Evaporites with inherited marine and continental signatures: the Gulf of Carpentaria, Australia, at ~70 ka

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Elsevier B. V.
Changes in sea-level and associated climatic fluctuations resulted in extreme and cyclic changes in depositional environments in the Gulf of Carpentaria region (N, Australia). Disconnection from the sea led to the establishment of “Lake Carpentaria”. In this environment, evaporitic conditions at ~70 ka produced an alternation of μm to mm-thick evaporitic and micritic laminae. These precipitates are primary features, deposited in a shallow lake. Elemental and isotope geochemistry of gypsum and micrite laminae show a complex evaporitic environment where initially marine waters evaporated with the input of continental waters compensating for evaporative losses. Reduced continental input could not support a lake of the initial dimensions and the lake retracted to the deepest part of the basin along the north-eastern side. In a lake with smaller water volume, continental solutes became dominant. The strontium contents of gypsum range from 691 to 1353 ppm, gypsum-δ34S values from +21.8 to +22.5%, gypsum-δ18O values from +14.1 to +16.5% and 87Sr/86Sr from 0.7093 to 0.7098. While Sr contents and sulfur isotopes indicate marine contributions, strontium isotopes and oxygen isotopes in sulfates reveal continental inputs and processes such as recycling of evaporites, sulfate reduction and potential reservoir effects. Carbonate-δ13C and δ18O values in micrite also reveal a continental influence and perhaps variations in organic matter signatures associated with climatic and vegetation changes. In order to assess the provenance of continental waters reaching Lake Carpentaria at this time, REE elements in evaporitic gypsum were analysed and compared to results from modern rivers in the area. The REE-normalized patterns in gypsum samples are like those found in northern Cape York rivers (and unlike seawater), restricting the potential continental inputs into the evaporatic basin to a limited geographical area. The thickness of the calcite-gypsum couplets is consistent with those precipitated annually in modern evaporitic environments. This and the marked fluctuation between dry (gypsum laminae) and wet (micritic layer) suggests a reduced monsoon-like rainfall pattern operating in northern Australia during evaporite precipitation. © 2007 Elsevier
Australia, Queensland, Sea level, Climatic change, Environment, Geochemistry, Isotopes, Strontium, Gypsum, Lakes, Evaporation, Precipitation
Cendon, D., Playa, E., Chivas, A. R., Trave, A., Wyndham, T., Garcia, A., & Hankin, S. I. (2007). Evaporites with inherited marine and continental signatures: the Gulf of Carpentaria, Australia, at ~70 ka. Paper presented to the XVII INQUA Congress 2007, 28th July to 3rd August 2007 Cairns, Queensland, Australia. In Quaternary International, 167-168, 65. doi:10.1016/j.quaint.2007.04.001