Sedimentation rates, coastal delta accretion, and stratigraphic datum of the Late Pleistocene–Mid-Holocene transition in the East Equatorial Atlantic: New concept from calcareous nannoplankton

This study examines the sedimentation rates (SR) during the last 20 kyr in the Niger Delta using selected biostratigraphic datum levels. Three gravity cores (GCs) collected at −40 m below sea level from the shallow offshore Niger Delta (GC1 = Western, GC2 = Central, and GC3 = Eastern) were analysed for their calcareous nannoplankton species ( Emiliania huxleyi , Gephyrocapsa oceanica , Helicophaera sellii and Reticulofenestra asanoi ). Successive datums were established mainly from the informal biozones and ranges of Gephyrocapsa oceanica and Emiliania huxleyi marker species due to their abundance. By correlating the First Occurrence (FOC) and Last Occurrence (LOC) datums of the marker species in the cored sequences (GCs), SRs were reconstructed. Based on the constructions, the FOC of Gephyrocapsa oceanica (20 kyr) reflects a position towards the bottom of the GCs, the FOC of Emiliania huxleyi (11–8.5 kyr) delineates the middle of the GCs, and the LOC of Emiliania huxleyi (6.5 kyr) marks the uppermost part of the GCs. The sediment load by average calculated from each location in the Western, Central, and Eastern Niger Delta shows sequences of sedimentation rates of ~36.7 cm/kyr for the late Pleistocene, ~174 cm/kyr for the early Holocene, and ~18.6 cm/kyr for mid-Holocene time periods. Consequently, on average, ~229.3 cm/kyr of sediment were deposited at −40 m water level over the last 20 kyr, with the early Holocene experiencing the highest sedimentation rates (~174 cm/kyr) across the three locations. Additionally, this study provides evidence that the Niger Delta sink deposits responded to the West African Monsoon (WAM) driven sedimentation rates during the late Quaternary (20–6.5 kyr). Furthermore, this sediment deposit facilitated the development of a high-resolution age-depth and sedimentation rate model linked to the regional sea level of the Eastern Equatorial Atlantic that succinctly delineates the late Pleistocene and early Holocene boundary of the Niger Delta. The outputs of this study bridged the research gap and knowledge on the impact of coastal accretion and depositional processes on sedimentation rates in the shallow offshore Niger Delta.