Abstract Microfacies analysis is a mature and sophisticated set of procedures for solving a variety of stratigraphic problems. One of the most important of these problems is the identification and definition of surfaces for stratigraphic correlation. There is virtually no end to the list of potential correlative surfaces that can be defined by microfacies analysis, particularly when used in conjunction with available mathematical techniques for the quantification of geologic data. Such procedures are particularly useful in stratigraphic units characterized by complex fades relationships, such as reef-associated paleoenviron-ments. The utility of microfacies analysis in evaluating potential sites for nuclear power plants and other engineered structures is exemplified by studies performed in conjunction with the NORCO-NP-1 nuclear power plant site in northern Puerto Rico. The definition of three microfacies (Globigerinidea, Nummulites cojimarensis, and A mphistegina spp., in ascending order) within the Quebradillas Limestone (Tertiary) at the NORCO-NP-1 nuclear power plant site demonstrated that two surfaces along which important natural gamma ray peaks occur are strati-graphically controlled rather than being controlled by dislocation surfaces, unconformities, jointing, or karstification. This was accomplished by showing that the surfaces defined by the gamma ray peaks are parallel or subparallel to two deposi-tional surfaces, the base and top of the N. cojimarensis microfacies, within the apparently massive carbonates of the Quebradillas Limestone.

At the close of the middle Eocene, most of the strong orogenic deformation in Cuba had occurred, and the general distribution of the pre–upper Eocene structures and stratigraphic units was essentially as it is now. The younger Tertiary sediments began to accumulate over the now-essentially inactive, largely peneplained, submarine mountain chain, reflecting some large-scale deformation that included folding and faulting. The overall movements during the remainder of the Tertiary have been of a slow, continuous uplift, with much of Cuba emerging by the Miocene. The younger Tertiary sedimentation consisted mostly of the filling of topographic depressions, although erosion of uplifts and filling of subsiding areas also occurred. It should be noted that Gulf Oil, with the exception of a few areas in central Cuba, did little work on the younger Tertiary; therefore, much of the following is derived from published information, namely, Iturralde-Vinent (1977 , 1988 ), Jakus (1983) , and Fernandez et al. (1987) . As shown in Figure 148 , the post–middle Eocene will be described according to the following areas: Northern coast = Havana to Oriente Provinces Southwestern basin = Los Palacios Basin, Habana-Matanzas, and western Las Villas South-central basin = Central Depression (Gulf of Ana Maria) Southeastern basins = Guanacayabo-Nipe Basin, central syncline, Guantanamo depression, and southern coast (only the stratigraphic unit of the Oriente southern coast will be listed). A characteristic of most upper Eocene and later sediments is their richness in fossils, mostly large and small