Degree

Candidate in Philosophy

Department

Geology and Geophysics

Document Type

Dissertation/Thesis

Abstract

The Monsoon is one of the most powerful climatic phenomena on Earth and controls environments in South Asia. Erosion and weathering patterns are influenced by monsoon variations and can be reconstructed through marine sediment records. However, such reconstruction is based on the assumption that such sediments are representative of the onshore basins from which they are sourced. Debate continues regarding the degree to which storage and recycling homogenize short-term variations in sediment compositions. The Indus Submarine Canyon links the river mouth and the deep-water fan of the Indus drainage system. Determining how sediment fluxes through this canyon is important if deep-water sediments are to be used as archives of erosion and weathering.

Continuous deep-water sedimentation is seen through the canyon since at least ~11 ka. Nd and Sr isotopes show that canyon sediments are similar to the Holocene Indus River, suggesting direct supply from the river to the canyon, with no more than ~8 k.y. of buffering. Climatically modulated sediment supply dominates in controlling canyon clay sedimentation since ~20 ka. However, detrital zircon U-Pb ages from the canyon are resolvably different from those at the river mouth, at least before 6.6 ka, implying a disconnection between the mouth and the canyon. Sandy sediment was stored near river mouth as sea level rose, while finer sediment was directly transferred into deeper water. Modern river detrital zircon populations contrast with those in the canyon and in part reflect significant anthropogenic impact on sedimentation.

Clay mineral assemblages are used to constrain provenance and evaluate the linkage between continental weathering and monsoon intensity. Smectite is systematically enriched in the Indus Delta compared to the canyon and eastern shelf clinoform, implying preferential deposition of smectite close to the river mouth. The rapid shift to a more smectite-rich assemblage in the canyon after ~5 ka is caused by a change in sediment sources, with less direct flux from the Himalaya and increased erosion of older weathered flood plains. I conclude that sediment buffering does not dominate sedimentary records in the Indus Canyon and with careful consideration, reliable records of continental erosion and weathering can be derived.

Date

3-19-2018

Committee Chair

Clift, Peter

Available for download on Monday, March 17, 2025

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