Minerals are the main components of sediments, whose terrigenous parts are carried into the ocean by rivers or winds and deposit directly or indirectly. The amount of the terrigenous minerals in marine sediments indirectly indicates the source area of supply and the strength of the transport agent. Minerals in sediment are strongly affected by tectonic movement and geomorphic evolution in long time scale. Therefore, large tectonic movement must lead to change of mineral components and fluxes. The South China Sea(SCS)basin experienced two tectonic expansions in Cenozoic; the second expansion occurred between 32～15.5Ma, formed the central basin. The Palawan block moved far away from the northern continent. The Tibet Plateau experienced three accelerated uplifts at 25～17Ma.B.P, 10～8Ma.B.P and ～4Ma.B.P～present In order to determine the effective tectonic movement proxy indexes and find more evidence for the two large tectonic events in marginal sea sedimentary mineral composition and their fluxes were studied. Quartz, feldspar, clay minerals and terrigenous minerals were extracted from the sediments of site 1 148 of ODP LEG 184 by chemical dissolution method, the contents and their mass accumulation rate(MAR)were calculated. According to the chronology data in the initial report of ODP LEG 184, vertical distribution of the terrigenous minerals and their content and fluxes against age were established. Therefore, the response of content and flux of terrigenous minerals to the expansion of South China Sea floor(SCS)and the uplift of the Tibet Plateau were discussed. The results showed that the highest terrigenous mineral components between 33～27.5Ma was correlated with the start of SCS floor expansion and the ridge jump while it was affected by the uplift of Tibet Plateau after 24.5Ma. The accelerated uplift phases were very prominently revealed in the sediments, especially the rapid uplift since 4Ma ago. The provenance of terrigenous mineral components changed from southeast to northwest at about 24.5Ma as
Particulate fluxes investigated in the central South China Sea (SCS) during 1993―1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470―900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420―450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The vari- ability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ 18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and temporal variations.
WANG RuJian JIAN ZhiMin XIAO WenShen TIAN Jun LI JianRu CHEN RongHua ZHENG YuLong CHEN JianFang
Based on a quantitative analysis of planktonic foraminifera in two gravity cores (17928 and 17954), the history of the upper-water structure of the eastern and western slopes of the South China Sea (SCS) over the last 220 Ka was reconstructed using the transfer function technique. Our results show that lower sea surface temperature (SST) and shallower depth of thermocline (DOT) exist at Core 17928, off Luzon, in the glacial periods; on the contrary, the same situation turned up in the interglacial at Core 17954, off Vietnam. These changes of the upper-water column structure in the two areas are induced by coastal up-welling, which in turn is driven by monsoons, namely, winter monsoon leads to upwelling at the eastern slope, and summer monsoon gives birth to upwelling on the western slope. Moreover, the intensity of upwellings is also closely related to the evolution of the East Asian monsoon. Therefore, we assume that the changes of the upwelling in the two sites indicate strengthenning of winter and
