柴达木盆地碱石山地区中新世介形类及其古环境

柴达木盆地中部碱石山地区碱石1井岩屑及岩心的微体古生物分析,在上油砂山组和下油砂山组发现少量的介形类化石,其中以Eucyprisobtus较为丰富,出现的其他分子还有Eucyprisstenoformi、Cyprideis和Cyprinotus(Heterocypris)等。据化石时代分布认为,碱石1井含介形地层的时代为新近纪中新世,以Cyprideis的大量出现作为下油砂山组的顶界。据介形类生态分布认为,上油砂山组和下油砂山组的沉积环境属少盐水-真盐水湖泊,并且上油砂山组比下油砂山组的沉积环境更为咸化。碱石山地区中新世至上新世,湖泊在向东迁移过程中经历了浅→深→浅的演化过程,沉积水体逐渐咸化。

The Miocene Ostracoda and Paleoenvironment in Jianshishan Area of Qaidam Basin

Based on analysis of micropaleontology on the cuttings and core samples from Jianshi Well 1 in Jianshishan area of middle Qaidam basin,a few ostracoda fossils dominated by Eucypris obtus and some others like Eucypris stenoformi,Cyprideis and Cyprinotus(Heterocypris) have been found in the Upper and Lower Youshashan formations.The era distribution of these fossils indicates that the strata with ostracoda in this well belongs to Miocene,abundant Cyprideis-bearing strata should be the top boundary of Lower Youshashan formation.The ecological distribution of the ostracoda shows that the sedimentary environment of Upper Youshashan formation and Lower Youshashan formation belongs to seldom-real brine lake,and the former is more salty than the latter.From Miocene to Pliocene,the lake was transported eastward and underwent the evolution from shallow to deep,then to shallow with brine being gradually salty in this area.