Preliminary research on Megalake Jilantai-Hetao in the arid areas of China during the Late Quaternary

We identified geomorphological, sedimentary and biological evidence of high lake levels around the current Jilantai Salt Lake through field investigations and through analyses of regional remote sensing images. There are four groups of shorelines at elevations of around 1060, 1050, 1044 and 1035 m a.s.l., being 37, 27, 21 and 12 m above the current salt lake surface, respectively. Littoral deposits of sand and gravels are found at elevations between 1070 and 1080 m a.s.l., 47 to 57 m higher than the current salt lake surface, although palaeoshoreline landforms are only preserved at several sites. At Herimuxini, on the northern margin of the Ulan Buh Desert, typical lacustrine sediments and sand-gravel littoral deposits also occur at elevations of 1080 m a.s.l. and below. A 11-km-long typical spit extends eastward from this shoreline gradually reducing in elevation from 1050 to 1035 m a.s.l. In some sand-gravel quarries along the southern bank of the Yellow River on its Great Bend, such as those located near the Hydrological Gauge Station and Shilazhao Town, shoreline features were identified. Littoral deposits overlying the alluvial-diluvial layers occur in a sand quarry near Balagong in Hangjin County. There are also beachrock and littoral deposits preserved on the cut-and-built terraces at several sites along the southern piedmont of Langshan-Yinshan Mountains. In addition, a profile revealing subaqueous delta sediments was identified near Wuhai, where the Yellow River enters the basin. Typical lake sediments also exist at the Togtoh Platform on the eastern end of the Hetao Plain. Aquatic Mollusk shells are common in the littoral deposits, including several species of Corbicula, Radix lagotis, R. xauricularia and Gyraulus convexiusculus. Ostracode shells can also be identified in finer sediments. Typical vertical prograding sequences are evident in outcrops where lacustrine sediments were well preserved. Wave-rolled cobbles and beachrock are very commonly preserved on the top of profiles in the embankments at higher elevations. All this evidence suggests that there was once a huge palaeo-lake covering the Jilantai region and most part of the Hetao Plain with the highest lake level reaching ∼1080 m a.s.l. We refer to the huge paleolake, which was larger than modern Lake Baikal, as “Megalake Jilantai-Hetao.” OSL dating results indicate that the megalake formed before ∼60—50 ka, and the four shorelines at elevations between 1060 and 1035 m a.s.l. likely represent the lake level variations from ∼60–∼50 ka to the early Holocene. The discovery of the Megalake Jilantai-Hetao likely will impact understanding of the development of the Yellow River during the late Quaternary, the evolution of the Ulan Buh and Kubq deserts, neotectonism in the region, and possibly regional climatic changes. Supported by the NSFC Innovative Research Team Project (Grant No. 40421101) and the International Cooperation Project (Grant No. 2002CB714004). Laboratory analyses are supported by the NSFC Key Project (Grant No. 90502008) and the NSFC (Grant No. 40502016)