Moderate Chemical Weathering of Subtropical Taiwan: Constraints from Solid‐Phase Geochemistry of Sediments and Sedimentary Rocks

The well‐known earthquake‐and‐storm‐triggered extremely high physical weathering rate in Taiwan is consistent with present geochemical studies of sediments from different subenvironments (offshore, coastal, river, and lake) and sedimentary rocks of different geological ages, indicating a moderate chemical weathering condition. Major and trace element concentrations normalized to the average upper crust of Yangtze Craton show that the sediments and the average composition of sedimentary rocks of Taiwan are depleted in Ca, Mg, Na, and Sr, enriched in Rb and Zr, and unchanged with respect to K, indicating their moderately altered nature. The mean chemical index of alteration (CIA; 71–75) and plagioclase index of alteration (PIA; 81–86) values of coastal and offshore sediments reveal the sediments' derivation from sedimentary rocks by moderate silicate chemical weathering processes. The mean CIA value (62) of sedimentary rocks of Taiwan is similar to that for Chinese sediment (61), further confirming the above inference. A‐CN‐K, (A‐K)‐C‐N, and A‐CNK‐FM plots ( \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\mathrm{A}\,=\mathrm{Al}\,_{2}\mathrm{O}\,_{3}$ \end{document} ; \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\mathrm{C}\,=\mathrm{CaO}\,^{\mathrm{*}\,}$ \end{document} ; \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsm