冰筏沉积与古气候、古地理

ICE-RAFTED DEPOSITS:PALAEOCLIMATIC AND PALAEOGEOGRAPHIC RECORDS

冰筏沉积(ice-rafted deposits)作为一种古气候、古地理再造的有效记录,在欧洲和北美已有许多研究,而在我国研究较少。本文为作者在查阅国外有关冰筏沉积文献基础上,对冰筏沉积做一综述,以期引起广大沉积学同行的注意。一、冰筏沉积的研究历史及现状对冰川作用的研究,始于1840年,地质学家们在试图解释覆盖于北欧、英格兰及北美等地的巨厚大陆冰川时开始了冰川作用的研究,提出了冰川作用的理论。冰筏作用是冰川作用中的一种特殊类型。早在1842年,英国地质学家Cnarles Darwin在研究Tierra del Fuego东部地区冰川时就认识到其中的冰筏沉积,并且总结了冰筏形成的两种作用。

lce-rafted deposits as direct indicators for the existence, of palaeoglaciation are very useful for the reconstruction of palaeoclimate and palaeogeography. Up to now very few studies about these deposits have been done in China. The authors here give an overview on the recent advances in our basic understanding of the ice-rafted deposits and their applications to palaeoclimatic and palaeogeo-graphic studies, and then describe the Cretaceous ice-rafted deposits in the Songliao Basin, which were recognized for the first time by Prof. L.A. Frakes, Prof. Wang Dongpo and the authors. In spite of being poor-studied on the whole, there are some criteria for identifying ice-rafted deposits, for example, the dropstone, cracks on grain surfaces, dramatic changes in grain size and the limited distribution in the strata. By recognition of the ice-rafted deposits and comparison with those in modern environments, the authors have revised the reconstruction of the palaeogeography of the Songliao Basin during Early Cretaceous, which can reasonably explain the coexistence of warm climate sporo-pollens with the cold ones.