Petrographic Analysis and Chemical Weathering Sources in the Choshui River Watershed on the High-Standing Island of Taiwan
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Date
2019-05
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The Ohio State University
Abstract
Taiwan is a high-standing oceanic island and experiences high rates of physical and chemical weathering, making it an optimum location to study sources of chemical weathering in relation to the Long-Term Carbon Cycle. This study determined the mineralogy of the bedrock of the Choshui River in west-central Taiwan and utilized water chemistry data from the river taken before, during, and after a typhoon to identify potential chemical weathering sources in the region. The observed mineralogy and predicted weathering sources were compared to previously hypothesized chemical weathering source provenances in the Choshui River. The mineralogy of rock samples from the Choshui River was determined by use of petrographic microscopy and X-ray Diffraction analysis. The geochemical modeling software PHREEQC was used to predict mineral weathering patterns in response to extreme weather. The samples in this study were categorized as meta-sandstones, slates, and quartzite. The mineral composition of the rock samples matched published descriptions of the Choshui River with one exception. K-feldspar was identified in multiple rock samples despite previous studies stating it does not exist in the bedrock. Several minerals commonly formed by hydrothermal alteration were identified in the rocks samples, indicating the significance of hydrothermal waters to weathering in the area. Many silicate minerals exist in the rock samples, and most of them are capable of serving as a carbon sink when chemically weathered. Due to their abundances, illite and plagioclase may play the largest role in the Long-Term Carbon cycle in this region. Geochemical modeling revealed that carbonate minerals, K-mica, and K-feldspar may be important to the weathering regime of the river during extreme weather. These findings enhance our understanding of the composition of dissolved fluxes to the ocean from the Choshui River and source material for chemical weathering on Taiwan in relation to the global carbon cycle.
Description
2019 Denman Undergraduate Research Forum Winner, 1st Place in Evolutionary Ecology and Environmental Science category
Keywords
Chemical weathering, Petrology, Choshui River, Taiwan, Global carbon cycle