Bajocian (Middle Jurassic) ammonites of stratigraphical and palaeobiogeographical importance from Mombasa, Kenya, East Africa

Collections of Middle Jurassic ammonites made at the Mwachi River locality, near Mombasa in the late 1980’s and early1990’s are described. They support previous research concluding a Late Bajocian age for the major or the upper part of the ‘Posidonia shales’, immediately below and above the dividing Massive (Coral) Limestone. The ammonite species are figured and briefly described. Two Upper Bajocian ammonite zones are evidenced: a lower assemblage indicates the Strenoceras niortense Zone and a higher one belonging to the Garantiana garantiana Zone. Most of the ammonites are Tethyan forms with abundant phylloceratids and lytoceratids, some indicating connections with coeval Arabian and Sinai faunas. Palaeobiogeographically the assemblages suggest a deep-water position on the East-African Gondwana margin, with strong faunistic influence from the open Tethys and very restricted connections with the Arabian shallow water regions.