摘要
近期在川西北旺苍地区早志留世南江组中首次发现了鲕粒灰岩.它们多以10cm左右的薄层夹持在页岩或粉砂质泥岩中,沉积相分析显示该段地层总体应属于均斜缓坡沉积体系.说明这些鲕粒是由异地搬运而来,在旺苍附近可能会存在相当规模的鲕粒滩.在显微镜下可观察到,其中的鲕粒类别单一,鲕粒紧密排列,并呈现一定程度的压缩变形,局部壳层呈锯齿状,也指示这些鲕粒曾经历过高能分选和搬运,以及压实成岩作用等.氧碳同位素测试显示,这些鲕粒灰岩沉积时的古温度大体为25～31℃,表明早志留世的上扬子地台应处于中低纬度干热或温暖的古气候带.除去古气候及古地理学方面的意义,当前鲕粒灰岩的发现还为该区油气勘探提供了重要的储层信息.
Oolitic limestone has been recognized for the first time in the Early Silurian （Telychian） Nanjiang Formation from Wangcang,NW Sichuan. Facies analyses show that this oolitic-bearing succession developed in a ramp environment. With the thickness less than 10 cm in general and interbedded in the ramp succession,it can be determined that the oolitic layers were moved by episodic currents probably from a large oolitic beach near Wangcang,NW Sichuan,Upper Yangtze platform. Under the microscope,the categories of the oolites are monotonous,and somewhat compressed and deformed,with close contacts and serrated appearances. It also indicates that the oolites should be well-sorted and transported under the high-energy environment,and then be compacted during the following diagenetic stage. The oxygen and carbon isotope analyses of the oolites indicate that the paleotemperature is 25-31 ℃,suggesting tropical to subtropical climates of the mediate to low latitude during the Early Silurian （Telychian） in the Upper Yangtze region. Besides the study of the paleoclimate and paleogeography,as the high-quality reservoir rock,the discovery of the Early Silurian oolitic beds and the possible related oolitic beach nearby is helpful for the oil-gas exploration in NW Sichuan.
出处
《地球科学（中国地质大学学报）》
EI
CAS
CSCD
北大核心
2011年第1期43-52,共10页
Earth Science-Journal of China University of Geosciences
基金
中石化海相烃源岩前瞻性项目(No.G0800-06-ZS-319)
国家自然科学基金项目(No.40772076)
斯伦贝谢--中国地质大学(北京)教育基金(No.SLBX0901)
关键词
鲕粒灰岩
古气候
志留纪
沉积作用
上扬子地台
oolitic limestone
paleoclimate
Silurian
sedimentation
Upper Yangtze platform.
