THE EDIACARAN IN SOUTH AUSTRALIA: PROPOSAL AND FIELD GUIDE SUPPORTING GSSP POSITION 'C' AT WEARING DOLOMITE, FLINDERS RANGES, 16TH-22ND JUNE, 1998
RICHARD J. F. JENKINS, DAVID M. MCKIRDY and CHRISTOPHER NEDIN
Department of Geology and Geophysics, University of Adelaide, South Australia 5005
|Jenkins, R.J.F.; McKirdy, D.M. & Nedin, C. (Compilers). 1998. The Ediacaran in South Australia: Proposal and Field Guide Supporting GSSP Position 'C' at Wearing Dolomite, Flinders Ranges, 16th to 22nd June 1998. University of Adelaide, Adelaide. pp.64 (+ 21 figs.). ISBN 0-86396-627-6|
Ideas concerning formal international chronostratigraphic divisions within the wider Proterozoic have an extended history (e.g. Harland and Herod 1975). The "Ediacarien" Stage of Termier and Termier (1960) emphasised the significance of the evolutionary appearance of megascopic soft-bodied metazoans near the close of the Proterozoic, and the same concept was linked to the specific setting of the Flinders Ranges with the nomination of an Ediacaran System and Period by Jenkins (1981) and parallel consideration of an Ediacarian System by Cloud and Glaessner (1982). Jenkins (1981, 1984) placed the apparently continuous cycle of deposition represented by the Wonoka Formation and the Pound Subgroup in the Ediacaran (Fig. 1), while the System of Cloud and Glaessner (1982) included nearly twice this stratal thickness embracing the complete Wilpena Group (Preiss 1987, Jenkins 1995). The lower boundary of the System of Cloud and Glaessner reflects the popular idea that a closing glacigenic cycle within the Proterozoic (the Elatina 'glaciation') preceded major metazoan radiations.
Leaving aside the significance of rare lonestones occurring in shales of the upper Burra Group in the Adelaide region (Preiss 1987, p. 114), two well recognised glacigenic intervals are present in the local thick Neoproterozoic succession, the 'Sturtian' and 'Elatina' mixtites (or equivalents) of the Umberatana Group, identified herein as "refrigerations" I and II respectively. New evidence points to the Bunyeroo Formation representing a further refrigeration "III" within the Wilpena Group and dropstones low in the Billy Springs Formation (DiBona 1991) indicate yet another refrigeration "IV".
The Wilpena Group does not have a uniform distribution. In the Adelaide region only its lower parts are present, the Sandison Subgroup of Dyson (1992) including equivalents of the Nuccaleena Formation, the Seacliff Sandstone and ABC Range Quartzite; isolated outliers of the Bunyeroo Formation are part of the Aruhna Subgroup of Dyson (1996a, b). Furthermore, modern sequence stratigraphic studies (e.g. Christie-Blick et al. 1995; Dyson 1996a, b) show the Wilpena Group to include a number of erosive surfaces variously bounding first or second order cycles of sedimentation and evidently of uncertain temporal significance.
Mapping in the Buckaringa, Quorn, Carrington area of the southern Flinders Ranges has disclosed a tectonic movement whereby sediments of the greater Neoproterozoic succession or 'Adelaidean' (named originally in the Adelaide region) extending as high as the Bunyeroo Formation were locally folded, lithified and acquired a cleavage prior to erosion of a rugged topography preceding the local start of deposition of the Wonoka Formation, part of the Depot Springs Subgroup of Dyson (1996a,b). Fluviatile deposits presently recognised as mantling valley floors in this topography include imbricate cobble conglomerates with common angular fragments of red porphyry derived from the Gawler Craton. This deformation will be referred to as the Bendleby Movement and evidently corresponds to uplift in the Adelaide area.