Reid_et_al_Ediacara_Member_Detrital_Zircon_Supplementary_Information_U_Pb_Data (xlsx)

The Ediacara Member of the Rawnsley Quartzite hosts the Ediacara biota in South Australia. These fossils are internationally recognised as representing the earliest complex life on Earth with the South Australian section representing the global boundary stratotype section and point of the Ediacaran period. Constraining the age, provenance and depositional environment of the sediments that host them is of great value. The Rawnsley Quartzite is also the terminal package of Neoproterozoic sediments in the Flinders Ranges region and therefore a comprehensive understanding of sediment provenance and palaeoenvironments will aid basin and palaeoenvironment reconstruction. This study focuses on detrital zircon from a broad geographic spread of sites across the Ediacara Member depositional zone. LA-ICP-MS zircon U-Pb analysis yielded a total of 924 concordant zircon grains. The primary peak in age probability distributions is centred between c. 1060 and 1260 Ma with smaller peaks in the ranges of c. 620-640 Ma and c. 1480–1800 Ma. The youngest concordant zircon is 574 +/-8 Ma and youngest statistically coherent group is 623 +/-5 Ma (n=4). We concur with previous studies that the primary sediment source is the uplifted regions of the Petermann and Paterson orogens which correlate to the basement provinces of the Musgrave and Rudall Province, respectively. Younger detritus may have been sourced from the Mount Arrowsmith Volcanics (c. 585 Ma) in the Koonenberry Belt, western New South Wales.<br><b>Data Acquisition Methods</b>Samples for zircon analysis were comminuted using a Bico jaw crusher and disk mill. Zircon grains were extracted from samples via traditional panning followed by magnetic and heavy liquid separation. Zircon grains were hand-picked in a representative manner (e.g. all grains within a microscope field of view) to ensure that the grains sampled were not biased by size, morphology or colour. In addition, four samples from Devils Peak and Reaphook Hill had a wide range of grain sizes and hence had an additional aliquot of grains picked that represented the smallest grains within the sample. This was done to maximise the likelihood for analysing any potential volcanic zircon and also to ensure that the smaller grains were not polished away while exposing the core of larger grains. Grains were annealed at 900°C for 48 hours prior to being mounted in epoxy and polished to expose their mid-point. Zircon grains were imaged via cathodoluminescence and analysed using LA-ICP-MS, utilising a 50 second background and a 50 second analysis time. Analyses are considered to be successful if they did not show evidence for common Pb (²⁰⁴Pb above background) and yielded constant isotopic ratios for the majority of the analysis with no evidence for inclusions. GJ-1 was used as the external standard and Plešovice and 91500 were used as internal standards. All zircon standards were also annealed to ensure consistent matrix effects during ablation. Data were processed using Iolite (version 3.7) and the U-Pb downhole fractionation correction of Paton et al. (2010). The weighted mean ²⁰⁶Pb/²³⁸U age for the Plešovice standard was 339.7 ±0.7 Ma (MSWD = 1.7, n = 101) and the weighted mean ²⁰⁷Pb/²⁰⁶Pb age for the 91500 standard was 1063 ±5 Ma (MSWD = 1.05, n = 131). Additional uncertainty has not been included in ²⁰⁶Pb/²³⁸U analyses (as indicated would be appropriate by the excess MSWD for Plešovice analyses), as precise weighted mean ages are not used in this study.<br>