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Deepwater Ventilation and Stratification in the Neogene South China Sea被引量:3
2007年
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 δ^13Cat ~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 Arc 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 ~6 Ma,followed by a dramatic escalation in planktonic fragmentation which indicates high dissolution especially after ~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
李前裕赵泉鸿钟广法翦知湣田军成鑫荣汪品先陈木宏
关键词:MIOCENEPLIOCENEPLEISTOCENE
新近纪南海深层水的增氧与分层被引量:5
2008年
综合南海ODP1148站、1146站和1143站沉积物物性、底栖有孔虫、同位素等资料,探讨早中新世以来南海深层水的演化特征.结果表明,在21~17Ma、15~10Ma和10~5Ma3个时间段分别对应3个富含红褐色粘土的岩性单元,其红色参数(a^*)增高指示南海深层水中溶解氧含量的增加.对比发现,前两阶段的深层水增氧与南极底层水和北大西洋组合水增强有关,说明10Ma前南海与外地的底层水基本是相互连通的.10Ma以后,南海深层水溶解氧降低,同时分别处于下深层水的1148站和上深层水的1146站之间的CaCO3含量变化加大,喜氧底栖有孔虫减少,底栖δ^13 C在~10Ma大幅度减轻,说明南海当时的深层水受大洋深层水的控制减弱.推测主要是南海海盆白16-15Ma停止扩张以后,南海逐渐关闭引起本地深层水开始形成的缘故.从6Ma左右开始出现大量的太平洋底层水和深层水的底栖有孔虫标志种,1148站和1146站在5~3Ma期间的CaCO3含量之差达到40%,标志南海深层水最大分异期.除了全球气候变冷、北半球结冰引起太平洋深层水扩张的影响之外,南海海盆由于更强烈向东俯冲而进一步下沉也可能是原因之一.3Ma以来南海深层水演化进入现代模式,两站之间的CaCO3含量之差稳定在10%左右,厌氧底栖种丰度增加.太平洋底层水和深层水的标志种相继在1.2Ma和0.9Ma大量减少,底栖δ^13 C也同时大幅度变轻到新近纪的最低值,表明太平洋底层水的影响基本消失,太平洋深层水的影响也大大减弱.因此,标准现代模式的南海深层水,推测主要由于“中更新世气候转型”时期巴士海峡下面的海槛抬升到接近目前~2600m的深度时,才开始形成.
李前裕赵泉鸿钟广法翦知湣田军成鑫荣陈木宏
关键词:上新世更新世增氧碳酸盐沉积
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