Figure 1. Climatology of the summer and winter monsoon circulation. Surface winds for the (A) winter (January) and (B) summer (July) seasons along with areas of high (H) and low (L) pressure. Precipitation (6 and 9 mm/day contours) for the (C) winter (January) and (D) summer (July) seasons. The pressure gradients and resulting wind and precipitation patterns reflect the land-sea heating contrasts, which are a function of solar radiation, elevation, and land-surface boundary conditions. Monthly data, 1990-1997, from National Oceanic and Atmospheric Administration, National Centers for Environmental Prediction/National Center for Atmospheric Research, Climate Data Assimilation System-1 (Kalnay et al., 1996).
Figure 2. Map of the South China Sea showing locations of Leg 184 drilling areas. BS = Bashi Strait, SCS = South China Sea.
Figure 3. Tectonic setting of the South China Sea. A. Major tectonic elements of the northern and central parts of the South China Sea. Thick dotted line outlines the Central Basin with selected magnetic anomaly lineaments. Thin dotted and solid lines are isobaths of 200 and 2000 m (Hayes et al., 1995a). Thick dashed box corresponds to Figure 3. B. Geological framework of the northern margin of the South China Sea (Ru et al., 1994). YGHB = Yinggehai Basin, QDNB = Qiongdongnan Basin, BBWB = Baibiwan Basin, PRMB = Pearl River Mouth Basin, SWTB = Southwest Taiwan Basin. Leg 184 sites are located south of Dongsha Island on the continental margin between the Pearl River Mouth Basin and the South China Sea Basin.
Figure 4. Marine and terrestrial observations indicating an intensification of the monsoon in the late Miocene (10-8 Ma) and a model simulation of a possible evolution of monsoon runoff. A. Abundance of planktonic foraminifer Globigerina bulloides and radiolarian Actinoma spp. that indicate active upwelling induced by southwest monsoonal winds (from ODP Site 722, Arabian Sea). B. Oxygen and carbon isotopes measured in pedogenic carbonates from Pakistan indicating more seasonal climates and a decrease in atmospheric CO2, possibly from monsoon-related weathering (data from Quade et al., 1989). Open circles = delta13C (); solid circles = delta18O (). C. Normalized, mean terrigenous sediment flux to the northern Indian Ocean that suggests active uplift and fluvial deposition in the late Miocene (from Rea, 1992). D. A model simulation of monsoon runoff, relative to control simulation, using the Molnar model for uplift history (11-8 Ma) and the coupled effects of elevation change and orbitally induced solar radiation changes.
Figure 5. Summary of monsoonal stages defined from land-based studies in China, after Wang (1997), Wang (1990), and Liu and Ding (1982). SCS = South China Sea.
Figure 6. A composite stratigraphy from industrial wells in the eastern part of the Pearl River Mouth Basin, which lies on the shelf and uppermost continental slope northwest of the northern sites (PRMB in Fig. 3 for bathymetry). These wells provide the seismic reflector sequence and general age structure to be correlated with the more marine ODP sites on the slope. Note the nonmarine sequence beginning from the upper Oligocene (modified from Jiang et al., 1994).
Figure 7. East Asian monsoon climate change in the northern SCS during the last glacial cycle from a core recovered during the SONNE 17940 cruise. The plots shown are, from top to bottom: total grain-size mode, clay content, stable oxygen isotope values from Globigerinoides ruber, and, for reference, the oxygen isotope record from the GISP2 ice core. EHPB = early Holocene/Preboreal, Y.D. = Younger Dryas, B/A = Boelling/Alleroed, H1-H4 = Heinrich Events 1-4, O.D. = Oldest Dryas, LGM = Last Glacial Maximum. Data from Wang et al. (1999).
Figure 8. Site location map for the southern South China Sea Site 1143. The irregular seafloor bathymetry reflects both the highly irregular bathymetry and the low abundance of survey data in the Spratly Island or Dangerous Grounds area.
Figure 9. Site location map for the northern South China Sea Sites 1144-1148.
Figure 10. Precruise seismic line across Site 1143. Line NS95-240, common depth point (CDP) 3617. Water depth = 2774 m. Penetration depth = 500 mbsf. Graphic presentation is approximate.
Figure 11. Summary diagram of coring results at Site 1143 on the mcd scale. Maximum penetration measured with the drill pipe is 500 mbsf. The core recovery column is a graphic presentation of the cored and recovered intervals for each hole. Larger gaps are the result of coring problems (<100% nominal recovery); smaller gaps (typically 0.5-2.0 m), revealed by hole-to-hole correlation, occur even when nominal core recovery is 100% or more. The graphic lithology column presents the major sediment types: horizontal line patterns are clay; diagonal dashed patterns are nannofossil ooze with foraminifers. Lithologic units are also shown. Mass accumulation rates (MARs) were calculated for total sediment (light gray histograms) and carbonate only (darker gray, solid histograms) from 5-m interval sampling of the smoothed depth-age model, dry density, and carbonate concentration. The smoothed depth-age curve (line) is overlain with control points from nannofossil (squares) and foraminifer (circles) biostratigraphy and magnetostratigraphy (crosses [shown for other sites]). The color reflectance lightness (L*) parameter (solid line) was measured every 2-4 cm and smoothed with a 20-point moving average for this figure. Carbonate concentration, expressed as percent calcite (dots with dashed line), was measured every ~3.5 m. Magnetic susceptibility (thicker line) and natural gamma radiation (thinner line) were measured every 2-5 cm, and the records presented here are smoothed with a 20-point moving average. Porosity (solid line) and grain density (dots with dashed line) were calculated from moisture and density measurements on samples taken every 1.5-3.0 m. Bulk density (solid line) and dry density (dots with dashed line) were calculated from moisture and density measurements on samples taken every 1.5-3.0 m.
Figure 12. Precruise seismic line across Site 1144. Line SO95-10, CDP 9700 (4:20). Water depth = 2037 m. Penetration depth = 453 mbsf. Graphic presentation is approximate.
Figure 13. Summary diagram of coring results at Site 1144 on the mcd scale. Maximum penetration measured with the drill pipe is 453 mbsf. See Figure 11 for further explanation.
Figure 14. Precruise seismic line across Site 1145. Line SO-95-10, CDP 4680 (11:10). Water depth = 3175 m. Penetration depth = 200 mbsf. Graphic presentation is approximate.
Figure 15. Summary diagram of coring results at Site 1145 on the mcd scale. Maximum penetration measured with the drill pipe is 200 mbsf. See Figure 11 for further explanation.
Figure 16. Leg 184 seismic line across Site 1146. Line JR184-3, shot point (SP) 3240. Water depth = 2092 m. Penetration depth = 607 mbsf. Graphic presentation is approximate.
Figure 17. Summary diagram of coring results at Site 1146 on the mcd scale. Maximum penetration measured with the drill pipe is 607 mbsf. See Figure 11 for further explanation.
Figure 18. Leg 184 seismic line across Sites 1147 and 1148. Site 1147: Line JR184-1, SP 1940. Water depth = 3246 m. Penetration depth = 86 mbsf. Site 1148: Line JR184-1, SP 1980. Water depth = 3294 m. Penetration depth = 853 mbsf. Graphic presentation is approximate.
Figure 19. Summary diagram of coring results at Site 1147 on the mcd scale. Maximum penetration measured with the drill pipe is 86 mbsf. See Figure 11 for further explanation.
Figure 20. Summary diagram of coring results at Site 1148 on the mcd scale. Maximum penetration measured with the drill pipe is 853 mbsf. See Site Figure 11 for further explanation.
Figure 21. Coring penetration and lithologic units as a function of age in the Leg 184 drilling sites. Horizontal dashed pattern = clay, brick pattern = nannofossil ooze with foraminifers. Gray bands = the occurrence of frequent green clay layers.
Figure 22. Age-depth relationships for Leg 184 sites. Solid lines = smoothed depth-age models, gray dots = the actual shipboard age calls from nannofossil and foraminifer biostratigraphy and from paleomagnetism. The thicker line highlights the different trend for the southern South China Sea Site 1143 as compared to the northern sites. The inset presents the past 3 m.y. at a greater resolution than the main diagram.
Figure 23. Summary of total (stippled histograms) and carbonate (solid histograms) mass accumulation rates (MARs) vs. age, and linear sedimentation rates (LSRs; solid line). A. The three longest records from Leg 184. B. Close-up for the last 3 m.y. for all Leg 184 sites.
Figure 24. Summary of carbonate concentration vs. age for the three longest records obtained on Leg 184. Note the common pattern of high values in the upper Miocene that decline toward the present.
Figure 25 Downhole logs as a function of depth. A. Total gamma radiation (American Petroleum Institute [API] units) and P-wave velocity. B. Magnetic susceptibility and photoelectric effect (PEF). Because the sedimentation rates differ greatly between the sites, epoch boundaries are shown to correlate with similar age intervals between the sites.
Figure 26. A. Downhole temperature gradients from Leg 184 sites, presented as linear best fits to 4-5 measurements per site. B. Temperature gradients plotted as functions of the water depths for Leg 184 drill sites.
Figure 27. Summary of methane concentrations (headspace method) at the Leg 184 sites that showed significant amounts of gas.
Figure 28. Summary of silica (H4SiO4) concentration trends in interstitial water from all Leg 184 sites (except Site 1147), plotted (A) vs. meters composite depth (mcd), (B) vs. age (Ma), and (C) vs. the last 3 m.y. (Ma).
Operations Synopsis-Port Call and Transit to Site 1143
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