Reply to the Comment on “Sandstone caves on Venezuelan tepuis: Return to pseudokarst?”

Abstract

In Aubrecht et al. (2011) we brought new data showing that the arenitic caves in the Venezuelan tepuis did not necessarily originate through quartz cement dissolution (‘arenization’) but the main portion of the caves originated because of poor lithification prior to erosion. An additional important process is lateritization which is responsible for at least 30% of the caves' volume. Sauro et al. (2012) in their comment support the ‘arenization’ theory (quartz cement dissolution) and provide several arguments against some points of our research. Their main objections and arguments relate to the following topics: 1) the validity of the arenization theory, 2) the origin and importance of the ‘finger-flow’ pillars, 3) the importance of the Schmidt hammer measurements and, 4) metamorphism of the Matauí Formation. In our reply we present further documentation that:1)The quartz cement dissolution theory of cave evolution was far less documented petrographically than the new theory presented by us. Although the presence of quartz dissolution is evident, there is no current evidence that it is widespread or that it plays a trigger role. Many of the presented examples of corrosion on quartz grains could have been caused by local alkalization. In addition, the hydrogeochemical data presented in the comment to support the ‘arenization’ theory do not in fact contradict our speleogenetic interpretations.2)‘Finger-flow’ pillars are speleogenetic indicators and not speleogenetic factors. Their absence in some caves provides no evidence against our theory.3)Schmidt hammer measurements only objectivize the data on contrasting hardness in the Matauí Formation beds. They do not say anything about the origin of this difference.4)The arguments of Sauro et al. (2012) involve the metamorphic overprint of the Matauí Formation shown by the presence of pyrophyllite and quartz mobilizations. Because quartz mobilization also occurs in hypergenic conditions, it may be neglected as a metamorphic indicator. Pyrophyllite is mentioned as a metamorphic indicator in the literature (anchizone to epizone) but it does not explain why there is still a vast quantity of kaolinite that did not undergo this reaction in the soft arenitic beds. There is an evidence that pyrophyllite may originate at lower temperatures. Some phases of the alumino-silicate mineral phases existing at atmospheric pressure and 25°C temperature show that H4SiO4 concentration is a critical factor in kaolinite/pyrophyllite transition. An increase in this concentration can theoretically cause transformation of kaolinite to pyrophyllite without increased temperature or pressure.