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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >The influence of bedrock-derived acidity in the development of surface and underground karst: evidence from the precambrian carbonates of semi-arid northeastern brazil
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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

机译：基岩衍生的酸度对地表和地下岩溶发育的影响：来自半干旱东北巴西的前寒武纪碳酸盐的证据

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摘要

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 semiarid climate. The caves in the area display many morphological features characteristic of deep-seated hypogenic caves, such as lack of relationship with the surface, ramiformetwork 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 of 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.
机译：巴西东部Campo Formoso地区的前寒武纪Una Group碳酸盐岩开发了非常广泛的洞穴系统。相反，该地区基本上没有明显的地表喀斯特地貌，这是半干旱气候所期望的。该地区的溶洞表现出深层的假山溶洞的许多形态特征，例如与地表的关系，网状/网状图案，通道横截面的突然变化和河流沉积物的缺乏，但没有证据表明垂直通道标志着酸性水的上升路径，也没有大量的酸性粘土矿床石膏。对当今地下水的水化学分析表明，基岩硫化物的氧化是一个活跃的过程，硫酸可能是驱动该地区碳酸盐溶解的主要因素。因此提出了一种浅层的洞穴形成方式，其中通过碳酸盐中硫化物床的氧化而产生的硫酸控制着洞穴的形成和发展。此外，该地区在古代稳定的被动边缘地区的地质情况排除了深层酸度来源的可能性。在干燥气候下，由于缺乏补给，固溶地貌将在地表大部分被制服。如果存在低速过程，则很可能会占主导地位，从而形成一种以地表和地下地貌的相对发展程度明显不同为特征的景观。传统上是从气候角度分析岩溶地貌发育速率的，径流是促进岩溶发育的主要控制因素。鉴于人们越来越认识到与假性酸度来源有关的与气候无关的过程的重要性，需要重新评估这种观点。

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