北美东部威斯康星中、晚期古环境与气候变化的甲虫化石证据

北美Laurentide冰盖于末次冰期的大部分时间在北美东北部一直存在，冰盖的活动对北美东部冰期时的环境和气候有很大的影响。甲虫分析表明，北美东部中纬度地区在威斯康星中、晚期的气候以寒冷为主，中间分别在42000aB.P.,34000aB.P.和28000aB.P.出现3次明显的气候变暖。此区威斯康星中期气候冷暖波动的幅度和出现的时间可以与同期的格陵兰冰芯记录及北大西洋Heinrich事件对比。

FOSSIL BEETLE EVIDENCE FOR MIDDLE AND LATE WISCONSINAN PALAEOENVIRONMENTAL AND PALAEOCLIMATIC CHANGE IN EASTERN NORTH AMERICA

Numerous fossil beetle assemblages have been described from mid-latitudinal eastern North Amtrica, which provide rich evidence for palaeoenvironmental and palaeoclimatic change during the last interglacial-glacal cycle. In this article, beetle assemblages of Middle and Late Wisconsinan age are summarized with an attempt to examine possible pattern of gladal climatic change. Fossil tale studies suggest that cold climatic conditions were dominant in the eastern North America between ca. 45000～15000aB.P. During the Middle Wisconsinan time, three apparently short warm intervals occurred at ca.42000aB.P., 34000aB.P. and 28000aB.P. The first warm interlude in well defined by the Titusville equence^6].  The second warm interlude is inferred from the record of St. Charles site, Iowa^12]. Although there is no direct fossil beetle evidence available immediately pre and post the St. Charles beetle assemblage, cold-adaptal mammoth fossil found underneath the fond beetle layer and cryogenic structure found between the fossil beetle layer and above Farmdalian palaeosol at the St. Charles site do suggest probable climatic change.The lower assemblage of the Biggsivlle the, Illinois, contains several spedes which occur today only south of southern boreal fond zone^5], indicating climatic warming during the Farmdalian Interstadial. The Biggsville sequence probably represents a transition from interstadial warm climate to late Wisconsinan cold climate, with evident faunal change occurred at ca. 26600aB.P. In addition to the Biggsville site, beetle assemblages from a number of other sites indicate continuous climatic cooling afterwards. The coldeSt climate occurred between ca. 21 500～15300aB.P. Late glacial climatic warming began at ca.15000aB.P.Middle Wisconsinan climatic changes revealed by the fossil beetle record seem to corre-late well with the climatic records from Greenland ice core and North Atlantic sediments^21,22].Palaeoenvironment and palaeoclimate in the Midwest and in the eastern Great Lakes re-gion Might have been strongly affected by the persistence of Laurentide ice sheet in the northeastern sector of North America during the Middle Wisconsinan. Climatic fluctuations in both the North Atlantic region and areas south of the Laurentide ice sheet might be resulted from the dynamics of Laurentide ioe sheet (Heinrich events). The apparent difference between there two regions in terms of climatic stability during the full gladal time is attrib-uted to the expansion of ice sheet in area and volume and the subsequently damping effect of northeastern ice sheet instability on atmospheric circulation south of the Laurentide ice sheet.