Publication Date:
2022-10-19
Description:
© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Zhou, P., Ireland, T., Murray, R. W., & Clift, P. D. Marine sedimentary records of chemical weathering evolution in the western Himalaya since 17 Ma. Geosphere, 17(3), (2021): 824–853, https://doi.org/10.1130/GES02211.1.
Description:
The Indus Fan derives sediment from the western Himalaya and Karakoram. Sediment from International Ocean Discovery Program drill sites in the eastern part of the fan coupled with data from an industrial well near the river mouth allow the weathering history of the region since ca. 16 Ma to be reconstructed. Clay minerals, bulk sediment geochemistry, and magnetic susceptibility were used to constrain degrees of chemical alteration. Diffuse reflectance spectroscopy was used to measure the abundance of moisture-sensitive minerals hematite and goethite. Indus Fan sediment is more weathered than Bengal Fan material, probably reflecting slow transport, despite the drier climate, which slows chemical weathering rates. Some chemical weathering proxies, such as K/Si or kaolinite/(illite + chlorite), show no temporal evolution, but illite crystallinity and the chemical index of alteration do have statistically measurable decreases over long time periods. Using these proxies, we suggest that sediment alteration was moderate and then increased from 13 to 11 Ma, remained high until 9 Ma, and then reduced from that time until 6 Ma in the context of reduced physical erosion during a time of increasing aridity as tracked by hematite/goethite values. The poorly defined reducing trend in weathering intensity is not clearly linked to global cooling and at least partly reflects regional climate change. Since 6 Ma, weathering has been weak but variable since a final reduction in alteration state after 3.5 Ma that correlates with the onset of Northern Hemispheric glaciation. Reduced or stable chemical weathering at a time of falling sedimentation rates is not consistent with models for Cenozoic global climate change that invoke greater Himalayan weathering fluxes drawing down atmospheric CO2 but are in accord with the idea of greater surface reactivity to weathering.
Description:
This study was made possible by samples provided by the IODP. The work was partially funded by a grant from The U.S. Science Support Program (USSSP), as well as additional funding from the Charles T. McCord Jr. Endowed Chair in petroleum geology at LSU.
Keywords:
Alteration
;
Arabian Sea
;
Arid environment
;
Asia
;
Bengal Fan
;
Chemical composition
;
Chemical weathering
;
Chlorite
;
Chlorite group
;
Clay minerals
;
Climate change
;
Cooling
;
Crystallinity
;
Emission spectra
;
Erosion
;
Expedition 355
;
Glaciation
;
Goethite
;
Grain size
;
Hematite
;
Himalayas
;
ICP mass spectra
;
Illite
;
Indian Ocean
;
Indus Fan
;
International Ocean Discovery Program
;
IODP Site U1456
;
IODP Site U1457
;
Kaolinite
;
Karakoram
;
Magnetic properties
;
Magnetic susceptibility
;
Marine environment
;
Mass spectra
;
Mineral assemblages
;
Moisture
;
Oxides
;
Paleoclimatology
;
Paleoenvironment
;
Paleomagnetism
;
Provenance
;
Reactivity
;
Reconstruction
;
Sediment transport
;
Sedimentary rocks
;
Sedimentation
;
Sedimentation rates
;
Sheet silicates
;
Silicates
;
Spectra
;
Terrestrial environment
;
Transport
;
Weathering
Repository Name:
Woods Hole Open Access Server
Type:
Article
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