Surficial weathering of kaolin regolith in a subtropical climate: Implications for supergene pedogenesis and bedrock argillization

Qian Fang, Hanlie Hong, Harald Furnes, Jon Chorover, Qing Luo, Lulu Zhao, Thomas J. Algeo

Research output: Contribution to journalArticle

Abstract

Regolith, or in situ weathered material overlying bedrock, develops through pedogenic processes such as clay-mineral formation (“argillization”). Research on products of argillization, such as kaolin, is commonly focused on its economic value rather than on an integrated understanding of the pedological, mineralogic, and geochemical processes taking place in the regolith. Here, we analyzed three kaolin-regolith drillholes from a subtropical climate zone in southern China using X-ray diffraction (XRD), major and trace element analyses, H and O isotopes, differential thermal-thermogravimetric analysis (DTA-TG), and scanning electron microscopy (SEM). Many kaolinite aggregates within regolith have fan-shaped stacks, a morphology that is closely associated with transformation of muscovite plates. Hypogene indicators such as a shallow level of granite emplacement, representative structural controls on kaolinization, mineral zoning, and hypothermal minerals cannot be observed. Mineral assemblages and morphologies, elemental binary plots (e.g., Zr vs. TiO2 and P2O5 vs. SO3), as well as chemical profiles all show characteristics typical of surfical weathering. The δ18O and δ2H values of the clay fractions range from +16.8 to +18.7‰ and from −70 to −51‰ respectively, suggesting that supergene weathering has played a key role in forming the kaolin regolith. Dominance of kaolinite over halloysite implies a near-surface, freely draining environment. Adopting the underlying weakly altered granite (saprolith) as the parent material, the kaolin regolith exhibits four elemental profile patterns as revealed by mass transfer coefficients: (1) depletion (e.g., Na), (2) depletion-enrichment (e.g., Al), (3) enrichment (e.g., Mn), and (4) biogenic (e.g., Ca). These profiles reflect a combination of chemical, geologic, and biologic processes that are typical of relatively thin, in situ regolith profiles, and that is not necessarily similar to those typically associated with deep (thick) granite weathering profiles. We propose that supergene kaolin regolith is intrinsically more similar to shallow, biologically active residual soil deposits, rather than deeply weathered granite-hosted regoliths.

LanguageEnglish (US)
Pages225-237
Number of pages13
JournalGeoderma
Volume337
DOIs
StatePublished - Mar 1 2019

Fingerprint

kaolin
pedogenesis
soil formation
bedrock
regolith
subtropics
weathering
granite
climate
kaolinite
minerals
mineral
muscovite
halloysite
thermogravimetry
differential thermal analysis
weathering profile
zoning
residual soil
structural control

Keywords

  • Chemical gradient
  • Chemical weathering
  • Clay mineral
  • Kaolinite
  • Regolith

ASJC Scopus subject areas

  • Soil Science

Cite this

Surficial weathering of kaolin regolith in a subtropical climate : Implications for supergene pedogenesis and bedrock argillization. / Fang, Qian; Hong, Hanlie; Furnes, Harald; Chorover, Jon; Luo, Qing; Zhao, Lulu; Algeo, Thomas J.

In: Geoderma, Vol. 337, 01.03.2019, p. 225-237.

Research output: Contribution to journalArticle

Fang, Qian ; Hong, Hanlie ; Furnes, Harald ; Chorover, Jon ; Luo, Qing ; Zhao, Lulu ; Algeo, Thomas J. / Surficial weathering of kaolin regolith in a subtropical climate : Implications for supergene pedogenesis and bedrock argillization. In: Geoderma. 2019 ; Vol. 337. pp. 225-237.
@article{42e50155a59a4621b89de880bc2aec8c,
title = "Surficial weathering of kaolin regolith in a subtropical climate: Implications for supergene pedogenesis and bedrock argillization",
abstract = "Regolith, or in situ weathered material overlying bedrock, develops through pedogenic processes such as clay-mineral formation (“argillization”). Research on products of argillization, such as kaolin, is commonly focused on its economic value rather than on an integrated understanding of the pedological, mineralogic, and geochemical processes taking place in the regolith. Here, we analyzed three kaolin-regolith drillholes from a subtropical climate zone in southern China using X-ray diffraction (XRD), major and trace element analyses, H and O isotopes, differential thermal-thermogravimetric analysis (DTA-TG), and scanning electron microscopy (SEM). Many kaolinite aggregates within regolith have fan-shaped stacks, a morphology that is closely associated with transformation of muscovite plates. Hypogene indicators such as a shallow level of granite emplacement, representative structural controls on kaolinization, mineral zoning, and hypothermal minerals cannot be observed. Mineral assemblages and morphologies, elemental binary plots (e.g., Zr vs. TiO2 and P2O5 vs. SO3), as well as chemical profiles all show characteristics typical of surfical weathering. The δ18O and δ2H values of the clay fractions range from +16.8 to +18.7‰ and from −70 to −51‰ respectively, suggesting that supergene weathering has played a key role in forming the kaolin regolith. Dominance of kaolinite over halloysite implies a near-surface, freely draining environment. Adopting the underlying weakly altered granite (saprolith) as the parent material, the kaolin regolith exhibits four elemental profile patterns as revealed by mass transfer coefficients: (1) depletion (e.g., Na), (2) depletion-enrichment (e.g., Al), (3) enrichment (e.g., Mn), and (4) biogenic (e.g., Ca). These profiles reflect a combination of chemical, geologic, and biologic processes that are typical of relatively thin, in situ regolith profiles, and that is not necessarily similar to those typically associated with deep (thick) granite weathering profiles. We propose that supergene kaolin regolith is intrinsically more similar to shallow, biologically active residual soil deposits, rather than deeply weathered granite-hosted regoliths.",
keywords = "Chemical gradient, Chemical weathering, Clay mineral, Kaolinite, Regolith",
author = "Qian Fang and Hanlie Hong and Harald Furnes and Jon Chorover and Qing Luo and Lulu Zhao and Algeo, {Thomas J.}",
year = "2019",
month = "3",
day = "1",
doi = "10.1016/j.geoderma.2018.09.020",
language = "English (US)",
volume = "337",
pages = "225--237",
journal = "Geoderma",
issn = "0016-7061",
publisher = "Elsevier",

}

TY - JOUR

T1 - Surficial weathering of kaolin regolith in a subtropical climate

T2 - Geoderma

AU - Fang, Qian

AU - Hong, Hanlie

AU - Furnes, Harald

AU - Chorover, Jon

AU - Luo, Qing

AU - Zhao, Lulu

AU - Algeo, Thomas J.

PY - 2019/3/1

Y1 - 2019/3/1

N2 - Regolith, or in situ weathered material overlying bedrock, develops through pedogenic processes such as clay-mineral formation (“argillization”). Research on products of argillization, such as kaolin, is commonly focused on its economic value rather than on an integrated understanding of the pedological, mineralogic, and geochemical processes taking place in the regolith. Here, we analyzed three kaolin-regolith drillholes from a subtropical climate zone in southern China using X-ray diffraction (XRD), major and trace element analyses, H and O isotopes, differential thermal-thermogravimetric analysis (DTA-TG), and scanning electron microscopy (SEM). Many kaolinite aggregates within regolith have fan-shaped stacks, a morphology that is closely associated with transformation of muscovite plates. Hypogene indicators such as a shallow level of granite emplacement, representative structural controls on kaolinization, mineral zoning, and hypothermal minerals cannot be observed. Mineral assemblages and morphologies, elemental binary plots (e.g., Zr vs. TiO2 and P2O5 vs. SO3), as well as chemical profiles all show characteristics typical of surfical weathering. The δ18O and δ2H values of the clay fractions range from +16.8 to +18.7‰ and from −70 to −51‰ respectively, suggesting that supergene weathering has played a key role in forming the kaolin regolith. Dominance of kaolinite over halloysite implies a near-surface, freely draining environment. Adopting the underlying weakly altered granite (saprolith) as the parent material, the kaolin regolith exhibits four elemental profile patterns as revealed by mass transfer coefficients: (1) depletion (e.g., Na), (2) depletion-enrichment (e.g., Al), (3) enrichment (e.g., Mn), and (4) biogenic (e.g., Ca). These profiles reflect a combination of chemical, geologic, and biologic processes that are typical of relatively thin, in situ regolith profiles, and that is not necessarily similar to those typically associated with deep (thick) granite weathering profiles. We propose that supergene kaolin regolith is intrinsically more similar to shallow, biologically active residual soil deposits, rather than deeply weathered granite-hosted regoliths.

AB - Regolith, or in situ weathered material overlying bedrock, develops through pedogenic processes such as clay-mineral formation (“argillization”). Research on products of argillization, such as kaolin, is commonly focused on its economic value rather than on an integrated understanding of the pedological, mineralogic, and geochemical processes taking place in the regolith. Here, we analyzed three kaolin-regolith drillholes from a subtropical climate zone in southern China using X-ray diffraction (XRD), major and trace element analyses, H and O isotopes, differential thermal-thermogravimetric analysis (DTA-TG), and scanning electron microscopy (SEM). Many kaolinite aggregates within regolith have fan-shaped stacks, a morphology that is closely associated with transformation of muscovite plates. Hypogene indicators such as a shallow level of granite emplacement, representative structural controls on kaolinization, mineral zoning, and hypothermal minerals cannot be observed. Mineral assemblages and morphologies, elemental binary plots (e.g., Zr vs. TiO2 and P2O5 vs. SO3), as well as chemical profiles all show characteristics typical of surfical weathering. The δ18O and δ2H values of the clay fractions range from +16.8 to +18.7‰ and from −70 to −51‰ respectively, suggesting that supergene weathering has played a key role in forming the kaolin regolith. Dominance of kaolinite over halloysite implies a near-surface, freely draining environment. Adopting the underlying weakly altered granite (saprolith) as the parent material, the kaolin regolith exhibits four elemental profile patterns as revealed by mass transfer coefficients: (1) depletion (e.g., Na), (2) depletion-enrichment (e.g., Al), (3) enrichment (e.g., Mn), and (4) biogenic (e.g., Ca). These profiles reflect a combination of chemical, geologic, and biologic processes that are typical of relatively thin, in situ regolith profiles, and that is not necessarily similar to those typically associated with deep (thick) granite weathering profiles. We propose that supergene kaolin regolith is intrinsically more similar to shallow, biologically active residual soil deposits, rather than deeply weathered granite-hosted regoliths.

KW - Chemical gradient

KW - Chemical weathering

KW - Clay mineral

KW - Kaolinite

KW - Regolith

UR - http://www.scopus.com/inward/record.url?scp=85053759876&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85053759876&partnerID=8YFLogxK

U2 - 10.1016/j.geoderma.2018.09.020

DO - 10.1016/j.geoderma.2018.09.020

M3 - Article

VL - 337

SP - 225

EP - 237

JO - Geoderma

JF - Geoderma

SN - 0016-7061

ER -