The role of Stylolites as Proto-Karsts in Speleogenesis

Karst features are often linked to fractures and faults, considered the main pathways for water circulation and dissolution. Our study shows this view is incomplete, highlighting the overlooked role of stylolites, serrated seams formed under compressive stress, as starting points for karst. Fieldwork in Apulia (Southern Italy), combined with laboratory analyses, reveals that stylolites can initiate porosityguide fluid flow, then acting as proto-karst structures. They concentrate insoluble minerals such as clays, micas, and oxides that, under the right conditions, promote localized dissolution. Microscopic analyses of 15 samples show higher porosity within stylolites than in the host rock, with pores often clustering at stylolite–matrix boundaries. This suggests that what begins as a sealing surface can later evolve into a porous interface once stress regimes change or insoluble residues are removed. Mineral re-precipitation and localized dolomitization confirm past fluid circulation along stylolites. Field surveys reinforce these findings: in Apulia, over 80% of stylolites display dissolution features, compared with far fewer in faults or fractures. Orientation data from caves such as Grave Rotolo show main passages often align with stylolites rather than other tectonic structures. We propose a three-stage model of stylolite evolution: (1) sealed seams enriched in insoluble residues, (2) microporosity nucleation under favorable conditions, and (3) growth of interconnected pores into early conduits. This model shows stylolites can shift from barriers to fluid pathways. Recognizing them as proto-karst has practical implications for hydrogeology and carbonate reservoir management.