基于粒度小波变换分析的四川盐源盆地沉积特征及其对盆地形成演化的指示意义

新生代期间的印度-亚欧板块碰撞及青藏高原隆升一直是国内外学者研究的热点。四川盐源盆地位于红河断裂带和鲜水河-小江断裂带之间的川滇地块，是板块碰撞过程中形成的构造逸出盆地，其形成演化对揭示板块碰撞及高原隆升的历史具有重要意义。系统测试了盐源盆地上新世-早更新世沉积地层的粒度，并对测试数据进行了小波变换分析，结果表明，小波变换能够直观地反映粒度变化的潜在周期，为沉积界面的定量划分提供了一种有效方式。依据粒度数据的小波变换分析结果，盐源盆地上新世-早更新世沉积地层可以划分出2个一级突变、6个二级突变和6个三级突变，这些突变反映了不同时间尺度构造、沉积环境的变化。对不同时段典型样品粒度分布特征的进一步分析表明，该序列为一套以湖泊、河流相沉积为主的地层，结合粒度小波变换的一级突变，将盐源盆地的形成演化划分为三个阶段:5.4~4.7 Ma是盆地的形成阶段，沉积类型主要为浅湖亚相，在粒度小波变换曲线中表现为高幅震荡特征；4.7~3.6 Ma是盆地的扩张阶段，沉积类型主要为深湖、半深湖亚相，粒度小波变换曲线表现为低幅震荡特征；3.6~1.8 Ma对应于盆地的萎缩、充填阶段，其沉积相和小波变化曲线特征与盆地的形成阶段相似。上新世早期的盆地形成（5.4~4.7 Ma）与印度-亚欧板块在此时期的一次碰撞事件密切相关，而发生于3.6 Ma的盐源盆地沉积环境巨变则对应于青藏高原的一个重要隆升期。

Sedimentary Characteristics of the Yanyuan Basin in Southwest Sichuan Province based on Grain Size Wavelet Transform Data and Their Effects on Basin Evolution

The Cenozoic India-Eurasia collision and uplift of the Tibetan Plateau remain hot topics. The Yanyuan Ba-sin in southwest Sichuan province is located in the Sichuan-Yunnan block,which is between the Red River and Xianshuihe-Xiaojiang fault zones. It is a tectonic escape basin that formed during the continental collision,and its evolution process is valuable in revealing the history of the continental collision and uplift of the Tibetan Plateau. In this paper,detailed grain size measurements were carried out on the Pliocene-Early Pleistocene sediments in the Yanyuan Basin,and the grain size data were processed using wavelet transform technology. The results indicate that wavelet transform data can clearly show potential cycles of grainsize variations and,therefore,can provide an effec-tive way to divide the sedimentary stratum interface quantitatively. According to the wavelet transform grain-size anal-ysis,the sedimentary stratum in the Yanyuan Basin can be divided into two level-1,six level-2,and six level-3 muta-tions,which reflect the tectonic and sedimentary environment changes on different time scales. Further analysis of the grain-size distributions within the representative samples for different periods prove that this sequence is mainly com-posed of sediments from lake and river facies. Combined with the grainsize level-1 mutation of the wavelet transform data,the formation and evolution of the Yanyuan Basin can be divided into three stages:5.4-4.7 Ma is the formation phase of the basin,the sedimentary type is mainly a shallow lake subfacies,and the wavelet transform curve shows a high amplitude shift feature;4.6-3.6 Ma is the expansion phase of the basin,the sedimentary types are mainly deep and half-deep lake subfacies,and there is a low amplitude shift feature in the wavelet transform grainsize curve; 3.6-1.8 Ma corresponds to the basin contraction and filling phase,and the features of sedimentary facies and wavelet transform curves are similar to those of the basin formation phase. The formation of the Yanyuan Basin in the Early Pliocene (5.4-4.7 Ma) is related to an India-Eurasia collisional event,while the sedimentary environment change that occurred following 3.6 Ma corresponds to an important uplift event of the Tibetan Plateau.