Late Miocene\u2013Early Pliocene planktic foraminiferal biostratigraphy of deep offshore southwestern Niger Delta

Abstract

The planktic foraminiferal biostratigraphy of the deep offshore southwestern Niger Delta has been studied from three wells (DPW-1, DPW-2 and DPW-3). A total of 418 ditch cutting samples (104 samples from DPW-1, 165 from DPW-2 and 149 from DPW-3) taken at 18-m intervals were subjected to standard micropaleontological processing techniques. In total, 42, 52 and 40 planktic foraminiferal species were identified from DPW-1, DPW-2 and DPW-3, respectively. The identified planktic species allow the delineation of the studied section into four biozones—Globorotalia acostaensis (N16), Globigerinoides obliquus extremus/Globorotalia merotumida (N17), Globorotalia margaritae primitiva (N18) and Globorotalia margaritae evoluta/Globigerina nepenthes (N19) zones, based on the first appearance datums (FADs), last appearance datums (LADs) of the nominate taxa and associated assemblages. The well sections dated Late Miocene to Early Pliocene based on the occurrence of certain diagnostic planktic foraminiferal datums such as FADs Globorotalia acostaensis, Globigerinoides obliquus extremus, Globorotalia merotumida/plesiotumida, Globorotalia margaritae primitiva and the LADs Globigerina nepenthes, Globorotalia margaritae primitiva and Globorotalia margaritae evoluta. The Miocene/Pliocene boundary was placed at the FAD Globorotalia margaritae primitiva. In the Niger Delta, this boundary is commonly placed at the FADs Globorotalia margaritae margaritae and Globorotalia crassaformis probably due to nonrecovery of Globorotalia margaritae primitiva. However, in this studied section of the deep offshore southwestern Niger Delta, FAD Globorotalia margaritae primitiva occurs consistently in the three study wells and is therefore considered an appropriate datum for the placement of the Miocene/Pliocene boundary.