冕宁地区中更新世早期沉积环境与古环境演化研究

Sedimentary Environment and Paleoenvironment Evolution of Early Middle Pleistocene Stage in Mianning Area

昔格达组地层是我国西南地区晚新生代典型的沉积地层之一,但针对其沉积环境和古环境的研究记录较少。为此以冕宁县城西北方向钻孔揭示的昔格达组沉积物为研究对象,通过沉积物年代、粒度和孢粉测试分析,结合沉积序列、岩性岩相、沉积构造特征等,可知736~719 ka期间沉积物以滨湖亚相的沉积环境为主,植被分布存在显著的垂直地带性,气候整体温暖湿润;719~563 ka期间沉积物以深湖-滨湖亚相的沉积环境为主,此阶段针叶类植被花粉含量增加,禾本花粉含量稍有下降,气候较上一阶段变冷干;563~455 ka期间沉积物以半深湖-浅湖亚相沉积环境为主,此阶段针叶类植被花粉含量增高,阔叶类植被花粉含量稍有减少,指示该时期古环境较为冷湿。

The Xigeda Formation is a typical late Cenozoic sedimentary formation in southwest China,but there are few records of its sedimentary environment and paleoenvironment.This research mainly focuses on the sediments of the Xigeda Formation revealed by drilling in the northwest direction of Mianning county.Through the analysis of sediment chronology,particle size and palyore,the comprehensive sedimentary sequence,lithology and sedimentary structure characteristics,results show that the sedimentary environment of Binhu subfacies was dominant during 736~719 ka,and the vegetation distribution showed significant vertical zonality,and the overall climate was warm and humid;during 719~563 ka,the sedimentary environment of deep lake-Binhu subfacies increased the content of conifer,decreased the content of grass,and the climate became cold and dry;during 563~455 ka,the sedimentary environment was dominated by semi-deep lacustrine and shallow lacustrine subfacies.The content of coniferous vegetation increased while that of broad-leaved vegetation decreased slightly,indicating that the paleoenvironment in this period was relatively cold and wet.