Distribution of land plant markers in oils from the Gippsland Basin

Abstract

The Gippsland Basin is commonly cited as an outstanding example of a province dominated by oil from coal, and the most likely source rock for many of the oils is the Upper Cretaceous Latrobe Formation. Gippsland Basin oils contain abundant molecular fossils (biomarkers) for land plants, but to our knowledge there are no studies showing compelling evidence on whether the oils were predominantly generated from coal seams or from carbonaceous mudstones. In addition, the Latrobe Formation occurs in a range of maturity and facies expressions, and the degree to which other source rocks in the Gippsland Basin have also generated oil remains unclear. In this contribution, we will demonstrate how the distribution of land plant markers, in particular: di-, tri- and tetracyclic diterpanes; aromatic land plant markers such as retene and cadalene; pentacyclic land plant makers such as oleanane, lupane and their A-ring contracted counterparts; as well as, bicadinanes vary within a set of 23 oils from the Gippsland Basin. The variation with other aliphatic biomarkers and carbon stable isotopes is discussed, and source rocks with different floral assemblages in the Gippsland Basin are inferred.