Site 1148, the deepest site drilled during Ocean Drilling Program (ODP) Leg 184, is located at 18°50.169´N, 116°33.939´E. At a water depth of ~3294 m, it lies on the lower continental slope of China, close to the continent/ocean crust boundary (Fig. F1. One of the objectives of Site 1148 was to recover a continuous Oligocene–Miocene sequence of hemipelagic sediments for studying the early paleoclimate history of the South China Sea (SCS) as related to Himalayan–Tibetan uplift and sea level change (Wang, Prell, Blum, et al., 2000).
Drilling at Site 1148 recovered a 857-m-long Cenozoic sediment sequence comprising two main sections: a much expanded (mainly lower) Oligocene and the relatively slower accumulated Miocene to Pleistocene. The lower section represents synrift sediments filled during the later Paleogene rifting in half grabens, whereas the upper section corresponds to wider sedimentation during the broad subsidence in the Neogene SCS (Ru et al., 1994; Wang, Prell, Blum, et al., 2000). These two sections are separated by a slumped interval between 457 and 495 meters composite depth (mcd). Imaged as a double reflector in seismic profiles (Wang, Prell, Blum, et al., 2000), the slump may be related to a change in the pattern and direction of seafloor spreading, or "ridge jump" (Briais et al., 1993), which marks the onset of a new tectonic and sedimentological regime beginning in the early Miocene in the SCS region (Wang, Prell, Blum, et al., 2000).
On the basis of initial shipboard data and postcruise results, this study aimed to recover more biostratigraphically useful datums of planktonic foraminifers and to provide a more accurate stratigraphic framework for better dating of Oligocene and Miocene climatic and tectonic events in the region.