Highlights
- Infill dominated by high-density sediment flows
- Mainly allochthonous sediments derived from slopes
- Dynamics since ~107 kyr, with aggradation-incision cycles
- Discontinuous and heterogeneous sediment storage
- Results contradict classical models of fluvial caves
Abstract
Clastic sedimentation in sandstone caves remains poorly understood, particularly in systems with tubular morphology. This study investigates sedimentation, reworking, and sediment removal dynamics in the Legru Cave system, southern Brazil, based on the integrated analysis of sedimentary facies, microstructures, and microfeatures, combined with optically stimulated luminescence dating. The results indicate that conduit infilling is dominated by high-density flows, including cohesive debris flows, partially diluted multiphase flows, and flows with intermediate rheological behavior between mud flow and hyperconcentrated flow, in addition to shallow flow alternations. Sediment supply is predominantly allochthonous, related to hillslope-derived material delivered by overland flow and mud flows, evolving into high-density conditions, with a subordinate contribution of autochthonous material derived from roof collapse. The chronology indicates that sedimentary dynamics date back to the Late Pleistocene (~107 kyr) and are characterized by alternations between episodic aggradation, prolonged depositional hiatuses, sediment removal by incision, and phases of quiescence associated with redox-driven diagenesis controlled by water table oscillations. In contrast to classic models based on low-density fluvial flows, the results demonstrate that sediment infilling in tubular sandstone caves is governed by high-energy, gravity-driven processes and strongly controlled by hillslope sediment supply and hydrological connectivity. The system exhibits highly dynamic behavior, with discontinuous sediment storage in time and heterogeneous storage in space, being controlled by hydrological connectivity and episodic events. These findings contribute to refining facies-based interpretations in cave systems by emphasizing the role of high-density processes in clastic cave sedimentation. The results enable the proposal of a conceptual framework for the sedimentary dynamics of the studied system, based on cycles of sediment infilling and incision, which may serve as a reference for investigations in similar environments and for the future development of depositional models in tubular sandstone caves.
DOI
https://doi.org/10.5038/1827-806X.ijs2611
Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.
Recommended Citation
Bianchini, L., Paisani, J.C., 2026. Sedimentary dynamics in tubular sandstone caves, Porto União, Southern Brazil. International Journal of Speleology, 55(2), ijs2611. https://doi.org/10.5038/1827-806X.ijs2611
Supplementary information
