四川盆地西南部第三纪盆地原型及其演化

第三纪是四川盆地大范围陆相沉积历史的最后阶段, 同时又是四川盆地重要的构造定形期.探究该时期原型盆地沉积充填规律与构造演化特征, 是揭示四川盆地形成演化过程, 还原其古地理、古气候演变的关键.在综合利用古地磁、地震、野外露头等资料的基础之上, 从盆-山结合的角度出发, 以地质历史时间为主要线索, 对第三纪原型盆地分阶段、分区域地进行了动态化分析研究.重建了各沉积时期原型盆地构造-古地理格局, 分析了盆地沉积充填规律并复原了不同阶段沉积相带的空间展布特征.主要受周缘山系逆冲推覆作用产生的构造负载和盆地基底构造的影响, 第三纪时期四川盆地沉积范围局限于西南部、南部地区, 以河、湖沉积环境为主, 处于持续地挤压、充填过程而具有萎缩消亡的趋势.现今残余第三系地层由老到新, 主要由名山组、芦山组、大邑砾岩组等地层组成(先后经历了: 受造山带挤压推覆作用和温暖干旱气候等因素影响, 发育湖盆边缘冲积扇和沙漠沉积环境, 处于快速沉降阶段的名山组沉积时期; 以及构造活动相对稳定, 湖盆面积不断减小, 以沙泥质沉积互层为特征的芦山组沉积时期; 和沿山前带由南向北迁移, 以发育大型冲积扇为特征的大邑砾岩组沉积时期).纵观整个第三纪构造演化历史, 反映出四川盆地西南部地区在第三纪时期表现为典型的陆内坳陷沉积盆地性质.同期的大地构造活动和气候变化等因素对原型盆地的形成与演化起到了重要的控制作用, 同时也对该时期盆地古地理格局和沉积充填规律产生了重要影响.

The prototype and its evolution of the southwestern Sichuan Basin in Tertiary

Tertiary is the final stage of the wide continental sedimentary in Sichuan Basin, and also the important tectonic deformation period. To analyze the sedimentary-filling pattern and the tectonic evolution characteristic of the prototype basin is significant to reveal the evolution of the Sichuan Basin forming process, and it is the key to restore the paleogeography and paleoclimate of the Sichuan Basin. In this paper, from the viewpoint of basin-mountain combination, we reconstructed the structure-paleogeographic pattern, analyzed the sedimentation-filling characteristics and restored sedimentary facies belt distribution characteristics in different periods on the basis of seismic, drilling, outcrops and various geological data. Obviously controlled by the tectonic load derived from the adjacent orogenic thrust and preexistent tectonic blocks in the basin basement, the sedimentary region limited to the southwestern, southern of Sichuan Basin and mainly composed of fluvial and lacustrine facies sedimentary environment with the process of continuous compressing, sediment filling, trend to shrink and ultimately disappears in Late Tertiary. The remnants of tertiary strata consisting of Mingshan, Lushan and Dayi conglomerate formations from the bottom up. Experienced several depositional stages including: Firstly, with alluvial fan and desert sediment on the edge of the lake duo to the tectonic load derived from the adjacent orogenic thrust and the warm and dry climate, with fast deposition at the stage of the Mingshan Formation; Secondly, is characterized by sand shale interbed and in the process of continuous shrink and the tectonic activity is relatively stable at the stage of the Lushan Formation; Finally, alluvial fan deposition developed along strike from SW to NE at the stage of the Dayi conglomerate stage. The southwestern Sichuan Basin has been demonstrated to be a typical intercontinental depression basin in the Tertiary Period in accordance with tectonic and sedimentary evolutions. The factors such as tectonic activity and climate change played an important role in the formation and evolution of the prototype basin, at the same time, it is deeply affected the paleogeographic and the rule of the sedimentation-filling pattern in Tertiary.