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The standard hydrochloric/hydrofluoric acid treatment used to remove most minerals in kerogen preparation often leaves abundant pyrite. This pyrite is a major obstacle to establishing elemental composition and functional group distributions in kerogen by both chemical and spectroscopic techniques. Quantitative pyrite removal by other conventional means such as nitric acid, lithium aluminum hydride, and sodium borohydride has not been possible without objectionable alterations of the organic matter. Experiments reported here demonstrate that acidic chromous chloride reduction can remove pyrite quantitatively without causing significant alteration of the organic matter

Geochemistry of Sulfur in Petroleum Systems Geochemistry of Sulfur in Coal Environmental Aspects of the Combustion of Sulfur-Bearing Fuels Polysulfide Reactions in the Formation of Organosulfur and Other Organic Compounds in the Geosphere Isolation of Sulfur Compounds from Petroleum Microbial Metabolism of Organosulfur Compounds in Petroleum Geochemistry of Organic and Inorganic Sulfur in Ancient and Modern Lacustrine Environments: Case Studies of Freshwater and Saline Lakes Characterization of Organic Matter in Sulfur-Rich Lacustrine Sediments of Miocene Age Incorporation of Sulfur into Recent Organic Matter in a Carbonate Environment Sulfur and Pyrite in Precursors for Coal and Associated Rocks: A Reconnaissance Study of Three Modern Sites Formation of Iron Sulfides in Modern Salt Marsh Sediments Sulfur K-Edge X-ray Absorption Spectroscopy of Petroleum Asphaltenes and Model Compounds Direct Determination of Total Organic Sulfur in Coal Elemental Sulfur in Bituminous Coals Multiple-Heteroatom-Containing Sulfur Compounds in a High Sulfur Coal Organosulfur Consituents in Rasa Coal Distribution of Organic-Sulfur-Containing Structures in High-Organic-Content Sulfur Coals Characterization of Organic Sulfur Compounds in Coals and Single-Coal Macerals Spatial Variation of Organic Sulfur in Coal Characterization of Organosulfur Compounds in Oklahoma Coals by Pyrolysis-Gas Chromatography Coal Desulfurization by Programmed-Temperature Pyrolysis and Oxidation Nature and Geochemistry of Sulfur-Containing Compounds in Alberta Petroleums Identification of Alkylthiophenes Occurring in the Geosphere by Synthesis of Authentic Standards Organic Sulfur Compounds and Other Biomarkers as Indicators of Palaeosalinity Alkylthiophenes as Sensitive Indicators of Palaeoenvironmental Changes: A Study of a Cretaceous Oil Shale from Jordan Characterization of Organically Bound Sulfur in High-Molecular-Weight, Sedimentary Organic Matter Analysis of Maturity-Related Changes in the Organic Sulfur Composition of Kerogens by Flash Pyrolysis-Gas Chromatography Isotopic Study of Coal-Associated Hydrogen Sulfide Pyrolysis of High-Sulfur Monterey Kerogens: Stable Isotopes of Sulfur, Carbon, and HydrogenWSulfur Isotope Data Analysis of Crude Oils from the Bolivar Coastal Fields Distribution of Organic Sulfur Compounds in Mesozoic and Cenozoic Sediments Carbon Isotope Fractionation during Oxidation of Light Hydrocarbon Gases: Relevance to Thermochemical Sulfate Reduction in Gas Reservoirs

Monterey oils in the Santa Maria Basin onshore and offshore are generally low maturity oils because of low thermal exposure (relatively shallow burial for short times). They are generated as heavy high-sulfur oils because of the composition of the unusual Type II source kerogens which are exceptionally rich in organic sulfur (8–14%). These high-sulfur kerogens, which we designate Type II-S, appear to generate oil at significantly lower thermal exposures than ordinary Type II kerogens with less than 6% S. In contrast to common Type II kerogens which generate oil largely by cleavage at oxygen bridge groups and carbon-carbon bonds (eliminating CO2, H2O, and hydrocarbon fragments), Type II-S kerogens have an additional complement of weak bonds associated with bound sulfur. The preferential cleavage at weak sulfur linkages tends to produce larger fragments, leading to high initial amounts of asphaltenes, resins, and sulfur-rich aromatics together with smaller amounts of saturated hydrocarbons. Elemental analyses of Monterey kerogens and asphaltenes clearly support the concept that the asphaltenes are essentially fragments of kerogen cleaved sufficiently to be soluble or peptized in this heavy oil system. Solubilization of asphaltenes is attributed to their interactions with the abundant resins and aromatics. This sysstem is sufficiently stable under source and reservoir conditions to allow expulsion and migration for reasonable distance without significant fractionation or changes in gross properties. Initial asphaltenes have essentially the same atomic H/C ratios as the source kerogen but have significantlyy lower O/C ratios and slightly lower S/C ratios. The N/C ratios are nearly the same for kerogens and their derived asphaltenes. With increasing maturity the H/C ratios in asphaltenes decrease much like maturation changes in kerogen. The S/C ratio also decreases significantly. However, the O/C ratios (initially low in asphaltenes) and N/C ratios increase slightly due to material balance caused by other losses. These element composition and atomic ratio relationships allow some important inferences concerning source kerogen composition from analysis of asphaltenes alone. This can be useful when potential source-rock samples are not available for analysis and/or when a choice between alternate source-rock possibilities must be made.

The parameters derived from analyses of vanadyl petroporphyrins in a suite of con-familial (single-source) oils from the Big Horn Basin were found to reflect thermal stress and to correlate well with the bulk maturity parameters, except in one case (i.e. Manderson ). Interestingly, the low vanadyl porphyrin concentration in Manderson (10 μg/g) was consistent with that expected of a quite mature petroleum rather than one of low maturity as indicated by the biomarker profile. Hence, it is argued that the Manderson porphyrins are not representative of the major portion of this petroleum, but rather of a minor amount ( ca 5–10%) of less mature petroleum or bitumen picked up during migration to or in the current reservoir. It is concluded that, in general, reliability of biomarker based ratio parameters must be considered contingent on occurrence in expected concentrations and concurrence with bulk petroleum parameters.

A rapid method is given for routine determination of acetone-soluble chlorophyll derivatives in marine sediments. The pigments are extracted from 10–100 g of wet sediment by acetone and transferred to chloroform for spectrophotometric determination. Major pigments have absorption maxima at ca. 668 mμ from which the pigment content is calculated as pheophytin a . Analysis requires about four hours per sample and can be carried out with a precision of about 3 per cent in sediments containing 1–100 p.p.m. of pigments. Analysis of surface samples of basin sediments off southern California shows a range of 4–100 p.p.m. based on dry sediment. Some shallow sediments and deep sea sediments are below 1 p.p.m.

To assess the extent and significance of nutrient regeneration in marine sediments, the depth distribution of nitrogen, phosphorus and silicon in three basin sediments and their overlying waters were determined. The data obtained were interpreted on the assumption that in a relatively constant depositional environment steady state conditions exist and therefore the change of a property with depth of burial is a measure of the change of the property with time in an isolated mass of sediment. The three sediments differ in p h , Eh, organic matter content and other properties, and it was possible to correlate some of the regeneration processes with the biological and physical-chemical environments. The nitrogenous part of organic matter deposited in the basin sediments is partially regenerated as ammonia that becomes oxidized to nitrate in sediments of positive Eh and in the overlying water. Phosphate regeneration occurs most intensively in anaerobic sediment; locally net deposition occurs in aerobic sediments of low p h . Dissolved silicate increases with depth in all the sediments. Water immediately overlying the sediment surface is enriched in these nutrients where regeneration in the sediment is active. The return of nutrients from sediment to water is less than 1 per cent of the annual use by phytoplankton. Calculations show that in one basin a minimum of 1·6 μg-atoms of ammonia per cm2 of sediment surface pass into the basin water annually. At this rate of regeneration the basin water must be renewed from the open ocean in a period of less than twenty years to maintain existing concentrations of nitrate. Calculations based on an oxygen balance for the sediment and water require renewal in about two years. These results indicate a much more rapid circulation of basin water than had been generally suspected.

Sediments from the sea floor off southern California have been examined for acetone-soluble chlorophyll derivatives which are regarded as the source material of the major porphyrins in crude oils. For quantitative estimation, the pigments in sediment extracts were calculated as pheophytin a which is believed to be the most abundant of several similar pigments present. Approximately 120 surface sediment samples were examined: their sources ranged from beach and marsh through various sea-floor environments to the deep sea. Determinations were made for pheophytin, nitrogen, carbonate, and grain size. In addition, detailed analyses of seven cores were made. A dependence of pheophytin content on grain size is evident in surface samples and in cores. The pheophytin content of cores from nearshore basins decreases with depth of burial, the most abrupt change being near the mud-water interface. Deeper basins farther offshore show only slight decreases in pheophytin with depth of burial. Aside from the marsh deposit, the highest concentration of pheophytin occurs in the shallow basins that contain water having a low oxygen content. The data indicate that the pheophytin content of sediments is almost independent of the production rate of chlorophyll-containing plankton and of dilution with sediments--other than coarse-grained turbidity-current deposits. Instead, the chief factor controlling its abundance appears to be the amount of decomposition undergone in settling through the water column and before burial in the sediment. The decomposition is controlled primarily by water depth, oxygen content of the water, and bottom topography. The chlorophyll derivatives found in sediments are intermediate in structure between chlorophyll and the porphyrins found in petroleum. Magnesium has been lost but vanadium and nickel have not yet been introduced into the pigments. Further changes in the organic structure which must occur to convert these pigments into those found in petroleum involve simple reactions such as reduction of carbonyl groups, hydrogenation of carbon-carbon double bands, dehydrogenation, and decarboxylation. All of these changes may be expected to occur gradually in the sedimentary environment. Chlorophyll derivatives in basin sediments are intermediate in quantity as well as structure between those of phytoplankton and those of petroleum. If as much as 1% of the pigments preserved in the surface zones of basin sediments are eventually converted to the porphyrins found in petroleum, the amounts are ample to furnish crude oils with a normal porphyrin content. End_Page 925

Changes in sulfur content and sulfur-isotope ratios with "thermal maturation" have been studied using Big Horn basin (Wyoming) Paleozoic oils as examples of "single source" oils which have attained different stages of maturity as a result of variations in thermal history. With increasing maturity, API°, GOR, S/N, ^dgrC13, and ^dgrS34 all increase, whereas percentage S and percentage N decrease. Except for the increase in ^dgrS34 and S/N, these changes generally are recognized as typical of the thermal-maturation process. Hydrogen sulfide produced in low concentrations by microbial sulfate reduction in shallow reservoirs varies in ^dgrS34 and generally does not appear to change ^dgrS34 of associated oil. Isotopically unrelated H2S and organic sulfur may remain for long times because of negligible reaction between H2S and oil at low temperatures and low H2S pressures. The major new conclusion from this study is that thermal maturation in high-temperature reservoirs (more than 80-120°C) with sulfate present may involve nonmicrobial sulfate reduction with a negligible isotopic fractionation, producing reduced sulfur species with nearly the same isotopic composition as the reservoir sulfate. In this case, sulfurization and desulfurization of oil compete in kinetically controlled processes resulting in isotopic exchange. The ^dgrS34 of H2S and organic sulfur in oils change toward that of reservoir sulfate. Exchange is faster for H2S than for oil. Initial oils with a homogeneous ^dgrS34 distribution with boiling point and compound type become heterogeneous; the lower boiling fractions approach reservoir s lfate values faster than high-boiling fractions. The large increase in S/N ratio with maturation is attributed to percent S being maintained at a significant level by competing sulfurization and desulfurization processes, whereas percent N continues to decrease. The mechanism for high-temperature sulfate reduction is proposed to be the reaction of H2S and SO4= to produce elemental sulfur and polysulfides, which react rapidly to oxidize and dehydrogenate organic compounds and distribute the sulfur between oil and H2S. High concentrations of H2S may accumulate in this case, and oils or condensates may develop abnormally high concentrations of thiols. H2S is a catalyst as well as a product of the reaction; the process, therefore, may be autocatalytic.

As part of a program to evaluate the inßuence of environment on the composition of organic matter in marine sediments and the changes in composition that occur in the upper zones of sediment, cores from several basins representing different environments ofI southern California were examined for extractable organic matter, hydrocarbon content, and certain other properties. The data are of particular interest in considera­tions of the early stages of petroleum formation. Hydrocarbon fractions were separated from extractable organic matter by chroma­tognphy on alumina. This technique permitted semiquantitative separations of a paraf­fin-naphthene hydrocarbon fraction and an aromatic fraction. The aromatic fraction, in the present work, contained }arge amounts of nonhydrocarbon aromatic compounds, and a more refined procedure seems necessary for a detailed study of aromatic hydro­carbon distribution. While the number of samples is too small to allow definite geologic conclusions, the following are indicated: (1) The sediment in the shallowest basin with the fastest sedimentation rate contains the highest proportion of material soluble in organic solvents and the highest hydrocar­bon content even though this sediment is lowest in total organic matter. (2) Hydrocarbons comprisc 2.3-18.6 per cent of the extractable organic matter and 0.05-0.64 per cent of the total organic matter in the three basins examined. The hydro­-carbon content does not differ greatly in the different basins, nor with depth (to 4 meters) in a given basin. Variations with depth appear to be random. (3) Pyrolysis of sediments at 500° C (modified Fischer retort assay) shows only ran­dom variations with depth to 4 meters in a given basin, and the average yield of oil indicates about 7-9 per cent conversion of organic matter to oil. Compared to typical oil-shales, which give 50-75 per cent conversion, this low conversion indicates that basin sediments and oil-shales differ significantly either in the nature of the organic matter or in catalytic activity of the mineral components. (4) The average potential oil yield, computed from hydrocarbons extracted from the sediments, is about 10 times the eventual recovery from oil fields of the Los Angeles Basin, but is only one-tenth the yield of oil obtained by pyrolysis. (5 ) The proportions of hydrocarbons and more complex materials separated from the sediments difier from their proportions in petroleum. These diflerences may result from Jater changes and/or fractionation during migration from source beds.