Focused methane migration formed pipe structures in permeable sandstones: Insights from uncrewed aerial vehicle?based digital outcrop analysis in Varna, Bulgaria

Focused fluid flow shapes the evolution of marine sedimentary basins by transferring fluids and pressure across geological formations. Vertical conduits may form where localized overpressure breaches a cap rock (permeability barrier) thereby transports overpressured towards shallower reservoirs or surface. Field outcrops an Eocene system at Pobiti Kamani Beloslav Quarry (ca 15 km west Varna, Bulgaria) reveal large carbonate-cemented conduits, which formed in highly permeable, unconsolidated, sands northern Tethys Margin. An uncrewed aerial vehicle with RGB sensor camera produces ortho-rectified image mosaics, digital elevation models point clouds two kilometre-scale outcrop areas. Based on these data, field observations petrological analysis rock/core samples, fractures vertical were mapped analyzed centimetre accuracy. The results show that both comprise several hundred (pipes), oriented perpendicular to bedding, least seven bedding-parallel calcite cemented interbeds differ from hosting sand formation only their increased amount cementation. carbonate precipitation likely initiated around areas focused flow, methane entered underlying fractured subsurface. These first carbonates outer walls pipes continued grow inward, leading self-sustaining self-reinforcing flow. results, supported literature-based carbon oxygen isotope analyses carbonates, indicate ambient seawater advected fresh/brackish water involved microbial oxidation. Similar structures also modern settings advects into overlying sand-dominated formations, has wide implications for understanding how focusing works broad consequences migration water, oil gas.