Ca-Fe-Mg olivines: phase relations and a solution model     

Paula M. Davidson  Dilip K. Mukhopadhyay 《Contributions to Mineralogy and Petrology》1984,86(3):256-263

Reversed phase equilibrium experiments in the system (Ca, Mg, Fe)₂SiO₄ provide four tielines at P?1 bar and 1 kbar and 800° C–1,100° C. These tielines have been used to model the solution properties of the olivine quadrilateral following the methods described by Davidson et al. (1981) for quadrilateral clinopyroxenes. The discrepancy between the calculated phase relations and the experimentally determined tielines is within the uncertainty of the experiments. The solution properties of quadrilateral olivines can be described by a non-convergent site-disorder model that allows for complete partitioning of Ca on the M2 site, highly disordered Fe-Mg cation distributions and limited miscibility between high-Ca and low-Ca olivines. The ternary data presented in this paper together with binary solution models for the joins Fo-Mo and Fa-Kst have been used to evaluate two solution parameters: $$\begin{gathered} F^0 \equiv 2(\mu _{{\rm M}o}^0 - \mu _{{\rm K}st}^0 ) + \mu _{Fa}^0 - \mu _{Fo}^0 = 12.660 (1.6) kJ, \hfill \\ \Delta G_*^0 \equiv \mu _{{\rm M}gFe}^0 + \mu _{FeMg}^0 - \mu _{Fo}^0 - \mu _{Fa}^0 = 7.030 (3.9) kJ. \hfill \\ \end{gathered} $$ . Ternary phase quilibrium data for olivines tightly constrain the value of F⁰, but not that for ΔG _* ⁰ which describes nonideality in Fe-Mg mixing. From this analysis, we infer a function for the apparent standard state energy of Kst: $$\begin{gathered} \mu _{{\rm K}st}^0 = - 102.79 \pm 0.8 - (T - 298)(0.137026) \hfill \\ + (T - 298 - T1n(T/298))(0.155519) \hfill \\ + (T - 298)^2 (2.8242E - 05)/2 \hfill \\ + (T - 298)^2 (2.9665E + 03)/(2T(298)^2 ) kJ \hfill \\ \end{gathered} $$ where T is in Kelvins and the 298 K value is relative to oxides.  相似文献   

Anthropogenic and climatic influences on the diatom flora within the Fallen Leaf Lake watershed,Lake Tahoe Basin,California over the last millennium     

Briana E. Johnson  Paula J. Noble  Alan C. Heyvaert  Sudeep Chandra  Robert Karlin 《Journal of Paleolimnology》2018,59(2):159-173

This study addresses the effects of climate, land-use, and atmospheric nitrogen (N) deposition on the Fallen Leaf Lake watershed, Lake Tahoe Basin, through diatom and geochemical analyses of sediment cores. Four diatom zones are recognized from a core taken at Fallen Leaf Lake (FLL), a site moderately impacted by human activities: (1) Pre-Little Ice Age Zone (840–1385), (2) Little Ice Age Zone (1385–1810) characterized by Stephanodiscus alpinus and Aulacoseira subarctica, (3) Transitional Zone (1810–1950) of warming and anthropogenic influence with increased Lindavia rossii-ocellata group and Discostella stelligera and decreased Pseudostaurosira brevistriata, and (4) Anthropogenic Zone (1950–2010) characterized by a rapid increase of mesotrophic diatoms of the Fragilaria tenera-nanana group, Tabellaria flocculosa strain IIIP, and Nitzschia gracilis. The Transitional Zone increases in elemental Co, Zn, and Sn that may be attributed to an increase in coal burning and smelting activities in California and Nevada. Beginning around 1910 and accelerating in the 1940s, increased building, land-use, and recreation around FLL caused an increase in terrestrial sedimentary input. Down core proxies for atmospheric N deposition in the FLL watershed are, at best, weakly expressed and appear to be overshadowed by stronger signals. Lack of support for N deposition includes the asynchrony in the appearance of the N-sensitive diatom Asterionella formosa in FLL and a lower impact site at Gilmore Lake, and an uninformative δ¹⁵N record. Asterionella formosa is a dominant component in the FLL water column today, but has been present in similar abundances for at least the last 1200 years. Asterionella formosa is present in the water column at Gilmore Lake and absent from the sediment, indicating a very recent appearance. The data collected show that the FLL record is sensitive to climatic cooling during the Little Ice Age and to anthropogenic activities commencing in the 1800s that increased throughout the latter half of the twentieth century; however the effects of anthropogenic N deposition in these lakes could not be substantiated.  相似文献   

Systematic increase in model complexity helps to identify dominant streamflow mechanisms in two small forested basins     

Paula C. David  Debora Y. Oliveira  Fernando Grison  Masato Kobiyama 《水文科学杂志》2019,64(4):455-472

This study shows how the use of increasing model complexity allows us to hypothesize about dominant streamflow mechanisms in two small Brazilian forested basins. Nine different structures from SUPERFLEX, an objective framework to systematically increase hydrological model complexity, were tested and we extended the flexible modelling methodology to error models as well. We show that applying a rigorous methodology in a model evaluation framework, with residual analysis and control of model complexity, is essential for testing a model as a hypothesis for dominant hydrological controls. Our results indicate that the model architecture was more important than the increase in the number of model parameters. Better performing models were those with a parallel structure, which confirms our a priori belief about the dominant runoff mechanisms of the studied catchments, characterized by a rapid response to rainfall, but also a constant river discharge fed by water storage on the thick soil layer.  相似文献   

Decadal-scale changes in suspended wood after riparian recruitment in managed stands in headwater streams of coastal British Columbia,Canada     

Felipe Rossetti de Paula  John S. Richardson  Alex C.Y. Yeung  Stephen J. Mitchell  Devesh Bahuguna 《地球表面变化过程与地形》2020,45(9):1974-1989

Large wood (LW) affects several ecological and hydrogeomorphic processes in streams. The main source of LW is riparian trees falling inside channels. However, in confined valley floors, falling trees are more likely to be suspended above the channel. Eventually, these suspended trees will decompose and break to finally fall into the channel to better provide functions for streams. We evaluated changes in wood decay, length, diameter, and suspended status (suspended or non-suspended) 17 years post-harvest and nine years after the first sampling occurred in 2006 in 12 headwater streams of coastal British Columbia, Canada. We also evaluated whether changes differed among riparian management treatments (no-harvest buffers of 10 and 30 m in width, thinning, and unharvested reference sites), and identified the factors affecting wood changes and suspended status. Wood pieces advanced in decay, became shorter, and 34% of them (n = 108) changed status from suspended to non-suspended. Non-suspended wood pieces were more decayed and shorter than suspended wood. Suspended wood was longer, thicker, less decayed, and represented 46.5% (n = 147) of the wood sampled in 2006. Our findings revealed limited influences of riparian management on many aspects of wood changes considered in this study. Changes in wood characteristics were more likely for pieces that were smaller in diameter, longer, and suspended closer to the water. The transition from suspended to non-suspended LW can be a long-term process that can increase wood residence time and reduce LW in-stream functions particularly in confined stream valleys. The suspended stage is also an important mechanism underlying time lags in stream ecosystem responses to riparian tree fall. © 2020 John Wiley & Sons, Ltd.  相似文献   

Forecasting annual precipitation to improve the operation of dams in the Comahue region,Argentina     

Paula Elisa Romero  Alfredo Luis Rolla  Fernando Losano 《水文科学杂志》2020,65(11):1974-1983

ABSTRACT

This paper attempts to design statistical models to forecast annual precipitation in the Neuquen and Limay river basins in the Comahue region of Argentina. These forecasts are especially useful as they are used to better organize the operation of hydro-electric dams, the agriculture in irrigated valleys and the safety of the population. In this work, multiple linear regression statistical models are built to forecast mean annual rainfall over the two river basins. Since the maximum precipitation occurs in the winter (June–August), forecasting models have been developed for the beginning of March and for the beginning of June, just before the rainy season starts. The results show that the sea-surface temperatures of the Indian and Pacific oceans are good predictors for March models and explain 42.8% of the precipitation index variance. The efficiency of the models increases in June, adding more predictors related to the autumn circulation.  相似文献   

Anurans from the Candeleros Formation (?Cenomanian-Turonian) of west-central Argentina: new evidence for pipoid evolution     

Ana M. Bez  Paula Muzzopappa  Laura Nicoli 《Cretaceous Research》2007,28(6):1005-1016

The fluvio-lacustrine deposits of the ?Cenomanian-Turonian Candeleros Formation in the northwestern fringe of Patagonia have yielded numerous remains of vertebrates, including anurans. A new, partially articulated immature specimen of a small pipimorph pipoid from the upper part of this unit is described herein. Although incompletely preserved, the morphology and proportions of the skeleton are strongly reminiscent of corresponding elements of the holotype of Avitabatrachus uliana from the lower section of the same formation at a nearby locality, thus suggesting that these specimens might represent the same, or a closely related, taxon. The new specimen is a metamorphosing individual: it has a zygapophyseal articulation between the sacrum and the neural arch of a postsacral vertebra that bears conspicuous transverse processes, and four pairs of ribs. These traits are not present in the available material of A. uliana, but they might have occurred within the normal range of variation of a single species. Although the generic and specific allocation of the new material is uncertain, a parsimony analysis performed to clarify the relationships of A. uliana supports a phylogenetic placement of this taxon outside the crown Pipidae. The evidence provided by the Candeleros anurans confirms the presence of stem pipids in Patagonia in the early Late Cretaceous.  相似文献   

Net aboveground primary production and soil properties of floating and attached freshwater tidal marshes in the Río de la Plata estuary,Argentina     

Paula Pratolongo  Patricia Kandus  Mark M. Brinson 《Estuaries and Coasts》2007,30(4):618-626

In the lower delta of the Paraná River, at the head of the Río de la Plata estuary (Argentina), we compared net aboveground primary production (NAPP) and soil properties of the dominant macrophyteScirpus giganteus (Kunth) in a floating and an attached marsh community. Both marshes are tidally influenced but in different ways. The floating marsh site is relatively isolated from tidal influences because its ability to float makes it resistant to overland flow and to sediment inputs from the estuary. The attached marsh lacks the capacity to float and receives sediment supplies from the estuary through overland flow. These hydrologic differences are reflected in lower mineral content in sediments of the floating marsh. Using a leaf tagging technique, estimated NAPP was 1,109 ± 206 g m⁻² yr⁻¹ for the floating marsh and 1,866 ±258 g m⁻² yr⁻¹ for the attached marsh. We attribute the lower NAPP of the floating marsh to isolation from sediment input from overland flow.  相似文献   

Effects of local site and building parameters on damage distribution in Angra do Heroísmo—Azores     

Paula Teves-Costa  Carlos S. Oliveira  M. Luisa Senos 《Soil Dynamics and Earthquake Engineering》2007,27(11):986-999

During the M_w=6.9 January 1, 1980 earthquake in the Azores, the damage distribution in the town of Angra do Heroísmo, in Terceira Island, had a non-homogeneous spatial character. In order to understand the observed pattern of damage a microtremor survey was carried out, using ambient vibrations, and the data were analysed with the J-Sesame software, following the H/V Nakamura methodology. The results are in good agreement with the surface geology and they show a good correlation with the observed damages. Two building surveys were performed, in 1980 on damage evaluation and in 2000 on characterization of few building parameters. With all these elements (surface geology type, soil peak frequency, building type, number of stories and damage level) for 2111 buildings it was possible to perform several interparameter analysis, which enabled the identification of indicators that could be used to improve the damage estimation for future events.  相似文献   

A 1500-year record of temperature and glacial response inferred from varved Iceberg Lake, southcentral Alaska     

Michael G. Loso  Robert S. Anderson  Suzanne P. Anderson  Paula J. Reimer 《Quaternary Research》2006,66(1):12-24

We present a varve thickness chronology from glacier-dammed Iceberg Lake in the southern Alaska icefields. Radiogenic evidence confirms that laminations are annual and record continuous sediment deposition from A.D. 442 to A.D. 1998. Varve thickness is positively correlated with Northern Hemisphere temperature trends, and more strongly with a local, ∼600 yr long tree ring width chronology. Varve thickness increases in warm summers because of higher melt, runoff, and sediment transport (as expected), but also because shrinkage of the glacier dam allows shoreline regression that concentrates sediment in the smaller lake. Varve thickness provides a sensitive record of relative changes in warm season temperatures. Relative to the entire record, temperatures implied by this chronology were lowest around A.D. 600, warm between A.D. 1000 and A.D. 1300, cooler between A.D. 1500 and A.D. 1850, and have increased dramatically since then. Combined with stratigraphic evidence that contemporary jökulhlaups (which began in 1999) are unprecedented since at least A.D. 442, this record suggests that 20th century warming is more intense, and accompanied by more extensive glacier retreat, than the Medieval Warm Period or any other time in the last 1500 yr.  相似文献   

Index to volume 4     

F. Quattrocchi  R. Pik  L. Pizzino  M. Guerra  P. Scarlato 《Journal of Seismology》2000,4(4):601-607

Authors Index

Index to volume 4  相似文献