ORGANIC PETROLOGY OF LIPTINITES IN THE DENISON TROUGH, QUEENSLAND

Abstract

Liptinite macerals in the Denison Trough are derived from a wide range of organisms including marine acritarchs, and non-marine algae, lycopods, articulates, ferns and gymnosperms. They are formed from the lipid and wax-rich components of these organisms, in particular from specialised tissues, leaves and reproductive organs developed for protection and/or energy storage. They occur chiefly in terrestrially deposited sediments and coals, yet their distribution is variable amongst the seven coal facies assemblages and six disseminated organic matter (DOM) suites distinguished in the trough. The most abundant liptinites are derived from miospores, leaf cuticles and algae. Miosporinite averages 2.6 per cent of total rock and is most abundant in coal seams, banded coals and carbonaceous mudstones that were deposited in ponds, abandoned channels and intraswamp lakes, where it ranges up to 14 per cent. Cutinite averages 0.7 per cent of total rock, and is most abundant in coal seams and banded coals that were deposited as leaf banks in shallow water marginal to peat swamps, where it ranges up to 10 per cent. Alginite averages 0.1 per cent of total rock, and is most abundant in mudstones that were deposited in lake margin ponds, where it ranges up to 22 per cent. Preservation of liptinites (as determined by fluorescence) is best where they were deposited in a quiet regime, at or near their sites of origin, in concentration. In some of these situations they occur in association or juxtaposition with the highly fluorescing, non-structured macerals sporogenite, phylloresinite and fluorinite. The latter are suggested as remnants of material that has otherwise yielded oil.