Chapter 70 The Elatina glaciation (late Cryogenian), South Australia

Deposits of the late Cryogenian Elatina glaciation constitute the Yerelina Subgroup in the Adelaide Geosyncline region, South Australia. They have a maximum thickness of c. 1500 m, cover 200 000 km2, and include the following facies: basal boulder diamictite with penetrative glaciotectonites affecting preglacial beds; widespread massive and stratified diamictites containing faceted and striated clasts, some derived from nearby emergent diapiric islands and others of extrabasinal provenance; laminated siltstone and mudstone with dropstones; tidalites and widespread glaciofluvial, deltaic to marine-shelf sandstones; a regolith of frost-shattered quartzite breccia up to 20 m thick that contains primary sand wedges 3+ m deep and other large-scale periglacial forms; and an aeolian sand sheet covering 25 000 km2 and containing primary sand wedges near its base. These deposits mark a spectrum of settings ranging from permafrost regolith and periglacial aeolian on the cratonic platform (Stuart Shelf) in the present west, through glaciofluvial, marginal-marine and inner marine-shelf in the central parts of the Adelaide Geosyncline, to outer marine-shelf in sub-basins in the present SE and north. The Elatina glaciation has not been dated directly, and only maximum and minimum age limits of c. 640 and 580 Ma, respectively, are indicated. Palaeomagnetic data for red beds from the Elatina Formation (Fm.) and associated strata indicate deposition of the Yerelina Subgroup within 10° of the palaeoequator. The Yerelina Subgroup is unconformably to disconformably overlain by the dolomitic Nuccaleena Fm., which in most places is the lowest unit of the Wilpena Group and marks Early Ediacaran marine transgression.成冰纪（Cryogenian）晚期埃拉蒂娜冰期（Elatina glaciation）的沉积体，构成澳大利亚南部阿德莱德地槽（Adelaide Geosyncline）区域内的耶雷利纳亚群（Yerelina Subgroup）。该沉积体最大厚度约1500米，分布面积达20万平方千米，包含如下岩相：具穿透性冰构造（glaciotectonites）、改造冰前地层（preglacial beds）的基底砾石型混杂岩；广泛分布的块状与层状混杂岩，内含具刻面、擦痕的岩屑（clasts），其中部分岩屑来自附近出露的底辟岛（diapiric islands），其余则源自盆地外物源（extrabasinal provenance）；含坠石（dropstones）的纹层状粉砂岩与泥岩；潮汐沉积岩（tidalites）及广泛分布的冰水河成、三角洲至陆架砂岩；厚度可达20米的霜碎石英岩角砾岩（frost-shattered quartzite breccia）风化壳，内含深度超3米的原生砂楔（primary sand wedges）及其他大型冰缘地貌（periglacial forms）；以及面积达2.5万平方千米的风成砂席（aeolian sand sheet），其底部附近发育原生砂楔。这些沉积体记录了完整的沉积环境谱系：从现今西部的克拉通台地（斯图亚特陆架，Stuart Shelf）上的永久冻土风化壳与冰缘风成环境，经阿德莱德地槽中部的冰水河成、近岸海洋与内陆陆架环境，延伸至现今东南部和北部次盆地中的外陆架环境。埃拉蒂娜冰期尚未被直接定年，目前仅限定其上下限年龄分别约为640 Ma和580 Ma。埃拉蒂娜组（Elatina Formation，Fm.）及相关地层的红层古地磁数据表明，耶雷利纳亚群的沉积环境位于古赤道10°范围以内。耶雷利纳亚群被白云质努卡里纳组（Nuccaleena Fm.）以不整合或假整合覆盖；该组在多数区域为威尔皮纳群（Wilpena Group）的最低地层单元，标志着埃迪卡拉纪早期的海侵事件。