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1.
The franciscana dolphin, Pontoporia blainvillei, is endemic to the coastal waters of the southwestern Atlantic Ocean and the most endangered dolphin in the area. Four Franciscana Management Areas (FMAs) are currently recognised; however, results of genetic studies suggest the requirement for additional FMAs and highlight the need for more detailed studies in the southern extreme of the species distribution. With this aim, we studied the genetic diversity and population structure of the species analysing an mtDNA control region fragment (434?bp) in 44 individuals collected in four sampling sites located in Southern Buenos Aires. Haplotype diversity (H?=?0.75?±?0.05) was mostly higher than the observed in endangered or near threatened odontocetes. Population structure analyses suggest that three different genetic populations should be recognised within FMA IV: Northern, Eastern and Southern Buenos Aires. Altogether, these results should be taken into account in future conservation plans for the species. 相似文献
2.
DARIO TERRIBILINI OTTO EUGSTER MARIO BURGER ALFRED JAKOB URS KrHENBÜHL 《Meteoritics & planetary science》1998,33(4):677-684
Abstract— We report the elemental and isotopic composition of the noble gases as well as the chemical abundances in pyroxene, maskelynite/mesostasis glass, and bulk material of Shergotty and of bulk samples from Chassigny and Yamato 793605. The 40K-40Ar isochron for the Shergotty minerals yields a gas retention age of 196 Ma, which is, within errors, in agreement with previously determined Rb-Sr internal isochron ages. Argon that was trapped at this time has a 40Ar/36Ar ratio of 1100. For Chassigny and Y-793605, we obtain trapped 40Ar/36Ar ratios of 1380 and 950, respectively. Using these results and literature data, we show that the three shergottites, Shergotty, Zagami, and QUE 94001; the lherzolites ALH 77005, LEW 88516, and Y-793605; as well as Chassigny and ALH 84001 contain a mixture of Martian mantle and atmospheric Ar; whereas, the trapped 40Ar/36Ar ratio of the nakhlites, Nakhla, Lafayette, and Governador Valadares cannot be determined with the present data. We show that Martian atmospheric trapped Ar in Martian meteorites is correlated with the shock pressure that they experienced. Hence, we conclude that the Martian atmospheric gases were introduced by shock into the meteoritic material. For the Shergotty minerals, we obtain 3He-, 21Ne-, and 38Ar-based cosmic-ray exposure ages of 3.0 Ma, and for the lherzolite Y-793605, 4.0 Ma, which confirms our earlier conclusion that the lherzolites were ejected from Mars ～1 Ma before the shergottites. Chassigny yields the previously known ejection age of 11.6 Ma. 相似文献
3.
海拉尔盆地基底晚古生代adakite的发现及其地质意义 总被引：5，自引：1，他引：4
海拉尔盆地的前中生代基底隶属中亚造山带东段的兴蒙造山带。 在盆地基底地层中发现了具有adakite成分特征的粗面安山岩、英安岩和闪长玢岩。 这些火成岩与晚古生代沉积地层交互或伴生, 共同构成晚中生代裂陷盆地的基底。 地球化学研究表明, 这些火成岩基本上属于高钾钙碱性和准铝质岩石系列, 具有高SiO2和Al2O3含量, 高Sr、Sr/Y和La/Yb值, 富集轻稀土(LREE), 亏损重稀土(HREE)、Y和高场强元素(HFSE),Eu表现弱的负异常或轻微的正异常, 相容元素Mg、Cr和Ni含量低, 这些特征与增厚下地壳部分熔融成因的adakite非常相似, 而明显不同于典型的由俯冲洋壳熔融形成的adakite。 样品的(87Sr/86Sr)i值基本一致,为0.7041, (143Nd/144Nd)i值为0.51243~0.51247, εNd (t)为正值(+3.7~+4.5), 显示其岩浆源区可能源于弱亏损地幔, 或亏损地幔受到地壳物质混染。 本文认为海拉尔地区晚古生代adakite型岩浆很可能是由当时新底侵的玄武质下地壳在角闪岩相向榴辉岩相过度或榴辉岩相条件下部分熔融形成。 这些adakite岩石的出现反映了兴蒙造山带晚古生代受到了古亚洲洋的俯冲消减引起的强烈的地幔玄武质岩浆底侵作用, 并由此导致地壳垂向上显著的增生加厚过程。 相似文献
4.
阿尔泰造山带富蕴基性麻粒岩折返过程:来自裂变径迹热年代学的限定 总被引：1，自引：1，他引：0
论文在阿尔泰造山带富蕴县乌恰沟基性麻粒岩的锆石SHRIMP年代学、地球化学、变质温压条件和形成的大地构造背景研究基础上,利用麻粒岩、围岩片麻岩和侵入到麻粒岩的辉绿岩岩墙的裂变径迹热年代学探讨了麻粒岩从深部折返至地表的过程。裂变径迹年代学研究发现基性麻粒岩的锆石裂变径迹年龄为三叠纪,而麻粒岩、围岩片麻岩和侵入到麻粒岩的辉绿岩岩墙的磷灰石裂变径迹年龄均显示为晚白垩世至新生代早期。对磷灰石裂变径迹测试所得到的径迹长度和单颗粒年龄数据进行热史模拟表明,三叠纪时,基性麻粒岩抬升至约地表以下7.8km的上地壳,温度冷却至锆石裂变径迹的封闭温度;晚白垩世至新生代早期(约100～50Ma),麻粒岩、围岩片麻岩和辉绿岩抬升至约地表以下3.5km,温度冷却至磷灰石裂变径迹的封闭温度;约50～15Ma,三者滞留在约地表以下1.7km的磷灰石部分退火带;约15Ma以来,喜马拉雅运动使得它们被抬升剥蚀至地表。 相似文献
5.
Age verification of rubyfish (Plagiogeneion rubiginosum) was sought using the bomb radiocarbon chronometer procedure. Stable isotopes were investigated for life history characteristics. Radiocarbon (14C) and stable isotope (δ18O and δ13C) levels were measured in micro-samples from five otoliths that had been aged using a zone count method. All the core 14C measurements were ‘pre-bomb’ indicating ages of at least 45 years, and the 14C measurements across the otolith sections suggested that the zone-count ageing method described herein is not biased. Maximum estimated age was 100 years. There was no significant between-sex difference in the von Bertalanffy growth curves. The δ18O values indicated that rubyfish are near-surface as juveniles, and move deeper with age. Adults appear to reside in 600–1000 m; this is deeper than most trawl-capture data suggest, but not implausible, and has stock assessment implications. The δ13C values reflect fish metabolic rates, trophic feeding levels and oceanographic conditions. The stable isotopes record the environmental life history of each fish, and have value in distinguishing stocks and/or indicating vertical and latitudinal migratory patterns. 相似文献
6.
北秦岭西段冥古宙锆石(4.1～3.9Ga)年代学新进展 总被引：15，自引：13，他引：2
2007年王洪亮等报道在北秦岭西段火山岩中获得一粒年龄为4079±5Ma的冥古宙捕虏锆石。之后,对这一发现开展了深入的调查研究,我们除利用SHIMP技术方法对原4079Ma的锆石进行验证外,新获得了两粒~(207)Pb/~(206)Pb年龄为4007±29Ma和3908±45Ma捕获的变质成因锆石,表明早在4.0Ga已经有变质作用的发生,这或许说明在冥古宙时期地球已经具有相当规模和厚度的地壳。同时开展的岩石学研究表明,蕴含古老锆石的母岩属于火山碎屑熔岩类而不是火山熔岩。 相似文献
7.
火山岩风化壳储层发育模式——以三塘湖盆地马朗凹陷石炭系火山岩为例 总被引：4，自引：1，他引：3
中国的火山岩油气勘探近年来进展非常快,并不断在许多盆地发现了优质火山岩储层,其中风化壳型储层作为非常重要的火山岩储集体类型而倍受重视。三塘湖盆地马朗凹陷石炭系风化壳型储层储集空间以溶蚀孔洞缝为主,储层物性非常好。通过火山岩油气勘探中的野外露头观察、钻井取心、镜下薄片鉴定,及主量元素、微量元素等分析化验资料,并结合火山岩岩石学特征和物性特点,初步建立了该区的风化壳储层的发育模式,将火山岩风化壳储层在垂向上自上而下划分为五个带: ①最终分解产物带; ②水解带; ③淋滤带; ④崩解带; ⑤未风化带(母岩)。淋滤带储集物性最好,该区风化淋滤是改善储层的关键。 相似文献
8.
Weibiao HSU Aicheng ZHANG Rainer BARTOSCHEWITZ Yunbin GUAN Takayuki USHIKUBO Urs KRÄHENBÜHL Rainer NIEDERGESAESS Rudolf PEPELNIK Ulrich REUS Thomas KURTZ Paul KURTZ 《Meteoritics & planetary science》2008,43(8):1363-1381
Abstract— We report here the petrography, mineralogy, and geochemistry of lunar meteorite Sayh al Uhaymir 300 (SaU 300). SaU 300 is dominated by a fine‐grained crystalline matrix surrounding mineral fragments (plagioclase, pyroxene, olivine, and ilmenite) and lithic clasts (mainly feldspathic to noritic). Mare basalt and KREEPy rocks are absent. Glass melt veins and impact melts are present, indicating that the rock has been subjected to a second impact event. FeNi metal and troilite grains were observed in the matrix. Major element concentrations of SaU 300 (Al2O3 21.6 wt% and FeO 8.16 wt%) are very similar to those of two basalt‐bearing feldspathic regolith breccias: Calcalong Creek and Yamato (Y‐) 983885. However, the rare earth element (REE) abundances and pattern of SaU 300 resemble the patterns of feldspathic highlands meteorites (e.g., Queen Alexandra Range (QUE) 93069 and Dar al Gani (DaG) 400), and the average lunar highlands crust. It has a relatively LREE‐enriched (7 to 10 x CI) pattern with a positive Eu anomaly (?11 x CI). Values of Fe/Mn ratios of olivine, pyroxene, and the bulk sample are essentially consistent with a lunar origin. SaU 300 also contains high siderophile abundances with a chondritic Ni/Ir ratio. SaU 300 has experienced moderate terrestrial weathering as its bulk Sr concentration is elevated compared to other lunar meteorites and Apollo and Luna samples. Mineral chemistry and trace element abundances of SaU 300 fall within the ranges of lunar feldspathic meteorites and FAN rocks. SaU 300 is a feldspathic impact‐melt breccia predominantly composed of feldspathic highlands rocks with a small amount of mafic component. With a bulk Mg# of 0.67, it is the most mafic of the feldspathic meteorites and represents a lunar surface composition distinct from any other known lunar meteorites. On the basis of its low Th concentration (0.46 ppm) and its lack of KREEPy and mare basaltic components, the source region of SaU 300 could have been within a highland terrain, a great distance from the Imbrium impact basin, probably on the far side of the Moon. 相似文献
9.
MARK D. JOHNSON YLVA STÅHL 《Boreas: An International Journal of Quaternary Research》2010,39(2):199-214
Johnson, M. D. & Ståhl, Y. 2009: Stratigraphy, sedimentology, age and palaeoenvironment of marine varved clay in the Middle Swedish end‐moraine zone. Boreas, 10.1111/j.1502‐3885.2009.00124.x. ISSN 0300‐9483 Deglaciation of the Middle Swedish end‐moraine zone and age of the sediment in and between the moraines have been discussed for about a hundred years. The goal of this project was to determine the stratigraphy and age of the sediment in and between the moraines. Inter‐moraine flats are underlain by clay, 10–25 m thick, overlying thin sand and gravel or till on bedrock. The clay is overlain by a few metres of sand and gravel. Much of the clay beneath the flats consists of rhythmites that grade from grey to red and are 2–74 cm thick. Our interpretation of these rhythmites as being varves is supported by grain size and mineralogical and elemental variations. Foraminifera and ostracods show that the clay was deposited in an arctic marine environment, while radiocarbon dating of the microfossils indicates that the clay was deposited 12 150 cal. 14C years ago, during the Younger Dryas chronozone (YD). Most of the optical stimulated luminescence dates on the clay are much older, containing quartz sand that was insufficiently bleached. The stratigraphy indicates that the moraines are composed of YD clay pushed into ridge forms during ice‐front oscillations. It is not possible to determine how far north the Scandinavian Ice Sheet retreated prior to the YD advance. We neither support nor reject the suggestion that the ice margin retreated to the northern edge of Mt. Billingen during the Allerød, causing the Baltic Ice Lake to drain. 相似文献
10.
THOMAS LITT CHRISTIAN SCHÖLZEL NORBERT KÜHL ACHIM BRAUER 《Boreas: An International Journal of Quaternary Research》2009,38(4):679-690
Lakes Holzmaar and Meerfelder Maar are located in the Westeifel Volcanic Field less than 10 km apart. Both maar lakes are well known for their annually laminated (varved) sediments covering the past 15 000 years. Here, we focus on reconstructing the history of Holocene vegetation, human impact and climate using high-resolution pollen data. Detailed correlation between the two records using palynologically defined tie-points provides for the first time a test of the precision of the individual varve chronologies. The high-resolution pollen records of both Holzmaar and Meerfelder Maar show continuous natural successions of vegetation during the early and mid-Holocene controlled by the development of soil, climate, immigration and competitive expansion of thermophilous tree species. From 6500 varve yr BP onwards, human impact became an increasingly more important factor. Given the high chronological precision of both records, regional similarities, but also local differences of anthropogenically influenced vegetation changes, can be recognized. The reconstructed July temperature between 8500 and 5000 varve yr BP is around 1 °C higher than today, most likely in response to higher summer insolation related to orbital forcing. High variability of reconstructed July and January temperatures as well as annual precipitation around 5000 varve yr BP is a prominent climatic signal. This is consistent with other records in several areas of Europe which also identify this period as climatically highly variable. 相似文献