Quaternary bedrock erosion and landscape evolution in the Sør Rondane Mountains, East Antarctica: Reevaluating rates and processes     

Norikazu Matsuoka  Cline E. Thomachot  Chiaki T. Oguchi  Tamao Hatta  Masahiro Abe  Hiroyuki Matsuzaki 《Geomorphology》2006,81(3-4):408-420

Rates and processes of rock weathering, soil formation, and mountain erosion during the Quaternary were evaluated in an inland Antarctic cold desert. The fieldwork involved investigations of weathering features and soil profiles for different stages after deglaciation. Laboratory analyses addressed chemistry of rock coatings and soils, as well as ¹⁰Be and ²⁶Al exposure ages of the bedrock. Less resistant gneiss bedrock exposed over 1 Ma shows stone pavements underlain by in situ produced silty soils thinner than 40 cm and rich in sulfates, which reflect the active layer thickness, the absence of cryoturbation, and the predominance of salt weathering. During the same exposure period, more resistant granite bedrock has undergone long-lasting cavernous weathering that produces rootless mushroom-like boulders with a strongly Fe-oxidized coating. The red coating protects the upper surface from weathering while very slow microcracking progresses by the growth of sulfates. Geomorphological evidence and cosmogenic exposure ages combine to provide contrasting average erosion rates. No erosion during the Quaternary is suggested by a striated roche moutonnée exposed more than 2 Ma ago. Differential erosion between granite and gneiss suggests a significant lowering rate of desert pavements in excess of 10 m Ma^− 1. The landscape has been (on the whole) stable, but the erosion rate varies spatially according to microclimate, geology, and surface composition.  相似文献   

The evolution of groundwater in the Tyrrell catchment, south-central Murray Basin, Victoria, Australia     

B. Petrides  I. Cartwright  T. R. Weaver 《Hydrogeology Journal》2006,14(8):1522-1543

The Tyrell catchment lies on the western margin of the Riverine Province in the south-central Murray Basin, one of Australia’s most important groundwater resources. Groundwater from the shallow, unconfined Pliocene Sands aquifer and the underlying Renmark Group aquifer is saline (total dissolved solids up to 150,000 mg/L) and is Na-Cl-Mg type. There is no systematic change in salinity along hydraulic gradients implying that the aquifers are hydraulically connected and mixing during vertical flow is important. Stable isotopes (¹⁸O+²H) and Cl/Br ratios indicate that groundwater is entirely of meteoric origin and salts in this system have largely been derived by evapotranspiration of rainfall with only minor halite dissolution, rock weathering (mainly feldspar dissolution), and ion exchange between Na and Mg on clays. Similarity in chemistry of all groundwater in the catchment implies relative consistency in processes over time, independent of any climatic variation. Groundwater in both the Pliocene Sands and Renmark Group aquifers yield ages of up to 25 ka. The Tyrrell Catchment is arid to semi-arid and has low topography. This has resulted in relatively low recharge rates and hydraulic gradients that have resulted in long groundwater residence times.  相似文献   

Paleoproterozoic accretion in the Northeast Siberian craton: Isotopic dating of the Anabar collision system   总被引：1，自引：0，他引：1  

O. M. Rosen  L. K. Levskii  D. Z. Zhuravlev  A. Ya. Rotman  Z. V. Spetsius  A. F. Makeev  N. N. Zinchuk  A. V. Manakov  V. P. Serenko 《Stratigraphy and Geological Correlation》2006,14(6):581-601

Geochronological database considered in the work and characterizing the Anabar collision system in the Northeast Siberian craton includes coordinated results of Sm-Nd and Rb-Sr dating of samples from crustal xenoliths in kimberlites, deep drill holes, and bedrock outcrops. As is inferred, collision developed in three stages dated at 2200–2100, 1940–1760, and 1710–1630 Ma. The age of 2000–1960 Ma is established for substratum of mafic rocks, which probably originated during the lower crust interaction with asthenosphere due to the local collapse of the collision prism. Comparison of Sm-Nd and Rb-Sr isochron dates shows that the system cooling from ≈700 to ≈300°C lasted approximately 300 m.y. with a substantial lag relative to collision metamorphism and granite formation. It is assumed that accretion of the Siberian craton resulted in formation of a giant collision mountainous structure of the Himalayan type that was eroded by 1.65 Ga ago, when accumulation of gently dipping Meso-to Neoproterozoic (Riphean) platform cover commenced.  相似文献   

Hydrochemistry and isotope geochemistry as tools for groundwater hydrodynamic investigation in multilayer aquifers: a case study from Lomellina, Po plain, South-Western Lombardy, Italy     

Giorgio Pilla  Elisa Sacchi  Gianmaria Zuppi  Giovanni Braga  Gianfranco Ciancetti 《Hydrogeology Journal》2006,14(5):795-808

A multicriteria approach in studying hydrodynamics of a multilayer aquifer system has been used in the Lomellina region (Northern Italy). It involves the reconstruction of the hydrogeological framework coupled to the definition of the hydrochemical and isotopic features of the aquifers. A shallow phreatic aquifer, reaching depths of about 60–80 m from the surface, and deeper aquifers containing confined groundwater, were distinguished. Groundwater generally shows mineralisation decreasing with depth; dissolved ions depict calcium-bicarbonate hydrochemical facies and stable isotopes define the recharge mechanisms, the origin of groundwater, and the hydraulic confinement of deep aquifers. The phreatic aquifer is fed by local infiltration and by streams and irrigation channels. Tritium and Carbon-14 groundwater dating indicate long residence times (on the order of thousands of years) for confined aquifers. The confined aquifers show essentially passive hydrodynamic conditions and maintain a higher piezometric level than the phreatic aquifer. This inhibits the possibility of recent water penetrating far below the surface. The hydrogeological setting of the Lomellina region displays features which are common to other sectors of the Po plain. As a consequence, the results of this study, although conducted on a restricted area, are highly illustrative of groundwater hydrodynamics in large sedimentary aquifers.  相似文献   

西藏岗巴晚白垩世锶同位素曲线的地层学意义及问题讨论   总被引：5，自引：3，他引：5  

石和  黄思静  沈立成 《地层学杂志》2005,29(1):28-33

地质历史时期古海洋中的锶同位素组成具有全球基本一致的演化规律 ,并主要受全球性海平面变化影响。根据从西藏岗巴宗山上白垩统剖面中 6 3个海相碳酸盐样品获得的锶同位素测试数据建立了锶同位素演化曲线 ,与北美同时代锶同位素曲线进行了对比 ,证明晚白垩世有一次全球性海平面升降事件 ,在宗山剖面宗山组近底部的年龄值为 89.4 Ma,并讨论了西藏岗巴宗山地区晚白垩世地层划分对比中的一些问题。  相似文献   

新疆葫芦铜镍硫化物矿床的地质特征与成矿时代   总被引：32，自引：1，他引：32  

陈世平  王登红  屈文俊  陈郑辉  高晓理 《新疆地质》2005,23(3):230-233

哈密葫芦铜镍矿是东天山地区典型的与基性-超基性岩有关的岩浆成因块状硫化物矿床.对其中含铜镍硫化物的基性-超基性岩用Re-Os等时线法定年,获得(283±13)Ma的等时线年龄.这表明,葫芦与东天山其他铜镍矿床乃至喀拉通克和箐布拉克铜镍硫化物矿床一样,主要形成于海西期,同位素年代学界定的成岩成矿时间大致在320~280 Ma,表明海西晚期在新疆北部为一个与基性-超基性岩有关的铜镍矿床成矿高峰期.  相似文献   

同位素地质学定年方法评述   总被引：16，自引：1，他引：16  

赵玉灵  杨金中等 《地质与勘探》2002,38(2):63-67

详细分析了当前同纱年代学的常用定年方法，如K-Ar法，U-Pb法，Rb-Sr法和Sm-Nd法等的适用性和局限性。讨论了地质事件定年过程中存在的一些问题，提出了准确定年的注意事项。  相似文献   

羌塘盆地那底岗日地区中侏罗世层序地层与碳、氧、锶同位素响应   总被引：7，自引：0，他引：7  

谢渊  王剑  刘家铎  罗建宁  张哨楠  杨宝星  李明辉 《沉积学报》2002,20(2):188-196

羌塘盆地那底岗日地区中侏罗世沉积了一套稳定的滨浅海相碳酸盐岩与碎屑岩地层,通过层序地层研究划分出五个三级层序。对其中四个层序内碳酸盐岩碳、氧、锶稳定同位素测试分析得出,不同层序、层序界面及层序内不同体系域的δ13 C、δ180、N(87Sr/86Sr)值均有明显的差异,并具规律性变化,整体上反映出研究区中侏罗世发生了多次海平面升降变化和气候、构造活动的演变,为层序地层研究提供了定量的地质地球化学依据。  相似文献   

道虎沟生物群(前热河生物群)的发现及其地质时代   总被引：31，自引：1，他引：31  

张俊峰 《地层学杂志》2002,26(3):173-177,215,T003

根据最新发现的动、植物化石 ,确立了“道虎沟生物群”,这一新的生物群属前热河生物群 ,生存时代大体相当于晚侏罗世的牛津期 (Oxfordian)至基末利期 (Kim meridgian)。这一发现大大补充了我国这一地质时期贫乏的化石记录 ,为探讨热河生物群的起源提供了较丰富的第一手材料。  相似文献   

沐川太平砂岩型铼钼（饿）矿点的地质特征和矿化时代   总被引：1，自引：0，他引：1       下载免费PDF全文

曹志敏  骆耀南等 《地质学报》2002,76(1):95-99

四川沐川县民主-太平-带含钼砂岩为一新矿化类型——沉积砂岩型铼钼（锇）矿点。X-射线粉晶衍射分析结果表明其中微-细晶鳞片状含钼矿物为晶质辉钼矿；高精度质谱分析发现辉钼矿中分散元素Re和铂族元素Os含量很高，具有重要的综合利用价值；高精度Re-Os同位素测年证明辉钼矿形成年龄与含矿的中生代红物学和矿床学均具有重要的理论意义和应用价值。  相似文献