Distribution of calcareous nannofossils in Oligocene to Pleistocene sediments of the Southern Ocean

Detailed calcareous nannofossil range charts for the Oligocene-Pleistocene sections from high-latitude Ocean Drilling Program Sites 747, 748, and 751 in the southern Indian Ocean are presented in this report. Calcareous nannofossils are generally low in abundance in Pliocene-Pleistocene sediments, whereas they are very abundant throughout the Miocene and Oligocene. Species diversity, however, is low compared with assemblages in the lower latitudes. Nannofossil reworking is extensive in the middle Miocene at Site 751, less extensive in the lower Miocene at Site 748, and negligible for the entire Neogene at Site 747. Six nannofossil datums, which have previously been correlated with magnetostratigraphy in the Southern Ocean, were recognized in the upper Oligocene-Pleistocene sequence at Site 747. Three such nannofossil datums are available for the Neogene at Sites 748 and 751. A new subspecies, Coccolithus pelagicus floralis, is described.

本报告收录了印度洋南部高纬度海区大洋钻探计划（Ocean Drilling Program, ODP）747、748及751站位渐新统-更新统剖面的详细钙质超微化石（calcareous nannofossils）延限图表。钙质超微化石在上新统-更新统沉积物中通常丰度较低，但在整个中新统与渐新统中则极为富集。不过相较于低纬度地区的化石组合，其物种多样性偏低。751站位中中新统的钙质超微化石再沉积现象极为广泛，748站位下中新统的再沉积程度稍弱，而747站位整个新近系的钙质超微化石再沉积作用则可忽略不计。在747站位的上渐新统-更新统序列中，共识别出6个此前已在南大洋地区与磁地层学建立对比关系的钙质超微化石基准面。748与751站位的新近系中仅可识别出3个此类钙质超微化石基准面。本研究还描述了一个全新亚种：大洋颗石藻花状亚种（Coccolithus pelagicus floralis）。