Mineralogy and Geochemistry of Fluvial-Lacustrine Pisolith Micronodules from the Roztoka Odrzańska, Odra River, NW Poland

Abstract

Small-sized ferruginous micronodules or pisolith nodules, frequently occurring in inland freshwater systems in moderate climate zones, are important indicators of groundwater level changes and early diagenetic processes, especially within the Pleistocene post-glacial sedimentary systems, including swamps, peatbogs, rivers, or lakes. Compared to the other geochemical environments, pisolith nodules are usually dominated by iron hydroxides and oxides. In most cases, described micronodules indicate high phosphatization, significant contribution of allogenic detrital components, and low manganese content. The major aim of the article is to present textural, geochemical, and mineralogical variability of pisolith nodules recovered from the Roztoka Odrzańska, Odra river mouth area, NW Poland. We describe genetical relations between different types of pisoliths and try to interpret the possible formation phenomena. Analyzed loose ferruginous micronodules were separated from the lacustrine silty-clayey sapropel muds and gyttja, later analyzed using optical microscopy, SEM-energy dispersive x-ray (EDX), and XRD methods. As a reference material, we use archival iron bog ores and geochemical data of different types of nodules. Additionally, we describe previously unknown siderite-rich nodules found in neighboring sites of the Dąbie Lake and the Szczecin Lagoon.