APTIAN–ALBIAN PLANKTIC FORAMINIFERA FROM DSDP SITE 364 (OFFSHORE ANGOLA): BIOSTRATIGRAPHY, PALEOECOLOGY, AND PALEOCEANOGRAPHIC SIGNIFICANCE KARLOS G. D. KOCHHANN 1,4 ,EDUARDO A. M. KOUTSOUKOS 2 ,GERSON FAUTH 1 AND ALCIDES N. SIAL 3 ABSTRACT This work presents a taxonomic, biostratigraphic and paleoecological study of planktic foraminifera recovered from the Aptian–Albian carbonate-dominated succession of Deep Sea Drilling Project (DSDP) Site 364, located in the Kwanza Basin (offshore Angola). Twenty-nine planktic foraminiferal species were identified, enabling the identification of late Aptian–late Albian biozones, from the Hedbergella trocoidea Zone to the Pseudothalmanninella ticinensis Zone. A major unconformity from the latest early–earliest late Albian was identified in core 31, with the Microhedbergella rischi Zone in direct contact with the Pseudothalmanninella ticinensis Zone. The recovered assemblages are characterized by open marine epipelagic dwellers and indicate predominant mesotrophic environmental conditions throughout the studied stratigraphic succession. Aptian planktic foraminiferal assemblages have a tropical/subtropical paleobiogeographic affinity, supporting a surface-water connection between the central proto-Atlantic Ocean and the northern South Atlantic Ocean (north of the Walvis Ridge-Rio Grande Rise) by the late Aptian. Trends in isotopic values for d 13 C suggest a late Aptian age (Globiger- inelloides algerianus Zone) for the stratigraphic interval from core 42 to ,core 37, where age-diagnostic foraminiferal species are missing. Black shale levels in cores 42–39 are probably the local expression of the ‘‘late Aptian anoxic event.’’ INTRODUCTION The Aptian–Albian is a unique time interval in Earth’s history due to the common occurrence of organic-rich sedimentary rocks, which are frequently related to oceanic anoxic events (OAEs; e.g., Arthur and Premoli Silva, 1982; Jenkyns, 1995; Jenkyns and Wilson, 1999). These anoxic events are characterized by the widespread occurrence of black shales and drastic shifts in the carbon isotope ratio (Leckie and others, 2002), leading to major reorganizations in the marine ecosystem, including planktic foraminifera (e.g., Leckie, 1984; Koutsoukos and others, 1991b; Premoli Silva and others, 1999; Leckie and others, 2002). Although events in this time interval are highly relevant for understanding coupled global paleoceanographic and paleoclimatic changes, stratigraphic problems may hamper their accurate investigation. For instance, no section has been chosen yet for a Global Boundary Stratotype Section and Point (GSSP) at the base of the Albian stage, although several candidates have been proposed (e.g., Kennedy and others, 2000; Hancock, 2001), including a promising sequence at Pre ´-Guittard (Vocontian Basin, SE France; Petrizzo and others, 2012). The main reason for this indefiniteness is the elevated degree of endemism of the ammonoid assemblages, commonly used to define Creta- ceous stages boundaries (Birkelund and others, 1984). This problem causes several discrepancies between age assign- ments when biostratigraphic schemes based on different fossil groups are applied to the same sedimentary succession (e.g., Bolli and others, 1978), making it difficult to study the paleoceanographic events mentioned above (e.g., OAEs). The objectives of this study are to present the taxonomy and biostratigraphy of the Aptian–Albian planktic forami- nifera recovered from Deep Sea Drilling Project (DSDP) Site 364 (Fig. 1), Kwanza Basin (offshore Angola), and to use their distributions to infer paleoecological aspects of the studied fauna and their paleoceanographic significance. Despite the generally poor preservation of the studied material, poor core recovery and absence of some tropical/ subtropical biostratigraphic markers, the studied fauna remains relevant for a better understanding of the Aptian– Albian interval and associated environmental conditions of the northern South Atlantic Ocean (north of the Walvis Ridge-Rio Grande Rise). GEOLOGICAL SETTING Se ´ranne and Anka (2005) proposed the physiographic subdivision of the African margin into the equatorial western African margin (with the occurrence of evaporitic and carbonate units in the Cretaceous) and the southwest African margin (dominated by clastic deposition in the Cretaceous), which are divided by the high-standing Walvis Ridge (Fig. 1). Historically, the entire basin and continental shelf of the equatorial western African margin has been called the Angola Basin, as it is the largest depression in the northeastern South Atlantic Ocean. Its physical isolation by the Walvis Ridge was inherited from its origin in the Barremian–Aptian (cf. Se ´ranne and Anka, 2005), allowing the formation of a thick layer of evaporites that exceeds 3 km in some locations. In the context of the Angola Basin, recent studies proposed the recognition of the Kwanza Basin, in which DSDP Site 364 is located (cf. Brownfield and Charpentier, 2006), classified as an Atlantic-type marginal sag basin with the deposition of evaporitic units during the Aptian (e.g., Clifford, 1986; Brownfield and Charpentier, 2006). The Kwanza Basin is bordered to the north by the Ambriz Arch, to the south by the Benguela High, to the east by the edge of the sedimentary basins and to the west by the 4-km bathymetric depth. 1 ITT FOSSIL—Instituto Tecnolo ´ gico de Micropaleontologia, Uni- versidade do Vale do Rio dos Sinos, Bloco 6K, Av. UNISINOS, 950, 93022-000, Sa ˜ o Leopoldo, RS, Brazil 2 Institut fu ¨ r Geowissenschaften, Universita ¨t Heidelberg, Im Neuen- heimer Feld 234, 69120 Heidelberg, Germany 3 3 NEG-LABISE, Departamento de Geologia, Universidade Fed- eral de Pernambuco, 50670-000, Recife, PE, Brazil 4 Correspondence author. E-mail: kkochhann@unisinos.br Journal of Foraminiferal Research, v. 43, no. 4, p. 443–463, October 2013 443