The cretaceous Aguas Buenas and Río Matón limestones of southern Puerto Rico

Abstract

The Aguas Buenas and Río Matón Limestones occur as small lenses along two stratigraphic horizons in the volcaniclastic sequence of southern Puerto Rico. The Aguas Buenas suite forms the base of the coarsely volcaniclastic Torrecilla Breccia (probably mid Cretaceous), and the Río Matón suite forms the base of the distal volcaniclastic rocks of the Robles Formation (probably mid- to Upper Cretaceous). The limestones are biosparrudites and biomicrudites in which the principal allochems are pelecypods (rudists and oysters) plus variable amounts of unidentified molluscs, echinoderms, and red algae. All rocks were deposited in shoal environments, but reef frameworks and extensive back-reef deposits are absent. Thus, the limestones appear to have developed on either: 1) small, isolated prominences constructed by volcanism from a deep-water base; or 2) banks temporarily maintained at sea level as underlying subaerial volcanic suites subsided through sea level when the locus of active volcanism shifted away from the area. The covering of the Río Matón shoals by distal subaqueous materials appears to have been caused by rapid subduction possibly associated with plate reorganization in the northeastern Caribbean.