Geochemical Record of the Cenomanian–Turonian Anoxic Event in Tunisia: Is it Correlative and Isochronous to the Biotic Signal?     

Mohamed SOUA  Dalila ZAGHBIB-TURKI  Hela BEN JEMIA  Jalel SMAOUI  Amel BOUKADI 《《地质学报》英文版》2011,85(6):1310-1335

In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy (foraminifera and radiolarians) and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian–Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Al and K/Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni (organic matter related trace elements) suggests that the Bahloul, deposited during a relatively short period (0.5 Ma), was of relatively elevated primary productivity and minimal detrital input. While higher D* values concurrent with lower Ti/Al ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/(V+Ni), U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo-environmental relevant indicators. High Baxs values and Uauth may indicate anoxic conditions at least at the water–sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.  相似文献   

Modeling of soil salinity within a semi-arid region using spectral analysis   总被引：4，自引：0，他引：4  

Hela Triki Fourati  Moncef Bouaziz  Mourad Benzina  Samir Bouaziz 《Arabian Journal of Geosciences》2015,8(12):11175-11182

  相似文献   

青藏高原汛期降水异常空间分布及水汽配置          下载免费PDF全文

王传辉  周顺武  杨玮  贲海荣  丁锋  张宇 《大气科学学报》2015,38(4):566-572

青藏高原汛期(5—9月)降水具有南北反相的空间分布特征,利用青藏高原67个台站1967—2008年逐月降水资料,分别讨论了汛期各月降水的主要空间分布型以及初夏(5—6月)和盛夏(7—8月)对应的水汽配置和环流异常.结果表明:初夏高原降水以南北反相型(North-South Reverse Type,NSRT)为主,全区一致型(Whole Region Consistent Type,WRCT)次之;盛夏高原降水以WRCT为主.高原降水呈现NSRT分布时,初夏水汽由高原南部输向北部,而盛夏高原北部为水汽辐合区,南部为水汽辐散区.高原降水呈现WRCT分布时,初夏高原水汽主要来自西太平洋,盛夏水汽主要来自阿拉伯海向东转向的水汽输送,该水汽输送由高原西南地区进入高原.在500 hPa位势高度场上,初夏(盛夏)降水两种主要空间分布型的位势高度差异以经(纬)向差异为主,且影响高原降水异常分布的系统多为深厚系统.  相似文献   

Subsidy Removal and Farm-Level Stewardship in Northland     

BEN BRADSHAW  CHRIS COCKLIN  BARRY SMIT 《New Zealand geographer》1998,54(2):12-20

Illustrating one facet of farm-level environmental management in post-1984 New Zealand, this paper assesses changes in stewardship among Northland pastoralists. On-farm activities which protect or enhance the environment continue to be undertaken without state support. However, the withdrawal of environmental grants, in tandem with the wider agricultural policy changes, has reduced the propensity and ability of farmers to undertake stewardship, especially during cyclical downturns.  相似文献   

High-Grade Reworking of Central Australian Granulites: Metamorphic Evolution of the Arunta Complex   总被引：2，自引：2，他引：0  

GOSCOMBE  BEN 《Journal of Petrology》1992,33(4):917-962

The poly-metamorphic evolution of the Strangways Range granulitesof central Australia has been constrained by the phase stabilityrelationships of silica-saturated aluminous gneisses in KFMASH,in conjunction with geothermobarometry and equilibrium thermodynamics.Two contrasting, but overlapping, P-T paths are proposed. Thefirst (M1, at 1800 Ma) had an ‘anticlockwise’ P-Tpath (i.e., increasing P/T with time) and was terminated byisobaric cooling from 850–950 C, at 8–9 kb, toa stable crustal geotherm (<700C). In contrast, the secondgranulite metamorphism (M2–M5, suggested to be at 1400–1500Ma; Goscombe, 1992a) followed a ‘clockwise’ P-Tpath(i.e., decreasing P/T with time) terminated by decompressionand cooling to {small tilde}6–7 kb on a stable crustalgeotherm. M2–M5 occurred during reworking of M, granulitesby compressional orogenesis (Goscombe, 1992a). Initially, loadingand prograde metamorphism accompanied non-coaxial ductile shearand fold repetition (D2–D3). Prograde metamorphism wasfollowed by uplift and retrogression accompanying oblique transpressionand shear zone development while still under compression (D4–D5)(Goscombe, 1992a). The poly-metamorphic evolution indicatesthat ductile deformation reworked the M₁ granulites in an orogenicepisode unrelated, both temporally and tectonically, to M₁,metamorphism (Goscombe, 1992b).  相似文献   

时间域航空电磁系统瞬变全时响应正演模拟   总被引：16，自引：10，他引：6       下载免费PDF全文

殷长春  黄威  贲放 《地球物理学报》2013,56(9):3153-3162

近年来很多专家学者致力于时间域航空系统正反演的研究.本文针对一维均匀层状介质和三维模型进行正演.不仅计算垂直方向上的电磁响应,还计算了同线方向上的电磁响应,为航空电磁多分量观测提供理论依据.通过比较航空电磁系统的脉冲响应和阶跃响应特征,发现脉冲响应在早期时间存在奇异性,造成计算不稳定.然而,阶跃响应在早期时间没有奇异性,因而利用系统的阶跃响应可得到一种计算时间域航空电磁系统全时响应的稳定算法.该算法具有较高的精度,并很好地保持了磁场强度B和磁感应dB/dt关系的一致性.该算法推广到三维地质体的时间域正演模拟亦取得很好的效果.  相似文献   

Bed‐thickness and grain‐size trends in a small‐scale proglacial channel–levée system; the Carboniferous Jejenes Formation,Western Argentina: implications for turbidity current flow processes     

MASON DYKSTRA  BEN KNELLER  JUAN‐PABLO MILANA 《Sedimentology》2012,59(2):605-622

Preserved in Quebrada de las Lajas, near San Juan, Argentina, is an ancient subaqueous proglacial sedimentary succession that includes a small‐scale (ca 50 m thick and ca 200 m wide) channel–levée system with excellent exposure of the channel axis and levée sediments. Coeval deposition of both the channel axis and the levées can be demonstrated clearly by lateral correlation of individual beds. The channel axis consists predominantly of a disorganized, pebble to boulder conglomerate with a poorly sorted matrix. The channel axis varies from 10 to 20 m wide and has a total amalgamated thickness of around 50 m. Beds fine gradationally away from the cobble–boulder conglomerates of the channel axis within a few metres, transitioning to well‐organized pebble to cobble conglomerates and sandstones of the channel margin. Within 60 m outboard of the channel axis in both directions, perpendicular to the trend of the channel axis, the mean grain size of the beds in the levées is silt to fine‐grained sand. Deposits in this channel–levée system are the product of both debris flows (channel axis) and co‐genetic turbidity currents (channel margins and levées). Bed thicknesses in the levées increase for up to 10 to 25 m away from the channel axis, beyond which bed thicknesses decrease with increasing distance. The positions of the bed thickness maxima define the levée crests, and the thinning beds constitute the outer levée slopes. From these relationships it is clear that the levée crest migrated both away from and toward the channel axis, and varied in height above the channel axis from 4 to 5 m (undecompacted), whereas the height of the levée crest relative to the distal levée varied from 4·5 to 10 m, indicating that the channel was at times super‐elevated relative to the distal levée. Bed thickness decay on the outside of the levée crest can be described quite well with a power‐law function (R² = 0·85), whereas the thickness decay from the levée crest toward the channel axis follows a linear function (R² = 0·78). Grain‐size changes are quite predictable from the channel margin outward, and follow logarithmic (R² = 0·77) or power‐law (R² = 0·72) decay curves, either of which fit the data quite well. This study demonstrates that, in at least this case: (i) levée thickness trends can be directly related to channel‐flow processes; (ii) individual bed thickness changes may control overall levée geometry; and (iii) levée and channel deposits can be coeval.  相似文献   

经纬度坐标与QTM编码的三向互化算法及其精度评价标准   总被引：1，自引：1，他引：1  

童晓冲  张永生  贲进 《武汉大学学报(信息科学版)》2006,31(1):27-30

在总结现有的经纬度和QTM编码转换算法的基础上，提出了基于辅助地心坐标系的经纬度坐标与QTM编码的三向互化算法，算法以三向地理格网坐标系为出发点，从三个方向递归逼近QTM地址码。同时，提出了QTM编码精度的评价标准转化误码率。实验证明，三向互化算法在保证速度和绝对精度的情况下，等积转换误码率为0。  相似文献   

一种通用球面等积离散网格生成算法     

贲进  童晓冲  张衡  李勇 《测绘科学技术学报》2005,22(4):252-255,258

球面离散网格模型是管理海量数据的有效途径,如何构建球面网格是这类模型的基础问题.文中利用Snyder等积多面体投影建立了平面与球面的对应关系,设计了球面等积三角形和四边形离散网格的生成算法.结合实验分析了两种网格的最大/最小边长比和单元周长均方差两项指标,结果表明全部网格的指标均收敛,适合用作多分辨率地理空间信息的管理.  相似文献   

碳氧比能谱测井精细解释方法研究及应用     

孟凡顺  冯庆付  贲亮  张绍亮 《西北地质》2005,38(2):102-107

利用碳氧比规范化处理，将碳氧比值限制在广义动态范围之内解决零值漂移问题，使用通用解释模型处理碳氧比资料。利用试验数据分析了碳氧比能谱测井零值漂移与产额的关系。建立了高精度碳氧比能谱精细解释标准。在精细研究和动态分析的基础上，结合多种测井资料，综合评价储层，取得了很好的地质效果。该方法实际处理了大庆、辽河等油田的多口井，效果表明，该解释方法的综合解释符合率在80％以上。  相似文献