Hypogenic contribution to speleogenesis in a predominant epigenic karst system: A case study from the Venetian Alps, Italy

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• 作者：Nicola Tisato^a ; ^{nicola.tisato@erdw.ethz.ch} ; Francesco Sauro^b ; ^{francesco.sauro2@unibo.it} ; Stefano M. Bernasconi^a ; ^{stefano.bernasconi@erdw.ethz.ch} ; Rolf H.C. Bruijn^a ; ^{rolf.bruijn@erdw.ethz.ch} ; Jo De Waele^b ; ^{jo.dewaele@unibo.it}
• 关键词：Calcarenites ; Pyrite ; Hypogenic speleogenesis ; Sulfur isotopes ; Karst
• 刊名：Geomorphology
• 出版年：2012
• 期刊代码：31_0169555x
• 类别：soc
• 出版时间：15 May, 2012
• 卷：151-152
• 期：Complete
• 页码：156-163
• 文件大小：2178 K

摘要

Buso della Rana and Buso della Pisatela are two karstic caves located in north-east Italy. They are part of the same karst system and are developed in the Castelgomberto calcarenitic marine sediments, which were deposited in a shallow Caribbean-type sea during the Eocene. The Buso della Rana-Pisatela system developed mostly at the contact between the Castelgomberto calcarenite and underlying volcanic rocks. The system of caves is ~ 37 km long and has only three entrances, two of which are semi-artificial. The overlying karst plateau is not directly connected to the Buso della Rana-Pisatela system and, with the exception of one deep abyss, exhibits a rather poorly developed karst. This is unexpected considering the presence at depth of such a large and long cave.

Gypsum (CaSO₄路2H₂O) has locally been observed on the walls of the Buso della Pisatela cave. Energy dispersive X-ray spectroscopy (EDS), performed with a scanning electron microscope (SEM), reveals the presence of sulfur-bearing minerals within the host rock. Gypsum was formed by oxidation of these minerals as indicated by negative 未³⁴S values. The oxidation of sulfide minerals forms a sulfuric-acid solution that dissolves the Castelgomberto calcarenite and, once it is oversaturated in calcium, precipitates as gypsum.

The lack of well-developed karst on top of the plateau and the analyses suggest that the formation mechanisms for the Buso della Rana-Pisatela system differ from classical epigenic speleogenesis.

The 鈥減yrite-effect鈥?has been recognized in other caves and described in literature. In our case pyrite is responsible of two hypo-speleogenetic processes: i) the dissolution of a portion of the host rock and ii) the enlargement of the karst voids as a consequence of the haloclastic effect.