EGU21-457
https://doi.org/10.5194/egusphere-egu21-457
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Silicification and mechanical stratigraphy control on flow pathways and hypogenic karst development in carbonate rocks

Luca Pisani1, Marco Antonellini1, Francisco Hilario Bezerra2, Augusto Auler3, and Jo De Waele1
Luca Pisani et al.
  • 1University of Bologna, Department of biological, geological and environmental sciences, Bologna, Italy
  • 2Universidade Federal do Rio Grande do Norte, Departamento de Geologia, Natal, Brasil
  • 3Instituto do Carste, Brasil

Fractured and karstified carbonate rocks are important targets for the hydrocarbon exploration industry as they usually represent very productive reservoirs. Most of the karst features in carbonate reservoirs are the result of rising fluid flow in deeply buried settings (i.e., hypogenic karst), whose origin and solutional efficiency are not connected to surface processes. Hypogenic conduits are often intercepted by drilling during hydrocarbon exploration, and their occurrence is sometimes associated with high-permeability horizons characterized by intense silicification. Silicification is a common diagenetic process in sedimentary basins, in which Si-rich fluids modify textures, mineralogy, and petrophysical properties of the host rock.  

We present the preliminary results of a multidisciplinary study performed in a cave developed within a mixed carbonate-siliciclastic succession of the Salitre Formation, in Northeastern Brazil (Calixto Cave). This cave offers the opportunity to study an accessible and extensive (more than 1 km long) conduit system associated with silicification. We performed a detailed stratigraphic and structural characterization of the sedimentary sequence in the cave, identifying different SiO2 facies and textural associations. Furthermore, we described cave geometry and pattern by topographic and morphometric observations using terrestrial laser scanner 3D models. Petrographic observations at the optical microscope were complemented with porosity-permeability analyses on rock plugs, XRD, XRF, and SEM-EDX analyses to highlight composition and petrophysical properties of the different lithostratigraphic units in the cave.

We found that silicification and mechanical stratigraphy determined the formation of high-permeability and seal units, whose distribution was fundamental for controlling paleo-flow pathways, karstification, and the spatial-morphological organization of the resultant conduit system. Cave morphologies, evidence of silica dissolution, crystalline quartz deposits and their associated paragenesis suggest that the speleogenetic phase contributing to the main karst formation happened in deeply buried hypogenic conditions, involving rising alkaline fluids probably of hydrothermal origin.

How to cite: Pisani, L., Antonellini, M., Bezerra, F. H., Auler, A., and De Waele, J.: Silicification and mechanical stratigraphy control on flow pathways and hypogenic karst development in carbonate rocks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-457, https://doi.org/10.5194/egusphere-egu21-457, 2021.

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