The Neoproterozoic climatic paradox:equatorial palaeolatitude for Marinoan glaciation near sea level in South Australia

• Published in: Earth and Planetary Science Letters
• Main Authors: Schmidt, Phillip W., Williams, George E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1995
• Subjects: Flinders; permafrost; wedge*
• Online Access: https://researchers.mq.edu.au/en/publications/66364f71-94e8-4f4c-9292-521060d76008; https://doi.org/10.1016/0012-821X(95)00106-M; http://www.scopus.com/inward/record.url?scp=0029542067&partnerID=8YFLogxK

New palaeomagnetic analyses have been carried out for the Neoproterozoic (650-600 Ma) Elatina Formation, an important redbed unit of the Marinoan glaciogenic sequence in the Adelaide Geosyncline, South Australia, and flat-lying equivalent facies on the adjacent cratonic Stuart Shelf and Torrens Hinge Zone. The Marinoan rocks display strong evidence of marine glacial deposition, and coeval periglacial sand wedges in permafrost regolith on the Stuart Shelf indicate in-situ cold climate near sea level and marked seasonality. The palaeomagnetic data define a palaeopole for the formation and indicate that Marinoan glaciation, including permafrost, grounded glaciers and marine glacial deposition, occurred near the palaeoequator. Rocks analysed include 97 oriented outcrop samples from 15 sites at three widely separated sections (∼ 65-115 m thick) of gently folded and unmetamorphosed sandstone, siltstone and tillite spanning the Elatina Formation in the Central Flinders Zone of the Adelaide Geosyncline, soft-sediment folds from tidal rhythmites, and 60 specimens from 54 core samples from six deep drillholes on the Stuart Shelf and Torrens Hinge Zone. The most stable remanence components were only completely demagnetised by 685°C, indicating that haematite is the likely carrier of the remanent magnetisation. This conclusion is supported by the presence of ultrafine haematitic pigment coating clastic grains and filling interstices in the rocks. The observation of mixed polarities within some sandstone samples suggests that such lithologies acquired their remamence as chemical remanent magnetisation (CRM). A positive fold test on syndepositional soft-sediment folds in tidal rhythmites confirms that the rhythmites acquired a detrital remanent magnetisation (DRM) by the settling of haematite grains from suspension in quiet waters. Concordant palaeomagnetic directions determined for the rhythmites and other facies of the Elatina Formation show that the formation acquired its CRM close to the time of deposition. The existence ...