川西凹陷地区更新统砾石层沉积成因探讨

笔者通过野外地质调查和相关资料,从宏观形态和沉积特征多方面对川西凹陷地区的更新统砾石层的成因进行综合分析.发现各时期更新统砾石层平面上均呈扇状,具多级阶地.各砾石层的岩性结构柱、基本层序、砾石的组构特征均表现为河流相冲洪积成因.并通过ESR和孢粉、充填序列和地貌标志探讨了区内各更新统砾石层的沉积时代、古气候特征.综合研究表明区内存在4套不同特征的更新统砾石层,它们不仅在空间位置上存在密切联系,而且在沉积特征和形成时代上也具继承性.沉积环境均为温暖潮湿热环境下,出龙门山的古青衣江在盆地中不同时期、不同位置的沉积响应.并反演古青衣江水系在前陆盆地中不同时期的迁移及变化规律.

The origin of the Pleistocene gravel in western Sichuan depression

Combining related materials with regional geological mapping,the authors analyzed the cause for the formation of the Pleistocene gravel strata in the light of the space-time distribution and sedimentary features.The Pleistocene gravel strata are fan-shaped and have multi-level terrace.The Pleistocene gravel is genetically of fluvial deposition,as shown in such aspects as lithologic column structure,basic sequence and fabric characteristics.The authors also probed into the deposition epochs and the paleoclimate on the basis of ESR measurement,sporopollen and filling sequence.The results have led the authors to believe that there exist four sections of Pleistocene sequence which are not only related to each other in space but also have inheritance in deposition epochs and sedimentary features.It is thus concluded that the formation of the Pleistocene sequence was completed by the river from Longmen Mountain and the deposition was carried out in different epochs on the foreland basin under the condition of warm-humid climate.Finally,the authors made inversion for the regularity of the change of the Qingyi River in the foreland basin in Pleistocene.