Implications of structural inheritance in oblique rift zones for basin compartmentalization: Nkhata Basin,Malawi Rift (EARS)

The Cenozoic East African Rift System (EARS) is an exceptional example of active continental extension, providing opportunities for furthering our understanding of hydrocarbon plays within rifts. It is divided into structurally distinct western and eastern branches. The western branch comprises deep rift basins separated by transfer zones, commonly localised onto pre-existing structures, offering good regional scale hydrocarbon traps. At a basin-scale, local discrete inherited structures might also play an important role on fault localisation and hydrocarbon distribution. Here, we consider the evolution of the Central basin of the Malawi Rift, in particular the influence of pre-existing structural fabrics.Integrating basin-scale multichannel 2D, and high resolution seismic datasets we constrain the border, Mlowe-Nkhata, fault system (MNF) to the west of the basin and smaller Mbamba fault (MF) to the east and document their evolution. Intra basin structures define a series of horsts, which initiated as convergent transfers, along the basin axis. The horsts are offset along a NE–SW striking transfer fault parallel to and along strike of the onshore Karoo (Permo-Triassic) Ruhuhu graben. Discrete pre-existing structures probably determined its location and, oriented obliquely to the extension orientation it accommodated predominantly strike-slip deformation, with more slowly accrued dip-slip.To the north of this transfer fault, the overall basin architecture is asymmetric, thickening to the west throughout; while to the south, an initially symmetric graben architecture became increasingly asymmetric in sediment distribution as strain localised onto the western MNF. The presence of the axial horst increasingly focussed sediment supply to the west. As the transfer fault increased its displacement, so this axial supply was interrupted, effectively starving the south-east while ponding sediments between the western horst margin and the transfer fault. This asymmetric bathymetry and partitioned sedimentation continues to the present-day, overprinting the early basin symmetry and configuration. Sediments deposited earlier become increasingly dissected and fault juxtapositions changed at a small (10–100 m) scale. The observed influence of basin-scale transfer faults on sediment dispersal and fault compartmentalization due to pre-existing structures oblique to the extension orientation is relevant to analogous exploration settings.     

三沙湾盐田港养殖海域沉积物中的有机碳、氮和磷

于2012年8月(夏季)、11月(秋季)和2013年2月(冬季)、5月(春季)共4个航次对三沙湾盐田港养殖海域表层沉积物组成成分及其变化趋势进行调查分析,并采用单因子污染指数(Pi)对沉积物质量进行评价。结果表明不同功能区沉积物中有机氮(TN)、总磷(TP)和有机碳(OC)含量差异显著(P0.05),TN和TP含量4季变化范围分别是0.15~1.39 g/kg和0.11~1.08 g/kg,平均值分别为(0.89±0.36)g/kg和(0.56±0.26)g/kg。OC含量在1.00~14.71 g/kg之间,平均值为(8.26±3.78)g/kg。各站位沉积物中TN污染指数4季变化范围为0.25~2.53,4季超标率分别为67%、81%、80%和90%;各站位TP污染指数4季变化范围为0.18~2.63,4个季节超标率分别为35%、80%、40%和51%;各季节OC含量均未超标;OC/N原子比全年变化范围在8.4~10.3之间,平均值为8.9±0.6。较弱的水流交换条件和海水养殖,特别是海水网箱养殖,是造成沉积物污染的主要原因,开展多营养层次的综合养殖模式是促进盐田港海水养殖可持续发展的有效途径。     

微波消解―ICP―MS法测土壤和水系沉积物样品中的碘

介绍了用微波消解处理土壤和水系沉积物样品,用电感耦合等离子质谱仪(ICP-MS)快速高效测试碘的方法。方法的检出限为0. 012μg/g。所选的12个土壤和水系沉积物国家一级标准物质12次测定,除GBW07307a的RSD小于10%外,其余RSD值均小于5%,12次测试的平均值和标准值对数差绝对值均小于0. 05。方法加标回收率在98. 6%104. 6%之间。     

羌塘盆地晚侏罗世夏里组磁学参数指示的沉积环境及其成盐意义

羌塘盆地位于青藏高原中部,是一个具有沉积钠盐、钾盐远景的蒸发岩盆地。最近在羌塘盆地上侏罗统夏里组中发现多处具有钾、钠异常的盐泉这一重要的找钾盐线索,然而目前对上侏罗统夏里组的古环境演变仍然不甚了解,限制了对晚侏罗世羌塘盆地的成盐(成钾)条件和可能的层位等重大科学问题的理解。因此本文以热磁分析为主,对羌塘盆地雁石坪地区上侏罗统夏里组沉积物进行高分辨率岩石磁学研究,并讨论其古环境意义。最后,根据成盐(成钾)理论,综合分析羌塘盆地上侏罗统夏里组成盐(成钾)的构造、气候和物源条件。κ-T曲线、磁滞回线和热退磁结果共同表明磁铁矿和赤铁矿是夏里组的主要载磁矿物;磁学参数分析表明夏里组上段赤铁矿含量相对增加,揭示夏里组上段形成于干旱气候环境;综合分析构造、气候和物源条件表明,羌塘盆地上侏罗统夏里组上段最为具备良好的成盐(成钾)条件。     

SEDIMENT PROPERTIES AND DYNAMICS IN THE TAIHU LAKE, CHINA

1 INTRODUCTION Large amounts of nutrients and contaminants such as trace metals are transported into large lakes frominflow rivers and then absorbed onto or associated with fine-grained sediment particles (Sheng and Lick,1979). The nutrients and contamina…     

Hydrodynamics of salt marsh creek systems: Implications for marsh morphological development and material exchange

Integrated ebb-aligned drainage systems are a feature of tide-dominated marshes, and are generally regarded as major conduits for material exchange. In north Norfolk, highly unsteady creek flows exhibit well-developed velocity and stress transients which result from the discontinuous nature of the tidal prism and the interaction of shallow water tidal inputs with hydraulically rough vegetated surfaces. Marsh morphological development is governed by a form-process feedback, in the sense that the marsh surface acts as a topographic threshold separating the depositional regime of below-marsh tides from the erosional (ebb-dominated) regime of over-marsh tides. Vertical marsh growth results in increasing intermittency of creek sediment transport. Furthermore, velocity transients are associated with large discharges which must be allowed for in material flux computations. Creek flux measurements are not in themselves sufficient to estimate total material budgets, since a large proportion of tidal exchange may take place via the marsh edge. Such studies should focus instead on direct measurement of marsh surface processes. These findings have relevance beyond this back-barrier setting to marshes of different geometry, occupying a broad range of the tidal energy spectrum.     

长江河口南汇嘴潮滩近期演变分析

南汇嘴潮滩位于长江口和杭州湾的交汇地带,受长江口和杭州湾北岸两股潮流的控制,近年来由于低潮滩促淤围垦工程导致其水流和泥沙运移、沉积和地貌发生了显著的变化。根据近期水文泥沙观测资料及1993年、1998年、2003年、2005年的实测地形图资料,分析了南汇嘴潮滩近期演变特征。研究结果表明:1993-1998年为淤涨期;1998-2003年为冲淤调整期;2003-2005年呈现向外淤涨的趋势。而造成这一趋势的原因主要包括潮滩海洋动力作用、长江入海泥沙变化及近岸海岸工程建设等。     

Sediment transport patterns at Trafalgar offshore windfarm

A simple analytical model of wave propagation has been developed in order to study the potential sediment transport patterns due to the action of currents and waves in the neighborhood of cylindrical structures as well inside a group of these structures. The attention is focused on the study of Trafalgar offshore windfarm, a case in which it has been necessary to analyze the flow trough porous structures in order to model fish growing-cages planned to be installed at each aerogenerator structure. The results are obtained by averaging over one period of wave in order to evaluate the net potential sediment transport. The analysis of the results reveals how the processes of wave diffraction and reflection give rise to periodic patterns of sediment transport around and between the structures.