湖泊碎屑岩沙坝成因机制及构型表征研究进展*

湖泊碎屑岩沙坝因波浪和沿岸流的反复冲刷,成熟度较高,显示出巨大的油气勘探潜力,已成为隐蔽油气藏勘探的重点。作者在大量文献调研的基础上,总结了近年来前人在滩坝定义、沉积特征、主控因素、成因机制及内部构型研究中的重要进展,在此基础上提出了沙坝演化阶段及沉积构型的新认识。结果表明,沙坝完整的演化历程主要包括4个阶段,分别是弱波浪作用阶段、动荡水流—冲洗回流阶段、风成阶段及沼泽化阶段。影响沙坝发育的控制因素多样,其中物源和风场是沙坝发育的根本因素,两者分别影响了沙坝发育的物质来源和能量供给;而风场所决定的水动力是影响沙坝储集体发育的最直接因素;构造运动和层序演化则控制沙坝的分布位置及保存程度;各因素综合作用决定了坝的形态、发育规模及保存状况。依据前人构型理论,将沙坝构型按照正序方案依次划分为6级,对构型表征方法和沙坝3~5级构型定量表征进行了初步探索,以期为滩坝砂体勘探开发提供理论和实践支持。     

Heavy Minerals Concentration along the Baluchistan Coast, Pakistan from Gadani to Phornala

Sorting and concentration of a variety of heavy minerals along the coast between Gadani and Phornala, Baluchistan, are facilitated by the coincidence of the periods of maximum turbulence and wave activity, maximum percipitation, and sediments discharge. Sediment samples from different intertidal zones between Gadani and Phornala were collected for grain size analysis and petrographic/petrological study. Variations in grain size and mineral assemblage in the intertidal zones have been noted. Concentration of dark color heavy minerals has been noted in fine grain sediments, light color minerals are ubiquitous. The sediments exhibit wide ranges of sorting.     

Exploring Placer Gold Deposits through Integrated Geophysical and Geochemical Techniques at the Confluence of the Indus and Kabul Rivers, NW Pakistan

Analysis of the anomalous magnetic mineral intensities and geochemistry for placer gold deposits are presented for those of the Attock area at the confluence of the Indus and Kabul rivers in northwestern Pakistan. Two grids covering an area of 10 x18 m² and 8 x10 m² were analyzed using a G-858 Cesium Vapor Magnetometer. The anomalous zones obtained were plotted on contour maps, 2 D and 3 D magnetic intensity maps. Based on the magnetic anomalies, grid-1 of the study area wa...     

Holocene stratigraphy-of the Lower Ganges-Brahmaputra River delta in Bangladesh

Major part of the Holocene Ganges-Brahmaputra delta occupies the southern and southwestern part of Bangladesh with a smaller part extending beyond the international boundary in the west. Five facies assemblages are documented in the lower deltaic plain in five different depositional environments: levee or levee complex, bil or depression, abandoned meander belt, interdistributary plain and estuarine plain. The thickness of the Holocene sediments ranges from 30 m to 70 m in the deltaic plain, usually floored by the Pleistocene stiff clays, with the exception of the abandoned meander belt deposit where Holocene channel sand deposited directly on the Pleistocene sand. Radiocarbon dates indicate that low-rate sedimentation has occurred in the northern part, where 4-6 m thick sediments were deposited since the mid-Holocene, whereas 10-30 mthick sediments were deposited in the southern part during the same span of time. In addition, significant coastal subsidence (3 mm/a on average), added by sea-level rise (1.5 mm/a, conservative rate) occurs in the study area, which serves as a negative factor in degrading the coastal plain of Bangladesh in the future, while taking into consideration the weaker sedimentation in the area.     

KRISP 85 — An international seismic investigation of the Kenya Rift

British, German, American and Kenyan seismologists undertook a preliminary crustal seismic programme in the Kenya Rift in the summer of 1985. Thirteen explosions, totalling 7 tonnes, were fired in lakes and boreholes, and were recorded by 42 three-component stations. Preliminary results show that the deep structure along the axis of the Rift is more complex than previous models have suggested.     

QUADRATIC PLS REGRESSION

We treat here an extension of linear PLS regression to include regression on quadratic PLS components.The quadratic regression can be viewed as a natural extension of linear PLS regression to quadratic PLSaccording to the H-principle of mathematical modelling.The numerical implementation is treated indetail.It is shown that this approach can be used for models with large numbers of variables.Somemodelling strategies are discussed depending on the purpose of the modelling.Applications of thisapproach are treated.     

Biodiverse rotifer assemblage(Rotifera: Eurotatoria) of floodplain lakes of the Brahmaputra basin of lower Assam,northeast India: composition and ecosystem diversity

The study aims to ascertain the hypothesis on the rich rotifer biodiversity of the floodplain lakes(beels) of the Brahmaputra river basin and to use these metazoans to assess trophic status or to characterize habitat variations of wetlands. The plankton samples collected from four beels of lower Assam revealed 160 Rotifera species belonging to 35 genera and 19 families. The richness is of biodiversity value as ~38.0% and ~57.0% of the rotifer species known till date from India and northeast India(NEI), respectively. One species each is new to the Oriental region and NEI, and three species are new to Assam; 23 species merit global biogeography interest and several exhibit distribution values in the Indian sub-region. The diverse Lecanidae Brachionidae Lepadellidae Trichocercidae and speciose littoral-periphytic L ecane Lepadella Trichocerca, and richness of Brachionus spp. following removal of aquatic macrophytes are noteworthy. Overall rotifer composition showed homogeneity amongst beels while lower monthly richness and community similarities affirmed heterogeneity within individual beels. We propose L/B quotient based on L ecane : Brachionus species ratios to characterize habitat variations of the sampled wetlands. Sláde?ek's B/T quotient based on B rachionus : T richocerca species ratios affirmed general 'meso-trophic' status of diff erent beels. Our results provided little insight on the influence of individual abiotic factors but the canonical correspondence analyses asserted higher cumulative influence of ten abiotic parameters on Rotifera richness in each beel.     

Influence of rainfall infiltration on the stability of unsaturated coal gangue accumulated slope

The slope instability is associated with increasing rate of rainfall infiltration which cause shear strength reduction and suction loss and the slope tend to fa...     

Climate politics at a crossroad: views on building a consensus

The climate change issue faces a big challenge, perhaps the biggest challenge of all—politics. Pakistan has taken many noticeable steps in relation to climate change: (1) it is the only country in which the Prime Minister is heading an inter-ministerial task force on climate change, (2) it is the first developing country to establish a specialized, self-financed scientific centre to research the impact of climate change, and (3) it is the lead country to earmark budgetary funds for a national carbon sequestration programme. Pakistan, together with many developing countries, has much to offer the climate change issues. The author proposes five approaches to build consensus among climate policy negotiators: (1) reinforcing the polluter pays principle and ‘common but differentiated responsibility’, (2) active partnership by developing countries, (3) recognizing the voluntary actions taken by developing countries, (4) reinforcing the issue of adaptation, and (5) considering the option of equal per capita entitlements.     

Petroleum hydrocarbon distribution in continental shelf region of southeast coast of India

In the surface sediment samples collected from 7 transects in the continental shelf region off Karaikkal, Parangipettai, Cuddalore-SIPCOT, Cheyyur, Chennai, Tammenapatanam and Singarayakonda in the s...