Understanding clay-mineral assemblages forming in saline lakes aids in reconstructing paleoenvironments on Earth and other terrestrial planets; this is because authigenic phyllosilicates are sensitive to the prevailing geochemical conditions present during formation. In most geochemical models, evaporative concentration favors sepiolite with increasing silica and Mg 2+ concentrations without considering the role of the biogenic removal of silica from solution by diatoms. In the present study, phyllosilicates occurring in the mudflats of Bolivian salars were investigated to aid in understanding the geochemical factors that control mineral assemblages forming in (SO 4 2– )- and (Cl – )-rich environments in relation to dissolved silica. From transects across the mudflats, the physical, chemical, and mineralogical characteristics of the bulk sediment and the <2 μm fraction of each sedimentary layer were analyzed. From these analyses, three types of sediments were identified: (1) regolith sediments dominated by Al-dioctahedral smectite, illite, and chlorite; (2) detritus-rich mudflat sediments with Mg-trioctahedral smectite and Al-dioctahedral smectite along with illite and chlorite; and (3) authigenic mudflat sediments dominated by poorly formed Mg-trioctahedral smectite, kerolite, and biogenic silica. The absence of sepiolite-palygorskite in the salars is the result of excessively high Mg:Si ratios within the waters. In the surface water Mg becomes enriched relative to Si as diatoms remove dissolved Si from solution through biologically mediated uptake. The geochemical conditions present within the salars that act to preserve the diatom frustules and prevent their dissolution include: neutral–slightly alkaline pH solutions, cold temperatures, shallow water, and high salinity. Under these conditions the formation of sepiolite is restricted by the small amount of dissolved silica, despite the silica-rich environment. The formation of Mg-smectite and kerolite is favored under these conditions.

中文翻译：

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玻利维亚撒拉族泥滩中粘土矿物的形成

了解盐湖中形成的粘土矿物组合有助于重建地球和其他类地行星上的古环境；这是因为自生层状硅酸盐对形成过程中存在的主要地球化学条件很敏感。在大多数地球化学模型中，随着二氧化硅和 Mg 2+ 浓度的增加，蒸发浓度有利于海泡石，而没有考虑硅藻从溶液中生物去除二氧化硅的作用。在本研究中，对发生在玻利维亚盐沼泥滩中的页硅酸盐进行了研究，以帮助了解与溶解二氧化硅相关的在富含 (SO 4 2– ) 和 (Cl – ) 的环境中形成矿物组合的地球化学因素。从穿过泥滩的横断面，物理、化学、分析了大块沉积物的矿物学特征和每个沉积层的 <2 μm 部分。从这些分析中，确定了三种类型的沉积物：（1）风化层沉积物以铝双八面体蒙脱石、伊利石和绿泥石为主；(2) 含镁三八面体蒙脱石和铝二八面体蒙脱石以及伊利石和绿泥石的富含碎屑的泥滩沉积物；(3) 自生泥滩沉积物，以形成不良的镁三八面体蒙脱石、角纹石和生物硅石为主。盐沼中没有海泡石-坡缕石是由于水中的 Mg:Si 比例过高造成的。在地表水中，镁相对于硅变得富集，因为硅藻通过生物介导的吸收从溶液中去除溶解的硅。盐沼中保护硅藻壳并防止其溶解的地球化学条件包括：中性-微碱性 pH 值溶液、低温、浅水和高盐度。在这些条件下，尽管富含二氧化硅的环境，海泡石的形成受到少量溶解二氧化硅的限制。在这些条件下有利于形成 Mg-蒙脱石和 kerolite。