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Soil
Published in Stanley E. Manahan, Environmental Chemistry, 2022
Typical soils exhibit distinctive layers called horizons, with increasing depth (Figure 15.2). Horizons form as the result of complex interactions among processes that occur during weathering, the disintegration of rock by physical, chemical, and biological processes. Rainwater percolating through soil carries dissolved and colloidal solids to lower horizons where they are deposited. Biological processes, such as bacterial decay of residual plant biomass, produce slightly acidic CO2, organic acids, and complexing compounds that are carried by rainwater to lower horizons where they interact with clays and other minerals, altering the properties of the minerals. The top layer of soil, widely varying in thickness (typically 10–20 cm) is known as the A horizon, or topsoil. This is the layer of maximum biological activity in the soil, contains most of the soil organic matter, and is essential for plant productivity.
Impact of humans on tropical landscapes: The challenge of soil erosion for rural development in the Black Volta River Basin, Ivory Coast
Published in Jürgen Runge, Assogba Guézéré, Laldja Kankpénandja, Natural Resources, Socio-Ecological Sensitivity and Climate Change in the Volta-Oti Basin, West Africa, 2020
S. Kambire, K. Alla, B. Kambire
Soil composition, moisture and compaction are also widely cited as factors in determining precipitation erosion (Blanco & Rattan 2010). According to Fournier (1967), in the absence of vegetation cover, the characteristics of surface horizons play a key role in the initiation and development of erosion, particularly structural stability and soil permeability. But the effect of the soil parameter is not always obvious without the influence of the slope. Thus, in the Black Volta River basin, most of hydrographic valleys and the tops of certain tabular mountains, with very slight slops (0 to 1°), are very sandy. However, it is not certain that these sandy areas are always sensitive to water erosion, because water can quickly infiltrate. In contrast, on hills, tropical eutrophic brown soils contain enough clay and organic matter to bind particles, coagulate colloids and give to the soil a more stable structure, i.e. a more resistance to erosion. Due to the steep slope, these areas have deep ravines which are advanced stages of morphogenic land degradation.
Soil: Earth’s Lifeline
Published in Stanley Manahan, Environmental Chemistry, 2017
Typical soils exhibit distinctive layers called horizons, with increasing depth (Figure 15.2). Horizons form as the result of complex interactions among processes that occur during weathering, the disintegration of rock by physical, chemical, and biological processes. Rainwater percolating through soil carries dissolved and colloidal solids to lower horizons where they are deposited. Biological processes, such as bacterial decay of residual plant biomass, produce slightly acidic CO2, organic acids, and complexing compounds that are carried by rainwater to lower horizons where they interact with clays and other minerals, altering the properties of the minerals. The top layer of soil, widely varying in thickness (typically 10–20 cm) is known as the A horizon, or topsoil. This is the layer of maximum biological activity in the soil, contains most of the soil organic matter, and is essential for plant productivity.
Tectonic subsidence and uplift within Canterbury Basin, South Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
Katherine Dvorak, Michelle Kominz, Martin Crundwell
Biostratigraphic ages are based on micro and nano planktic fossils and the New Zealand Geological Time Scale of Raine et al. (2015). For boreholes at Site 317-U1351 and Site 317-U1353, the ages of unconformities from the Middle and Late Miocene to the Pleistocene were estimated by Expedition 317 Scientists (2011a, 2011c). While the sediments in the boreholes reveal many changes in lithology and paleoenvironment, the highest and lowest occurrences of marker species occur less frequently. Many sedimentary units were defined based on changes in lithology or environment that fall between dated horizons. In these cases (zero ages in the input data in Data Supplemental File 1), estimates were interpolated based on the thickness of each unit at the time of deposition (e.g. Bond et al. 1989). By decompacting each unit to its thickness at the time of deposition, thickness variations resulting from different degrees of burial and, thus, compaction are reduced.
Targeting VHMS mineralisation in metamorphosed volcanic terranes
Published in Applied Earth Science, 2019
S. P. Hollis, J. Kelly, D. Podmore, A. Webber, S. Roberts, M. James, J. F. Menuge
The King Zn deposit (2.15 Mt at 3.47% Zn) occurs as a 2–5 m thick stratiform lens dominated by iron sulphides within an overturned metamorphosed volcanic rock-dominated sequence located ∼140 km east of Kalgoorlie. The local stratigraphy is characterised by garnet amphibolite and strongly banded intermediate to felsic schists, with rare horizons of graphitic schist. Massive sulphide mineralisation occurs as stratiform pyrite–pyrrhotite–sphalerite at the contact between quartz-muscovite schists (‘the footwall dacite’) and banded quartz-biotite/amphibole ± garnet schists. A zone of pyrite-(sphalerite) and pyrrhotite–pyrite–(chalcopyrite) veining extends throughout the stratigraphic footwall. Footwall garnet-amphibolites are of sub-alkaline basaltic affinity, with a central zone dominated by chlorite ± magnetite interpreted to represent the Cu-bearing feeder zone. Hydrothermal alteration in stratigraphically overlying intermediate to felsic rocks is characterised by a mineral assemblage of quartz-muscovite ± chlorite ± albite ± carbonate. Zones of cordierite and anthophyllite schist are locally significant and indicative of zones of Mg-metasomatism prior to metamorphism. Increases of SiO2, Fe2O3T, pathfinder elements (e.g. As, Sb, Tl), and depletions of Na2O, CaO, Sr, and MgO occur in footwall quartz-muscovite schists approaching massive sulphide mineralisation.
Lithospheric evolution, thermo-tectonic history and source-rock maturation in the Gippsland Basin, Victoria, southeastern Australia
Published in Australian Journal of Earth Sciences, 2022
J. Röth, A. Parent, C. Warren, L. S. Hall, D. Palmowski, N. Koronful, S. S. Husein, V. Sachse, R. Littke
A zoom into inline 4719 reveals high-amplitude reflectors, which clearly crosscut the concordant strata in the Kipper area at the edge of the Northern Terrace (Figure 4c, d). These are characteristic of magmatic intrusions (Planke et al., 2003) and support earlier observations (e.g. Meeuws, Holford, et al., 2016; Meeuws, Reynolds, et al., 2016; McPhail, 2000; O’Halloran & Johnstone, 2001). The magmatic features vary in thickness between 10 m and 100 m and many have been confirmed by drilling. The type can be interpreted from impedance: higher impedance relates to intrusions and subaerial flows, lower impedance generally relates to tuff, volcanic ash and weathered horizons. As shown in Figure 4d, extrusive and intrusive bodies are crosscutting and intercalated with the siliciclastic post- and syn-rift deposits. Further, the volcanic bodies appear in growth packages and in obvious spatial relationship to large faults (Figure 5a, b). The type of volcanism can be described as fissure volcanism and is characterised by non-explosive eruptions of low viscosity basaltic material and a possible basinward (southward) flow. Deep-seated extensional and transtensional fault segments were reactivated by northeast–southwest-directed dextral movement along the RFS during the Late Cretaceous (E3) and gave way for ascending magma, which migrated along the faults, intruding the Emperor Subgroup (sills, dykes, and funnels), and covering the surface of the paleo-floodplain (subaerial lava flows). The diameter of the intrusive bodies rarely exceeds 5 km (Figure 5a), while the subaerial flows typically spread over distances of 10–20 km (Figure 5a) as interpreted from the seismic megacube, respectively.