# Differential subsidence and gravity collapse of the eastern and western Niger Delta lobes: Evidence from 2-D kinematic structural modelling

Kelvin Ikenna Chima, Estelle Leroux, Marina Rabineau, Didier Granjeon, Maryline Moulin, Philippe Schnurle, Daniel Aslanian

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## To cite this version:

Kelvin Ikenna Chima, Estelle Leroux, Marina Rabineau, Didier Granjeon, Maryline Moulin, et al. Differential subsidence and gravity collapse of the eastern and western Niger Delta lobes: Evidence from 2-D kinematic structural modelling. Tectonophysics, 2025, 913, pp.230874. 10.1016/j.tecto.2025.230874. hal-05263728

HAL Id: hal-05263728

https://ifp.hal.science/hal-05263728v1

Submitted on 16 Sep 2025

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# Differential subsidence and gravity collapse of the eastern and western Niger Delta lobes: Evidence from 2-D kinematic structural modelling

Kelvin Ikenna Chima<sup>a,b,*†</sup>, Estelle Leroux<sup>a</sup>, Marina Rabineau<sup>a</sup>, Didier Granjeon<sup>c</sup>, Maryline Moulin<sup>a</sup>, Philippe Schnurle<sup>a</sup>, Daniel Aslanian<sup>a</sup>

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## ARTICLE INFO

### Keywords:

- The Niger Delta

- Divergent margin

- Gravitational collapse systems

- Differential subsidence

- Backtripping

- Crustal architecture

## ABSTRACT

The Niger Delta prism is well-known and has been described as gravitationally deformed above an overpressured shale décollement, leading to complex geometries. However, it remains unclear whether failures were initiated simultaneously and propagated synchronously over time in the eastern and western parts of the delta. This study investigates this issue using backstripping and kinematic structural restoration of regional 2-D seismic cross-sections from the eastern and western Niger Delta lobes (ENDL and WNDL). Our results suggest that the Niger Delta is controlled by the interplay between gravitational collapse processes and the crustal architecture of a divergent margin. At the delta scale, gravitational extension typically exceeds gravitational contraction, with intervening overpressured shales partially accommodating strain. Gravitational contraction initiated earlier in the offshore ENDL (Early Messinian) compared to the offshore WNDL (Plio-Pleistocene), but the WNDL has been relatively more active and has spread faster than the ENDL. A dip in the ENDL basal décollement facilitated more basinward translation of the lobe, coupled with gravity spreading due to delta lobe progradation in the Late Tortonian. In contrast, the relatively gentle dip of the offshore WNDL's regional décollement, aided by depositional loading, favoured rapid gravity spreading of the lobe in the Plio-Pleistocene. Cross-section restoration suggests that the ENDL localizes subsidence on the modern shelf, while the WNDL shows homogeneous spatial subsidence. The inferred differential spatial subsidence along the ENDL and WNDL cross-sections could be linked to (i) differences in crustal architecture (oceanic versus intermediate) and/or (ii) differences in geodynamic location (strike-slip versus divergent setting).

## 1. Introduction

Large-scale gravity-driven collapse of sedimentary wedges is a common feature of continental margins. Failure generally occurs on multiple scales and through various processes, giving rise to a wide range of complex structures (Butler and Paton, 2010; Moscardelli and Wood, 2008; Rowan, 2020; Scarselli et al., 2022). Deformation is typically characterised by proximal extension and distal contraction, detached at weak stratigraphic levels, typically salt or overpressured shale (Rowan, 2020). Gravity gliding and spreading have traditionally been applied to thin-skinned deformation on margins and are linked to margin tilt and depositional loading, respectively (Butler and Paton,

2010; Cobbold and Szatmari, 1991; Dejong and Scholten, 1973; Demercian et al., 1993; Ings and Beaumont, 2010; Loncke et al., 2006, 2010; Morley et al., 2011; Ogata et al., 2019; Peel, 2014; Rowan, 2020; Sellier et al., 2013; Silva et al., 1999). Gravity gliding is defined as a rigid translation of a rock mass down a dipping décollement, while gravity spreading refers to the vertical collapse and lateral spreading of a body of rock under its own weight (Ramberg, 1967). Gravity gliding and spreading are generally difficult to differentiate in natural systems (e.g., Schultz-Ela, 2001). Rowan and Ratliff (2012), based on evidence from several margins, demonstrated the importance of both processes, concluding that while gravity gliding is typically the trigger (due to thermal subsidence of oceanic crust and the consequent margin tilt),

<footnote><sup>a</sup> Geo-Ocean, Univ-Brest, CNRS, Ifremer, UMR6538, 29280 Plouzané, France</footnote>

<footnote><sup>b</sup> Alex-Ekwume Federal University, Ndufu-Alike, Ebonyi State, Nigeria</footnote>

<footnote><sup>c</sup> IFP Energies Nouvelles (IFPEN), Rueil Malmaison, France</footnote>

<footnote>* Corresponding author at: Geo-Ocean, Univ-Brest, CNRS, Ifremer, UMR6538, 29280 Plouzané, France.</footnote>

<footnote>E-mail address: kelvini.chima@gmail.com (K.I. Chima).</footnote>

<footnote n="1">¹ Present address of corresponding author: Institut des Sciences de la Terre de Paris; UMR 7193 - Sorbonne Université; 4 place Jussieu 75,252 Paris Cedex 05 - France.</footnote>
gravity spreading often becomes increasingly important due to the waning of thermal subsidence and the progradation of large deltaic lobes.

The increasing interest in the geologic structures associated with gravity-driven deformation as targets for ge resource exploration has drawn attention to the study of these systems at various scales, from the gigantic roll-over anticlines within the extensional domain of mega- slides in the Niger Delta (e.g., Corredor et al., 2005; Fatoke and Bhat- tacharya, 2010; Wiener et al., 2010) to rotated blocks at the headscarp of submarine slumps in the Statfjord Field, North Sea (Welbon et al., 2007). Furthermore, gravity-driven sediment deformation poses geohazards for offshore platforms and pipelines (Frey-Martínez et al., 2011; Lu and Shipp, 2011) and could potentially trigger tsunamis that may affect coastal infrastructure and communities (Løvholt et al., 2015; Masson et al., 2006; Urgeles et al., 2019).

Divergent margins with shale-detached gravity-driven deformation include the Niger Delta (e.g., Ajakaiye and Bally, 2002; Chima et al., 2022a; Corredor et al., 2005; Doust and Omatsola, 1990; Restrepo-Pace, 2018; Rowan et al., 2004; Spina et al., 2025), the Orange Basin along the west African margin (e.g., Butler and Paton, 2010; Scarselli et al., 2016), the Amazonas and Para-Maranhão basins along the South American margins (e.g., Cobbold et al., 2004; Reis et al., 2010; Silva et al., 1999; Zalan, 2011), and the northern Gulf of Mexico (e.g., Madof et al., 2017; Soto and Hudec, 2023). Gravity collapse of sedimentary wedges in these margins typically occurs above intervals of overpressured shales, known as décollements. A décollement is typically a zone of overpressured, weak sediments that developed mainly due to some combination of rapid sedimentation, disequilibrium compaction, and hydrocarbon generation (de Souza et al., 2020; Morley and Guerin, 1996; Osborne and Swarbrick, 1997; Swarbrick and Osborne, 1998; Tingay et al., 2009).

The Niger Delta (Fig. 1) is one of the largest modern deltas and the twelfth-largest petroleum province in the world (Tuttle et al., 1999). Previous studies based on seismic and borehole data, as well as analogue and numerical modelling, show that the gravitational collapse of the Niger Delta above décollement layers reflects the development of overpressure within marine shales, in response to disequilibrium compaction and delta progradation (Ajakaiye and Bally, 2002; Chima et al., 2022a, 2022b; Cobbold et al., 2009; Corredor et al., 2005; Damuth, 1994; Cohen and McClay, 1996; Jermannaud et al., 2010; Krueger and Grant, 2011; Morley and Guerin, 1996; Mourgues et al., 2009; Restrepo-Pace, 2018; Rouby et al., 2011; Rowan et al., 2004; Wiener et al., 2010; Spina et al., 2025; Wu et al., 2015). Analogue modelling of the impact of differential thickening of overpressured shale décollements across relict oceanic fracture zones on the gravity collapse of the eastern and western Niger Delta lobes (ENDL and WNDL, Fig. 1) suggests that the WNDL has been relatively more active and prograded faster than the ENDL (Wu et al., 2015). Despite numerous studies of the Niger Delta, the question of whether gravity-driven deformation initi- ated and propagated synchronously through geologic time in the ENDL and WNDL remains poorly understood. This study investigates this through backstripping and sequential structural restoration of regional seismic cross-sections that image the Late Cretaceous and Neogene se- ries in the eastern and western Niger Delta lobes. This approach allows us to compare the structural evolution of the two regions, their defor- mation rates, and the interplay between deformation and sedimentation, and, finally, to discuss the potential controlling factors.

## 2. Geological setting

### 2.1. Geodynamic setting

The modern Niger Delta extends approximately 75,000 km² onshore and approximately 110,500 km² offshore, beneath the present-day coastline, reaching a thickness of 12 km in its deepest section (Allen, 1965; Fig. 1A, B). The offshore segment of the delta is subdivided into

the ENDL and WNDL by a stepped basement relief associated with the fossil Charcot Fracture Zone (Briggs et al., 2009a, 2009b; Corredor et al., 2005; Chima et al., 2022a; Fig. 1B, C). The Oligocene-Holocene Cameroon Volcanic Line forms an eastern buttress to the progradation of the Niger Delta (Burke, 1972; Fig. 1C).

The Niger Delta is located at the southern end of a NE-SW inverted- rift basin (the Benue Trough), which developed in the Late Jurassic- Eocene (Maluski et al., 1995). The Nigerian margin initiated as a rif- ted basin following the breakup of Gondwana in the Late Jurassic and the subsequent opening of the Equatorial segment of the South Atlantic Ocean between the African and South American plates (Gaina et al., 2013; Moulin et al., 2010; Reeves et al., 2016; Seton et al., 2012; Torsvik et al., 2009). During the opening of the South Atlantic Ocean in the Cretaceous, the counter-clockwise rotation of the African plate at ca. 130, 90, and 68 Ma, relative to the mantle around a pole situated in the vicinity of the Benue Trough, contributed to intraplate magmatism in the region (Gaina et al., 2013). The corresponding change in far-field stress led to the development of a series of NE-SW trending ocean fracture zones (palaeotransform faults) that underlie the Niger Delta (Gaina et al., 2013; Moulin et al., 2010; Reeves et al., 2016; Seton et al., 2012; Torsvik et al., 2009; Fig. 1C). During the opening of the Equatorial Atlantic, the Benue Trough became filled with Late Cretaceous and younger post-rift sediments (Reijers, 2011). By the Late Eocene, a delta had begun to prograde over the Nigerian margin, consequent to the Middle Eocene uplift of the Hoggar, north of the Niger catchment (Chardon et al., 2016; Fig. 2), and the cessation of the Palaeocene ma- rine incursion of the Benue Trough (Damuth, 1994; Reijers, 2011). Geodynamical reconstruction of the South Atlantic margin (Gaina et al., 2013; Moulin et al., 2010; Reeves et al., 2016; Seton et al., 2012; Torsvik et al., 2009) and published seismic data (e.g., Briggs et al., 2009a, 2009b; Spina et al., 2025; Wiener et al., 2010) suggest that a significant portion of the Niger Delta is underlain by Lower Cretaceous oceanic crust, which transitions landwards through the intermediate domain of extended continental crust.

### 2.2. Stratigraphy and structural setting

The Cenozoic Niger Delta is composed of the Miocene to Plio- Quaternary siliciclastic sedimentary wedge, rooted on overpressured, mud-rich sediments speculated to be Late Cretaceous-Palaeocene to Late Eocene-Oligocene in age (Wiener et al., 2010; Bellingham et al., 2014; Fig. 1D, E). The Late Cretaceous-Oligocene overpressured mud-rich sediments unconformably overlie the crust and generally act as a regional décollement for gravity-driven deformation of the overlying Miocene and Plio-Quaternary sediments (Fig. 1D, E). Tectonic and climate-driven progradation of the Niger Delta above overpressured mud-rich sediments formed two main segments: eastern and western lobes, separated by the Charcot Fracture Zone (Fig. 1A, C; Reijers, 2011). Both lobes are affected by two main gravity-collapse-linked structural zones: the extensional and contractional zones, separated by an inter- mediate/translational zone (Fig. 1D, E). The Extensional Zone (paleo- extensional zone, PEZ, and modern extensional zone, MEZ) features regional and counter-regional normal faults; the Contractional Zone (CZ) shows imbricate toe-thrusts; and the intervening Translational Zone (TZ) is dominated by mobile shales and décollement folds (Fig. 1B, D, E; Bilotti et al., 2005; Chima et al., 2022a; Damuth, 1994).

## 3. Methodology

In this study, we rely on backstripping and kinematic structural restoration of two regional 2-D seismic cross-sections located on the ENDL and the WNDL. The cross-section on the ENDL has previously been described by Wiener et al. (2010) and extends 300 km from the onshore to the basin (Fig. 1B, D). Similarly, the seismic cross-section on the WNDL was described in a recent publication by Chima et al. (2022a) and extends 203 km from the platform to the basin (Fig. 1B, E). These seismic
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<figure><img src="image_5.png" /><figcaption>**Fig. 1.** A. Location of the Niger Delta on the Equatorial Atlantic margin of West Africa. B. Superposed topographic and bathymetric maps (GEBCO, 2023), showing the structural zones of the Niger Delta (indicated by double-headed yellow arrows). C. Gravity map of the Niger Delta showing the Charcot and Chain Fracture Zones. D, E. Line drawings (VEx3) of the regional cross-sections investigated in the ENDL and WNDL (see dashed and continuous red lines in panel B for locations). The ENDL profile extends from onshore to the basin, while the WNDL profile extends from offshore to the basin, highlighting contrasting structural styles on the modern continental shelves. The ENDL profile is adapted from Wiener et al. (2010), and the WNDL profile is adapted from Chima et al. (2022a). Structural geology in panel B is adapted from Rouby et al. (2011). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Fig. 2.** Evolution of the Niger catchment (after Chardon et al., 2016). Note the absence of significant relief in the middle Eocene, and the increase in sediment flux to the margin following the uplift of the Hoggar in the late Eocene.</figcaption></figure>

cross-sections image the upper part of the crust and Late Cretaceous-Holocene sediments of the Niger Delta (Fig. 1D, E). For a detailed description of the 2-D seismic reflection data, biostratigraphic and chronostratigraphic dating of seismic units, velocity analysis, and time-depth conversion, see Wiener et al. (2010) for the ENDL and Chima et al. (2022a) for the WNDL. In this study, we use the ages given by these authors for the key reflectors. Note that the ages differ in each case: 34, 17.3, 9.3, 7, 5.7, 3.2, and 0 Ma in the ENDL, and 39.5, 18.5, 12.5, 9.5, 4.9, 2.6, and 0 Ma in the WNDL (Fig. 1D, E).

### 3.1. 2-D kinematic structural restoration

The 2-D kinematic structural restoration described in this study was conducted using the KronosFlow™ tool, which incorporates three geo-mechanical algorithms/manipulators: (1) the bi-deformation/moving least squares, (2) sliding, and (3) the manual/complex manipulator. The bi-deformation manipulator facilitates rigid movement/translation between two constraints (e.g. a fault and a décollement surface). In contrast, the sliding manipulator allows for translation along an inclined surface (e.g. a listric fault or a décollement surface). The manual/complex manipulator facilitates a combination of brittle and ductile or viscous deformation (e.g. listric faults and mobile shale or salt). As the 2-D cross-sections that we studied are characterised by complex extensional and compressional structures, underlain by thick overpressured shales (Fig. 1D, E), we combined the bi-deformation and complex algorithms to construct different geological scenarios. A 2-D structural restoration in KronosFlow™ requires an initial geometry in depth, the

absolute age of horizons, and the lithological composition of stratigraphic units, while accounting for bathymetry, compaction, and isostasy. We used the sequence stratigraphic schemes and lithological compositions of the WNDL (see Chima et al., 2019, 2020, 2022a, and the references therein) and the ENDL (see Wiener et al., 2010; Zhang et al., 2018). We followed the backstripping and structural restoration workflow for passive margins described by Steckler et al. (1999). At each restoration step in KronosFlow™, the stratigraphic layer above the horizon of interest (top unit) was removed (flexural unloading), accounting for sediment loading that occurred since the time of deposition. This was followed by sequential restoration of geometries through time based on the relation between faults, sediment thicknesses, and mobile shales. Palaeobathymetry was imposed assuming variation along a similar depositional profile (in our case, the present-day geometry was used as a reference surface). Finally, the best-fit geological scenario (reconstructed geometry), with minimal variation in sediment thicknesses, was decompacted, accounting for burial compaction that occurred since the time of deposition. Mechanical decompaction in KronosFlow™ is automatically computed based on the defined lithologies and the embedded exponential decrease in porosity with depth law for each lithology. We imposed four constraints to facilitate the structural restoration:

(i) Plain strain and material balance with no significant change in cross-sectional area at every time step.

(ii) The basal/regional décollement surface (within overpressured shale) is a sliding horizon.

(iii) Palaeobathymetry varied minimally at every time step.

(iv) Structural deformation initiated on the platform and propagated
basinward through time.

The main uncertainty in the structural restoration lies in the lithol-
ogies assigned to stratigraphic units based on limited well data, which
directly affects mechanical decompaction and the estimates of sedi-
mentation rates. In addition, flexural unloading produces a smooth
isostatic response, which may affect the depth of horizons, while
compaction (which depends on the weight of the local overburden
removed) may affect the thickness of the reconstructed sediment
(Steckler et al., 1999). Here, we lacked palaeobathymetry data to
accurately adjust the reference level of the seismic cross-sections and the
correct loading/unloading effect of the water column through time.
However, through the sequential adjustment of the palaeobathymetry of
the present-day cross-sections, we achieved structural restorations that
are geologically consistent and comparable to published studies
(Krueger and Grant, 2011; Wiener et al., 2010). Another uncertainty is
that the plain strain and material balance assumptions may not be
entirely realistic, as overpressured mud-rich sediments have been shown
to deform in 3-D (interfingering with sediments) and occasionally rise to
the seafloor as mud volcanoes (Chima et al., 2022b; Graue, 2000;
Mazzini and Etiope, 2017; Soto and Hudec, 2023). Finally, the version of
KronosFlow™ (2022) used in this study is better suited to brittle
deformation, making the structural restoration of mobile shales more
challenging. Despite this challenge, the definition of ‘virtual faults’ at
the borders of the large mobile shale in the WNDL (Fig. 1E) and the use
of the manual/complex manipulator allowed us to restore the top of the
mobile shale.

3.2. Estimation of sedimentation rates and stratigraphic growth index

We estimated sedimentation rates on the structurally restored cross-
sections by measuring the cross-sectional area (km²) of each strati-
graphic unit, defined as a polygon (length and height in kilometres), at
the time of their deposition. To obtain the average sediment thickness in
metres for each stratigraphic unit, we divided the cross-sectional area by
the length of the regional cross-section. The average sediment thickness
was, in turn, divided by the duration of deposition (Ma) of the unit to
obtain average sedimentation rates (m/Myr).

The thickening of a depositional unit across a syn-sedimentary fault is expressed by the stratigraphic growth index, indicated as the ratio of sediment thickness on the hanging wall of a fault to the thickness on the footwall (Childs et al., 2003). We estimated the stratigraphic growth index along the four major syn-sedimentary normal faults on the continental shelf (labelled F1, F2, F3a, and F3b in Figs. 1D, E) by dividing the stratigraphic thickness of the hanging wall by the stratigraphic thickness of the footwall. We plotted the stratigraphic growth index against age (Ma) and investigated the interplay between sedimentation and syn-sedimentary deformation of the Niger Delta continental shelf. Finally, we compiled the continent-ocean boundary (COB) and the tightest pre-drift situation between the African and South American plates (FIT) along the equatorial Atlantic Ocean and investigated the potential control of crustal nature and/or geodynamic setting on the gravity-driven deformation of the Niger Delta.

4. Results

4.1. 2-D restoration of growth and deformation of the eastern and western Niger Delta lobes

We performed 2-D kinematic structural restoration of regional
seismic cross-sections to investigate structural evolution, deformation
rates, and the interplay between sedimentation and deformation during
the Neogene growth and gravity collapse of the Niger Delta's siliclastic
wedge. Structural restorations were constructed from the Late Eocene/
Oligocene to the Pleistocene.

4.1.1. The eastern Niger Delta lobe (ENDL)

The structural restoration of the eastern ENDL's cross-section (from
onshore to basin) shows a general basinward progradation of the leading
edge of the extensional and contractional domains through time. Based
on our cross-section restoration, the top of the mud-rich (Late Eocene/
Oligocene) unit was buried >4 km by 34 Ma, but remained relatively
undeformed until the Burdigalian (Fig. 3A). In the Burdigalian (17.3
Ma), extensional deformation dominated the proximal shelf/palaeo-
extensional zone in the up-dip area and was accommodated by shale
deformation on the distal shelf and the upper slope (Fig. 3A). During the
Late Tortonian (9.3 Ma), extensional deformation prograded from the
proximal to the distal/modern shelf, leading to a coupling of gravity-
driven deformation between the distal shelf and the IFTB (Fig. 3A).
Deposition and deformation on the modern shelf were mainly controlled
by a down-to-the-basin listric Counter-Regional Normal Fault (CRNF),
located above a step in the basement (Fig. 3A). Although cross-section
restoration suggests that the CRNF initiated in the Burdigalian (17.3
Ma), deformation on the hanging wall of the growth fault became more
evident in the Late Tortonian (Fig. 3A). Mobile shales on the distal shelf
and the inner-fold-thrust belt (IFTB), as well as thrust faults on the IFTB
(Fig. 3A), accommodated extensional deformation during the Late
Tortonian (9.3 Ma). In the Early Messinian (7 Ma), a coupling of gravity-
driven deformation occurred between the modern extensional zone and
the modern/distal contractional zone (outer-fold-thrust belt, OFTB;
Fig. 3A). Extensional deformation of the CRNF on the distal shelf and a
Regional Normal Fault (RNF) located basinward were accommodated by
imbricate toe-thrust features on the OFTB (Fig. 3A). At this time, shale
deformation ceased on the distal shelf, landward of the CRNF, but
continued on the IFTB (Fig. 3A). During the Late Messinian/Early Plioc-
cene (5.7 Ma), extensional deformation continued on the CRNF on the
distal shelf, while the RNF experienced relative quiescence (Fig. 3A).
Extensional deformation was accommodated by shale deformation on
the IFTB and middle slope, and imbricate toe-thrusts on the distal part of
the OFTB (Fig. 3A). In the Late Pliocene/Early Pleistocene (3.2 Ma),
extensional deformation prograded basinward onto a new CRNF,
establishing the present-day shelf break, while contractional deforma-
tion prograded basinward and established the present-day limit of the
OFTB (Fig. 3A). Extensional deformation was partially accommodated
by shale deformation on the IFTB and middle slope (Fig. 3A). Based on
our 2-D kinematic structural restoration, the leading edge of the offshore
ENDL's extensional zone migrated ~50 km basinward from the Late
Tortonian to the Late Pliocene/Early Pleistocene (9.3-3.2 Ma; Fig. 3A).
The estimated 50 km extent of normal faulting on the ENDL modern
shelf excludes up-dip extensional deformation in the paleo-extensional
zone, which lies beyond the limits of the studied ENDL cross-section
(Fig. 1). The leading edge of the ENDL contractional zone migrated
60 km basinward from the Late Messinian to the Late Pliocene/Early
Pleistocene (7-3.2 Ma), with 10.5 km of shortening estimated on the
present-day cross-section (Fig. 3A). The estimated initial cross-sectional
area of shale on the Late Eocene/Oligocene cross-section restoration
(decompacted) and the final cross-sectional area of shale on the present-
day cross-section (compacted) (Fig. 3A) are 1223 km² and 1056 km²,
respectively, implying a ~ 14% reduction in the cross-sectional area of
shale on the present-day cross-section (Fig. 3A).

4.1.2. The western Niger Delta lobe (WNDL)

The structural restoration of the offshore WNDL's cross-section
shows an overall basinward migration of the leading edge of the
contractional zone since the Early Pliocene (Fig. 3B). Similar to the
ENDL's cross-section, the top of the mud-rich (Late Eocene/Oligocene)
unit was buried >4 km by 39.5 Ma, but remained relatively undeformed
until the Serravallian (Fig. 3B). In the Serravallian (12.5 Ma), shale
deformation initiated on the distal part of the continental shelf (Fig. 3B).
During the Late Tortonian (9.5 Ma), a coupling between distal gravita-
tional extension and contraction was marked by normal faulting on the
modern shelf and thrusting on the IFTB, respectively (Fig. 3B).
<figure><img src="image_7.png" /><figcaption>Fig. 3. 1:1 regional 2D seismic cross-sections and structural restorations.</figcaption></figure>

A. 2D kinematic structural restoration of the ENDL (see location in Fig. 1B), showing the spatial and temporal basinward migration of extensional and contractional zones. Note the initiation of shale deformation on the distal shelf in the Burdigalian (17.3 Ma), and the basinward progradation of extensional deformation from the present-day onshore to the distal shelf in the Late Tortonian (9.3 Ma). Also note the accumulation of thick sediments on the hanging walls of normal growth faults (labelled F1, F2, and F3a) on the modern shelf, and the initiation of imbricate toe-thrusting in the Early Messinian (7 Ma). B. 2D kinematic structural restoration of the WNDL (see location in Fig. 1B), showing the initiation of mobile shale deformation in the Serravallian (12.5 Ma), and the basinward progradation of imbricate toe-thrust structures in the Early Pliocene-Pleistocene (4.9–2.6 Ma). Note the dominance of counter-regional normal faults on the ENDL’s continental shelf, compared to the WNDL’s shelf, where regional normal faults dominate. Cross-sections A and B are adapted from Wiener et al. (2010) and Chima et al. (2022a), respectively.

Extensional deformation was partially accommodated by mobile shales on the modern shelf and the IFTB (Figs. 3B). In the Early Pleistocene (2.6 Ma), a coupling of gravity-driven deformation occurred between the distal extensional zone and the proximal part of the OFTB (Fig. 3B). Extensional deformation at this time was accommodated by mobile shales on the shelf and the IFTB, and imbricate toe-thrusting, which had now prograded to the distal part of the OFTB (Fig. 3B). Based on our 2-D kinematic structural restoration, the leading edge of the offshore WNDL’s extensional zone prograded ~12 km basinward from the Late Tortonian to the present day (9.5–0 Ma; Fig. 3B). This value excludes the significant portion of the extensional deformation in the up-dip (palaeo-extensional zone), which lies beyond the WNDL’s cross-section that we studied (Fig. 1). On the other hand, the leading edge of the contractional zone migrated 33 km basinward from the Early Pliocene to the Early Pleistocene (4.9–2.6 Ma), with 9 km of shortening estimated on the present-day cross-section (Fig. 3B). The estimated initial cross-sectional area of shale on the Late Eocene/Oligocene cross-section restoration (decompacted) and the final cross-sectional area of shale on the present-day cross-section (compacted) are 429 km² and 364 km² respectively, implying a ~15% reduction in the cross-sectional area of shale on the

present-day cross-section (Fig. 3B).

Animated videos of the 2-D kinematic structural restoration described above are illustrated in supplementary files S1 (for the ENDL) and S2 (for the WNDL): Animated videos here. In addition, schematic maps and the Geologic Time Scale showing the structural evolution and the relative timing of gravity-driven collapse of the ENDL and WNDL are shown in Fig. 4A-D.

## 4.2. Stratigraphic growth index

The stratigraphic growth index along the four major syn-sedimentary normal faults on the present-day continental shelf of the ENDL (labelled F1, F2, and F3a) and the WNDL (labelled F3b) is displayed in Fig. 5A-D. The results show an overall increase in the estimated growth index from the Late Miocene to the Plio-Quaternary (Fig. 5A-D). In the ENDL, the CRNF (labelled F1), highlighted by the dashed red line (Fig. 5A), displays a relatively low growth index of 35 in the Burdigalian (17.3 Ma). The stratigraphic growth index increases from 183 to 934 over the Late Tortonian-Late Pliocene/Early Pleistocene (9.3–3.2 Ma). The RNF (labelled F2), highlighted by the dashed black line (Fig. 5A), shows a
<figure><img src="image_8.png" /><figcaption>Fig. 3. (continued).</figcaption></figure>

decrease in growth index from 193 in the Early Messinian (7 Ma) to 53 in the Late Messinian/Early Pliocene (5.7 Ma). F2 then increases in growth index from 850 to 1500 over the Late Pliocene/Early Pleistocene to the Present-day (3.2–0 Ma). The CRNF (labelled F3a), marked by the dashed green line (Fig. 5A), shows an estimated growth index ranging from 17 to 860 over the Late Pliocene/Early Pleistocene to the Present-day (3.2–0 Ma). In the WNDL, the RNF (labelled F3b), marked by the continuous red line (Fig. 5B), shows an increase in growth index from 40 in the Late Tortonian (9.5 Ma) to 43 in the Early Pliocene (4.9 Ma). The stratigraphic growth index then increases from 165 to 860 from the Early Pleistocene to the Present-day (2.6–0 Ma).

### 4.3. Sedimentation rates and crustal subsidence

The estimated decompacted sedimentation rates on the offshore ENDL and WNDL display relatively low values over the Late Eocene/Oligocene to Late Tortonian but higher values over the Plio-Quaternary. In the ENDL, sedimentation rates (indicated by the dashed blue line in Fig. 5C) decreased slightly from 93 m/Myr in the Late Eocene/Oligocene (34 Ma) to 85 m/Myr in the Burdigalian (17.3 Ma). They then increased from 143 m/Myr in the Late Tortonian (9.3 Ma) to 190 m/Myr in the Early Messinian (7 Ma). Sedimentation rates then decreased to 92 m/Myr in the Late Messinian/Early Pliocene (5.7 Ma), increased to 307 m/Myr in the Late Messinian/Early Pliocene (3.2 Ma), and peaked at 860 m/Myr, as estimated for the present-day section (Fig. 5C).

In the offshore WNDL, the estimated decompacted sedimentation rates (indicated by the continuous blue line in Fig. 5D) decreased slightly from 49 m/Myr in the Late Eocene/Oligocene (39.5 Ma) to 45

m/Myr in the Burdigalian (18.5 Ma). They then decreased again from 73 m/Myr in the Serravallian (12.5 Ma) to 65 m/Myr in the Late Tortonian (9.5 Ma). Sedimentation rates then increased steadily from 154 m/Myr in the Early Pliocene (4.9 Ma) to 170 m/Myr in the Early Pleistocene (2.6 Ma) and peaked at 397 m/Myr, as estimated for the present-day section (Fig. 5D).

Palaeo-depths of the reflector 'top crust' at its initial depth at ~34–39.5 Ma and the present-day are built from the restored cross-sections shown in Fig. 3A and B. These suggest two different subsidence dynamics between the eastern and western Niger Delta: preferential subsidence on the ENDL's modern shelf, as opposed to spatially homogeneous subsidence along the WNDL's cross-section (Fig. 6). The resulting geometry also allows for the assessment of total and mean total subsidence rates since the Late Eocene/Oligocene (~34–39.5 Ma). On the modern shelf, subsidence reaches 3.7–4.5 km on the ENDL's cross-section (with a mean subsidence rate of ~110 m/Myr-130 m/Myr) and 2.7–4 km on the WNDL's cross-section (with a mean subsidence rate of ~70–100 m/Myr) (Fig. 6). This will be discussed further in Section 5.3.

## 5. Discussion

This section will discuss the likely controlling factors of margin architecture/evolution, in particular the differential gravity collapse of the eastern and western Niger Delta lobes.
<figure><img src="image_9.png" /><figcaption>Fig. 4. Schematic maps illustrating the structural evolution of the eastern and western Niger Delta lobes (ENDL and WNDL). A. Burdigalian (18.5–17.3 Ma) structural map, showing the location of the extensional zone in the present-day onshore and the initiation of shale deformation on the ENDL’s modern shelf. B. Late Tortonian (9.5–9.3 Ma) structural map, showing the basinward progradation of the extensional zone from its initial position in the present-day onshore to the ENDL’s modern shelf, and the initiation of thrusting in the inner fold-and-thrust belt (IFTB).</figcaption></figure>

C. Late Messinian-Early Pliocene (5.7–4.9 Ma) structural map, showing the initiation of thrusting in the proximal part of the WNDL’s outer fold-and-thrust belt (OFTB), the basinward progradation of the ENDL’s OFTB, and the coupling of deformation in these zones with Late Miocene extension on the modern shelf. D. Late Pliocene-Early Pleistocene (3.2–2.6 Ma) structural map, showing the basinward progradation of the ENDL’s and WNDL’s OFTBs to their present-day positions on the lower slope (see also Fig. 3). The timing of the gravity-driven collapse of the ENDL and WNDL is indicated on the Geological Time Scale (GTS) in the upper right corner. The GTS is adapted from Walker and Geissman, 2022).

## 5.1. Differential gravity collapse of the eastern and western Niger Delta lobes

A recently published study of the eastern and western Niger Delta shows that gravitational extension initiated in the onshore area in the Late Eocene and was accommodated by shale deformation on the inner shelf (Spina et al., 2025). In this study, the limited nature of the WNDL’s cross-section (lack of data on the proximal shelf and the palaeo-extensional zone; Fig. 1) makes it difficult to compare the onset of gravitational extension on the eastern and western Niger Delta lobes. However, the extension of the cross-sections from the continental shelf to the basin (Fig. 1) allows us to investigate and compare the onset of gravitational contraction on the ENDL and WNDL (Figs. 3A, B). Our results show that imbricate toe-thrusting on the OFTB initiated earlier on the ENDL (Early Messinian) than on the WNDL (Early Pliocene/Pleistocene; Figs. 3A, B; 4 A-D; 5; S1, S2). Cross-section restoration suggests that the OFTB prograded ~60 km basinward on the ENDL over the Late Messinian-Late Pliocene/Early Pleistocene, but ~33 km on the WNDL over the Early Pliocene to Present-day (Fig. 3A, B). However, the earlier initiation of imbricate toe-thrusting on the ENDL (see also Spina et al., 2025, there Figs. 12 and 13), suggests that gravitational

contraction initiated earlier there, but the WNDL has been relatively more active and spread faster during the Pliocene-Pleistocene (Figs. 3A, B, 4A-D; S1, S2). This interpretation is in agreement with Wu et al. (2015), who demonstrated through analogue modelling that the WNDL spread basinward more rapidly than the ENDL.

On the other hand, our cross-section restoration suggests that gravitational extension initiated on the ENDL’s distal shelf in the Burdigalian (17.3 Ma) but intensified in the Late Tortonian (9.3 Ma), following the basinward progradation of deposition at that time (Fig. 3A). The Late Tortonian (9.3 Ma) initiation of thrusting on the ENDL’s Inner-Fold-Thrust Belt (IFTB) suggests a coupling of up-dip gravitational extension with down-dip gravitational contraction (Fig. 3A). This interpretation is in agreement with previous studies of the ENDL (e.g. Jolly et al., 2016; Wiener et al., 2010), which showed that gravitational collapse of the ENDL increased in the Late Tortonian. Similarly, the restored WNDL’s cross-section suggests that gravitational extension on the distal shelf intensified in the Late Tortonian (9.5 Ma) and was partially accommodated by thrusting on the IFTB (Fig. 3B). Jolly et al. (2016), through a detailed analysis of a 3D seismic data cube on the ENDL’s OFTB, documented a general reduction in shortening rates in the Pli-Pleistocene (after 3.7 Ma). Jolly et al. attributed this observation to a
<figure><img src="image_10.png" /><figcaption>**Fig. 5.** A, B. Stratigraphic growth indices along major normal faults on the modern continental shelves of the ENDL (F1, F2, and F3a) and the WNDL (F3b). Note the general increase in the growth index of normal faults from the Late Tortonian to the Pleistocene, except F2 in panel A, which shows a decrease in the Late Messinian-Early Pliocene (5.7 Ma). C, D. Decompressed sedimentation rates on the offshore ENDL and WNDL. Note the relatively low sedimentation rates from the Burdigalian to the Late Tortonian, and higher sedimentation rates during the Plio-Quaternary. Also note the higher sedimentation rates (2×) on the ENDL's modern shelf during the Plio-Quaternary than on the WNDL's shelf. See text for a more detailed explanation.</figcaption></figure>

slowdown in up-dip gravitational extension during the Plio-Pleistocene. In addition, Jermannaud et al. (2010) and Rouby et al. (2011) recorded a general reduction in sedimentation on the ENDL during the Plio-Quaternary. Jermannaud et al. attributed this observation either to regional delta lobe migration/shift in sediment flux to the WNDL or to climate warming in West Africa/aridification of the Niger catchment. Our structural restoration of the ENDL's cross-section suggests that gravitational extension and sedimentation rates on the modern shelf have persisted to the Present-day, while imbricate toe-thrusting slowed down after the Late Pliocene/Early Pleistocene (3.2 Ma; Figs. 3A, 5B). The observed difference could be linked to a combination of factors: limited observation on the single cross-section we studied, along-strike local variation/distortion of the depositional record by local transient storage and/or lateral input/output, or growth faulting (Chima et al., 2022a; Hooper et al., 2002; Grimaud et al., 2017; Krueger and Grant, 2011). Despite the increase in gravitational extension and sedimentation rates on the ENDL's cross-section in the Plio-Quaternary, compared to Jolly et al. (2016), Jermannaud et al. (2010), and Rouby et al. (2011), the Late Tortonian intensification of gravity-driven deformation on the ENDL and WNDL (Figs. 3A, B) is consistent with the results of Jolly et al. (2016), Spina et al. (2025), and Wiener et al. (2010). Subject to more detailed regional studies, the observed general increase in sedimentation rates and gravitational collapse of the WNDL during the Plio-Quaternary (Figs. 3B, 5D) could record the proposed delta lobe

migration/shift in sediment flux from the ENDL to the WNDL (Jermannaud et al., 2010).

The estimated ~14% and ~15% reduction in the cross-sectional area/volume of mobile shale on the ENDL's and WNDL's present-day cross-sections, respectively, are interpreted as effects of sediment loading and burial compaction that occurred since the time of deposition. The estimated 60 km and 33 km basinward progradation of the leading edge of the ENDL's and WNDL's OFTB (Fig. 3A, B) is minimal compared to the total size of the extensional zone, including the >100 km palaeo-extensional zone in the present-day onshore (Fig. 1B). Hence, at the scale of the Niger Delta gravity-collapse system, extension typically exceeds contraction, with intervening shales partially accommodating strain (see also Spina et al., 2025; Figs. 1B, D, E; 3A, B). Similar observations have been documented on other shale-dominated passive margins (see review in Morley et al., 2011).

## 5.2. Controls of margin architecture on gravitational collapse of the Niger Delta

Margin tilt and depositional loading have been shown to accelerate gravity gliding and spreading of sedimentary wedges above incompetent layers (Rowan and Ratliff, 2012; Rowan, 2020). Earlier studies of the Nigerian divergent margin identified the presence of a basal décollement and high sedimentation rates as the main triggers for
<figure><img src="image_11.png" /><figcaption>**Fig. 6.** Palaeo-depths of the 'top crust' reflector at its initial depth (~34–39.5 Ma) and at present-day, based on the restored cross-sections shown in Fig. 3A and B. The resulting geometry along the ENDL cross-section suggests the localisation of subsidence on the modern shelf, while a more spatially homogeneous subsidence is observed along the WNDL cross-section. See Fig. 1 for profile locations and legend.</figcaption></figure>

gravity collapse of delta lobes above overpressured shales (Peel, 2014; Krueger and Grant, 2011; Restrepo-Pace, 2018; Rowan et al., 2004; Spina et al., 2025). However, a recent study of gravity-driven deformation above a shale décollement offshore Namibia, in the central South Atlantic Ocean, suggests that substratum dip does not play a significant role in gravity-driven failures (Scarselli et al., 2022, and references therein).

In this study, the observed dip in the basal décollement of the ENDL, and gravity spreading due to delta progradation in the Late Tortonian (Figs. 1D, 3A, 4A-D; S1), are inferred to have favoured greater basinward gravity gliding. This interpretation is supported by the nearly twofold (2×) lateral propagation of the ENDL's imbricate toe-thrust front compared to that of the WNDL (Figs. 1D-E, 3A-B, 4A-D; compare S1 to S2). In addition, the high sedimentation rates estimated on the ENDL's cross-section during the Plio-Quaternary (Fig. 5B) are inferred to have contributed to the more extensive progradation of the outer contractional front. In contrast, the relatively gentle dip of the offshore WNDL's basal décollement (Figs. 1E, 3B) suggests that gravity spreading-mainly driven by high sedimentation rates during the Plio-Quaternary (Fig. 5D), controlled the basinward progradation of the outer contractional front (Figs. 3B, 4; S2). The dip in the décollement beneath both the ENDL (Corredor et al., 2005; Wiener et al., 2010) and the WNDL (Haack et al., 2000) may be attributed to a combination of:

(i) structural inheritance (Briggs et al., 2009a, 2009b; Davies et al., 2005), (ii) margin tilting during the Late Eocene-Early Oligocene uplift of the Hoggar region, north of the Niger catchment (Chardon et al., 2016; Fig. 2), and (iii) progressive increase in depositional loading (Fig. 6A). This interpretation aligns with Restrepo-Pace (2018), who showed that along-strike variations in slope and décollement dip in the Niger Delta reflect delta-wide changes in the mechanical strength of the prism, lithology, and geopressure, that influence margin failure. The onset of shale deformation on the ENDL's cross-section in the Burdigalian and on the WNDL's in the Serravallian suggests that fluid overpressure within the mud-rich décollement facilitated gravitational collapse of the delta, partially accommodating strain (Figs. 3A, B). Elsewhere, in the Kwanza Basin offshore Angola (central South Atlantic Ocean), an increase in bathymetric slope linked to post-rift margin uplift has been shown to accelerate gravity gliding above a salt décollement

(Hudec and Jackson, 2004, and references therein).

**5.3. Differential structural styles and subsidence: a consequence of contrasting crustal nature?**

The dominance of CRNF on the ENDL's modern shelf and RNF on the WNDL's shelf (Figs. 1D, E, 3A, B; S1, S2) has previously been linked to either the proximity to fracture zones/buried volcanoes or the presence of buried thrusts (Chima et al., 2022b and the references therein). However, Ings and Beaumont (2010), demonstrate through numerical modelling that basinward shale flow and overburden deformation, facilitate the development of regional and counter-regional normal faults (their model 2). The inferred localisation of subsidence on the ENDL's shelf (above steps on the basement Fig. 6A), compared to the WNDL, which displays homogenous subsidence (Fig. 6B), suggests that basement architecture partly controlled the gravitational collapse of the Niger Delta (see also Spina et al., 2025). In particular, the observed basement steps within the ENDL's extensional and translational zones (Figs. 1D, 6A; S1) could reflect crustal zones of weakness. To further explore the possible explanation of the inferred differential subsidence, we discuss the implication of previous reconstructions on the margin segmentation for four kinematic models. We rely on the compilation of COBs (Continent-Ocean Boundaries, i.e. the location where the first true oceanic crust begins; Schmitt et al., 2018; Fig. 7A) and FITs (i.e. the tightest pre-opening reconstructions prior to any horizontal displacement; Gaina et al., 2013; Heine et al., 2013; Moulin et al., 2010; Wiener et al., 2010; Torsvik et al., 2009; Macdonald et al., 2003; Nürnberg and Müller, 1991; Fig. 7B), and we use average crustal width values derived from deep wide-angle seismic data (see below).

Margin subsidence depends on the crustal nature of the basement and its evolution. On passive margins, the crust transitions from unthinned continental crust to true oceanic crust via an intermediate domain, which may consist of thinned continental crust, exhumed lower crust with or without magmatism, and proto-oceanic crust (Aslanian et al., 2021, 2024; Moulin et al., 2021). In rare cases, parts of the exhumed upper mantle may also be observed (Spina et al., 2025; Sapin et al., 2021, and references therein). Due to the lack of deep wide-angle seismic data for the Nigerian margin, the basement morphology, nature
<figure><img src="image_12.png" /><figcaption>**Fig. 7.** A. Free-air gravity anomaly (Sandwell and Smith, 2009), showing the published continent-ocean boundary (COB) in the equatorial Atlantic region (Schmitt et al., 2018; highlighted in white). See text for a more detailed explanation.</figcaption></figure>

<caption>**B.** Free air gravity anomaly (Sandwell and Smith, 2009) showing compilation of FIT in the equatorial Atlantic region (e.g. Gaina et al., 2013, highlighted in olive; Heine et al., 2013, yellow; Moulin et al., 2010, dark green; Wiener et al., 2010, purple; Torsvik et al., 2009, light green; MacDonald et al., 2003, pink; Nürnberg and Müller, 1991, light blue). See text for a more detailed explanation. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</caption>
and extent of intermediate crust, and true oceanic crust position remain uncertain-hence our reliance on kinematic models. COB locations and FIT positions vary between authors and are rarely presented together: some authors prefer to show the COB instead of the FIT. The COB by Schmitt et al. (2018) is based on a compilation of multiple sources derived from the Gondwana geological map (IGCP-628) and is notably parallel to the modern coastline (Fig. 7A). The FITs (Fig. 7B) show a difference of more than 200 km between the most overlapping hypothesis (Torsvik et al., 2009) and the less overlapping ones. Re-constructions (by Heine et al., 2013, Wiener et al., 2010 and Moulin et al., 2010) considered the presence of the oceanic Fracture Zone in the initial breakup, but not at the same location. These differences imply different boundaries of the intermediate domain. Several compilations of passive margins have been proposed (see Sapin et al., 2021; Péron-Pinvidic et al., 2019), but they do not refer to the wide-angle seismic data acquired on the South Atlantic passive margins in collaboration with Petrobras. However, true crustal geometry and velocity profiles of passive margins can only be reliably obtained using wide-angle seismic data, as reflection data may show significant artefacts when

investigation depth exceeds streamer length (see Loureiro et al., 2018, their Figs. 13–14, for comparison with ION-GXT industry multichannel seismic [MCS] lines). We therefore used the general morphology based on combined interpretations of industry and academic multichannel and deep wide-angle seismic data from the passive margins of the equatorial and central South Atlantic (Aslanian et al., 2021, 2024; Aslanian and Moulin, 2012; Evain et al., 2015, 2023; Gonçalves et al., 2023; Loureiro et al., 2018, 2023; Moulin et al., 2005, 2021; Pinheiro et al., 2018; Schnürle et al., 2023). This compilation typically described on average 50–100 km-wide necking zone and an intermediate domain of approximately 200 km before a true oceanic crust (Aslanian et al., 2024).

Based on this general morphology, Fig. 8 shows the boundaries of the necking zone and intermediate domain for four kinematic models (Schmitt et al., 2018; Torsvik et al., 2009; Heine et al., 2013; Moulin et al., 2010), using the authors’ Euler poles. Regardless of the size of the necking and intermediate domains, it is worth noting that these boundaries overlap north of the Chain Fracture Zone during the initial post-breakup movement in three of the reconstruction models (see red box in Fig. 8A-C). Using the general segmentation of the Atlantic

<figure><img src="image_13.png" /></figure>

**Fig. 8.** Free air gravity anomaly map (Sandwell and Smith, 2009), showing a compilation of COB and FIT on the equatorial Atlantic region. These limits were shifted by 100, 200 and 300 km (dashed lines) following the compilation of Aslanian et al., 2024, which described on average, a 100 km-wide necking zone and an intermediate domain of 200 km before a true oceanic crust. A. COB (continuous green line) based on Schmitt et al. (2018) compilation of multiple sources derived from the Gondwana geological Map (IGCP-628). The COB has been offset 100 km, 200 km and 300 km landwards using the author’s Euler poles (dashed green lines) to represent intermediate and necking zones. In Schmitt’s hypothesis, a significant portion of the ENDL’s seismic profile (including the extensional zone) lies within the 200 km-wide zone while a significant portion of the WNDL’s profile (including part of the extensional zone) lies within the oceanic crust domain. B. FIT based on Torsvik et al. (2009): both the ENDL’s and WNDL’s seismic profiles lie within the oceanic crust domain. C. FIT based on Heine et al. (2013): a significant portion of the ENDL’s and WNDL’s seismic profiles (including the extensional zone), lies within the 200 km-wide domain after the necking zone, while the rest lies within the oceanic crust zone. D. Moulin et al. (2010): the two profiles are in different settings: the ENDL’s profile lies entirely in the 200 km-wide intermediate domain of a divergent margin while the WNDL’s profile is situated in a strike-slip margin. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
margins described above, the Schmitt et al hypothesis (Fig. 8A) presents a fit that is even more overlapping on the African plate than the Torsvik et al model (Fig. 8B). In both models, the ENDL and WNDL profiles are mainly located on an oceanic domain assumed to be of similar age, with probably similar subsidence evolution. However, in addition to the issues of overlaps and gaps associated with the more overlapping models (see Moulin et al., 2010; Aslanian and Moulin, 2010, 2012), the overlaps observed north of the Chain Fracture Zone during the initial stage of African and South American plates evolution cast doubt on these reconstructions.

In the Heine et al model (Fig. 8C), while the WNDL profile is mainly located in the transition domain, the ENDL profile is located at the boundary of the intermediate-oceanic domains, which will produce differential subsidence between the eastern and western halves of this portion of the margin. However, this model shows a similar overlap to previous ones north of the chain fracture zone (Fig. 8C). In the Moulin et al model (Fig. 8D), the two profiles are located in different geodynamic settings, implying different crustal natures and subsidence evolutions, with a slip margin linked to the Chain Fracture Zone for the WNDL's profile, and a divergent margin for the ENDL's profile.

It is beyond the scope of this paper to argue between these different propositions, nevertheless, it should be noted that (i) three of them exhibit wide overlaps north of the Chain Fracture Zone during the first movement after the breakup, and (ii) the uncertainty of the dimension of the intermediate domain is significant. Nevertheless, assuming an average morphology of the passive margin in the equatorial and the central segment of the South Atlantic Oceans, two propositions may explain the observed difference in crustal subsidence: (i) difference in crustal nature (oceanic versus intermediate, Heine et al., 2013) or (ii) difference in geodynamic setting (strike-slip versus divergent setting, Moulin et al., 2010).

## 6. Conclusions

The western and eastern Niger Delta lobes (WNDL and ENDL) cross-sections lie parallel or oblique to palaeo-continent-ocean transform zones that interact with both oceanic and continental lithospheres beneath the Nigerian margin. These features have been linked to the complex gravitational collapse systems and structural deformations described in this study. Further insights into the margin's crustal structure, flexural patterns, and the controlling thermal, mechanical, mantle, and sedimentary processes require additional geophysical data-particularly wide-angle seismic surveys-and broader regional studies. Specifically, backstripping and 2D kinematic restoration of the ENDL and WNDL 2D regional cross-sections allow us to draw the following conclusions regarding the Neogene gravitational collapse of the Niger Delta:

* The Niger Delta is controlled by gravity-driven processes and the crustal architecture of a divergent margin. At the scale of the margin's gravity-collapse system, extension generally exceeds contraction, with strain partially accommodated by overpressured shales.

* Gravitational contraction initiated earlier in the offshore ENDL (Early Messinian) compared to the offshore WNDL (Plio-Quaternary); however, the WNDL has been relatively more active and has spread more rapidly than the ENDL. The earlier initiation of gravitational contraction in the ENDL's outer fold-and-thrust belt (OFTB) increases the likelihood of discovering structural traps of Late Miocene to Early Pliocene age in the region, while the faster gravity spreading of the WNDL's OFTB implies a higher risk to hydrocarbon traps due to reactivated structures.

* The presence of a dip in the ENDL's basal décollement facilitated more basinward translation (gravity gliding) of the sedimentary wedge, accompanied by gravity spreading driven by delta lobe progradation in the Late Tortonian. In contrast, the relatively gentle dip

of the WNDL's regional décollement, aided by depositional loading, favoured gravity spreading, particularly during the Plio-Quaternary.

* The inferred location of the WNDL's cross-section within a palaeo-transform zone implies increased exploration risk, as transform structures can complicate petroleum systems correlation.

* The localisation of subsidence on the ENDL's cross-section, compared to spatially homogeneous subsidence on the WNDL's cross-section, may be attributed to differences in crustal nature (oceanic versus intermediate; Heine et al., 2013) and/or differences in geodynamic setting (strike-slip versus divergent; Moulin et al., 2010).

The results presented in this study may be applied on a broader scale to refine our understanding of how gravity-driven deformation is linked to the wider tectono-stratigraphic evolution of divergent margins.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.tecto.2025.230874.

## CRediT authorship contribution statement

**Kelvin Ikenna Chima:** Writing – review & editing, Writing – original draft, Software, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Estelle Leroux:** Validation, Supervision, Methodology, Conceptualization. **Marina Rabineau:** Validation, Supervision, Methodology, Conceptualization. **Didier Granjeon:** Validation, Supervision, Methodology, Conceptualization. **Maryline Moulin:** Validation, Supervision, Methodology, Conceptualization. **Philippe Schnurle:** Validation, Supervision, Methodology. **Daniel Aslanian:** Validation, Supervision, Methodology, Conceptualization, Writing – review & editing.

## Declaration of competing interest

I, Kelvin Ikenna Chima, hereby declare that there is no conflict of interest in this study. I have fully acknowledged the sources of the seismic cross-sections presented in the paper. In addition, the funding provided for this research by the French Government through the PAUSE Programme in patnarship with Ifremer, and does not constitute any conflict of interest.

## Acknowledgements

My gratitude goes to Nicolas Mouchot, Mattieu Gravitto, and Emmanuel Pettinotti (Beicip-Franlab, Paris) for their insights and support with KronosFlow. KronosFlow™ is the 2D structural restoration tool embedded in the OpenFlow Suite, developed by IFP Energies Nouvelles and commercialised by Beicip-Franlab. I would also like to thank Yoann Bichot (Ifremer) for his assistance with ArcGIS Pro. Our sincere gratitude goes to Chris Morley, Chris Elders, and François Sapin for their detailed reviews and suggestions, which significantly improved the final version of this paper. This research was funded by the French Government through the PAUSE Programme, in partnership with Ifremer.

## Data availability

The seismic cross-sections analysed in this study were adapted from published sources. The eastern Niger Delta cross-section was adapted from Wiener et al. (2010), published in *AAPG Bulletin*, while the western Niger Delta cross-section was adapted from Chima et al. (2022a), published in *Basin Research*.

While the eastern Niger Delta seismic profile may be requested directly from CGG Veritas (now Viridien), our confidentiality agreement with Shell Nigeria does not permit us to share the seismic profile for the western Niger Delta.
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