中更新世撞击事件对海洋环境的影响——南海ODP 1144站的高分辨率记录

MID-PLEISTOCENE IMPACT AND MARINE ENVIRONMENTAL CHANGES——A HIGH-RESOLUTION RECORD FROM ODP SITE 1144, SOUTH CHINA SEA

本文对采自南海北部 ODP114 4站 (2 0°3.18′N,117°2 5 .14′E,水深 2 0 37m) 385 .8— 386 .4 m层段的 2 8个沉积物样品进行了微玻陨石、浮游有孔虫及其同位素分析 ,以评估中更新世撞击事件对环境的影响。微玻陨石见于孔深 386 .12— 386 .38m,而集中分布在 386 .2 2— 386 .2 5 m厚约 3cm的地层中。研究结果表明 ,中更新世撞击事件对环境的影响很可能只是小幅度和短时间 (百年左右 )的 ,尽管引起了南海表层海水温度约 2°C的下降及其相应的δ1 8O的加重、浮游有孔虫冷水种含量的上升和暖水种含量的减少 ,但没有造成海水稳定同位素重大偏移和全球气候的灾难性影响 ,也没有引起浮游有孔虫在生物演化上的变化。

Total 28 samples were collected from the section of 385.8—386.4 mcd at ODP Site 1144 (20°3.18′N , 117°25.14′E , water depth 2 037 m), northern South China Sea, and microtektite, planktonic foraminifera and stable isotope analyses were performed in order to evaluate the effect of the mid-Pleistocene impact on microplanktonic communities and environment. Mid-Pleistocene microtektites were recovered from the interval between core depth 386.12 and 386.38 mcd but concentrated in a 3 cm-thick layer between 386.22 and 386.25 mcd. The average sedimentation rate was estimated 38 cm/ka and sample's time resolution 26 a/cm for the section studied. The results show that the mid-Pleistocene impact appears to have minor and short-period (～100 year) effect, causing an ～2°C decrease in surface sear temperature, corresponding increase in δ 18 O value and in cool-water species abundance, and decrease in warm-water species abundance. However, no planktonic foraminiferal extinction or origination, major shift in sea-water stable isotope and catastrophic change in environmental conditions could be observed.