A Quantitative Study On Morphological Variation Of Plio-Pleistocene Coccolith Genus Gephyrocapsa From The Northern Region Of SCS

In 1999, Ocean Drilling Program Legl84 drilled the South China Sea (SCS), the broad scientific themes of this leg were threefold:1. To document the Cenozoic history of the SCS, including its biostratigraphy, lithostratigraphy, chronology, paleoclimatology and paleoceanography.2. To reconstruct the evolution and variability of the East Asian monsoon during the late Cenozoic on millennial, orbital and tectonic time scales.3. To identify and better understand the links between tectonic uplift, erosion and weathering hemipelagic deposition, and climate change, including the evolution of the Asian Monsoon and the Neogene global cooling.This study is a post-cruise study of this Leg, calcareous nannofossil samples from Sites 1146, 1147 and 1148 of Leg 184 were analyzed to provide a high-resolution biostratigraphy for this Leg and to investigate morphological variation of coccolith genus Gephyrocapsa.The main results of this study are:1. 12 late Pliocene to Pleistocene bio-events were recognized and 6 zones of Martini (1971) were determined For the upper sediment sequences of Sites 1146 and 1148. This result was the biochronological base for estimating sample ages in the study on genus Gephyrocapsa.2. Morphological variation of Gephyrocapsa was investigated based on biometrically analyzing 6 morphological features of a coccolith placolith, e.g. (1) length of placolith, (2) width of the placolith, (3) bridge angle, (4) roundness of placolith, (5) width of center pore and (6) size of center pore.The results suggest that a number of species of Gephyrocapsa can be separated by using three pairs of following morphological features: 1) placolith length against bridge angle, 2) bridge angle against roundness, 3) placolith length against placolith width.In Pleistocene, at about 1.3 Ma, a notable variation in placolith length and bridge angle occurred, while the genus boosted according to the result of earlier studies on this genus (Su, 1996).This study also observed, in the morphological development of Gephyrocapsa, there is a significant negative correlation between placolith length and bridge angle, between placolith length and roundness, as well as between placolith length and pore size.