Chemical weathering in central Vietnam from clay mineralogy and major-element geochemistry of sedimentary rocks and river sediments

Abstract

Clay mineralogy and major-element geochemistry of Miocene sedimentary rock and modern river sediment samples collected from the Ba River basin in central Vietnam are used to evaluate the chemical weathering processes during the Miocene and the present time. The results show that Miocene andesitic sedimentary rocks consist of high smectite (average 72%) with moderate kaolinite (24%), while Miocene felsic sedimentary rocks display abundant kaolinite (65%) with moderate smectite (25%). In comparison, modern river sediments are characterized by moderate smectite (43%) and kaolinite (37%). The typical distribution of clay minerals in the Ba River basin can be resulted from abundant occurrence of felsic intrusive rocks and volcanic rocks along with weak tectonic uplift and the tropical East Asian monsoon climate during the Miocene and in the present time. Despite their different clay mineralogical compositions, major elements of these Miocene sedimentary rocks and modern river sediments display stronger depletion of Ca, Na and Mg than of K and Si during the chemical weathering. The chemical index of alteration (CIA) combined with kaolinite/illite ratio demonstrated moderate chemical weathering during the Miocene and in the present time in central Vietnam, demonstrating similar tectonic activity and climatic conditions occurred during these two periods.

Topographic and Climatic Control on Chemical Weathering of Mountainous Riverine Sediments of Hainan Island, South China Sea

“…The Malay Peninsula and Sumatra are benefited from stable tectonic settings and tropical climate (Liu et al, 2012), favoring the intensity of chemical weathering with strong hydrolysis. However, the sediments of Taiwan in tropical/ subtropical climate, highland part of the Mekong and Red River drainage basins in a subtropical climate, and even North Borneo in a tropical climate are characterized by strong physical erosion and moderate weathering conditions due to the combined effects of tectonic uplift and abundant monsoon rainfall (Liu et al, 2007;Liu et al, 2008;Liu et al, 2012;Sang et al, 2018). The correlations of CIA with kaolinite/(illite + chlorite) support our previous understandings based on the A-CN-K diagram analysis.…”

Mining waste acting as a precursor of environmental stress in sediments

“…The Chemical Index of Alteration (CIA) determines the degree of chemical weathering of river sediments as it reveals the resistance of aluminum silicates to the formation of clay minerals (GOMES; ALMEIDA; SPERANDIO, 2018;KUSIN et al, 2019;SANG et al, 2018). Equation 1 is used to calculate the CIA scores.…”

“…https://doi.org/10.1590/S1413-415220220230 Understanding the mobility of major oxides during the weathering processes has been proposed as an alternative to identify sediment formation zones (GOMES; ALMEIDA; SPERANDIO, 2018;SANG et al, 2018;SILVA et al, 2019;SOUSA et al, 2018). Additionally, sediment quality is often assessed by environmental geochemical indices based on average concentrations of local inorganic chemical compounds, the background values, compared to bottom levels as a tool for water resource management (BILLAH; KOKUSHI; UNO, 2019;MIZAEL et al, 2020).…”

Geochemical Study Geochemical Study of Injana Formation and its Tectonic Significances in Selected Areas-Iraq

“…Wherefore CIA values between 45-55 denote absent chemical weathering and indicate to cool and/or arid climatic conditions (Fedo et al 1995). CIA ≥ 60 infer low chemical weathering, between 60-80 imply very little-moderate chemical alteration, whereas those that are more than 80 refer to high intensity of chemical weathering (Sang et al, 2018). The CIA values of the Injana sediments in the studied sites are ranging from 31.1 to 59.1 with an average of 46.5 indicating absent to low chemical weathering.…”