河套地区新生代湖泊演化与“吉兰泰-河套”古大湖形成机制的初步研究

研究发现,河套地区在距今5～6万年前存在一个统一的"吉兰泰-河套"古大湖,覆盖吉兰泰和河套盆地的大部分地区。本研究试图依据钻孔资料和湖泊沉积物的测年结果,讨论新生代以来河套盆地的湖泊演化和古大湖的形成机制。结果表明,新生代以来,特别是早更新世以来吉兰泰盆地和河套平原的3个坳陷盆地就已经处于湖泊环境,但没有证据显示存在统一的湖泊。湖泊沉积及其OSL测年显示,"吉兰泰-河套"古大湖大约在距今10万年前后开始发育,至距今5～6万年之前湖面达到海拔1080m上下,随后湖泊衰退。我们认为,鄂尔多斯高原东北边缘距今12万年前后开始的快速构造隆升,可能导致了晋陕峡谷黄河外流受阻,最终在河套盆地积水形成统一湖泊,末次冰期中期(深海氧同位素3阶段)相对湿润的气候环境进一步促进了"吉兰泰-河套"古大湖的发育。

PRELIMINARY STUDY ON THE FORMATION MECHANISM OF THE "JILANTAI-HETAO" MEGALAKE AND THE LAKE EVOLUTIONARY HISTORY IN HETAO REGION

On the basis of borehole data and dating results on lacustrine sediments,we discussed the lake evolutionary history in Hetao Basin since Cenozoic and the formation mechanism of the "Jilantai-Hetao" Megalake in Late Quaternary.Our results suggest that lacustrine environments had existed in the three fault basins in Jilantai and Hetao area since Cenozoic,especially since Early Pleistocene,but there is no geological evidence indicating a unified paleo～lake.Lake sediments and OSL dating results suggest that the "Jilantai-Hetao" Megalake began to develop since ca.100ka ago and reached its highest lake level at 1080m a.s.l.About 50～60ka ago and began to contract thereafter.We believe that the rapid tectonic uplift of the northeast margin of the Ordos Plateau at ca.120kaB.P.may have blocked the outflow of the Huanghe River at "Jin-Shan" Canyon,which resulted in the development of the Megalake in Hetao Basin.The relative humid climate during the mid-last glacial period(MIS 3)was favorable for the expansion of the "Jilantai-Hetao" Megalake,which once covered most part of the Jilantai and Hetao Basins at around 50～60ka ago when the lake was at its maximum.