Thirty million year deep-sea records in the South China Sea

In the spring of 1999 the Ocean Drilling Pro-gram (ODP) Leg 184 Shipboard Party cored 17 holes at 6 deep water sites in the northern and southern parts of the South China Sea (SCS). Chinese scientists actively partici-pated in the entire process of this first deep-sea drilling leg off China, from proposal to post-cruise studies. More than 30 categories of analyses have been conducted post-cruise in various Chinese laboratories on a large number of core sam-ples, and the total number of analyses exceeded 60 thousand. The major scientific achievements of the Leg 184 studies are briefly reported in three successive papers, with the first one presented here dealing with deep-sea stratigraphy and evolu-tion of climate cycles. This ODP leg has established the best deep-sea stratigraphic sequences in the Western Pacific: the 23-Ma isotope sequence from the Dong-Sha area is unique worldwide because of its continuity; the last 5-Ma sequence from the Nansha area represents one of the best 4 ODP sites worldwide with the highest time-resolution for that time in-terval, and the sequences of physical properties enable a de-cadal-scale time resolution. All these together have provided for the first time high-quality marine records for paleoenvi-ronmental studies in the Asian-Pacific region. This new set of stratigraphic records has revealed changes in climate cyclic-ity over the last 20 Ma with the fluctuating power of the 100 ka, 400 ka, 2000 ka eccentricity cycles, indicating the evolv-ing response of the climate system to orbital forcing along with the growth of the Antarctic and Northern Hemisphere ice sheets.

Evolution of the South China Sea and monsoon history revealed in deep-sea records

As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropaleontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkable diagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ～3 Ma.

Recurrence of Yuan Dynasty sluice from Zhidanyuan relics and paleostream evolution

The excavation of Shanghai Zhidanyun relics makes the recurrence of a splendid Yuan Dynasty sluice. It is a good example for the study of Shanghai history in the Wusongjiang River irrigation, the ancient shipping and the town development. Based on the data of microfossil Pediastrum, Zygnema, Concentricystes, diatom, foraminifera and ostracods from the sediment section of the relics, the paleostream change after the construction of the sluice was guessed. The paleostream was influenced by the sea water due to the connection with the sea in the earlier stage. The upstream of the sea water was enhanced in the middle stage that was indicated by the increase of marine diatoms and foraminifera. The decrease of marine diatoms and foraminifera in abundance reflected that the connection of the paleostream with the sea was reduced, and the sea influence was decreased gradually in the later stage.