AGE-DEPTH MODEL AND DATING TECHNIQUE ACROSS THE SHALLOW OFFSHORE OF THE NIGER DELTA PASSIVE MARGIN: CHALLENGES AND PROGRESS DURING THE LATE QUATERNARY

The importance of an age/depth model in any stratigraphic study especially when working on the Quaternary sediment cannot be over-emphasized. To achieve this, it is important to consider the depositional setting, depth of coring, sedimentation rate, tectonic control, and material availability of the setting in order have a successful age-depth model and dating. These scenarios are complex issues based on the three gravity cores (~ 3m) samples analyzed from the Eastern, Central, and Western parts of the Niger Delta passive margin.

Given these challenges, this study considered biostratigraphic-dating method (foraminifera, nannofossils, and palynology) because of unavailability of monospecific planktonic foraminifera / broken shells in the samples that hindered radiometric or isotope dating. After a careful interpretation, the palynological dating method was not successful because most of the pollen and spores species (Verrucatosporites usmensis, Stereisporites sp., Poaceae, and Zonocostites ramonae) identified are stratigraphically ubiquitous (found everywhere) and not viable for succinct dating. In addition, palynology (pollen and spores) among the dating methods is generally unsuccessful and difficult in dating sediments older than mid Pleistocene, considering the regional and global chronostratigraphic chart.

Given these conditions, the successful outcome of the age optimization recovered in this study is based on foraminifera and nannofossils biostratigraphic dating methods. These were achieved on the principle of First Occurrence (FOC) and Last Occurrence (LOC) of foraminifera: Globorotalia truncatulinoides (late Pleistocene) and Globorotalia tumida (mid-Holocene), and nannofossil: Gephyrocapsa oceanica (late Pleistocene) and Emiliania huxleyi (mid-Holocene), respectively. Thus, the three gravity cores recovered the late Pleistocene (~20/ ~20 ka) to mid-Holocene (~6.5ka) time span for the Late Quaternary Niger Delta. These results enabled the development of an age model (depth/age related) and sedimentation rates at different depths.