中国煤炭地震勘探技术发展

我国煤炭地震勘探技术的发展有着近50年的历史。从无到有,从使用光点仪、模拟仪、数字仪到无线遥测仪;从折射到反射,从单次覆盖到多次覆盖;从二维到三维;从单波到多波。经过几代人的不断努力,逐步形成了中国特色的煤炭地震勘探技术体系,整体技术达到国际先进水平。煤炭地震勘探技术的应用,为我国煤炭工业的发展作出了巨大的贡献。在中国煤炭地质总局成立50周年之际,回顾我国煤炭地震勘探在不同历史时期对煤炭地质勘探的作用和贡献,提出当前地震勘探面临的新课题,展望前景,为我国煤炭能源生产提供地质保障,将具有十分重要的意义。     

Point Mass Method Applied to the Regional Gravimetric Determination of the Geoid

The determination of the local gravity field by means of the point mass inversion method can be performed as an alternative to conventional numerical methods, such as the least-squares collocation. Based on the first derivative of the inverse-distance Newtonian potential for the representation of the gravity anomaly data, it is possible to compute any wavelength component of the geoid in planar approximation with sufficient accuracy. In order to exemplify the theoretical concept, two applications are presented of the computation of two different wavelength components of the geoid, the long wavelength component in a local solution and the short wavelength component in a regional solution. The results are compared with corresponding least-squares collocation solutions, using a global geopotential model to remove and to restore the long wavelength component.     

Eutrophication and some European waters of restricted exchange

Regions of Restricted Exchange (RREs) are an important feature of the European coastline. They are historically preferred sites for human settlement and aquaculture and their ecosystems, and consequent human use, may be at risk from eutrophication. The OAERRE project (EVK3-CT1999-0002) concerns ‘Oceanographic Applications to Eutrophication in Regions of Restricted Exchange’. It began in July 2000, and studies six sites. Four of these sites are fjords: Kongsfjorden (west coast of Spitzbergen); Gullmaren (Skagerrak coast of Sweden); Himmerfjärden (Baltic coast of Sweden); and the Firth of Clyde (west coast of Scotland). Two are bays sheltered by sand bars: Golfe de Fos (French Mediterranean); and Ria Formosa (Portuguese Algarve). Together they exemplify a range of hydrographic and enrichment conditions. The project aims to understand the physical, biogeochemical and biological processes, and their interactions, that determine the trophic status of these coastal marine RRE through the development of simple screening models to define, predict and assess eutrophication. This paper introduces the sites and describes the component parts of a basic screening model and its application to each site using historical data. The model forms the starting point for the OAERRE project and views an RRE as a well-mixed box, exchanging with the sea at a daily rate E determined by physical processes, and converting nutrient to phytoplankton chlorophyll at a fixed yield q. It thus uses nutrient levels to estimate maximum biomass; these preliminary results are discussed in relation to objective criteria used to assess trophic status. The influence of factors such as grazing and vertical mixing on key parameters in the screening model are further studied using simulations of a complex ‘research’ model for the Firth of Clyde. The future development of screening models in general and within OAERRE in particular is discussed. In addition, the paper looks ahead with a broad discussion of progress in the scientific understanding of eutrophication and the legal and socio-economic issues that need to be taken into account in managing the trophic status of RREs.     

Significant hot and cold events at the Fabra Observatory, Barcelona (NE Spain)

Summary A long series of maximum and minimum daily temperatures recorded at the Fabra Observatory (Barcelona) from 1917 to 1998 has permitted a detailed study of significant hot and cold events, based on the crossing theory and on the Markovian process. The former allows us to obtain statistical distributions of the number of hot and cold events per year, the starting date and the magnitude of an event. The Poisson, the normal and the exponential distributions are the respective models. On the other hand, the Markovian process estimates probabilities for the duration of several hot and cold events above or below different temperature threshold levels. It should be stressed that the threshold levels, which define the significant hot and cold events, are almost coincident with those whose lengths follow a Markovian process. From a more applied point of view, two examples of hot and cold events of high magnitude are shown and their associated synoptic situations discussed. Some other typical synoptic situations leading to relevant hot and cold events in Barcelona and the surrounding areas are also summarised. Received March 1, 2001 Revised July 30, 2001     

Distribution of major and trace elements in La Luna Formation, Southwestern Venezuelan Basin

The La Luna Formation (Maraca section), Maracaibo Basin, was studied by means of V and Ni analysis of the bitumen, total organic carbon (TOC), total sulfur (St), major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), trace elements (V, Ni, Co, Cr, Cu, and Zn), and electron microprobe analysis (EPMA) of the whole rock, and St, major elements (Si, Al, Fe, Mg, Mn, Ca, Ti, Na, K, P), trace elements (V, Ni, Co, Cr, Cu, Zn, Mo, Ba, U, Th) and rare earth elements (La, Ce, Nd, Sn, Eu, Th, Yb, Lu) of the carbonate-free fraction. The results are discussed based on the organic and inorganic association of trace elements and their use as paleoenvironmental indicators of sedimentation. An association between V and organic matter is suggested by means of correlation between V and Ni vs. TOC, the use of EPMA (whole rock) and V and Ni concentrations (carbonate-free fraction), whereas Ni is found in the organic matter and the sulfide phase. Fe is present as massive and framboidal pyrite, whereas Zn precipitates into a separate phase (sphalerite), and Ni, Cu and, in some cases, Zn, can be found as sulfides associated with pyrite. Concentrations of V and Ni (bitumen), TOC, St, V, Ni, Cr, Cu and Zn (whole rock), U, Th, Mo (carbonate-free fraction) are indicative of changes in the dysoxic sedimentation conditions in the chert layers (TOC, St, V, Ni, Cu and low Zn and V/Cr <4) to euxinic anoxic conditions in the argillaceous limestone (TOC, St, V, Ni, Cu and high Zn and V/Cr >4). In the sequence corresponding to the argillaceous limestone, variations in the concentrations of TOC, St, V, Ni, Zn, Cu and Cr (whole rock) can be observed, also suggesting variable sedimentation conditions. The following is proposed: (i) sedimentation intervals under euxinic conditions associated with high contribution and/or preservation of organic matter, allowing a high concentration level of V and Ni in the organic phase and the accumulation of Cu, Zn and Ni (in a smaller proportion) in the sulfide phase; (ii) sedimentation intervals under anoxic conditions and in the presence of relatively lower H₂S, which allowed lower concentrations of V and Ni in the organic phase and higher concentrations of Cu, Zn, and Ni in the sulfide phase. Rare earth elements (REE) concentrations exhibit a marked increase in Ce, Nd, Sm, Eu, Y and Lu for the QM-3 interval, relative to Post-Archean Average Shale (PAAS). REE enrichment in shales has been related to the presence of phosphate minerals such as monazite or apatite. However, these minerals were not detected through XRD or EPMA in the whole rock or in the carbonate-free fraction. The association of REE with organic matter is suggested due to the absence of phosphate minerals, although assessment of these elements require further analysis.     

Évolution thermique des séries sédimentaires de la Marge ardéchoise : étude pétrographique de la matière organique et des argilesThermal evolution of the sedimentary series of the Ardèche Margin: petrological studies of organic matter and clays

Two wells, Balazuc (BA1) and Morte-Mérie (MM1), located in a confined area (1200 m apart) and separated by the Uzer fault (a Liassic structure with a dip fault of 1300 m) were analysed using conventional methodologies and techniques (PRV, TAI, XRD, STEM) in order to compare the diagenetic evolution of clays and organic matter. The thermal convective process allows the circulation of hot fluids and the oxidation of organic matter. The conductive process allows the maturation of the organic matter, the expulsion of hydrocarbons and the deposit of pyrobitumes in the migration channels. To cite this article: L. Martinez et al., C. R. Geoscience 334 (2002) 1021–1028.     

Influence de la microporosité sur le piégeage du gaz dans un milieu poreux naturel

Trapped-gas content in natural porous media, also called residual gas saturation (Sgr), corresponds to the imbibition end-point. To define the parameters controlling Sgr, two parameters were studied: the influence of rock characteristics (on 400 sandstone samples) and initial gas saturation (Sgi), on the basis of 60 experimental curves between Sgr and Sgi. Based on an extensive experimental database, this study establishes the dominant influence of microporosity on trapped gas saturation, and indirectly that of the contained clays. To cite this article: K. Suzanne, J. Billiotte, C. R. Geoscience 336 (2004).     

4.4 billion years of crustal maturation: oxygen isotope ratios of magmatic zircon

Analysis of δ¹⁸O in igneous zircons of known age traces the evolution of intracrustal recycling and crust-mantle interaction through time. This record is especially sensitive because oxygen isotope ratios of igneous rocks are strongly affected by incorporation of supracrustal materials into melts, which commonly have δ¹⁸O values higher than in primitive mantle magmas. This study summarizes data for δ¹⁸O in zircons that have been analyzed from 1,200 dated rocks ranging over 96% of the age of Earth. Uniformly primitive to mildly evolved magmatic δ¹⁸O values are found from the first half of Earth history, but much more varied values are seen for younger magmas. The similarity of values throughout the Archean, and comparison to the composition of the “modern” mantle indicate that δ¹⁸O of primitive mantle melts have remained constant (±0.2‰) for the past 4.4 billion years. The range and variability of δ¹⁸O in all Archean zircon samples is subdued (δ¹⁸O(Zrc)=5–7.5‰) ranging from values in high temperature equilibrium with the mantle (5.3± 0.3‰) to slightly higher, more evolved compositions (6.5–7.5‰) including samples from: the Jack Hills (4.4–3.3 Ga), the Beartooth Mountains (4.0–2.9 Ga), Barberton (3.5–2.7 Ga), the Superior and Slave Provinces (3.0 to 2.7 Ga), and the Lewisian (2.7 Ga). No zircons from the Archean have been analyzed with magmatic δ¹⁸O above 7.5‰. The mildly evolved, higher Archean values (6.5–7.5‰) are interpreted to result from exchange of protoliths with surface waters at low temperature followed by melting or contamination to create mildly elevated magmas that host the zircons. During the Proterozoic, the range of δ¹⁸O(Zrc) and the highest values gradually increased in a secular change that documents maturation of the crust. After ∼1.5 Ga, high δ¹⁸O zircons (8 to >10‰) became common in many Proterozoic and Phanerozoic terranes reflecting δ¹⁸O(whole rock) values from 9 to over 12‰. The appearance of high δ¹⁸O magmas on Earth reflects nonuniformitarian changes in the composition of sediments, and rate and style of recycling of surface-derived material into magmas within the crust. Electronic Supplementary Material Supplementary material is available for this article at     

The Greer Lake leucogranite, Manitoba, and the origin of lepidolite-subtype granitic pegmatites

The Archean Greer Lake leucogranite intruded metabasalts of the Bird River Greenstone Belt in the southwestern part of the Superior Province of southeastern Manitoba. The considerably evolved, multiphase, peraluminous, B-, P-, and S-poor leucogranite (K/Rb 132 to 24) was probably generated by fault-friction-assisted anatexis of dominantly metatonalitic rocks and subsequent differentiation. The leucogranite produced interior, transitional, non-crosscutting pods of barren, beryl-columbite- and lepidolite-subtype pegmatites that solidified from local segregations of highly fractionated residual melt. Steep fractionation gradients characterize the granite-to-pegmatite transition, most conspicuously so in the case of the most evolved, Li, Rb, Cs, Be, Mn, Sn, Nb-Ta, F-rich, lepidolite-subtype pod AC #3 (with K/Rb ≥ 16 and Cs 330 ppmwt in accessory K-feldspar, ≥2.5 and ≤11,200 ppmwt, respectively, in lepidolite, Cs ≤28,000 ppmwt in beryl, and Ta/(Ta+Nb) at. ≤ 0.95 in manganotantalite). The Greer Lake example documents beyond any doubt the igneous derivation of lepidolite-subtype pegmatites from a plutonic parent. Most cases of generally very scarce lepidolite-subtype pegmatites obscure this relationship, as the volatile-rich, highly fluid melts stable to relatively low temperatures commonly migrate to great distances from their plutonic sources.     

Pliocene marine deposits at Punta Maldonado, Guerrero state, Mexico

Diverse and abundant Foraminifera and Ostracoda assemblages were recovered from a measured stratigraphic section at Punta Maldonado, Guerrero state, Mexico. The planktonic species indicate an early Pliocene age, between 5.3 and 3.6 Ma; an early late Pliocene (around 2.4 Ma) planktonic assemblage also was recorded from isolated deposits. These ages contradict the Cretaceous–Paleogene age previously assigned to the sedimentary succession at Punta Maldonado. All indicators—benthic assemblages, ichnofacies, lithology, grain size, primary structures, mineralogy, body rock geometry, and facies—suggest deposition in the foreshore and offshore transition zones of a storm-dominated shallow siliciclastic shelf. The Ostracoda and Foraminifera indicate deposition around the outer neritic/upper bathyal boundary, which suggests an uplift of 320–400 m in the area during the Pliocene. This study represents the first report of Pliocene marine rocks in the southwestern coast of Mexico; the data presented contribute to regional geotectonic models.