Within the 1800 to 1900 my old Flin Flon-Snow Lake greenstone belt, Amisk Group volcanics are overlain by Missi Group fluvial sediments. Several localities along the Missi-Amisk contact, the volcanics show evidence of subaerial weathering. Field relationships, mineralogical evidence, and chemical analyses confirm that this alteration zone is a paleosol. Pedogenic fabrics and mineralogy were somewhat obscured by greenschist-grade metamorphism associated with the Hudsonian orogeny (1750 my). This is especially true in the upper meter of the paleosol, where metamorphic paragonite and sericitic micas developed in a crenulated fabric. This metamorphism did not, however, obliterate the imprint of weathering on the Amisk volcanics. Features characteristic of well-drained modern soils are evident in the paleosol. Corestones of spheroidally weathered pillow lavas occur at depth within the paleosol (Cr horizon). The corestones decrease in size upward and eventually disappear into a hematite-rich horizon at the top of the paleosol. These macroscopic changes are accompanied by a decrease in CaO and MgO and by an increase in Al2O3, TiO2, and total iron toward the paleosol-Missi contact. Ferrous iron decreases upward toward the contact; FeO was apparently oxidized to ferric iron and retained within the paleosol during weathering. The oxidation and retention of iron within the Flin Flon paleosol indicates that PO2 was probably > or = 10(-2) P.A.L. at the time of weathering. The behavior of iron in the Flin Flon paleosol contrasts sharply with its behavior in the 2200 my Hekpoort paleosol, which is strongly depleted in iron. This difference suggests that a significant increase in the ratio of PO2/PCO2 in the atmosphere took place between 2200 and 1800 mybp.

中文翻译：

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Flin Flon Paleosol 和大气的组成 1.8 BYBP

在 1800 年至 1900 年我的旧弗林弗隆-雪湖绿岩带中，阿米斯克群火山被米西群河流沉积物覆盖。Missi-Amisk 接触沿线的几个地方，火山显示出地下风化的证据。现场关系、矿物学证据和化学分析证实，这个蚀变带是一个古土壤。与哈德逊造山运动（1750 年）相关的绿片岩级变质作用在某种程度上掩盖了成土结构和矿物学。这在古土壤的上米尤其如此，在那里，变质的云母和绢云母在锯齿状织物中发育。然而，这种变质作用并没有消除阿米斯克火山上风化的印记。排水良好的现代土壤的特征在古土壤中很明显。球状风化枕状熔岩的核心岩出现在古土壤深处（铬层）。芯岩向上减小尺寸，最终消失在古土壤顶部富含赤铁矿的地层中。这些宏观变化伴随着 CaO 和 MgO 的减少以及 Al2O3、TiO2 和总铁向古土壤-Missi 接触面的增加。亚铁向接触处向上递减；FeO 显然被氧化成三价铁并在风化过程中保留在古土壤中。Flin Flon 古土壤中铁的氧化和保留表明，风化时 PO2 可能 > 或 = 10(-2) PAL。铁在 Flin Flon 古土壤中的行为与其在 2200 my Hekpoort 古土壤中的行为形成鲜明对比，后者严重缺乏铁。