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Deepwater ventilation and stratification in the Neogene south China Sea
Li, QY; Zhao, QHH; Zhong, G; Jian, ZM; Jun, T; Cheng, XR; Wang, PX; Chen, MH;
摘要Combined data of physical property, benthic foraminifera, and stable isotopes from ODP Sites 1148, 1146, and 1143 are used to discuss deep water evolution in the South China Sea (SCS) since the Early Miocene. The results indicate that 3 lithostratigraphic units, respectively corresponding to 21-17 Ma, 15-10 Ma, and 10-5 Ma with positive red parameter (a*) marking the red brown sediment color represent 3 periods of deep water ventilation. The first 2 periods show a closer link to contemporary production of the Antarctic Bottom Water (AABW) and Northern Component Water (NCW), indicating a free connection of deep waters between the SCS and the open ocean before 10 Ma. After 10 Ma, red parameter dropped but stayed higher than the modern value (a*=0), the CaCO3 percentage difference between Site 1148 from a lower deepwater setting and Site 1146 from an upper deepwater setting enlarged significantly, and benthic species which prefer oxygen-rich bottom conditions dramatically decreased. Coupled with a major negative excursion of benthic delta(13) C at similar to 10 Ma, these parameters may denote a weakening in the control of the SCS deep water by the open ocean. Probably they mark the birth of a local deep water due to shallow waterways or rise of sill depths during the course of sea basin closing from south to east by the west-moving Philippine Are after the end of SCS seafloor spreading at 16-15 Ma. However, it took another 5 Ma before the dissolved oxygen approached close to the modern level. Although the oxygen level continued to stabilize, several Pacific Bottom Water (PBW) and Pacific Deep Water (PDW) marker species rapidly increased since similar to 6 Ma, followed by a dramatic escalation in planktonic fragmentation which indicates high dissolution especially after similar to 5 Ma. The period of 5-3 Ma saw the strongest stratified deepwater in the then SCS, as indicated by up to 40% CaCO3 difference between Sites 1148 and 1146. Apart from a strengthening PDW as a result of global cooling and ice cap buildup on northern high latitudes, a deepening sea basin due to stronger subduction eastward may also have triggered the influx of more corrosive waters from the deep western Pacific. Since 3 Ma, the evolution of the SCS deep water entered a modern phase, as characterized by relative stable 10% CaCO3 difference between the two sites and increase in infaunal benthic species which prefer a low oxygenated environment. The subsequent reduction of PBW and PDW marker species at about 1.2 Ma and 0.9 Ma and another significant negative excursion of benthic delta C-13 to a Neogene minimum at similar to 0.9 Ma together convey a clear message that the PBW largely disappeared and the PDW considerably weakened in the Mid-Pleistocene SCS. Therefore, the true modern mode SCS deep water started to form only during the "Mid-Pleistocene climatic transition" probably due to the rise of sill depths under the Bashi Strait.
部门归属Tongji Univ, State Key Lab Marine Geol, Shanghai 200092, Peoples R China; Univ Adelaide, Sch Earth & Environm Sci, Adelaide, SA 5005, Australia; Chinese Acad Sci, S China Sea Inst Oceanol, Guangzhou 510301, Peoples R China
关键词South China Sea Miocene Pliocene Pleistocene Deep Water Evolution Ventilation Carbonate Accumulation Oxygen And Carbon Isotopes.
学科领域Geology ; Geosciences, Multidisciplinary
GB/T 7714
Li, QY,Zhao, QHH,Zhong, G,et al. Deepwater ventilation and stratification in the Neogene south China Sea[J]. JOURNAL OF CHINA UNIVERSITY OF GEOSCIENCES,2007,18(2):95-108.
APA Li, QY.,Zhao, QHH.,Zhong, G.,Jian, ZM.,Jun, T.,...& ventilation and stratification in the Neogene south China Sea.JOURNAL OF CHINA UNIVERSITY OF GEOSCIENCES,18(2),95-108.
MLA Li, QY,et al."Deepwater ventilation and stratification in the Neogene south China Sea".JOURNAL OF CHINA UNIVERSITY OF GEOSCIENCES 18.2(2007):95-108.
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