Original paper

On the age of the Zapotal Sands of Southwest Ecuador

Bristow, C. Roger


Various sandstone outcrops of supposed Middle Oligocene age in the Santa Elena Península of Ecuador have been grouped together previously as the Zapotal Formation. Difficulties have been experienced in the past in reconciling the Upper Eocene microfauna obtained from some of these deposits with the Oligocene molluscs - the Hannatoma fauna. In reality rocks of two different ages have been mis-correlated: those of the Zapotal type locality and Posorja with its rich molluscan fauna are of Upper Oligocene age; those at Ancón Point, Mambra Point and Centinela Point are of Upper Eocene age. The Zapotal rocks and their true correlatives constitute the Zapotal Member, which forms the basal transgressive bed of the Tosagua Formation.