oa Devonian Miospore Stratigraphy and Palaeogeography of the Northern Margin of Western Gondwana

Well-preserved Devonian miospore assemblages from Saudi Arabia and North Africa allow a good<br>correlation of the studied sections and the establishment of a biozonation for the northern margin of<br>Western Gondwana. More than 200 miospore species, including many new species endemic to Western<br>Gondwana, have been identified in 16 sections. Although the standard Devonian miospore zonations<br>established in Euramerica are commonly used in most palynological studies, they are not always easily<br>applicable to Western Gondwanan localities because of the endemic nature of the assemblages.<br>Therefore, a new regional biozonation based on Gondwanan miospore species has been established. It<br>consists of nine assemblage zones, eight interval zones and two acme zones, from the late Pragian to<br>the early Frasnian. A biozonation based on the first downhole occurrence of species is also developed<br>for oil exploration. This provisional downward biozonation consists of eight interval zones. Although it<br>seems relatively reliable by comparison with the previously defined upward biozonation, it needs to be<br>further tested. The review of the miospore assemblages from the literature has allowed evaluation the<br>provincialism of assemblages on a worldwide scale for the Emsian-Givetian interval. Coefficient of<br>similarity has been calculated between palynofloras from northern and southern Euramerica and<br>eastern, southwestern and northwestern Gondwana. The resulting low values correspond to low to<br>moderate similarity of miospore assemblages. The provincialism may be explained by a latitudinal<br>climatic gradient as no significant palaeogeographic barrier is known during this time. Despite a certain<br>degree of provincialism, floristic interchanges existed. Saudi Arabia and North Africa constituted an<br>intermediate warm temperate region and shared taxa mainly from more arid Euramerican localities in<br>the north, and cooler Southwestern Gondwanan localities in higher latitudes. It seems that a<br>progressive homogenization of the vegetation took place in Middle Devonian as the standard<br>Euramerican biozones are more easily recognized in Givetian than in Eifelian and Emsian. This<br>transition from provincialism to cosmopolitanism during the Devonian is not only shown by palynofloras<br>but also by the palaeogeographic distribution of many other fossil groups. It is likely due to a decrease<br>of the latitudinal climatic gradient in Middle Devonian.