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The influence of bedrock-derived acidity in the development of surface and underground karst: evidence from the Precambrian carbonates of semi-arid northeastern Brazil

Auler, Augusto S. ; Smart, Peter L.

Earth surface processes and landforms, 2003-02, Vol.28 (2), p.157-168 [Periódico revisado por pares]

Chichester, UK: John Wiley & Sons, Ltd

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  • Título:
    The influence of bedrock-derived acidity in the development of surface and underground karst: evidence from the Precambrian carbonates of semi-arid northeastern Brazil
  • Autor: Auler, Augusto S. ; Smart, Peter L.
  • Assuntos: Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Geomorphology, landform evolution ; hypogenic karst ; semi-arid karst ; speleogenesis ; sulphide oxidation ; sulphuric acid ; Surficial geology
  • É parte de: Earth surface processes and landforms, 2003-02, Vol.28 (2), p.157-168
  • Notas: ark:/67375/WNG-MC14B0K2-R
    istex:E41F2125DBBE871E7D8D2274C5A15955B6D8CF99
    CNPq (Brazilian Research Council) - No. 200711-95.4
    ArticleID:ESP443
    ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
  • Descrição: Very extensive cave systems are developed in Precambrian Una Group carbonates in the Campo Formoso area, eastern Brazil. In contrast, the area is largely devoid of significant surface karst landforms, as would be expected given its semi‐arid climate. The caves in the area display many morphological features characteristic of deep‐seated hypogenic caves, such as lack of relationship with the surface, ramiform/network pattern, abrupt variations of passage cross‐sections and absence of fluvial sediments, but do not show evidence of vertical passages marking the ascending path of acidic water nor present extensive gypsum or acid clay mineral deposits. Hydrochemical analyses of present‐day ground water indicate that oxidation of bedrock sulphide is an active process, and sulphuric acid may be the main agent driving carbonate dissolution in the area. A shallow mode of speleogenesis is thus proposed, in which sulphuric acid produced through the oxidation of sulphide beds within the carbonates controls cave initiation and development. Moreover, the geological situation of the area in an ancient stable passive margin precludes the possibility of deep‐seated sources of acidity. Under dry climate, due to the absence of recharge, solutional landforms will be largely subdued in the surface. Hypogenic processes, if present, are likely to predominate, producing a landscape characterized by a marked disparity in the comparative degree of development between surface and underground landforms. Rates of karst landform development have traditionally been analysed through a climatic perspective, runoff being the main controlling factor in promoting karst development. This view needs to be reassessed in the light of the growing awareness of the importance of climate‐independent processes related to hypogenic sources of acidity. Copyright © 2003 John Wiley & Sons, Ltd.
  • Editor: Chichester, UK: John Wiley & Sons, Ltd
  • Idioma: Inglês
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