Ammonium in aqueous fluids to 600 °C, 1.3 GPa: A spectroscopic study on the effects on fluid properties, silica solubility, and K-feldspar to muscovite reactions

The behavior of ammonium, NH₄⁺, in aqueous systems was studied based on Raman spectroscopic experiments to 600 °C and about 1.3 GPa. Spectra obtained at ambient conditions revealed a strong reduction of the dynamic three-dimensional network of water with addition of ammonium chloride, particularly at small solute concentrations. The differential scattering cross section of the ν₁-NH₄⁺ Raman band in these solutions was found to be similar to that of salammoniac.The Raman band of silica monomers at ∼780 cm⁻¹ was present in all spectra of the fluid at high temperatures in hydrothermal diamond-anvil cell experiments with H₂O ± NH₄Cl and quartz or the assemblage quartz + kyanite + K-feldspar ± muscovite/tobelite. However, these spectra indicated that dissolved silica is less polymerized in ammonium chloride solutions than in comparable experiments with water. Quantification based on the normalized integrated intensity of the H₄SiO₄⁰ band showed that the silica solubility in experiments with H₂O + NH₄Cl was significantly lower than that in equimolal NaCl solutions. This suggests that ammonium causes a stronger decrease in the activity of water in chloridic solutions than sodium.The Raman spectra of the fluid also showed that a significant fraction of ammonium was converted to ammonia, NH₃, in all experiments at temperatures above 300 °C. This indicates a shift towards acidic conditions for experiments without a buffering mineral assemblage. The estimated pH of the fluid was ∼2 at 600 °C, 0.26 GPa, 6.6 m initial NH₄Cl, based on the ratio of the integrated ν₁-NH₃ and ν₁-NH₄⁺ intensities and the HCl⁰ dissociation constant. The NH₃/NH₄⁺ ratio increased with temperature and decreased with pressure. This implies that more ammonium should be retained in K-bearing minerals coexisting with chloridic fluids upon high-P low-T metamorphism. At 500 °C, 0.73 GPa, ammonium partitions preferentially into the fluid, as constrained from infrared spectroscopy on the muscovite and from mass balance.The conversion of K-feldspar to muscovite proceeded much faster in experiments with NH₄Cl solutions than in comparable experiments with water. This is interpreted as being caused by enhancement of the rate-limiting alumina solubility, suggesting complexation of Al with NH₄. Nucleation and growth of mica at the expense of K-feldspar and NH₄⁺/K⁺ exchange between fluid and K-feldspar occurred simultaneously, but incorporation of NH₄⁺ into K-feldspar was distinctly faster than K-feldspar consumption.     

Determination of Total Organic Carbon Content and δ13C in Carbonate-Rich Detrital Sediments

The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (C_org) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble C_org respectively. In Himalayan and Amazon river sediments, the proportion of C_org solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the C_org content for the dissolved organic carbon content measured after decarbonation. Data presented here show that C_org dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment.     

Une méthode globale d'estimation des températures des réservoirs alimentant les sources thermales. Exemple du Massif Central Français

A chemical model based on the equilibrium of water with quartz, albite, adularia, calcite, kaolinite or illite, and chlorite can explain the chemical composition of the main groups of hot springs in Massif Central. Temperature is the principal variable for determining this composition. Model temperatures generally agree with those given by classical cation geothermometers (t ? 135–150° C for Vichy. La Bourboule. Evaux and Châteauneuf; t ? 175–180° C for Chaudes Aigues and Saint Nectaire). The model fails to represent the composition of Mont Dore waters: the high temperatures given by classical geothermometers are considered doubtful.     

A Preliminary Study of the Physiography of the Foochow Basin

正 TOPOGRAPHIC SETTING Foochow City lies about 34 miles above the mouth of the Min River at approximately 119 degrees East Longitude and 26 degrees North Latitude.Foochow Basin(Pl. 1)contains about 150 square miles. It is surrounded on     

Determining the trophic guilds of fishes and macroinvertebrates in a seagrass food web

We established trophic guilds of macroinvertebrate and fish taxa using correspondence analysis and a hierarchical clustering strategy for a seagrass food web in winter in the northeastern Gulf of Mexico. To create the diet matrix, we characterized the trophic linkages of macroinvertebrate and fish taxa present inHalodule wrightii seagrass habitat areas within the St. Marks National Wildlife Refuge (Florida) using binary data, combining dietary links obtained from relevant literature for macroinvertebrates with stomach analysis of common fishes collected during January and February of 1994. Heirarchical average-linkage cluster analysis of the 73 taxa of fishes and macroinvertebrates in the diet matrix yielded 14 clusters with diet similarity ≥ 0.60. We then used correspondence analysis with three factors to jointly plot the coordinates of the consumers (identified by cluster membership) and of the 33 food sources. Correspondence analysis served as a visualization tool for assigning each taxon to one of eight trophic guilds: herbivores, detritivores, suspension feeders, omnivores, molluscivores, meiobenthos consumers, macrobenthos consumers and piscivores. These trophic groups, corss-classified with major taxonomic groups, were further used to develop consumer compartments in a network analysis model of carbon flow in this seagrass ecosystem. The method presented here should greatly improve the development of future network models of food webs by providing an objective procedure for aggregating trophic groups.     

Coesite and pure pyrope in high-grade blueschists of the Western Alps: a first record and some consequences

A pyrope-quartzite originally described by Vialon (1966) from the Dora Maira massif was resampled and reinvestigated. Garnet (up to 25 cm in size), phengite, kyanite, talc and rutile are in textural equilibrium in an undeformed matrix of polygonal quartz. The garnet is a pyrope-almandine solid solution with 90 to 98 mol % Mg end-member. It contains inclusions of coesite which has partially inverted to quartz, resulting in a typical radial cracking of the host garnet around the inclusions. Several lines of evidence show that coesite crystallised under nearly static pressure conditions and that the whole matrix has once been coesite. The formidable pressures of formation implied (≧28 kbar) are independently indicated by i) the coexistence of nearly pure pyrope with free silica and talc, ii) the coexistence of jadeite with kyanite, iii) the high Si content of phengite. Water activity must have been low. The stability of talc-phengite and the presence of rare glaucophane inclusions in pyrope point to low formation temperatures (about 700 °C) and to a probable Alpine age for the assemblage. This is evidence that low temperature gradients, how essentially transient they are, may nevertheless persist to considerable depths. Moreover, the upper crustal (evaporite-related?) origin of the quartzite and its interbedding within a continental unit implies that continental crust may also be subducted to depths of 90 km or more. The return back to the surface is problematic; the retrograde assemblages observed show that it must be tectonic. If the rocks remain at depth, new perspectives open for the genesis of intermediate to acidic magmas. Eventually, the role of continental crust in geodynamics may have to be reconsidered.     

MedFlux: Investigations of particle flux in the Twilight Zone

The MedFlux project was devised to determine and model relationships between organic matter and mineral ballasts of sinking particulate matter in the ocean. Specifically we investigated the ballast ratio hypothesis, tested various commonly used sampling and modeling techniques, and developed new technologies that would allow better characterization of particle biogeochemistry. Here we describe the rationale for the project, the biogeochemical provenance of the DYFAMED site, the international support structure, and highlights from the papers published here. Additional MedFlux papers can be accessed at the MedFlux web site (http://msrc.sunysb.edu/MedFlux/).     

Economic‐Development Stakeholder Perspectives on Boomtown Dynamics in the Eagle Ford Shale,Texas

Unconventional oil and gas production in the United States reversed a decades‐old trend of rising oil imports, provided an argument for lifting the U.S. crude oil export ban and motivated the development of domestic natural gas export facilities. But the most visible impact of unconventional‐hydrocarbon extraction is the creation of boomtowns in rural regions. Despite widespread media coverage, scholarly analysis of boomtowns is restricted to regional econometric studies with little attention to how economic stakeholders understand and respond to booming economies. Here we analyze interviews with key economic stakeholders in the Eagle Ford Shale in Texas. Respondents consider their community's economic success relative to the price of oil and indicate concerns about the deterioration of roads, high housing demand, and skyrocketing wages. We also re‐examine John Gilmore's foundational work on boomtowns in the 1970s in the context of contemporary unconventional extraction.     

A sediment budget for a grazed semi-arid catchment in the Burdekin basin, Australia

In catchments adjacent to the Great Barrier Reef World Heritage Area in Queensland, Australia, there is a growing concern that sediments and nutrients being exported from the land are having a detrimental effect on coral reef communities. There is a need to determine the processes and rates of erosion from the major land use types, so that management intervention can be initiated to reduce sediment yields where required. This paper presents a sediment budget for Weany Creek, a 13.5 km² grazed semi-arid sub-catchment of the Burdekin River catchment, Australia. A range of field methods was used to measure erosion from hillslopes, gullies and stream banks, as well as identify the amount of sediment being deposited and remobilised on the bed of gullies and the stream network. The data suggests that at least during drought conditions, the primary erosion source in this catchment is gully erosion. However, the largest source of sediment in the budget is actually associated with the remobilisation of in-channel sediment stores. Overall, the sediment budget is comprised of  81% coarse material and 19% fine sediment and an agreement between the fine sediment yield estimated in the sediment budget and the yield measured at the catchment outlet is within 10%. The total sediment yield estimated for this catchment is  4205 t yr^− 1 and is much lower than expected for a catchment of this size. This may reflect the drought conditions during the measurement period; however, there is also the possibility that the primary erosion sources have been exhausted, and the rates of sediment loss may be much lower now than they may have been in the past. Nonetheless, the results show that stored sediment, which may have been deposited in the channel many decades ago, is an important contributor to end of catchment sediment yields and warrants further investigation.