海洋碳酸盐相模式

在碳酸盐层序中打过钻孔以及为成败提供事后解释的人都对潜在的碳酸盐储层的基本岩相模式、三维分布感兴趣。从沉积作用的观点看,这些岩体主要是由潮坪沉积物、各种类型礁体和砂洲组成。一旦被成岩交代,多种作用会形成／破坏碳酸盐中的孔隙度,但对这些作用还不太了解。...     

Numerical implementation of a backward probabilistic model of ground water contamination

Backward location and travel time probabilities can be used to characterize known and unknown sources or prior positions of ground water contamination. Backward location probability describes the position of the observed contamination at some time in the past; backward travel time probability describes the amount of time prior to observation that the contamination was released from its source or was at a particular upgradient location. The governing equation for backward probabilities is the adjoint of the governing equation for contaminant transport, but with new load terms. Numerical codes that have been written to solve the forward equations of contaminant transport, e.g., the advection-dispersion equation, can also be used to solve the adjoint equation for location and travel time probabilities; however, the interpretation of the results is different and some new approximations must be made for the load terms. We present the governing equations for backward location and travel time probabilities, and provide appropriate numerical approximations for these load terms using the cell-centered finite difference method, one of the most popular numerical methods in ground water hydrology. We discuss some additional numerical considerations for the backward model including boundary conditions, reversal of the flow field, and interpretation of the results. We illustrate the implementation of the backward probability model using hypothetical examples in one- and two-dimensional domains. We also present a three-dimensional application of a pump-and-treat remediation capture zone delineation at the Massachusetts Military Reservation. The illustrations are performed using MODFLOW-96 for flow simulations and MT3DMS for transport simulations.     

赣东北信江盆地的虚骨龙类化石

赣东北信江盆地中首次发现了虚骨龙类化石,对其产出层位,区域分布,古地理及古气候特征进行了分析研究,为我国东南部白垩纪地层的区域对比提供了重要的依据。     

Use of multimetric indices to classify estuaries with different hydromorphological characteristics and different levels of human pressure

The assessment of estuaries based on benthic communities is widely used to determine impacts caused by human pressure and is one of the required tools for the implementation of the European Water Framework Directive (WFD). Our study compared multimetric approaches (B-IBI and TICOR) to assess the benthic condition of three Portuguese estuaries (Mondego, Tejo, and Mira rivers) with different levels of natural and human induced stress. Benthic community condition was classified into quality status categories of the WFD and compared for consistency with a priori status categories based upon physical-chemical criteria. Both multimetric indices discriminated equally well between locations classified above or below the good status category but were unable to provide good separation between other quality classes (high/good, moderate, poor/bad). Metrics included in these indices are greatly affected by natural stress and we recommend the development of habitat-specific thresholds to increase the discriminatory ability of any benthic condition index.     

Enormous PCBs increase in oysters from the coast of Guangdong, China

PCBs equivalent to Aroclor 1242 and 1254 in soft tissues of oysters Crassostrea rivularis from the Guangdong coast, China, were measured using a GC-ECD. PCB concentrations (ng g⁻¹ d.w.) ranged from 30 to 2040 with an average of 315 in 2003-2007, and 0.35-1.43 with an average of 0.56 in 1989-1991. Annual averages were 0.61, 0.65, 313, 290 and 342 ng g⁻¹, respectively in 1989, 1991, 2003, 2006 and 2007. In east Guangdong, the Pearl River Estuary, and west Guangdong, regional means were 444, 273, 194 ng g⁻¹, respectively in 2003-2007, and 0.43, 0.78, 0.38 ng g⁻¹, respectively in 1989-1991, indicating PCB levels in oysters have risen greatly by ratios of 350-1032 compared with earlier data. PCB sources may derive from older transformers, printing materials and pressworks. Fortunately, current residual PCBs in the oysters were 0.004-0.253 mg kg⁻¹ (w.w.), still below hygienic criteria of China and developed countries.     

Polycyclic aromatic hydrocarbons in the atmospheres of Titan and Jupiter

Polycyclic aromatic hydrocarbons (PAHs) are important components of the interstellar medium and carbonaceous chondrites, but have never been identified in the reducing atmospheres of the outer solar system. Incompletely characterized complex organic solids (tholins) produced by irradiating simulated Titan atmospheres reproduce well the observed UV/visible/IR optical constants of the Titan stratospheric haze. Titan tholin and a tholin generated in a crude simulation of the atmosphere of Jupiter are examined by two-step laser desorption/multiphoton ionization mass spectrometry. A range of two- to four-ring PAHs, some with one to four alkylation sites are identified, with net abundance approximately 10(-4) g g-1 (grams per gram) of tholins produced. Synchronous fluorescence techniques confirm this detection. Titan tholins have proportionately more one- and two-ring PAHs than do Jupiter tholins, which in turn have more four-ring and larger PAHs. The four-ringed PAH chrysene, prominent in some discussions of interstellar grains, is found in Jupiter tholins. Solid state 13C NMR spectroscopy suggests approximately equal to 25% of the total C in both tholins is tied up in aromatic and/or aliphatic alkenes. IR spectra indicate an upper limit in both tholins of approximately equal to 6% by mass in benzenes, heterocyclics, and PAHs with more than four rings. Condensed PAHs may contribute at most approximately 10% to the observed detached limb haze layers on Titan. As with interstellar PAHs, the synthesis route of planetary PAHs is likely to be via acetylene addition reactions.     

Vestiges of life in the oldest Greenland rocks? A review of early Archean geology in the Godthabsfjord region, and reappraisal of field evidence for > 3850 Ma life on Akilia

The Godth?bsfjord region of West Greenland contains the most extensive, best exposed and most intensely studied early Archean rocks on Earth. A geological record has been described of numerous magmatic events between ~3.9 and 3.6 Ga, and evidence of life at >3.85 Ga and ~3.8-3.7 Ga has been proposed from two widely-separated localities. Some of these claims have recently been questioned, and the nature of the best preserved remnants of the oldest known terrestrial volcanic and sedimentary rocks in the Isua greenstone belt are being reinvestigated and substantially reinterpreted. The first part of this article reviews the evolution of geological research and interpretations, outlining the techniques by which the geological history has been determined and the ensuing controversies. The second part re-examines crucial field evidence upon which the antiquity of the oldest terrestrial life is claimed from the island of Akilia.