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Organic Geochemisty Of Holocene Lacustrine Carbonates In The Coorong Region, South Australia.

Hayball, Anthony John

Honours Degree, 1990

Flinders University of South Australia


Holocene lacustrine carbonate sediments retrieved by coring of North Stromatolite Lake were analysed using a variety of geological and geochemical techniques in order to determine whether a correlation exists between sedimentary and organic facies. Five distinct sedimentary facies are identifiable in core and are associated with four different carbonate mineral assemblages. Results from total organic carbon (TOC) analysis, organic petrology, Rock-Eval pyrolysis and gas chromatography demonstrate a strong correlation between sedimentological processes and the distribution, type and abundance of organic matter in the sediments. Geochemical profiles reveal TOC values in the range 0.7-11.7%, and a variation in the composition of the organic matter (kerogen Types I-IV) which reflects systematic changes in the relative proportions of terrestrial, algal and bacterial input:

The five facies recognised are:

  1. Basal Unit: Mollusc-quartz wackestone to packestone rich in inertinitic material. Organic facies III-IV.
  2. Sapropel A: Laminated algal-pelletal mudstone to wackestone with abundant Botryococcus braunii and filamentous algae. Organic facies I-II.
  3. Sapropel B: Massive pelletal wackestone containing abundant filamentous algae and varying amounts of inertinite and cutinite. Organic facies II-III.
  4. Laminated Unit: Laminated pelletal mudstone to wackestone rich in coccoid cyanobacteria and inertinite. Bimodal organic facies II-III and III-IV.
  5. Massive Unit: Massive pelletal wackestone to packstone with abundant inertinite, cutinite and common coccoid cyanobacteria. Organic facies II-III.
Australian School of Petroleum



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