Evolution of porosity and clay mineralogy associated with chemical weathering of black shale: A case study of Lower Cambrian black shale in Chongqing, China

摘要: Abstract This work aimed to evaluate the evolution of pore networks and clay mineral in black shale weathering systems Chongqing, China. The pore-size distributions, relationships between fractal dimensions minerals, pathways were evaluated for three profiles, A, B, C, which characterized as weak, weak moderate, moderate intense based on Chemical Index Alteration. It was found density decreased, porosity specific surface area increased with decreasing depth during weathering. largest diameter peak a distribution graph shifted further right degree increased. Micro-transition pores ( 1 μm) dominated saprock regolith zones. dimension micro-transition positively correlated pyrite carbonate content, but negatively secondary content. By contrast, macropores content These indicate that at became smoother rougher Inherited micas, including illite, predominated fractions along transects proceeded. pedogenic minerals (i.e., smectite, vermiculite, kaolinite, mixed-layer minerals) minor components Smectite formation likely due direct transformation from mica or illite under strongly acidic conditions. A second possibility is proceeded through intermediates, i.e., mica-smectite/illite-smectite mica-vermiculite/illite-vermiculite. stages mica/illite → mica-smectite/illite-smectite mica-vermiculite/illite-vermiculite → “chlorite” (including hydroxy-interlayered vermiculite?, chlorite?) → smectite → kaolinite → gibbsite. study revealed geometry depends transport-limited solutions facilitate breakdown formation. controlled by environment duration.