• Journal of The Geomorphological Association of Korea
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• v.18 no.3
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• pp.53-64
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• 2011

Grus weathering mantles are widely distributed in Southern Korean Peninsula and are considered to be results of chemical weathering related to palaeoclimate milieu. This paper attempts to address this issue by CIA(chemical index of alteration). The climatic approach to the formation of grus mantles offers limited explanation of field occurrences, as these materials are widespread across climatic zones, from the humid tropics to cool temperate areas, although rates of grusification are likely to be influenced by climatic parameters. CIA values for granitoid weathering mantles in S. Korea are 50, which is the same of unweathered granitic rocks. Grus mantles in Korean peninsula show very low level in chemical alteration by CIA.

• Journal of the Korean Geographical Society
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• v.50 no.5
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• pp.505-514
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• 2015

This study analyzes a correlation between water content values and chemical index of alteration (CIA) for coarse sedimentary rocks of Mt. Cheonsaeng in Gumi-si, Kyeongsangbuk-do. Through measurement of various water values of 20 samples including water content rate, water absorption rate and equipment measuring we comparatively analyzed the values with CIA of the samples obtained by X-ray fluorescence. As a result of analysis water content rate and water absorption rate in a sedimentary rock are likely to be higher when matrix is psephitic and less compact. Furthermore the higher water content rate is, the higher CIA is due to increase of $SiO_2$ and $Al_2O_3$ and decrease of CaO and $Na_2O$ derived by chemical weathering of felspar. This correlation between water content rate and CIA represents a similar result with previous studies targeting granite.

• Journal of the Korean association of regional geographers
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• v.18 no.1
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• pp.17-26
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• 2012

In Hwangtohyun, meaning 'red soil pass', reddish surface mantles is widespread. Other granitic hills, exceptionally Naju and Youngam area, in Korean peninsula don't commonly have that color. This paper attempts to address this issue by CIA(chemical index of alteration). CIA data and A-CN-K diagram provide crucial insights into the changes in the relative contributions of chemical physical weathering in difference of grus regolith and saprolite. CaO and $Na_2O$ show strong depletion and $K_2O$ is progressive loss. In grus regolith, weathering trends are (sub)parallel to the CN-A join of the A-CN-K diagram, but the sample's composition plot ever closer to the A-K join in saprolite. The difference of weathering trend obtained using CIA data corresponds closely with the visual interpretation of soil color and texture.

• The Journal of Engineering Geology
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• v.27 no.1
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• pp.67-79
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• 2017

Evaluation of the weathering index using the quantitative element composition of rocks is very effective in predicting the degree of weathering of rocks and the secondary weathering residuals. While the process of weathering varies according to the types of rocks, the study of weathering in Korea is concentrated on acidic igneous rocks. This study calculated the weathering indices using whole rock analysis (X-ray fluorescence analysis) of sandstone, mudstone, and shale belonging to clastic sedimentary rocks. The statistical significance of the indices was examined based on the correlation of the calculated weathering indices. Clastic sedimentary rocks showed higher significance of Wp, CIA, CIW and PIA weathering index indicating weathering of feldspar. Chemical Index of alteration (CIA) has the advantage of predicting weathering pathway and clay mineral production, but it is effective to consider chemical index of weathering index (CIW) simultaneously to improve accuracy. In order to reduce uncertainties due to carbonate rocks and to estimate the accurate weathering index, rock samples with high CaO content should be excluded from the evaluation of weathering index.

• Journal of The Geomorphological Association of Korea
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• v.19 no.1
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• pp.57-68
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• 2012

Red saprolites are appeared in granitic hills in Naju, Southern Korean Peninsula. These red saprolites were analyzed for their geochemistry, including CIA, A-CN-K and A-CNK-FM ternary plots, to understand the chemical weathering trend and rubefaction of the saprolites. These saprolites were compared with kaolinitic saprolites of Guadalquivir Basin in Spain formed under paleo-humid tropical conditions. Chemical Index of Alteration(CIA) value for Naju in Korea is 80, and 87 in Guadalquivir, suggesting moderate and strong weathering in both. Relative to kaolinitic saprolite of Guadalquivir in Spain, red saprolites in Naju are commonly weak loss of CaO, $Na_2O$, especially in $K_2O$. The A-CNK-FM ternary plots of Naju saprolites relative to Kaolinitic saprolites of Guadalquivir shows weak chemical alteration owing to slow removal of $K_2O$, but high mafic constituents, $Fe_2O_3$ and MgO, for most of the samples. In the saprolites of Naju, mafic oxides, $Fe_2O_3$ and MgO, become enriched because of the fast and massive removal of CaO, $Na_2O$ and $K_2O$ relative to other elements, resulting in rubefaction of the surface layer of the saprolites, so more redness than kaolinitic saprolites of Guadalquivir. It is found that the rubefaction of the saprolites is not necessarily proportional to chemical weathering intensity.

• Journal of the Korean Geotechnical Society
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• v.28 no.5
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• pp.41-54
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• 2012

The weathering process of rocks leads to the reduction of geotechnical bearing capacity. The weathering of granite is frequently used to refer to the degradation of geotechnical property in the design and construction of infra-structure. In this study, the range of values of CIA (chemical index of alteration) and the change of mineral compositions by weathering have been analysed with igneous rock, which covers 45.5% in South Korean territory. Several weathering indices were studied for various rocks found in Korea and significant relationships between different indices were delineated via statistical analysis. The applicability of CIA was found to be the most significant among all weathering indicies. The composition of illite, the secondary weathering residual, generally increases for the felsic rock, and swelling clay material is not included. The weathering of felsic rock will follow a sequential process, starting from bed rock, illite, and chlorite to kaoline. The mafic rock will show weathering process, from bed rock, smectite, and chlorite to kaoline. The intermediate rocks such as andesite and tuff will show similar weathering procedure and the composition of kaoline, chlorite, and smectite tends to increase more than that of illite when the mafic rock is dominated. This means the increase of rock material which has high CEC (cation exchange capacity) during secondary weathering process. However, the characteristics of a specific rock cannot be completely analyzed using merely CIA, since it is exclusively based on chemical composition and corresponding alteration. The CIA can be used to quantify the weathering process in a limited range, and further considerations such as rock composition, strength characteristics will be required to configure the comprehensive weathering impact on any specific region.

• Journal of The Geomorphological Association of Korea
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• v.23 no.2
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• pp.29-45
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• 2016

Chemical composition of fine sediments from Jeongdongjin area are analyzed with XRF method. The results are compared with previously reported results of sandstones of the nearest Simgok port. The weight percentage of $SiO_2$ of the samples are far lower than those of sandstones of Simgok. It is supposed to be happened by the selective elution of $SiO_2$ from the sediment layer of coastal terrace, as there's no evidence of selective input or precipitation of other elements from outside. As a result of chemical alteration or weathering of sediment at coastal terrace, weight percentage of $Al_2O_3$ and $Fe_2O_3$ of samples show far higher values than those of Simgok sandstone. In addition, the relative portion of $Al_2O_3$ and $Fe_2O_3$ are decreased to upward within outcrop of terrace sediment layers. It could be caused by the chemical weathering progress with time. However Chemical Index of alteration(CIA) of sediment samples are no larger than 90 and it could be interpreted that it would take over 100ka for total weathering of sediment in this area. Meanwhile the ratio of $SiO_2/Al2O_3$ of terrace sediment showed as 3.48~6.0 and it is far smaller than those of Simgok sandstones(23.9~49.0). The ratio of $SiO_2/Fe_2O_3$ of terrace sediment(19.19~55.85) showed similar pattern with $SiO_2/Al2O_3$ (Simgok sanstone: 119.6~601.8). The ratios have a weak trend of decreasing upwards within the outcrop, there also a huge difference in value among the samples. Chemical composition of reddish brown and gray layers which suspected as the result of psudogleization reveals that reddish brown parts have higher concentration of $Fe_2O_3$ than other parts, while there was no significant difference in concentration of $Al_2O_3$ and CaO.

• Journal of the Korean Geographical Society
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• v.39 no.3
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• pp.425-443
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• 2004

Fluvial terraces is poorly developed along Bukhan River in Central Korea. Altitude from riverbed of T1 terraces are 18-29m, T2 terraces 2539m, respectively. Rubification index of T2 is 0.66, T1 is 0.54, and thickness of gravel weathering rind on gneiss of T2 are 14.0mm, granites of T2 are $\infty$, gneiss of T1 are 5.0mm and granites of T2 are 8.0mm, because weathering in deposits of T2 terraces, older than T1, is severer than T1 terraces. Since deposits in T2 have more active and longer weathering than T1, SiO$_2$/Al$_2$O$_3$ is 3.32 in T2 and 4.06 in T1, and SiO$_2$/R$_2$O$_3$ is 2.64 in T2 and 3.19 in T1. CIA(Chemical Index of Alteration) is 87.85％ in T2 and 85.88％ in T1. Kaolinite and halloysite are founded in deposits of T2 indicating high weathering, and are founded gibbsite made tv eluviation of kaolinite. However, deposits of T1 have no kaolinite, and are found plagioclase, weak mineral in weathering process. Comparing to previous researches by estimated age as altitude from riverbed, rubification index, thickness of gravel weathering rind, element contents and mineral composition, forming age of T2 terraces in Bukhan River are estimated in marine oxygen isotope stage 6 (130-190ka), and T1 terraces are marine oxygen isotope stage 4(59-74ka).

• Journal of the Korean earth science society
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• v.45 no.5
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• pp.449-455
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• 2024

Characteristics of riverine sediments entering the marine realm reflect the geology, geography, topography, and climate of the drainage basin. Chemical weathering in hinterland is known to play a significant role in regulating atmospheric CO₂ levels. This study examines the intensity of chemical weathering and the composition of source rocks of surface sediments near the Nakdong River estuary on the southern coast of the Korean Peninsula. The degree of chemical weathering of the study samples is relatively low to moderate (average Chemical Index of Alteration=68), and the weathering trend inferred in the A-CN-K diagram suggests that the source rock composition is close to the average upper continental crust. It indicate that the source rock composition represents a mixture of the Mesozoic granitoids and the Gyeongsang Supergroup distributed in the Nakdong River drainage basin. The surface sediments exhibit fractionated chondrite-normalized rare eath element patterns and negative Eu anomalies, again similar to the upper continental crust. Comparison of our result with data from global estuarine sediment and large rivers in Korea allow us to parse the potential impacts of geology and topography on chemical weathering in watersheds.

• Journal of The Geomorphological Association of Korea
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• v.21 no.4
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• pp.19-40
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• 2014

Rock rebound values and chemical compositions of Gamak island at Sangha, Gochang, Jeollabuk do are analysed as a part of geomorphic survey of that area. Some corestones are formed by deep weathering found from the summit of rock mass of Gamak island, while the rocks a part of weathering front are exposed at the foot of the island. Rebound values of rock increase toward coastal plain, so summit would be weak in resistance to erosion. It can be assumed that chemical weathering is more active at the summit by the chemical index of alteration and changes in chemical composition ratio. However it should be mentioned that the samples are taken from the surface of the rock mass that more fresh part will be exposed when the weathered parts are removed. The chemical composition and CIA values of the polygonal cracks found from on the surface of weathering rind showed that this part has values between those of the summit and the footslope. The bottom of weathering rind with polygonal cracks has higher CIA value than those of the surface. Though it supports the result from the Bisul Mt., there also difference in the ratio of SiO2. It looks caused by the difference in weathering environment and chemical difference in parent rock. In summary Gamak island is the remnants of weathering front after removal of weathered material. The removal processes are more active at the footslope where the coastal processes are stronger than the summit.