Special Issue "Clays, Clay Minerals and Geology"

A special issue of Minerals (ISSN 2075-163X).

Deadline for manuscript submissions: 31 October 2020.

Special Issue Editor

Dr. Francesco Cavalcante
Website
Guest Editor
Institute of Methodologies for Environmental Analysis, Italian National Research Council, Rome, Italy
Interests: clays; clay minerals; geodynamic; climate change; provenance; diagenesis; low grade metamorphism; mixed-layers clay minerals and quantitative analysis of clays

Special Issue Information

Dear Colleagues,

Sedimentary rocks cover about 80% of the Earth’s surface, and clays represent well over 40% of sedimentary rocks. The wide diffusion of these sediments and their characteristics (large specific surface, cation exchange capacity, water retention capacity, thixotropy, etc.) make clays extremely important for their large use in the last thousand years. The main environment where clay minerals form and evolve is represented by soils, where parent minerals are transformed into clay due to weathering the interaction with living organisms. Other important environments include hydrothermal systems, where clay minerals form due to the rise of high-temperature fluids. After their formation, clay minerals are transported by streams, wind, and glaciers and settle mainly in deep marine environments. The current distribution of clay minerals in the oceans suggests that the climate plays a fundamental control on the formation of these mineral phases. Subsequently, these minerals undergo important transformations at low temperatures within sedimentary basins, due to the sedimentary and/or tectonic load. From the above statements, it appears that clay minerals are crucial in the various disciplines of the earth sciences, such as geodynamics, basin analysis, sedimentology, climate change, reconstruction of depositional environments, tectonics, etc. Contributions focusing on clay minerals aimed at solving geological problems and understanding the formation and evolution of clay minerals within constrained geological environments are welcome.

Dr. Francesco Cavalcante
Guest Editor

Manuscript Submission Information

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Keywords

  • clays
  • clay minerals
  • geodynamic
  • climate change
  • provenance and characteristics of the formation environment of clay minerals
  • diagenesis
  • low grade metamorphism

Published Papers (4 papers)

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Research

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Open AccessArticle
Mineralogical Record for Stepwise Hydroclimatic Changes in Lake Qinghai Sediments Since the Last Glacial Period
Minerals 2020, 10(11), 963; https://doi.org/10.3390/min10110963 - 28 Oct 2020
Abstract
Lake Qinghai is sensitive to climatic changes because of its pivotal location between mid-latitude Westerlies and the low-latitude East Asian monsoon. An 18.6 m long drilling core (1Fs) from Lake Qinghai provides new information on the hydroclimatic dynamics since the last glacial period. [...] Read more.
Lake Qinghai is sensitive to climatic changes because of its pivotal location between mid-latitude Westerlies and the low-latitude East Asian monsoon. An 18.6 m long drilling core (1Fs) from Lake Qinghai provides new information on the hydroclimatic dynamics since the last glacial period. Here, we present the results of bulk mineral assemblages of this core. X-ray diffraction (XRD) results showed that the bulk minerals of the core sediments consist of major clastic minerals (e.g., quartz, feldspar, muscovite), carbonates (e.g., calcite, aragonite, dolomite), and minor clay minerals (e.g., chlorite). Quartz as an exogenous detrital mineral in lake sediments, its abundance is related to lake level changes resulting from regional climate changes via fluvial/aeolian transportation. Aragonite was precipitated from water solutions or chemical alteration of pre-existing minerals or biogenic mediation, closely related to lake hydroclimate change. Mineral assemblages revealed remarkable stepwise hydroclimatic changes. High quartz content and low calcite without aragonite suggested a cold-wet climate condition under predominant westerlies during the last glacial period from 35 to 25.3 ka. Afterward, quartz decreased and aragonite occasionally appeared, indicating an unstable hydroclimatic condition during the last deglaciation. Since the Early Holocene (11.9–8.2 ka), predominant minerals shifted from terrigenous quartz to authigenic carbonates, suggesting an increasing lake level, possibly due to intensified Asian summer monsoon with increased effective moisture. Aragonite became the primary carbonate mineral, implying a warming and humid hydroclimate environment with a relatively higher lake-level. During the Middle Holocene (8.2–4.2 ka), aragonite showed a decreasing trend indicating a higher lake level with weak evaporation. During the Late Holocene since 4.2 ka, there were lower quartz and aragonite, suggesting a deep lake with a weak summer monsoon. Our quartz and carbonate minerals record provided essential clues to reconstruct hydroclimate change in Lake Qinghai since the last glacial period. Full article
(This article belongs to the Special Issue Clays, Clay Minerals and Geology)
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Open AccessArticle
Geochemical Significance of Clay Minerals and Elements in Paleogene Sandstones in the Center of the Northern Margin of the Qaidam Basin, China
Minerals 2020, 10(6), 505; https://doi.org/10.3390/min10060505 - 31 May 2020
Cited by 1
Abstract
The average thickness of Paleogene sandstones reaches about 3000–4000 m at the northern margin of the Qaidam Basin. However, the provenance and sedimentary environment of these sandstones are uncertain; thus, more comprehensive research is needed. Integrated research is conducted on the provenance and [...] Read more.
The average thickness of Paleogene sandstones reaches about 3000–4000 m at the northern margin of the Qaidam Basin. However, the provenance and sedimentary environment of these sandstones are uncertain; thus, more comprehensive research is needed. Integrated research is conducted on the provenance and weathering process based on petrographic characteristics, clay minerals, and geochemical compositions of sandstones in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction accretion, or a fold-thrust belt. The average illite content in the Paleogene clay minerals is more than 50%, followed by chlorite and smectite, which reflect climatic and environmental characteristics that were arid to semi-arid, whereas the characteristics of carbon–oxygen isotopes reveal a mainly freshwater sedimentary environment. The corrected chemical index of alteration (CIAcorr) is between 56.3 and 75.7, with an average value of 66.5. These results indicate that the provenance of the Paleogene sandstones in the center of the northern Qaidam Basin mainly formed under cold and dry climatic conditions and experienced limited chemical weathering with a small amount that underwent intermediate chemical weathering under warm and humid conditions. Full article
(This article belongs to the Special Issue Clays, Clay Minerals and Geology)
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Open AccessArticle
Distinguishing Features and Identification Criteria for K-Dioctahedral 1M Micas (Illite-Aluminoceladonite and Illite-Glauconite-Celadonite Series) from Middle-Infrared Spectroscopy Data
Minerals 2020, 10(2), 153; https://doi.org/10.3390/min10020153 - 11 Feb 2020
Cited by 1
Abstract
A representative collection of K-dioctahedral 1M micas ranging in composition from (Mg, Fe)-poor illites to aluminoceladonites through Mg-rich illites (Fe-poor varieties) and from Fe-bearing, Mg-rich illites to celadonites through Fe-illites, Al-glauconites and glauconites (Fe-bearing varieties) was studied by Fourier-transform infrared (FTIR) spectroscopy [...] Read more.
A representative collection of K-dioctahedral 1M micas ranging in composition from (Mg, Fe)-poor illites to aluminoceladonites through Mg-rich illites (Fe-poor varieties) and from Fe-bearing, Mg-rich illites to celadonites through Fe-illites, Al-glauconites and glauconites (Fe-bearing varieties) was studied by Fourier-transform infrared (FTIR) spectroscopy in the middle-infrared region. Analysis and comparison of the relationships between the band positions and cation compositions of Fe-poor and Fe-bearing K-dioctahedral micas provided a generalized set of FTIR identification criteria that include the band positions and profiles in the regions of Si–O bending, Si–O stretching, and OH-stretching vibrations. FTIR data allow unambiguous identification of illites, aluminoceladonites, and celadonites, as well as distinction between Fe-illites and illites proper, as well as between Al-glauconites and glauconites. Specifically, a sharp maximum from the AlOHMg stretching vibration at ~3600 cm−1, the presence of a MgOHMg stretching vibration at 3583–3585 cm−1, as well as characteristic band positions in the Si–O bending (435–439, 468–472 and 509–520 cm−1) and stretching regions (985–1012 and 1090–1112 cm−1) are clearly indicative of aluminoceladonite. The distinction between Fe-illites and Al-glauconites, which have similar FTIR features, requires data on cation composition and unit-cell parameters. Full article
(This article belongs to the Special Issue Clays, Clay Minerals and Geology)
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Review

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Open AccessReview
Clay Minerals in Hydrothermal Systems
Minerals 2020, 10(10), 919; https://doi.org/10.3390/min10100919 - 16 Oct 2020
Abstract
The study of active and fossil hydrothermal systems shows clay minerals to be a fundamental tool for the identification and characterization of hydrothermal alteration facies. The occurrence and composition of hydrothermal alteration facies could provide useful information on the physicochemical conditions of the [...] Read more.
The study of active and fossil hydrothermal systems shows clay minerals to be a fundamental tool for the identification and characterization of hydrothermal alteration facies. The occurrence and composition of hydrothermal alteration facies could provide useful information on the physicochemical conditions of the hydrothermal activity affecting a rock volume. In particular, clay minerals (i.e., smectite group, chlorite, illite, kaoline group, pyrophyllite, biotite) are pivotal for extrapolating important parameters that strongly affect the development of water/rock interaction processes such as the temperature and pH of the hydrothermal environment. This work aims to give a general reference scheme concerning the occurrence of clay minerals in hydrothermal alteration paragenesis, their significance, and the information that can be deduced by their presence and chemical composition, with some examples from active and fossil hydrothermal systems around the world. The main mineralogical geothermometers based on chlorite and illite composition are presented, together with the use of hydrogen and oxygen isotope investigation of clay minerals in hydrothermal systems. These techniques provide a useful tool for the reconstruction of the origin and evolution of fluids involved in hydrothermal alteration. Finally, a list of oxygen and hydrogen fractionation factor equations between the main clay minerals and water is also provided. Full article
(This article belongs to the Special Issue Clays, Clay Minerals and Geology)
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