A paleoenvironmental reconstruction of Laguna Babícora, Chihuahua, Mexico based on ostracode paleoecology and trace element shell chemistry     

Manuel R. Palacios-Fest  Ana Luisa Carreño  José R. Ortega-Ramírez  Guillermo Alvarado-Valdéz 《Journal of Paleolimnology》2002,27(2):185-206

Paleoecology of Laguna Babícora, Chihuahua, Mexico was reconstructed using ostracode faunal assemblages and shell chemistry. The paleolimnological record is used to show the magnitude of paleoclimatic changes in the area from 25,000 years to the present.Faunal assemblages consist of four species of the genus Limnocythere: L. sappaensis, L. ceriotuberosa, L. bradburyi and L. platyforma, all associated with Candona caudata, Candona patzcuaro and Cypridopsis vidua. A paleosalinity index developed from these assemblages indicates that the lake's salinity fluctuated frequently from oligo- to meso-haline conditions during the last 25,000 years. This pattern and low salinity range are in good agreement with modern TDS (here used as an indicator of salinity) values recorded from 26 wells and one spring from the area (258–975 mg l^–1). To estimate paleotemperature we examined the trace element content (Mg/Ca ratios) from individual valves of L. ceriotuberosa and L. platyforma, the two species most commonly recorded in Laguna Babícora.Shell Mg/Ca ratios of 204 specimens of these two species were used to estimate water temperature (Mg/Ca) by means of experimental standard coefficients. Our data show that paleowater temperature ranged from 5.6–21.3 °C (with 2 values ranging from 0.2–4.8 °C), which suggest a close correlation with atmospheric temperatures around the lake. These results are in good agreement with a modern mean winter temperature (3.5 °C) and mean summer temperature (20 °C) recorded in the area between 1970 and 1980.  相似文献   

Conceptual problems with remote element synthesis     

O. K. Manuel 《Journal of Earth System Science》2000,109(1):195-203

The notion of remote element synthesis has recently been modified to explain the presence of nucleogenetic isotopic anomalies and decay products of short-lived nuclides by injection of a small amount ofexotic nucleogenetic material. Even with this modification, remote element synthesis seems inconsistent with the following observations:

–	Evidence of coupled variations in the chemical and isotopic compositions of the source material for meteorites.
–	Residual coupling of chemical and isotopic heterogeneities across planetary distances in the solar system today.
–	The mass-fractionation relationship seen across isotopes of elements in the planetary system, in the solar wind, and in solar flares.
–	Linkage of short-lived radioactivities with isotopic anomalies and with physical properties of their host grains, as expected for early condensate of fresh stellar debris.
–	Temporal and spatial distributions of short-live nuclides and their decay products.
–	Mirror-image (+ and −) isotopic anomalies in meteorite grains that sum to “normal” isotopic ratios, as expected of unmixed products of the same nuclear reactions that produced our bulk elements.
–	The lac supporting evidence for “presolar” grains or nearby stars that injectedexotic material into the early solar nebula.

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Enforcing smoothness and assessing uncertainty in non-linear one-dimensional prestack seismic inversion   总被引：1，自引：0，他引：1  

Omar J. Varela  Carlos Torres-Verdín  Mrinal K. Sen 《Geophysical Prospecting》2006,54(3):239-259

Estimation of elastic properties of rock formations from surface seismic amplitude measurements remains a subject of interest for the exploration and development of hydrocarbon reservoirs. This paper develops a global inversion technique to estimate and appraise 1D distributions of compressional‐wave velocity, shear‐wave velocity and bulk density, from normal‐moveout‐corrected PP prestack surface seismic amplitude measurements. Specific objectives are: (a) to evaluate the efficiency of the minimization algorithm (b) to appraise the impact of various data misfit functions, and (c) to assess the effect of the degree and type of smoothness criterion enforced by the inversion. Numerical experiments show that very fast simulated annealing is the most efficient minimization technique among alternative approaches considered for global inversion. It is also found that an adequate choice of data misfit function is necessary for a reliable and efficient match of noisy and sparse seismic amplitude measurements. Several procedures are considered to enforce smoothness of the estimated 1D distributions of elastic parameters, including predefined quadratic measures of length, flatness and roughness. Based on the general analysis of global inversion techniques, we introduce a new stochastic inversion algorithm that initializes the search for the minimum with constrained random distributions of elastic parameters and enforces predefined autocorrelation functions (semivariograms). This strategy readily lends itself to the assessment of model uncertainty. The new global inversion algorithm is successfully tested on noisy synthetic amplitude data. Moreover, we present a feasibility analysis of the resolution and uncertainty of prestack seismic amplitude data to infer 1D distributions of elastic parameters measured with wireline logs in the deepwater Gulf of Mexico. The new global inversion algorithm is computationally more efficient than the alternative global inversion procedures considered here.  相似文献   

地下水水源保护区范围计算的KLF法及其在徐州张集地区的应用          下载免费PDF全文

毛媛媛  王连生  方瑞 《水科学进展》2006,17(6):808-811

详细介绍了地下水水源保护区范围的计算方法:Krijgsman-Lobo-Ferreira(KLF)法,分别推导出了正水流梯度方向、负水流梯度方向和垂直于地下水流方向保护区范围的计算公式,并就方法的适用性及参数取值等问题进行了探讨.在徐州张集地区应用的结果表明,KLF法提供了一种计算地下水保护区范围的便捷、科学、有效的方法,计算结果对于确定地下水源保护区范围及有效保护地下水源具有实际意义.  相似文献   

Climate Warming and Water Management Adaptation for California   总被引：1，自引：3，他引：1  

Stacy K. Tanaka  Tingju Zhu  Jay R. Lund  Richard E. Howitt  Marion W. Jenkins  Manuel A. Pulido  Mélanie Tauber  Randall S. Ritzema  Inês C. Ferreira 《Climatic change》2006,76(3-4):361-387

The ability of California's water supply system to adapt to long-term climatic and demographic changes is examined. Two climate warming and a historical climate scenario are examined with population and land use estimates for the year 2100 using a statewide economic-engineering optimization model of water supply management. Methodologically, the results of this analysis indicate that for long-term climate change studies of complex systems, there is considerable value in including other major changes expected during a long-term time-frame (such as population changes), allowing the system to adapt to changes in conditions (a common feature of human societies), and representing the system in sufficient hydrologic and operational detail and breadth to allow significant adaptation. While the policy results of this study are preliminary, they point to a considerable engineering and economic ability of complex, diverse, and inter-tied systems to adapt to significant changes in climate and population. More specifically, California's water supply system appears physically capable of adapting to significant changes in climate and population, albeit at a significant cost. Such adaptation would entail large changes in the operation of California's large groundwater storage capacity, significant transfers of water among water users, and some adoption of new technologies.  相似文献   

Neo-liberal ruptures: Local political entities and neighbourhood networks in El Alto, Bolivia     

Juan Manuel Arbona 《Geoforum》2007,38(1):127-137

In October 2003, hundreds of thousands of Bolivians took to the streets demanding the resignation of President Gonzalo Sánchez de Lozada. After 20 years of neo-liberal policies - and the failures to improve the living conditions of the majority - the proposal to export natural gas via Chile was taken by the population as yet another step to sustain an unjust political order. Facing a direct challenge by the population the Sánchez de Lozada administration responded with indiscriminate military force. The result was 63 dead and over 300 wounded, which deepened and extended the social rage and eventually forced the resignation of the President. The neo-liberal project - promoted and defended by Sánchez de Lozada - collapsed. The city of El Alto was the epicentre of the challenges to the legitimacy of this political order. This article focuses on the role of local political entities and neighbourhood networks from El Alto in articulating political spaces that challenged the legitimacy of the institutional infrastructure and led to the October 2003 ruptures in the neo-liberal project. Furthermore, I make the case that the particular histories and memories (of “relocalized” miners and indigenous/peasants) that converged in and defined this city were pivotal in the organization of a “political subsoil” that surged to the surface during the October 2003 events.  相似文献   

On the Intensity Thresholds of the Network and Plage Regions     

Michael Steinegger  Jose A. Bonet  Manuel Vázquez  Antonio Jiménez 《Solar physics》1998,177(1-2):279-286

A period of minimum solar activity in April and May 1996 was used to analyze full-disk CaK spectroheliograms with the aim of deriving the intensity thresholds of the quiet network and the plages by applying the so-called inflexion point method. The average network intensity threshold is found to be influenced mainly by the seeing, whereas the average plage threshold shows an increasing trend from disk center towards the solar limb. Both parameters are compared with the results of other authors.  相似文献   

Site-Testing Results at La Palma Observatory     

A.M. Varela  C. Muñoz-Tuñón  T. Mahoney 《Astrophysics and Space Science》1998,263(1-4):373-376

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Noble gases in the earth's mantle     

D.P. Thompson  A.R. Basu  E.W. Hennecke  O.K. Manuel 《Physics of the Earth and Planetary Interiors》1978,17(2):98-107

The abundances and isotopic compositions of noble gases in two samples from ultramafic xenoliths in alkali basalt, a young kaersutitic amphibole separated from a peridotite xenolith from Dish Hill, California and an ancient whole-rock lherzolite xenolith from Baja California, are reported and compared with the results of analyses on other mantle samples. In addition to previously recognized excesses of ³He and ¹²⁹Xe, our results indicate that ambient gases in the mantle show a general enrichment of the lighter-mass nonradiogenic isotopes of Ar, Kr and Xe, and Ar with ⁴⁰Ar/³⁶Ar = 3 · 10².  相似文献   

Low-degree partial melting trends recorded in upper mantle minerals     

Pierre Schiano  Bernard Bourdon  Robert Clocchiatti  Dominique Massare  Maria E. Varela  Yan Bottinga 《Earth and Planetary Science Letters》1998,160(3-4):537-550

The study of glass inclusions inside mantle minerals provides direct information about the chemistry of naturally occurring mantle-derived melts and the fine-scale complexity of the melting process responsible for their genesis. Minerals in a spinel lherzolite nodule from Grande Comore island contain glass inclusions which, after homogenization by heating, exhibit a continuous suite of chemical compositions clearly distinct from that of the host basanitic lava. The compositions range from silicic, with nepheline–olivine normative, 64 wt% SiO₂ and 11 wt% alkali oxides, to almost basaltic, with quartz normative, 50 wt% SiO₂ and 1–2 wt% alkali oxides. Within a single mineral phase, olivine, the inferred primary melt composition varies from 54 to 64 wt% SiO₂ for MgO content ranging from 8 to 0.8 wt%. An experimental study of the glass and fluid inclusions indicates that trapped melts represent liquids that are in equilibrium with their host phases at moderate temperature and pressure (T≈1230°C and P≈1.0 Gpa for melts trapped in olivine). Quantitative modelling of the compositional trends defined in the suite shows that all of the glasses are part of a cogenetic set of melts formed by fractional melting of spinel lherzolite, with F varying between 0.2 and 5%. The initial highly silicic, alkali-rich melts preserved in Mg-rich olivine become richer in FeO, MgO, CaO and Cr₂O₃ and poorer in SiO₂, K₂O, Na₂O, Al₂O₃ and Cl with increasing melt fractions, evolving toward the basaltic melts found in clinopyroxene. These results confirm the connection between glass inclusions inside mantle minerals and partial mantle melts, and indicate that primary melts with SiO₂ >60 wt%, alkali oxides >11%, FeO <1 wt% and MgO <1 wt% are generated during incipient melting of spinel peridotite. The composition of the primary melts is inferred to be dependent on pressure, and to reflect both the speciation of dissolved CO₂ and the effect of alkali oxides on the silica activity coefficient in the melt. At pressures around 1 GPa, low-degree melts are characterized by alkali and silica-rich compositions, with a limited effect of dissolved CO₂ and a decreased silica activity coefficient caused by the presence of alkali oxides, whereas at higher pressures alkali oxides form complexes with carbonates and, consequently, alkali-rich silica-poor melts will be generated.  相似文献