PALEOENVIRONMENTAL SIGNIFICANCE OF APECTODINIUM IN THE LATE PALEOCENE OF WEST AFRICA

The Early Paleogene (~ 66 to 47.8 My) represents a highly dynamic period in earth’s history during which the Paleocene-Eocene thermal maximum (PETM) marked major perturbations in the carbon cycle, high surface temperatures, significant evolutionary turnovers and extinctions in the marine and terrestrial biota. A palynological investigation of 51 samples from the Early Paleocene-Early Eocene interval at two West African localities, Alo-1 well (Anambra Basin, Southeastern Nigeria) and Ocean Drilling Program (ODP) Hole 959D (Côte d'Ivoire-Ghana Transform Margin), provided an opportunity to study these effects on tropical organic-walled dinoflagellate cysts.

Numerous palynological studies, mainly of mid and high latitude localities, have documented an Apectodinium acme (40% increase in the dinoflagellate cyst assemblage) during the PETM, and related this increase to global climatic warming. Apectodinium appeared in the study area at the Danian-Selandian boundary, and substantially increased in abundance during the Late Thanetian, apparently recording episodes of intense global climatic warming.

Apectodinium thrived in low salinity, inner to shallow outer neritic environments with strong nutrient availability. Therefore, the differences in the quantitative distribution of Apectodinium at the two localities – 80% in Alo-1 vs. 20% in ODP Hole 959D – can be related to different depositional settings. Dinoflagellate cyst assemblages and lithologic characteristics indicate that the early Paleogene interval in Alo-1 was deposited in an inner neritic shallow marine environment, whereas farther offshore conditions prevailed in ODP Hole 959D.