青海循化盆地晚渐新世沉积物中坡缕石的特征及其古气候指示意义

采用X射线衍射和扫描电子分析方法，对青海循化盆地晚渐新世沉积物的矿物组成、坡缕石的矿物学特征以及古气候指示作用进行了深入的研究。结果表明，晚渐新世循化盆地沉积物中粘土矿物组成主要有蒙脱石、伊利石、坡缕石和绿泥石等；坡缕石一般呈纤维状或者针状，沿片状蒙脱石的边缘及表面交代生长，为典型自生成因的坡缕石。坡缕石是干旱-半干旱气候条件的特征矿物，其出现表明循化地区晚渐新世气候特征较为干旱，与粘土矿物组合及伊利石结晶度所反映的气候环境信息相吻合；沉积物中坡缕石相对含量及有序度自下而上逐渐增大，说明循化地区的干旱化逐渐加剧。循化地区晚渐新世(～23 Ma)的干旱化可能与青藏高原隆升或者全球气候变冷事件密切相关。

Characteristics of Clay Mineralogy of Late Oligocene Sediments in Xunhua Basin,Qinghai Province and Their Implications for Palaeoclimate

Mineral compositions and palaeoclimatic indicator of palygorskite of the Late Oligocene sediments in Xunhua basin,Qinghai,were investigated using X-ray diffraction(XRD) and scanning electron microscopy(SEM) methods.The results show that mineral compositions of the sediments are smectite,illite,palygorskite and chlorite,and the fibrous or acicular palygorskites are typically authigenic,which grew along the edges or the surfaces of platy smectite,respectively.Palygorskite is a characteristic clay mineral unde...