Abstract The detrital clay mineral assemblage contained within sedimentary archives has long been used as a proxy for palaeo-tectonic, -climate, and -environmental reconstructions as well as provenance analysis of sediments. However, many clay minerals such as smectite are highly reactive and thus prone to post-depositional alteration, or commonly form diagenetic replacement phases, which can fundamentally change clay abundance and composition within sedimentary successions. Although a critical requirement for making robust palaeo-environmental reconstructions, there are difficulties in distinguishing and quantifying clay minerals of detrital versus diagenetic origin in fine-grained sediments and in sedimentary rocks using bulk analytical techniques. A new generation of electron imaging and mineral mapping tools, optimized for analyzing fine-grained geo-materials, has the potential to resolve this long-standing challenge, if diagnostic criteria to systematically differentiate (clay) minerals of varying origin can be established. Here we define the petrographic criteria required to differentiate various classes of detrital and diagenetic illite, chlorite and kaolinite/dickite, based on a case study of continental palaeo-weathering recorded in late Neoproterozoic sequences of the Adelaide Geosyncline, South Australia. Comparison to quantitative XRD data demonstrates the accuracy of SEM-based mineral identification and quantification. After correcting for the effects of diagenesis, the original sediments are shown to have an immature mineralogy (e.g., high abundance of feldspar: 23–33% and detrital mica/2M1 illite: 7–26%, no pedogenic clays), indicative of limited chemical weathering in the late Cryogenian Enorama Shale and the early Ediacaran Brachina Formation. The mid-Ediacaran Bunyeroo Formation, by contrast, is characterized by a substantially higher content (~20–23%) of pedogenic 1M and 1Md illite coupled with trace amounts of readily weathered phases such as feldspar (~1–4%). This is indicative of enhanced chemical weathering, consistent with previous studies arguing for a growing influence of biologically-mediated pedogenic weathering in the Ediacaran.

中文翻译：

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海洋沉积序列中碎屑与成岩粘土矿物的定量岩相学差异：对生物土壤兴起的影响

摘要 沉积档案中包含的碎屑粘土矿物组合长期以来一直被用作古构造、气候和环境重建以及沉积物物源分析的代表。然而，许多粘土矿物如蒙脱石具有高反应性，因此容易发生沉积后蚀变，或者通常形成成岩置换相，这可以从根本上改变沉积层序中的粘土丰度和组成。尽管是进行稳健的古环境重建的关键要求，但在使用批量分析技术区分和量化细粒沉积物和沉积岩中碎屑与成岩成因的粘土矿物方面存在困难。新一代电子成像和矿物测绘工具，如果可以建立系统地区分不同来源的（粘土）矿物的诊断标准，那么针对细粒地质材料的分析进行优化，就有可能解决这一长期存在的挑战。在这里，我们根据南澳大利亚阿德莱德地槽晚新元古代序列中记录的大陆古风化案例研究，定义了区分各种碎屑和成岩伊利石、绿泥石和高岭石/地开石所需的岩相标准。与定量 XRD 数据的比较证明了基于 SEM 的矿物识别和定量的准确性。在校正成岩作用的影响后，原始沉积物显示出不成熟的矿物学（例如，高丰度的长石：23-33% 和碎屑云母/2M1 伊利石：7-26%，无成土粘土），表明低温纪晚期 Enorama 页岩和早期埃迪卡拉纪 Brachina 组的化学风化作用有限。相比之下，埃迪卡拉纪中期 Bunyeroo 组的特征是成土 1M 和 1Md 伊利石含量显着更高（~20-23%），并伴有痕量的易风化相，如长石（~1-4%）。这表明化学风化作用增强，这与之前的研究一致，即埃迪卡拉纪生物介导的成土风化影响越来越大。