Precambrian Research 106 (2001) 149 – 186 A chemostratigraphic overview of the late Cryogenian interglacial sequence in the Adelaide Fold-Thrust Belt, South Australia David M. McKirdy a, *, Jamie M. Burgess a,1 , Nicholas M. Lemon b , Xinke Yu a , Andrew M. Cooper b,2 , Victor A. Gostin c , Richard J.F. Jenkins c , Ross A. Both c a Organic Geochemistry in Basin Analysis Group, Department of Geology and Geophysics, Uniersity of Adelaide, Adelaide, 5005 SA, Australia b National Centre for Petroleum Geology and Geophysics, Uniersity of Adelaide, Adelaide, SA 5005, Australia c Department of Geology and Geophysics, Uniersity of Adelaide, Adelaide, SA 5005, Australia Abstract Within the Neoproterozoic sequence of the Adelaide Fold-Thrust Belt, South Australia, two of the most severe ice ages in Earth history (Sturtian and Marinoan) are recorded in the glacigenic rocks which mark the base and top of the 4.5 km-thick Umberatana Group, the focus of the present chemostratigraphic study. Rock units from three drillholes and ten measured outcrop sections, located in the southern and central Flinders Ranges and on the Stuart Shelf, were sampled for isotopic analysis of their co-existing calcite ( 13 C cal ), dolomite ( 13 C dol ) and kerogen ( 13 C org ). Strontium and sulphur isotopic analyses were also run on selected samples. The sample sites are in tectonic domains where regional metamorphism has been insufficient to significantly alter the isotopic composition of the kerogen. The resulting data, when integrated with the lithostratigraphy of the Umberatana Group, yield one of the most complete records of secular variation in the C-isotope signature of the late Cryogenian ocean between 750 and 680 Ma. Its composite  13 C carb curve begins with a sharp positive excursion ( -3 to +1.5‰ in the dolomitic Tindelpina Shale which caps Sturtian glacial diamictites (Wilyerpa Formation). Then follows a steady climb through the shoaling upward Tapley Hill Formation reaching +4‰ in the Brighton Limestone and culminating in a plateau of 13 C enrichment within the platformal carbonates of the Etina Formation ( +8 to +10‰). The upper part of the temporal trend shows a decline to +6 to +7‰ in the stromatolite reef facies of the Enorama Shale; and a dramatic drop to -8 to -9.5‰, followed by a recovery to – 3‰, in the youngest carbonate unit (Trezona Formation) beneath the Marinoan glacigenic Elatina Formation. The latter is capped by a thin dolostone, the Nuccaleena Formation, which records a consistent up-section decrease in  13 C( -1 to -3‰). Superimposed on this overall pattern of C-isotopic variation are second and third-order fluctuations attributable to eustatic sea-level change. Pyritic sulphur in the lower www.elsevier.com/locate/precamres * Corresponding author. Tel.: +61-8-83035378; fax: +61-8-83034347. E-mail address: david.mckirdy@adelaide.edu.au (D.M. McKirdy). 1 Present address: Northern Territory Geological Survey, PO Box 2901, Darwin, NT 0801, Australia. 2 Present address: URS Corporation, 20 Terrace Road, East Perth, WA 6004, Australia. 0301-9268/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S0301-9268(00)00130-3