Correlating terrestrial signatures from biomarker distributions, δ13C, and palynology in fluvio-deltaic deposits from NW Australia (Triassic-Jurassic)

Abstract

A multidisciplinary study using molecular and organic isotope geochemistry, petrology and palynology has been used to establish palaeoenvironmental conditions of fluvio-deltaic deposits from the Delambre-1 well, Western Australia (Triassic–Jurassic). Changes in higher plant biomarker distributions correlate with (1) brackish water environments; (2) major changes in composition of spore and pollen assemblages; (3) variations in types of sedimentary facies; and (4) stable carbon isotopic composition of higher plant biomarkers. These changes are all consistent with the occurrence of climatic shifts in northwestern Australia during Triassic–Jurassic periods established by [Parrish, J.T., Bradshaw, M.T., Brakel, A.T., Mulholland, S.M., Totterdell, J.M., Yeates, A.N., 1996. Palaeoclimatology of Australia during the Pangean interval. Palaeoclimates 1, 241–281].The combustion marker benzo[e]pyrene is abundant in samples that contain pollen from Falcisporites australis. The decline of F. australis and the rapid emergence of assemblages dominated by Corollina spp. at the end of the Triassic marks a rapid-pollen spore extinction event. At the Triassic–Jurassic boundary there is an increase in relative abundance of the higher plant biomarkers (cadalene and simonellite) in a prodeltaic facies. The δ13C values of between −26.9‰ and −24.9‰ for retene are consistent with a source from class I conifer resinites and relate to samples abundant in Araucariacian conifers in the Early–Middle Jurassic where facies are characterized as pro-distal deltaic.