The local geologic history of Sistema Zacatón presents conditions favorable for karstification processes. Thick beds of limestone were deposited during the Late Cretaceous as the ancestral Gulf of Mexico covered the area (Enos, 1989, Goldhammer, 1999). Following aerial exposure and lithification, these limestone beds were uplifted during the late Laramide Orogenic event (40 ma), forming the Tamaulipas Arch, a 200-kilometer long domal anticline that makes up the Sierra de Tamaulipas. The axial trace of this structure is immediately west of Rancho La Azufrosa.  (BELOW)

By the late Oligocene, intrusive volcanic structures began to dissect the Sierra de Tamaulipas.  Next, the extensive volcanic field around Villa Aldama became active in the late Pliocene, producing basaltic lava flows throughout most of the Pleistocene (Camacho, 1993).    During the period of active volcanism, thick deposits of travertine were precipitated from springs discharging hydrothermal, mineralized water.

Surrounding geologic conditions allow for the development of this group of deep-seated subsidence shafts.    The surface expression results from the collapse of large underground cavities that dissolved from circulating groundwater (White, 1988).  Recharge from the Sierra de Tamaulipas moves down gradient through permeable limestone until reaching the Pleistocene volcanic extrusion east of Rancho La Azufrosa where a fracture zone has provided a line of structural weakness.  A groundwater-mixing zone occurs here as meteoric water comes into contact with hydrothermal, mineralized water adjacent to the volcanic extrusion (BELOW).  This zone provides an ideal environment for dissolution as the mixing waters adjust to chemically equilibrate with each other.

Local Grology Map

Hydrogeologic model of the area shows primary recharge for the Sistema Zacatón
groundwater comes from the Sierra de Tamaulipas.  As the water passes through
the Cretaceous limestone, it approaches the Pleistocene volcanic zone that likely
continues to be a substantial source of thermodynamic energy to drive
arge-scale dissolution

 LANDSAT image

Back tp previous page