| 

甘肃平凉奥陶系平凉组深水沉积特征及沉积环境分析 ——以银洞官庄剖面为例

作    者:王季欣1,2, 何幼斌1,2, 李 华1,2, 郝 烃1,2, 张 灿1,2
单    位:1 长江大学地球科学学院; 2 长江大学油气资源与勘探技术教育部重点实验室
基金项目:受国家自然科学基金项目“鄂尔多斯盆地西南缘中奥陶统等深流沉积及其主控因素研究”等资助
摘    要:
甘肃平凉上奥陶统平凉组深水沉积发育。对银洞官庄剖面进行实测,出露地层厚146 m,自下而上分为30个小层,岩性以砂屑灰岩、泥晶灰岩、粉屑灰岩及页岩为主,夹有砾屑灰岩及泥岩等,伴有水平层理、平行层理、交错层理及波状层理等沉积构造,按岩性变化由下到上可划分为3段。在前人研究成果的基础上,通过野外实测、室内薄片鉴定和地球化学分析等综合研究,认为银洞官庄剖面平凉组沉积环境为半深海,主要发育深水原地沉积、等深流沉积、浊流沉积及碎屑流沉积等4种沉积类型。剖面深水原地沉积普遍发育,下部主要发育碎屑流沉积与浊流沉积,向上浊流与等深流相互作用,等深流沉积逐渐增多。根据V含量、Sr含量、87Sr/86Sr、Sr/Ba、Sr/Cu、Rb/Sr、B/Ga、U/Th、V/Cr、Ni/Co、V/(V+Ni)、Ceanom及Ce/La等地球化学指标的垂向变化特征对古沉积环境的反演表明:平凉组沉积时期,相对海平面整体呈上升趋势,古气候由湿润向干旱转变,古盐度逐渐增大,沉积环境还原性逐渐增强。对剖面样品(中上部为主)的地球化学参数和沉积类型的统计分析表明,V含量、87Sr/86Sr、Rb/Sr可在一定程度上反映平凉组不同深水沉积类型的差异:古水深较深、古气候较干旱、古盐度较大且还原性较强的沉积环境有利于等深流沉积的形成,古水深较浅有利于重力流沉积的发育,古水深较深、古气候较温湿且古盐度较小则有利于深水原地沉积的发育。
关键词:奥陶系; 平凉组; 深水沉积; 沉积环境; 地球化学; 甘肃

Deep water deposits and sedimentary environment of Ordovician Pingliang Formation in Pingliang, Gansu: a case of Yindongguanzhuang Section

Author's Name: WANG Jixin, HE Youbin, LI Hua, HAO Ting, ZHANG Can
Institution: School of Geosciences, Yangtze University
Abstract:
Deep water deposits developed in Ordovician Pingliang Formation in Pingliang of Gansu Province. According to the field measurement of Yindongguanzhuang Section with thickness of 146 meters, it can be divided into 30 small layers, and 3 segments on larger scale. There are mainly calcarenite, micrite, calcisiltite, and shale, with calcirudite and mudstone interbeds, and many types of sedimentary structure such as horizontal bedding, parallel bedding, cross bedding, and wavy bedding developed in the formation. On the basis of comprehensive analysis including field measure, thin section, and geochemical data, it is concluded that four types of deep water sedimentation developed in Pingliang Formation at Yindongguanzhuang Section, i.e., deep water autochthonous deposit, contour current deposit, turbidite deposit, and debris flow deposit. Besides the autochthonous deposit, the turbidite deposit and debris flow deposit mainly developed in lower part, in upper part the mixed sedimentation of turbidite and contour current developed, and the contour current deposit increased on scale. According to the vertical variation of some geochemical indicators including V, Sr, 87Sr/86Sr, Sr/Ba, Sr/Cu, Rb/Sr, B/Ga, U/Th, V/Cr, Ni/Co, V/(V+Ni), Ceanom, and Ce/La, it is shown that the sedimentary evolution in Plingliang Formation is sea level relatively increasing, climate from humid to drought, salinity gradually increasing, and reducing environment gradually strengthening. In addition, many indicators such as V, 87Sr/86Sr, and Rb/Sr can reflect different types of deep water sediments based on typical samples mainly in medium-up part of the section. It is shown that deeper water, drier climate, larger salinity, and stronger reducing environment were favorable for the contour current deposits; shallower water were favorable for gravity flow deposits; deeper water, warmer and wetter climate, and smaller salinity were favorable for autochthonous deposits.
Keywords: Ordovician; Pingliang Formation; deep water deposits; sedimentary environment; geochemistry; Gansu Province
投稿时间:2018-08-07  
查看pdf文件    


 
版权所有《海相油气地质》编辑部
地址:浙江省杭州市西溪路920号 邮编:310023 电话:0571-85224922,85224923,85224932 传真:0571-85229509
本系统由南京杰诺瀚软件科技有限公司设计开发