【作者】 匡永生；

【导师】 宋春晖；

【作者基本信息】 兰州大学 ， 矿物学、岩石学、矿床学， 2007， 硕士

【摘要】 天水-秦安地区位于青藏高原北部重要的昆仑山-西秦断裂带和祁连山-海源-六盘山断裂带交汇处，也是青藏高原与黄土高原接壤地带，其新生代沉积较完整的记录了青藏高原东北缘构造变形过程和古气候变迁历史。本文通过对其新生代地层序列、沉积体系、沉积相和沉积环境及其沉积对构造活动的响应等广泛野外考察和大量室内研究，结合周边已取得的沉积-构造资料，主要获得了以下认识：1、天水盆地经历三幕式构造演化，第一幕：古近纪天水地区岩石圈发生旋转拉伸变薄，天水盆地沉积一套山麓洪积扇相棕红色砂岩，源于地幔热源的钾霞橄黄长质火山岩喷溢而出。第二幕：新近纪岩石圈旋转拉伸停止，转变为挤压凹陷盆地的演化，该期构造作用使古近纪沉积强烈变形，并使西秦岭与华家岭隆起之间形成新近纪统一的沉积盆地，新近系地层超覆不整合于老的老地层之上，说明至少此时印度板块与欧亚大陆碰撞的远程效应已传递到达本区。第三幕：3.6Ma左右天水盆地进入了青藏运动A幕，天水盆地南部地区再次凹陷。2、天水盆地新生代沉积物根据岩性、沉积结构和构造，划分出21个岩相和冲积扇、宽浅湖泊、洪泛平原和河流四种沉积环境。同时将新近系地层从下而上划分为“下红层”、“斑马层”、“上红层”和“上绿层”四个单元，结合化石和古地磁测量结果，其磁性地层年代分别为＞9.23Ma、9.23-7.1Ma、7-1-3.6Ma、3.6Ma-1.4Ma。3、对秦安郭嘉新近纪外貌类似于黄土-古土壤序列的地层经过沉积结构和构造、地球化学组成、生物化石组合等分析，表明郭嘉一带新近系沉积序列属盆地边缘洪泛平原水下沉积与气下环境成壤作用改造的交互产物，而非风成堆积产物。4、古近纪在天水盆地局部地区沉积一套山麓洪积扇相紫红色粗碎屑岩。新近纪来自西秦岭的物质广泛沉积于天水盆地，并从盆地南部山前凹陷向北至广阔盆地洪泛平原带沉积厚度迅速变薄，沉积物粒径变细，沉积相水平分异明显。15.6MaB．P．以来经历了四个阶段的沉积演化过程：15.6-9.23Ma洪泛平原和河流沉积，沉积以红色泥岩与钙质泥岩或钙质层(calcrate)韵律互层为主的“下红层”；9.23-7.1Ma盆地广泛接受湖侵，沉积灰绿色泥灰岩与红色泥岩互层的“斑马层”；自7.1Ma开始湖泊大范围退缩、盆地广大地区转变为洪泛平原沉积，7.1-3.6Ma形成以红色泥质层和粉砂层为主的“上红层”沉积，并且在其顶部局部地区出现膏盐沉积；3.6Ma左右受青藏高原强烈隆升的影响，在靠近西秦岭的盆地南部再次断陷成湖，3.6Ma-1.4Ma沉积灰绿色泥岩与蓝灰-灰白泥灰岩互层的“上绿层”；约1.4Ma左右青藏高原强烈隆升使该区结束湖泊发育史，此后该区转为上升剥蚀、河流阶地演化以及接受风尘黄土沉积阶段。更多还原

【Abstract】 The Tianshui - Qin’an area is located at the convergence of Liupan Mountains and west of Qinling Mountains on the north margin of the Tibetan Plateau, and is the connection between the Tibetan Plateau and the Loess Plateau. Sediment in the basin has perfectly recorded the process of weather, denudation, transition and deposition in river system in orogenic belt, so the sediment not only can reflect the dynamic properties in filling process and the basic characteristics of the surrounding orogenic belt, but also record the climate and environmental change information in all kinds of geological processes. Based on wide field investigation, data analysis, synthesized various kinds of indices and correlative data, we have mainly obtained the following findings:1 Tianshui basin has experienced three stages of tectonic evolution, stage 1: Lithospheric thinning by the rotate and Stretch, sediment in Tianshui basin is brown alluvial fan red sandstone the kamafugitic series lava from mantle eruption out.Stage2:Tian shui Basin Lithospheric stretching stop to depress basin evolution and causes the Paleogene strata intense tectonic deformation in Neogene. A uniform basin has been formed between west Qinling and Huajia Mountains . Neogene strata formed and unconformably overlaped on the Paleogene sandstone. Note that at least that time India and Eurasia plate collision effects of the long-distance transmission has arrived in the area .Stage3: Tianshui basin enter the the Qinghai-Tibet Campaign A stage 3.6Ma ago, the southern region of Tianshui Basin again Depression.2 Tianshui Cenozoic sedimentary basin under the sedimentary structure of construct features were divided into 21 facies and the alluvial fan, wide-shallow lakes, flood plains, rivers four sedimentary environment,Neogene strata division into the "lower red bed", "zebra bed" "upper red bed" "upper red bed" of the four lithology Stage Magnetostratigraphy era is 15.6-9.23Ma, 9.23-7.1Ma .1-3.6Ma, 3.6Ma-1.4Ma respectively.3 the appearance of Guojia Neogene section is similar to the Loess-paleosol series, However based on the grainsize, geochemistry and microstructure analysis of the sediment deposited during 22-6.2Ma in Guojia, Qin’an, suggested that this set of red beds was it should be an alternative series which is composed of finegrain lake shoal mudflat deposition on the margin of the basin, floodplain deposition and those products of pedogenensis in the air.4 The Paleogene red coarse clastic rocks with the characters of piedmont alluvial fan facies were deposited in Tian shui basin Local area. The thickness of the Neogene deposition decreased rapidly from west Qinling piedmont depression to the broad floodplain in the basin. The sediments become finer and the horizontal difference of sediments facies is obvious. The deposition evolution experienced the following stage since 15.6MaB.P.:15.6-9.23Ma: floodplain and fluvial deposition, the "lower red bed" consists of red mudstone and calcareous mudstone or calcrate with alternate appearance; 9.23-7.1Ma, the lake invasion took place in the basin broadly, the "zebra bed" consists of celadon marlite interbeded with red mudstone; Since 7.1Ma, the lake began to shrink in large scale and floodplain developed in vast area of the basin. 7.1-3.6M, "upper red bed" came into being and consisted mainly of red argillaceous beddings and siltstone beddings, moreover, gypsum-salt deposition has been found at the top of "upper red bed" in some area; About 3.6Ma, affected by the Tibetan Plateau uplift, the south part near the west Qinling Mountains in the basin downfaulted and became lake again; 3.6Ma-1.4Ma, "upper green bed" came into being and consists of celadon mudstone interbeded with offwhite marlite; About 1.4Ma, affected by the intense uplift of the Tibetan Plateau, the development history of the lake in the study area ended. After that, the study area began to experience uplift ,denudation, river terraces development and eolian Loess deposition.更多还原