Abstract: Background, aim, and scope Coccolithophores is extremely sensitive to the ocean environment and climate change response because of its main growth in the upper light layer of the seawater, and be controlled by the temperature, acidity, light intensity and nutrient quality of the sea water. Coccolith was formed by Coccolithophores through a procedural process of biomineralization. Calcite fossil contained rich geochemical information, which is an ideal material for paleoceanography study. However, the acquisition of typical samples and the detailed research on minerology are the premise and foundation of obtaining reliable information. In this study, we performed a detailed mineralogical study of Marine pore columnar samples from the upwelling area in the South China Sea off eastern Vietnam, in order to extract the sedimentary environment information related to Coccoliths, and explore new ideas and methods of paleo-marine research. Materials and methods In the presented study, sediment samples were selected from core MD05-2901 which is in the upwelling area in the South China Sea off eastern Vietnam (14°22′50″N, 110°44′60″E), which belongs to the summer upwelling area off the coast of Vietnam in the west of the South China Sea, with a water depth of 1454 m and a column core length of 36.49 m. The bottom age of the sample was MIS 12, about 450 ka, and the time resolution was about 0.3 ka. The mineralogical characteristics of coccolith fossil species, biogenic components, mineral phases and FTIR spectra were identified for discussing coccoliths-related environmental information. New idea and method for study ancient marine environment were explored through presented study. Results The results show that: (1) columnar samples from the top to the bottom (with the increase of depth) have higher fossil content in the surface, the highest in the middle, and less in the bottom. (2) The organic carbon content ranged from 1.19% to 2.78, and the average content is 1.99%, which decreased with the increase of depth. (3) The inorganic carbon content of calcium carbonate, which is dominated by pellets, fluctuates between 1.13% and 1.65%, and the average content is 1.12%, which shows obvious periodicity and is strongly related to the distribution characteristics of the pellets. (4) Columnar C/N analysis show that the sediments in this period were mainly marine authigenic deposits. (5) The mineralogical facies of the samples are mainly composed of calcite, illite, montmorillonite, chlorite, kaolinite and a small amount of quartz, etc. (6) FTIR analysis shows that montmorillonite may adsorb organic matter, which is worthy of further study by mineralogists. Discussion The changes of the species of coccoliths in the column reflect the trend of the vegetative cline depth in this area. It is believed that the variation of F. profunda content in the South China Sea is manifested as the characteristics of nutrient cline depth, interglacial deep and shallow deep glaciation, reflecting the change of wind intensity. The C/N in the late Pleistocene columnar section showed a decreasing trend, indicating that the productivity reflected by coccolithophores decreased with the decrease of land source input. The quartz content increased with the increase of deposition depth, indicating that the columnar deposition environment changed to high-energy environment gradually. It is also found that the clay minerals and their compositions in the samples can reflect the control of terrestrial weathering by the East Asian Monsoon. Conclusions Based on the study of mineralogical characteristics of coccolith fossil species, biogenic components, mineral phases and FTIR spectra, we obtained the vegetative cline changes reflected by the content of coccolithophores in the column samples, as while as productivity reflected by carbonaceous composition and clay mineral was revealed. All this work shows that the detailed research on minerology are the premise and foundation of obtaining reliable information. Recommendations and perspectives The mineralogical characteristics of the sedimentary environment of Phaeophyllum are found to be rich in sedimentary information, which provides a new approach for the study of paleoceanography.
Keywords: coccolithophores; coccolith fossil; mineralogical characteristic; Late Quaternary; South China Sea