Oligocene biogenic siliceous deposits on the slope of the northern South China Sea |
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| Authors: | WANG Rujian FANG Dianyong SHAO Lei CHEN Muhong XlA Peifen Ql Jingyu |
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| Institution: | 1. Key Laboratory of Marine Geology, Ministry of Education, Tongji University, Shanghai 200092, China
2. Open Laboratory of Marginal Sea Geology and Paleoenvironment, South China Sea Institute of Oceanology,Chinese Academy of Sciences, Guangzhou 510301, China |
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| Abstract: | The abundance of radiolarian, diatom and sponge spicule and H4SiO4 in pore-waters increase abruptly at the boundary between Early and Late Oligocene (about 30-27.5 Ma) at Site 1148 of the
northern South China Sea (SCS), indicating high biogenic silica accumulation during this time. At the same time (about 30-28
Ma), high biogenic silica deposition occurred in the central equatorial Pacific. Comparison of the biogenic silica accumulation
at Site 1148 of the SCS with that at Site 929 of the Atlantic verifies that the biogenic silica accumulation between the low
latitude Pacific and Atlantic oceans expresses the evident relationship of compensation during the Oligocene. Biogenic silica
accumulation decreased in the Atlantic, whereas it increased in the Pacific at the boundary between the Early and Late Oligocene.
It resulted from the formation and presence of North Atlantic deep water (NADW) in the Atlantic basin, indicating an intensive
basin-basin fractionation. XRD analysis and SEM observation of the samples from Site 1148 demonstrate that most of radiolarian,
diatom and sponge spicule have suffered from dissolution and reprecipitation, suggested by the opal-A→opal-CT transformation.
As a result of the transformation, porosity increased, but dry and bulk densities decreased, reflecting the consequence of
diagenesis on the physical property of sediment. |
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| Keywords: | biogenic silica accumulation North Atlantic deep water fractionation silica preservation Oligocene the northern South China Sea |
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