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Patterns of geochemical variability across weakly developed paleosol profiles and their role as regional stratigraphic markers (Upper Pleistocene, Po Plain)
Palaeogeography, Palaeoclimatology, Palaeoecology ( IF 2.6 ) Pub Date : 2021-04-23 , DOI: 10.1016/j.palaeo.2021.110413
Alessandro Amorosi , Luigi Bruno , Bruno Campo , Andrea Di Martino , Irene Sammartino

Weakly developed paleosols from two distinct interfluve surfaces of Late Pleistocene age provide excellent keys to high-resolution stratigraphic correlation and may serve to trace large-scale genetic packages (systems tract equivalents) across the continental portion of the Po Basin. Twenty-four paleosol profiles from 17 sediment cores were identified and characterized for bulk-geochemical analysis. X-ray fluorescence data were used to trace the degree of weathering. Paleosols, 0.5–1.5 m thick, are pedogenically altered floodplain deposits, developed over time spans of a few thousand of years and mostly partitioned into A-Bk horizons. The most notable paleosol features are dark, organic-matter-rich and carbonate-free mineral surface horizons (A) that overlie bright calcic horizons (Bk) typified by the accumulation of secondary carbonates in the form of pedogenic nodules.

Paleosol profiles exhibit a homogeneous geochemical signature that fingerprints a moderate degree of weathering, with little strike- and dip-oriented variability across the different study localities. Plots of Al-normalized calcification and base loss indices against depth reveal systematic increasing values from intensely altered A horizons to underlying Bk horizons. These trends reflect consistent patterns of Ca translocation from surface horizons deeper into the profile, with significant to almost complete Ca removal from A horizons through leaching and accumulation in Bk horizons. Selected trace element ratios (Ba/Sr, Rb/Sr), redox-sensitive trace elements and Zr contents display opposite, up-profile increasing trends that reflect Sr loss in A horizons, with selective Zr concentration in residual minerals.

Vertical trends in element ratios are laterally extensive and consistent on a regional basis and represent key pedochemical/stratigraphic markers that can be traced over great distances (tens of kms) throughout the inland portion of the basin. Through quantitative assessment of the degree of weathering, geochemical profiling provides high potential for robust subsurface paleosol correlation that might not be captured by visual core descriptions alone.



中文翻译:

弱发育古土壤剖面的地球化学变异模式及其作为区域地层标志物的作用(上更新世,蒲平原)

来自晚更新世年龄的两个不同冲积表面的弱发育古土壤为高分辨率地层学相关性提供了极好的关键,并且可能有助于追踪波盆地的整个大陆部分的大规模遗传组合(系统域等价物)。从17个沉积物岩心中鉴定出了24个古土壤剖面,并对其进行了特征分析,以进行整体地球化学分析。X射线荧光数据用于追踪风化程度。古土壤厚度为0.5–1.5 m,是受成因改变的洪泛区沉积物,在数千年的时间跨度内发育,大部分被划分为A-Bk层。最明显的古土壤特征是深色,

古土壤剖面显示出均一的地球化学特征,该特征可以对中等程度的风化进行指纹识别,并且在不同的研究地区之间几乎没有走向和倾斜方向的变化。Al归一化钙化和基础损失指数相对于深度的图显示了从剧烈变化的A层到下层Bk层的系统性增加值。这些趋势反映了从地表深部到剖面的钙转运的一致模式,通过在Bk地层中的淋溶和积累,钙从A地层中去除到几乎完全清除了Ca。选定的痕量元素比率(Ba / Sr,Rb / Sr),氧化还原敏感的痕量元素和Zr含量显示出相反的向上趋势,反映了A层中Sr的损失,而残留矿物质中的Zr选择性较高。

元素比例的垂直趋势在横向上是广泛的,并且在区域上是一致的,并且代表了关键的化学化学/地层标志,可以在整个盆地内陆的很长一段距离(几十公里)内追踪到。通过对风化程度的定量评估,地球化学特征分析提供了强大的潜在地下古土壤相关性,而仅凭视觉核心描述可能无法捕获。

更新日期:2021-05-20
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