The Geochemistry Research On Cold-seep Bivalve Fossils Of The Northern Continental Slope, South China Sea

Methane hydrates are increasingly recognized as future potential energy resources because of their unique physicochemical properties and other virtues such as high mineral utilities and low pollution. The South China Sea is a marginal sea in western Pacific Ocean, and has very good accumulative conditions and exploration prospect for natural gas hydrate. We have studied forming conditions of gas hydrates in northern slope of the South China and achieve something, but there are some problems concerning them. Scientists have attached great importance on researching gas hydrate of geochemical method which has been applied in respective research region.Marine bivalves are important palaeoenvironmental archives. High resolution studies on sections of bivalve shells would provide useful information on changes of these environmental parameters during the growth of the animals. This thesis will greatly contributes to researching the gas hydrate in the South China Sea.This research relies on an international corporation project between the IFM-GEOMAR of Germany and GMGS, with an abbreviation of SiGer. This thesis studied the geochemical characteristics of the samples which were bivalves taken in the voyage S0177 of the German"Sun Cruise". This thesis is divided into three parts:(1)A representative set of five samples were analyzed by X-ray diffractometer. The bivalve shells are mostly aragonite and contain small amounts of calcite. Clearly the samples are all chemically very well preserved. There are little diagenetic effects in the species which are of researching importance and significance.A representative set of nine samples were analyzed by oxygen and carbon isotopes composition. We knowδ18O andδ13C values. Stable isotopic compositions of bivalve shells have often been used for the reconstruction of high-resolution records of palaeotemperature. Estimated ambient seawater temperatures can be calculated by using the palaeotemperature equation based on the relationship between seawater temperature and the isotopic composition of biogenic carbonate proposed by Sch?ne K et al. in this thesis.t(℃)=20.6-4.34[δ18Oar-(δ18Oseawater-0.2)] We calculate ambient seawater temperature ranging between 9.00℃and 14.81℃.At a given temperature, there is a linear relationship between either the carbon or oxygen isotopic composition and the salinity of the water in which the bivalves live. In this thesis, the carbon and the oxygen isotope compositions do not exhibit a significant linear relationship, which do not yield realistic values for fully marine salinity. As a consequent, we can not calculate the salinity from the carbon composition. Key words: bivalve, oxygen isotope, carbon isotpe,Sr/Ca...