Reconstructing Early Permian tropical climates from chemical weathering indices

Jianghai Yang, Peter Cawood, Yuansheng Du, Wenqian Li, Jiaxin Yan

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Paleoflora studies suggest that continental drying occurred associated with the Early Permian deglaciation in southern North America, but not in North China. Both regions occupied tropical latitudes during the Early Permian, but they were separated by the Tethys Ocean. To further constrain the tropical paleoclimate conditions during the Early Permian glacial to deglacial transition, we undertook a weathering geochemistry study on Early Permian mudstone and siltstone samples from southeastern North China and evaluated the climate impact on regional weathering patterns. Whole-rock major- and trace-element geochemistry, and X-ray diffraction mineralogy data suggest that sample compositions, and resultant calculated values of most weathering indices, are dominated by chemical weathering from a source akin to the average upper continental crust (UCC) of the adjoining southern North China craton. Values of the chemical index of alteration (CIA) and other well-correlated weathering indices, including the index of sodium depletion fraction (τNa), indicate high chemical weathering intensity (e.g., CIA > 80 and τNa < –0.80) in the southern North China craton source region related to intense climate forcing. Based on modern surface weathering data from granitic landscapes, we propose that the dependence of land surface soil chemical weathering intensity on the air temperature can be described by a τNa-MAT (mean annual temperature) transfer function, where humidity control is demonstrated by the consistently high τNa values of surface soils at sites with low annual precipitation rates (<400 mm/yr) despite temperature variation. By applying this modern weathering-climate relationship, we compare the Early Permian (Asselian-Sakmarian) terrestrial climate between North China and west tropical Pangea (present-day west Colorado). Using the southern North China craton as an average source composition, the average τNa valueof ~–0.90 for the Asselian-Sakmarian sediments of North China transforms to a MATof ~20 ± 2.7 °C and suggests a warm-humid climate. Using average UCC as an average source composition, the Asselian-Sakmarian loessites in west Colorado have an average τNa value ~–0.20, which either denotes an arid climate or corresponds to a cold (or cold-dry) climate with MAT of ~4 ± 2.7 °C. If valid, this estimated MAT is consistent with inferred upland glaciation within the ancestral Rocky Mountains of west tropical Pangea. The τNa-MAT transfer function provides a quantitative method for deep-time paleoclimate study and enhances our understanding of the dependence of continental chemical weathering on climate conditions.
Original languageEnglish
Pages (from-to)739-751
Number of pages13
JournalGeological Society of America Bulletin
Volume128
Issue number5-6
DOIs
Publication statusPublished - 2016
Externally publishedYes

Keywords

  • Provenance
  • CIA values
  • Tectonic setting

Cite this

Yang, Jianghai ; Cawood, Peter ; Du, Yuansheng ; Li, Wenqian ; Yan, Jiaxin. / Reconstructing Early Permian tropical climates from chemical weathering indices. In: Geological Society of America Bulletin. 2016 ; Vol. 128, No. 5-6. pp. 739-751.
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abstract = "Paleoflora studies suggest that continental drying occurred associated with the Early Permian deglaciation in southern North America, but not in North China. Both regions occupied tropical latitudes during the Early Permian, but they were separated by the Tethys Ocean. To further constrain the tropical paleoclimate conditions during the Early Permian glacial to deglacial transition, we undertook a weathering geochemistry study on Early Permian mudstone and siltstone samples from southeastern North China and evaluated the climate impact on regional weathering patterns. Whole-rock major- and trace-element geochemistry, and X-ray diffraction mineralogy data suggest that sample compositions, and resultant calculated values of most weathering indices, are dominated by chemical weathering from a source akin to the average upper continental crust (UCC) of the adjoining southern North China craton. Values of the chemical index of alteration (CIA) and other well-correlated weathering indices, including the index of sodium depletion fraction (τNa), indicate high chemical weathering intensity (e.g., CIA > 80 and τNa < –0.80) in the southern North China craton source region related to intense climate forcing. Based on modern surface weathering data from granitic landscapes, we propose that the dependence of land surface soil chemical weathering intensity on the air temperature can be described by a τNa-MAT (mean annual temperature) transfer function, where humidity control is demonstrated by the consistently high τNa values of surface soils at sites with low annual precipitation rates (<400 mm/yr) despite temperature variation. By applying this modern weathering-climate relationship, we compare the Early Permian (Asselian-Sakmarian) terrestrial climate between North China and west tropical Pangea (present-day west Colorado). Using the southern North China craton as an average source composition, the average τNa valueof ~–0.90 for the Asselian-Sakmarian sediments of North China transforms to a MATof ~20 ± 2.7 °C and suggests a warm-humid climate. Using average UCC as an average source composition, the Asselian-Sakmarian loessites in west Colorado have an average τNa value ~–0.20, which either denotes an arid climate or corresponds to a cold (or cold-dry) climate with MAT of ~4 ± 2.7 °C. If valid, this estimated MAT is consistent with inferred upland glaciation within the ancestral Rocky Mountains of west tropical Pangea. The τNa-MAT transfer function provides a quantitative method for deep-time paleoclimate study and enhances our understanding of the dependence of continental chemical weathering on climate conditions.",
keywords = "Provenance, CIA values, Tectonic setting",
author = "Jianghai Yang and Peter Cawood and Yuansheng Du and Wenqian Li and Jiaxin Yan",
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Reconstructing Early Permian tropical climates from chemical weathering indices. / Yang, Jianghai; Cawood, Peter; Du, Yuansheng; Li, Wenqian; Yan, Jiaxin.

In: Geological Society of America Bulletin, Vol. 128, No. 5-6, 2016, p. 739-751.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Reconstructing Early Permian tropical climates from chemical weathering indices

AU - Yang, Jianghai

AU - Cawood, Peter

AU - Du, Yuansheng

AU - Li, Wenqian

AU - Yan, Jiaxin

PY - 2016

Y1 - 2016

N2 - Paleoflora studies suggest that continental drying occurred associated with the Early Permian deglaciation in southern North America, but not in North China. Both regions occupied tropical latitudes during the Early Permian, but they were separated by the Tethys Ocean. To further constrain the tropical paleoclimate conditions during the Early Permian glacial to deglacial transition, we undertook a weathering geochemistry study on Early Permian mudstone and siltstone samples from southeastern North China and evaluated the climate impact on regional weathering patterns. Whole-rock major- and trace-element geochemistry, and X-ray diffraction mineralogy data suggest that sample compositions, and resultant calculated values of most weathering indices, are dominated by chemical weathering from a source akin to the average upper continental crust (UCC) of the adjoining southern North China craton. Values of the chemical index of alteration (CIA) and other well-correlated weathering indices, including the index of sodium depletion fraction (τNa), indicate high chemical weathering intensity (e.g., CIA > 80 and τNa < –0.80) in the southern North China craton source region related to intense climate forcing. Based on modern surface weathering data from granitic landscapes, we propose that the dependence of land surface soil chemical weathering intensity on the air temperature can be described by a τNa-MAT (mean annual temperature) transfer function, where humidity control is demonstrated by the consistently high τNa values of surface soils at sites with low annual precipitation rates (<400 mm/yr) despite temperature variation. By applying this modern weathering-climate relationship, we compare the Early Permian (Asselian-Sakmarian) terrestrial climate between North China and west tropical Pangea (present-day west Colorado). Using the southern North China craton as an average source composition, the average τNa valueof ~–0.90 for the Asselian-Sakmarian sediments of North China transforms to a MATof ~20 ± 2.7 °C and suggests a warm-humid climate. Using average UCC as an average source composition, the Asselian-Sakmarian loessites in west Colorado have an average τNa value ~–0.20, which either denotes an arid climate or corresponds to a cold (or cold-dry) climate with MAT of ~4 ± 2.7 °C. If valid, this estimated MAT is consistent with inferred upland glaciation within the ancestral Rocky Mountains of west tropical Pangea. The τNa-MAT transfer function provides a quantitative method for deep-time paleoclimate study and enhances our understanding of the dependence of continental chemical weathering on climate conditions.

AB - Paleoflora studies suggest that continental drying occurred associated with the Early Permian deglaciation in southern North America, but not in North China. Both regions occupied tropical latitudes during the Early Permian, but they were separated by the Tethys Ocean. To further constrain the tropical paleoclimate conditions during the Early Permian glacial to deglacial transition, we undertook a weathering geochemistry study on Early Permian mudstone and siltstone samples from southeastern North China and evaluated the climate impact on regional weathering patterns. Whole-rock major- and trace-element geochemistry, and X-ray diffraction mineralogy data suggest that sample compositions, and resultant calculated values of most weathering indices, are dominated by chemical weathering from a source akin to the average upper continental crust (UCC) of the adjoining southern North China craton. Values of the chemical index of alteration (CIA) and other well-correlated weathering indices, including the index of sodium depletion fraction (τNa), indicate high chemical weathering intensity (e.g., CIA > 80 and τNa < –0.80) in the southern North China craton source region related to intense climate forcing. Based on modern surface weathering data from granitic landscapes, we propose that the dependence of land surface soil chemical weathering intensity on the air temperature can be described by a τNa-MAT (mean annual temperature) transfer function, where humidity control is demonstrated by the consistently high τNa values of surface soils at sites with low annual precipitation rates (<400 mm/yr) despite temperature variation. By applying this modern weathering-climate relationship, we compare the Early Permian (Asselian-Sakmarian) terrestrial climate between North China and west tropical Pangea (present-day west Colorado). Using the southern North China craton as an average source composition, the average τNa valueof ~–0.90 for the Asselian-Sakmarian sediments of North China transforms to a MATof ~20 ± 2.7 °C and suggests a warm-humid climate. Using average UCC as an average source composition, the Asselian-Sakmarian loessites in west Colorado have an average τNa value ~–0.20, which either denotes an arid climate or corresponds to a cold (or cold-dry) climate with MAT of ~4 ± 2.7 °C. If valid, this estimated MAT is consistent with inferred upland glaciation within the ancestral Rocky Mountains of west tropical Pangea. The τNa-MAT transfer function provides a quantitative method for deep-time paleoclimate study and enhances our understanding of the dependence of continental chemical weathering on climate conditions.

KW - Provenance

KW - CIA values

KW - Tectonic setting

U2 - 10.1130/B31371.1

DO - 10.1130/B31371.1

M3 - Article

VL - 128

SP - 739

EP - 751

JO - Geological Society of America Bulletin

JF - Geological Society of America Bulletin

SN - 0016-7606

IS - 5-6

ER -