BENTHIC FORAMINIFERAL RECORD IN THE MIOCENE-PLIOCENE SEQUENCE OF THE AZUA BASIN, DOMINICAN-REPUBLIC

The Miocene-Pliocene sedimentary sequence in the Azua basin, Dominican Republic, contains rich assemblages of benthic foraminifera. Principa l Components Analysis of the faunal data aided in the recognition of e ight environmentally significant species associations in the Sombrerit o, Trinchera, Quita Coraza, and Arroyo Blanco Formations. The Lower-Mi ddle Bathyal assemblage (B1) includes Cibicides wuellerstorfi, Pleuros tomella alternans, Bolivina paula, B. sp. A, B. sp. C, B. pisciformis, B. marginata multicostata, and B. inflata. A Bolivina-dominated assem blage (B2) suggests low-oxygen bottom-water conditions and is characte rized by high abundances of Bolivina paula, B. plicatella mera, and B. sp. A. The Middle-Upper Bathyal assemblage (B3) includes Oridorsalis umbonatus, Hoeglundina elegans, Bulimina socialis, Sigmoilopsis schlum bergeri, Bermudezinella riveroi, Gyroidina trincherasensis, Uvigerina peregrina, Cibicidoides pachyderma bathyalis, Cibicides wuellerstorfi and Recurvoides trincherasensis. The Bathyal-Neritic Boundary assembla ge (B4) is defined by Bolivina minima, Cassidulina norcrossi australis , Gyroidina regularis, Gyroidina umbonatus, Bolivina alata, Uvigerina auberiana, Uvigerina parvula, Siphonina pulchra, Melonis affinis, Cibi cidoides barnetti and Uvigerina azuana. The Middle-Outer Neritic assem blage (N1) includes Cassidulina subglobosa, Cassidulina carinata, Cibi cidoides pachyderma sublittoralis, Reussella spinulosa, Gyroidina umbo nata, Valvulineria mexicana, Melonis affinis, Angulogerina jamaicensis and Hanzawaia sp. A. The Inner Neritic assemblage (N2) is defined by Haynesina depressula, Buliminella elegantissima, Rosalina concinna, Re usella spinulosa, and Ammonia parkinsoniana typica. The Stressed Nerit ic assemblage (N3) is characterized by Bolivina sp. K, Cancris sagra, Bolivina lowmani, Gavelinopsis sp. A and Cibicidoides pachyderma subli ttoralis. The Carbonate shelf assemblage (N4) is dominated by Cibicide s lobatulus and Asterigerina carinata. Cluster analysis reveals seven sample associations that correspond almost directly to foraminiferal z ones described in the Azua basin by Bermudez (1949); their paleoenviro nmental significance is reflected by sample factor scores: Sombrerito (lower to middle bathyal), Basal Trinchera (middle bathyal), Gaspar (m iddle to upper bathyal), Lower Bao (upper bathyal), Upper Bao (upper b athyal to outer neritic), Quita Coraza (inner to middle neritic), and Arroyo Blanco (inner neritic). Placed within the biostratigraphic fram ework for the basin, these benthic foraminiferal trends indicate migra tion of paleoenvironments toward the Caribbean during the Miocene and Pliocene. This parallels a similar time-transgression of lithofacies a nd appears to represent rapid filling of a ''ramp valley'' basin by se diments derived from the uplift of the nearby Cordillera Central, coin cident with the activation of the Hispaniola restraining bend.