Rhizoliths in Devonian and Early Carboniferous Paleosols and Their Paleoecological Interpretation
T. V. Alekseeva
Abstract
Collected in situ rhizoliths (>20) from Devonian and Early Carboniferous paleosols in the southern part of the Russian Platform (Kaluga, Belgorod, and Voronezh oblasts) were studied by means of scanning electron microscopy, X-ray diffraction, XRF and mass spectrometry. In Devonian paleosols developed from volcanic–sedimentary deposits, rhizoliths are represented by petrified individual roots of different plants, rooting systems, and their diagenetically transformed products—ferruginous concretions and wedges. Mineralogically, they are dominated by goethite and siderite in different proportions. Some of them include charcoals and/or pyrite-substituted plant tissues. This kind of rhizoliths was developed under reducing conditions in (semi)hydromorphic paleosols or under flooding during the soil burial stage. In the Carboniferous period, paleosols developed from marine limestones contained several types of rhizoliths: casts (predominate), imprints and root channels (less abundant), and few rhizocretions with arbuscular mycorrhiza. All of them are characterized by complete mineralization of plant tissues. Casts and rhizocretions are substituted with calcite. The isotopic composition of C in the latter is within –5.68 < δ13C < –1.16‰. The data obtained show that rhizoliths are important sources of information on biodiversity, physiology of plants, and paleoenvironments at different scales, including the global scale. The volume of information depends on the type of rhizolith.