The Gulf of Batabano, on the southwest coast of Cuba, is about 180 miles long and 90 miles wide. The floor of the Gulf is a shallow submerged platform area with water depths ranging between 0 and 40 feet. A precipitous declivity, a narrow structural trend, bounds the southern edge of the platform separating shoals of the platform from deep-water facies on the south.

On the platform, foraminiferal abundance and diversity are greatest in the northern and western areas of Batabano Bay. Although ostracodes are common in many of the samples, foraminifera are from 10 to more than 50 times as abundant as ostracodes throughout most of the bay. General biofacies patterns include abundant miliolids in perimeter areas of the bay, an Elphidium facies in the central inner area of the bay, and an Archaias facies in the southeastern area of the bay. Areas of mud matrix characterize the first two biofacies, whereas non-skeletal grains correlate with the Archaias facies.

Detailed and specific dominant foraminiferal faunas include: (1) a brackish Ammonia beccarii tepida (Cushman) assemblage in the small embayment in the northeastern part of the bay; (2) a transitional miliolid-Elphidium facies in much of the inner bay area; (3) an Archaias high-energy biofacies in the southeastern outer part of the bay associated with coarse sediment, relatively stable salinity values, and a rather high oxygen content; (4) a Discorbis-miliolid low-energy assemblage in the southwestern outer part of the bay in areas of mud matrix; and (5) a reef tract facies composed of Amphistegina lessonii d'Orbigny, Asterigerina carinata d'Orbigny, and Rotorbinella rosea (d'Orbigny) which are associated with coarse well-sorted sediments, strong currents, and a high oxygen content. Pl nktonic foraminifera do not occur in the platform biofacies.

Deep-water cores off the Batabano platform show high percentages of displaced platform foraminifera within the benthic faunas, more than 80 per cent planktonic foraminifera in deeper water cores, foraminiferal numbers in the thousands, and rare reworked Miocene foraminifera.

Transgressive and regressive phenomena produce an intercalation of different types of biofacies demonstrating contemporaneity; also, faunal mixing by transportation and displacement provide a degree of correlation between what would otherwise be totally dissimilar biofacies.

Lagoonal areas and the embayment behind the reef-complex have an abundance of miliolids and other smaller foraminifera in fine-grained sediments; in these back-reef areas, an increase in larger foraminifera suggests the probable direction toward the reef-complex and improved reservoir potential in carbonate sediments. Fore-reef deposits exhibit progressively greater abundances of planktonic foraminifera and mixed deep and shallow types of foraminifera with increasing depth of water. Increasing percentages of displaced larger foraminifera in basin deposits may identify basin slopes leading up to fore-reef deposits. Both reef deposits and displaced sands may provides significant reservoir beds for petroleum.

Rapid lateral transitions from shallow-water to deep-water facies suggest the existence of prominent synchronous structural trends.