Artai A. Santos (et al.)-
Palynological assemblages from palaeo-islands are scarce in the fossil record and represent an opportunity to explore plant dispersal patterns and colonization strategies in isolated ecosystems. We present a palynological study of a Middle Jurassic volcanic island located in a shallow epicontinental sea, c. 150 km from the palaeo-mainland. The study is based on a 2-m thick succession of calcareous marlstones in the El Pedregal Formation in the eastern part of the Iberian Basin, and the palaeo-island is termed Camarena Island after the village nearest to the fossil site. Eleven samples yielded equivalent assemblages that are here treated as a single palynological suite containing 47 fossil-species belonging to 36 fossil-genera. The abundance of Araucariacites australis and Klukisporites variegatus, together with accessory Cycadopites spp. and the scarcity of Callialasporites turbatus, Manumia irregularis, Staplinisporites caminus and Kekryphalospora distincta, suggest a Toarcian–Aalenian age. Additional stratigraphical data resolve the likely age for the Camarena Island as lower–middle Aalenian. Many palynomorphs in this assemblage have apparent anemophilous and hydrophilous adaptations facilitating long-distance transport. On this basis, some parent plants probably derive from the adjacent mainland or neighbouring islands. Marine palynomorphs or pollen and spores with few adaptations for dispersal may have derived from plant groups that evolved in situ on the volcanic island. The palynological assemblage has some differences from coeval palynofloras from the central Iberian Peninsula, but there are also some similarities with assemblages from post-volcanic deposits and other oceanic islands. It is likely that the seaway separating the volcanic island from the mainland acted as a biological filter enabling colonization by only a selected range of plant groups.
GeoUCMpublica 