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Impact Craters as Biospheric Microenvironments, Lawn Hill Structure, Northern Australia

机译：作为生物圈微环境的撞击坑，北澳大利亚草坪山结构

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摘要

Impact craters on Mars act as traps for eolian sediment and in the past may have provided suitable microenvironments that could have supported and preserved a stressed biosphere. If this is so, terrestrial impact structures such as the 18-km-diameter Lawn Hill Structure, in northern Australia, may prove useful as martian analogs. We sampled outcrop and drill core from the carbonate fill of the Lawn Hill Structure and recorded its gamma-log signature. Facies data along with whole rock geochemistry and stable isotope signatures show that the crater fill is an outlier of the Georgina Basin and was formed by impact at, or shortly before, approximately 509-506 million years ago. Subsequently, it was rapidly engulfed by the Middle Cambrian marine transgression, which filled it with shallow marine carbonates and evap-orites. The crater formed a protected but restricted microenvironment in which sediments four times the thickness of the nearby basinal succession accumulated. Similar structures, common on the martian surface, may well have acted as biospheric refuges as the planet's water resources declined. Low-pH aqueous environments on Earth similar to those on Mars, while extreme, support diverse ecologies. The architecture of the eolian crater fill would have been defined by long-term ground water cycles resulting from intermittent precipitation in an extremely arid climate. Nutrient recycling, critical to a closed lacustrine sub-ice biosphere, could be provided by eolian transport onto the frozen water surface.
机译：火星上的撞击坑是风沙沉积的陷阱，过去可能提供了合适的微环境，可以支撑和保护受压的生物圈。如果是这样的话，诸如澳大利亚北部直径18公里的Lawn Hill结构之类的地面撞击结构可能被证明是火星类似物有用的。我们从Lawn Hill结构的碳酸盐岩填充物中取样露头和钻芯，并记录其伽马测井曲线特征。岩相数据以及整个岩石地球化学和稳定的同位素特征表明，火山口填充物是乔治娜盆地的一个离群值，是在大约509-506百万年前或不久之前的撞击形成的。随后，它被中寒武纪海侵迅速吞没，并在其中充斥着浅海碳酸盐和火山岩。火山口形成了受保护但受限制的微环境，其中沉积物的厚度是附近盆地陆续堆积厚度的四倍。火星表面常见的类似结构，很可能已成为地球水资源减少的生物圈避难所。地球上的低pH水性环境类似于火星，但极端情况下却支持多种生态。风沙陨石坑填充物的结构将由极端干旱气候中间歇性降雨产生的长期地下水循环来定义。营养物质的循环对于封闭的湖相亚冰生物圈至关重要，可以通过风能输送到冷冻水表面来实现。

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