The chemical weathering indices of the sediments can serve as tools for estimating the intensity of weathering in the sediment source rock area and its changes in response to the dynamic interplay of climate, tectonics, and bioevolution. The siliciclastic terrigenous component, comprising sediment particles formed during weathering, carries information regarding weathering. Nevertheless, the presence of volcanic material with silicate composition in the sedimentary record can introduce bias to the weathering estimate by incorporating pyroclastic material that has not undergone weathering but is susceptible to diagenetic alteration. Therefore, a comprehensive understanding of the nature and significance of the volcanic component in sediments is imperative for accurately interpreting weathering derived from sedimentary successions. Our study focuses on investigating the presence of the volcanic component and its influence on weathering indices calculation in the Upper Ordovician sedimentary succession of the Baltic Basin. The results from geochemical massbalance mixing modelling reveal that volcanic material is not confined solely to discrete altered volcanic ash beds (bentonites), and a substantial amount of volcanic material is dispersed or re-deposited into the host rock. Within the interval containing discrete bentonite beds, the volcanic component in the carbonate host rock sections ranges from 50% to 90%, and significantly impacts the terrigenous fraction weathering index calculations. This underscores the necessity of considering the nature and significance of the volcanic component when interpreting geochemical-mineralogical signals.

中文翻译：

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火山碎屑成分对海洋沉积物风化指数评估的影响——波罗的海盆地上奥陶统的教训

沉积物的化学风化指数可以作为估计沉积物源岩区风化强度及其随气候、构造和生物进化的动态相互作用而变化的工具。硅质碎屑陆源成分包含风化过程中形成的沉积物颗粒，携带有关风化的信息。然而，沉积记录中含有硅酸盐成分的火山物质的存在可能会因纳入未经历风化但易受成岩蚀变影响的火山碎屑物质而给风化估计带来偏差。因此，全面了解沉积物中火山成分的性质和意义对于准确解释沉积序列的风化作用至关重要。我们的研究重点是调查波罗的海盆地上奥陶统沉积序列中火山成分的存在及其对风化指数计算的影响。地球化学质量平衡混合模型的结果表明，火山物质不仅仅局限于离散的蚀变火山灰床（膨润土），并且大量的火山物质分散或重新沉积到主岩中。在包含离散膨润土层的层段内，碳酸盐岩主岩部分中的火山成分范围为50％至90％，并且显着影响陆源部分风化指数的计算。这强调了在解释地球化学矿物学信号时考虑火山成分的性质和重要性的必要性。