Cretaceous Paleogeographic, Climate, Drainage and Topographic Maps of Africa

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Late Valanginian to Early Hauterivian 135+-5Ma

Clastic sedimentation rates rise substantially on NW African margins north of Senegal. Around 400,000 cubic kilometres of sediment (compacted, authors estimate from published cross-sections) are deposited between the Berriasian and Barremian in the Aaiun (AA) Delta, at rates comparable to the Cenozoic Nile and Niger systems.  Based on the scaling relationships of Somme et al (2009), a catchment area of the order of 106 km3 is required as well as a wet climate. AFTA data indicate a wide area of uplift and erosion at this time, extending into the Taoudenni (TA) basin (Girard, 2015), that must supply this depocentre. The Moroccan carbonate bank terminates , though the bank continues to form on the Senegal margin.  A wide, partly faulted depression (the ‘Afro-Brazilian depression) forms over what is now Gabon and NE Brazil, as a prelude to the main syn-rift phase (Chaboureau, 2017).

There is paleofloral (Burgoyne, 2005) and other evidence for a general wettening of the climate of north Africa around this time, despite only minor movements in paleolatitude belts.  This is probably related to the opening of the Central Atlantic. Warm generally dry conditions characterise southern Africa. Late Jurassic to Cretaceous drainage in the Cuvette Centrale in the Mesozoic was south to north (Agyemang et al, 2016). , though it is not clear where the eventual outlet to the sea was.

Barremian 128+-7Ma

A similar pattern of topography and drainage is suggested to the Valanginian-Hauterivian map. Carbonates continue to develop on the northern margin of the plate, while non-marine depocentres are established in rifts not connected to Tethyan oceans. Clastic sedimentation dominates on the northern part of the NW African margin, though at reduced rates, while the carbonate platform persists to the south (Ye et al, 2017). A dominance of carbonates on the Somali margin pass southwards into clastics, which is likely an indicator of a contrast in hinterland topography as a high centred on the Tanzanian Craton starts a slow rise. Anoxic lacustrine shales are particularly common in the Barremian syn-rift and/or ‘sag’  sections of West Africa and Brazil (Chaboureau, 2017). A major river derived probably from the Cuvette Centrale, appears to enter the northern part of the Dentale Trough (DT) in the Late Barremian-early Aptian and then turns southwards (Tiesserenc et al 1989), depositing a very thick fluvial clastic section, though no marine outlet is apparent. The familiar post-break up pattern of opposing carbonate banks is developed in the southern South Atlantic.

Climate conditions appear similar to the Hauterivian, with the majority of the evidence in northern Africa indicating humid equatorial conditions and that in southern Africa much drier conditions. Water supply must clearly be sufficient to fill the deep anoxic lakes illustrated. Widespread anoxic conditions in these lakes indicate low wind activity incapable of driving circulation cells from lake surfaces to the lake bottoms.

Aptian 118+-7Ma

A complex array of facies are developed above and below the presumed Late Aptian break-up unconformity in the South Atlantic between Gabon and the Rio Grande Ridge (Chaboureau, 2017) . The Early Aptian is clastic prone in the north (stipple below salt symbol) but carbonate prone in the south (carbonate symbol below salt symbol) . The lacustrine carbonates below the unconformity are the ‘Coquinas’ : those above (equivalent to the Gamba-Vemba sequence in the north) have been termed ‘microbialites’ (but may in fact be predominantly carbonate evaporites (Wright , 2022).  The overlying salt (after Borsato 2012), is increasingly thought to be ponded on both sides by an emerging oceanic ridge (e.g. cross-sections of Caixeta et al (2014). Marton and Pascoe (2020) report salt overlying oceanic crust in the deep Namibe Basin.

Within Southern Africa, Moore and Larkin (2009) interpret the first phase of uplift of the southern Africa plateau, centred on the Cape Fold Belt. As the intensity of erosion in the Agulhas basins increases eastwards, this may be driven by transpression of the Maurice Ewing Bank (MEB) passing on the Agulhas Fault. Hunt (2021, Geological Society presentation) presented a model to suggest that a river which originally flowed out further south was diverted by this uplift to feed the first reservoir sands of the Orange Basin (OB). Early stage uplifts are suggested by AFTA data on the Leo Massif and in East Africa in addition to ongoing uplift of the Reguibat (RE , Charton et al 2020). Northwest Africa is becoming more clastic prone, though sand inputs rarely penetrate beyond the carbonate bank (Mourlot et al 2018 ; Casson, 2019). Lacustrine and fluvial clastics fill the deep pull-apart basins formed off the Equatorial Margin at this time.

Lithological indicator mapping in Boucot et al, 2013 indicates humid tropical conditions at this time in Egypt (e.g. Baioumy, 2012), and largely arid or semi-arid elsewhere.

Late Albian 102+-7Ma

A sharp change occurs on the Senegal/Guinea margin from carbonates to clastics in the Early Albian (Clayburn, 2018). This carbonates to clastics change is notably younger than in Morocco, this difference being related to differing ages of hinterland uplift in the two regions. New drainage systems seem to be sourced from the uplifted Leo Massif, where a watershed is evidenced by mineralogical data between rivers draining north and south (Ye , PESGB Presentation, 2021). The massif may have been formed by transpression as South America departs from Africa. The Orange River has become the most significant depocenter off Africa : this commences an outboard progradation at this time as the South African Plateau starts to rise. Carbonates develop over salt between Gabon and northern Namibia, with a short phase of a ‘proto-Congo river’ depositing clastics off Cabinda (Anka, 2009). A sharp deepening occurs on the Equatorial Margin around the Albian-Cenomanian boundary (Macgregor, 2003). With the whole of the South and Central Atlantic then connected, contourite deposits become common (e.g. Mourlot et al 2018)

Climates seem to have wettened somewhat since the Aptian, with sedimentological interpretations indicating increased variability between dry and wet periods. This is associated with a rise in sedimentation rates on the various margins. A major eustatic rise occurs in the early Cenomanian that causes major transgression, particularly in north and north-central Africa, with Tethyan and South Atlantic waters then connected through the active Niger rifts and the Benue trough. The extent of this Cenomanian transgression, largely taken from Sahagian (1988) and Bonne (2014), is portrayed on this map as a purple line.


Santonian 86+-6Ma

The topographic model for southern Africa from now on follows the ‘Hybrid Late’ model of Stanley et al (2021) who summarise the evidence for (and against) Late Cretaceous and Neogene uplift phases. It is accepted that a major expansion of the South African plateau occurs between 93-66Ma (Baby et al, 2019). Effects are also seen on AFTA profiles as far interior as Zambia (Daly et al, 2020). The broad nature of the uplift and the association with alkaline magmatism and kimberlites seemingly point to a mantle origin. The uplift and increasingly wet climate cause an increase in clastic sedimentation rate and progradation in various outlets, including the Orange (OR) and Zambezi (ZA), the latter only accessing sediment as far as the Luangwa Basin.  Some authors consider the Limpopo to have been a more significant river and depocenter than the Zambezi, though this is not suppored by the sedimentary rates presented here.  AFTA data and increasing sedimentation rates also indicate the uplift of a large area of Kenya and Tanzania (Noble, 1997), including the deeply eroding rift shoulders of the active Anza Rift (AN, Morley et al, 1997).  Unpublished Zircon Fission Track Data from Tanzanian sediments (Geotrack PESGB presentations) indicate this high likely formed the African watershed. Westwards drainage was therefore from here towards the Ogouee Delta of Gabon, with other parts of West Africa being sediment starved.

High sea levels have persisted since the Cenomanian. Due to rapid fault subsidence at this time, deep marine strata are developed in the interior of Africa in the Termit (TE) Basin (Zhou et al, 2017) . However inversion in the Benue (BE) Trough has likely blocked the connection between the Tethyan and South Atlantic oceans Bonne (2014). Wet climates are now established over much of the continent, with arid conditions confined to the interior in the south and to northwest Africa.

Maastrichtian to Danian 65+-5Ma

In North Africa the Late Cretaceous transgression has become even more advanced, with the shoreline reaching into Sudan (Selim, 2015) and periodically into the Iullemeden (IU, Moody 1997) Basin of Niger. A particularly string pulse of transgression in Egypt and Sudan occurred in the Coniacian.The inlet through Niger has been closed due to uplift. This results in the deposition of large volumes of chalk over northern Africa. 

The South African plateau has been uplifted between 93-66Ma (Baby et al, 2019) so topography has expanded considerably since the Santonian. A sharp reduction occurs in the Danian in sedimentation rates in all surrounding sinks (Macgregor, 2012). This is assumed to be due to a sharp drying of the climate in that region, which essentially freezes the topography established at that time. AFTA fission track ages on the Tanzanian Craton (TC) and Anza rift shoulders also peak around this time, suggesting maximum topography.  For the first time, a river is interpreted flowing down the Benue Trough (i.e. a paleo-Benue, which is the dominant branch of the Niger even today, Whiteman, 1982)


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