TY - JOUR
T1 - Deep weathering along a granite ridgeline in a subtropical climate
AU - Liu, Wenjing
AU - Liu, Congqiang
AU - Brantley, Susan L.
AU - Xu, Zhifang
AU - Zhao, Tong
AU - Liu, Taoze
AU - Yu, Chong
AU - Xue, Dingshuai
AU - Zhao, Zhiqi
AU - Cui, Lifeng
AU - Zhang, Zhuojun
AU - Fan, Bailin
AU - Gu, Xin
N1 - Funding Information:
This work was financially supported by the National Basic Research Program of China (“973 Program”, Grant No. 2013CB956401 ), the “Strategic Priority Research Program” of the Chinese Academy of Sciences (Grant No. XDB15010405 ), National Natural Science Foundation of China (Grant No. 41130536 and 41402323 ) and the International Postdoctoral Exchange Fellowship Program (Grant No. 20140045 ). Susan L. Brantley and Wenjing Liu acknowledge the support from grant DE-FG02-OSER15675 from the U.S. Department of Energy Office of Basic Energy Sciences for work on chemical weathering. The authors are grateful to Shanke Liu in Institute of Geology and Geophysics, Chinese Academy of Sciences, and Dr. Scott Hynek in the Earth and Environmental Systems Institute, The Pennsylvania State University for their communication. The paper benefited much from insightful comments and suggestions from the handling editor and an anonymous reviewer.
Publisher Copyright:
© 2016 Elsevier B.V.
PY - 2016/6/1
Y1 - 2016/6/1
N2 - Bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11-meter profile weathering on a granite ridgeline under subtropical climate conditions in south China. The weathering sequence is delineated by mineralogy and major element variations. Apatite, biotite, hornblende and plagioclase dissolve early during weathering, resulting in nearly 100% Ca and Na loss and significant Mg, Fe and P depletion at depth. The K-feldspar reaction front begins at the depth of depletion of plagioclase, leading to a loss of ~80% of the K at the land surface near the bottom of the ridgeline and almost 100% at the top. Dissolution of quartz and other silicates releases about 60% of Si in the profiles. Kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer. The soil horizon (upper 100 cm) is the zone dominated by pedogenic processes, including active biological activity, physical erosion and influx of high concentrations of atmospheric components (especially CO2 and O2). The pedogenic processes are characterized by low pH (~4.54 to 5.85), high clay content (kaolinite: 6-16 wt.%; gibbsite: 2-8 wt.%) and total organic carbon content (0.13-3.93%) and intensive fracturing and dissolution of quartz and K-feldspar compared with the lower horizons.Accumulation of organic material and resistant minerals downslope is attributed to down-ridge movement of water (termed here, interflow) and weathering products in the uppermost 100 cm down the ridgeline. Using a mass balance model calculation for the catena that assumes steady-state soil thickness at all sites, the bottom profile shows the highest apparent total chemical weathering loss rate (~14 g m-2 y-1) whereas the middle position shows the highest physical erosion loss rate (~44 g m-2 y-1). SiO2 accounts for about 84% of the chemical weathering outflux from the soil horizons along the ridgeline hillslope. Chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite.This study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena.
AB - Bulk chemical composition and mineralogy were examined in three soil profiles and a deeper 11-meter profile weathering on a granite ridgeline under subtropical climate conditions in south China. The weathering sequence is delineated by mineralogy and major element variations. Apatite, biotite, hornblende and plagioclase dissolve early during weathering, resulting in nearly 100% Ca and Na loss and significant Mg, Fe and P depletion at depth. The K-feldspar reaction front begins at the depth of depletion of plagioclase, leading to a loss of ~80% of the K at the land surface near the bottom of the ridgeline and almost 100% at the top. Dissolution of quartz and other silicates releases about 60% of Si in the profiles. Kaolinite is the dominant clay mineral and it transforms to gibbsite in the uppermost layer. The soil horizon (upper 100 cm) is the zone dominated by pedogenic processes, including active biological activity, physical erosion and influx of high concentrations of atmospheric components (especially CO2 and O2). The pedogenic processes are characterized by low pH (~4.54 to 5.85), high clay content (kaolinite: 6-16 wt.%; gibbsite: 2-8 wt.%) and total organic carbon content (0.13-3.93%) and intensive fracturing and dissolution of quartz and K-feldspar compared with the lower horizons.Accumulation of organic material and resistant minerals downslope is attributed to down-ridge movement of water (termed here, interflow) and weathering products in the uppermost 100 cm down the ridgeline. Using a mass balance model calculation for the catena that assumes steady-state soil thickness at all sites, the bottom profile shows the highest apparent total chemical weathering loss rate (~14 g m-2 y-1) whereas the middle position shows the highest physical erosion loss rate (~44 g m-2 y-1). SiO2 accounts for about 84% of the chemical weathering outflux from the soil horizons along the ridgeline hillslope. Chemical weathering rates at the bottom of the hillslope may be accelerated by high concentrations of organic material and by dissolution of kaolinite.This study demonstrates that mineral reaction fronts in granite become separated over depth intervals of meters and that elemental fluxes and release mechanisms vary with position along a ridgeline catena.
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U2 - 10.1016/j.chemgeo.2016.02.014
DO - 10.1016/j.chemgeo.2016.02.014
M3 - Article
AN - SCOPUS:84959255839
VL - 427
SP - 17
EP - 34
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
ER -
