Geochemistry of red residua underlying dolomites in karst terrains of Yunnan-Guizhou Plateau I. The formation of the Pingba profile

Hongbing Ji*, Shijie Wang, Ziyuan Ouyang, Shen Zhang, Chenxing Sun, Xiuming Liu, Dequan Zhou

*Corresponding author for this work

Research output: Contribution to journalArticle

72 Citations (Scopus)

Abstract

We present a set of bulk chemical and mineralogical compositions of the Pingba red residua on karst terrains of the Yunnan-Guizhou Plateau that show evidence pertaining to the source and to evolution of the profile. The known potential sources of clay-rich deposits on the plateau include: (1) Triassic dolomites, (2) Quaternary sediments, (3) Chinese loess, (4) Early Pliocene-Late Holocene volcanic ash (although the existence of volcanic ash is not supported by geological or mineralogical data), or a mixture of the four sources. The mineralogical compositions of the profile have shown an obvious inheritance relationship between the regolith and insoluble residues from the underlying dolomites, without allochthonous components involved. In the regolith, the contents of Al2O3 and Zr are fairly constant and both the TiO2/Al2O3 and Fe2O3T/Al2O3 ratios are consistent with those of bedrock below in the profile. The chemical index of alteration (CIA) for the profile varies from 84 to 94. An obvious variation is only found in the lower regolith. In the Al2O3-CaO*+Na2O- K2O (A-CN-K) triangular diagram, almost all the samples are concentrated, and cannot be distinctly distinguished, close to the A-K joint, and they tend to the A end. The SiO2/ Al2O3 ratio in the samples from the regolith is less variable and low (≈1), but the K2O/Na2O ratio is very variable (2-18). The above two ratios are quite different from those of PAAS, upper continental crust (UCC) and Chinese loess. Average UCC-normalized spiderdiagrams for the samples from the regolith and the insoluble residues in the dolomites share much in common with respect to element distribution pattern. The ratios of mobile to immobile elements (Ca/Al, Mg/Al, Na/Al, K/Al and Mn/Al) and between the immobile elements (Al/Zr, Ti/Zr and Ti/Nb) reflect the characteristics of in situ weathering rather than a sedimentary origin. The above lends great support to a cognate relation between the dolomite and its overlying regolith.The chemical weathering of dolomite can be divided into two stages in the major element and high field strength element (HFSE) diagrams-namely for "leaching-accumulating trend" and "weathering trend". The research results of this paper demonstrate that the Pingba red residua is a typical in situ chemical weathering crust and material sources of the profile are derived from underlying Triassic dolomites. The previously postulated two-stage development model for red residua in the karst terrain can be discriminated clearly, among them, the change of chemical composition occurs notably in the transition periods of the two stages. Moreover, it is the leaching processes that have an important meaning in the formation of horizons of the soil and ferruginous crust from the profile.

Original languageEnglish
Pages (from-to)1-27
Number of pages27
JournalChemical Geology
Volume203
Issue number1-2
DOIs
Publication statusPublished - 15 Jan 2004
Externally publishedYes

Keywords

  • Elements
  • Karst terrain
  • Material sources
  • Red residua
  • Weathering

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