西菲律宾海末次冰期以来的浊流沉积及其古环境意义

菲律宾海西部吕宋岛岸外MD98－2188钻孔揭示末次冰期以来发生过数次浊流沉积事件。研究发现浊流沉积层具有密度高、颜色亮度大等物理特征，含有较多粗沉积组分和翼足类化石碎片，说明其来源于浅海沉积物。本文运用AMS 14C测年和浮游有孔虫氧同位素建立精细的年龄模式，发现浊流沉积层段主要与末次盛冰期、冰期Heinrich变冷事件以及氧同位素4期等低海平面时期相对应，推测与千年尺度北半球气候冷期相关的海平面快速上升可能是西菲律宾海浊流沉积的触发原因。这对于认识快速气候变化的环境后果和开展西菲律宾海晚第四纪地层划分对比都有重要意义。

TURIDITE DEPOSITION OF THE LAST GLACIAL STAGE IN THE WESTERN PHILIPPINE SEA AND ITS PALEOENVIRONMENTAL IMPLICATIONS

Several sets of turbidite deposit were recognized from a Late Quaternary core MD 98-2188 (14.82°N, 123.49°E, water depth 730m) in the Western Philippine Sea off the Luzon Island. The turbidite layers with higher wet bulk density and lighter color contain a large amount of coarser sandy sediment and pteropod fragments, indicating that their source is shallower-water sediment. On the basis of a well-constrained age model derived from AMS ~(14)C dating and planktonic foraminiferal δ~(18)O ,it has been found that the time spans of the turbidite layers are 12.9 ～ 29.2kaB. P., 38.6 ～ 41.2kaB. P.,54. 8 ～ 55.5kaB. P.,60.1 ～ 61.1 kaB. P. And 65.1 ～ 69.7kaB. P., respectively. Accordingly, the occurrence times of the turbidite events could be inferred by the upper limit of the time spans: 12.9kaB. P., 38. 6kaB. P.,54. 8kaB. P.,60. lkaB. P. And 65. lkaB. P.,respeetively. They should correspond to the rapid sea-level rise associated with the Melt Water Pulse 1A, and the Heinrich cooling events 4,5 and 6 in Marine Isotope Stage (MIS)3,and MIS 4. Although active tectonic movement in the vicinity of the Philippine Islands could provide a possible dynamic mechanism for the destabilization of shallower-water sediments, few reliable evidences have been found to show coincidence among these turbidite events,the tephra units uncovered in core MD 98-2188 and those reported in the South China Sea and the Sulu Sea. Therefore,we suggest that the rapid sea-level rise in the last glacial and the last deglaciation might be the trigger of the turbidite deposition in core MD98-2188. This study provides new evidence to correlate the Late Quaternary sediments in the Western Philippine Sea, and to understand the environmental consequence of rapid climate change.