Pyrolysis Of Organic Matter Research Articles

Thermal Analysis and Decomposition Kinetics of Chinese Forest Peat under Nitrogen and Air Atmospheres

The mechanism of forest ground fire is thermal decomposition and smoldering combustion of forest peat or duff. The availability of oxygen is believed to influence the processes. This paper aims to investigate the thermal decomposition of peat under inert and oxidative atmospheres. Experiments were monitored under nitrogen and air atmospheres, using the non-isothermal thermogravimetric (TG) and differential thermal analysis (DTA) methods. The pyrolysis curves of peat showed three main stages, i.e., the stage of moisture evaporation (together with low stability of organic compounds) (315−432 K, with the heating rate of 10 K/min), organic matter pyrolysis (432−805 K), and inorganic compound decomposition (805−1075 K). The stage of organic matter pyrolysis also contained three steps, corresponding to hemicellulose, cellulose, and lignin pyrolysis. Because the temperature of inorganic compound decomposition was higher than the peat-smoldering temperature, this stage of inorganic compound decomposition was not ...

Dike intrusions into bituminous coal, Illinois Basin: H, C, N, O isotopic responses to rapid and brief heating

Unlike long-term heating in subsiding sedimentary basins, the near-instantaneous thermal maturation of sedimentary organic matter near magmatic intrusions is comparable to artificial thermal maturation in the laboratory in terms of short duration and limited extent. This study investigates chemical and H, C, N, O isotopic changes in high volatile bituminous coal near two Illinois dike contacts and compares observed patterns and trends with data from other published studies and from artificial maturation experiments. Our study pioneers in quantifying isotopically exchangeable hydrogen and measuring the D/H (i.e., 2H/ 1H) ratio of isotopically non-exchangeable organic hydrogen in kerogen near magmatic contacts. Thermal stress in coal caused a reduction of isotopically exchangeable hydrogen in kerogen from 5% to 6% in unaltered coal to 2–3% at contacts, mostly due to elimination of functional groups (e.g., OH, COOH, NH 2). In contrast to all previously published data on D/H in thermally matured organic matter, the more mature kerogen near the two dike contacts is D-depleted, which is attributed to (i) thermal elimination of D-enriched functional groups, and (ii) thermal drying of hydrologically isolated coal prior to the onset of cracking reactions, thereby precluding D-transfer from relatively D-enriched water into kerogen. Maxima in organic nitrogen concentration and in the atomic N/C ratio of kerogen at a distance of ∼2.5 to ∼3.5 m from the thicker dike indicate that reactive N-compounds had been pyrolytically liberated at high temperature closer to the contact, migrated through the coal seam, and recombined with coal kerogen in a zone of lower temperature. The same principle extends to organic carbon, because a strong δ 13C kerogen vs. δ 15N kerogen correlation across 5.5 m of coal adjacent to the thicker dike indicates that coal was functioning as a flow-through reactor along a dynamic thermal gradient facilitating back-reactions between mobile pyrolysis products from the hot zone as they encounter less hot kerogen. Vein and cell filling carbonate is most abundant in highest rank coals where carbonate δ 13C VPDB and δ 18O VSMOW values are consistent with thermal generation of 13C-depleted and 18O-enriched CO 2 from decarboxylation and pyrolysis of organic matter. Lower background concentrations of 13C-enriched carbonate in thermally unaffected coal may be linked to 13C-enrichment in residual CO 2 in the process of CO 2 reduction via microbial methanogenesis. Our compilation and comparison of available organic H, C, N isotopic findings on magmatic intrusions result in re-assessments of majors factors influencing isotopic shifts in kerogen during magmatic heating. (i) Thermally induced shifts in organic δD values of kerogen are primarily driven by the availability of water or steam. Hydrologic isolation (e.g., near Illinois dikes) results in organic D-depletion in kerogen, whereas more common hydrologic connectivity results in organic D-enrichment. (ii) Shifts in kerogen (or coal) δ 13C and δ 15N values are typically small and may follow sinusoidal patterns over short distances from magmatic contacts. Laterally limited sampling strategies may thus result in misleading and non-representative data. (iii) Fluid transport of chemically active, mobile carbon and nitrogen species and recombination reactions with kerogen result in isotopic changes in kerogen that are unrelated to the original, autochthonous part of kerogen.

Hydrothermal pyrolysis of organic matter in Riphean mudstone

The catagenesis of organic matter (OM) was modeled by the hydrothermal pyrolysis of a source rock (Riphean mudstone from eastern Siberia). Isothermal experiments 72-h long were carried out in an aqueous environment in autoclaves at temperatures of 300, 310, 320,..., 370°. The pyrolysis products were analyzed for yield of extract, organic carbon, and parameters of Rock-Eval pyrolysis. The amount of the generated liquid hydrocarbon (HC) compounds increased to a temperature of 340°C and then decreased. The experimental trend of the hydrogen index (HI) dependence on the T Max temperature generally coincided with that for natural OM maturation. The carbon isotopic composition of the insoluble (in organic solvents) OM remained practically unchanged in the course of the experiments. The carbon structure of the solid remnants of the experimental samples was ordered (after the experiments) with the origin of turbostratic graphite with a spacing of d 002≈3.5 A°. We also conducted pyrolysis in a diamond anvil cell equipped with a digital camera in order to obtain additional qualitative and quantitative information on oil generation and emigration in the source rock and isolated kerogen. Chemical kinetic parameters of kerogen cracking were calculated for pyrolysis in an open system. The extrapolation of the high-temperature experimental results is discussed with reference to natural OM maturation.

Characteristics and Kinetics of Forest Peat Pyrolysis

Peat smoldering is one of the main combustion modes of forest ground fires. Research into the pyrolysis kinetics of peat is an essential step in studying the peat smoldering mechanism and ground fire behavior. We measured the elemental composition of one typical peat sampled from the northeast forest zone of China by means of spectrofluorometry and studied the pyrolysis characteristics of peat with thermogravimetry-differential thermal analysis (TG-DTA). Results show that the peat sample is composed of more than 45 elements. The pyrolysis process of peat may be divided into three stages, i.e., dehydration, organic matter pyrolysis and mineral decomposition. Because organic matter pyrolysis played an important role in peat smoldering, the pyrolysis kinetics of organic matter was determined. Using thermal kinetic analysis theory and optimization methods, the model that three-component react parallelly was established to describe the scheme of peat pyrolysis. We found that the scheme containing three-parallel-reactions could describe the pyrolysis kinetics very well.

Efeito do processamento na contaminação de cana-de-açúcar e derivados por hidrocarbonetos policíclicos aromáticos

Polycyclic aromatic hydrocarbons (PAHs) constitute a large class of environment contaminants formed during incomplete combustion or pyrolysis of organic matter. Many of these compounds are considered clearly carcinogenic and genotoxic. In the present study, samples of sugar cane juice (produced with burnt and not-burnt sugar cane), intermediary products and by-products of the cane sugar industry were analysed for the presence of 5 PAHs. The analyses were carried out by HPLC with fluorescence detection. Results show relatively higher levels of PAHs in cane juice from burnt sugar cane samples. This confirms that the practice of burning sugar cane before harvest is a source of PAHs emission in the environment which may be transferred to the sugar cane. Analysis of intermediary products of the process shows a decrease in the levels of PAHs along the cane sugar process (cane juice, clarified cane juice, syrup and sugar). This indicates a positive effect of clarification, floatation and centrifugation steps on the PAHs levels reduction on the final product.

Compositional differences in biomarker constituents of the hydrocarbon, resin, asphaltene and kerogen fractions: An example from the Jet Rock (Yorkshire, UK)

Soluble and insoluble fractions of the Jet Rock sedimentary organic matter have been subjected to hydropyrolysis to evaluate their biomarker content. Hydropyrolysis is the temperature-programmed pyrolysis of organic matter in an open system fixed bed reactor under high hydrogen pressure in the presence of a sulfided molybdenum catalyst. The hydrocarbon products contain fossil lipids and biomarkers including high carbon number homologues and compounds with stereochemical configurations that are sensitive to exposure to high temperatures. Distinct differences exist between the concentrations and composition of biomarkers present in the different organic matter fractions. The sterane carbon number distribution, the dominant hopane carbon number and the proportions of tricyclic terpanes and extended tricyclic terpanes are different in each fraction, so biomarker parameters measured for different fractions are not directly comparable. The samples are of early oil window maturity and yet the quantities of biomarkers covalently bound into the kerogen fraction are of equal magnitude to the quantities that are present in the extractable aliphatic hydrocarbon fraction. However, the quantities of biomarkers in the polar resin and asphaltene fractions are two orders of magnitude lower and these two organic matter fractions contain biomarkers that are compositionally very different from the bulk of the biomarkers present in the total sedimentary organic matter. Isorenieratene derivatives were found in all fractions, indicating that green sulfur bacteria were present during sedimentation and that water column anoxia extended into the photic zone periodically if not continuously during the deposition of the Jet Rock.

Mid-Cretaceous uplift and erosion on the northern margin of the Ligurian Tethys deduced from thermal history reconstruction

The paleogeography during Early Cretaceous of the northern margin of the Ligurian Tethys is poorly constrained because of deformation and erosion during Pyrenean and Alpine orogenic phases. The present-day limit between Lower Cretaceous sediments in the South–East basin, located at the northwestern margin of the Ligurian Tethys, and basement rocks is the consequence of a protracted erosion history. Lower Cretaceous sediments observed today in the basin, even close to the present-day outcropping border, are characteristic of pelagic environments. A larger extent of a Lower Cretaceous cover on the basement must then be considered. This study focuses on the western part of this margin (the Causses basin), in the South of the Massif Central (France), using several thermochronometers and geothermometers to decipher the former extent of the sedimentary cover. Apatite fission track thermochronology on basement rocks surrounding the Causses basin suggests that these rocks cooled from temperatures higher than 110°C during the mid-Cretaceous. Average fluid inclusion homogenisation temperatures between 94°C and 108°C are recorded in calcite veins from outcropping Toarcian and Aalenian shales. In the shales, Tmax values, temperature obtained by Rock–Eval pyrolysis of organic matter, are in agreement with these elevated temperatures. Different explanations for these relatively high temperatures, which cannot be explained by the present-day sedimentary serie in the basin, have been tested using a 1D thermal modelling procedure (Genex). For a 95±10-mW/m2 paleoflux, thick sedimentary deposits (2.5±0.3 km) including 1.3±0.3 km of Lower Cretaceous sediments cover the South of the Massif Central; these formations have been subsequently eroded from mid-Cretaceous time onwards. This study confirms that the South of the Massif Central was a site of marine sedimentation during the Early Cretaceous where a thick sedimentary sequence was once deposited.

Early diagenesis of the Upper Devonian Escuminac Formation in the Gaspé Peninsula, Québec: sedimentological and geochemical evidence

Abstract Clay mineral investigations, pyrolysis of organic matter, and microscopic observation of palynomorphs are used to interpret the diagenetic conditions of the Upper Devonian Escuminac Formation, Quebec, Canada. Pyrolysis of kerogen, vitrinite reflectance, and the presence of smectite show that the sediments of this formation have been subjected only to a shallow burial diagenesis; hence, the geochemical signatures are informative on the palaeoenvironment. Concretions are observed in the Escuminac Formation. Sedimentological and geochemical evidence suggest that these concretions were formed during early diagenesis from biodegradation of organic matter. The well-known fish-fauna of the Escuminac Formation show good preservation, due in part to extensive early diagenetic carbonate cementation. The occurrence of calcite cements and fibrous calcite is attributed to the early diagenetic transformation of pre-existing organic matter.

Geoenvironmental protocol for site and waste characterization of former manufactured gas plants; worldwide remediation challenge in semi-volatile organic wastes

The most common and difficult of all hazardous waste sites are those that historically produced artificial (manufactured) gas; for gas-making was international in scope and at the very core of the industrial revolution. With former manufactured gas plants (FMGPs), virtually no geologic region in the industrialized or urbanized world or its trade centers and ports escaped the gas industry. These plants applied pyrolysis of organic matter (roasting to drive off volatiles in the form of useful gases) to illuminate the world and to fuel all manner of progress. Gas was and is the universal fuel. Its prominence stemmed from the omnipresence of organic matter and the universal process for the extraction of its volatile contents to manufacture useful gas. Furthermore, for most of the century and a half-long history of manufactured gas, natural gas was unavailable to slow or daunt the production of man-made gas and the universal creation of its toxic tar residues and other harmful waste residuals. Today we face the presence of toxic organic gas manufacturing residuals as a unique threat to both the health and welfare of contemporary society, as well as being a long-term threat to the environment that is dominantly geologic in character. Most of these tar residuals are highly resistant to natural degradation or attenuation in the environment and their lives, therefore, they are measured in geologic time. Given its environmental persistence, potential problems associated with tar may exist centuries to thousands of years. Engineering geologists and geological engineers are, by training and experience, particularly well equipped to plan, manage and conduct site and waste characterization efforts for FMGPs and related coal-tar sites.

Sorption–desorption behavior of phenanthrene elucidated by pyrolysis–gas chromatography‐mass spectrometry studies of soil organic matter

AbstractCommonly used partitioning models of hydrophobic organic contaminant sorption in soil, which treat all soil organic matter (SOM) as having identical structure, are unable to explain differences in organic carbon–normalized sorption coefficients (KOC) among sorbents, isotherm nonlinearity, and sorption–desorption hysteresis. This study relates one index of SOM composition, structural fragments quantified by pyrolysis–gas chromatography‐mass spectrometry, to aqueous and supercritical carbon dioxide (SC CO2) sorption–desorption parameters. Results show positive correlations between aqueous KOCs and hydrocarbon fragment peak areas and negative correlation to N‐ and O‐containing peaks, which is consistent with hypotheses attributing sorption of phenanthrene to hydrophobic sorbent domains. Positive correlation between Freundlich n values in SC CO2 and hydrocarbon fragments with negative correlation to N‐ and O‐containing fragments suggests that energetic heterogeneity of polar environments controls nonlinearity in this solvent of limited polarity. Aqueous sorption–desorption hysteresis appears to be surpressed by N‐ and O‐containing moieties and correlates with decreased thermal desorption of phenanthrene at 800°. The SC CO2 extraction efficiency and, to a lesser degree, the desorption response when methanol is added as a cosolvent indicate that polar functional groups play a role in retarding phenanthrene desorption during SC CO2 extraction. Organic matter pyrolysis under varying time and temperature conditions indicates that pyrolysis fragments that do not significantly correlate with functional trends likely evolve by a different pyrolytic mechanism and are generally poorly correlated with sorption–desorption properties. The level of structural detail utilized in structure–function correlations in this work exceeds previous efforts to relate sorption behavior to sorbent structure. However, the work reveals that certain sorption parameters, notably Freundlich n values in aqueous systems, require even more detailed characterization of sorbent structures.

A currently forming petroleum associated with hydrothermal mineralization in a submarine caldera, Kagoshima Bay, Japan.

Petroleum-like products have been found in hydrothermally altered recent sediments of the submarine Wakamiko Caldera (depth = 200 m) in the northern Kagoshima Bay, southern Kyushu, Japan. High concentrations of polynuclear aromatic hydrocarbons (PAHs) of pyrolytic origin and biomarkers signatures representing diverse degrees of maturation have indicated that the associated bitumen is a typical hydrothermal petroleum. This is the first report on a significant content of hydrothermal petroleum related with a submarine volcanism of island-arc. The petroleum was generated by pyrolysis of organic matter in recent sediments deposited in the caldera. The hydrothermal petroleum and massive sulfide deposits are concluded to be currently forming within the caldera by hydrothermal activities below the seafloor where presently forming Kuroko-type sulfide deposits were also reported. Considering simultaneous formation of the hydrothermal petroleum and the Kuroko-type deposits in the Wakamiko Caldera, we propose a hypothesis that, during the middle Miocene, the same phenomena happened extensively in northeast Japan in association with the large-scale marine volcanisms, resulting in the formation of both petroleum and sulfide ore deposits (Kuroko) in the same geological horizons.

Oxygen-18 measurement by continuous flow pyrolysis/isotope ratio mass spectrometry of vegetable oils

Stable isotopes are now increasingly used for the control of the origin or authenticity of food products. Among these techniques, the measurement of the 18O content of organic compounds has rarely been carried out because of technical difficulties in the preparation and measurement of the samples. Recently a few laboratories have worked on the setting up of on-line methods to allow easier access to the information that can be obtained from 18O/16O ratios. In this work, such a technique was developed by modifying an elemental analyser device for carrying out the pyrolysis of organic matter. This device is coupled to an isotope ratio mass spectrometer for 18O determination in the CO resulting from the pyrolysis of the compound to be analysed, with good results. The relationship between the 18O content of various oils and their geographical origins is discussed. © 1998 John Wiley & Sons, Ltd.

Are time and temperature the only constraints to the simulation of organic matter maturation?

Confined pyrolysis, hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples (Toarcian shale and kerogen, Woodford shale and kerogen, Manakam coal) and under different experimental conditions, in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter. Results show that: (i) experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models; (ii) increasing confining pressure (300–1300 bars) in gold cell experiments performed on Woodford samples has a limited influence on the reduction rate of the oil potential, the TSOM (Total Soluble Organic Matter) yield and the structure of the polars; (iii) the presence of excess liquid water (0–100 weight %) in confined pyrolysis experiments does not significantly influence organic matter maturation. However, comparisons with classic hydrous pyrolysis (200 weight % water) could indicate major differences in timing and composition of the TSOM (bitumen + expelled fraction) as well as of the solid residue. It appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined. Hydrous pyrolysis conditions (low partial pressure of products) delay Woodford kerogen conversion. In addition, results concerning the Mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect; (iv) increasing water pressure in hydrous conditions (220–1300 bars) drastically lowers and delays Woodford kerogen maturation. Quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis. This study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation.

Hydrothermal pyrolysis of organic matter in Guaymas Basin: I. Comparison of hydrocarbon distributions in subsurface sediments and seabed petroleums

The bitumens of a selection of subsurface sediments from Guaymas Basin, Gulf of California, have been analyzed in order to assess the hydrothermal effects on the organic matter and to better delineate the processes influencing the generation, deposition, and alteration of the hydrothermal petroleums at the seabed. Although the thermally generated subsurface bitumens are generally rich in polar/asphaltic materials, as are the seabed oils, the hydrocarbon transformations parallel the extent of hydrothermal alteration as reflected in the downcore mineralogy at DSDP Sites 477 and 478. At Site 477, a progressive change from n-alkane- to aromatic hydrocarbon-dominated patterns in the high resolution gas chromatography-resolvable fractions of the bitumens accompanies decreases in organic carbon and bitumen yields with depth. These transformations are indicative of sequential hydrothermal alteration of the sediments with depth, due to increasing temperature and/or progressive passage of hydrothermal fluid through the sedimentary column. The polycyclic aromatic hydrocarbon (PAH) distributions undergo extensive transformations (e.g. dealkylation) consistent with hydrothermal alterations, are dominant at depth, and have the broadest range as thermal maturation indices. The aliphatic and aromatic components of the seabed oils can be transported to the seabed independently as a result of their generation under different temperature or depth regimes and sequentially over time during pyrolysis. The concentrations of the parent PAH in the thermally altered subsurface bitumens are comparable to those in the seabed oils. The differential dissolution of the more soluble aromatics and selective solidification/condensation of the higher molecular weight PAH out of the high-temperature fluids exiting at the seabed (chimneys) result in aromatic distributions of the oils significantly skewed towards the larger components [e.g. benzo(ghi)perylene] relative to the subsurface bitumens. Comparison of the downcore hydrocarbon distributions with those in the seabed petroleums support the contention that the hydrothermal oils are mixtures of pyrolysates from different depths or thermal regimes and are significantly altered by differential solubilization during transport and at the seabed.

Non-isothermal retorting of rock phosphate containing organic matter

The pyrolysis of organic matter enclosed in natural phosphate was investigated under non-isothermal conditions in order to analyse the kinetics of the reactions involved in the release of gases. Such retorting is often conducted industrially to increase the purity of the phosphate and to minimize the manufacturing cost of phosphoric acid. Hydrogen release occurs in a series of three overlapping waves covering a large range of temperature (300–950 °C). Methane evolution starts at 350 °C and continues up to 750 °C. An increase in the H 2 concentration in the carrier gas leads to the appearance of a second wave of CH 4. Hydrogen sulphide evolves at lower temperatures; it originates essentially from thiophenic compounds. The release of CO 2 occurs in three peaks which are attributed to the decomposition of CaCO 3 and to subsequent reactions of the residual carbon with the phosphate matrix. At temperatures > 600 °C the formation of all the gases analysed involves a complex network of reactions.

Internal exposure to organic substances in a municipal waste incinerator.

Fifty-three persons occupied in a municipal waste incinerator were examined with respect to their internal exposure to organic substances which may be produced during pyrolysis of organic matter. For this purpose the levels of benzene in blood, polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) in plasma, and mono- (MCPs), di- (DCPs), tri- (TCPs), tetra- (TCEPs) and pentachlorophenol (PCP) and hydroxypyrene in urine were determined. For control purposes, 431 men and women were examined. Significantly higher values for the workers were found for the excretion of hydroxypyrene [median (m): 0.24 vs 0.11 microgram/l; non-smokers], 2,4/2,5-DCP (m: 10.5 vs 3.9 micrograms/l) and 2,4,5-TCP (m: 1.2 vs 0.8 micrograms/l) and for the HCB level in plasma (m: 4.4 vs 2.8 micrograms/l). For the concentrations of 4-MCP and 2,3,4,6/2,3,5,6-TECP, the controls had significantly higher concentrations in urine than did the workers in the incineration plant (m: 4-MCP 1.7 vs 1.2; 2,3,4,6/2,3,5,6-TECP: 1.2 vs 0.3 micrograms/l). No significant differences between workers and controls were detected with respect to benzene in blood (m: 0.20 vs 0.28 microgram/l; non-smokers), 2,4,6-TCP and PCPs in urine (m: 0.85 vs 0.60 and 2.2 vs 2.2 micrograms/l) or the levels of PCB congeners in plasma (m: sigma 138, 153, 180: 5.6 vs 4.1 micrograms/l). The elevated levels of hydroxypyrene, 2,4/2,5-DCP, 2,4,5-TCP and HCB in biological material may be related to the incineration of the waste. These elevations, however, are very small and are of interest more from the environmental than from the occupational point of view.

Aromatic hydrocarbon degradation: a molecular approach.

Aromatic hydrocarbons have a ubiquitous distribution in nature. The majority of these compounds are formed through the pyrolysis of organic matter. Pyrolysis at high temperatures leads to the formation of unsubstituted polycyclic aromatic hydrocarbons (1). Pyrolysis at low temperatures, such as those at which crude petroleum is formed, leads to the formation of alkyl-substituted aromatic hydrocarbons (1). Many of these compounds are suspected carcinogens. Increased use of petrochemicals by modern society has increased the amount of aromatic hydrocarbons found in air and soil samples (2,3). It is not surprising then that due to the ubiquitous nature and increasing concentrations of aromatic hydrocarbons microorganisms can be found that have the ability to degrade these compounds. The varied mechanisms by which microorganisms utilize aromatic hydrocarbons as carbon and energy sources have been the focus of several reviews (4–10).

Igneous activity and organic maturation in the Midland Valley of Scotland

The general relationship of Erich Stach's research work to the effects of igneous activity on organic maturation is briefly considered. The geological history of the Midland Valley of Scotland is then reviewed. As a graben which developed in Devonian (Old Red Sandstone) times, and continued to do so as lithospheric tensional stretching was maintained throughout the Carboniferous, a significant factor in relation to the development of organic maturation was the widespread igneous activity that persisted throughout much of Upper Palaeozoic times. Calc-alkaline volcanic rocks are a major feature within the molasse-type deposits of the Old Red Sandstone. After a period of quiescence in later Old Red Sandstone times, the continuing tensional stretching initiated or rejuvenated major crustal fractures. Extensive volcanic, sill and dyke activity exercised an important influence on the predominantly shallow-water deltaic deposits of the Carboniferous. Alkaline-olivine basalts were erupted in the Early Carboniferous, while volcanic activity in the later Carboniferous was essentially phreatic. Two major intrusive episodes occurred; the first of alkaline sills in Early to mid-Carboniferous times which were closely related to volcanic plugs and eruptive centres, the second in post-Westphalian times when tholeiitic sills and dykes with no known relationships with any extrusive rocks were injected. The effects of this igneous activity on organic maturation can be considered under four headings. 1. (1) Although the general development of maturation of Carboniferous organic matter, which includes many coal seams and oil shales, was controlled to some degree by burial history, the regional pattern of igneous activity was also influential. Thus, there is a gradual increase of coalification from east to west in the Midland Valley which corresponds with an increasing thickness of volcanic pile in the central and westerly parts of the graben, suggesting that there may have been a greater regional “heat sink” in the west during the Carboniferous. The level of coalification is nowhere particularly high, except where affected by intrusions, and regional reflectance gradients generally vary between % R oil (vitrinite) = 0.2/km to 0.4/km, without displaying any consistent pattern. 2. (2) The post-Westphalian tholeiitic (quartz-dolerite) Midland Valley Sill, which underlies most of the central and eastern parts of the graben, has produced extensive reflectance (thermal) aureoles in the organic matter above and below the intrusion. The olivine-dolerite and teschenite sills of Namurian—early Westphalian times, many of similar thickness to the quartz-dolerite intrusions, fail to produce significant reflectance (thermal) aureoles. This major difference in organic matter response to the intrusions can only be explained in terms of the initial rank level of the organic matter, differences in degree of compaction of the sediments and particularly in the amount of water the sediments contained at the time of intrusion. 3. (3) Maturation of organic matter closely associated with extensive Surtseyan-type volcanic activity in the eastern part of the graben displays no relationship to the regionally developed coalification in associated sediments. Although some vitrinite clasts in the pyroclastic deposits have had their reflectances raised to meta-anthracitic rank, reflectance levels of clasts in tuffs and agglomerates are generally not much raised above the regional reflectance level, suggesting incorporation of organic matter in ash streams in which water was an important cooling and protective component. 4. (4) The close relationship of organic matter of all kinds with volcanic and intrusive igneous rocks has led to a marked increase of parent polycyclic aromatic hydrocarbons (PAH) in the aromatic fractions of organic extracts. The source of these hydrocarbons is the combustion and/ or pyrolysis of organic matter caused by the high temperatures of the igneous materials, whether volcanic or intrusive. These PAH may be directly generated or absorbed from the surrounding environment.

Pyrolysis of organic matter in cold-seal pressure autoclaves. Experimental approach and applications

Comparison of natural series of type III coals and type II kerogens with experimental results have shown that the cold-seal autoclave system offers the possibility to simulate the maturation of organic matter. The experimental vessel as well as the temperature regulation and monitoring systems are described in some detail. Limitations of the technique for mass balance calculations and simulations on whole rocks are discussed and indicate necessary improvements of this system for organic geochemistry purposes.

Multiple origins of methane in the Earth

Methane occurrences in the Earth's crust are predominantly of biogenic origin, i.e. their ultimate source is biologically formed organic matter. Methane can also form through inorganic reactions and is consequently termed abiogenic. Biogenic methanes can either form through bacterial or thermogenic processes. Bacterial processes follow a CO 2 reduction and/or fermentation pathway. The fermentation processes are quantitatively more important in recent fresh sediments and swamps. Methane formed by CO 2 reduction, however, is most common in older sediments and commercial gasfields. Temperature, organic substrate and age may be the major factors controlling the relative importance of the two pathways. Stable-isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter, the timing of gas expulsion, and trapping. The different character of methane in individual sedimentary basins may be a result of the geologic history. Geothermal methanes are most likely derived from pyrolysis of organic matter. Abiogenic methane occurs in hydrothermal vents and ophiolite complexes. Inorganic reactions, either surficial or deep-seated, are the likely source of such methanes. A uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes.