Early Pliocene agglutinated foraminiferal morphotypes from DPH 1 A well: Implications for the paleoebathymetry and paleoceanography of the offshore southeastern Niger Delta

Abstract

The Early Pliocene paleobathymetry and paleoceanographic conditions of the offshore southeastern Niger Delta were investigated from the agglutinated foraminiferal assemblages recovered from the DPH-1A well. 60 ditch cutting samples obtained from the well section were subjected to the kerosene method of foraminiferal sample processing. Samples from the basal interval (2940 – 3100 m) yielded exclusively calcareous forms, while the overlying section consist entirely of agglutinated assemblages. The agglutinated taxa were categorized into 6 morphotypes with their supposed life habit and designated M1 (tubular, suspension feeding, erect epifaunal), M2a (globular, deposit feeding, shallow infaunal), M2b (rounded trochospiral, surficial epifaunal, active deposit feeding), M3a (flattened planispiral, surficial epifaunal, active deposit feeding), M4a (rounded planispiral, surficial epifaunal / shallow infaunal, active deposit feeding) and M4b (elongate tapered, deep infaunal, active deposit feeding). The section was constrained to the N17 late Miocene – N18 early Pliocene biochron based on important foraminiferal datums; first appearance datums (FADs) Neogloboquadrina dutertrei, Globigerinoides obliquus extremus, Globorotalia pseudopima, Globorotalia pseudomiocenica and last appearance datum (LAD) Cyclammina cf. minima. Agglutinated foraminiferal morphotype and lithologic analyses indicate outer neritic to lower bathyal (deep water) paleobathymetric setting, high organic matter productivity, low oxygen bottom water and muddy sediment substrate typical of oxygen minimum zones. Exclusive agglutinated assemblages of the early Pliocene samples point to intense carbonate dissolution which might have been caused by bottom water acidification triggered by increased CO 2 generation from the bacterial decomposition of sediment organic matter. • Morphotype categorization of Early Pliocene agglutinated foraminiferal assemblages of the Niger Delta. • Implications of the agglutinated foraminiferal morphotypes for paleobathymetry in the offshore Niger Delta. • Indication of the paleoceanographic conditions such as organic matter productivity and bottom water oxygenation level in the early Pliocene southeast offshore Niger Delta.