[M-IS14] Evolution of Pelagic Realm

[MIS14-P03] Phyletic evolution and paleogeographic distribution of the Early Cretaceous radiolarian Turbocapsula

*XIN LI¹, Matsuoka Atsushi² (1.State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 2. Department of Geology, Faculty of Science, Niigata University)

Keywords:Early Cretaceous, radiolarian, Turbocapsula , Phyletic evolution, paleogeographic distribution

A radiolarian biostratigraphic study ranging from the latest Barremian to the Aptian of a pelagic sequence (section BB1) near Babazhadong in southern Tibet revealed phyletic relationships of species belonging to the genus Turbocapsula. Three species and two subspecies are included in this genus: Turbocapsula tetras LI & MATSUOKA, T. fugitiva O'DOGHERTY, and T. costata (T. costata (WU) multicostata LI & MATSUOKA, and T. costata (WU) costata). Turbocapsula fugitiva appears to have arisen from T. tetras by losing the septa between the third and the fourth segments. Turbocapsula fugitiva seems to have given rise to T. costata multicostata following the development of thicker costae between its two to five rows of pores. With the decrease in the number of the costae and the development in the costae, T. costata multicostata evolved into T. costata costata. The phyletic evolution of the genus Turbocapsula has a high stratigraphic value.An overview of localities where Turbocapsula costata (Wu) has been reported and lithology, depositional setting, associated fossil records, Paleomagnetic data from these localities are summarized. All these data lead to the conclusion that locations of known T. costata-bearing strata are restricted to the low to mid-latitude Mediterranean and eastern Tethys. This indicate that the zonation established by the phyletic evolution of the genus Turbocapsula cannot be utilized for Early Cretaceous zonal correlations between the Pacific, the Atlantic and other regions.