罗布泊盐湖"大耳朵"盐盘特征、成因及古环境意义

干盐湖蒸发岩沉积是干旱内陆封闭盆地的主要成盐模式,其地表盐壳沉积特征、蒸发盐类矿物具有明显的分带性.罗布泊干盐湖,保存了完整的"耳轮"型环状沉积模式和演化序列,在世界干盐湖中实属罕见.通过对罗布泊"大耳朵"干盐湖区多级环状亚沉积环境下发育的盐壳地貌、沉积结构、龟裂形态、矿物组成以及地下卤水的地表排泄情况进行地面调查和实...     

Hydrologic and climatic implications of a multidisciplinary study of late Holocene sediment from Kenosee Lake, southeastern Saskatchewan, Canada

Sediment lithology and mineralogy, as well as ostracode, plant macrofossil and stable isotope stratigraphies of lake sediment cores, are used to reconstruct late Holocene hydrologic changes at Kenosee Lake, a relatively large, hyposaline lake in southeastern Saskatchewan. Chronological control is provided by AMS radiocarbon ages of upland and shoreline plant macrofossils. All indicators outline an early, low-water, saline phase of lake history (4100–3000 BP), when the basin was occupied by a series of small, interconnected, sulfate-rich brine pools, as opposed to the single, topographically-closed lake that exists today. A rapid rise in lake-level (3000–2300 BP) led to the establishment of carbonate-rich, hyposaline lake conditions like those today. Lithostratigraphic data and ostracode assemblages indicate peak salinities were attained early in this period of lake infilling, suggesting that the lake-level rise was initially driven by an influx of saline groundwater. Lake-level and water chemistry have remained relatively stable over the last 2000 years, compared to earlier events. Because of a lack of datable organic material in sediments deposited during the last 2000 years, the chronology of recent events is not well resolved. Plant macrofossil, lithostratigraphic and ostracode evidence suggests that lake draw-down, accompanied by slightly higher than present salinites, occurred sometime prior to 600 BP, followed by peak lake-level and freshwater conditions. This most recent high lake stand, indicative of a high water table on the surrounding upland, may also have led to the establishment of an extensive cover of Betula in the watershed, possibly in response to paludification. Ostracode assemblages indicate that peak freshwater conditions occurred within the last 100 years. Since historically documented lake-level fluctuations correlate with decadal scale climatic fluctuations in the meteorological record, and late-Holocene hydrologic dynamics correspond to well documented climatic excursions of the Neoglacial and Little Ice Age, Kenosee Lake dynamics offer insight into the susceptibility of the region's water resources to climate change.     

大兴安岭地区内生铜矿床的成因类型、成矿时代与成矿动力学背景

大兴安岭地区位于兴蒙造山带的东段,构造、岩浆活动强烈,蕴藏着丰富的内生有色金属、贵金属矿产资源。本文通过对该区内生铜矿床的地质特征、成因类型和年代学研究,初步将区内内生铜矿床划分为斑岩型、浅成热液高硫化型(铜银、铜锡)和接触交代型三种成因类型,除铜锡矿床外,它们的成矿作用均与高钾钙碱系列I型花岗质岩浆密切相关;其中斑岩型和浅成热液高硫化型(铜、银)的成矿分别发生在485Ma、180~170Ma和170~160Ma;而浅成热液高硫化型(铜锡)矿床与A型花岗质岩浆相关,成矿在150~135Ma之间;接触交代型与它们相伴生,主要发生在180~160Ma和150~135Ma。其成矿动力学背景分别与早古生代兴安地块与松嫩地块的拼合碰撞造山、中侏罗世的西伯利亚板块和华北板块的陆缘增生带碰撞缝合造山与早白垩世碰撞造山后的地壳伸展减薄作用过程相适应,矿床在不同阶段的造山挤压与伸展转换或造山期后的伸展阶段就位,这项研究为深入研究该区内生多金属成矿规律提供了科学依据。     

A 2000-yr reconstruction of air temperature in the Great Basin of the United States with specific reference to the Medieval Climatic Anomaly

A sediment core representing the past two millennia was recovered from Stella Lake in the Snake Range of the central Great Basin in Nevada. The core was analyzed for sub-fossil chironomids and sediment organic content. A quantitative reconstruction of mean July air temperature (MJAT) was developed using a regional training set and a chironomid-based WA-PLS inference model (r²_jack = 0.55, RMSEP = 0.9°C). The chironomid-based MJAT reconstruction suggests that the interval between AD 900 and AD 1300, corresponding to the Medieval Climate Anomaly (MCA), was characterized by MJAT elevated 1.0°C above the subsequent Little Ice Age (LIA), but likely not as warm as recent conditions. Comparison of the Stella Lake temperature reconstruction to previously published paleoclimate records from this region indicates that the temperature fluctuations inferred to have occurred at Stella Lake between AD 900 and AD 1300 correspond to regional records documenting hydroclimate variability during the MCA interval. The Stella Lake record provides evidence that elevated summer temperature contributed to the increased aridity that characterized the western United States during the MCA.     

BOOK REVIEWS

Books reviewed in this article: Boundary Control and Legal Priniciples . Curtis M. Brown , Walter G. Robillard and Donald A. Wilson . Lost Initiatives: Canada's Forest Industries, Forest Policy, and Forest Conservation . R. Peter Gillis and Thomas R. Roach . The Navajo Atlas: Resources, People, and History of the Dine Bikeyah . James M. Goodman . The City and the Sign . M. Gottdiener AND Alexandros Ph . Lagopoulos , EDS. The Comfortable House: North American Suburban Architecture 1890–1930 . Alan Gowans . Arabic-Islamic Cities. Building and Planning Principles . Besim Salim Hakim . Contemporary Climatology . Ann Henderson -Sellers and Peter J. Robinson . A Trace of Desert Waters . Samuel G. Houghton . Geography, Resources and Environment. Vol. 1: Selected Writings of Gilbert F. White. Vol. 2: Themes from the Work of Gilbert F. White . Robert W. Kates AND Ian Burton , ED. Spatial Dimensions of Unemployment and Underemployment (A Case Study of Rural Punjab) . Gopal Krishan . Maps of the Holy Land: Cartobibliography of Printed Maps, 1475–1900 . Compiled by Eran Laor , assisted by Shoshana Klein . The Geography of Third World Cities . Stella Lowder . A Perspective on U.S. Farm Problems and Agricultural Policy . Lance Mc Kinzie , Timothy G. Baker AND Wallace E. Tyner . Soil Erosion and Its Control. R.P.C . Morgan , ED Geopolitics . Patrick O'Sullivan . Landscape, Meanings and Values . Edmund C. Penning -Rowsell AND David Lowenthal , EDS.     

南极长城站区土壤重金属含量特征及来源分析

频繁的人类活动对南极生态环境的影响越来越受到关注,在南极长城站周边人类活动密集区对土壤进行采样的基础上,分析长城站周边地区表层土壤中重金属含量特征,并结合近20年来长城站周边土壤中主要重金属含量的分布,展开对比研究,探讨长城站区主要重金属元素的来源。结果表明,8种主要重金属在长城站表层土壤中都有不同程度的富集,站区频繁的车辆活动使得汽车尾气排放及汽车轮胎磨损产生大量含重金属的有害气体和粉尘,这些物质沉降在站区土壤表层或许是南极长城站区土壤重金属富集的重要原因之一。     

Middle Jurassic–Early Cretaceous tectonic evolution of the Bayanhushuo area,southern Great Xing’an Range,NE China: constraints from zircon U–Pb geochronological and geochemical data of volcanic and subvolcanic rocks

This study presents new zircon U–Pb geochronology, geochemistry, and zircon Hf isotopic data of volcanic and subvolcanic rocks that crop out in the Bayanhushuo area of the southern Great Xing’an Range (GXR) of NE China. These data provide insights into the tectonic evolution of this area during the late Mesozoic and constrain the evolution of the Mongol–Okhotsk Ocean. Combining these new ages with previously published data suggests that the late Mesozoic volcanism occurred in two distinct episodes: Early–Middle Jurassic (176–173 Ma) and Late Jurassic–Early Cretaceous (151–138 Ma). The Early–Middle Jurassic dacite porphyry belongs to high-K calc-alkaline series, showing the features of I-type igneous rock. This unit has zircon ε_Hf(t) values from +4.06 to +11.62 that yield two-stage model ages (T_DM2) from 959 to 481 Ma. The geochemistry of the dacite porphyry is indicative of formation in a volcanic arc tectonic setting, and it is derived from a primary magma generated by the partial melting of juvenile mafic crustal material. The Late Jurassic–Early Cretaceous volcanic rocks belong to high-K calc-alkaline or shoshonite series and have A₂-type affinities. These volcanics have ε_Hf(t) and T_DM2 values from +5.00 to +8.93 and from 879 to 627 Ma, respectively. The geochemistry of these Late Jurassic–Early Cretaceous volcanic rocks is indicative of formation in a post-collisional extensional environment, and they formed from primary magmas generated by the partial melting of juvenile mafic lower crust. The discovery of late Mesozoic volcanic and subvolcanic rocks within the southern GXR indicates that this region was in volcanic arc and extensional tectonic settings during the Early–Middle Jurassic and the Late Jurassic–Early Cretaceous, respectively. This indicates that the Mongol–Okhotsk oceanic plate was undergoing subduction during the Early–Middle Jurassic, and this ocean adjacent to the GXR may have closed by the Late Middle Jurassic–Early Late Jurassic.     

大兴安岭岩石圈地幔特征——哈拉哈河-绰尔河橄榄岩捕虏体的证据

大兴安岭哈拉哈河-绰尔河第四纪火山岩中含有尖晶石相和石榴石相橄榄岩捕虏体.本文报道的尖晶石相橄榄岩包括方辉橄榄岩和二辉橄榄岩两类,前者分布数量略高于后者.方辉橄榄岩多数具有较高的平衡温度(1072～1193℃),矿物化学成分变化大,含有高Mg橄榄石和高Cr#尖晶石,这些特征一致表明是古老岩石圈地幔残余的样品.而二辉橄榄岩显示相对均一的矿物化学成分和很宽的平衡温度变化范围(636～1178℃),代表了明显受到改造的岩石圈地幔,可能反映岩石圈地幔的不同深度和局部经历了软流圈与岩石圈相互作用.通过与华北克拉通的对比,发现地处兴蒙造山带的大兴安岭岩石圈地幔中仍保留有相当量的古老岩石圈地幔残余,区别于遭受强烈改造和破坏的华北克拉通东部地区的岩石圈地幔.     

BOOK REVIEWS

Book Reviews in are this Article Northern Waters . Clive Archer and David Scivener , EDS. Principles of Geographical Information Systems for Land Resources Assessment . P. A. Burrough . The Great Lakes: An Environmental Atlas and Resource Book. Environment Canada , United States Environmental Protection Agency , Brock University , AND Northwestern University . Uneven Development in Southern Europe: Studies of Accumulation, Class, Migration and the State. Rays Hudson AND Jim Lewis , EDS. Hazards: Technology and Fairness. Robert W. Kates and Alvin M. Weinberg . The Price of War. Urbanization in Vietnam 1954–85. Nigel Thrift and Dean Forbes . Population Structures and Models: Developments in Spatial Demography. Robert Woods and Philip Rees , EDS. Evaluating Earthquake Hazards in the Los Angeles Region-An Earth-Science Perspective. J. I. Ziony , ed .     

Deep seismic reflection study over the Vindhyans of Rajasthan: Implications for geophysical setting of the basin

This paper presents results of high-resolution deep seismic reflection profiling of the Proterozoic Vindhyan basin of the Rajasthan area along the Chandli-Bundi-Kota-Kunjer profile. Seismic images have been used to estimate the thickness of Vindhyan strata as well as to understand the tectonic framework of the basin. The results are constrained by gravity, magnetic and magnetotelluric data. The study reveals gentle SE-dipping reflection bands representing the Vindhyan strata. The seismic sections depict gradual thickening of the Vindhyan succession towards southeast from Bundi. The velocities of the upper and lower Vindhyans are identified as 4.6-4.8 km/s and 5.1-5.3 km/s. The NW limit of the Vindhyan basin is demarcated by the Great Boundary Fault (GBF) that manifests as a 30 km wide NW dipping thrust fault extending to a depth of 30 km.