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Establishing Palaeoenvironmental Conditions in the Jurassic Through Changes in Terrestrial Signatures

The higher plant fingerprint (HPF), as defined by van Aarssen et al. (2000), comprises the relative abundances of retene, cadalene and 6-isopropyl-1-isohexyl-2-methylnaphthalene (ip-iHMN). In these studies, the HPF was determined from sediments spanning the Jurassic from Western Australia and Scotland and correlated with the 13C/12C signatures of corresponding carbonates in order to gain insights into the palaeoenvironmental conditions of deposition.

Fluvio-deltaic deposits from the Delambre-1 well from the Dampier Sub-basin, Western Australia were subjected to biomarker and 13C/12C analyses. Results have shown that changes in higher plant biomarker distributions correlate predominantly with, 1) brackish conditions with some marine influence (2) major changes in composition of spore and pollen assemblages and 3) classification of the delta facies. Higher plant biomarkers were found to be abundant in sediments containing Corallina spp, which has been related to a dry climatic episode in the Early Jurassic. These higher plant biomarkers also correlate with sediments that contain Exesipollenites spp. in the Early Jurassic and Araucariacean conifers in the Early-Middle Jurassic. The biomarker retene is abundant in sediments that contain only Araucariacean conifers in the Early-Middle Jurassic. Distributions of higher plant biomarkers also co-vary, with the prodelta and the distal facies types reflecting environmental changes. For example, cadalene and simonellite are most abundant in prodelta and distal deltaic facies, whereas retene is most abundant at the prodelta-distal facies boundary (where maximium sea level transgression is prevalent).

Personnel

K. Grice, N. Marshall, J. Backhouse, R. Alexander, G. Logan

Funding

Centre of Excellence in Mass Spectrometry

Collaborators

Woodside Petroleum, University of Western Australia, Geoscience Australia