Foraminiferal Biostratigraphy, and Paleoenvironmental Interpretations in the Masa-01 Well, Western Offshore, Niger Delta Basin, Nigeria

Abstract

Mayowa Daniel Ajayi and Saka Adelayo Opeloye

A foraminiferal biostratigraphy and paleoenvironmental studies were carried out on fifty (50) ditch-cut samples retrieved from the MASA-01 well, western offshore region, Niger Delta, Nigeria. The studied intervals ranged from 6810 feet (2076 m) to 8310 feet (2533 m) and were analyzed at intervals of 30 feet (9 m). The samples were subjected to foraminiferal and lithostratigraphy analyses to determine the biozonation and paleoenvironment of deposition. Standard foraminiferal preparation techniques completed with strata-bug software analysis were employed. Lithological studies indicate that the depth intervals belong to the upper paralic Agbada Formation. Seventy-six (76) foraminifera species were retrieved from the well comprising 34 calcareous benthic, 5 agglutinated benthic, and 37 planktic species. Three (3) planktic foraminifera zones, the Sphaeroidinellopsis seminulina/Bulimina marginata Zone, the Globorotalia margaritae/Amphistegina lessonii Zone, and the Globigerina nepenthes/Marginulina costata Zone corresponding to the N20/PL3 and N19/PL2 zones, were identified. The important markers recorded were Globorotalia plesiotumida/merotumida (FDO) and Globorotalia crassaformis crassaformis (LDO) at 7230feet; the lone occurrences of Amphicoryna scalaris caudata at 7470feet; Globorotalia margaritae margaritae (FDO) and Globorotalia margaritae margaritae (LDO) at 7650feet and 8010feet; and Globigerinoides nepenthes (FDO) and depressed Globigerinoides bollii (FDO) at 7920feet and Sphaeroidinellopsis seminulina (FDO) at 8040feet. The well was dated to the early Pliocene (N20/PL3–N19/PL2) based on the occurrence of marker species. The two (2) condensed sections that are associated with maximum flooding surfaces (MFS) were dated to 3.82 Ma at 7230 feet and 4.16 Ma at 7830 feet based on peak faunal abundance and diversity. A hypersaline outer neritic to the upper bathyal environment is deduced from paleoecological indices of bathymetry and planktic/benthic ratio.

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