Chapter 68 Billy Springs glaciation, South Australia

Abstract

An interval several hundred metres thick in the lower part of the late Ediacaran Billy Springs Formation (Fm.) of the NE Flinders Ranges, South Australia, includes both diamictic levels, 'dropstones' and isolated 'stone-clusters' in a thin-bedded, silty or fine sandy matrix, which is commonly laminated. Slumping at a variety of scales is prevalent, but extensive panels of 'right-way-up', moderately dipping beds host dropstones, which disturbed the laminae. It is difficult to explain laminated sediments peppered with dropstones other than by ice-rafting, and the stone-clusters comply with sinking pieces of ice loaded with debris. Although common reworking occurred in channels, larger erratics in this material are out of hydrodynamic equilibrium. Deposition occurred offshore on an unstable slope.Isotopic d 13 C carb measurements show a strong negative excursion through the preceding Wonoka Fm., and several further similar negative excursions in the Billy Springs Fm. This record shows similarities to that of Ediacaran carbonates on the Yangtze platform, south China. Compilation based on a survey of palaeomagnetic data for Gondwana continents, Baltica and Laurasia permits a possible palaeogeography indicating a relatively high palaeolatitude at the time of deposition. Indications of age are imprecise but may be com-

Sedimentology, depositional environments and significance of an Ediacaran salt‐withdrawal minibasin, Billy Springs Formation, Flinders Ranges, South Australia

“…Both diamictic intervals and isolated exotic stones are found exclusively in convolute‐laminated (slumped) mudstones, although it should be noted that, in bed OSCN‐P, the surrounding context of the clast‐bearing interval was unclear due to exposure. Although Jenkins () notes the presence of exotic clasts (‘dropstones’) in both planar‐laminated and convolute‐laminated mudstones in the same section studied here, clasts were not observed in planar‐laminated or sandy sediments. A thorough investigation of outcrop in the vicinity of the measured sections showed only the association between exotic clasts and convoluted laminae.…”

“…Previous sedimentological interpretations of this interval generally favour a marine lower shelf or slope depositional environment for the Billy Springs deposits (e.g. Von der Borch & Grady, ; Jenkins, ). DiBona et al .…”

“…In the interpretation by Jenkins (), slumping associated with exotic clasts may be the result of ice blocks overloaded with detritus which sank to the bottom and deformed the existing planar‐laminated sediment or, alternatively, from icebergs deforming the sea floor and depositing entrained debris while initiating slumps. However, interaction of ice with the sea floor is known to produce large, straight furrows and gouges with ridges (Weeks, ) unlike the slumped beds seen here.…”

“…Exact stratigraphic correlations with other units in the basin have varied with different authors, although it is generally agreed upon that Billy Springs Formation sediments tie to either the upper Wonoka Formation, the lower Bonney Sandstone, or both (Coats & Blissett, ; Reid, ; Pell et al ., ; Von der Borch & Grady, ; Table ). In addition, various authors have differently interpreted the presence of large clasts within mudstones and siltstones of the Billy Springs Formation as the product of either glacial processes (Jenkins, ) or mass flow deposits (Von der Borch et al ., ). Previous investigations have recognized the basic depositional framework of the Billy Springs Formation, but have mostly been brief or reconnaissance studies in speciality journals, have focused on exposures elsewhere or have not been published in peer‐reviewed literature.…”

Chapter 66 Mid-Ediacaran ice-rafting in the Adelaide Geosyncline and Officer Basin, South Australia

“…The classic Cryogenian Sturt and Elatina glaciations in South Australia are reviewed elsewhere in this volume Williams et al 2011). Additionally, there is growing evidence from the Adelaide Geosyncline and eastern Officer Basin of later, Ediacaran frigid climate and possible glaciation in South Australia (Gostin et al 2010;Jenkins 2011). Here we summarize the sedimentological evidence for a glacial influence during deposition of the Ediacaran Bunyeroo Formation (Fm.)…”