Redoximorphic Paleosols in Alluvial and Lacustrine Deposits, 1.8 Ga Lochness Formation, Mount Isa, Australia: Pedogenic Processes and Implications for Paleoclimate
Redoximorphic Paleosols in Alluvial and Lacustrine Deposits, 1.8 Ga Lochness Formation, Mount Isa, Australia: Pedogenic Processes and Implications for Paleoclimate
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澳大利亚伊萨山冲积层和湖相沉积物 1.8 Ga Lochness 地层中的氧化还原古土壤：成土过程及其对古气候的影响
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
K. Eriksson
中科院分区：
文献类型：
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作者：
S. Driese;E. Simpson;K. Eriksson
澳大利亚Lochness组（1.8 Ga）的古土壤包括罕见的非红色和丰富的强烈红色，它们形成于短暂的河流和湖泊环境下的地面暴露面。物理过程主导着非红色古土壤，其特征是反复发生干燥、收缩和开裂，与湿润交替发生，并将沙、粉、粘土和铁氧氢氧化物引入平面空隙。红色古土壤的氧化还原过程尤为强烈；铁和锰的氧化还原浓度（准膜层）发生在与干燥相关的大孔隙和土壤附近，而铁和锰的氧化还原浓度（准膜层）发生在与氧化还原消耗相邻的古土壤基质中。在平面大孔和ped表面上也常见亮铁和氧化铁涂层和低涂层。湖尼斯组古土壤的氧合特征表现为周期性的水入渗和饱和，并伴有沿平面大孔和凹面发育的还原性条件。土壤饱和度的变化分别由湖泊沉积物中湖泊水位的季节性波动和洪泛平原沉积物中栖息饱和带的形成引起。在Lochness组中红色、赤色古土壤的出现与先前对弱氧合1.8 Ga古大气的解释相一致。古土壤的氧合性特征与第四纪氧合性土壤相似，表明古气候为暖至冷温带（年平均土壤温度5 ~ 20℃），具有季节性饱和特征。在这些元古代土壤中，必须存在最低浓度的有机C（至少1wt %），可能是微生物或细菌来源，以允许铁的还原。
ABSTRACT Paleosols in the Lochness Formation (1.8 Ga, Australia) include both rare, non-red and abundant, strongly reddened varieties that formed at subaerial exposure surfaces in both ephemeral-river and lacustrine settings. Physical processes dominated non-red paleosols, which were characterized by repeated episodes of desiccation, shrinking, and cracking alternating with wetting and introduction of sand, silt, clay, and iron oxyhydroxides into planar voids. Redoximorphic (oxidation-reduction) processes were especially intense for the red paleosols; redox depletions of Fe and Mn (hypoalbans) occur immediately adjacent to desiccation-related macropores and peds, whereas redox concentrations of Fe and Mn (quasi-coatings) occur within paleosol matrix adjacent to redox depletions. Illuviated cla and Fe-oxide coatings and hypocoatings are also common in planar macropores and on ped faces. Redoximorphic features indicate periodic water infiltration and saturation, accompanied by development of reducing conditions along planar macropores and ped surfaces in Lochness Formation paleosols. Variations in soil saturation were caused by seasonal fluctuations of lake level in lacustrine deposits, and by formation of perched saturation zones within floodplain deposits, respectively. Occurrences of red, hematitic paleosols in the Lochness Formation are compatible with previous interpretations of a weakly oxygenated 1.8 Ga paleoatmosphere. Redoximorphic features in the paleosols suggest a warm to cool temperate paleoclimate (mean annual soil temperature 5-20°C) characterized by seasonal saturation, by analogy with Quaternary redoximorphic soils. A minimal concentration of organic C (at least 1 wt %), possibly of microbial or bacterial origin, must have been present in these Proterozoic soils to allow for Fe reduction.