青藏高原五道梁地区中新世湖相叠层石特征、分类及古气候意义

CHARACTERS AND CLASSIFICATION OF MIOCENE LACUSTRINE STROMATOLITES IN WUDAOLIANG AREA,NORTHERN TIBETAN PLATEAU:IMPLICATIONS FOR PALEOCLIMATE

通过对青藏高原五道梁地区中新世湖相叠层石样品岩石薄片、扫描电镜的观察,发现叠层石纹层主要有层带状、波状和柱状3种形态,且明暗纹层的结构极不相同,富屑层颗粒结构明显,富藻纹层由致密状含有机质泥晶方解石构成,呈泥晶结构;在此基础上,对叠层石进行了成因分类,认为研究区发育骨架叠层石、凝集叠层石和细粒叠层石。综合叠层石的沉积学、矿物学和稳定C,O同位素值特征,认为叠层石沉积期气候湿润,而纹层层偶则形成于呈季节性变化的气候条件下,亮层代表湿润期,暗层形成于相对干旱期。

According to the observation of thin section and SEM,3 types of shape patterns of Miocene lacustrine stromatolite laminations, occurred in Wudaoliang area, Tibetan Plateau, are recognized, they are strip-shaped, ripple-shaped and column-shaped respectively. The texture of stromatolite laminations is extremely different, such as grain-rich layers （light layers） show clear granular texture, while algae-rich layers are made of high content of organic matters with micrite texture. The stromatolites in Wudaoliang area may be classified as skeleton stromatolite, agglutinated stromatolite and fine grained stromatolite, and they are of different genesis. Based on the synthesis of sedimentation, mineralogy and stable C/O isotope,it is considered that the lacustrine stromatolite reflects a moist climate and different types of laminae are resulted from the variation of seasonal climate change. Light colored laminae represents wet climate while dark laminae form under a relative dry condition.