The shipboard scientific party of Leg 184 sought to better understand the history and variability of the Asian monsoon system, which is a major component of the regional climate of Asia as well as global climate. Evolution of monsoonal climates in southern Asia is linked to the growth of the Himalayan-Tibetan orogeny (see papers and references in Ruddiman, 1997), the opening and closing of marginal seas (Wang et al., 1999), and changes in global climate, including atmospheric CO2 levels (see papers and references in Ruddiman, 1997). The South China Sea (SCS) experiences both summer and winter monsoons, and its sediments record the erosion and weathering of surrounding rocks by tectonic orogens as well as the changes in global and regional climate. Parts of the major scientific objectives of Leg 184 are to obtain continuous sequences of hemipelagic sediments that record the East Asian climate history during the late Cenozoic, establish records of monsoonal proxies for the SCS, and establish stratigraphy ties between the SCS marine records and terrestrial records of China. It should thus be possible to accomplish the objectives by examining specific assemblages of terrigenous and marine components. Lipid biomarker compositions, which provide information on different types of terrigenous lipid sources and a detailed view of marine plankton groups contributing to the sedimentary organic matter, can play an important role in concerned studies.
For these purposes, a detailed molecular organic geochemical study was performed on downhole samples from Ocean Drilling Program (ODP) Sites 1147 and 1148 in the northern SCS, where we recovered a 861-m-long composite section spanning the last 30 m.y. Compilation of this data could elucidate the origin of sedimentary organic matter and determine various proxy signals of paleoenvironmental parameters. In addition, identifying and quantifying the major biomarkers for Sites 1147 and 1148 will add to the inventory of data for further molecular stratigraphic studies.