Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia

Geological mapping in 1970 of lower Cambrian outcrop in the eastern Flinders Ranges of South Australia included the description and naming of the Moorowie Formation, representing the uppermost Hawker Group. The mapping is supported by 885 m of measured sections. An early Cambrian regressive-marine shelf-margin succession is described, from the massive Wilkawillina Limestone (base), the grey laminated limestones, syndepositional slump-induced intraformational folds and breccias, collapse talus, and graded sediment gravity flow deposits of the Mernmerna Formation, terrace-edge attrition megabreccias and reefs of the Moorowie Formation, passing up to the red beds of the Billy Creek Formation (top). Rapid changes in sedimentary facies are attributed to basement block movements and diapiric influence on sedimentation with abrupt vertical relief and paleoslope indicated by syndepositional slumping and platform margin collapse. Tuffs in the Mernmerna Formation record contemporaneous volcanism. Massive archaeocyathan limestones, ooid grainstones, peloid limestones, reef-sourced megabreccias and red shales define five members in the overlying Moorowie Formation, signalling shallow-marine regressive conditions and the development of a biologically diverse carbonate platform seaward of evaporitic lagoons and supratidal sabkhas. The megabreccias of the Moorowie Formation formed as thin semi-autochthonous debris aprons or shallow tidal-channel infills resulting from gradual and persistent wave attrition and repeated collapse of a carbonate terrace that was vigorously reworked by tidal currents. Shale interbeds within the Moorowie Formation represent lightly channelised shallow-marine ramp deposits, with adjacent mud flats, as easterly equivalents of the Oraparinna Shale, the earliest of which formed the substrate to the attrition megabreccias. Emergent evaporite diapirs near Mt John and Mt Frome are the probable sources of coarse siliciclastics within the carbonates. Some of the siliciclastics were likely transported onto the carbonate platform by sandstorms or migrating dunes. Late in the Cambro-Ordovician Delamerian Orogeny, earlier salt diapirs at depth were compressed and reactivated as highly mobile evaporite-rubble breccias and intruded as small plugs and dykes into fissures in a lithified and folded cover. The intrusive breccias include metasediment and metabasic xenoclasts attributable to the Callanna Group, while diapir-related faults also host minor copper, lead and barite mineralisation. Documentation of this unique record contributes to wider investigations of the Ediacaran-to-early-Cambrian succession of the Flinders Ranges sector of the Arrowie Basin, adding to its global heritage values, effective management and appreciation by the wider community.

1970年对南澳大利亚州东部弗林德斯山脉（Flinders Ranges）下寒武统露头开展的地质填图工作，对代表霍克群（Hawker Group）最上部层位的穆罗威组（Moorowie Formation）进行了描述与命名。此次填图以885米的实测剖面作为支撑依据。文中描述了一套早寒武世海退陆架边缘沉积序列，自下而上依次为：作为基底的块状威尔基威利纳灰岩（Wilkawillina Limestone）、灰色纹层灰岩、同沉积滑塌成因的层内褶皱与角砾岩、崩塌塌积物，以及默姆梅纳组（Mernmerna Formation）的粒序沉积重力流沉积；穆罗威组的台地边缘磨蚀巨角砾岩与礁体向上过渡为顶部的比利溪组（Billy Creek Formation）红色地层。沉积相的快速变化被归因于基底块体运动与底辟作用对沉积过程的影响，同沉积滑塌与台地边缘崩塌所指示的陡直古地形起伏与古斜坡，也佐证了这一点。默姆梅纳组中的凝灰岩记录了同期火山活动。上覆的穆罗威组可划分为五个段，分别为块状古杯灰岩（archaeocyathan limestones）、鲕粒颗粒灰岩（ooid grainstones）、球粒灰岩（peloid limestones）、礁源巨角砾岩与红色页岩，这指示了浅海海退环境，以及蒸发泻湖（evaporitic lagoons）与潮上萨布哈（supratidal sabkhas）环境向海一侧生物多样性丰富的碳酸盐台地（carbonate platform）的发育。穆罗威组的巨角砾岩形成于薄而半原地的碎屑裙或浅潮道充填物，其成因是碳酸盐台地持续遭受波浪磨蚀、反复崩塌，并被潮流强烈改造。穆罗威组内的页岩夹层代表了轻度水道化的浅海缓坡沉积，伴生潮坪沉积，其对应东侧的奥拉帕里纳页岩（Oraparinna Shale），其中最早期的页岩构成了磨蚀巨角砾岩的基底。约翰山（Mt John）与弗罗姆山（Mt Frome）附近出露的蒸发岩底辟，可能是碳酸盐岩中粗陆源碎屑的物源区。部分陆源碎屑可能通过沙尘暴或迁移沙丘被搬运至碳酸盐台地上。在寒武-奥陶纪德拉梅里安造山运动（Cambro-Ordovician Delamerian Orogeny）晚期，深部早期盐底辟受到挤压活化，形成高流动性的蒸发岩碎屑角砾岩，并以小型岩栓与岩脉的形式侵入至固结成岩且褶皱的盖层裂隙中。这些侵入角砾岩包含可归属于卡兰纳群（Callanna Group）的变质沉积岩与变基性岩捕虏体；与底辟作用相关的断层还伴生有少量铜、铅与重晶石矿化。本套独特地质记录的研究成果，有助于对阿罗盆地（Arrowie Basin）弗林德斯山脉区段埃迪卡拉纪至早寒武世地层序列开展更广泛的研究，同时提升了该区域的全球遗产价值，助力其更有效的管理与大众认知。