Pliocene and Pleistocene stratigraphic evolution of the western Niger Delta intraslope basins: A record of glacio-eustatic sea-level and basin tectonic forcings
Introduction
Deep-water sediments are important archives of the Earth's history not only because they record past climatic, geodynamic, environmental and hydrodynamic changes (e.g. Burbank, 1992; Molnar, 2004; Catuneanu, 2006; Posamentier and Kolla, 2003; Zecchin et al., 2010), but also because they host viable hydrocarbon fields (see review in Morley et al., 2011). Understanding the complex interplay between allocyclic (e.g. eustasy, tectonics, climate and indirectly sediment supply), and autocyclic (e.g. channel avulsion) or regional forcings (e.g. delta lobe switching, shale tectonics etc.), is critical for interpretation of the evolution of deep-water sedimentary systems (e.g. Elliott, 1975; Jervey, 1988; Posamentier et al., 1988; Pulham, 1989; Einsele et al., 1991; Wiener et al., 2010; Miall, 2010; Morley et al., 2011; Catuneanu et al., 2011).
The Pliocene and Pleistocene are ideal time intervals for this kind of study because eustasy and climate proxies (δ18O) are well constrained and show significant variations both in amplitude and frequency (e.g. Ruddiman et al., 1989; Imbrie et al., 1993; Bassinot et al., 1994; Leroy et al., 1999; Shackleton, 2000; Lisiecki and Raymo, 2005; Miller et al., 2005; Gibbard et al., 2010; Gibbard and Lewin, 2016; Raymo et al., 2018). Published climate proxies across the worlds' ocean basins show that the Pliocene and Pleistocene were controlled by orbital forcing (Milankovitch cycles) of three major periods namely: (i) precession (23 ka), (ii) obliquity (41 ka), and (iii) eccentricity (400 and 100 ka) (Lisiecki and Raymo, 2007). The early Pliocene from (5.3 Ma) to the early Pleistocene was dominated by obliquity cycles (41 ka), while the middle Pleistocene (circa 1.4 Ma) to the present was dominated by eccentricity (400–100) (Head and Gibbard, 2015a, Head and Gibbard, 2015b; Gibbard et al., 2014; Gibbard and Lewin, 2016). Although the switch to the eccentricity cycles is poorly understood and a transition period from 1.4 to 0.4 Ma was suggested by Head and Gibbard, 2015a, Head and Gibbard, 2015b, and Gibbard and Lewin (2016), a marked change to increasingly severe glacial cycles, the so-called ‘0.8 Ma event’ (Lisiecki and Raymo, 2007; Head and Gibbard, 2015a, Head and Gibbard, 2015b) or ‘0.9 Ma’ (Miller et al., 2005; Eldefield et al., 2012), is usually interpreted as the Middle Pleistocene Transition (MPT).
Sedimentary records all over the world show the imprint of tectonic, climatic and glacio-eustatic cycles of different orders (Haq et al., 1987). Fourth-order climate cycles lasting 400 ka have been reported during the Pliocene e.g. on the continental shelf offshore Foz do Amazonas Basin (Brazil), with incised valleys, slope canyons and mass wasting (Gorini et al., 2014). During the Pleistocene, fifth-order glacio-eustatic sea-level changes with 100 ka periodicity are also well documented with marked shoreline progradation on the shelf and increased deep-water sedimentation during glacials e.g. in the Mediterranean Sea over the last 500 ka (Rabineau et al., 2006; Ridente et al., 2008; Lafosse et al., 2018). During the Pliocene, sediment architecture in the Mediterranean Sea does not appear to be much imprinted by the 400 ka cycles as shown in seismic (Rabineau et al., 2014) and numerical simulations (Leroux et al., 2014), probably because of an anomaly in accommodation created by the erosion of the entire margin after the Messinian Salinity Crisis. 100-ka glacio-eustatic cycles have also been described worldwide e.g. offshore Alaska (Gulick et al., 2015), in the Gulf of Mexico (Galloway, 2001) and the Bengal fan (Weber et al., 1997).
In the eastern Niger Delta, Jermannaud et al. (2010) and Rouby et al. (2011), documented a transition from global climate-controlled sequences from circa 4–2.5 Ma to sediment supply-controlled sequences from 2.5 Ma to the present. These authors also demonstrated a general progradation and an increase in sedimentation rates from 4 to 2.5 Ma, followed by a retrogradation and a decrease in sedimentation rates over the last 2.5 Ma. Additionally, Riboulot et al. (2012), showed that eccentricity forcing of 100 ka periodicities has controlled the stratigraphic evolution of the eastern Niger Delta continental shelf over the last 0.5 Ma.
In the western Niger Delta slope, where the present study was conducted (Fig. 1), Jobe et al., 2015, Jobe et al., 2016; red box in Fig. 1A, D), linked changes in sedimentation rates during the last 130 ka (MIS 5e to the present) to glacial/interglacial cycles with increased sedimentation rates during the lowering of the sea level (MIS3 and MIS2) and an overall reduction in sedimentation during a rapid post-glacial sea-level rise associated with the Meltwater pulse 1A at 14 ka. Earlier studies e.g. Lézine et al. (2014); Weldeab et al. (2011); Collins et al. (2014); Govin et al. (2014) and Armitage et al. (2015), linked the increase in sedimentation rates in the Gulf of Guinea during the Quaternary to the West African Monsoon. A recent high-resolution, 3D seismic and sequence stratigraphic study of the western Niger Delta slope (yellow box in Fig. 1A, C, D, E) by Chima et al. (2019, dated the Neogene stratigraphic record from the Burdigalian (18.5 Ma) to the late Miocene (5.5 Ma), and described interactions between mobile shale and erosional submarine channel over the last 5.5 Ma. However, the lack of biostratigraphic data for the Pliocene and Pleistocene poses a challenge to constraining the timing of major changes in sedimentary records.
Despite the above-mentioned studies of the Pliocene and Pleistocene sedimentary records in the Niger Delta, no study has investigated its control by orbital forcings from the late Messinian (5.5 Ma) to the present. Hence, the objective of this paper is to perform a detailed analysis of the stratigraphic evolution of the western Niger Delta intraslope basins over the last 5.5 Ma with a view to (i) proposing a sequence stratigraphic framework for the Pliocene and Pleistocene intervals; and (ii) investigating their control by orbital forcings.
The Niger Delta is an ideal laboratory to study climate stratigraphy and slope depositional processes because it is located on a passive margin where the imprints of regional/global climate dynamics, sea-level variation, gravity-tectonics, drainage evolution and sediment supply are well imaged on high-resolution 3D seismic reflection data.
Section snippets
Regional setting
The Cenozoic Niger Delta is located in the Gulf of Guinea on the equatorial Atlantic margin of West Africa (Fig. 1A). The delta is the twelfth largest petroleum province in the world (Tuttle et al., 1999). It covers an area of ~140,000 km2 with a maximum sediment thickness of ~12 km (Allen, 1965; Evamy et al., 1978; Doust and Omatsola, 1990). The Niger Delta is divided into the Eastern and the Western lobes by a Cretaceous basement high [the Charcot Fracture Zone (CFZ)] (Corredor et al., 2005;
Dataset
We used high-resolution 3D seismic data and lithologic logs from five boreholes (see Fig. 1A, D, E), to study the Pliocene and the Pleistocene stratigraphic evolution of the western Niger Delta.
Seismic facies analysis
The Pliocene and Pleistocene stratigraphy of the western Niger Delta intraslope basins were subdivided into two mega seismic units named MSU 1 and MSU 2, based on the observed changes in seismic geometries and depositional environments. MSU 1 and MSU 2 correspond to Unit 6 and Unit 7 respectively in Chima et al. (2019). Although a detailed seismic facies analysis of the study area was presented in Chima et al. (2019) (Fig. 1A, C, D, E; 2A), the present study sheds more light on facies
Discussion
We discuss the Pliocene and Pleistocene stratigraphic evolution of the western Niger Delta intraslope basins over the last 5.5 Ma in relation to allocyclic (glacio-eustatic) sea-level and basin tectonic forcings, and propose a deep-water depositional model.
Conclusions
Detailed seismic stratigraphy and 3D geomorphological analysis of high-resolution 3D seismic data over the Pliocene and Pleistocene stratigraphic record of the western Niger Delta intraslope basins, showed that:
- 1.
Glacio-eustatic sea-level changes since the last 5.5 Ma are recorded at regional scale in the intraslope basins of the western Niger Delta.
- 2.
The depositional sequence in the intraslope basins of the western Niger Delta is generally defined by the falling stage erosional surface (FSES) at
Declaration of Competing Interest
I, Kelvin Ikenna Chima, wish to state clearly that I have dully acknowledged the donor of the dataset used in this study (Shell Nigeria) and also the sponsor, Petroleum Technology Development Fund (PTDF) of the Federal Republic Nigeria. I also wish to clearly state that there is no conflict of interest in this study.
Acknowledgments
We thank the Federal Republic of Nigeria for sponsoring the PhD of Kelvin Ikenna Chima through the Petroleum Technology Development Fund (PTDF) Scholarship Programme. We are grateful to Shell Nigeria not only for providing the data used in this study but also for permission to publish it. PTDF provided the computer workstation used in this study. Many thanks to Schlumberger for providing Petrel (™) software, which we used to interpret the data. The first author would like to thank the
References (95)
- et al.
The astronomical theory of climate and the age of the Brunhes-Matuyama magnetic reversal
Earth Planet. Sci. Lett.
(1994) - et al.
Canyon-confined pockmarks on the western Niger Delta slope
J. Afr. Earth Sci.
(2015) - et al.
On the origin of Cenozoic and Mesozoic “third-order” eustatic sequences
Earth-Sci. Rev.
(2011) - et al.
Seismic stratigraphy and depositional architecture of Neogene intraslope basins, offshore western Niger Delta
Mar. Pet. Geol.
(2019) - et al.
Sedimentation and shale tectonics of the northwestern Niger Delta front
Mar. Pet. Geol.
(1996) - et al.
Insolation and glacial-interglacial control on southwestern African Hydroclimate over the last 140,000 years
Earth Planet. Sci. Lett.
(2014) Neogene gravity tectonics and depositional processes on the deep Niger Delta continental margin
Mar. Petrol. Geol.
(1994)- et al.
Architecture and evolution of upper fan channel-belts on the Niger Delta slope and in the Arabian Sea
Mar. Pet. Geol.
(2003) Cenozoic evolution of sediment accumulation in deltaic and shore-zone depositional systems, northern Gulf of Mexico Basin
Mar. Petrol. Geol.
(2001)- et al.
Partitioning the quaternary
Quat. Sci. Rev.
(2016)