Sulfur-Rich Caves of Southern Tabasco, Mexico

Abstract

Sulfur-rich karst springs that drain middle to Late Cretaceous carbonates in southern Tabasco, Mexico, contain elevated total dissolved solids with high chloride and either high sulfide or sulfate. The mostly meteoric waters circulate along intermediate-depth flow paths, interacting with Jurassic evaporites and then mixing with shallow-circulating rainwater to produce brackish, sulfur- and NaCl-rich spring waters. Several caves, notably Cueva de Villa Luz and Cueva de Luna Azufre near Tapijulapa, are developing from these waters. Both are fed by small, warm subterranean springs that release hydrogen sulfide and carbon dioxide at the water–air interface. These gases combine with water vapor in the air and moisture on cave walls to form acidic solutions, which enlarge the cave passages. Speleogenesis is aided by abundant chemoautotrophic microbes that facilitate oxidation and the production of acid solutions. Cave walls and ceilings display several distinctive colonies of these microbes, notably filamentous bundles (snottites) and biovermiculations. The organisms also reside in unusual mineral deposits, including sulfur folia, sulfur crusts, and gypsum paste. Pore fluids in these deposits and growths have very low pH despite their proximity to limestone walls. Speleogenesis appears to follow a three-step process: (1) an early sulfide-rich phreatic phase; (2) a sulfide-rich, vadose–phreatic phase of chemical alteration and mechanical stoping; and (3) a tertiary sulfide-depleted phase of epigenic speleogenesis. The second phase of development dominates speleogenesis in Cuevas de Villa Luz and Luna Azufre.