Characteristics and genesis of hypogenic karsts in carbonate successions

Abstract

Multiscale karst systems, typically below seismic resolution, are important contributors to permeability but also provide significant challenges in drilling operations and in flow simulations. A substantial portion of subsurface karsts is of hypogenic origin, that is, is associated with upward movement of chemically aggressive fluids. The Morro Vermelho Karst System and Cave developed within Proterozioc shallow water carbonates and is an inspiring analog for buried hypogenic karsts. MVKS formed in association with a regional strike-slip fault. In an initial stage, deformation in the “softer” carbonates overlying more rigid quartzites and basement was accommodated by a 100s of m wide semi-ductile shear zone. Wholesale dolomitization took place and numerous dolomite-filled veins formed. With progressing strike-slip, the fault propagated upward creating an anticline parallel to the fault zone, causing the development of m-long extensional fractures, the arrival of SiO2 rich fluids in the karts and, eventually, the formation of the cave. Vertical fracture corridors and/or faults capturing deep, generally layer parallel flow are present in different settings, from foredeeps to rifted margins and are primary candidates for widespread hypogenic karst development.