Pedofeatures Associated to Soil Processes

As stipulated by G. Stoops, “the aim of micropedology is to contribute to solving problems related to the genesis, classification and management of soils, including soil characterization in palaeopedology and archaeology. The interpretation of features observed in thin sections is the most important part of this type of research, based on an objective detailed analysis and description” (Stoops et al. 2018). To answer such questions, two major books contributed to the comparative knowledge necessary to tackle this objective: the first one was published in 1985 and used micromorphology to distinguish between different classes of soils (Douglas and Thompson 1985); the second one is an extensive guide of more than 1000 pages to the interpretation of micromorphological features encountered in thin sections of soil (Stoops et al. 2018). The aim of this Atlas is neither to be a substitution for these books nor a way to enter directly into the interpretation of soil genesis and classification. Nonetheless, this chapter presents the imprints of major soil processes that can be easily deduced from specific features observed in thin sections. These processes involve the dynamics of (a) clay, both translocation and swelling, (b) water, such as waterlogging, evaporation, and its role as ice and frost, (c) carbonate, gypsum, and iron oxyhydroxides, and finally (d) biogeochemical reactions within the solum.

Palygorskite in a Paleosol from Zagros mountain belt, NE Iraq

<p>In the semi-arid region south of Sulaimani city, paleosols can be found. The genesis of these paleosols needs to be elucidated. Here, we investigated a section of an Oligocene paleosol from that region. The section is about 7m thick with lower, middle and upper horizons, which consisted of partially weathered dolomitic limestone; conglomerate or lithified pebbly paleosol; and sandy-silty claystone or lithified clayey paleosol, respectively. These horizons were studied mineralogically and stratigraphically using X-ray diffraction, scanning electron microscopy, Simultaneous Thermal Analysis (STA) and granulometric analysis. Palygorskite content was higher in the conglomerate (lithified gravely paleosol) and in the partially weathered dolomitic limestone than in clayey paleosol.</p><p>Palygorskite is a trace mineral that allows to estimate climatic conditions during soil genesis. In hand specimen, palygorskite occurs as green patches of crystalline coating that covers pores and cavities on limestone and dolostone. Under scanning electron microscope, it appears as linear and fibrous loose bundles that occupy the interstice between the dolomite crystals and is mainly associated with dolostone and limestone facies.</p><p>We thus conclude that the climate was arid, and that the terrestrial land cover in this part of the Oligocene Basin in Northern Iraq was limestone and dolostone.</p><p>On this land, soil genesis and intermittent stream and sheet erosion was occurring during the entire Oligocene and it is well known, stratigraphically, as Oligocene Unconformity.</p><p>The possible origin of the palygorskite was the development during Oligocene by upward accumulation under hydrothermal condition in partially high weathered dolomitic limestone of Pila Spi formation during burial. Palygorskite occurs in marine, lacustrine and soil environments. Limited occurrences are associated with hydrothermal activity, in both marine and continental environments. Palygorskite-containing soils are limited almost exclusively to arid and semiarid areas of the world and are rather unstable in humid conditions.</p><p>The present paleosol was developed on Oligocene terrestrial land that bordered the sea covering Middle and Southern Iraq. Due to non-deposition weathering and mass wasting, calcareous gravely soil (limestone conglomerate) was generated. Sandy and clay soil were developed on the terrestrial land which stratigraphically formed an unconformity. This land was covered by water of a closed lagoon. Limestones are deposited as Lower Fars Formation.</p><p>These occurrences are associated with aquatic conditions characterized by alkaline solutions with high activities of Si and Mg. The most common setting for lacustrine palygorskite genesis are playa deposits, ancient lacustrine terraces, or closed-basin deposits of other types. While traces of palygorskite can be identified in a wide variety of soils, significant amounts of the pedogenically formed mineral are commonly associated with one specific situation of soil genesis like soils have been affected by fluctuating ground water, soil morphology that includes distinct and sharp textual transitions. This groups includes many paleosols. Most of these Paleosols are non-saline or only slightly saline.</p>

Actinobacteria Structure in Autogenic, Hydrogenic and Lithogenic Cultivated and Non-Cultivated Soils: A Culture-Independent Approach

The aim of the study was to determine the Actinobacteria structure in cultivated (C) versus non-cultivated (NC) soils divided into three groups (autogenic, hydrogenic, lithogenic) with consideration its formation process in order to assess the Actinobacteria sensitivity to agricultural soil use and soil genesis and to identify factors affecting their abundance. Sixteen C soil samples and sixteen NC samples serving as controls were taken for the study. Next generation sequencing (NGS) of the 16S rRNA metagenomic amplicons (Ion Torrent™ technology) and Denaturing Gradient Gel Electrophoresis (DGGE) were applied for precise determination of biodiversity. Generally, greater abundance of Actinobacteria in the NC soils relative to the C soils was found. Moreover, it was indicated that the actinobacterial diversity depended on both the soil genesis and the land use; however, this effect directly depended on the particular family and genera. Two factors: redox potential (Eh) and total carbon (TC) seemed to had a significant effect on the diversity of Actinobacteria. More precisely, Actinobacteria from the NC soils displayed a greater affinity for each other and were clearly influenced by Eh, whilst those from the C soils were mostly influenced by TC.