Abstract Reports of bitumen stranding on the ocean beaches of southern Australia date back to the early days of European settlement. Previous investigations have shown that this ‘coastal bitumen’ comprises three categories of stranded petroleum: waxy bitumen, asphaltite and oil slicks. All three varieties are physically and chemically distinct from each other, and bear no geochemical resemblance to any indigenous Australian crude oil. This study focuses on the most common variety, waxy bitumen, which accounted for 90% of the strandings on six South Australian beaches repeatedly surveyed during 1991–1992. Geochemical analysis of 96 individual specimens collected from these survey sites and other beaches in South Australia and western Victoria has shown them to be variously weathered high-wax crude oils of paraffinic to aromatic-intermediate bulk composition. Elemental, isotopic and biomarker differences allow their assignment to at least five oil families with inferred source facies that range from deep freshwater lacustrine through paludal and deltaic to euxinic marine, possibly deposited within different sedimentary basins. Family 1, 2 and 3 waxy bitumens all contain biomarkers derived from the freshwater alga Botryococcus sp. and tropical angiosperms (notably dipterocarps). Similar biomarker assemblages are unknown in Australian sedimentary basins but are common in Cenozoic crude oils and source rocks throughout western Indonesia. Family 4 waxy bitumens lack these biomarkers, but do contain dinosterane and 24-n-propylcholestane, indicative of a marine source affinity, while the carbon isotopic signatures and high pristane/phytane (Pr/Ph) ratios of Family 5 waxy bitumens are consistent with their origin from coal-rich source rocks deposited in fluvial to deltaic sedimentary successions. The majority of these waxy bitumens represent an oceanic influx of non-indigenous, Southeast Asian crude oils carried into the waters of southern Australia by the Leeuwin Current. Although they are likely to originate from natural seepage within the Indonesian Archipelago, it is unknown whether the parent oils emanate from submarine seeps or from inland seepages which are then carried to the sea by rivers. The common practice of tanker cleaning operations in the Java and Banda seas may augment the supply of natural bitumen to the beaches of Australia.

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澳大利亚南部的蜡质沥青搁浅：对多个油族及其可能来源的地球化学研究

摘要 关于在澳大利亚南部海滩上搁浅的沥青的报告可以追溯到欧洲人定居的早期。先前的调查表明，这种“沿海沥青”包括三类搁浅石油：蜡质沥青、沥青岩和浮油。这三个品种在物理和化学上彼此不同，并且与任何澳大利亚本土原油没有地球化学相似之处。本研究侧重于最常见的蜡质沥青品种，在 1991 年至 1992 年期间反复调查的六个南澳大利亚海滩搁浅事故中，这种沥青占 90%。对从这些调查地点以及南澳大利亚和维多利亚西部的其他海滩收集的 96 个个体样本进行的地球化学分析表明，它们是不同风化的高蜡原油，具有链烷烃到芳香族中间体的散装成分。元素、同位素和生物标志物的差异允许将它们分配给至少五个具有推断来源相的油族，这些相的范围从深淡水湖相到浅滩和三角洲再到富生海相，可能沉积在不同的沉积盆地内。家族 1、2 和 3 蜡质沥青都含有源自淡水藻类葡萄球菌属的生物标志物。和热带被子植物（特别是龙脑香属植物）。类似的生物标志物组合在澳大利亚沉积盆地中是未知的，但在整个印度尼西亚西部的新生代原油和烃源岩中很常见。第 4 族蜡质沥青缺乏这些生物标志物，但确实含有二甾烷和 24-正丙基胆甾烷，表明其具有海洋来源的亲和力，而第 5 族蜡质沥青的碳同位素特征和高原始烷/植烷 (Pr/Ph) 比率与它们起源于沉积在河流至三角洲沉积序列中的富煤烃源岩。这些蜡质沥青中的大部分代表了非本土的东南亚原油被列文洋流带到澳大利亚南部水域的海洋涌入。虽然它们很可能源自印度尼西亚群岛内的自然渗流，但尚不清楚母油是来自海底渗流还是来自内陆渗流，然后通过河流进入大海。