Clay Mineralogical Study On Environmental Change Of Hainan Island Offshore

Clay minerals are a widely distributing phenomenon in modern marine environment. And become the important components of the marine sediments which act as an enormous information basement storing abundance messages about the globe history and environment evolvement. Because of the structural characteristic and physic– chemical properties, during the proceeding and evolution disciplinarian, clay minerals carries along rich information about the global climate change. Meanwhile considering the widely distributing and easily sampling, clay minerals has become the one of effective auxiliary research subjects for the paleoclimate research.The investigation firstly using the X-RAY Diffraction Analysis (XRD) to fix on the variety and relative content of the clay minerals in offshore sediments around Hainan Island. The XRD analytical results from 357 samples show that, in the research area the clay minerals are composed by illite/smectite interstratified clay minerals, illite, kaolinite and chlorite. In 182 surface sediments samples, the average content of the four types is about 34.2%, 27.3%, 21.1% and 17.4%. In Sediments of the Central South China Sea, it is the first time to discovering the high-content (>1/3) of illite/smectite interstratified clay mineral. So in the investigation, the genesis of it has been discussed especially. For giving the accuracy judgment of the assemblages characteristic and the distributed tendency of the clay minerals in surface sediments, the investigation use the method that combining the two way for the subarea: the manual distinguishing and the Q-type Clustering Analysis and divide the 3 surface clay mineral association area. Combining the geology environments and hydrodynamic characteristic in Hainan Island, the article further discusses the genesis and controlled factors of clay minerals. Comparing the future research on using illite/smectite interstratified clay minerals, illite, kaolinite and chlorite as the identification of climate, according to the dating for AMS14C in surface sediments(0~20cm), this article found that in Hainan Island and its peripheral districts the climate environment has been in wet and warm since 1500a.Secondly, the investigation analyzes the contents and distribution of the claymineral in the 7 sediments core (175 samples) and the significance of them. Then discuss the material resources and depositional environment of each core. According to the disturbed events of deposit , it deduce that climate was fluctuated in the years of 3500～6000Cal.aBP in this area.At last, using the qualitative and quantitative analyzing of the clay mineral in the offshore sedimentary core B106 from Hainan Island and according to the dating for AMS14C, meanwhile comparing the future research on palaeoclimate environmental event, which using different methods and subjects, this article found that from the content ratio about (illite/smectite interstratified clay minerals+ illit)/ kaolinite ([I/S+I]/K) can also indicate the palaeoclimate environmental event. The results showed that clay mineral of the sedimentary core B106 reveal seven palaeoclimate events since 16725 Cal.aBP, such as"Bolling Warming Events"in 13100±45 aBP,"Younger Dryas Cooling Events"in 10393±45 aBP,"Early Holocene Cold Event"in 8000aBP,"South of China Cooling Events"in 4624±35 aBP, Cooling Events in 3370±40 aBP, Drought Incident Cooling Events in 922BC and"Cooling Events of Northern and Southern Dynasty"in 514AD. All of those corresponding events show that under certain conditions using the result of the analyzing about clay mineral in marine sedimentary core also can reveal the palaeoclimate environmental event around 1ka scales.