六盘山北部寺口子砂岩研究现状、问题及意义

古近纪内陆古环境重建是我国第四纪和新生代地质研究面临的前沿课题。位于青藏高原东北缘六盘山北部,作为著名寺口子组的正层型剖面,寺口子砂岩剖面是该期内陆环境变化重建的一个理想剖面。但其成因认识尚存在水成与风成两大分歧,以致其时代、成因、环境等一系列问题尚无定论。前人研究的基础上,通过对寺口子剖面进行野外调查与研究,进一步厘定沉积时代,澄清沉积特征,揭示成因类型,恢复沉积过程,重建其古地理环境与演变过程,并与区域及全球有关地质环境及古气候事件记录进行对比,探讨其对全球气候环境演变的响应机理,有助于解决该地层的成因与环境问题,有望建立一个典型古近纪内陆沉积剖面,促进中国内陆古近系记录及其古环境研究,并为青藏高原隆升—季风变迁—沙漠演化等耦合机制研究提供新的证据,同时,对类似砂岩地层的研究具有一定的推动作用。

Some Problems of Sikouzi Sandstone in Northern Mt. Liupanshan, China

The Paleogene is a key period for the environment changes from the Mesozoic to the Cenozoic, not only in China, but also even in the world. Concerning the global environmental evolution of this period, it is an important frontier topic faced by the study of Quaternary geology. The gap of the establishment of Paleogene continental section needs to be filled seriously in the study of red desert turnning into yellow desert in the northwestern part of China. Sikouzi sandstone is famous for its positive stratotype section of Sikouzi Formation, and also an important record of environmental evolution in the period. It is located in the northwest of Guyuan city of Ningxia Hui Autonomous Region of China, and also in the northern part of Mt. Liupanshan which is at the northeastern edge of Qinghai Tibet Plateau. From the 1920s to now, geologists have done many researches on it. However, there are still serious arguments on the following aspects such as the age, sedimentary characteristics, cause and environment of the section. One problem is about its age, namely, there are two different dating results that one is from late Oligocene to early Miocene, and the other is from Middle Eocene to late Oligocene. The other problem is about its formation, namely, there is an argument between hydraulic origin and eolian origin. In order to solve the two problems, it is necessary to conduct key investigation in field, and extract the paleoenvironment information such as its age, sedimentary structure, particle size, minerals, chemical elements, pollen and color so that we can construct its sequence of stratigraphic section, confirm its formation age, and clarify its sedimentary characteristics, process, cause and environment, according to the methods of geomorphology, Quaternary geology and stratigraphy. By analyzing and comparing with the related records of geological environment issues of regions and the world in the same period, we can explore its response mechanism. These have important significance on accurately understanding the relationship between the regional paleogeography and the surrounding environment in the northeastern margin of Qinghai-Tibet Plateau from the Paleogene to the Neogene, and exploring the paleoclimate and its relationship with planetary wind system and environment evolution mechanism.