Diagenesis of Middle Tertiary carbonates in the Toa Baja Well, Puerto Rico

Abstract

The Toa Baja Well drilled in northern Puerto Rico to adepth of 2705 m (8872 ft.) penetrated over 550 m (1800 ft.) of Tertiary carbonates. The limestone-dominated portion of the well consists mostly of shallow-water backreef carbonates. Metastable carbonates have been either calcitized, dolomitized or dissolved. The pétrographie character of the Tertiary carbonates in the Toa Baja Well, and those reported by Monroe [1980], the cathodoluminescence petrography, and the stable isotopic compositions indicate that these carbonates were rapidly cemented in the marine environment (limiting compaction), that replacement of metastable carbonates by calcite and precipitation of sparry calcite took place mostly in meteoric diagenetic environments and dolomitization probably occurred in a meteoric-marine mixing zone. Given the history of numerous drainage systems that dissected the Tertiary carbonates throughout their depositional history [Monroe, 1980] and the repeated Cenozoic sea level oscillations [Monroe, 1980; Seiglie and Moussa, 1984], it is likely that alteration of metastable carbonates took place during lowstands. Interstratified fluvial deposits suggest the continued influence of meteoric fluids in local highlands [Monroe, 198O].