A recent Geoscience Australia sampling survey in the Bight Basin recovered hundreds of dredge samples of Early Cenomanian to Late Maastrichtian age. Given the location of these samples near the updip northern edge of the Ceduna Sub-basin, they are all immature for hydrocarbon generation with vitrinite reflectance - 0.5% RVmax, Tmax < 440oC and PI < 0.1. Excellent hydrocarbon generative potential is seen for marine, outer shelf, black shales and mudstones with TOC to 6.9% and HI up to 479 mg hydrocarbons/g TOC. These sediments are exclusively of Late Cenomanian-Early Turonian (C/T) in age. The high hydrocarbon potential of the C/T dredge samples is further supported by a dominance of the hydrogen-rich exinite maceral group (liptinite, lamalginite and telalginite macerals), where samples with the highest HI (> 200 mg hydrocarbons/g TOC) contain > 70% of the exinite maceral group. Pyrolysis-gas chromatography and pyrolysis-gas chromatography mass spectrometry of the C/T kerogens reveal moderate levels of sulphur compounds and the relative abundances of aliphatic and aromatic hydrocarbons predict the generation of a paraffinic-naphthenic-aromatic low wax oil in nature. Not enough oom for rest of Abstract

The Vulcan Sub-basin has been actively explored for over twenty years, with oil production from the Jabiru and Challis-Cassini fields, and the depleted Skua Field, all of which were sourced by the Upper Jurassic Lower Vulcan Formation within the Swan Graben. The need to discover other oil-prone petroleum systems led to this study focussing on oils that have a different composition to those of the aforementioned oils. Geochemical analyses (bulk and compound-specific isotopes, GC and GC-MS of saturated and aromatic hydrocarbons) have characterised the Vulcan Sub-basin oils and condensates into three families (Fig 1); a marine oil family (with some terrigenous influence) comprising Jabiru, Challis, Skua, Talbot and Tenacious; a terrestrially-influenced oil family comprising Maret, Montara, Padthaway and Bilyara which have more varied geochemistry; and, a family of condensates from Tahbilk, Swan and Eclipse. The composition of these condensates is more reflective of reservoir alteration effects (such as leakage and gas flushing) than the type of organic matter in their source rocks. The terrestrially-influenced oil family is located in the southernmost part of the Vulcan Sub-basin and in the northern Browse Basin, most probably having being source from the Lower-Middle Jurassic Plover Formation. The Plover Formation contains liquid-prone source rocks within the Skua Trough, albeit immature for hydrocarbon generation. Similar source rocks are believed to occur beneath the Swan and Paqualin grabens since oils with mixed composition are found at Puffin, Pituri and Oliver.

This is a compilation of all proven and probably producing source rocks from Australia. These can be grouped into 15 intervals ranging in age from Late neoproterozoic to Late Cretaceous-Eocene.

The polar lipid and macromolecular compositions of three samples from the marine-influenced Heartbreak Ridge lignite deposit (Bremer Basin, Western Australia) were investigated for chemical changes wrought during early diagenesis. The results of Rock-Eval, microscope Fourier transform infrared spectroscopic and thermal extraction/pyrolysis-gas chromatography-mass spectrometric analyses indicate that the composition of the lignite and its extract are typical of immature Type III organic matter, and thus contain a high proportion of aromatic and oxygen-containing functionalities. Down-seam variation in the proportions of these functionalities, together with changes in the carbon preference index (CPI) of the pyrolysate n-alkenes, and the wax indices of straight chain n-alkyl pyrolysis products, is consistent with more pronounced degradation of the lowermost lignite horizon. This profile is also reflected in the diagenetic products of higher plant triterpenoids, identified in the lignite extracts by gas chromatography-mass spectrometry. The extent of aromatisation, demethylation, ring opening and defunctionalistion is recorded through this depth profile by the compositions of the free, sulfurised and oxygenated higher plant triterpenoids. In contrast, degradation of the extended hopanoids had come to a hiatus by the onset of sulfurisation in the Heartbreak Ridge lignite. Oxygen-containing lipids are implicated as the primary source of the sulfurised hydrocarbons, although not necessarily via direct sulfurisation of the identified oxygenated lipids, but through the formation of more reactive intermediate species. These results suggest that the onset of marine incursion and associated sulfur fixation inhibits, and through preservation illuminates, the typical biogeochemical transformation of lipids and biopolymers in coal-forming environments.

The geological debate about whether, and to what extent, humic coals have sourced oil is likely to continue for some time, despite some important advances in our knowledge of the processes involved. Both liptinites and perhydrous vitrinites have the potential to generate oil; the key problem is whether this oil can be expelled. Expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries. The relative timing of release of generated CO2 and CH4 could have considerable importance in promoting the expulsion of liquid hydrocarbons. The main reason for poor expulsion from coal is the adsorption of oil on the organic macromolecule, which may be overcome (1) if coals are thin and interbedded with clastic sediments, or (2) if the coals are very hydrogen rich and generate large quantities of oil. Review of the distribution of oil-prone coals in time and space reveals that most are Jurassic-Tertiary, with key examples from Australia, New Zealand and Indonesia. Regarding establishing oil-coal correlations, a complication is that the molecular geochemistry of coals is often very similar to that of the enclosing, fine-grained rocks containing terrestrial organic matter. One potential solution to this problem is the use of carbon and hydrogen isotopes of n-alkanes, which have recently been shown to be powerful discriminators of mudstone and coal sources in the Turpan Basin (China). There is a continuum from carbonaceous shales to pure coals, but the question as to which of these are effective oil sources is an extremely important issue, because volumetric calculations hinge on the result. Unambiguous evidence of expulsion from coals is limited. Bitumen-filled microfractures in sandstones interbedded with coals in offshore mid-Norway and in Scotland have been interpreted to be the migration routes of hydrocarbons from the coal seams towards the sandstones. In the San Juan Basin, USA, direct evidence for the primary migration of oil within coal is provided by the sub-economic quantities (10s to 100s of barrels per well) of light oil produced directly from coal beds of the Upper Cretaceous Fruitland Formation. The Gippsland Basin (Australia) is commonly cited as the outstanding example of a province dominated by oil from coal, but there is no literature that explicitly demonstrates that generation and expulsion has been from the coal seams and not the intervening carbonaceous mudstones. The best evidence for coals as source for oil in the Gippsland appears to be volumetric modelling, which indicates that it would have been impossible to generate the volume of oil discovered to date from the organic-rich shales alone. However, early reports that mid-Jurassic coals in mid-Norway were a major source of the reservoired oils, also based to a large extent on oil generation and expulsion modelling, have now been shown to be inaccurate by detailed biomarker, isotope, whole oil and pyrolysis studies. The most convincing commercial oil discoveries that can be correlated to coals are: (1) Taranaki Basin oils in New Zealand, where Late Cretaceous and Tertiary coals, shaly coals and carbonaceous mudstones are likely to have sourced oils in approximate proportion to their volumes and organic contents, and (2) the oils and condensates in the Harald, Amalie and Lulita oilfields (Danish North Sea) which are likely to have been sourced are least partially from mid-Jurassic coals. New oil-source correlation studies based on diterpane, triterpane and sterane distributions in the Bass Basin (Australia), which lies adjacent to the Gippsland Basin and contains sub-economic reserves of oil and gas, has shown that the Tertiary coals and not the associated shales are best correlated with the oils.

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The technique of reaction-gas chromatography-mass spectrometry (R-GCMS) has been used to characterise the polar fractions of sediment extracts and crude oils. R-GCMS was shown to be rapid, to require only small quantities of sample for analysis and the products formed during analysis were readily identified. To undertake R-GCMS, glass liners for split vaporising injection containing the catalyst, palladium black, were placed into the injection port of a gas chromatograph. Hydrogen gas was used both as an effective reactant for gas phase hydrogenation/hydrogenolysis and as the carrier gas for the subsequent separation. The reaction products were mostly hydrocarbons, which were swept on to the column and readily resolved by the non-polar stationary phase and then identified by mass spectrometry. The fully active catalyst was effective in hydrogenating and isomerising alkenes and partially hydrogenating aromatic moieties. Desulphurisation of thiols, sulphides, and thiophenes also readily occurred. Primary alcohols, acids, esters and ethers were transformed into a hydrocarbon of one carbon atom less, while secondary alcohols were reduced to the parent hydrocarbon. Polar fractions, isolated by column chromatography from the bitumen extracts of the Heartbreak Ridge lignite (Bremer Basin, Western Australia; Eocene age) and the Monterey Formation shale (Naples Beach, USA; Miocene age), reacted to produce compound distributions that were characteristic of the organic matter sources. In contrast, polar fractions from crude oils of the Exxon Program release low to minuscule quantities of hydrocarbons during R-GCMS, and their distributions were remarkably similar to each other and thus not diagnostic of organic matter sources. R-GCMS experiments also demonstrate that asphaltenes, even when redissolved and reprecipitated repeatedly, contain a proportion of functionalised material of low molecular weight.

First paragraph of abstract: The importance of organic sulphur fixation in the preservation of organic matter in humic coal-forming environments is demonstrated in this thesis. The transgression of coal depositional systems by marine waters during their deposition and early diagenesis enables the production of reduced inorganic sulphur species by sulphate-reducing bacteria. The presence of these reactive sulphur species, in combination with the altered chemical and microbial regime, influences the preservation and petroleum potential of humic coal.

The transgression of coal depositional systems by marine waters enables the preservation of functionalised lipids, such as steranes, hopanes and higher plant triterpanes, via their reaction with reduced inorganic sulphides produced by sulphate-reducing bacteria. Using compound specific isotopic analysis, higher plant and microbial sources of these lipids can be identified. The carbon isotopic compositions of the lipids are invariant to differences in the degree or timing of marine incursion. This indicates that the introduction of marine waters at any stage of mire and peat development preserves the inherited lipid composition and does not overwhelm this biotic signature during sulphate reduction. Consequently, the selective preservation of certain biomarkers enables their use in the reconstruction of coal palaeoenvironments and facilitates oil-source rock correlations. The presence of these coal-derived chemical markers in crude oils is testament to the petroleum generation potential of marine-influenced coals.