In order to study vegetation evolution and environmental changes around 2.5 Ma B.P., a total of 146 pollen samples with an average time resolution of 7 000 years were analyzed in the deep-sea record at the depth of 13...In order to study vegetation evolution and environmental changes around 2.5 Ma B.P., a total of 146 pollen samples with an average time resolution of 7 000 years were analyzed in the deep-sea record at the depth of 135 - 95 m （in composition depth） from ODP Site 1143 （9° 22＇ N, 113° 17＇ E） in the southern South China Sea. The results show that the pollen influx has a distinct change. During 2.6 - 2.0 Ma B.P., the average value of pollen influx increased evidently compared with that of 3.0 - 2.6 Ma B.P. It shows that the sea level of SCS dropped dramatically around 2.6 Ma B.P., corresponding to the formation of the Northern Hemisphere ice-sheets and the enhancement of the East Asian Monsoon. The pollen influx variations reflect the glacial-interglacial cycles corresponding with the deep-sea oxygen isotope curve and indicate that the sea level of SCS rose and dropped many times after 2.6 Ma B.P. The spectrum analysis results of pollen influx show that there are cycles at 0.1Ma （eccentricity） and 46.9 ka （obliquity） during 3.0 - 2.0 Ma B.P.展开更多
Three layers of volcanic tephra, sampled from ODP 1143 Site in the South China Sea, were observed at the mcd depth of 5.55 m, 42.66 m, and 48.25 m, and named, in this paper, layers of A, B, and C, respectively. All of...Three layers of volcanic tephra, sampled from ODP 1143 Site in the South China Sea, were observed at the mcd depth of 5.55 m, 42.66 m, and 48.25 m, and named, in this paper, layers of A, B, and C, respectively. All of these tephra layers have an average thickness of ca. 2 cm. They were constrained in age of ca. 0.070 Ma, ca. 0.80 Ma, and ca. 1.00 Ma, respectively, by the microbiostratigraphy data. These tephra layers were predominated by volcanic glass shards with a median grain size of 70-75μm in diameter. Major chemical compositions analyzed by EMPA and comparison with the previous data from other scatter areas suggest that these three layers of tephra can correspond to the three layers of Toba tephra, YTT, OTT, and HDT, respectively, erupting during the Quaternary. The occurrence of these tephra layers in the South China Sea implies that the Toba eruptions often occurred in the summer monsoon seasons of the South China Sea during the Quaternary, and that the strength of eruptions was probably stronger than that previously estimated.展开更多
基金the National Natural Science Foundation of China projects （40371116） the National Major Basic Research Program of China （G200078502）.
文摘In order to study vegetation evolution and environmental changes around 2.5 Ma B.P., a total of 146 pollen samples with an average time resolution of 7 000 years were analyzed in the deep-sea record at the depth of 135 - 95 m （in composition depth） from ODP Site 1143 （9° 22＇ N, 113° 17＇ E） in the southern South China Sea. The results show that the pollen influx has a distinct change. During 2.6 - 2.0 Ma B.P., the average value of pollen influx increased evidently compared with that of 3.0 - 2.6 Ma B.P. It shows that the sea level of SCS dropped dramatically around 2.6 Ma B.P., corresponding to the formation of the Northern Hemisphere ice-sheets and the enhancement of the East Asian Monsoon. The pollen influx variations reflect the glacial-interglacial cycles corresponding with the deep-sea oxygen isotope curve and indicate that the sea level of SCS rose and dropped many times after 2.6 Ma B.P. The spectrum analysis results of pollen influx show that there are cycles at 0.1Ma （eccentricity） and 46.9 ka （obliquity） during 3.0 - 2.0 Ma B.P.
基金the NSFC, the National Natural Science Foundation of China (Grant No. 49999560).
文摘Three layers of volcanic tephra, sampled from ODP 1143 Site in the South China Sea, were observed at the mcd depth of 5.55 m, 42.66 m, and 48.25 m, and named, in this paper, layers of A, B, and C, respectively. All of these tephra layers have an average thickness of ca. 2 cm. They were constrained in age of ca. 0.070 Ma, ca. 0.80 Ma, and ca. 1.00 Ma, respectively, by the microbiostratigraphy data. These tephra layers were predominated by volcanic glass shards with a median grain size of 70-75μm in diameter. Major chemical compositions analyzed by EMPA and comparison with the previous data from other scatter areas suggest that these three layers of tephra can correspond to the three layers of Toba tephra, YTT, OTT, and HDT, respectively, erupting during the Quaternary. The occurrence of these tephra layers in the South China Sea implies that the Toba eruptions often occurred in the summer monsoon seasons of the South China Sea during the Quaternary, and that the strength of eruptions was probably stronger than that previously estimated.
