Michael A. Kruge

Organic facies and maturation of Jurassic/Cretaceous rocks, and possible oil-source rock correlation based on pyrolysis of asphaltenes, Scotian Basin, Canada

Abstract This paper establishes source rock characterization and oil-oil and oil-source rock correlations of selected organic-rich shale source rocks and selected light oils and condensates from Jurassic and Cretaceous formations of the Scotian Basin. Multiple source rocks of Kerogen Types IIA (oil-prone), IIA-IIB (oil- and condensate-prone), IIB (condensate and gas prone), III (gas-prone), and IV (nonsource) are identified in various stratigraphic horizons. Vitrinite reflectance and T inmax data indicate variable maturation histories, in different parts of the basin, which are related to differences in lithology-related heat conductivity and the presence of older sediments closer to areas of rifting. Multiple linear regression and cluster analyses of aromatic hydrocarbon ratios reveal two oil families. Some Kerogen Type IIB rock extracts match many of the light oil and condensates in terms of the aromatic hydrocarbon distributions. A second family of oils could not be correlated with any of the analyzed source rock extracts. Pyrolysis-gas chromatography of asphaltenes from the Cohasset A-52 and Sable Island 3H-58 wells are significantly different in n -alkane, aromatics and phenol content. The asphaltene pyrolyzates of samples from Venture B-52 and S. Desbarres O-76 have a high aromatic content, low content of n -alkanes, and high phenol values (S. Desbarres), which is typical of a terrestial source. They correlate well with one another and also with Sable Island light oil. The N. Triumph G-43 whole rock and extract asphaltene pyrolyzates are dominated by normal hydrocarbons, with aromatic, phenolic and thiophenic compounds in low concentrations suggesting an algal source. Algal type organic matter may have made a contribution to the Cohasset petroleum, as its asphaltene pyrolyzate is also dominated by normal hydrocarbons.

Determination of thermal maturity and organic matter type by principal components analysis of the distributions of polycyclic aromatic compounds

Abstract The thermal maturity and organofacies sensitivity of polycyclic aromatic compound (PAC) distributions was explored by examination of the aromatic fractions of solvent extracts from a diverse set of 53 shales, coals and kerogen macerals which have undergone either natural or artificial maturation and which represent all three principal sedimentary organic matter (OM) types. Systematic changes with maturation were observed in the following groups of isomers: tri- and tetramethylnaphthalenes, methyl- and dimethylphenanthrenes, methyl- and dimethyldibenzothiophenes, methylpyrenes, and methylchrysenes. The maturity differences were quantified by mathematical ratios of the relative concentrations of the more thermally stable isomers to the less stable, on the basis of theoretical considerations and empirical observations. The PAC maturity parameters, unlike those derived from saturated biomarker stereoisomers, are typically effective across the entire oil generation window. To compensate for the effects of OM type on the maturity parameters, they were combined using principal components analysis. The resulting first principal component was in good agreement with independent indicators of maturity. The relative distributions of C0–C3 alkylphenanthrenes, dibenzothiophene, methyldibenzothiophenes and methyldibenzofurans were evaluated by a separate principal components analysis. The results permitted an independent grouping of the samples by OM type and suggested additional, simple molecular ratios that allow graphical recognition of OM type, including the ratio of dibenzothiophenes to dibenzofurans and a ratio using C2-alkylphenanthrene isomers.

Preservation of biomolecules in sub-fossil plants from raised peat bogs — a potential paleoenvironmental proxy

The relationship between changes of peat bog hydrology and the mechanisms of decomposition suggests that the chemical modification of biopolymers of peat macrofossils might be used in paleoenvironmental reconstructions. A series of sedge (Eriophorum vaginatum) macrofossils from an Upper Holocene peat profile has been studied by analytical pyrolysis (Py-GC/MS). The major diagenetic changes of biopolymers included loss of ester-bound ferulic and coumaric acids, an increase of oxidation (particularly due to Cα ketones) and shortening of alkyl side-chains, demethylation of methoxy groups of the lignin/polyphenol fraction, loss of pentosan polysaccharides and modification of cellulose (relative increase in the pyrolytic yield of anhydroglucose). The yield of oxidized methoxy-moieties (particularly of Cα ketones) and shortening of alkyl side-chains of methoxyphenols were suggested as the best indicators of oxidative degradation. Statistically significant differences in chemical composition between samples from individual depth increments occur, in part in agreement with a sequence of wet and dry phases determined by paleobotanical analysis. The paleoenvironmental significance of the chemical record of degradation and relationship of paleohydrology reconstructed by the present technique and by means of botanical analysis is discussed. The former was proposed to respond primarily to the frequency of seasonal droughts.

A geochemical study of macerals from a Miocene lignite and an Eocene bituminous coal, Indonesia

Optical and chemical studies of maceral concentrates from a Miocene lignite and an Eocene high-volatile bituminous C coal from southeastern Kalimantan, Indonesia were undertaken using pyrolysis, optical, electron microprobe and FTIR techniques. Pyrolysis products of vitrinite from bituminous coal were dominated by straight-chain aliphatics and phenols. The huminite of the Miocene lignite produced mostly phenolic compounds upon pyrolysis. Differences in the pyrolysis products between the huminite and vitrinite samples reflect both maturation-related and paleobotanical differences. An undefined aliphatic source and/or bacterial biomass were the likely contributors of n-alkyl moieties to the vitrinite. The resinite fraction in the lignite yielded dammar-derived pyrolysis products, as well as aliphatics and phenols as the products of admixed huminite and other liptinites. The optically defined resinite-rich fraction of the bituminous coal from Kalimantan produced abundant n-aliphatic moieties upon pyrolysis, but only two major resin markers (cadalene and 1,6-dimethylnaphthalene). This phenomenon is likely due to the fact that Eocene resins were not dammar-related. Data from the electron microprobe and Fourier transform infrared spectrometry strongly support the results obtained by Py-GC-MS and microscopy.

Environmental and botanical controls on peatification—a comparative study of two New Zealand restiad bogs using Py-GC/MS, petrography and fungal analysis

Abstract This study shows that chemical properties of two restiad species, Empodisma minus and Sporadanthus traversii , may contribute to their success as peat-formers in a climate of the North Island of New Zealand which is not conducive to raised mire development. Unlike Sphagnum , the equivalent northern hemisphere peat-former, restiads possess lignin in their tissues. In addition, the presence of non-lignin polyphenols (including tannins and phenolic acids) in restiads may be an important factor in peat formation due to the allelopathic decay retardation. Patterns of degradation of plant biopolymers have been examined and the pathway of degradation of monocotyledons (loss of non-lignin phenolic fraction, depolymerization via modification of side chains of β -O-4 lignin, depletion of hemicelluloses) was identified. Trends in chemical change for lignin were not necessarily paralleled by a similar change in the degree of plant structure preservation—an expression of a complex nature of degradation involving the contributions of several processes affecting different classes of biopolymers to different extents. A further finding of this study is that the degree of lignin breakdown, together with proportions of fungal hyphae and petrographic character, indicate that one of the two bogs studied, Moanatuatua, has undergone far more aerobic decay throughout its development than has its climatic and vegetational equivalent, Kopouatai. This is thought to be due to differing water tables in the two sedimentary environments. Moanatuatua developed in a flood plain distant from the sea with a migrating river system, while Kopouatai developed near the sea. A high degree of natural peat decomposition at Moanatuatua most probably precluded any further rapid decay after recent agricultural drainage.

FOSSIL CHARCOAL IN CRETACEOUS-TERTIARY BOUNDARY STRATA : EVIDENCE FOR CATASTROPHIC FIRESTORM AND MEGAWAVE

Abstract Organic matter separated from calcareous sandstone from the upper portion of a deep-water tsunami deposit at Arroyo el Mimbral, Taumalipas, Mexico, which marks the biostratigraphically defined Cretaceous-Tertiary boundary, consists primarily of fossil charcoal, including semifusinite and pyrofusinite. Analytical pyrolysis-gas chromatography/mass spectrometry revealed the highly aromatic and polyaromatic character of the organic matter assemblage, typical of the products of partial combustion. The organic matter probably originated as terrestrial vegetation that was caught in a firestorm and subsequently transported far offshore in the backwash of a megawave. These data are consistent with the hypothesis of combustion of large masses of vegetation triggered by a giant extraterrestrial impact in the Gulf-Caribbean region (probably forming the Chicxulub crater in Yucatan) at the very end of the Cretaceous Period.

Bacterial Residues in Coprolite of Herbivorous Dinosaurs: Role of Bacteria in Mineralization of Feces

Abstract The Cretaceous Two Medicine Formation of northwestern Montana has yielded blocky, calcareous coprolites that contain abundant fragments of conifer wood and were produced by large herbivorous dinosaurs. The coprolites are generally dark gray to black in color due to a dark substance confined chiefly within what originally were the capillaries of tracheid and ray cells of xylem. This substance is a kerogen that consists in part of thin-walled vesicles 0.1–1.3 μm in diameter. Pyrolysis products of this kerogen are diagnostic of a bacterial origin with a possible contribution from terrestrial plants. The vesicular component is interpreted as the residue of bacterial cells, whereas a second filamentous component, closely associated with the vesicles, may be the residue of an extracellular binding material, such as glycocalyx. At least two episodes of calcification of the coprolite are recognized by manganous cathodoluminescence. The earlier of these infilled the capillary channels of the conifer fragments. Wood cell walls, voids, cracks, and small burrows were filled during the later episode. Microprobe data confirm these results and show that phosphate is sequestered in the capillaries. These observations suggest that bacteria within the capillaries induced initial mineralization of the coprolite, and, in so doing, created barriers that protected organic residues from subsequent destruction. Early onset of mineralization is consistent with the degree of preservation of woody xylem found in the coprolites.

Biological markers in Lower Jurassic synrift lacustrine black shales, Hartford basin, Connecticut, U.S.A.☆

Abstract The East Berlin Formation (Lower Jurassic, Hartford basin, Connecticut, U.S.A.) is distinctive for its six cyclic units of lacustrine black shale and gray mudstone, separated by playa and fluvial redbeds. The black shales are each about a meter thick and were deposited in subtropical, thermally strastified, oligomictic lakes, the youngest of which (lakes 3 through 6) were large enough to flood most of the basin and attained depths of several tens of meters. The saturate fractions of solvent extracts of organic-rich black shales from each of the six lakes, collected at fresh roadcuts near East Berlin, are dominated by extended homologous series of n-alkanes, alkylcyclohexanes, and branched chain alkanes. A striking feature of the black shales is the presence of a series of extended tricyclic terpanes from C20 to at least C41. Hopanes are either not detectable or present only in subordinate quantities relative to the tricyclic terpanes. The samples are depleted in hopanes in part because of the elevated maturity level (mid to late oil window). Tricyclic terpane concentrations may also have been enhanced by fractionation effects related to oil expulsion out of the black shales. In addition, the original organic matter may have been exceptionally rich in tricyclic terpane precursors, i.e. fossil lipids of prokaryotes present in anoxic, moderately saline, alkaline lakes.

Organic geochemistry and petrology of oil source rocks, Carpathian Overthrust region, southeastern Poland—implications for petroleum generation

Abstract The organic matter rich Oligocene Menilite black shales and mudstones are widely distributed in the Carpathian Overthrust region of southeastern Poland and have excellent hydrocarbon generation potential, according to TOC, Rock-Eval, and petrographic data. Extractable organic matter was characterized by an equable distribution of steranes by carbon number, by varying amounts of 28,30-dinor-hopane, 18α(H)-oleanane and by a distinctive group of C24 ring-A degraded triterpanes. The Menilite samples ranged in maturity from pre-generative to mid-oil window levels, with the most mature in the southeastern portion of the study area. Carpathian petroleum samples from Campanian-Oligocene sandstone reservoirs were similar in biomarker composition to the Menilite rock extracts. Similarities in aliphatic and aromatic hydrocarbon distributions between petroleum asphaltene and source rock pyrolyzates provided further evidence genetically linking Menilite kerogens with Carpathian oils.

Lacustrine shales and oil shales from Stellarton Basin, Nova Scotia, Canada: organofacies variations and use of polyaromatic hydrocarbons as maturity indicators

Abstract The Post-Acadian Stellarton Basin is a small pull-apart basin in northern Nova Scotia. The Coal Brook Member, which is the main focus of this study, contains the thickest and most extensive development of oil shales within the Late Carboniferous Stellarton Formation. Bulk and molecular geochemistry indicate that the organic-rich oil shales and black shales contain Type I/II kerogen with a mixed assemblage of aquatic and terrestrial organic matter that is dominated by the former. Biomarker evidence indicates that these sediments were deposited under deep, anoxic and fresh-to-brackish water lake conditions. Organofacies distinctions were made on the basis of several parameters that are independent of maturity and therefore suggest organic matter changes. The organofacies identified are the result of water-level fluctuations that are climate controlled. All of the aromatic compounds evaluated as maturity parameters were seen to experience alterations in proportion to temperature in the form of either depth or geologic age, that can be correlated with maturity. These alterations are believed to result from changes in molecular composition. Maturity parameters based on the alkylbenzothiophenic and alkylnaphthalenic compounds are shown to be effective maturity parameters in lacustrine sequences, particularly over the higher maturity ranges where standard maturity parameters based on steranes and hopanes are not effective.