Doctor of Philosophy
Department of Geology
Hutton, Adrian C., Organic petrology of oil shales, Doctor of Philosophy thesis, Department of Geology, University of Wollongong, 1982. https://ro.uow.edu.au/theses/2102
Oil shales are a diverse group of rocks that may become an important source of liquid fuel and chemical feedstocks. The bulk of the organic matter in oil shales is generally exinite derived from a variety of organisms ranging from terrestrial higher plants to freshwater and marine algae. In this study reflected light and fluorescence mode petrography provide data not readily available through chemical, transmitted light and palynological studies. The petrographic studies elucidate the mode of preservation and mineral-maceral relationships usually destroyed during mineralization and pyrolysis.
Previous petrographic terminology for algal components is revised and two new terms, lamalginite and telaginite, are defined. Type of exinite is used to classify oil shales into three primary and six secondary groups.
Telalginite derived from Reinschia and Pila, both related to the extant green alga Botryococcus braunii, is the major exinite in torbanite which is formed in shallow lakes associated with coal forming swamps. The reflectance of vitrinite in torbanite decreases as the alginite content increases.
Lamosites are freshwater, laminated oil shales and are divided into Rundle type and Green River type. Australian Tertiary lamosites belong to the Rundle type and contain discrete lamalginite derived in part from the colonial green alga Pediastrum, the freshwater dinoflagellate Septodinium, and the acritarch Cleistosphaeridium. Botryococcus telalginite and huminite are minor constituents. Green River lamosite contains layered lamalginite with minor bitumen and huminite. Differences between the two forms of lamalginite in the Rundle and Green River type lamosites indicate that the environments of deposition were not the same for both types.
Australian Tertiary lamosites were deposited in fresh to brackish water, probably nearshore lakes. Recognition of phytoplanktonic algae, but not benthonic or mat-forming algae, suggests that the bulk of the exinite in these lamosites was derived from planktonic precursors.
The Rundle-Stuart and Byfield deposits have a brown coal unit overlying the lamosite units. In the Condor and Byfield deposits a brown coal unit underlies the lamosite units. The boundaries between the coal and lamosite units represent significant changes in the environments of deposition. The Duaringa deposit has brown coal interbedded with lamosite (as occurs in several of the Rundle-Stuart lamosite units) in a lower unit that is overlain by a younger lamosite unit containing a different assemblage of alginite to the older unit.
Within the lamosite units of Australian Tertiary deposits the abundance of lamalginite changes vertically (but is not related to depth) but type does not. Lateral variation in the type of lamalginite was not observed in any deposit.
Cannel coal contains abundant exinite derived from higher plants.
Tasmanite, contains abundant telalginite derived from Tasmanites punctatus and related algae that have affinities with Pachysphaera pelagica.
Lamalginite, derived from dinoflagellates, acritarchs and other algae, or bituminite is the dominant exinite in marinite. Marinite also contains tasmanitid telalginite and in some specimens, vitrinite-like organic matter of probable algal origin.
Kukersite is composed of telalginite derived from Gloeocapsomorpha prisca, an alga that is closely related to Botryococcus.
The classification and characterization of oil shales provides much-needed data from which a framework for further studies can develop. More meaningful comparisons of the chemical properties of kerogen and shale oil can be attempted and the behaviour of the oil shale during retorting can be more readily understood.