Pyrolysis gas chromatography-mass spectrometry to characterize organic matter and its relationship to uranium content of Appalachian Devonian black shales     

Joel S. Leventhal 《Geochimica et cosmochimica acta》1981,45(6):883-889

Gas Chromatographic analysis of volatile products formed by stepwise pyrolysis of black shales can be used to characterize the kerogen by relating it to separated, identified precursors such as land-derived vitrinite and marine-source Tasmanites. Analysis of a Tasmanites sample shows exclusively $\text{n-}\text{alkane}$ and -alkene pyrolysis products, whereas a vitrinite sample shows a predominance of one- and two-ring substituted aromatics. For core samples from northern Tennessee and for a suite of outcrop samples from eastern Kentucky, the organic matter type and the U content (<10?120ppm) show variations that are related to precursor organic materials. The samples that show a high vitrinite component in their pyrolysis products are also those samples with high contents of U.  相似文献   

An unusual basalt fragment in Luna 20 sample L2010     

Mireille Christophe Michel-Lévy  Zdenek Johan 《Geochimica et cosmochimica acta》1973,37(4):805-809

A Luna 20 basaltic fragment contains 70 per cent pyroxene, 25 per cent plagioclase (An₈₀) and 5 per cent ilmenite. There are two varieties of augite which differ markedly in their alumina content. The composition of this fragment, calculated from the analyses of the minerals, shows that the $\text{Al}{}_2\text{O}{}_3\text{FeO}$ ratio is different from that of other lunar basalts.  相似文献   

Interstellar organic matter in meteorites     

Jongmann Yang  Samuel Epstein 《Geochimica et cosmochimica acta》1983,47(12):2199-2216

Hydrogen which is highly enriched in deuterium is present in organic matter in a variety of meteorites including non-carbonaceous chondrites. The concentrations of this hydrogen are quite large. For example Renazzo contains 140 μmoles/g of the 10,000‰ δD hydrogen. The $\text{D}\text{H}$ ratios of hydrogen in the organic matter vary from 8 × 10^?5 to 170 × 10^?5 (δD ranges from ? 500‰ to 10,000‰) as compared to 16 × 10^?5 for terrestrial hydrogen and 2 × 10^?5 for cosmic hydrogen. The majority of the unequilibrated primitive meteorites contain hydrogen whose $\text{D}\text{H}$ ratios are greater than 30 × 10^?5. If the $\text{D}\text{H}$ ratios in these compounds were due to enrichment relative to cosmic hydrogen by isotope exchange reactions, it would require that these reactions take place below 150 K. In addition the organic compounds having $\text{D}\text{H}$ ratios above 50 × 10^?5 would require temperatures of formation of < 120 K. These types of deuterium enrichments must take place by ion-molecule reactions in interstellar clouds where both ionization and low temperatures exist. Astronomically observed $\text{D}\text{H}$ ratios in organic compounds in interstellar clouds are typically 180 × 10^?5 and range between about 40 × 10^?5 and 5000 × 10^?5. The $\text{D}\text{H}$ values we have determined are the lower limits for the organic compounds derived from interstellar molecules because all processes subsequent to their formation, including terrestrial contamination, decrease their $\text{D}\text{H}$ ratios.In contrast, the $\text{D}\text{H}$ ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites we have analyzed with an average value of 14 × 10^?5; very similar to the terrestrial value. These phyllosilicates values suggest equilibration of H₂O with H₂ in the solar nebula at temperatures of about 200 K and higher.The ${}^{13}\text{C}{}^{12}\text{C}$ ratios of organic matter, irrespective its $\text{D}\text{H}$ ratio, lie well within those observed for the earth. If organic matter originated in the interstellar medium, our data would indicate that the ${}^{13}\text{C}{}^{12}\text{C}$ ratio of interstellar carbon five billion years ago was similar to the present terrestrial value.Our findings suggest that other interstellar material, representing various inputs from various stars, in addition to the organic matter is preserved and is present in the meteorites which contain the high $\text{D}\text{H}$ ratios. We feel that some elements existing in trace quantities which possess isotopic anomalies in the meteorites may very well be such materials.  相似文献   

Hydrogen and carbon isotopes of petroleum and related organic matter     

Hsueh-Wen Yeh  Samuel Epstein 《Geochimica et cosmochimica acta》1981,45(5):753-762

$\text{D}\text{H}$ and ${}^{13}\text{C}{}^{12}\text{C}$ ratios were measured for 114 petroleum samples and for several samples of related organic matter. δD of crude oil ranges from ?85 to ?181‰, except for one distillate (?250‰) from the Kenai gas field; δ¹³C of crude oil ranges from ?23.3 to ?32.5‰, Variation in δD and δ¹³C values of compound-grouped fractions of a crude oil is small, 3 and 1.1%., respectively, and the difference in δD and δ¹³C between oil and coeval wax is slight. Gas fractions are 53–70 and 22.6–23.2‰ depleted in D and ¹³C, respectively, relative to the coexisting oil fractions.The δD and δ¹³C values of the crude oils appear to be largely determined by the isotopic compositions of their organic precursors. The contribution of terrestrial organic debris to the organic precursors of most marine crude oils may be significant.  相似文献   

Erosion of particulate inorganic and organic matter in the Gulf of LionÉrosion de la matière particulaire inorganique et organique dans le golfe du Lion     

Estelle Schaaff  Christian Grenz  Christel Pinazo 《Comptes Rendus Geoscience》2002,334(15):1071-1077

Critical shear stress of erosion and erosion rate of particulate inorganic and organic matter were measured in a flume at three muddy stations. Critical shear stress ranged between 0.022 and $\text{0.038 }\text{N}\text{m}{}^{\mathrm{?2}}$. At the deepest site, annual erosion of particulate organic nitrogen and phosphorus could exceed net deposition fluxes, showing the importance of erosion processes. Erosion may modify total system mineralisation rates by introducing sedimentary particulate organic matter into the water column and thus this process must be taken into account in studies of biogeochemical cycles. To cite this article: E. Schaaff et al., C. R. Geoscience 334 (2002) 1071–1077.  相似文献   

Organic geochemistry of suspended and settling particulate matter in Lake Michigan   总被引：1，自引：0，他引：1  

P.A. Meyers  M.J. Leenheer  B.J. Eaoie  S.J. Maule 《Geochimica et cosmochimica acta》1984,48(3):443-452

Organic matter contained in particulate matter in Lake Michigan waters and sediments has been characterized by $\text{C}\text{N}$ ratios and by distributions of biomarker fatty acids, alkanols, sterols, and aliphatic hydrocarbons. Differences in organic constituents of particulate matter from various depths and distances from shore indicate a complex interaction of production, transformation, and destruction of the organic matter contained in sinking particles. Near-surface material contains important contributions of landderived organic matter, presumably of eolian input. Midwater particles have predominantly aquatic organic material of algal origin. At the sediment-water interface, selective suspension of the finer fractions of surficial sediments enriches bottom nepheloid layers with these sediment size classes. As a result, near-bottom particulate matter has an aquatic biomarker character. Organic matter associated with sinking particles undergoes substantial degradation during passage to the bottom of Lake Michigan, and aquatic components are selectively destroyed relative to terrigenous components.  相似文献   

Composition of the Descartes region,lunar highlands     

S.R Taylor  M.P Gorton  P Muir  W.B Nance  R Rudowski  N Ware 《Geochimica et cosmochimica acta》1973,37(12):2665-2683

Analytical data for 40 elements are reported for Apollo 16 soils 60601, 61181, 61501, 64801, 67701, 68501, 65701 and breccias 60015, 60017, 60018, 60315, 61016, 61175, 65015 and 66055. The soils are uniform except for the North Ray Crater rim sample which is richer in Al₂O₃.The breccia components show great diversity in composition. Low-K Fra Mauro basalt, Highland basalt (anorthositic gabbro) and plagioclase are important constituents. Medium-K Fra Mauro basalt is an important constituent of breccias 65015 and 60315.The breccias contain many meteorite fragments and high nickel contents, evidence of the early highland bombardment.Most of the refractory elements (REE, Th, U, Zr, Hf, Nb, Ba) show strong positive correlations, interpreted as resulting from mixing. The REE patterns of the breccias show extreme variation relative to chondrites. There is a good inverse correlation between REE and the europium anomaly ($\text{Eu}\text{Eu}{}^{\mathrm{x}}$). The $\text{La}\text{Yb}$ ratio is constant at 3.1 except in plagioclase. Eu depletion or enrichment is interpreted as due to addition or removal of plagioclase.The Cayley and Descartes formations cannot be distinguished chemically and the differences in surface expression are not due to chemical distinctions. They are interpreted as structural differences, related to early highland cratering and mare basin formation.The complex soil and breccia compositions are related to mixing of four components. These are Low-K Fra Mauro basalt, Highland basalt (anorthositic gabbro) and subordinate plagioclase and Medium-K Fra Mauro basalt. These compositions have been used in a computer program (PETMIX III) to provide fits for the analytical data in terms of the end-members.An average highland composition is proposed, based on the Apollo 15 and 16 orbital data for Si, Al, Mg and Th. Abundances for most other elements are derived from the interelement relationships and correlations, and checked by the mixing program.The resulting composition consists of 69 per cent Highland basalt (anorthositic gabbro) and 31 per cent Low-K Fra Mauro basalt. There is no significant Eu anomaly. The abundances are: SiO₂: 45.2 per cent; TiO₂: 0.68 per cent; Al₂O₃: 24.9 per cent; FeO: 6.3 per cent; MgO: 8.5 per cent; CaO: 13.8 per cent; Na₂O: 0.4 per cent; K₂O: 0.11 per cent; Cr₂O₃: 0.11 per cent; Ba: 144 ppm; Th: 1.8 ppm; U: 0.46 ppm; Pb: 1.6 ppm; Zr: 156 ppm; Hf: 3.2 ppm; Nb: 10.8 ppm; Y: 32 ppm; ΣREE: 85 ppm.  相似文献   

Chemical composition of Luna 20 rocks and soil and Apollo 16 soils     

J.C Laul  E.A Schmitt 《Geochimica et cosmochimica acta》1973,37(4):927-942

The abundances of 24 major, minor and trace elements have been measured by INAA in Luna 20 metaigneous rocks 22006,1 and 22007,1, breccia 22004 and soil 22001,9 and in Apollo 16 soils 62281, 66041 and 66081. An additional 12 trace meteoritic and non-meteoritic elements have also been determined in 22001 and 62281 soils by RNAA. The bulk compositions of L 20 and Ap 16 rocks and soils show close similarity between the two highland sites. There are appreciable differences in bulk compositions between the L 20 highland and the L 16 mare site (120 km apart), suggesting little intermixing of rocks and soils from either site. Luna 20 rocks 22006 and 22007 are nearly identical in chemical composition to Ap 16 metaigneous rocks 61156 and 66095. Luna 20 rocks are feldspathic and are similar to low K-type Fra Mauro basalts. Such rocks and anorthositic gabbros appear to be the major components in highland soils. Luna 20 soil can be distinguished from Ap 16 soils by lower abundances of Al₂O₃, CaO and large ion lithophilic elements. Luna 20 breccia 22004 probably is compacted soil. All L 20 samples show negative Eu anomalies with $\text{Sm}\text{Eu}$ ratios of 5.8, 7.2, 3.9 and 3.3 for rocks 22006, 22007, breccia 22004 and soil 22001, respectively. Norite-KREEP is insignificant, ≤1 per cent, at the L 20 highland site. The derivation of the L 20 soil may be explained by ≈33 per cent of L 20 metaigneous rocks and ≈ 65 per cent anorthositic gabbroic breccia rocks like 15418 (with a positive Eu anomaly) and ≈ 2 per cent meteoritic contributions. Interelement correlations observed previously for maria are also found in highland samples. Luna 20 and Ap 16 soils are low in alkalis. Both soils show an apparent Cd-Zn rich component similar to that observed at the mare sites and high 11 abundances relative to mare sites. The Ap 16 (62281) soil contains a fractionated meteoritic component (probably ancient) of ≈ 1.5 per cent in addition to ≈ 1.9 per cent Cl like material. Luna 20 soil may simply contain 1.9 per cent Cl equivalent.  相似文献   

Sedimentary pyrite formation: An update   总被引：1，自引：0，他引：1  

Robert A Berner 《Geochimica et cosmochimica acta》1984,48(4):605-615

Sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time. The amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter, dissolved sulfate, and reactive detrital iron minerals. Organic matter appears to be the major control on pyrite formation in normal (non-euxinic) terrigenous marine sediments where dissolved sulfate and iron minerals are abundant. By contrast, pyrite formation in non-marine, freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic-rich fresh water shales from marine shales. Under marine euxinic conditions sufficient H₂S is produced that the dominant control on pyrite formation is the availability of reactive iron minerals.Calculations, based on a sulfur isotope model, indicate that over Phanerozoic time the worldwide average organic carbon-to-pyrite sulfur ratio of sedimentary rocks has varied considerably. High $\text{C}\text{S}$ ratios during Permo-Carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time. Low $\text{C}\text{S}$ ratios, compared to today, during the early Paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean. The latter could have been due to lower oceanic oxygen levels and/or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time.  相似文献   

Revision of lunar Rb-Sr ages     

J.R De Laeter  M.J Vernon  W Compston 《Geochimica et cosmochimica acta》1973,37(3):700-702

Becalibration of ‘spikes’ using stoichiometric Rb and Sr salts recently issued by the National Bureau of Standards shows that our determinations of the ratio ${}^{87}\text{Rb}{}^{86}\text{Sr}$ in lunar samples have been low by 1.8 per cent, which we attribute to non-stoichiometry of the salts previously used for calibration, particularly RbCl. As a result, our lunar age-determinations must be decreased by this amount.  相似文献   

The major-element chemistry of suspended matter in the Amazon Estuary     

E.R. Sholkovitz  N.B. Price 《Geochimica et cosmochimica acta》1980,44(2):163-171

Suspended matter from the surface waters of the Amazon Estuary were collected during May and June 1976 on the ‘R/V Alpha Helix’, and their major-element compositions (Al, Si, Ti, K, Mg, Ca, P, Fe and Mn) were measured.Between salinities of 0 and 10%. the suspended material, predominantly terrigenous in derivation, decreases in load from 500 to 3 mg/l, but has a chemical composition which remains essentially constant. With the onset of a large amount of biological productivity at approximately 10%. salinity, there are large increases in the ratios of $\text{Si}\text{Al}$, $\text{P}\text{Al}$, $\text{Ca}\text{Al}$, $\text{Mg}\text{Al}$, $\text{Ti}\text{Al}$ and $\text{Mn}\text{Al}$ which are maintained at higher salinities. Calculations of “excess” concentrations of elements held in the non-terrigenous components of the suspended material further support our main conclusion that Si, P, Ca, Mg, Ti and Mn are incorporated into the skeletal and organic phases of marine phytoplankton (predominately diatoms) of the Amazon Estuary. The data suggest, but with less certainty, that Fe and K follow the above elements.This study has demonstrated that the chemical composition of river-introduced suspended matter can be significantly altered by biological activity within estuarine waters as can be the geochemical cycle of inorganic elements.  相似文献   

Characteristics of amorphous kerogens fractionated from terrigenous sedimentary rocks     

Noriyuki Suzuki 《Geochimica et cosmochimica acta》1984,48(2):243-249

A preliminary attempt to fractionate amorphous kerogens from terrigenous bulk kerogen by a benzene-water two phase partition method under acidic condition was made. Microscopic observation revealed that amorphous kerogens and structured kerogens were fractionated effectively by this method. Characteristics of the amorphous and structured kerogens fractionated by this method were examined by some chemical analyses and compared with those of the bulk kerogen and humic acid isolated from the same rock sample (Haizume Formation, Pleistocene, Japan). The elemental and infrared (IR) analyses showed that the amorphous kerogen fraction had the highest atomic$\text{H}\text{C}$ ratio and the lowest atomic $\text{N}\text{C}$ ratio and was the richest in aliphatic structures and carbonyl and carboxyl functional groups. Quantities of fatty acids from the saponification products of each geopolymer were in agreement with the results of elemental and IR analyses. Distribution of the fatty acids was suggestive that more animal lipids participate in the formation of amorphous kerogens because of the abundance of relatively lower molecular weight fatty acids (such as C₁₆ and C₁₈ acids) in saponification products of amorphous kerogens. On the other hand, although the amorphous kerogen fraction tends to be rich in aliphatic structures compared with bulk kerogen of the same rock samples, van Krevelen plots of elemental compositions of kerogens from the core samples (Nishiyama Oil Field, Tertiary, Japan) reveal that the amorphous kerogen fraction is not necessarily characterized by markedly high atomic $\text{H}\text{C}$ ratio. This was attributed to the oxic environment of deposition and the abundance of biodegraded terrestrial amorphous organic matter in the amorphous kerogen fraction used in this work.  相似文献   

Carbon in natural goethites     

《Geochimica et cosmochimica acta》1986,50(6):1213-1220

  相似文献   

The geochemistry of iodine in oxidised and reduced recent marine sediments     

N.B Price  S.E Calvert 《Geochimica et cosmochimica acta》1973,37(9):2149-2158

Surface sediments from the South West Africa shelf and the Gulf of California have been analysed for iodine and organic carbon. The iodine contents range from 96 to 1990 ppm. While iodine and organic carbon show certain anomalies on the South West Africa shelf, the trend of the $\text{I}\text{C}$ ratios is smooth and decreases from the shelf edge, an area of oxidising surface sediment, shorewards to reducing sediments, formed as a result of intense water upwelling. In the Gulf of California, a similar distribution of $\text{I}\text{C}$ ratios with surface sediment type occurs; lowest values occur in the reduced sediments and highest in oxidised sediments. Values of the $\text{I}\text{C}\text{(× 10}{}^4\text{)}$ ratio of the oxidised sediments (~250) are more than an order of magnitude higher than in reduced sediments, and are similar to some other surface oxidised sediments.The high I content of oxidised sediments is mostly due to uptake of I on to plankton seston on the seabed. In reduced sediments, I contained in planktonic matter originating in surface waters forms the bulk of iodine in the sediment.With sediment burial, oxidised sediments lose most of the iodine through degradation of unspecified organic constituents. This does not happen to the same extent in reduced sediments. The geological implications of these reactions are briefly discussed.  相似文献   

On the observation of 92Nb and 94Nb in nature     

K.E Apt  J.D Knight  D.C Camp  E.W Perkins 《Geochimica et cosmochimica acta》1974,38(9):1485-1488

Radioactivity measurements have shown evidence for long-lived ⁹²Nb and $\text{2.03 × 10}{}^4\text{yr}{}^{94}\text{Nb}$ in natural niobium. The specific activity of ⁹⁴Nb was observed to be 0.32 ± 0.03 dis/min. kg Nb and that of ⁹²Nb to be 0.058 ± 0.035 dis/min. kg Nb. With $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ taken as ≈ 1.7 × 10⁸yr, the isotopic abundance of ⁹⁸Nb is 1.2 × 10^?10 per cent.  相似文献   

Carbon and oxygen isotopes in epigenetic hydrothermal rocks from Hamam-el-Farun,Sinai     

Mordechai Magaritz  Arie Issar 《Chemical Geology》1973,12(2):137-146

Rock samples from an Eocene cliff above the thermal spring of Hamam-el-Farun (west coast of Sinai) show various degrees of dolomitization and calcitization ${}^{18}\text{O}{}^{16}\text{O}$ and ${}^{13}\text{C}{}^{12}\text{C}$ ratios indicate that dolomite and secondary calcite precipitated from hot brines.  相似文献   

Meteoritic trace elements in lunar rock 14321, 184     

John W Morgan  R Ganapathy  Urs Krähenbühl 《Geochimica et cosmochimica acta》1975,39(3):261-264

The 16 trace elements (Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Rb, Re, Sb, Se, Te, Tl and Zn) were measured by radiochemical neutron activation analysis in six samples of 14321, 184: microbreccia-2 (15), microbreccia-3 (14A, 16A and 19A), basaltic clast (1A), and light matrix material (9A). The 14321 microbreccias typically contain a siderophile-rich ancient meteoritic component, poor in volatiles, which is characterized by low $\text{Ir}\text{Au}$ and $\text{Re}\text{Au}$ ratios (0.25-0.38 and 0.34-0.50, respectively, normalized to Cl). This component also occurs in Apollo 12 KREEP glasses, norite fractions of Apollo 14 1–2 mm soils, Apennine Front breccias, and Cayley Formation material, and may represent ejecta from the Imbrian basin.The basaltic clast 14321, 184-1A closely resembles 14053 in trace element content, and both are 5–10 times higher than mare basalts in volatile trace elements (Br, Cd, Tl). The light matrix material contains 9.2 ± 0.5 per cent of microbreccias, judging from its siderophile content.  相似文献   

$\text{K}\text{Rb}$ ratios in Precambrian granulite terranes     

Jerry D. Lewis  Charles M. Spooner 《Geochimica et cosmochimica acta》1973,37(5):1111-1118

Concentrations of potassium and rubidium are reported for 62 Precambrian shield whole-rock samples belonging to the pyroxene granulite facies of world-wide distribution. Compared with the Main Trend established by Shaw (1968) for igneous and quasi-igneous rocks of the upper crust, the high-grade metamorphic granulites exhibit a similar correlation but with a measurable depletion in Rb for a given K content. The Metamorphic Trend may be described by the equations: log₁₀ (ppm Rb) = 1.136 log₁₀ (per cent K) + 1.495 or ppm Rb = 31.28 (per cent K)^1.136. The square of the product moment correlation coefficient shows that 80 per cent of the variation in Rb is associated with variation in K.All suites studied have initial ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios less than 0.707. This low value argues against repeated extraction of Rb and K through time on a regional scale. Rather, the major depletion in these lithophile elements occurred in the early stages of crustal evolution.  相似文献   

Variability of the He³ and Ne²¹ production rates in ordinary chondrites     

G.F Herzog 《Geochimica et cosmochimica acta》1973,37(9):2125-2133

Al²⁶ and noble gas contents of 6 ordinary chondrites with $\text{He}{}^3\text{Ne}{}^{21}$ ratios above 6.0 or below 4.0 are used to infer the variability of the production rates of He³ and Ne²¹ (P_He³ and P_Ne²¹). The ratio of the observed Al²⁶ content to a calculated, normal value is taken as a measure of the change of P_Ne²¹ from its normal value. The corresponding change in P_He³ is then computed from the observed $\text{He}{}^3\text{Ne}{}^{21}$ ratio and an average value of P_He³.According to these calculations which exclude orbital effects, P_He³ will be near the average value in meteorites with high $\text{He}{}^3\text{Ne}{}^{21}$ ratios, while P_Ne²¹ will be about 30 per cent below normal. In meteorites with low $\text{He}{}^3\text{Ne}{}^{21}$ ratios, P_He³ may be depressed by as much as 25 per cent from normal while P_Ne²¹ may be 15–20 per cent above the average.  相似文献   

Secular variations in kerogen structure and carbon,nitrogen and phosphorus concentrations in pre-Phanerozoic and Phanerozoic sedimentary rocks     

Togwell A. Jackson  Carleton B. Moore 《Chemical Geology》1976,18(2):107-136

Variations in the chemical composition of sedimentary rocks and the nature of kerogen through geologic time were investigated in order to obtain information on biological and environmental evolution during the pre-Phanerozoic eon. Rock samples differing in lithology, depositional environment, and age were pulverized, pre-extracted with organic solvents, and analyzed for total nitrogen (N), phosphorus (P) and organic carbon (org. C or C_T). Variations in the molecular structure of kerogen were measured by determining the ratio of org. C content after pyrolysis (C_R) to org. C content before pyrolysis (C_T), the $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratio being considered an index of the degree of condensed-aromatic (as opposed to aliphatic) character. The rocks included mudstones (Early Archean (> 3 · 10⁹ years old) to Miocene), carbonate rocks (mid-Proterozoic (1.3 · 10⁹ years old) to Eocene), cherts (Early Archean (> 3 · 10⁹ years old) to Late Proterozoic (0.8 · 10⁹ years old)), and coal (Archean (> 2.7 · 10⁹ years old) to Early Proterozoic (～1.8 · 10⁹ years old)).The mudstones and carbonates showed progressive increase in org. C content with decreasing age, as reported by other investigators, but the cherts unexpectedly showed a decrease in org. C content with decreasing age. In all samples, a simple inverse correlation between $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratio and org. C was observed, each rock type forming its own trend separate from but parallel to those of the other rock types. Thus, the older cherts tend to be richer in org. C and have lower $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratios, but the older carbonates and mudstones are poorer in org. C and have higher $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratios. For a given org. C concentration, chert has the highest $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratio and carbonate rock the lowest, mudstone being intermediate; this may mean that chert is relatively ineffective as a catalyst for the thermal cracking of kerogen or that it inhibits cracking. N appears to be correlated with org. C. The relationship between $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratio and org. C or N suggests that the concentrations of org. C and N in sedimentary rocks are largely determined by selective elimination of labile aliphatic and nitrogenous groups of kerogen during post-depositional maturation, although the nature, abundance and depositional environment of the organic source material must be taken into consideration as well. The observed secular variations of org. C, N and $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratio may be ascribed to several possible causes, including age-dependent post-depositional alteration of kerogen, secular decrease in the $\text{CO}{}_2\text{O}{}_2$ ratio of the atmosphere and hydrosphere during pre-Phanerozoic time, secular increase in rates of accumulation of organic matter in sediments and evolutionary changes in the composition of the biological source material. The secular variations of the carbonates and mudstones could be accounted for by age-dependent cumulative effects of post-depositional alteration alone, whereas the secular variations of the cherts probably reflect changes in the nature of the biological source material and the composition of the atmosphere and hydrosphere. The available evidence suggests that primary characteristics of kerogen are better preserved in chert than in the other types of sediment.The $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratios of the carbonates and cherts correlate negatively with the $\text{A}{}_{\mathrm{<mtext>465</mtext><mtext>m</mtext><mtext>\mu </mtext>}}\text{A}{}_{\mathrm{<mtext>665</mtext><mtext>m</mtext><mtext>\mu </mtext>}}$ absorbance ratios of “humic matter” extracted from the same rock samples with benzene—methanol. Thus, the greater the degree of condensed-aromatic character of the kerogen, the greater the degree of condensed-aromatic character of the solvent-extractable bituminous “humic matter” with which it is associated. In addition, the ratio of aliphatic to carbonyl-type groups ($\text{CH}{}_2\text{C=O}$) in the extractable “humic matter” of carbonates and cherts correlates with the non-extractable org. C content of the rocks, suggesting that the org. C data are related to the degree of aliphatic character of the kerogen. The chemical similarity between extractable “humic matter” and its associated kerogen is evidence that the “humic matter” is as old as its rock matrix and can be accepted as a valid chemical fossil. It also suggests that information obtainable from kerogen may be gotten more easily, rapidly and cheaply from solvent-extractable organic matter. The mudstones showed little or no relationship between $\text{A}{}_{\mathrm{<mtext>465</mtext><mtext>m</mtext><mtext>\mu </mtext>}}\text{A}{}_{\mathrm{<mtext>665</mtext><mtext>m</mtext><mtext>\mu </mtext>}}$ ratio and $\text{C}{}_{\mathrm{<mtext>R</mtext>}}\text{C}{}_{\mathrm{<mtext>T</mtext>}}$ ratio, or between $\text{CH}{}_2\text{C=O}$ ratio and org. C content. The data are consistent with the hypothesis that the kerogen in the carbonates and cherts is autochthonous, whereas the kerogen in the mudstones is partly allochthonous, implying the existence of soil humus and soil organisms in pre-Phanerozoic times. Moreover, the existence of coal in Archean sediments is consistent with the existence of very shallow-water and possibly terrestrial microfloras possessing adaptations for protection against ultraviolet solar radiation.The P content of the sediments showed a complicated zig-zag pattern of variation through geologic time. All the different suites of samples gave similar results, indicating that the variations represent phenomena whose effects were worldwide and independent of local environment. P levels are low in the early pre-Phanerozoic but rise with decreasing age until ～ 1 · 10⁹ years B.P., then fall to a minimum at (～0.7–0.8) · 10⁹ years B.P., and rise again to a lower Paleozoic (Ediacarian?) maximum, decline to a later Paleozoic minimum, and then rise again. The low P content of early pre-Phanerozoic sediments could be due to several factors, including high CO₂ content of seawater, anaerobic conditions in the sea, absence of stable-shelf environments, and low rates of primary production. The minimum in the Late Proterozoic is tentatively attributed to the Late Proterozoic glaciations. The data are consistent with the theory that the glacial episode was of worldwide extent.  相似文献