Speleological characterisation of the Aspargo Cave, Pains, Minas Gerais, Brazil

It is well established that the inventory of geosites to preserve geodiversity is the first step in any geoconservation strategy, regardless of the size of the area under analysis. In Brazil, there are efforts to inventory geosites, but the main challenge is its territory size. Another significant difficulty for the inventory of karst geosites in Brazil is that the territory has not yet been continuously and homogeneously properly investigated. In the case of the Arcos-Pains Karst Region, located in the central-western portion of Minas Gerais, many geosites were inventoried by Timo (2019; 2020), especially those with educational and scientific value at a regional level. It was done basically to support establishing a geoconservation strategy for the region. One of the sites was classified as a geosite of national relevance, named the Aspargo Cave. The cave and its surroundings have classic representative features of the region's karst. On the cave walls, one can identify folds that conditioned the development of the main conduit, showing traces of the speleogenetic processes.

Initially, the authors did a bibliographic review, and then field works for the measurements. The speleological characterisation was carried out from the analysis of the physical aspects of the cave, such as its insertion in the landscape, morphology, lithology, structures, hydrology, description of sedimentary and chemical deposits, all in addition to the evaluation of the speleogenetical processes. The geological and structural characterisation was done by describing the lithotypes and analysing the attitude of the observed structures. A Brunton-type compass was used, with a magnetic declination of -22°. As for the notation of attitudes, the Dip Direction/Dip method was used. For planar structures, the azimuth of the dip direction/dip angle was measured, and for linear structures, the slope direction/fall angle was measured.

The cave is developed in a laminated limestone with tight folds, and the opening of the single conduct is conditioned along the fold axis and short flank of the main structure. A wider room in the distal portion, with a high ceiling, ends in an expressive depression with a ponor. Speleothems occur uniquely in this hall, with a profusion of flowstones, curtains and stalactites, in addition to stalagmites, columns, helictites, gypsum flowers and cave needles. As for the clastic deposits, one can identify many autogenic fragments sized pebbles to angular blocks in the initial portion, indicating a dismantle of the cave. In the distal hall, the floor is covered with allogeneic clay, brought to the cave in periods of rain, when the place is flooded by water that enters through the cave ponor at its end. In the portion of the cave where the flood does not reach nowadays, there is a trace that sediments completely obstructed the distal hall. With a change in the sedimentation dynamics, the sediments were excavated, leaving evidence of the stages of speleogenesis in the cave. Further research is planned to prove the connection between the cave, the lake system and the region's base level.