呼伦湖晚第四纪湖相地层沉积学及湖面波动历史

SEDIMENTOLOGY OF LATE QUATERNARY LACUSTRINE DEPOSITS AND HISTORY OF LAKE LEVEL FLUCTUATION IN HULUN LAKE

对内蒙古呼伦湖盆地扎赉诺尔地区晚第四纪湖泊沉积物进行了沉积学(沉积构造、结构、垂向层序等)和^(14)C年代地层学研究,并逐层识别出地层剖面的各种沉积相类型,包括开阔湖、近岸带、滨岸沙滩、滨岸沼泽和滨岸沙丘等不同类型沉积,依此恢复了30kaB.P.以来的湖泊演化和湖面波动历史。其中13～11kaB.P.是湖面最高时期,10.9～0.6kaB.P.的低湖面可能与新仙女木事件有关。

A well-exposed late Quaternary lacustrine deposit section was excavated by East Opencut Coal Mine at Jalai Nur in northern Hulun Lake Basin. The 14. 6m-section is divided into 7 lithologic beds and 9 sub-beds according to lithology, sedimentary structures, fossils and vertical sequences. Bed 1 (14. 59 ~ 12. 48m): Thick-layered gray gravels with intercalated thin-layered sands. The well-rounded gravel shape, positive cyclothem and planar cross-bedding indicate their alluvial origin. Bed 2 (12. 49~8. 89m) : Thick-layered gray silty muds with thinly interlayered bedding or lamination, formed in an open-lake environment. Bed 3 (8. 89~6. 83m ): Gray muddy silts with thin intercalation of light-gray fine sands, light-gray fine sands with faster bedding. Neritic zone and coastal sand beach environments are considered. Bed 4 (6. 83 ~ 4. 13m): Thick-layered gray-yellow fine sands with typical aeolian sedimentary structures such as inclined foreset laminae and wind scour-filling structure, formed in coastal sand dune environment. Bed 5 (4. 13 ?2. 23m): Thick-layered dark-gray organic muddy silts containing large amount of bivalve, woody plant and herb, formed in coastal marsh environment j Bed 6 (2. 23~0. 68m) : Thick-layered light-gray yellow fine sands with steeply inclined foreset laminae and lag gravels, indicating the aeolian sand dune. Bed 7 (0. 68~0. 27m) : Paleosol. The lake level variation and environmental evolutionary history of Hulun Lake in the past 30 ka can be inferred based on the sedimentological analysis of the strata, i. e. : (1) Before 13ka B. P. : The study site was occupied with fluvial environment, which implies that Hulun Lake did not come into being until about 13ka B. P. (2) 13~llka B. P. : The highest lake level appeared, of which the altitude might be up to 560m estimated by the lake terrace. (3) 11~10 ka B. P. : On the background of regression, the lake level fluctuated frequently. The most obvious falling of lake level occured in 10. 9~ 10. 6ka B. P. , related possibly to Younger Dryas event. (4) 10 ~ 7. 1 Ka B. P. : The lake level dropped and the lake area shrank dramatically. (5) 7. 1~5. 3ka B. P. : The lake level rose again, reaching the altitude of 550m estimated on the lake terrace. (6) 5. 3~3. Ika B. P. : The lake level descended greatly. The study site exposed subaerially after 3. Ika B. P.