Geology of Madagascar: A Brief Outline     

《Gondwana Research》1999,2(3):335-339

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The Thakkhola–Mustang graben in Nepal and the late Cenozoic extension in the Higher Himalayas     

《Journal of Asian Earth Sciences》1999,17(5-6):683-702

The Thakkhola–Mustang graben is located at the northern side of the Dhaulagiri and Annapurna ranges in North Central Nepal. The structural pattern is mainly characterised by the N020–040° Thakkhola Fault system responsible for the development of the half-graben. A detailed study of the substrate and the sedimentary fill in several outcrops indicates polyphased faulting:-pre-sedimentation faulting (Miocene), with a mainly NNW–SSE to N–S compressional stress expressed in the substratum by N020–040° and N180–N010° sinistral and N130–140° dextral conjugate strike-slip faults;-syn-sedimentation faulting (Pliocene–Pleistocene), characterised by a W–E to WNW–ESE extensional stress and tectonic subsidence of the half-graben during the Tetang period (Pliocene probably), followed by a doming of the Tetang deposits and a short period of erosion (cf. Pliocene planation surface and unconformity between the Tetang and Thakkhola Formations); the Thakkhola period (Pleistocene) is characterized by a W–E to WNW–ESE extensional stress and a major subsidence of the half graben;-post-sedimentation recurrent extensional faulting and N–S and NE–SW normal faults in the late Quaternary terrace formations.Geodynamic interpretation of the faulting is discussed in relation to the following:

• 1.the geographic situation of the Thakkhola–Mustang half-graben in the southern part of Tibet and its setting in the Tethyan series above the South Tibetan Detachment System (STDS);
• 2.the geodynamic conditions of the convergence between India and Eurasia and the dextral east–west shearing between the High Himalayas and south Tibet;
• 3.the possible relations between the sinistral Thakkhola and the dextral Karakorum strike-slip faults in a N–S compressional stress regime during the Miocene.

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Cenozoic magmatism in Kalimantan and its related geodynamic evolution     

《Journal of Asian Earth Sciences》1999,17(1-2):25-45

The NE–SW Tertiary magmatic belt of central Kalimantan is related to two separate periods of subduction; during the Eocene–Oligocene and Late Oligocene–Miocene. The younger magmatic belt is superimposed upon the earlier belt. This magmatic belt is characterized chiefly by Late Oligocene–Miocene volcanic products, among which limited exposures of the Eocene volcanics have also been mapped by previous investigators. This calc-alkaline magmatic belt has become known as the ‘gold belt’ of Central West Kalimantan on account of a number of discoveries of Neogene epithermal gold mineralization. This mineralization is found in central to proximal volcanic settings and occurred at relatively shallow depths. The earliest known subduction-related magmatism took place in the Eocene–Early Oligocene with the emplacement of calc-alkaline silicic pyroclastics, followed by a period of continental collision. Subsequent subduction-related magmatism continued from Late Oligocene–Pleistocene, during which time the magma evolved from calc-alkaline to potassic calc-alkaline. Plio-Pleistocene magmatism resulted in the formation of basalt flows. The present available K–Ar ages of the Cenozoic volcanics range from 51 to 1 Ma.  相似文献   

印度河扇水道堤岸外侧更新世沉积物波发育特征与形成过程分析^*          下载免费PDF全文

浩克  纪友亮  张胜久  刘炎鑫  Khurram Shahzad  Saad Ahmed Mashwani  刘笑语  姜燕 《古地理学报》1999,24(2):389-404

印度河扇更新世发育的沉积物波结构复杂、形态多样,其形成过程的认识程度低。本次研究通过高分辨率地震数据和地震解释技术,研究了印度河扇沉积物波的波长、形态、波峰变化等形态特征;阐述了沉积物波与沉积物变形特征的差异、识别了两者的区分标志;总结了水道堤岸斜坡和区域斜坡上沉积物波的分布规律;在此基础上,讨论了沉积物波的形成机理和控制因素,分析了沉积物波的形成过程,并建立了印度河扇沉积物波的形成模式。研究表明: (1)研究区沉积物波波长平均为486.84 m,最大1473 m;波高在10~60 m之间,平均30 m。(2)沉积物波的形态有对称型和非对称型,其迁移方式有上坡迁移型、加积型和下坡迁移型;沉积物波主要发育在水道堤岸的斜坡上,在区域斜坡上也发育少量的沉积物波,这2种沉积物波波脊的走向差异很大,水道堤岸斜坡上的沉积物波主要分布于水道凹岸堤岸的外侧,距离水道越远其规模(波长、波高)越小,波脊走向近于NE-SW方向,与水道的走向平行或斜交;区域斜坡上的沉积物波波脊的走向多为NW-SE向,平行于区域斜坡的走向,离源区越远规模越大。(3)水道堤岸斜坡上的沉积物波是由水道型浊流在离心力的作用下,溢出水道的凹岸,在堤岸外侧的斜坡上沉积形成的,堤岸斜坡的角度对沉积物波的发育规模影响不大,浊流的强度和输沙量对其规模影响大;区域斜坡上发育的沉积物波是由顺坡而下的非水道化的浊流沉积形成;滑塌变形造成的起伏地貌以及早期沉积物波的存在,也都影响了后期沉积物波的发育。  相似文献   

Spatial pattern of ozone injury in aleppo pine and air pollution dynamics in the Mediterranean     

《Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science》1999,24(5):495-498

Interdisciplinary studies, combining the evaluation of ozone effects with the meso-meteorological interpretation of the ozone data have been carried out in eastern Spain since 1994. Mesoscale circulations are very important from the point of view of how and where forest ecosystems are affected by point sources and regional air pollution in the Mediterranean Area. First results of these field surveys show that during 1994, 95 and 96, ozone visual injury (chlorotic mottle) in Pinus halepensis Mill. was well correlated with the penetration of the sea breeze in coastal valleys of Castellón. Patterns of ozone injury, chlorotic mottle, have been positively correlated with needle-age classes looking at tree level.  相似文献   

Factors controlling the burial of organic carbon in laminated and bioturbated sediments off NW Mexico: implications for hydrocarbon preservation     

《Geochimica et cosmochimica acta》1999,63(11-12):1723-1734

Factors controlling the burial of organic carbon (OC) in Late Quaternary sediments on the NW Mexican continental margin are assessed using a suite of box and piston cores strategically located on the shelf-slope rise with respect to the intense oxygen minimum in this region. An OC concentration maximum occurs on the mid-slope, below the core of an intense water-column O₂ minimum, due to current winnowing on the outer shelf, the preferential accumulation of organic matter in fine-grained deposits, and the offshore decrease in the settling flux of organic detritus. The organic matter at all water depths is overwhelmingly marine. Hydrogen indices (HI) are higher on the slope (>300 mg HC/g TOC) than on the shelf (<300 mg HC/g TOC), where current winnowing has promoted organic matter degradation, but there is no difference in HI in slope sediments accumulating under well oxygenated and O₂-deficient conditions. The degree of winnowing appears to be the primary factor affecting the preservational quality of organic matter deposited on this margin.Rates of accumulation of OC and opal are all higher in the interglacial intervals when compared with the glacial deposits over the last 140,000 yr. However, matrix-corrected HI values in the mid- and lower-slope cores are invariant and are similar to values in the laminated intervals from the oxygen-minimum site. Thus, cyclic changes in organic carbon accumulation on this margin have been controlled by production variations rather than differential preservation. HI values in Late Quaternary sediments from several continental margins, including NW Mexico, and euxinic basins correspond to type II kerogen, irrespective of bottom water O₂ concentrations. Therefore, the preservation of oil-prone kerogen in productive margin settings does not appear to be restricted to sediments deposited under conditions of low bottom water O₂ concentrations as envisioned in models of petroleum source-rock deposition.  相似文献   

Characterizing random wave surface elevation data     

《Ocean Engineering》1999,26(5):401-430

The definition and subsequent use of dimensional and dimensionless parameters to characterize various nonlinear aspects of ocean surface waves has again become a matter of great interest to the offshore community. The desire to ascertain whether laboratory simulations are adequately representing the surface waves found in the oceans and the concern over the mechanisms behind platform response phenomena, like ringing, has driven this resurgence of interest. This paper presents a depth independent characterization of single design waves, from which improved estimates of localized wave crest front and back slopes follow that are consistent with discrete time series analysis. Characterization of the nature of the entire wave data recorded requires a combination of spectral parameters and probabilistic models in addition to those used in the design wave characterization. A new expression for the direct evaluation of the kurtosis from knowledge of the spectral bandwidth, the relationship between some of the common spectral parameters, and some modified spectral parameters are presented and discussed. Three illustrative examples are presented. The first example provides a detailed examination of wave data measured from a series of random amplitude and random phase tests in a large model basin. The second presents estimates of the various parameters for the Pierson-Moskowitz and Wallops wave spectrum models. The third example investigates the use of the spectral peakedness ratio for comparing data with selected wave spectrum models. The examples illustrate how the formulae can provide a comprehensive local and global parametric characterization of surface wave elevation data.  相似文献   

STCW ’95: implementation issues: What is the pass mark?     

《Marine Policy》1999,23(1):11-24

By 1 August 1998 Regulation I/7 of the 1995 amendments to the International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (1978) requires a comprehensive submission of information to the International Maritime Organization supporting an Administration’s claim that it complies fully with, or is in the process of implementing, STCW ’95 via policy and legislative processes. Once the complete information is received by the International Maritime Organization, the Secretary-General must submit a report to this effect to the Maritime Safety Committee. Three questions emerging from this controversial provision in STCW ’95 are:

• &#x02022;When, if ever, is the information from an Administration complete?
• &#x02022;What is the time frame allocated for confirmation by the IMO Secretariat?
• &#x02022;How does IMO assess whether the claim by an Administration is valid?

The absolute nature of the phraseology within Regulation I/7, in the author’s view, handcuffs the certification verification process by ‘competent persons’. Equally unfortunately for Administrations, STCW is mute on establishing time frames for the processing of their submissions within IMO. Conceivably, a submission by a proponent aspiring for ‘white listing’ may be delayed sufficiently long for the Secretary-General’s report to miss the MSC regular meetings. What would be the impact of such a delay?Perhaps of greater importance though are two key issues linked to the third question. These issues lie at the heart of the amendments to STCW. Firstly, there is not an appeal or challenge mechanism to IMO’s decision; whether it is favourable or not. It is difficult to gauge at this time either the international shipping community’s reaction to an unfavourable report by IMO or an Administration’s position/policy to recognize a chastised Party’s submission. Secondly, the notion of ‘black- listing’ an Administration for sub-standard marine certification and training may not be sustainable under international jurisprudence. Advocates for IMO’s new role as a ‘watchdog’ of global marine certification and standardization organ for the United Nations would, no doubt, take a contra-position.This article attempts to illuminate the complexity of issues nested within Regulation I/7 of STCW ’95. Emerging controversy could strain international relations to such an extent that the high aspirations of the Convention’s drafters for marine certification transparency may not be realized.  相似文献   

Short-chain carboxylates in fluid inclusions in minerals     

《Applied Geochemistry》2000,15(1):13-25

The carboxylate (formate, acetate, propionate and oxalate) and common inorganic anions (F⁻, Cl⁻ and SO²⁻₄) compositions for aqueous fluid inclusion leachates from 17 mineral samples collected from various deposits have been determined using ion chromatography in conjunction with microthermometric measurements on the fluid inclusions of their host minerals. The minerals, quartz, fluorite, barite, beryl and a few `ore' minerals (wolframite, pyrite and galena), came from hydrothermal vein-type deposits in felsic igneous rocks or Archean metamorphic rocks. The results indicate that short-chain carboxylates are common components in hydrothermal fluids and can be present in considerable amounts. Formic acid (as formate) is the dominant species over other carboxylic acids. The present study raises new questions about the origin and geochemical significance of carboxylates in hydrothermal ore-forming processes.  相似文献   

Identification of common error signatures in global digital elevation models based on satellite altimeter reference data     

《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(1):95-99

The generation of a near-global set of orthometric height data derived from satellite altimetry has allowed for the first time an independent evaluation of the accuracy of existing Global Digital Elevation Models (GDEMs) on a near-global scale. This paper presents results from an intercomparison of GLOBE v1, GLOBE β and JGP95E with altimeter based datasets derived from the ERS-1 geodetic mission, together with ERS-1 and ERS-2 35 day data.One result of this research is the identification of common error signatures, where correlated height differences are seen to exist between the altimeter data and several of the DEMs. The ability to identify such erroneous ground truth data using altimetry facilitates the improvement of these global and regional models. Having targetted regions where the height data are inaccurate, it enables examination of these data for mis-registration and reference datum errors, which can then be corrected using altimetry derived heights.  相似文献