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Baffin Bay, Texas is the flooded Last Glacial Maximum incised valley of the Los Olmos, San Fernando and Petronila Creeks along the north‐western Gulf of Mexico. Cores up to 17 m in length and high‐resolution seismic profiles were used to study the history of Baffin Bay over the last 10 kyr and to document the unusual depositional environments within the valley fill. The deposits of the Baffin Bay incised valley record two major and two minor events. Around 8·0 ka, the estuarine environments backstepped more than 15 km in response to an increase in the rate of sea‐level rise. Around 5·5 ka, these estuarine environments changed from environments similar to other estuaries of the northern Gulf of Mexico to the unusual suite of environments found today. Another minor flooding event occurred around 4·8 ka in which several internal spits were flooded. Some time after 4·0 ka, the upper‐bay mud‐flats experienced a progradational event. Because of its semi‐arid climate and isolation from the Gulf of Mexico, five depositional environments not found in the other incised‐valley fills of the northern Gulf of Mexico are found today within Baffin Bay. These deposits include well‐laminated carbonate and siliciclastic open‐bay muds, ooid beaches, shelly internal spits and barrier islands, serpulid worm‐tube reefs and prograding upper‐bay mud‐flats. Based on these unusual deposits, and other characteristics of Baffin Bay, five criteria are suggested to help identify incised valleys that filled in arid and semi‐arid climates. These criteria include the presence of: (i) hypersaline‐tolerant fauna; (ii) aeolian deposits; and (iii) carbonate and/or evaporite deposits; and the absence of: (iv) peat or other organic‐rich deposits in the upper bay and bay‐margin areas; and (v) well‐developed fluvially dominated bayhead deltas. 相似文献
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Saraswoti SAPKOTA ;Achyut ARYAL ;Shanta Ram BARAL ;Matt W.HAYWARD ;David RAUBENHEIMER 《资源与生态学报(英文版)》2014,5(3):237-243
人与野生动物冲突是全世界自然保护工作所面临的最大挑战之一。为降低这些冲突的影响,各国采取了各种保护策略,但这些策略常常得不到足够的监测,其效力也得不到充分的评估。近年来,作为降低人与野生动物冲突的一项措施,尼泊尔各保护区周围建起了电篱笆。到目前为止,未见有其他针对保护工作中采用电篱笆的成本效率及其功效开展分析的研究。本研究的目的是检验尼泊尔近年来设立于旺国家公园东区的电篱笆的成本效率。印度犀牛（Rhinoceros unicornis）、野猪（Sus scrofa）、亚洲象（Elephas maximus）、老虎（Panthera tigris）是该国家公园周边缓冲区涉及人与野生动物冲突的主要物种,这里建有电篱笆。电篱笆使庄稼受损减少78%,家畜损失减少30%-60%。研究区的人类死亡数未表现出显著下降,而是继续维持较低数值。我们的分析表明,至2009/2010财政年度,电篱笆成本的总净现值,卡根社区（KMUC）为1 517 959尼泊尔卢比（21 685美元）,姆瑞加社区（MKUC）为3 530 075卢比（50 429美元）;而净现收益,卡根社区为16 301 105卢比（232 872美元）,姆瑞加社区为38 304 602卢比（547 208美元）。至2009/2010基准财政年度,电篱笆的成本-效益比率,卡根社区为10.73,姆瑞加社区为10.85。这些结果表明,在大型哺乳动物出没的保护区周围,电篱笆计划在降低人与野生动物冲突方面,既有经济效益,又有很好的社会效益。 相似文献
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Reversed Na-K exchange data between mica and a 2 molal aqueous(Na,K)Cl fluid (Flux & Chatterjee, 1986) have been employedto model the thermodynamic mixing behaviour of muscovite-paragonitecrystalline solutions on the basis of the Redlich-Kister equation.For these binary micas, Gexm may be expressed as
where A=11222+1.389 T+0.2359 P, B=–1134+6.806 T–0.0840 P, and C=–7305+9.043 T, with T in K, P in b, Gexm, A, B, and C in joules/mol. Gmex is well constrained between 450 and 620?C, and may be extrapolatedbeyond that range with caution. The calculated solvi are skewedtoward the paragonite end member. In the range up to 15 kb,the critical temperature, Tc and the critical composition, Xcmay be expressed as a function of P by the relations:
and
with P indicated in bars. Calculated phase relations of muscovite-paragonite crystallinesolutions have been depicted in terms of the system KAlSi3O8-NaAlSi3O8-Al2O3-SiO2-H2O.These data may be applied to appropriate assemblages involvingmica, alkali feldspar, an Al2 polymorph, and quartz to estimateP, T and aH2O conditions of their equilibration. In principle,the muscovite limb of the solvus may be used to obtain geothermometricdata for coexisting muscovite-paragonite pairs, provided theequilibrium pressure is independently known. However, such applicationmust be restricted for the present to micas on the ideal muscovite-paragonitejoin. Mica-alkali feldspar-Al2SiO5-quartz or mica-plagioclase-Al2SiO5-quartzassemblages may be used to deduce aH2O in the coexisting fluid,if P, and T of equilibrium are independently known. Examplesof such geological applications are given. 相似文献
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Single-phase 2M1 muscovite-paragonite crystalline solutionsin the range 0?00–0?10 and 0?70–1?00 Xms have beensynthesized by hydrothermal treatment of gels of appropriatecompositions at 600–700?C, and 7 to 18 kb PH2O. The molarvolumes of these micas may be expressed as V(J/b?mol) = 13?1845+1?463Xms+0?0160 Xms2–0?1679 Xms3 (?0?005), which translateto a substantial positive excess molar volume of mixing. Na-K ion exchange experiments between presynthesized 2M1 micacrystalline solutions and 2 molal aqueous (Na,K)Cl fluids failedto proceed to completion despite 98 day runs at 500–600?C,6 kb Ptotal. Results of analogous exchange experiments provedencouraging however, when a much finer-grained 1M mica was usedas starting material. Applying the tie line rotation technique,reversal of ion exchange experiments could be achieved in the2-phase fields, not, however, in the 3-phase field of the ms-pg-NaCl-KClreciprocal ternary. Using gels as starting material, reversalexperiments were eventually successful both in the 2-phase andthe 3-phase fields; the results of reversal experiments withinthe two-phase fields being identical to those obtained earlierusing 1M micas. Four isobaric-isothermal sections through the ms-pg-NaCl-KClternary were reversibly determined at 450?C/5 kb, 550?C/6 kb,550?C/15 kb, and 620?C/7 kb. At 450?C, the coexisting mica compositionsin the 3-phase field (2 micas plus 1 fluid) are 0?10 and 0?77Xms, at 550?C they are 0?10 and 0?60 Xms, and finally, at 620?Cthese are 0?12 and 0?51 Xms. To the extent that internal equilibriumwas accomplished between the coexisting micas, these data wouldindicate a wide solvus at 450?C, narrowing gradually with increasingtemperature to 620?C. The critical temperature will be wellin excess of 620?C, although the mica at the critical conditionwill prove to be metastable with respect to the assemblage alkalifeldspars+corundum+H2O. The companion paper by Chatterjee & Flux (1986) presentsa thermodynamic analysis of the above experimental data. 相似文献
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