Spatial heterogeneity of burial-related fracture networks controls compartmentalized fluid flow in volcano-sedimentary sequences

Fracture networks fundamentally control subsurface fluid flow in sedimentary basins, yet the characteristics and controls of burial-related fractures that developed prior to localized tectonic deformation remain poorly understood in sedimentary rocks with marked volcanic input. We investigate fracture network heterogeneity in a Cretaceous volcano-sedimentary sequence from Wi Island, South Korea, which displays negligible tectonic deformation. Through integrated sedimentary petrological analyses and geometrical/topological fracture characterization of outcrop exposures, we demonstrate distinct spatial variations in fracture intensity and permeability anisotropy across different stratigraphic positions. Fracture intensity correlates strongly with lithological parameters, reaching maximum values at lithological boundaries with high brittle mineral content, and showing elevated intensity in areas with high matrix content and cryptocrystalline texture compared to other stratigraphic levels. Calculated permeability characteristics reveal compartmentalized, anisotropic fluid flow patterns that vary with stratigraphic position. These bed-confined fracture networks predominantly provide lateral connectivity within individual layers while maintaining vertical sealing capacity across fine-grained layers, thereby preventing cross-layer fluid migration. This architecture of fracture networks provides critical insights for predicting initial permeability structure in volcano-sedimentary basins before tectonic modification.