Lloyd, Jarred C.1,2; Van Der Wolff, Erica1; Blades, Morgan L.1; Virgo, Georgina M.2,1; Collins, Alan S.1; Amos, Kathryn J.2
1Tectonics and Earth Systems Group, Mawson Centre for Geoscience; and MinEx CRC, Adelaide, Australia, 2Australian School of Petroleum and Energy Resources, Adelaide, Australia
The Adelaide Superbasin is a vast Neoproterozoic to middle Cambrian sedimentary basin in southern Australia that initiated due to the break-up of central Rodinia and, evolved into the Australian passive margin on edge of the Pacific Basin. We present over 2000 new detrital zircon analyses from more than 20 Tonian–Cryogenian formations of the central Adelaide Rift Complex of the Neoproterozoic–middle Cambrian Adelaide Superbasin. These new data focus on understudied formations from within the Burra and Umberatana Groups that were identified in Lloyd et al. (2020, Precambrian Research, 10.1016/j.precamres.2020.105849). Building on the >7,500 data previously published we now consider that we are getting an adequate idea of the spatial variation of detrital zircon populations for time-equivalent formations within this large basin. The same statistical method of Lloyd et al. (2020) is applied to this dataset. Samples of Burra and Umberatana Groups from the Mount Lofty Range region in the south of the superbasin, preserve local sources (Barossa Complex/Gawler Craton, ca. 2500–1560 Ma), suggesting local derivation. This contrasts time-equivalent formations from the north of the of basin (central and northern Flinders Ranges), where zircon sources include distal regions (Musgrave Orogen ca. 1550–1050 Ma) and suggest axial transport through the Willouran Trough. Samples in the south then show increasing zircon source diversity up sequence, similar to, although not as pronounced as, the progression seen in the north of the basin. All areas are then punctuated by the Sturtian Cryogenian ice-transported deposits. Post-Sturtian glacial deposits preserve younger zircon sources (ca. <1000 Ma), potentially from southern sources (Antarctica?). Notably ca. 980–950 Ma zircon populations are more common in the samples from the south of the basin than in the north of the basin. These observations and interpretations are suggestive of a progressive southward opening of the Superbasin, consistent with the current interpretation of lithostratigraphy.
Jarred Lloyd is a PhD student at the University of Adelaide with a passion for the evolving Earth system during the Neoproterozoic, South Australian geology, education, and outreach.