Environmental impact of weathering and soil formation in geomorphological research
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Abstract:
Weathering is a part of geomorphic processes leading to the disintegration and decomposition of rocks and minerals on the earth’s surface as a result of physical and chemical action that leads to the formation of soil being a most vital natural resource of rock weathering. Development of soils in an environment enhances plants dependence on it for growth, and man depends directly or indirectly on plants for food, thus the functions of soil as a fundamental interface, providing an excellent example of the integration among many parts of the earth system. Hence, geomorphology research being based on processes of the earth’s surfacing that result into most of the physical features seen on the face of the earth.Keywords:
Soil production function
Earth materials
Parent material
Parent material
Soil production function
Bedrock
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Halloysite
Gibbsite
Charnockite
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Over geologic timescales, chemical weathering in mountain landscapes may play an important role in regulating atmospheric CO2. Understanding the feedbacks between climate, tectonics, erosion rates, biota, and weathering has been a recent focus of research, but disentangling these complex relationships remains a challenge. One area of particular interest has been the potential for a kinetic limit to weathering and soil production. Studies in New Zealand's Southern Alps were among the first to clearly exceed proposed kinetic limits on soil production and demonstrate thresholds in the influence of precipitation on chemical weathering. Here we present a new dataset that addresses chemical weathering, soil production rates, and surface erosion rates, measured across an altitudinal transect in the Tararua Range on New Zealand's North Island. The transect spans a kilometer in relief, and receives 3.5-5.5 m of annual precipitation. Underlying bedrock comprises silty and sandy members of the same Cretaceous Greywacke, but subtle lithologic changes correspond to abrupt shifts in soil production rates and total weathering. Total weathering across the transect is roughly invariant for each lithology and reflects near-complete depletion of weatherable species, consistent with a previously proposed threshold in the influence of precipitation. However, spatial patterns in weathering differ markedly in saprolite and in soils. Deep weathering in saprolite decreases with elevation and makes up a large fraction of the total weathering. This pattern suggests that climate may influence saprolite weathering, even where the total weathering is supply-limited. Spatial patterns in saprolite and total weathering do not correlate with an abrupt vegetation transition from dense forest to alpine tussock, which may suggest that biota are more strongly affected by a temperature threshold or more complex biogeochemical cycling. We contrast these results with new and previously published data from the Southern Alps, which have a similar climate but experience rapid tectonic uplift. There, the fresh supply of minerals to soils provided by uplift and erosion may enable much faster weathering and soil production rates. Taken together, these observations suggest a strong lithologic and tectonic control on soil production and weathering rates in humid climates.
Saprolite
Soil production function
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Lithology
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[1] Large areas distributed on the Earth's surface are covered by regolith, an unconsolidated heterogeneous material overlying bedrock. In high-latitude areas, most of the land surface has been reworked and eroded by both glacial and fluvial processes, leaving only remnants of formerly extensive regolith covers. In an effort to further the understanding of weathering patterns and processes in old regolith covers, a comprehensive study of localities spread across Norway was carried out. On the basis of the distribution of minerals and elements within regolith, as well as its internal structure and geomorphologic setting, we ascertained that it was formed in situ and originated in pre-Quaternary times. There are similarities between the study sites with respect to regolith thickness, zonation, and composition. The Chemical Index of Alteration (CIA) and the Weathering Index of Parker (WIP) suggests that the degree of chemical weathering in the regolith is advanced compared to the parental bedrock with a maximum change of over 80%, which indicates a substantial increase in the proportion of secondary versus primary minerals. Mineral analysis identified kaolinite and gibbsite, which are considered indicative of advanced weathering and therefore support this observation. On the basis of statistical relationships between different grain size fractions (<125 μm), we observed a consistent pattern, which revealed that physical weathering becomes progressively less important in the production of grains smaller than 32 μm. On the basis of this finding, we infer that chemical weathering progressively dominates the production of fine silt, very fine silt, and clay, whereas physical weathering primarily controls the production of grain size fractions larger than 32 μm. This particular pattern is suggested to be an intrinsic feature in the formation of weathered high-latitude regolith.
Regolith
Bedrock
Silt
Soil production function
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Saprolite
Gibbsite
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Weathering is a part of geomorphic processes leading to the disintegration and decomposition of rocks and minerals on the earth’s surface as a result of physical and chemical action that leads to the formation of soil being a most vital natural resource of rock weathering. Development of soils in an environment enhances plants dependence on it for growth, and man depends directly or indirectly on plants for food, thus the functions of soil as a fundamental interface, providing an excellent example of the integration among many parts of the earth system. Hence, geomorphology research being based on processes of the earth’s surfacing that result into most of the physical features seen on the face of the earth.
Soil production function
Earth materials
Parent material
Cite
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Rock weathering, an important geological process on the earth’s surface, plays a key role in shaping surface morphology, providing nutrients needed by the ecosystem, and regulating the global climate. However, the regimes for controlling rock weathering in different regions are still controversial. In this respect, the heavy minerals, elements, Sr-Nd isotope, magnetic susceptibility, and chromaticity of the granite weathering profile in Harbin, a high latitude area of China, were analyzed for understanding the weathering characteristics and mechanisms of the granite weathering profile in the cold area. The results indicate that the profile underwent strengthened physical weathering (large volumes of cracks in the granite parent rock) and low–moderate chemical weathering (CIA = 56~68). However, the chemical weathering does not clearly affect the composition of the weathering products, making the weathering products a good inheritance from the parent rocks, as evidenced by the binary diagram (e.g., TiO2-Zr, and La/Sc-Co/Th) and geochemical genes (LG01 and LG03). The development process of the weathering profile has been affected by the input of external materials and biological activities, as evidenced by the Sr-Nd isotopic composition, Th/Zr values, chemical depletion fractions, ΔAl/Ti ratios, χfd%, and geochemical genes (LG03). Notably, a progressively decreasing weathering degree with a reduced depth is observed in the profile, which is likely to be related to an addition of external materials and/or effects of biological activities. In addition, the weathering regime of the profile does not vary in geology time, characterized by a kinetic-limited weathering regime with a limited supply.
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Soil production function
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Bedrock
Soil production function
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Bedrock
Soil production function
Soil horizon
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