Clay Mineral Variations in Holocene Terrestrial Sediments from the Indus Basin: a Response to SW Asian Monsoon Variability?

Anwar Alizai, Steve Hillier, Peter Dominic Clift, Liviu Giosan, Andrew Hurst, Sam VanLaningham, Mark Macklin

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.

Original languageEnglish
Pages (from-to)368-381
Number of pages14
JournalQuaternary Research
Volume77
Issue number3
Early online date23 Feb 2012
DOIs
Publication statusPublished - May 2012

Fingerprint

clay mineral
monsoon
Holocene
smectite
basin
weathering
sediment
chemical weathering
illite
chlorite
marine record
clay
climate change
new mineral
reworking
mudstone
kaolinite
mineralogy
X-ray diffraction
Indus

Keywords

  • monsoon
  • climate change
  • XRD
  • clay mineralogy
  • Himalaya
  • Indus Delta
  • floodplain
  • fluvial processes
  • large rivers

Cite this

Clay Mineral Variations in Holocene Terrestrial Sediments from the Indus Basin : a Response to SW Asian Monsoon Variability? / Alizai, Anwar; Hillier, Steve; Clift, Peter Dominic; Giosan, Liviu; Hurst, Andrew; VanLaningham, Sam; Macklin, Mark.

In: Quaternary Research, Vol. 77, No. 3, 05.2012, p. 368-381.

Research output: Contribution to journalArticle

Alizai, Anwar ; Hillier, Steve ; Clift, Peter Dominic ; Giosan, Liviu ; Hurst, Andrew ; VanLaningham, Sam ; Macklin, Mark. / Clay Mineral Variations in Holocene Terrestrial Sediments from the Indus Basin : a Response to SW Asian Monsoon Variability?. In: Quaternary Research. 2012 ; Vol. 77, No. 3. pp. 368-381.
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abstract = "We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.",
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N1 - Acknowledgments We are indebted to the Hutton Institute, Aberdeen, for providing facilities from preparation and running of analyses for clay samples. The paper was improved by two careful, anonymous reviewers and we also thank here our editor Alan Gillespie for his helpful comments in improving the quality of the paper. The study was partially supported by a grant from the Leverhulme Trust. PC thanks the Hanse Wissenschaftskolleg, Germany, for the chance to think about these issues. LG acknowledges NSF funding (award OCE-0623766)

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N2 - We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.

AB - We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.

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KW - floodplain

KW - fluvial processes

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