Processos de sedimentação e suas relações com a dinâmica de preenchimento clástico no Sistema de Cavernas Areníticas Legru (Porto União - SC)

Abstract

Caves developed in sandstones of the Botucatu Formation, at the transition between the Volcanic Plateau and the Sedimentary Plateau of the Paraná Basin, are frequently interpreted as paleoburrows associated with Quaternary megafauna. However, uncertainties remain regarding the genesis of these structures and the dynamics of the clastic sediments that fill their conduits. This dissertation aimed to characterize the clastic sedimentation processes responsible for the infilling of the Legru Cave System, located in Porto União, Santa Catarina State, Brazil, and to evaluate their implications for the geomorphological evolution of these cavities, based on speleometric, stratigraphic and sedimentological analyses, as well as Optically Stimulated Luminescence (OSL) dating. Six categories of primary clastic facies genesis were identified: (i) transitional flows between mud and hyperconcentrated flow (PMSm, AMSm, RMSm); (ii) cohesive debris flows stricto sensu (GMSm, GMm/SMD base); (iii) low-cohesion or partially washed debris flows with concentrated detrital input (MSGm, MSGs); (iv) collapse breccias (Gm); (v) shallow diluted mudflows (GMm/SMd top); and (vi) alternation of shallow mudflows of different densities, shallow non-cohesive debris flows (Gm lenses), diluted shallow mudflows and shallow mudflows (OMd and OMm lenses), configuring a small cavernous alluvial fan (LSMd [Gm+OMm/OMd]). Part of the facies records post-depositional diagenetic alterations, with three reducing and two oxidizing episodes in the main conduit and one reducing phase in the secondary conduit. OSL ages indicate sedimentation between approximately 107,000 and 16,000 years BP. Accumulation rates reveal slow and episodic sedimentation between MIS 5 and MIS 3 (0.0144 ± 0.0030 mm/year), with intensification between 32,000 and 16,000 years BP (0.077 ± 0.008 mm/year). It is concluded that cave infilling occurred episodically through high-density flows, controlled by the geological and hydrological dynamics of the sandstone, with megafauna acting as a secondary element during the Upper Pleistocene.