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1.
The upflow anaerobic sludge blanket process followed by the biological aerated filter process was employed to improve the removal of color and recalcitrant compounds from real dyeing wastewater. The highest removal efficiency for color was observed in the anaerobic process, at 8-h hydraulic retention time, seeded with the sludge granule. In the subsequent aerobic process packed with the microbe-immobilized polyethylene glycol media, the removal efficiency for chemical oxygen demand increased significantly to 75 %, regardless of the empty bed contact time. The average influent non-biodegradable soluble chemical oxygen demand was 517 mg/L, and the average concentration in effluent from the anaerobic reactor was 363 mg/L, suggesting the removal of some recalcitrant matters together with the degradable ones. The average non-biodegradable soluble chemical oxygen demand in effluent from the aerobic reactor was 87, 93, and 118 mg/L, with the removal efficiency of 76, 74, and 67 %, at 24-, 12-, and 8-h empty bed contact time, respectively. The combined anaerobic sludge blanket and aerobic cell-entrapped process was effective to remove the refractory compounds from real dyeing wastewater as well as in reducing organic loading to meet the effluent discharge limits. This integrated process is considered an effective and economical treatment technology for dyeing wastewater.  相似文献   

2.
The origin of life on Earth remains enigmatic with diverse models and debates.Here we discuss essential requirements for the first emergence of life on our planet and propose the following nine requirements:(1)an energy source(ionizing radiation and thermal energy);(2)a supply of nutrients(P.K.REE.etc.);(3)a supply of life-constituting major elements;(4)a high concentration of reduced gases such as CH_4,HCN and NH_3;(5)dry-wet cycles to create membranes and polymerize RNA;(6)a non-toxic aqueous environment;(7)Na-poor water;(8)highly diversified environments,and(9)cyclic conditions,such as dayto-night,hot-to-cold etc.Based on these nine requirements,we evaluate previously proposed locations for the origin of Earth's life,including:(1)Darwin's "warm little pond",leading to a "prebiotic soup" for life;(2)panspermia or Neo-panspermia(succession model of panspermia);(3)transportation from/through Mars;(4)a deepsea hydrothermal system;(5)an on-land subduct ion-zone hot spring,and(6)a geyser systems driven by a natural nuclear reactor.We conclude that location(6)is the most ideal candidate for the o rigin point for Earth's life because of its efficiency in continuously supplying both the energy and the necessary materials for life,thereby maintaining the essential "cradle" for its initial development.We also emphasize that falsifiable working hypothesis provides an important tool to evaluate one of the biggest mysteries of the universe-the origin of life.  相似文献   

3.
Seven graphite-containing xenoliths were found in the Krymka (LL3.1) chondrite. The xenoliths have the following chemical and mineralogical characteristics which distinguish them from the Krymka host: (1) low totals in bulk chemical analyses obtained by electron microprobe; (2) high bulk Fe abundances; (3) a uniform recrystallized, chondrule-free texture; (4) the presence of euhedral graphite and carbon-rich material; (5) higher quantities of troilite and metal; (6) a relatively homogeneous composition of silicates; (7) a distinctive composition of metal, chromite and phosphate; (8) isotopically heavy C in graphite compared to both bulk Krymka and graphite in other ordinary chondrites. The xenoliths are mineralogically similar, but not identical, to the Krymka carbonaceous clast K1, which bears graphite microcrystals, organic compounds and mysterite. They resemble carbonaceous chondrites, both chemically and isotopically. The mineralogical, chemical and isotopic data for the graphite-containing fragments suggest that this material represents metamorphosed varieties of a previously unknown type of unequilibrated carbonaceous matter. Most likely, the graphite has a metamorphic origin and was crystallized from C-containing precursor materials through the following transformation sequence: organic compounds → C-rich material → graphite.  相似文献   

4.
One of the technologies used for wastewater nitrogen removal consists in simultaneous nitrification–denitrification. The low microbial growth rate and the low availability of organic material for the denitrification stage make it necessary to study new operational conditions and the use of microbial supports. The aim of this study was to evaluate the operational behavior of a simultaneous nitrification–denitrification process in a sequential batch reactor utilizing zeolite as a biomass support and step-feed strategy. Two reactors of 2 L were used, one with zeolite and another without zeolite, both operated at constant temperature (31 °C), varying nitrogen loading rate (NLR) from 0.041 to 0.113 kg total Kjeldahl nitrogen (TKN/m3/day). After 209 days, removals higher than 86 and 96 % in nitrogen compounds and organic matter were obtained, respectively. There was not accumulation of nitrate and nitrite in any case; this means that there was a simultaneous nitrification–denitrification in the reactors. The incorporation of zeolite in the system held higher concentration of biomass in the reactor; this led to reduce start-up to 21 days and to improve 11.31 % removal kinetic. The use of a step-feed strategy prevents events of inhibition by substrate, even duplicating tolerance to higher NLR for the same operation time.  相似文献   

5.
有机粘土化学研究进展与展望   总被引：13，自引：0，他引：13  
有机粘土化学是研究粘土矿物与有机化合物之间相互作用的一门学科,其内容包括粘土矿物对有机化合物的吸附作用,粘土矿物对有机化合物转化的催化作用以及有机化合物对粘土矿物的合成与风化的影响。着重阐述了近20年来有机粘土化学的研究进展,并就这一学科领域的研究作了展望。  相似文献   

6.
The present research work was intended to find out the useful information on identification, separation and photocatalytic degradation of organic compounds present in leather industry wastewater. The separation of organic compounds present in leather industry wastewater was carried out by solvent extraction. The separated crude extracted products were purified through column chromatography and characterized by UV–vis spectrophotometer, gas chromatography–mass spectrophotometer, liquid chromatography–mass spectrophotometer, 1H and 13C Fourier-transform nuclear magnetic resonance spectroscopy. The elemental analysis of wastewater and solid residue was carried out by inductively coupled plasma-optical emission and X-ray fluorescence spectroscopy. The organic compounds such as nonadec-1-ene, 2-phenylethanol, 2,4-di-tert-butylphenol and other organic compounds in the leather industry wastewater were identified. Out of these organic compounds, 2-phenylethanol was photocatalytically degraded using standard Degussa P-25 TiO2 (100 mg) photocatalyst under the irradiation of UV light. Result has been shown that 2-phenylethanol was transformed into 2-tert-butyl-4,6-dimethylphenol, 2,6-di-tert-butyl-4-methylphenol then the prolonged time (30 h) irradiation leads to 100 % degradation of 2-phenylethanol. Further possible degradation mechanism of 2-phenylethanol was proposed based on the electrospray ionization mass spectrometry analysis of degraded samples. The degradation of 2-phenylethanol was confirmed by chemical oxygen demand analysis of degraded samples. The physicochemical parameters such as pH, color, chemical oxygen demand, total dissolved solids, electrical conductivity and ionic chromatography analysis of the leather industry wastewater were also measured.  相似文献   

7.
The removal of colour and organic compounds from vinasses derived from the wine distillery industry was studied using boron-doped diamond-based electrodes and dimensionally stable anodes. The maximum reduction of organic compounds and colour was attained with the use of boron-doped diamond-based electrode after 10 h of operation at a current density of 6.6 mA cm?2. The current efficiency obtained was about 90% with a specific energy consumption (measured in terms of removal of chemical oxygen demand) of 17 kWh kg?1 COD removed. The dimensionally stable anodes were capable of removing 6–47% of the organic material and reached 60% decolourisation but with a lower current efficiency (between 85 and 10%) and much higher specific energy consumption values. The anaerobic digestion of vinasse after 1 h of treatment using boron-doped diamond-based electrode showed an effective mineralisation of the organic matter contained in the sample leading to an increase in methane production during anaerobic digestion.  相似文献   

8.
http://dx.doi.org/10.1016/j.gsf.2016.07.005   总被引：1，自引：1，他引：0  
The Hadean history of Earth is shrouded in mystery and it is considered that the planet was born dry with no water or atmosphere. The Earth-Moon system had many features in common during the birth stage. Solidification of the dry magma ocean at 4.53 Ga generated primordial continents with komatiite. We speculate that the upper crust was composed of fractionated gabbros and the middle felsic crust by anorthosite at ca. 21 km depth boundary, underlain by meta-anorthosite (grossular + kyanite + quartz) down to 50–60 km in depth. The thickness of the mafic KREEP basalt in the lower crust, separating it from the underlying upper mantle is not well-constrained and might have been up to ca. 100–200 km depending on the degree of fractionation and gravitational stability versus surrounding mantle density. The primordial continents must have been composed of the final residue of dry magma ocean and enriched in several critical elements including Ca, Mg, Fe, Mn, P, K, and Cl which were exposed on the surface of the dry Earth. Around 190 million years after the solidification of the magma ocean, “ABEL bombardment” delivered volatiles including H2O, CO2, N2 as well as silicate components through the addition of icy asteroids. This event continued for 200 Myr with subordinate bombardments until 3.9 Ga, preparing the Earth for the prebiotic chemical evolution and as the cradle of first life. Due to vigorous convection arising from high mantle potential temperatures, the primordial continents disintegrated and were dragged down to the deep mantle, marking the onset of Hadean plate tectonics.  相似文献   

9.
Nitrate removal from water has been accomplished by heterotrophic biofilms using organic carbon as a source of reducing power. To overcome the natural limitation in organic carbon in water, a poly-ε-caprolactone based biofilm carrier that serves simultaneously as a biofilm carrier and as a source of organic carbon was developed and tested in the present work. The feasibility of the new biofilm carrier for nitrate removal from water was evaluated in a packed bed reactor. The combination of size and structure provided a carrier element having high surface area and void volume, 1,170 m2/m3 and 67 %, respectively. A maximum denitrification rate of 4.4 mg N–NO3 ?/(L.h) (9.2 mg N–NO3 ?/(m2.h)) was achieved in the packed bed reactor at 20 °C and pH 7.0. Main advantages of the biofilm carrier developed in the present work are its mechanical stability in water even after biofilm formation and controlled release of organic carbon by enzymatic reactions. The proposed biotechnology to remove nitrate from groundwater is robust and easy to operate.  相似文献   

10.
Sulphate mineralization precipitated around a geyser located above the village of Pinchollo, Chivay district and below Hualca Hualca volcano (6025 m a.s.l.) in the Western Cordillera of southern Peru is described. The geyser is one of many manifestations of thermal activity in the Arequipa department. Its age is estimated to be Upper Pleistocene–Holocene, as the discharge point lies at the intersection of a fault system with latitudinal dip-slip fault cutting a volcanic-debris avalanche of probably Pleistocene age. Thermal waters present in the Chivay district are mainly chloride-rich with a neutral pH. They are rich in Li, Sr, and B. The water erupting in the geyser boils at about 85 °C, as it lies at some 4353 m a.s.l.The minerals examined, of various habits and various yellow, orange and white colours were precipitated on the soil and on plants close to the geyser (location 1), on the walls of a 1 m diameter pothole filled with boiling water (location 1a) and at a distance of some 100 m to the west of the geyser (location 2). All are sulphates. Their chemical composition is fairly simple, consisting of Al, Fe, K, Mg, Ca, S, NH4 and O, and all display chemical zoning. But the phase composition is more complex. In all locations, alunogene, copiapite, coquimbite, tschermigite and gypsum are present. Close to the geyser (location 1) magnesium-containing sulphates, namely, boussingaultite and pickeringite also occur. Iron sulphates such as mohrite and rozenite precipitate on the walls of the pothole (location 1a). Sulphates containing potassium such as jarosite, alunite and voltaite–voltaite (Mg) dominate among the efflorescences in location 2, where hematite was also noted. Any quartz and kaolinite or illite/mica admixture identified in some samples derives from adjacent soil.The present geothermal system does not involve the deposition of precious-metal deposits such as those associated with an earlier deep-going epithermal system that scavenged a large volume of rock. Most likely, as the present-day thermal waters do not involve a juvenile-water component, the geyser waters derive from a shallower source.  相似文献   

11.
Concentration profiles of five C25 and C30 biogenic alkenes in a sediment core collected from the upper anoxic basin of the Pettaquamscutt River have been determined. The five alkenes were identified usin gas chromatography/mass spectrometry as three isomeric C25 dienes, a C25 triene and a bicyclic C30 diene. All five compounds exhibit subsurface concentration maxima, thought to result from either preservation of a past increase in alkene production or a current bacterial in situ production at depth. Similarities exist in the concentrations of two alkenes common to this core and a core from upper Narragansett Bay, despite significant differences in the origin and content of sedimentary organic matter (as inferred from organic carbon and δ 13C measurements) at each location. These observations support the proposed bacterial in situ synthesis of alkenes. Other alkenes, whose concentration in sediments had been previously correlated with the incidence of marine organic matter, were not detected in the upper basin sediments. Their absence is consistent with the range of organic carbon δ 13C values measured, which indicate that the component originating from marine sources is small. A comparison of organic carbon and δ 13C values in this core with those previously reported from a core collected in an adjoining basin indicate that the sedimentary regimes at the two sites differ despite their close proximity and similar hydrography.  相似文献   

12.
http://dx.doi.org/10.1016/j.gsf.2016.10.005   总被引：5，自引：4，他引：1  
The Earth was born as a dry planet without atmosphere and ocean components at 4.56 Ga, with subsequent secondary accretion of bio-elements, such as carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) which peaked at 4.37–4.20 Ga. This two-step formation model of the Earth we refer to as the advent of bio-elements model (ABEL Model) and the event of the advent of bio-elements (water component) as ABEL Bombardment. It is clear that the solid Earth originated from enstatite chondrite-like dry material based on the similarity in oxygen isotopic composition and among other isotopes. On the other hand, Earth's water derives primarily from carbonaceous chondrite material based on the hydrogen isotopic ratio. We present our ABEL model to explain this enigma between solid Earth and water, as well as secondary accretion of oxidizing bio-elements, which became a precursor to initiate metabolism to emerge life on a highly reductive planet. If ABEL Bombardment had not occurred, life never would have emerged on the Earth. Therefore, ABEL Bombardment is one of the most important events for this planet to evolve into a habitable planet. The chronology of ABEL Bombardment is informed through previous researches of the late heavy bombardment and the late veneer model. ABEL Bombardment is considered to have occurred during 4.37–4.20 Ga, which is the concept to redefine the standard late heavy bombardment and the late veneer models. Also, ABEL Bombardment is the trigger of the transition from stagnant lid tectonics to plate tectonics on this planet because of the injection of volatiles into the initial dry Earth.  相似文献   

13.
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14.
A universal conversion solid-electrolyte reactor (SER) based on zirconium dioxide stabilized by yttrium oxide is developed. It ensures the complete oxidation of organic compounds of complex molecular structure in different physical states or the complete reduction of water and organic oxygen-containing substances in a flow of helium carrier gas. The optimum oxidation operation mode of the solid-electrolyte reactor is the mode ensuring the complete oxidation of organic compounds at the boundary line of the oxidation of organic compounds and, at the same time, prevents the inflow of oxygen from the environment to the carrier gas. The potential of the working electrode selected for carrying out experiments was equal to–175 mV (oxidation operation mode). The temperature of the reactor was 940–950oC. The standard deviations δ13СVPDB for organic substances oxidized by SER varied from 0.11 to 0.57‰ and were smaller than standard deviations in the oxidation of corresponding compounds in a commercial reactor. In using the SER–IRMS method (isotope ratio mass spectrometry combined with the solid-electrolyte reactor), a minimum amount of water (60–100 ng) was required. Standard deviations δDVSMOW attained using SER and using a commercial pyrolytic reactor were close to each other. Because of the simplicity and reliability of the design, the developed SER can successfully replace commercial oxidation and reduction reactors in isotope ratio mass spectrometry. In addition, the solid-electrolyte reactor can serve as a chromatographic detector, requiring no calibration in contrast to other detectors.  相似文献   

15.
In the upper Amazon Basin, aluminum previously accumulated in lateritic formations is massively remobilised in soils by podzolization and exported in waters. We have investigated the speciation of aluminum in the clay-size fractions of eight horizons of waterlogged podzols lying in a depression of a plateau. The horizons illustrate the main steps involved in the podzolization of laterites. They belong to eluviated topsoil A horizons and illuviated subsoil Bhs, Bh and 2BCs horizons of weakly and better-expressed podzols located at the margin and centre of the depression. For the first time, aluminum speciation is quantitatively assessed in soils by spectroscopic methods, namely FTIR, 27Al magic angle spinning (MAS) and multiple-quantum magic angle spinning (MQMAS), nuclear magnetic resonance (NMR). The results thus obtained are compared to chemical extraction data.Solid-state 27Al MAS NMR spectra enable to distinguish Al bound to organic compounds from that incorporated in secondary mineral phases detected by FTIR. MQMAS experiments additionally show that both chemical shifts and quadrupolar constants are distributed for Al nuclei linked with organic compounds. Similar amounts of chelated Al are obtained from NMR spectra and chemical extractions. The study enables to highlight three major steps in the fate of aluminum. (i) Aluminum is first released by mineral weathering, feeds complexing sites of organic matter and accumulates in subsurface Bhs horizons of weakly expressed podzols (acidocomplexolysis). (ii) Complexes of aluminum with organic matter (Al-OM) then migrate downwards in sandy horizons of better-expressed podzols and accumulate at depth in less permeable 2BCs horizons. (iii) The minor amounts of aluminum present in the 2BCs horizon of the downslope podzol show that aluminum is eventually exported towards the river network, either complexed with organic matter or as Al3+ ions after desorption from organic compounds, due to decreasing pH or biodegradation of organic ligands. The direct spectroscopic determination of Al-speciation during the formation of podzolic soils opens new perspectives to trace metal loads in the rivers of the upper Amazon Basin.  相似文献   

16.
Palaeosols are ancient soils formed in sedimentary successions between events of sedimentation, erosion and volcanic activity. Soil formation is regulated by circumstances of climate, vegetation, topographic relief, parent material and time. These factors are quantified by nomopedology, in the form of climofunctions, chronofunctions and other relationships useful for interpreting conditions of the past from palaeosols. In deep time, palaeosols reveal the timing and extent of the Great Oxidation Event of 2.4 Ga. There is also circumstantial evidence for life in palaeosols back to 3.5 Ga on Earth and 3.7 Ga on Mars. These are the oldest known intact profiles, but pieces of palaeosols some 4.56 Ga in age may be represented by carbonaceous chondrite meteorites. Astropedology is the study of very ancient palaeosols and meteorites relevant to the origin of life and different planetary soil systems. Complex chemical assembly, metal catalysis of organic compounds, and the course of hydrolytic reactions as a kind of planetary metabolism make soils an attractive theoretical site for the origin of life. Because dilute solutions tend to an equilibrium that undoes organosynthetic reactions, life is more likely to have arisen on a soil planet like Mars than a water planet like Earth.  相似文献   

17.
Despite its location on sediment-free basalt, vent fluids from the Main Endeavour Field (MEF) contain chemical species that indicate fluids have interacted with sediments during circulation. We report on the distribution and isotopic abundances of organic compounds (C1-C3 alkanes and alkenes, benzene and toluene) in fluids collected from the Main Endeavour Field (MEF) in July, 2000, to understand the processes that regulate their abundances and characterize fluid sources. Aqueous organic compounds are derived from the thermal alteration of sedimentary organic matter and subsequently undergo further oxidation reactions during fluid flow. Fluid:sediment mass ratios calculated using ΣNH4 concentrations indicate that the sediments are distal to the MEF, resulting in a common reservoir of fluids for all of the vents. Following the generation from sediment alteration, aqueous organic compounds undergo secondary alteration reactions via a stepwise oxidation reaction mechanism. Alkane distributions and isotopic compositions indicate that organic compounds in MEF fluids have undergone a greater extent of alteration as compared to Middle Valley fluids, either due to differences in subsurface redox conditions or the residence time of fluids at subsurface conditions. The distributions of the aromatic compounds benzene and toluene are qualitatively consistent with the subsurface conditions indicated by equilibration of aqueous alkanes and alkanes. However, benzene and toluene do not achieve chemical equilibrium in the subsurface. Methane and CO2 also do not equilibrate chemically or isotopically at reaction zone temperatures, a likely result of an insufficient reaction time after addition of CO2 from magmatic sources during upflow. The organic geochemistry supports the assumption that the sediments with which MEF fluids interact has the same composition as sediments present in Middle Valley itself, and highlight differences in subsurface reaction zone conditions and fluid flow pathways at these two sites.  相似文献   

18.
Our blue planet Earth has long been regarded to carry full of nutrients for hosting life since the birth of the planet.Here we speculate the processes that led to the birth of early life on Earth and its aftermath, finally leading to the evolution of metazoans.We evaluate:（1） the source of nutrients,（2） the chemistry of primordial ocean,（3） the initial mass of ocean,and（4） the size of planet.Among the life-building nutrients,phosphorus and potassium play a key role.Only three types of rocks can serve as an adequate source of nutrients:（a） continent-forming TTG（granite）,enabling the evolution of primitive life to metazoans;（b） primordial continents carrying anorthosite with KREEP（Potassium,Rare Earth Elements, and Phosphorus） basalts,which is a key to bear life;（c） carbonatite magma,enriched in radiogenic elements such as U and Th,which can cause mutation to speed up evolution and promote the birth of new species in continental rift settings.The second important factor is ocean chemistry.The primordial ocean was extremely acidic（pH = 1-2） and enriched in halogens（CI,F and others）,S,N and metallic elements（Cd,Cu,Zn,and others）,inhibiting the birth of life.Plate tectonics cleaned up these elements which interfered with RNA.Blue ocean finally appeared in the Phanerozoic with pH = 7 through extensive interaction with surface continental crust by weathering,erosion and transportation into ocean.The initial ocean mass was also important.The birth of life and aftermath of evolution was possible in the habitable zone with 3-5 km deep ocean which was able to supply sufficient nutrients. Without a huge landmass,nutrients cannot be supplied into the ocean only by ridge-hydrothermal circulation in the Hadean.Finally,the size of the planet plays a crucial role.Cooling of massive planets is less efficient than smaller ones,so that return-flow of seawater into mantle does not occur until central stars finish their main sequence.Due to the suitable size of Earth,the dawn of Phanerozoic witnessed the initiation of return-flow of seawater into the mantle,leading to the emergence of huge landmass above sea-level,and the distribution of nutrients on a global scale.Oxygen pump also played a critical role to keep high-PO2 in atmosphere since then,leading to the emergence of ozone layer and enabling animals and plants to invade the land. To satisfy the tight conditions to make the Earth habitable,the formation mechanism of primordial Earth is an important factor.At first,a ’dry Earth’ must be made through giant impact,followed by magma ocean to float nutrient-enriched primordial continents（anorthosite + KREEP）.Late bombardment from asteroid belt supplied water to make 3-5 km thick ocean,and not from icy meteorites from Kuiper belt beyond cool Jupiter.It was essential to meet the above conditions that enabled the Earth as a habitable planet with evolved life forms.The tight constraints that we evaluate for birth and evolution of life on Earth would provide important guidelines for planetary scientists hunting for life in the exosolar planets.  相似文献   

19.
Nuclear waste from thermal plants poses a lasting risk to the biosphere because of its long radioactive life. The planned definitive storage place for it is in deeply buried repositories. Such repositories would need to be both impermeable to water, and plastic during deformation, in order to avoid the formation of cracks that may allow water in. One of the clay minerals, smectite, has these two properties and is an ideal candidate as a sealing material or even host rock for nuclear waste repositories. The chemical stability of smectite in the repository environment is sufficient to maintain good sealing properties during the active life of the relevant radionuclides.  相似文献   

20.
Cherts, shales, and carbonates containing small amounts of organic matter occur throughout the Precambrian sedimentary record. The oldest known organic-rich sediments have been dated at > 3,000 million years. Knowledge of the composition, origin, and fate of the organic content of these rocks relates to many facets of Precambrian earth history. Apart from its primary paleobiological significance, organic geochemical research is also concerned with problems in atmospheric and hydrospheric evolution, sedimentation, diagenesis, metamorphism, and ore genesis.Precambrian organic geochemistry to date has rested on the premise that ancient life process can be profitably studied at a chemical level, as well as by examination of the morphological fossils of conventional paleontology. A decade of intensive research on selected Precambrian carbonaceous and bituminous sediments has been made possible by the refinement of analytical techniques (notably gas chromatography and mass spectrometry) which are now capable of detecting and characterizing the minute quantities of complex organic mixtures found in geological materials. It has resulted in the development of criteria which allow discrimination between indigenous and adventitious organic matter. A diverse array of stable organic compounds has been isolated from Precambrian sedimentary rocks. The compounds, termed chemical fossils, are thought to be derived from ancestral microorganisms and as such have contributed to the formulation of the biological marker concept. Despite reports of possible abiotic occurrences, a biological origin for most of the organic matter preserved in Precambrian rocks (whether sedimentary or metamorphic) now appears likely.The possibility of secondary emplacement from migrating formation fluids means that an indigenous chemical fossil need not have been syngenetic with the deposition of its host sediment. No conclusive test of Precambrian age as yet exists for these compounds. The bulk of the organic material (kerogen) in Precambrian rocks is insoluble in organic and aqueous solvents. For this reason, kerogen is almost certainly both indigenous and syngenetic, but clarification of its chemical structure must await the development of new analytical procedures. The nature and extent of the modification that the soluble and insoluble organic fractions have undergone during late diagenesis and incipient metamorphism is still virtually unknown. Correlation of chemical fossils with specific biogenic precursor compounds, or a particular type of primitive organism, therefore remains equivocal. So also comparison of the organic geochemical facies of one sediment with that of another may be complicated by differences in their thermal history and mineralogy.Recent interest in the possible involvement of living and decayed microorganisms in the genesis of certain Precambrian Fe, U, Au, Cu, Pb, and Zn metal deposits signals the beginning of an important new phase in organic geochemical studies.  相似文献   

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