HR: 14:15h
AN: PP53A-02    [Abstracts]
TI: Relationship of Pleistocene Cave Sediments to Faunal Palaeoclimate Indicators: Pilot Study at Mt Etna, Queensland
AU: * Deer, L N
EM: l.deer@qut.edu.au
AF: Queensland University of Technology, 2 George Street, Brisbane, QLD 4001, Australia
AU: Webb, G E
EM: ge.webb@qut.edu.au
AF: Queensland University of Technology, 2 George Street, Brisbane, QLD 4001, Australia
AU: Hocknull, S A
EM: ScottH@qm.qld.gov.au
AF: Queensland Museum, PO Box 3300, Brisbane, QLD 4001, Australia
AB: Sediments occur within almost every cave system, but few studies have focused on retrieval of palaeoclimate information from those cave sediments. Exogenetic sediments, those derived from external sources and transported into the cave, could contain valuable indicators of surrounding climate. For example, previous studies have shown a relationship between the mineralogy of clays produced by weathering in different climatic regimes (i.e., illite and chlorite generally reflect weathering in cool and dry conditions, whereas kaolinite and smectite generally reflect chemical weathering in humid and warm settings). We carried out a preliminary case study on Pleistocene cave fills at Mt Etna, Queensland to test the hypothesis that the sediments record ambient weathering profiles and can therefore be used as palaeoclimatic indicators. Caves in this area occur within highly fractured and recrystallised limestone olistoliths that contain siliciclastic strata in places and are bound partly by serpentinites. We compared the clay mineralogy of cave sediments that contain: 1) rainforest vertebrate faunas and 2) more arid, open vertebrate faunas. We also compared sediments in varying positions relative to a sequence of five flowstones. In each case, sediments showed no bedforms and were limited to very fine grained detritus and were therefore interpreted as having been deposited from suspension. Visible bone and flowstone fragments were removed from samples prior to X-ray diffraction, major element and rare earth element (REE) analysis. Samples were also viewed using a scanning electron microscope (SEM). Preliminary results show no apparent difference in clay species in sediments containing rainforest and more arid vertebrate assemblages. Additionally, clay composition did not vary stratigraphically in relation to the positions of flowstone sequences. All samples contain mixtures of illite, kaolinite, smectite and mixed layer illite/smectite. Clays observed using SEM appear to be poorly crystalline suggesting an exogenetic origin. Investigation of rare earth elements of the clays are currently under way because it has been shown previously that endogenetic clays are characterised by light REE depletion with respect to heavy REE. The following hypotheses are being considered to explain the uniformity of clays in the deposits. 1) Changing climate regime did not affect the primary types of clays produced by weathering at Mt Etna. 2) The clays at Mt Etna largely represent endogenetic sources being liberated internally through limestone dissolution. 3) The local karst environment provided a relatively uniform local climate regime, whereas the vertebrate faunas sampled a broader geographic area with less uniform climate. 4) Clays were diagenetically homogenised secondarily within the cave setting.
DE: 1065 Major and trace element geochemistry
DE: 1637 Regional climate change
DE: 3675 Sedimentary petrology
DE: 9330 Australia
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly