蒙古南戈壁中洛霍考夫阶(泥盆系)牙形刺的首次发现

蒙古南戈壁新金斯特(Shine Jinst)地区Ulaan-Shand 剖面的查干安普拉格(Tsagaanbulag)组以前曾划归志留系(文洛克统至普里多利统). 但在Tsagaanbulag组及其上部的阿曼采尔(Amansair)组发现了非常重要的牙形刺, 包括Lanea omoalpha, Amydrotaxis johnsoni, “Ozarkodina” planililingua, Pedavis sp., 清楚地指明这两个组应当归下泥盆统中洛霍考夫阶. 中洛霍考夫阶的海相地层在中国和蒙古国广泛分布. 志留系文洛克统和洛德罗统下部的海相地层在蒙古是否存在是值得注意的问题.     

Rb-sr dating of epithermal vein mineralization stages in the eastern Harz Mountains (Germany) by paleomixing lines

A method is evaluated that enables the dating of binary isotopic paleomixing in hydrothermal alteration assemblages by iterative reconstruction and regression of corresponding two-component mixing lines from conventional Rb-Sr data. The model has been applied to illite-bearing granulometric fractions of hydrothermally altered sedimentary rocks associated with epithermal vein mineralization in the eastern Harz Mountains, Germany. These veins are characterized by a principal quartz-sulfide stage containing quartz, base metal sulfides, and siderite and a subsequent dominant calcite-fluorite-quartz stage. Rb-Sr analyses were performed on untreated granulometric fractions, HCl-treated residues, corresponding HCl leachates, and cogenetic vein minerals obtained from two silicified rock samples related to the quartz-sulfide and the calcite-fluorite-quartz mineralization, respectively.Neither the untreated nor the HCl-leached fractions of these rock samples yield statistically robust and geochronologically meaningful isochrons. When applying the binary mixing model, however, two well-defined paleomixing lines can be reconstructed for the HCl-treated fractions of the rock samples and associated vein minerals at model ages of 226 ± 1 Ma (quartz-sulfide alteration) and 209 ± 2 Ma (calcite-fluorite-quartz alteration). We examine the significance and reliability of these model ages and the corresponding paleomixing lines by means of statistical and geological criteria and discuss the effects of leaching experiments performed on the granulometric fractions using 1 N HCl as well as the nature and origin of the components dissolved in the acid leachates.Our results suggest that the mixing model provides a successful dating concept for isotopic disequilibrium processes during low-temperature hydrothermal events that produce binary mixtures among newly formed alteration phases.     

Origin and history of waters associated with coalbed methane: I, Cl, and stable isotope results from the Fruitland Formation, CO and NM

The Fruitland Formation of the San Juan Basin was deposited during the late Cretaceous and is associated with significant reservoirs of coalbed methane (CBM). The purpose of this study is to determine the origin and history of waters associated with the formation, using long-lived cosmogenic and stable isotope systems. Ratios of ¹²⁹I/I and stable isotope values (δD and δ¹⁸O) were determined in waters from close to 100 wells, ³⁶Cl/Cl ratios for a subset of these samples. A significant group of samples has ¹²⁹I/I ratios between 100 × 10⁻¹⁵ and 200 × 10⁻¹⁵, indicating minimum iodine ages close to 60 Ma. If these ages are corrected for the addition of fissiogenic ¹²⁹I, they are compatible with the depositional age of the Fruitland Formation (Late Cretaceous).Several sets of waters are clearly present within the data. A group dominated by infiltration of recent surface waters is restricted to the uplifted basin margins, with a lateral extent of less than 5 km from outcrop, and is characterized by ¹²⁹I/I ratios in excess of 1500 × 10⁻¹⁵ and meteoric δD, δ¹⁸O, and ³⁶Cl/Cl signatures. The rest of the basin is characterized by several subsets of formation waters which have undergone variable degrees of iodine enrichment through diagenesis as well as variable degrees of dilution. The first subgroup is found in coals of relatively low vitrinite reflectance and moderate enrichment of iodine. This subgroup predominantly consists of entrapped pore fluids, although it may also contain waters which infiltrated the coals at the time of the Laramide uplift, between 25 and 30 Ma. A second subgroup consists of formation waters associated with coals of high vitrinite reflectance. Despite subsequent uplift, the high iodine concentrations and low ¹²⁹I/I ratios of this subgroup, as well as a moderate depletion of deuterium relative to ¹⁸O, suggest that these waters were not significantly altered since the time when diagenetic reactions occurred in the deepest portion of the basin. A third subgroup, with higher δD and δ¹⁸O values as well as higher ¹²⁹I/I ratios, extends roughly west to east at the New Mexico-Colorado state line and corresponds to a region of extensive fracturing of the coalbeds. In this case, the higher ¹²⁹I/I ratios are probably due to contributions of fissiogenic ¹²⁹I through fracture flow, perhaps from deeper formation waters. Our results do not support models of subsequent basin-wide groundwater migration in the Fruitland Formation. The combined use of ¹²⁹I and ³⁶Cl with stable isotope studies provides valuable information as to the hydrologic history of coalbed methane deposits, as well as their potential for commercial exploitation.     

Grazing impact on forage quality and macronutrient content of rangelands in Qilian Mountains,NW China

An important indicator of the rangeland health, associated with land degradation, is the ability of semi-natural rangelands to provide forage of sufficient quality for livestock production. In Qilian Mountains(Gansu Province, NW China) biomass production and forage quality are dependent on the seasonality of precipitation and temperature; most of the precipitation falls during summer season, when sheep, goats and yaks graze mountain rangelands. To sustain the rangelands and to improve the management strategies, the assessment of the forage quality should be implemented. The purpose of this research was to study the response of biomass, forage quality and macronutrient content different levels of grazing intensity in Qilian rangelands. We sampled aboveground biomass in the growing seasons in 2012 and 2013 within spring/autumn or summer grazing regimes in two altitudinal zones below and above 3000 m a.s.l.(montane-subalpine and subalpine-alpine respectively). In order to estimate forage quality, biomass was sampled in 1 m × 1 m plots, assigned to the center of 10 ×10 m sites, fromwhich we collected different indicator parameters of rangeland health. Mineral and fiber content of forage biomass was estimated under different levels of grazing intensity with regard to the growing period. It was found that an increase in grazing intensity led to a decrease in dry matter weight. No linearity was observed in the relationship between nutritive value and grazing intensity. The highest fiber content(59.20 %) was found in plots mostly disturbed by grazing. The highest protein(16.30 %) and the lowest fiber(51.30 %) contents were associated with slightly grazing intensity. Concentrations of the mineral elements, such as Zn, P, K and S varied significantly and showed maximum values under low grazing intensity.     

The CM carbonaceous chondrite regolith Diepenveen

A carbonaceous chondrite was recovered immediately after the fall near the village of Diepenveen in the Netherlands on October 27, 1873, but came to light only in 2012. Analysis of sodium and poly‐aromatic hydrocarbon content suggests little contamination from handling. Diepenveen is a regolith breccia with an overall petrology consistent with a CM classification. Unlike most other CM chondrites, the bulk oxygen isotopes are extremely ¹⁶O rich, apparently dominated by the signature of anhydrous minerals, distributed on a steep slope pointing to the domain of intrinsic CM water. A small subset plots closer to the normal CM regime, on a parallel line 2 ‰ lower in δ¹⁷O. Different lithologies in Diepenveen experienced varying levels of aqueous alteration processing, being less aqueously altered at places rather than more heated. The presence of an agglutinate grain and the properties of methanol‐soluble organic compounds point to active impact processing of some of the clasts. Diepenveen belongs to a CM clan with ~5 Ma CRE age, longer than most other CM chondrites, and has a relatively young K‐Ar resetting age of ~1.5 Ga. As a CM chondrite, Diepenveen may be representative of samples soon to be returned from the surface of asteroid (162173) Ryugu by the Hayabusa2 spacecraft.     

Environmental responses of jellyfish polyps as drivers of medusa populations off the coast of Namibia

Jellyfish populations in the southeastern Atlantic off the coast of Namibia have increased subsequent to the decline of small pelagic fisheries at the end of the 1960s, although the environment there has also become warmer and the waters off Walvis Bay have become richer in zooplankton in recent years. Laboratory experiments were conducted with the scyphozoan jellyfish Chrysaora fulgida to investigate the effects of food density (0, 30, 70, 100 or 150 Artemia nauplii 200 ml^?1), feeding frequency (once daily or once every third day) and water temperature (12, 16 or 20 °C) on the asexual reproduction, growth and development of polyps. The results of a generalised linear mixed-effects model reveal that all variables impacted asexual reproduction, with greater polyp production attained at higher food concentrations, increased feeding frequencies and increased temperatures. The most common mode of asexual reproduction was by lateral budding. These laboratory results suggest that polyps of C. fulgida may have proliferated off Namibia in recent times, which would contribute to increased numbers of jellyfish there.     

Hydrous olivine alteration on Mars and Earth

Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars.     

POSTFIRE SUCCESSION IN AN ADIRONDACK FOREST*

ABSTRACT. Landscape diversity has increased with the surprising postfire establishment of aspen at upper elevations (700–945 meters above sea level) in the High Peaks of Adirondack Park in upstate New York. Tree seedlings returned quickly to the charred slopes west of Noonmark Mountain after an accidental fire consumed the forest in 1999. Aspen stands have replaced the spruce‐fir‐birch forests in the burned area even though mountain paper birch is expected to colonize burned sites at these elevations. Environmental conditions, historical events, and unique circumstances help explain why quaking aspen and bigtooth aspen rather than paper birch blanket the burned mountainside. Climate change over the past century to warmer, wetter conditions may have fostered this marked shift in species composition. In the unburned firebreak that people cleared to contain the flames, pin cherry has regenerated from seeds stored in the soil for nearly a century. The history of pin cherry on the site suggests that large fires or severe windthrow may have been more common in the region than was previously documented.