Cavernas em arenito da província espeleológica Altamira-Itaituba: dados espeleogenéticos com base no exemplo da Gruta das Mãos (PA), Amazônia, Brasil

Abstract

The caves in the Amazon region are mainly developed in non-carbonate rocks, particularly in sandstone and quartzites, volcanic and banded iron rocks and their weathered products. Few caves have been discovered in limestones. This has to do with the regional geological framework, with minor volumes of limestones, and foremost sandstones and weathered rocks in higher volume. This paper presents information regarding the Caverna das Mãos hosted in Devonian sandstones of the southern edge of the Amazon Basin in the Altamira Itaituba Speleological Province. The landscape is marked by plateaus in the southern highlands of the Amazon River valley. The Caverna das Mãos, in the Rurópolis (PA) district, has 942m of galleries following a main tectonic fracture system striking about 340oAz. The cave is drained by a juvenile fluvial flow responsible for relatively strong wall rock erosion. The presence of the cave is related to the mutual interaction of geological, geomorphological, hydrodynamic and climatic regional factors such as: (1) rock fracturing; (2) tectonic vertical changes of relief level; (3) water table fluctuations; (3) weathering of rocks by meteoric waters (arenitization); (4) erosion by high-pressure hydraulic flow along fractures (piping); and (5) late erosion under vadose conditions. The cave is stated to be under active development process, ingoing vadose regime, that cause strong influences on both the abiotic and biotic environment, and make difficult the conservation of archaeological records.