白垩纪红层冰筏沉积的古气候及古地理意义

THE PALAEOCLIMATIC AND PALAEOGEOGRAPHICSIGNIFICANCE OF THE CRETACEOUS RED-BED ICERAFTING DEPOSITS IN THE SONGLIAO BASIN,NORTHEASTERN CHINA

冰筏沉积是负载沉积物的冰块进入海洋或湖泊中，冰块融化沉积物坠落所形成的，它们可形成于高海拔具有明显气候垂直分带的低纬度地区或者是高纬度地区。我们在研究松辽盆地白垩纪古气候时，首次在泉头组红层中发现冰筏沉积。根据泉头组孢粉组合的研究表明，它们除了具有热带一亚热带植物的孢粉以外，还有少量喜冷分子混生现象。经研究这些矛盾现象，反映泉头组时期盆地外围地形高差大，形成明显的气候垂直分带现象，这是造成这些矛盾现象的主要原因。冰筏沉积的发现对松辽盆地古气候古地理的恢复皆具有十分重要的意义。

The authors in the present paper interprete the ice-rafting deposits to be originatedfrom the melting of the sediment-laden ice blocks which were transported into seas orlakes. These deposits may occur in the low-latitude regions with higher elevations,wherethe climates are vertically zoned,or in the mountainous area of the high-latitude regions.The present paper has reported the ice-rafting deposits identified for the first time in theCretaceous red beds of the Songliao Basin. These deposits appear as scattered or concentrated gravels in the Cretaceous red beds. The examination of the gravel compositions indicates that the principal source of detritus lay to the peripheral mountainous areas. In addition,the research results also show that the sporopollen assemblages consist mainly of thetropical and subtropical types,with minor amounts of Piceaepollenites and Cedripites,perhaps implying that there were greater height deviations around the Songliao Basin duringthe deposition of the Quantou Formation.The discovery of the Cretaceous ice-rafting deposits in the study area has important implications for the reconstruction of the palaeoclimates and palaeogeography of the Songliao Basin.