tuffs associated with hydrothermal deposits of Sn, Mo, and Be are extremely enriched in Li (1,000s of ppm); those from Spor Mountain have the highest Li abundance yet recorded (max 5,200 ppm, median 3,750 ppm). Forty-five to 98% of the Li present in pre-eruptive magma was lost to the environment from these rhyolite tuffs. The amount of Li lost from the small volumes (1–10 km3) of Li-enriched rhyolite deposited in closed basins is sufficient to produce world-class Li brine resources. After each eruption, meteoric water leaches Li from tuff, which drains into playas, where it is concentrated by evaporation. The localized occurrence of Li-enriched rhyolites may explain why brines in arid lacustrine basins seldom have economic concentrations of Li. Considering that hydrothermal deposits of Sn, Mo, Be, U, and F may indicate potential for Li brines in nearby basins, we surmise that the world’s largest Li brine resource in the Salar de Uyuni (10 Mt) received Li from nearby rhyolite tuffs in the Bolivian tin belt.

Obsidian Distribution: Evidence of West to East Movements in the Southern Plains Prior to the Plains Village Tradition

Eleven artifacts visually similar to obsidian were recovered from secure subsurface contexts in a Late Archaic component at the Pipeline site (41PT185/C) near Amarillo, Texas. X-ray florescence analysis of nine pieces yielded chemical results that indicate that eight obsidian pieces came from three separate sources in the Jemez Mountains of north central New Mexico. Two pieces were from El Rechuelos, three pieces were identified as Cerro Toledo Rhyolite, and three pieces were identified as Valles Rhyolite. One piece was chemically similar to modern glass. The radiocarbon dating of this Late Archaic component documents earlier west to east movement of obsidian onto the High Plains, the western section of the southern Plains, prior to the more extensive trading networks envisioned for the subsequent Plains Village tradition (Middle Ceramic period).

Pedogenic carbonate stable isotope record of environmental change during the Neogene in the southern Great Plains, southwest Kansas, USA: Carbon isotopes and the evolution of C4-dominated grasslands

Fossiliferous strata in the Meade Basin (southwest Kansas) preserve numerous superposed mammalian faunas and calcareous paleosols that range in age from the Clarendonian North American Land Mammal Age (NALMA; 12.0–9.0 Ma, early late Miocene) to the early Irvingtonian NALMA (ca. 2.5–ca. 1.0 Ma, early Pleistocene). Faunas from these sections document the evolution of the small mammal community of the modern grassland ecosystem of the region, and the stable isotope composition of paleosol carbonates provides a means by which the environmental context of the evolution of the modern ecosystem may be documented. We used the stable carbon isotope composition (δ 13 C relative to Vienna Peedee belemnite [VPDB]) of 194 pedogenic carbonates from 19 measured sections to reconstruct the history of C 4 grass abundance in the Meade Basin. Paleosol carbonate δ 13 C values reflect the proportion of C 3 (trees, shrubs, cool-climate grasses) and C 4 (warm-climate grasses) plants that grew in an ancient soil and provide a means with which to reconstruct past mammalian habitats. Paleosol carbonate δ 13 C values record a three-phase increase in the abundance of C 4 biomass during the Neogene in the Meade Basin. Late Miocene sections have mean δ 13 C values of −7.6‰ ± 0.90‰ (Clarendonian) and −6.5‰ ± 0.31‰ (Hemphillian NALMA, 9.0–4.9 Ma), consistent with 17% and 26% C 4 biomass, respectively. Miocene δ 13 C values from Meade are statistically identical to published δ 13 C values for Miocene paleosol carbonates elsewhere in the southern Great Plains, supporting the widespread presence of ∼20% C 4 biomass on average in the region throughout the Miocene. The abundance of C 4 biomass increased between the end of the Hemphillian section and the beginning of the early Blancan NALMA (5.0–3.0 Ma). Early and middle Blancan (3.0–2.5 Ma) carbonates have statistically identical δ 13 C values (−4.9‰ ± 0.90‰ and −5.0‰ ± 1.10‰, respectively), suggesting a stable ecosystem during the early Pliocene, although high δ 13 C variability in densely sampled intervals suggests a high degree of landscape-scale variation in C 4 abundance. The final phase, geochronologically controlled by two well-characterized ashes (Huckleberry Ridge, 2.10 Ma; Cerro Toledo B, 1.47–1.23 Ma) and magnetostratigraphy, is a trend to higher δ 13 C values from the late Blancan to early Irvingtonian (ca. 2.5–ca 1.0 Ma) from −4‰ at the base of the section to ∼1‰ at the top, corresponding to an increase from almost 50% to 65% C 4 biomass. The abundance of C 4 biomass first reaches modern levels for the region (78% ± 10.9%) around the level of the Cerro Toledo B ash, indicating that a modern-like grassland ecosystem first appeared in the region ca. 1.3 Ma, although δ 13 C values do not remain consistently high through the rest of the section.

Thermal History of the Bandelier Magmatic System: Evidence for Magmatic Injection and Recharge at 1.61 Ma as Revealed by Cathodoluminescence and Titanium Geothermometry

The rhyolitic Valles caldera complex, New Mexico, is one of the type examples of resurgent calderas and has experienced two well‐studied caldera‐forming eruptions. The first formed the Lower Bandelier Tuff (LBT) at 1.61 Ma, and the second emplaced the Upper Bandelier Tuff (UBT) at 1.22–1.26 Ma. During the time between the LBT and the UBT, the much smaller‐scale Cerro Toledo Rhyolite (CTR) was sporadically erupted. Quartz crystals from these stages of activity were imaged with cathodoluminescence microscopy, and growth zones in certain quartzes, due to varying Ti content, were revealed. Crystallization temperatures were obtained with a titanium‐in‐quartz geothermometer. The LBT quartzes are unzoned, with temperatures clustering between 660° and 715°C when a calculated $$a_{\mathrm{TiO}\,_{2}}$$ of 0.4 is applied to the system. These near‐solidus temperatures imply that the LBT magma chamber was highly crystalline at one point. However, the low crystal content and the widespread presence of resorption features in LBT crystals require that pervasive melting affected the LBT magma chamber at some point before eruption. This melting is hypothesized to result from a hot magmatic injection into the system, with the injection also being a likely trigger of the cataclysmic LBT volcanism. The earliest‐erupted CTR units contain many zoned quartz crystals. Inner zones are usually rounded and invariably reveal cold (∼660°–700°C) cores and hot (∼750°–825°C) rims. We interpret these results as thermal evidence of magmatic recharge, whereby new magma mixed vigorously with leftover magma and high‐temperature rims crystallized around low‐temperature restitic quartz cores. Thermal data for the rest of the CTR record the continuing cooling and evolution of this mixture of magma, while results for the culminating UBT reveal generally unzoned quartz crystals with a roughly constant temperature of 685°–725°C. Altogether, these results present an unprecedented glimpse into the thermal history of the Bandelier magma system, as well as strong evidence concerning the timing and overall importance of magmatic injections in silicic magma systems.

Late Quaternary vegetation, fire and climate history reconstructed from two cores at Cerro Toledo, Podocarpus National Park, southeastern Ecuadorian Andes

The last ca. 20,000 yr of palaeoenvironmental conditions in Podocarpus National Park in the southeastern Ecuadorian Andes have been reconstructed from two pollen records from Cerro Toledo (04°22'28.6"S, 79°06'41.5"W) at 3150 m and 3110 m elevation. Páramo vegetation with high proportions of Plantago rigida characterised the last glacial maximum (LGM), reflecting cold and wet conditions. The upper forest line was at markedly lower elevations than present. After ca. 16,200 cal yr BP, páramo vegetation decreased slightly while mountain rainforest developed, suggesting rising temperatures. The trend of increasing temperatures and mountain rainforest expansion continued until ca. 8500 cal yr BP, while highest temperatures probably occurred from 9300 to 8500 cal yr BP. From ca. 8500 cal yr BP, páramo vegetation re-expanded with dominance of Poaceae, suggesting a change to cooler conditions. During the late Holocene after ca. 1800 cal yr BP, a decrease in páramo indicates a change to warmer conditions. Anthropogenic impact near the study site is indicated for times after 2300 cal yr BP. The regional environmental history indicates that through time the eastern Andean Cordillera in South Ecuador was influenced by eastern Amazonian climates rather than western Pacific climates.

Solanum coalitum (Solanaceae), a New Endemic Species from Southern Ecuador

A new endemic species of Solanum L. sect. Holophylla (G. Don) Walpers s.l. is described from Ecuador: Solanum coalitum S. Knapp is only known from the páramo of Cerro Toledo in Parque Nacional Podocarpus in the province of Loja. Solanum coalitum had been confused with the more widespread S. stenophyllum Dunal; its differences from that species are detailed and its species group membership and potential relationships within section Holophylla are discussed. The species is illustrated and given a preliminary conservation assessment of Endangered.

Late Pliocene and early Pleistocene rodents from the northern Borchers Badlands (Meade County, Kansas), with comments on the Blancan-Irvingtonian boundary in the Meade Basin

New fossiliferous localities in the Borchers Badlands of southwestern Kansas add to our knowledge of rodent community change across the Plio-Pleistocene and Blancan-Irvingtonian boundaries. We report fossil rodents from ten local faunas in the Badlands that range stratigraphically from beneath the Huckleberry Ridge ash (2.10 Ma [million years ago]) to a level just beneath the Cerro Toledo B ash (1.23–1.47 Ma). The late Blancan Borchers local fauna (l.f.), includes the Meade Basin highest stratigraphic datum (HSD) for the following taxa that characterize or are found in earlier Blancan faunas:Alilepus, Geomys quinni, Sigmodon minor, andGeochelone. Borchers currently also has the HSDs forReithrodontomys pratincolaandOndatra zibethicus lidahoensis, but the prior temporal distribution of these taxa in the Meade Basin is unknown. The stratigraphically lowest Pleistocene (Irvingtonian) l.f. in the Badlands, Nash 72, includes the lowest stratigraphic datum (LSD) forCynomys, Reithrodontomys moorei, Microtus, andMictomys kansasensis, all of which are found above Nash 72 and beneath the Cerro Toledo B ash.Prodipodomysis last seen at Nash 72, andSigmodon curtisiis first encountered at Short Haul, a locality slightly younger than Nash 72. A preliminary hypothesis of age based on stratigraphic position places the Nash 72 l.f. at about 1.80 Ma, suggesting that this fauna and the genusMicrotusmay characterize both the Plio-Pleistocene and Blancan-Irvingtonian boundaries in the Borchers Badlands.

LATE PLIOCENE AND EARLY PLEISTOCENE RODENTS FROM THE NORTHERN BORCHERS BADLANDS (MEADE COUNTY, KANSAS), WITH COMMENTS ON THE BLANCAN-IRVINGTONIAN BOUNDARY IN THE MEADE BASIN

Abstract New fossiliferous localities in the Borchers Badlands of southwestern Kansas add to our knowledge of rodent community change across the Plio-Pleistocene and Blancan-Irvingtonian boundaries. We report fossil rodents from ten local faunas in the Badlands that range stratigraphically from beneath the Huckleberry Ridge ash (2.10 Ma [million years ago]) to a level just beneath the Cerro Toledo B ash (1.23–1.47 Ma). The late Blancan Borchers local fauna (l.f.), includes the Meade Basin highest stratigraphic datum (HSD) for the following taxa that characterize or are found in earlier Blancan faunas: Alilepus, Geomys quinni, Sigmodon minor, and Geochelone. Borchers currently also has the HSDs for Reithrodontomys pratincola and Ondatra zibethicus /idahoensis, but the prior temporal distribution of these taxa in the Meade Basin is unknown. The stratigraphically lowest Pleistocene (Irvingtonian) l.f. in the Badlands, Nash 72, includes the lowest stratigraphic datum (LSD) for Cynomys, Reithrodontomys moorei,...

Oxygen isotope disequilibrium between quartz and sanidine from the Bandelier Tuff, New Mexico, consistent with a short residence time of phenocrysts in rhyolitic magma

Oxygen isotope analyses are reported from co-existing quartz and feldspar from the Bandelier Tuff and Cerro Toledo high-silica rhyolitic pyroclastic deposits erupted from the Valles caldera, New Mexico. Quartz shows little variation outside analytical error, but δ 18O in feldspar varies over >1‰. In most samples, 18O/ 16O fractionation between quartz and feldspar is significantly less than is predicted for equilibrium at temperatures appropriate for rhyolitic magma. In the Tshirege (upper) Member of the Bandelier Tuff, isotopic fractionation between mineral pairs is close to equilibrium in the later erupted ignimbrite, but non-equilibrium in the initial Plinian deposit. These relationships are interpreted in terms of a model where most phenocrysts are derived from a highly porphyritic carapace around the magma chamber that was disrupted by eruption, thus scattering crystals throughout the magma. Carapace quartz and feldspar are initially isotopically lighter than the bulk aphyric magma, due to chemical communication with low-δ 18O country rock in the meteoric/hydrothermal system surrounding the chamber. We assume that quartz and feldspar were initially in isotopic equilibrium. Diffusive re-equilibration of crystals begins when the carapace disintegrates and the minerals are immersed in the bulk magma just prior to and during eruption. Feldspar is isotopically lighter than quartz at equilibrium, but responds more rapidly than quartz to an external change, due to a higher diffusion coefficient for oxygen. Hence, immersion in the isotopically heavier bulk magma causes feldspar and quartz δ 18O values to initially converge over ∼10 2 years, and then diverge over 10 3–10 4 years as first feldspar, and then quartz, re-equilibrate with the new magma. Higher δ 18O variability of feldspar than quartz indicates that the shorter timescale applies to the Bandelier and Cerro Toledo rhyolites. Two important implications of this interpretation are (1) that the Bandelier magmas developed in an aphyric condition, and their porphyritic character is an artifact of eruption; and (2) that a protective, mechanically rigid cognate carapace around a silicic magma chamber may limit interaction with low-δ 18O hydrothermally altered crust, thus hindering the development of significant volumes of low-δ 18O silicic magma.

Cerro Toledo Rhyolite, Jemez Volcanic Field, New Mexico: 40Ar/39Ar geochronology of eruptions between two caldera-forming events

The Cerro Toledo Rhyolite comprises a group of domes and tephra which were erupted during the interval between two caldera-forming ignimbrites, the Tshirege Member and Otowi Member of the Bandelier Tuff, in the Jemez Volcanic Field, New Mexico. To provide a chronologic framework for geochemical and isotopic studies on these rhyolites, which record the evolution of the Bandelier magma system during this interval, a 40 Ar/ 39 Ar geochronology study was undertaken. Pumice from major pyroclastic fall deposits within the rhyolite tephra and samples from the rhyolite domes were dated as well as the stratigraphically bracketing Bandelier Tuff. Analyzed crystal populations range from being fairly homogeneous juvenile material to very heterogeneous mixed juvenile and xenocrystic assemblages. In most cases dominant groups of juvenile sanidine crystals define 40 Ar/ 39 Ar ages which agree with stratigraphic constraints. Plagioclase analyses are distinctly more scattered and do not typically define reasonable ages. The 40 Ar/ 39 Ar ages for the two members of the Bandelier Tuff yield an interval of 380 ± 20 k.y. between these caldera-forming eruptions. During this interval nine major pyroclastic pumice units were deposited in the sections studied, for which six yield isochron ages, one a weighted mean age, one a maximum age, and one no reliable age due to lack of sanidine. 40 Ar/ 39 Ar dates on pumice fall units within the Cerro Toledo Rhyolite tephra indicate that eruptive activity occurred at >1.59, 1.54, 1.48, 1.37 and 1.22 Ma. 40 Ar/ 39 Ar dating of Cerro Toledo Rhyolite domes indicates these were erupted within the caldera at 1.54, 1.45, 1.38–1.34, and 1.27 Ma. The dates obtained indicate that eruptive activity occurred throughout the 380 k.y. interval between the two members of the Bandelier Tuff, but suggest that eruptions producing both tephra and domes occurred during discrete intervals at ca. 1.54, 1.48, and 1.38–1.34 Ma. The interval from 1.34 to 1.38 Ma was particularly active; 7 of 18 units dated are these ages.

Gas saturation and evolution of volatile and light lithophile elements in the Bandelier magma chamber between two caldera‐forming eruptions

We have studied the distribution of light and volatile elements (Li, Be, B, H2O, F, Cl) in matrix glasses and melt inclusions in quartz and sanidine phenocrysts from tephras of the Cerro Toledo Rhyolite, which were erupted from the Bandelier magma chamber between two caldera‐forming eruptions at 1.608 Ma and 1.225 Ma. Since the small‐volume tephras of the Cerro Toledo Rhyolite record chemical evolution of the upper parts of the magma chamber during this 383‐kyr period, we can track volatile evolution in the magma during its differentiation, specifically, the development of a separate fluid phase from the magma, the partitioning of volatile and light elements between this fluid and the magma, and the timing of the second caldera eruption at 1.225 Ma. The melt inclusion data reveal that Li, Be, and B were progressively enriched with time at the top of the magma chamber, showing a similar three fold enrichment. By contrast, F, Cl, and F2O show more variable behavior. F was enriched 3.6 times in the magma and Cl increased 2.5 times, while water concentrations remained constant. Evidence for a separate fluid phase includes (1) comparatively small magmatic enrichment factors for Cl and H2O, elements which are known to partition into fluid, (2) decline of the Cl/Be and Cl/B ratios in melt inclusions with time, indicating preferential loss of Cl, and (3) maximum Cl contents of 2900–3000 ppm in melt inclusions, which are concentrations at or close to the saturation limit for Cl in a two‐phase gas‐saturated magma. The lack of temporal H2O enrichment in the magma suggests that it became gas saturated at an early stage. The Cl fluid‐magma partition coefficient was initially low, due to the presence of a low‐salinity single‐phase vapor. The fluid is calculated to have increased its salinity from 0.76 wt % equivalent NaCl to 3.1 wt % NaCl by crystallization and Cl enrichment in the magma. Consequently, the fluid was transformed to two immiscible phases. As a result, the Cl partition coefficient increased, and the Cl content in the magma was buffered at 2900–3000 ppm. Overpressures in the magma chamber have been modeled as a function of crystallization, total pressure and depth, H2O solubility in rhyolite, resurgence, crystallization contraction, and initial fluid mass. For the large amounts of crystallization (40–70%) required by the geochemical relations, unrealistically large overpressures (>75 MPa) are indicated, unless (1) the magma existed as a foam or (2) the chamber was able to degas passively, and thus buffer the buildup of pressure. To maintain realistic overpressures in the magma chamber (<50 MPa), an equilibrium was required between gas buildup by crystallization and volatile loss by passive degassing. The change from a one‐phase vapor to a two‐phase immiscible fluid before the Upper Bandelier Tuff eruption may have promoted partial or complete sealing of the magmatic‐hydrothermal system, permitting significant overpressures to develop. The result could have been a cataclysmic caldera‐forming eruption.

Plio-pleistocene pumice floods in the ancestral Rio Grande, southern Rio Grande rift, USA

At least four times during the late Pliocene and early Pleistocene pyroclastic eruptions in the Jemez volcanic field, northern Rio Grande rift, flooded the ancestral Rio Grande with gravel-sized pumice. Following as much as 400 km of fluvial transport, the pumice was deposited in beds 0.2 to 2.0 m thick in the Camp Rice Formation of the southern Rio Grande rift. A combination of reversal magnetostratigraphy and single-crystal sanidine 40Ar/39Ar dating constrains the ages of pumice-clast conglomerates at 3.1, ∼2.0, 1.6, and 1.3 Ma. The coarsest pumice beds (cobbles, boulders) were deposited as antidune-like bedforms in a fluvial channel and as a crevasse-splay sheet. Granule and pebble-sized pumice was deposited as dune bedforms in fluvial channels and as ripple bedforms on the floodplain. The abundance of pumice clasts in the gravel fraction (60–100%) suggests very rapid transport downriver, probably in a few days or weeks. The two older pumice-clast conglomerates correlate with the Puye Formation in the Jemez volcanic field, whereas the younger two are coeval to the Lower Bandelier Tuff and Cerro Toledo Rhyolite.

Two New Species of Fuchsia Section Fuchsia (Onagraceae) from Southern Ecuador

Two new species of Fuchsia sect. Fuchsia (Onagraceae) from the Andes of southern Ecuador are described and illustrated. Fuchsia campii P. E. Berry is known from mid-elevation cloud forest of Azuay and Loja Provinces, and Fuchsia summa P. E. Berry is a high-elevation species currently known only from Loja Province. Both occur in Podocarpus National Park, together with several other rare species of Fuchsia. Studies and collections of plants from southern Ecuador have increased dramatically in the past decade, especially in areas such as Podocarpus National Park in Loja Province. Many novel plants have been located, and this paper describes two new species of Fuchsia that occur in cloud forest areas on the slopes of Cerro Toledo, one of them also known further north in Azuay Province. Three other species previously thought to be extremely rare in southern Ecuador are also known from Cerro Toledo: E andrei I. M. Johnston, E scherffiana Andre, and E steyermarkii P. E. Berry. All these taxa belong to the largest section of the genus, section Fuchsia, which now approaches 65 species. They are also examples of the high degree of local endemism in cloud forests of southern Ecuador, where moist montane habitats are often separated by dry valleys and show a wide range of precipitation regimes. Fuchsia campii P. E. Berry, sp. nov. TYPE: Ecuador. Azuay: Quebradas leading into the Rio Collay, 3-8 km N of Sevilla de Oro, 70008300 ft., 27 Aug. 1945, W H. Camp E-4994 (holotype, RSA herbarium # 71952; isotypes, G-DEL, MO, NY, UC, US). Figure 1. Frutex 1.5-4 m altus, foliis 3-vel 4-verticillatis, interdum oppositis, 3-9 X 1-3 cm, margine subintegro vel 710-dentato, floribus axillaribus apicem versus, pedicellis 18-30 mm longis, tubo florali roseo 29-45 mm longo, sepalis lanceolatis 12-15 mm longis, petalis auriantiacis 811 mm longis, 4-6 mm latis. Erect to recumbent shrub 1.5--4 m tall, well branched with mostly ascending branches; young growth pubescent, the trichomes 0.1-0.5 mm long, appressed to erect; branchlets terete to slightly angled, older branches with purplish, exfoliating bark. Leaves mostly in whorls of 3 or 4, sometimes opposite or subopposite; blade membranous, narrowly elliptic, 3-9 cm long, 1-3 cm wide, acute to acuminate at the apex, acute at the base, subglabrous to sparsely strigose when young on both surfaces and margin, trichomes persisting mainly along the midvein and secondary nerves on lower surface when fully expanded, upper surface smooth, shiny, and light to dark green, lower surface paler green; margin nearly entire, usually with 7-10 glandular teeth projecting slightly from the edge especially in the upper ? to 2/3 of the blade; secondary nerves (5-)8-10 on either side of the midvein; petiole strigose, (4-)6-25 mm long; stipules narrowly lanceolate when young, 1-1.5 mm long, ca. 0.2 mm wide, the tip quickly abscising and the thicker lower third persisting or abscising later. Flowers axillary in the upper leaf axils, 2-several per node, pedicel 18-30 mm long; floral tube narrowly funnelform, (29-)32-45 mm long, 2.5-3.5 mm wide at the base, narrowed to 2-2.5 mm wide in the lower ?, then gradually widened until 5--8 mm wide at the rim, sparsely strigose outside, densely pubescent inside in the lower narrowed portion; nectary a doughnutshaped ring 1-2 mm high and 2-3 mm wide at the base of the tube surrounding the style; ovary 4-angled, 5--6 mm long, 2-3 mm thick; sepals narrowly triangular or lanceolate, 12-15 mm long, 4-5 mm wide at the base; petals elliptic to obovate, 8-11 mm long, 46 mm wide, broadly acute at the apex, sometimes with a small mucro; tube and sepals bright pink except for the green sepal tips, petals orange and darker than the tube; style pink, 40-64 mm long, densely pubescent in lower third, stigma pink, capitate, ca. 2 mm high, ca. 2.5 mm wide; filaments 10-12 mm and 79 mm long, anthers oblong, 2-3 mm long, 1-1.5 mm wide. Fruit oblong-ellipsoid before maturity, subrotund when ripe, 9-15 mm long, 5-9 mm thick; seeds flattened, obtriangular in outline, 1.8-2.2 mm long, 1.2-1.6 mm wide, +200 per fruit. Gametic chromosome number n = 11. Ecology and distribution. Occurring in thickets, along streams, and along roadsides in pasture zones on moist mountain slopes, 2300-2700 (-3350) m, in Azuay and Loja Provinces, Ecuador. NovoN 5: 318-322. 1995. This content downloaded from 157.55.39.184 on Sun, 15 May 2016 04:31:27 UTC All use subject to http://about.jstor.org/terms Volume 5, Number 4 Berry 319 1995 Fuchsia from Southern Ecuador

Replenishment and crystallization in epicontinental silicic magma chambers: evidence from the Bandelier magmatic system

The Cerro Toledo Rhyolite (Jemez volcanic field, New Mexico) records the volcanism that occurred after the eruption of the Lower Bandelier Tuff ignimbrite, which formed Toledo caldera at 1.51 ± 0.03 Ma. Pumice samples from the top of this ignimbrite and from the base of the Cerro Toledo Rhyolite tephra sequence are stratigraphically and geochemically distinct from younger Cerro Toledo Rhyolite tephras that overlie this basal suite. All samples exhibit decreasing La/Lu with increasing Lu concentrations. For a given Lu content, however, the Lower Bandelier Tuff and basal member Cerro Toledo Rhyolites have higher La/Lu compared to overlying Cerro Toledo Rhyolites. This difference can be explained either by (1) differentiation of a single batch of magma in which trace mineral solubilities increased with time due to higher volatile contents, or (2) replenishment of the magma chamber by an input of silicic magma after caldera collapse at 1.51 Ma. Large-scale replenishment of epicontinental silicic magma chambers may be restricted to timescales of 10 5 years.

New Species of Pentacalia (Senecioneae: Asteraceae) from Ecuador, Peru, and Bolivia

New Species of Pentacalia (Senecioneae: Asteraceae) from Ecuador, Peru, and Bolivia

Variations in trace element partition coefficients in sanidine in the Cerro Toledo Rhyolite, Jemez Mountains, New Mexico: Effects of composition, temperature, and volatiles

Trace element partition coefficients have been measured for one plagioclase and five sanidine mineral separates from the Cerro Toledo Rhyolite, New Mexico. Sanidine partition coefficients vary substantially and systematically within the Cerro Toledo Rhyolite. Partition coefficients for Ca, Sr, Zn, La, and Eu are lowest in the most evolved rhyolites, whereas Sm and HREE partition coefficients are highest. Rubidium partition coefficients remain constant, while those for Ba, Ce, and Th are variable. Variations of the Sr, Zn, La, and Eu partition coefficients are correlated with the Ca contents and partition coefficients of the sanidines. Calcium may have controlled the distribution of these elements in the sanidine by modifying the feldspar structure. The low Ca partition coefficients in sanidines for the most evolved rhyolites may be the consequence of modification of the melt structure, possibly due to increased volatile contents at the top of the magma chamber(s) during evolution of the Cerro Toledo Rhyolite. The Zn and La partition coefficients between sanidine and melt also may have been controlled by this change in melt structure. Modelling using major elements and the constant Rb partition coefficient for sanidine indicates 70% crystallization of magma during Cerro Toledo Rhyolite time by removal of 68% sanidine and 32% quartz. Estimates of the volume (1) of initial parental magma and (2) of the magma that crystallized during this period are 11,670 km 3 and 8170 km 3, respectively. The average intrusion rate of silicic magma during Cerro Toledo Rhyolite activity was 35 × 10 −3 km 3/a.

40Ar/39Ar dating of the Bandelier Tuff and San Diego Canyon ignimbrites, Jemez Mountains, New Mexico: Temporal constraints on magmatic evolution

Abstract The Jemez Mountains volcanic field (JMVF), located in north-central New Mexico, has been a site of basaltic to rhyolitic volcanism since the mid-Miocene with major caldera forming eruptions occurring in the Pleistocene. Eruption of the upper Bandelier Tuff (UBT) is associated with collapse of the Valles Caldera, whereas eruption of the lower Bandelier Tuff (LBT) resulted in formation of the Toledo Caldera. These events were previously dated by K-Ar at 1.12 ± 0.03 Ma and 1.45 ± 0.06 Ma, respectively. Pre-Bandelier explosive eruptions produced the San Diego Canyon (SDC) ignimbrites. SDC ignimbrite “B” has been dated at 2.84 ± 0.07 Ma, whereas SDC ignimbrite “A”, which underlies “B”, has been dated at 3.64 ± 1.64 Ma. Both of these dates are based on single K-Ar analyses. 40Ar/39Ar dating of single sanidine crystals from these units indicates revision of the previously reported dates. Isochron analysis of 26 crystals from the UBT gives a common trapped 40Ar/36Ar component of 304.5, indicating the presence of excess 40Ar in this unit, and defines an age of 1.14 ± 0.02 Ma. Isochron analysis of 26 crystals from the LBT indicates an atmospheric trapped component and an age of 1.51 ± 0.03 Ma. An age of 1.78 ± 0.04 Ma, based on the weighted mean of 5 individual analyses, is indicated for SDC ignimbrite “B”, whereas 3 analyses from SDC ignimbrite “A” give a weighted mean age of 1.78 ± 0.07 Ma. Evidence for xenocrystic contamination in the SDC ignimbrites comes from analyses of a correlative air-fall pumice unit in the Puye Formation alluvial fan giving ages of 1.75 ± 0.08 and 3.50 ± 0.09 Ma. The presence of xenocrysts in bulk separates used for the original K-Ar analyses could account for the significantly older ages reported. Geochemical data indicate that SDC ignimbrites are early eruptions from the magma chamber which evolved to produce the LBT, as compositions of SDC ignimbrite “B” are virtually identical to least evolved LBT samples. Differentiation during the 270-ka interval between eruption of SDC ignimbrite “B” and the LBT produced an array of high-silica rhyolite compositions which were erupted to form the LBT. Mixed pumices associated with eruption of the LBT indicated an influx of more mafic magma into the system which produced shifts in some incompatible trace-element ratios. Lavas and tephras of the Cerro Toledo Rhyolite record the geochemical evolution of the Bandelier magma system during the 370-ka interval between eruption of the LBT and the UBT. The combined geochronologic and geochemical data place the establishment and evolution of the Bandelier silicic magma system within a precise temporal framework, beginning with eruption of the SDC ignimbrites at 1.78 Ma, and define a periodicity of 270–370 ka to ash-flow eruptions in the JMVF. These intervals are comparable to those in other multicyclic caldera complexes and are a measure of the timescales over which substantial fractionation of large silicic magma bodies occur.