https://ogma.newcastle.edu.au/vital/access/ /manager/Index en-au 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:48378 Wed 15 Mar 2023 13:55:00 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:39060 Tue 03 May 2022 10:14:45 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:18114 13C values are linked to low δ¹³C values of cave air and drip water during that time. This observation corresponds to times of reduced cave ventilation, high pCO₂ of cave air, low drip water pH, lower calcite supersaturation and typically high drip rates. In contrast, the translucent, dense laminae represent more or less complete lateral coalescence (inclusion-free) during the cold season (high calcite, drip water and cave air δ¹³C values), i.e. times of enhanced cave ventilation, low cave air pCO₂, increased drip water pH, relatively high calcite supersaturation and typically low drip rates. In essence, the relative development of the two lamina types reflects changes in the seasonality of external air temperature and precipitation, with a strong control of the winter air temperature on the intensity of cave-air exchange. Thick translucent, dense laminae are favoured by long, cold and wet winters and such conditions may be related closely to the North Atlantic Oscillation mode (weak westerlies) and enhanced Mediterranean cyclone activity during the cold season. Studies of speleothem lamination can thus help to better understand (and quantify) the role of seasonality changes, for example, during rapid climate events.]]> Sat 24 Mar 2018 08:04:36 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:18387 Sat 24 Mar 2018 07:52:37 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:5278 Sat 24 Mar 2018 07:46:27 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:26774 13C values range between ca -6⁰/₀₀ and +4⁰/₀₀, with the most 13C-depleted values in dolomites of the distal alluvial plain and flood basin, and the most ¹³C-enriched in dolomites of the tidal flat and lagoon. Uniform δ¹⁸O values ranging between 0⁰/₀₀ and +3⁰/₀₀ were found in all sedimentary facies. It is hypothesized that the primary dolomite with mosaic microstructure nucleated on extracellular polymeric substances secreted by sulphate reducing bacteria. A multi-step process involving sabkha and reflux dolomitization led to partial replacement and overgrowth of the primary dolomite, but replacement and overgrowth were facies-dependent. Dolomites of the landward, clay-rich portion of the sedimentary system were only moderately overgrown during late dolomitization steps, and partly retain an isotopic signature consistent with bacterial sulphate reduction with δ¹³C as low as -6⁰/₀₀. In contrast, dolomites of the marine, clay-free part of the system were probably transformed through sabkha and reflux diagenetic processes into calcian varieties, and exhibit δ¹³C values of ca +3⁰/₀₀. Major shifts of δ¹³C values strictly follow the lateral migration of facies and thus mark transgressions and regressions.]]> Sat 24 Mar 2018 07:24:46 AEDT ]]>