Duricrusts

Dixon, John C.; McLaren, Sue

doi:10.1007/978-1-4020-5719-9_6

Cited by 16 publications

(10 citation statements)

References 143 publications

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“…Lowest diversity was found in the northern samples where water availability reaches minimum values. These soils also had relatively high salt contents associated with high levels of Na, Ca, and S, and the presence of gypcrust close to the soil surface (within 10 cm), indicating persistent aridity over geological time [ 48 ]. Microbial diversity was significantly higher at the southernmost sampling localities where mean annual rainfall was one order of magnitude higher and near-surface soils were likely wetted yearly.…”

Section: Discussionmentioning

confidence: 99%

Colonization patterns of soil microbial communities in the Atacama Desert

et al. 2013

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BackgroundThe Atacama Desert is one of the driest deserts in the world and its soil, with extremely low moisture, organic carbon content, and oxidizing conditions, is considered to be at the dry limit for life.ResultsAnalyses of high throughput DNA sequence data revealed that bacterial communities from six geographic locations in the hyper-arid core and along a North-South moisture gradient were structurally and phylogenetically distinct (ANOVA test for observed operating taxonomic units at 97% similarity (OTU0.03), P <0.001) and that communities from locations in the hyper-arid zone displayed the lowest levels of diversity. We found bacterial taxa similar to those found in other arid soil communities with an abundance of Rubrobacterales, Actinomycetales, Acidimicrobiales, and a number of families from the Thermoleophilia. The extremely low abundance of Firmicutes indicated that most bacteria in the soil were in the form of vegetative cells. Integrating molecular data with climate and soil geochemistry, we found that air relative humidity (RH) and soil conductivity significantly correlated with microbial communities’ diversity metrics (least squares linear regression for observed OTU0.03 and air RH and soil conductivity, P <0.001; UniFrac PCoA Spearman’s correlation for air RH and soil conductivity, P <0.0001), indicating that water availability and salt content are key factors in shaping the Atacama soil microbiome. Mineralization studies showed communities actively metabolizing in all soil samples, with increased rates in soils from the southern locations.ConclusionsOur results suggest that microorganisms in the driest soils of the Atacama Desert are in a state of stasis for most of the time, but can potentially metabolize if presented with liquid water for a sufficient duration. Over geological time, rare rain events and physicochemical factors potentially played a major role in selecting micro-organisms that are most adapted to extreme desiccating conditions.

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Section: Discussionmentioning

confidence: 99%

Colonization patterns of soil microbial communities in the Atacama Desert

et al. 2013

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“…New silica rhizoliths may also have formed at this stage. Both types of silica accumulation (rhizoliths and glaebules) would lead to the formation of a pedogenic silcrete (Dixon and McLaren 2009). The micrite corrosion of opaline glaebules and the pendant vadose cements indicate a new stage of calcretization (stage 3, Fig.…”

Section: Sequences Of Processes and Environmentsmentioning

confidence: 99%

Root Calcretes and Uranium-Bearing Silcretes At Sedimentary Discontinuities In the Miocene of the Madrid Basin (Toledo, Spain)

Bustillo

Plet

Alonso-Zarza

2014

Journal of Sedimentary Research

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This paper reports a detailed study of the calcrete and silcrete profiles in the Miocene detrital deposits in the western area of Madrid, at the boundary of two main sedimentary units. The aims of this work were to better understand the pedogenic and diagenetic environments in which these profiles formed and to determine the cause(s) of their enrichment in uranium. Calcrete and silcrete duricrusts are characteristic features of closed continental basins in semiarid climates; this paper discusses the significance of duricrusts as indicators of important change in such basins.The detailed macromorphological, micromorphological, and geochemical study of three duricrust profiles revealed the sequence of pedogenic, vadose, and groundwater processes responsible for their formation. During the first stage of their development, carbonate laminae formed a white ''grill-like'' structure within the detrital parent materials. The microstructure and macrostructure of the carbonate, which includes alveolar septal structures and needle-fiber calcite, indicates the important role of roots and their associated microorganisms in calcrete formation. Early silicification occurred in the pedogenic-vadose environment affecting the detrital parent material, roots, and calcretes, forming an early silcrete defined by opaline glaebules and silica rhizoliths. The detailed preservation of the cells in the silicified roots denotes the early replacement of root organic matter. The green or green-yellowish fluorescence of the silicified root structures under short-wavelength UV shows their preferential enrichment in uranium. Calcitization and silicification coexisted in the pedogenic vadose environment, leading to several reversible replacements of calcite and silica. Later, the rise of the water table promoted silicification under phreatic conditions, as indicated by the good preservation of the texture of the detrital host rocks and calcretes. Other silcrete textures, such as ovoidal opaline accumulations, intraclasts produced by autobrecchification, and vadose silica cements, indicate later vadose environments, and consequently variations in the water table.The geochemical features of the calcretes and silcretes (major, minor, and rare earth elements) were inherited from their parent materials. The rare-earth-element patterns of some silcretes show them to have a positive Ce anomaly, suggesting that oxidizing conditions reigned during their formation. The good correlation between silica and uranium suggests that the silica phases acquired uranium through the direct silicification of roots that had fixed uranium from organic matter.This study shows that calcrete-silcrete duricrusts provide detailed information regarding the processes occurring in semiarid continental basins. In the studied basin, roots played a key role in both the development of the duricrust profiles and their enrichment in uranium. These duricrusts provide important information for understanding the overall stratigraphy of the studied basin and its large-scale ...

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“…The exact mechanism of crust formation on Tornillo loam inside BBNP is unknown. However, the mechanism of crust formation is likely not chemical precipitation (Dixon, 1994b), but more likely a result of a combination of surface wind (i.e., deflation) and water erosion processes often associated with the development and characteristics of aridic, desert-like soils, such as Tornillo loam (Dixon, 1994a). Aeolian deposition of fine sediments and/or chemical cementing agents (i.e., calcium carbonate) associated with dust (Aide and Smith, 2001;Aide et al, 2003) may also have contributed to crust formation.…”

Section: Soil Penetration Resistance and Crust Strengthmentioning

confidence: 99%