Jurassic Maps of Africa

Most of the Eastern Mediterranean likely now opens. Major alkaline flood basalts of latest Triassic age are erupted in Israel and a large unconformity is seen there of Norian to Hettangian age (Gardosh et al, 2011). The available window for the age of the Eastern Mediterranean oceanic crust seems to be from late Triassic to early Middle Jurassic : a younger date is precluded by the opening of the Ligurian Ocean in the Middle Jurassic. Horsts and grabens in the Levantine Basin (LE) trend NNE-SSW , implying transform movement along the sharp Egyptian margin (Longacre et al, 2007: Tari et al, 2012). At some point, extension is transferred to the Herodotus (HE) Basin, which hyperextended, leaving the Eratosthenes High as a stranded block (Gao et al, 2020). This can be connected with evidence of transform tectonics in the Gulf of Sirt (GOS, Jagger et al, 2018). and as far as the incipient Azores-Gibraltar transform. However the Menderes-Taurides blocks cannot be moved too far west while holding Apulia in place (as evidenced by paleomagnetics) and the phase of NNE-SSW spreading may thus have been short lived

The intensity of rifting has decreased in the Newark (NE), Nova Scotia (NS), Atlassic (AT) and Sicilian rifts (SI), though a second milder pulse is proposed in Morocco (Frizon et al, 2008, Escoca et al, 2021).  A major magmatic event occurs at the Triassic-Jurassic boundary, which is defined at the mass extinction associated with the Central Atlantic Magmatic Plume (CAMP). The distribution of these volcanics is largely after McHone (2000). Within tectonically controlled inlets such as the Triassic Basin (TR) and incipient Central Atlantic, evaporites are well developed. On the American side, there is magnetic evidence for the emplacement of seaward dipping reflectors around this time: the only reports of these on the African side come from presentations by Petrosen over Senegal.

The ‘Karoo’ rifts are now inactive (Macgregor (2018)).  Over the Zambian and Tanzanian rifts, an unconformity is seen between Triassic and Late Cretaceous, capping inversion structures that increase in intensity to the SW. The lack of any displacement on Pleinsbachian dyke swarms suggest this inversion could be placed in this time period. This inversion could indicate a reversal of the STASS wrench faults.

Africa is still moving north over the climatic belts, including an expanded arid zone (Boucot, 2013) , although this movement is now slowing. Despite the widespread evaporites in north Africa, there are still indications of periodically humid conditions, particularly in NE Africa, where coals are developed (Boucot, 2013). Humid conditions become more frequent in NW Africa as one moves into the Jurassic (Olsen, 2000). Increasingly hot and arid conditions are evidenced in the Great Karoo (GK) Basin, with aeolian sandstones now being deposited (Catuneanu et al, 2005).

The Eastern Mediterranean/Ionian seas may be approaching the end of their drift phase by this time, as extension is now commencing in the Ligurian Sea (Handy et al, 2010). However, the presence of Middle Jurassic  flood basalts on the western margins of the Ionian Sea (Reeh and Aifa, 2008) may suggest continued activity . The rate of drift is accelerating in the Central Atlantic, with oceanic crust now reaching south of the Blake Spur (BS) (Teasdale in Casson, 2020) . Sheridan (1988) interprets breakup on the Blake Plateau as  basal Callovian.

Indian Ocean unzipping and spreading is far more rapid. The Somali Basin is now opening, with oblique spreading extending to Tanzania and perhaps northern Mozambique (Reeves, 2018). The Davie Transform is yet to form (Phethean, 2016). A major transgression is observed in many of these basins around Bajocian times, which may mark break up (Macgregor (2018)). A volcanic margin is forming over the Mozambique margin. Figuerido et al (PESGB presentation, 2021) interprets first oceanic crust at 170Ma in the Angoche (AN) Basin and offshore Zambezi (ZA) , though this was abandoned in favour of more outboard spreading centre 10My later, leaving the Beira High (BH) as a stranded block. Roche et al (2023) transfers the extension in this region to the south on a large transform , where the proto-Weddell Sea could be opening. Rifting of the Agulhas Basins in South Africa may be commencing in the deepest half graben of the Gamtoos (GA) Basin (Mcmillan et al, 1997). This is likely to be an extension of the East Falklands (EF) Basin, where a very thick Jurassic section seems to open up over major bounding faults in a possible pull-apart setting.

The Middle Jurassic is a relatively inactive period with respect to intra-plate rifting . A notable exception is a second phase of rifting in the Western Desert (WD)  (Dolson et al, 2014).  This and later phases of Western Desert rifting are difficult to explain in a geodynamic framework : a SE Asia style model involving initial transtension (and later reversal and transpression), perhaps related to the Trans-African Lineament (TAL), can be speculated upon. Minor rifting continues in the northernmost Atlas Basins (Escoca et al, 2021), probably associated with sinistral movement on the Agulhas transform.

On a plate scale, carbonate deposition has become more widespread. Opposing carbonate platforms are now developed on the two Central Atlantic margins. The earliest transgressions in East Africa are marked by the formation of carbonates, particularly in the Bajocian, when opposing carbonate platforms formed in Tanzania/Kenya and Madagascar (Macgregor (2018). Relatively little climatic information is available in this time interval, though what is available suggests a continuation of the dominantly arid conditions of the Early Jurassic. Exceptions are increasingly humid conditions present in northern Africa, close to the Tethys ocean (e.g. coal development in the Western Desert). The only evidence for high topography gain comes from AFTA over NW Africa and the Leo Massif and is not supported by the presence of any clastic influxes to adjoining margins.