Doctor of Philosophy (PhD)
Geology and Geophysics
The influence of Quaternary climate variation on sediment generation, storage, and transport in two mountainous Asian river basin was examined in the largest tributary to the upper Indus River in the Himalayan rain shadow, the Zanskar River basin (~15,000 km2), and the smaller, subtropical Song Gianh basin (<3,500 km2) of central Vietnam. Spatial patterns of erosion in the Zanskar River Basin were established to quantify the dominant controls on Quaternary sedimentation in the Himalayan rain shadow on the edge of the Tibetan Plateau. Glacial erosion and precipitation along the High Himalaya together dominate sediment production and transport in the Zanskar River basin, in contrast to the monsoon-dominated frontal Himalaya and the arid plateau interior. Alluvial terrace document major phases of fluvial aggradation correlating with strong phases of monsoon and westerlies-derived precipitation during the Late Pleistocene (25–32 ka) and mid-Holocene (~6–8 ka), as similarly observed in the frontal Himalaya. Valley-fills in the Zanskar River Basin emphasize a long history of climate-modulated sediment buffering in the rain shadow. Results here indicate that only a modest proportion of stored volumes (40% of total) are exported to the trunk Indus River during the Holocene. The work further underscores that sediment buffering outside of low floodplain regions can be volumetrically significant to the total sediment flux. This work next explores the strongly monsoonal Song Gianh Basin of central Vietnam to better constrain how climate-driven erosional signals are transported and transformed downstream. Spatial patterns of erosion and dating of river terraces indicate that strong monsoonal rainfall drives modern sediment generation in the steep, upper reaches of the Song Gianh especially during the early Holocene (7.4–8.5 ka). Apparent contrast between sediment provenance proxies and younger terracing (medieval and 18–19th century) instead reflect high sediment flux related to agricultural disruption rather than in response to Holocene climatic change. Human-induced erosion inundates modern Song Gianh river sediment compositions with old, weathered soils. This implies that modern offshore sediment signals delivered by larger rivers may be strongly modified by human activities and so must be considered judiciously when used as analogs for the geologic record.
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Jonell, Tara Nicole, "Quaternary River Erosion, Provenance, and Climate Variability in the NW Himalaya and Vietnam" (2017). LSU Doctoral Dissertations. 4423.