川南黔北白垩—第三纪沙漠相及其意义

Cretaceous-Eogene Desert Facies in Southern Sichuan and Northern Guizhou and Its Significance

摘要:

虽然从1979年起就有人曾多次提出乐山大佛砂岩是沙漠沉积(李玉文、曾良鍷,1979;王孟筠、曾良鍷,1984;李玉文,1987),但从沉积学的角度进行专门研究,是地矿部成都地质矿产研究所白垩—第三纪课题组从1986年才开展的。本文则是该专题的摘要报道。鉴于沙漠沉积物,特别是古沙漠沉积物,是一个复杂的地质体,本文拟从地质背景、地层概况、沉积物结构构造特征,以及与现代风成砂沉积的对比等诸方面的综合分析,探讨其沉积环境及其意义。

Abstract:

This paper deals with Cretaceous-Eogene desert environments in southern Sichuan and northern Guizhou in terms of large amount of depositional indicators and features. It also discusses sedimentary environments, environmental evolution and their relations to palaeontology, palaeoclimate and palaeogeography based on a variety of sedimentary structures and textures in dune, sand sheet, interdune and extradune deposits as well as their geologic background. The well-sorted thick-bedded dune deposits(the maximum thickness=35m)were deposited in Cretaceous-Eogene desert environments in southern Sichuan and northern Guizhou, but the wet interdune deposits were not developed at that time, indicating a very dry climate. The ecologic environments are responsible for the early retreat of some large reptiles such as dinosaurs from the southern Sichuan-northern Guizhou area. The authous maintain in this paper that eolian sandstones in the study area not only have cerated very good hydrogeological conditions, but also may serve as a kind of industrial material of good quality. It is undoubted that the occurrence of the depositional events in Cretaceous-Eogene deserts will occupy a remarkable position in geological history of China and that the study of the events has also great significance for the division of sedimentary facies types and the interpretation of sedimentary environments in China.