Dinoflagellate cyst assemblages, biostratigraphy and paleoenvironment of a Paleocene-Early Eocene sedimentary succession in the northern Niger Delta Basin: Comparison with low, mid and high latitude regions

Abstract

This study represents a contribution to the Late Paleocene-Early Eocene biostratigraphy in a low latitude stratigraphic setting where, published studies are few in comparison with mid- and high latitude regions. We generated data for 62 dinoflagellate cysts from a comprehensive analysis of 33 samples covering a 713-m interval in the Alo-1 Well in the northern Niger Delta (Anambra) Basin, Nigeria. Dinoflagellate cyst recovery in the samples varies from very good to poor, and the specimens are commonly well preserved. We calibrate the dinoflagellate cyst data with recent biozonation schemes for ODP Hole 959D, Côte d'Ivoire-Ghana Transform Margin in the eastern Equatorial Atlantic, which allowed for a valid comparison with published studies in well-dated rock sections in northwestern Europe, the Mediterranean region, New Zealand, and Tasmania. Our observations show that there is better correlation between tropical and mid latitude dinoflagellate cyst assemblages compared to those in high latitude regions.We use the last occurrence and/or last abundance events of dinoflagellate cysts to identify four biostratigraphic zones (zone E to zone H) in the Alo-1 Well. Lithostratigraphic and biostratigraphic analyses suggest a late Selandian age for the contact between the Imo and Nsukka formations. Abundant thermophilic taxa that include the Cordosphaeridium group and Apectodinuim dominate the assemblage recovered in the depositional succession. The late Selandian to early Thanetian sediments are dominated by the Cordosphaeridium group, and are succeeded by abundant to superabundant marker species of Apectodinium in the late Thanetian to Ypresian. The superabundance of Apectodinium is significant because it is indicative of the global intense climatic warming that characterized the late Thanetian to early Ypresian. The Alo-1 Well dinoflagellate cyst data also suggest deposition under proximal, inner neritic conditions that preserved an assemblage dominated by species of Cordosphaeridium, Damassadinium, Ifecysta and Polysphaeridium.