The planktonic foraminifera of the Jurassic. Part II: Stratigraphy, palaeoecology and palaeobiogeography

The stratigraphy, palaeoecology and palaeobiogeography are outlined for two genera and ten species of Jurassic planktonic foraminifera described in Gradstein et al. (Swiss J Palaeontol 2017. doi: 10.1007/s13358-017-0131-z ). The two genera are Globuligerina and Conoglobigerina. Globuligerina probably appeared in late Toarcian (late Early Jurassic) and Conoglobigerina first occurred in Middle Oxfordian (early Late Jurassic). Within the two genera ten species are defined, including from older to younger: Globuligerina dagestanica (Morozova), G. avariformis (Kasimova), G. balakhmatovae (Morozova), G. oxfordiana (Grigelis), G. bathoniana (Pazdrowa), G. jurassica (Hofman), G. oxfordiana (Grigelis) calloviensis Kuznetsova emended, G. tojeiraensis Gradstein, Conoglobigerina helvetojurassica (Haeusler), C. grigelisi Gradstein and C. gulekhensis (Gorbachik and Poroshina). Globuligerina balakhmatovae, G. oxfordiana and G. bathoniana are longer ranging, although there are subtle evolutionary trends in these taxa that may refine stratigraphic usage. Other taxa have shorter stratigraphic ranges. Using stratigraphic trends, test morphology and wall texture changes, the species are tentatively assembled in four evolutionary groups, termed A–D, and in six zones from Late Toarcian through Tithonian. The greater species diversity and possibly also specimen abundance took place in the Kimmeridgian, a time of high global sea level and greenhouse palaeoclimatic conditions. Jurassic planktonic foraminifera preferred marine continental margin conditions instead of the distal open ocean and spread from offshore Eastern Canada to offshore Western Australia along the margins of the Tethys Ocean. The group did not venture into austral or boreal realms, likely reasons why migration probably failed to the west coasts of South and North America.