内蒙古中东部达里湖湖岸堤记录的12.5 cal ka BP以来湖面波动过程

Lake level fluctuations since 12.5 cal ka BP recorded by lakeshores of the Dali Lake in middle-east of Inner Mongolia

内蒙古中东部位于东亚夏季风过渡区,对气候变化响应敏感。广泛发育的湖泊沉积物提供了全新世以来的环境变化的理想材料。湖岸沉积物直接记录的古水位,与高分辨率的湖心钻孔记录相结合,有助于全面认识古气候的变化历史和湖面波动的定量重建。运用AMS14C测年和GPS、DEM及1︰5万地形图等相结合的方法确定了达里湖北侧湖岸堤的年代和高程,并结合湖岸堤剖面的沉积序列指示的湖面变化过程,重建了12.5cal ka BP以来达里湖的波动历史。12.5 cal ka BP,达里湖湖面海拔高度约为1253m,至12.3 cal ka BP湖面经历短暂上升,至海拔1266m左右;之后湖面下降,至全新世早期(11.2 cal ka BP),水位降至1254m左右;随后湖面开始逐步上升,10.7 cal ka BP湖面水位稳定在1274m左右;全新世中期湖面继续上升至某一高度(至少在1291m)后,于全新世晚期4.8 cal ka BP湖面高度降至1279m,并于4.6 cal ka BP湖面继续下降至1275m的高度。通过对比湖心钻孔记录的湖泊波动历史以及区域湖泊沉积记录,认为达里湖的水位波动受东亚季风活动的影响,具有区域的一致性。达里湖的水位变化较区域内的其他湖泊更为强烈,认为除了受区域气候变化的影响外,达里湖全新世晚期的湖面下降可能还与区域内强烈的构造活动和西拉木伦河溯源侵蚀导致区域水系的改变有关。

Middle-east of Inner Mongolia,located in the transitional region of East Asian SummerMonsoon,is sensitive to climate changes. Widely scattered lake sediments provide ideal materials for studying environment changes since the Holocene. Lakeshore sediment,recording the paleolake level directly,could help us understanding the paleoclimate history and reconstructing lake level fluctuations quantitatively combined with high-resolution lake center records. AMS^14 C dating,GPS,DEM and 1：50000 topographic map methods were applied to investigate the chronology and elevation of lakeshore in the north of Dali Lake. Combined with the sedimentary sequences,the lake level history since 12. 5 cal ka BP was reconstructed. The lake level was 1253m at 12. 5 cal ka BP followed by a short duration of transgression until 12. 3 cal ka BP（ 1266 m） and then began to decline. In early Holocene at 11. 2 cal ka BP,the lake level was at 1254m and showed a rise tendency till 10. 7 cal ka BP at 1274m. Up to mid-Holocene,the lake level continued to rise（ at least 1291m）. In late Holocene at 4. 8 cal ka BP, the level fell to1279m and then to 1275m at 4. 6 cal ka BP. By comparing with the records of Dali Lake core and other regional lakes,we considered that the lake level fluctuations were consistent with the regional pattern possibly controlled by the East Asian Monsoon. Moreover,the intense lake level fluctuations of the Dali Lake may also be affected by both the regional tectonic activity during late Holocene and drainage system changes caused by head-ward erosion of the Xilamulun River.