SPELEOLOGICAL AND SEDIMENTARY CHARACTERIZATION OF A CAVE IN THE SERRA SÃO JOSÉ QUARTZITE MASSIF, MINAS GERAIS

Abstract

Caves are considered natural traps for sediments and other external materials that are usually transported and deposited inside them. This material can be accumulated in a relatively stable environment for many years, which provides suitable conditions for sedimentological and paleoenvironmental studies. Stratigraphic and chronological studies of sediments present in quartzite caves can contribute to paleoenvironmental reconstitution, yet those are scarce. This study aimed to map the Galo Cave, located in the dip slope of the Serra São José quartzite massif (MG) as well as to characterize the cave sediment, physically, chemically and chronologically. The cave was mapped and the 2.5 m long, 0.47 m high and 0.5 m thick sediment package was described in situ, based on morphological attributes, and then sampled. Seventeen samples were collected and characterized by granulometric, geochemical and organic carbon content analyses. Three of these samples were selected for radiocarbon dating according to their position in the package (base, center and top) and their organic carbon content. The results were used in principal component analysis for the joint visualization of the variables (laboratory analysis results) and observations (sampled layers). Galo Cave was formed by meteoric waters and its morphology was influenced by the NNW/SSE faulting and the hardness difference between the component rocks (quartzite and phyllite). The sediment package was deposited on a convex curve of the northern side of the cave, where the water flow meets an obstacle, slowing its velocity and favoring sedimentation, filling the space from the base to the ceiling. The morphology, granulometric and chemical compositions of the sediments and the radiocarbon age vary throughout the package, evidencing oscillations in the intensity and duration of precipitation events, which may be associated with Holocene climatic changes.