Roadian–Wordian (Guadalupian, Middle Permian) global palaeobiogeography of brachiopods

A database of 4471 Roadian–Wordian (Guadalupian, Middle Permian) occurrences of 381 brachiopod genera in 44 different operational geographical units (stations) was analyzed by both Q-mode and R-mode quantitative methods. Four distinct brachiopod biogeographical realms and nine provinces, and 11 brachiopod associations are recognized. The Boreal Realm in the Northern Hemisphere includes the Verkolyman Province in the northern and northeastern Siberian Platform and the eastern European Province in the Ural seaway between the European and Siberian platforms. Both provinces are characterized by containing typical Boreal cold-water brachiopod associations. The Gondwanan Realm in the south also includes two provinces. The Austrazean Province in eastern Australia and New Zealand is probably the most stable province throughout the Permian and characterized by typical Gondwanan brachiopod associations. The Westralian Province centered in Western Australia is also characterized by typical Gondwanan brachiopods, but also demonstrates biogeographical links with the Tethyan stations. The Palaeoequatorial Realm located mainly in the palaeotropical zone contains highly diverse and abundant brachiopod faunas. Two regions/subrealms and four provinces are recognized within this realm. The North America Subrealm contains a distinct Grandian Province characterized by many endemic brachiopod genera and a few cold-water genera. East-central Alaska and Yukon Territory may constitute another brachiopod province. All the stations in the Tethyan Ocean (both Palaeotethys and Neotethys) constitute a distinct Asian–Tethyan Region/Subrealm and incorporate three different provinces. The Cathaysian Province is comprised of the stations in South China and its surrounding terranes/blocks and a few stations in the northern and western margin of the Palaeotethys. Two transitional provinces (Sino–Mongolian–Japanese Province and Cimmerian Province) in the northern and southern temperate zones are also recognizable. The brachiopod fauna from the Mino Belt in Japan is well distinguished from those from other regions, and is hence assigned to the palaeoceanic Panthalassan Realm. Principal coordinates analysis and minimum spanning tree analysis suggest that a latitude-related thermal gradient was the major control for the palaeobiogeography of Roadian–Wordian global brachiopod faunas and for the latitudinal of pattern of decreasing brachiopod generic diversities from the equator to the poles. In addition, geographic separation and oceanic currents may also have played some role in the spatial distribution of brachiopods during Roadian–Wordian times.     

城市化对江苏气候变化影响的数值模拟个例分析

利用MM5模式对2003年夏季6、7两个月典型区域气候极端事件进行数值模拟,研究城市化急剧扩张对区域气候极端事件的影响和可能机制.研究发现:苏南及邻近地区城市化区域的扩张,会引起区域降水分布的变化.在城市化区域,降水将减少,而在城市化的下风区会有局地的降水增加;同时,在苏南城市化区域中,太湖等湖泊的影响也很重要,会加强其邻近地区局地降水强度.城市化区域的地面气温有明显的上升,对高温天气的作用更大.城市化也会影响地面风场,阻挡穿越城市化区域的风;苏南沿海城市化区域扩张,会使海陆风环流增强,加大了海面向陆面的风.城市化区域的潜热通量明显减少,而感热通量显著增加.城市化增暖产生的局地热源,使城市化区域及邻近地区局地环流发生变化,增强了低层城市化区域向周边辐散的强度.随着高度的增加,城市化的影响也越来越小.     

豫东北主要农作物对气候变暖的响应

利用豫东北具有代表性的濮阳、南乐两个国家基本站1971-2000年的气象和农气观测资料,分析了气候变化趋势及其对农作物的影响,结果表明：濮阳和南乐30 a年平均气温呈逐年升高趋势,1993年后升高趋势明显。气候变暖使冬小麦播种期推延,返青提前,对冬小麦增产有利,也利于玉米生育期的延长和产量提高;终霜期明显提前,初霜期略推迟,霜期变短,使棉花平均生育期延长,霜后花率降低,对产量和质量提高有利。     

一次华南暴雨过程中不同区域降水特征的模拟分析

通过对2005年6月19-20日的一次华南大暴雨过程的诊断分析表明,本次降水过程的水汽来源有两个,一是来自于印度洋上的印度季风,另一个是来自于澳大利亚的东南信风.对不同暴雨中心的分析表明,福建北部的降水带为华南准静止锋锋面上的系统性降水,假相当位温的经向垂直剖面呈明显的Ω型结构,而广东河源附近的暴雨中心为暖区对流性降水,低层为强的不稳定.利用ARPS模式对这次暴雨过程进行了数值模拟,结果表明,锋面雨带主要来自于网格降水的贡献,而对流性降水主要来自于次网尺度降水的贡献.     

鄂托克旗自动站与人工观测风速记录的差异分析

利用鄂托克旗气象观测站2007年1-12月人工站和自动站平行观测的风速、风向资料,统计比较了人工站与自动站风速观测值和极值。结果表明：受观测仪器系统偏差和观测取值时间差异的影响,人工站比自动站的日平均风速偏小0．4m．S-1。风向完全相符的接近40％,2个以上方位的不相符率为4％。     

两类极区平流层异常增温的特征及其与850hPa温度的关系

采用NCEP/NCAR逐日再分析资料,将冬季极区平流层增温分为两种类型:Ⅰ型和Ⅱ型,并分析了两种类型增温的特征、机制及其与850hPa温度的关系。结果表明,波动强迫的强度和对流层的热量能否向上到达平流层是决定两类平流层异常增温的两个主要因素。Ⅰ型平流层增温期间,对流层也表现出了明显的增温特征,850hPa与平流层温度距平场呈现相当正压结构,极区和中纬度异常表现为反位相的振荡,呈现典型的北极涛动的特征;Ⅱ型平流层异常增温期间,增温异常仅局限在平流层范围内,平流层的中低层与高层呈现反位相的距平分布,850hPa温度距平场呈现无规则的分布特征。     

西藏南部晚始新世打拉埃达克质花岗岩及其构造动力学意义

打拉二云母花岗岩岩体位于雅拉香波穹隆的东南,侵入到中生代以前的变质岩系(眼球状花岗质片麻岩和石榴黑云母片麻岩)和特提斯沉积岩(页岩和砂岩)中,主要由石英、斜长石、钾长石、黑云母和白云母组成,形成于～44.3Ma。打拉二云母花岗岩地球化学特征表明:打拉花岗岩具有高Al_2O_3(16.0%～17.0%)、Na_2O/K_2O(1.2)以及A/CNK比值(1.05),表明打拉花岗岩为富钠过铝质花岗岩;轻稀土(LREE)富集,重稀土(HREE)相对亏损,HREE中的Ho到Lu元素有变平的特征((Ho/Lu)_N=1.11～1.46);具有微弱或无Eu异常,Eu/Eu~*=0.87～0.95;较高的初始Sr同位素比值(~(87)Sr/~(86)Sr(i)=0.71754～0.71785)和较低的初始Nd比值(ε_(Nd)(i)=-9.15～-12.4)。打拉花岗岩具有高Sr含量(为355×10~(-6)～416×10~(-6))和Sr/Y的比值(59.1～71.5)、高La/Yb比值、低Y及HREE亏损的特征,与埃达克质花岗岩类似。上述特征表明打拉花岗岩是在较高压力条件下,以角闪岩为主的深部岩石部分熔融的结果。     

鲁西新太古代济宁群含铁岩系形成时代——SHRIMP U-Pb锆石定年

济宁群以隐伏的地质体分布于华北克拉通鲁西地区,以往被划归古元古代。近年来在济宁群的钻探和地球物理研究中,发现存在较大规模条带状硅铁建造,其形成时代引起地学界极大关注。本文对济宁群变质碎屑沉积岩和长英质火山岩进行了锆石SHRIMP年龄测定。含砾绿泥绢云千枚岩的碎屑锆石年龄主要集中在～2.7Ga,可靠的最年轻碎屑锆石年龄为2.61±0.01Ga。变质长英质火山岩岩浆锆石年龄为2.56±0.02Ga。研究表明,济宁群形成于新太古代晚期,而不是以往认为的古元古代。华北克拉通条带状铁建造主要形成于新太古代晚期。济宁群在岩石组合、变质作用方面与鞍山、冀东以及五台地区同时代含硅铁建造的表壳岩系有差别,但是与本溪南芬铁矿的岩石组合有相似之处。这些可能为我国的隐伏太古宙BIF铁矿的研究与勘探提供了重要依据。     

Analytical solution for one-dimensional consolidation of clayey soils with a threshold gradient

General approximate analytical solutions are developed for one-dimensional consolidation with consideration of the threshold gradient under a time-dependent loading. A comparison is made between the present solution and some available numerical solutions for a particular case, and the results show that the approach employed in this article is reasonable. The influence of the threshold gradient and the loading period on consolidation behaviour is investigated, and the results show that the moving boundary of seepage moves downward gradually. The greater the threshold gradient is, the slower the boundary moves. The excess pore pressure will not be completely dissipated at the end of consolidation, and the larger the threshold gradient is, the greater the residual excess pore pressure is. The average degree of consolidation considering the threshold gradient defined by settlement is different from that defined by pore pressure. Moreover, the greater the threshold gradient is, the larger the average degree of consolidation in terms of strain, whereas the smaller the average degree of consolidation in terms of stress. It is also shown that the longer the loading period is, the longer the time moving boundary takes to reach the bottom of the layer, and the greater the average degree of consolidation is.     

A formation mechanism for hematite-rich spherules on Mars

Gray crystalline hematite on Mars has been detected in three regions, Sinus Meridiani, Aram Chaos, and Valles Marineris, first by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor (MGS) orbiter, and then confirmed by other instruments. The hematite-rich spherules were also detected by the Mars Exploration Rover (MER) Opportunity at Meridiani Planum (Sinus Meridiani). Formation mechanisms of the hematite-rich spherules have been discussed widely since then. Here, we argue for an alternative formation mechanism, that is, the spherules originally formed at Valles Marineris due to the interaction of volcanic deposits and acidic hydrothermal fluids, and then were transported to and deposited at Meridiani Planum and Aram Chaos as alluvial/fluvial sedimentary deposits with other materials such as sulfates and rock fragments during the wash-out flows from Valles Marineris to Meridiani Planum and Aram Chaos. Diagenesis of the hematite-rich spherules may have also been a possible mechanism following sediment transport and emplacement. The hypothesis is consistent with available relevant information to date and provides an insight into the understanding of Martian surficial processes.