Interpretation of palaeoweathering features and successive silicifications in the Tertiary regolith of inland Australia
Interpretation of palaeoweathering features and successive silicifications in the Tertiary regolith of inland Australia
复制标题
澳大利亚内陆第三纪风化层古风化特征及连续硅化作用解释
DOI：
10.1144/0014-764905-020
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发表时间：
2006
影响因子：
2.7
通讯作者：
R. Simon
中科院分区：
文献类型：
--
作者：
M. Thiry;A. Milnes;Véronique Rayot;R. Simon
对澳大利亚内陆大面积深部漂白风化风化层中硅灰岩的形态、微形态和地球化学特征进行了详细的研究，对风化层的历史及其第三纪的气候和形态演化提供了新的解释。土壤成因硅灰岩具有独特的形态和矿物学特征，它是在干湿交替的气候条件下，由于多次水的渗透和渗透而导致的一系列硅质溶解和重结晶的结果。这些是最古老的风化特征。从前寒武纪花岗岩到古生代砂岩、白垩纪沉积物和第三纪沉积，在广泛的区域内形成了深厚的漂白剖面，代表了风成岩发展的第二个主要阶段。在这些剖面中，高岭石与石膏、明矾石和蛋白石共存，由基质与咸水地下水反应形成，地下水位在该地区逐渐下降。广泛的白蚁洞穴在漂白的风化层中建造到很深的地方，跟随着地下水位下降。气候温暖干燥，缺水严重。地下水硅砾在漂白的风化层中形成了近水平的透镜体和孔雀石和碧玉豆荚。它们保留了主岩的主要结构。地下水硅酸盐是在白蚁洞穴建造之后形成的，形成于整个景观中地下水位上升的过程中，在广阔的景观洼地中，从一些地方到近地表环境。气候比较潮湿，但硅化过程中石膏的存在表明地下水仍然是咸水。红褐色硬壳是最年轻的硅化特征，代表了在高降雨或洪水事件期间连续渗透和渗漏以及内涝的时期。它们仅限于地势较低的地区。对漂白剖面的矿物学和地球化学分析，结合地球化学模拟，表明铁解作用最有可能是地下水酸化的原因，导致漂白剖面和/或明矾石的发育。今天的地下水位处于低水平，而且硫酸盐含量丰富。可能导致漂白的酸性蚀变在该地区广泛的普拉亚景观周围仍然活跃。
Detailed studies of morphological, micromorphological and geochemical characteristics of silcretes in the deep bleached and weathered regolith across a large area of inland Australia have provided a new interpretation of the history of the regolith and its climatic and morphological evolution during the Tertiary. Pedogenic silcretes have distinctive morphological and mineralogical features caused by a succession of phases of silica dissolution and recrystallization resulting from multiple episodes of water infiltration and percolation under alternately wet and dry climates. These are the oldest of the regolith features. Deep, bleached profiles formed over a wide area in a variety of substrates ranging from Precambrian granites to Palaeozoic sandstones, Cretaceous sediments and Tertiary deposits, and represent the second major stage in regolith development. These profiles, in which kaolinite coexists with gypsum, alunite and opal, formed by reaction of the substrates with saline groundwaters, the water-table levels of which progressively fell over the region. Extensive networks of termite burrows constructed to great depth in the bleached regolith followed the water tables down. The climate was warm and dry with a high water deficit. Groundwater silcretes formed near-horizontal lenses and pods of porcellanite and jasper in the bleached regolith. They preserve the primary fabric of the host rock. Groundwater silcretes post-date the construction of termite burrows and were formed during a rise in groundwater tables across the landscape, in places to near-surface environments in broad landscape depressions. The climate was more humid but the presence of gypsum during silicification demonstrates that the groundwaters were still saline. Red–brown hardpans are the youngest silicification features and represent periods of successive infiltration and percolation, and waterlogging, during high rainfall or flood events. They are confined to low regions in the landscape. Mineralogical and geochemical analysis of the bleached profiles, together with geochemical modelling, suggests that ferrolysis is the most likely cause of acidity in groundwater leading to the development of the bleach profiles and/or alunite. Present-day groundwater tables are both at low levels and sulphate-rich. It is possible that acidic alteration leading to bleaching is still active around the extensive playa landscapes in the region.