青藏高原东北缘老龙湾盆地新近系甘肃群地层划分  

Stratigraphic division of Neogene Gansu Group in Laolongwan Basin,northeastern Qinghai—Xizang(Tibet)Plateau

作　　者：王天宇 施炜[1,4] 侯贵廷 陈鹏[1,5] 王嘉琦 WANG Tianyu;SHI Wei;HOU Guiting;CHEN Peng;WANG Jiaqi(Chinese Academy of Geological Sciences,Beijing,100037;School of Earth and Space Sciences,Peking University,Beijing,100871;China National Gold Group Geology Company Limited,Beijing,101300;SinoProbe Laboratory,Chinese Academy of Geological Sciences,Beijing,100094;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing,100081)

机构地区：[1]中国地质科学院,北京100037 [2]北京大学地球与空间科学学院,北京100871 [3]中国黄金集团地质有限公司,北京101300 [4]自然资源部深地科学与探测技术实验室,北京100094 [5]中国地质科学院地质力学研究所,北京100081

出　　处：《地质论评》2025年第2期405-420,共16页Geological Review

基　　金：中国地质科学院基本科研业务费专项(编号:JKY202419);中国地质调查局项目(编号:DD20190018)的成果。

摘　　要：海原断裂带西段老龙湾盆地沉积一套晚新生代红色碎屑物,记录了青藏高原东北缘生长过程。由于缺乏高精度的地层年代学研究,现有的工作笼统地将这套晚新生代沉积物划分为新近系甘肃群,导致老龙湾盆地对青藏高原北东扩展响应的认识存在争议。本文在1∶5万区域地质调查的基础上,对老龙湾盆地晚新生代地层开展了高精度磁性地层年代学研究,建立了老龙湾盆地约13.61~2.58 Ma磁性地层年代学格架。结合岩性特征和沉积环境分析,将老龙湾盆地新近系甘肃群地层划分为2个岩石地层单位:咸水河组(N_(1)x)和临夏组(N_(1-2)l)。咸水河组沉积于晚中新世(约13.61~8.11 Ma),为一套砖红色砂质中砾岩、块状中砂岩、粉砂质泥岩,为晚中新世扇三角洲—滨浅湖相沉积,与下伏早志留世肮脏沟组灰绿色变质砂岩呈角度不整合接触。临夏组沉积时代为晚中新世—上新世末(8.11~2.58 Ma),为一套厚层浅砖红色中砂岩与中—粗砾岩互层,偶含巨砾岩,总体上表现为“砂砾互层”,为河流相沉积,与下伏咸水河组呈平行不整合接触。在区域上,老龙湾盆地新近系甘肃群咸水河组和临夏组两个岩石地层单位,可与邻区新近纪地层进行对比,从而统一了青藏高原东北缘的新近纪地层系统,为研究青藏高原东北缘新生代构造隆升提供了地层学依据。In the western segment of the Haiyuan Fault Zone,the Laolongwan Basin’s sedimentation encompasses a suite of Late Cenozoic red clastic deposits,which document the developmental processes of the northeastern periphery of the Tibetan Plateau.The lack of refined stratigraphic chronology research has led to a generalized classification of these Late Cenozoic deposits under the Neogene Gansu Group,sparking debates about the Laolongwan Basin’s geological response to the northeastward expansion of the Tibetan Plateau.This study,grounded in a 1∶50000 scale regional geological survey,undertakes an in-depth magnetostratigraphic chronology analysis of the Laolongwan Basin’s Late Cenozoic strata,resulting in the establishment of a magnetostratigraphic chronological framework spanning approximately 13.61~2.58 Ma for the basin.By integrating lithological features and sedimentary environment assessments,the Laolongwan Basin’s Neogene Gansu Group strata are differentiated into two distinct lithostratigraphic units:the Xianshuihe Formation(N_(1)x)and the Linxia Formation(N_(1-2)l).The Xianshuihe Formation,corresponding with the middle Miocene(ca.13.61~8.11 Ma),comprises a sequence of brick-red sandy conglomerates,blocky medium sandstones,and silty mudstones.This formation is indicative of Late Miocene fan delta and shallow lake depositional environments and is characterized by an angular unconformity with the underlying Early Silurian Angzanggou Formation,which consists of greenish-gray metamorphic sandstone.The Linxia Formation,age spanning the Late Miocene to Late Pliocene(8.11~2.58 Ma),is marked by thick layers of shallow brick-red medium sandstone and interbedded medium to coarse conglomerates,with sporadic occurrences of boulder conglomerate.This formation displays a distinctive"sand—gravel interlayering"arrangement and is associated with fluvial depositional processes,exhibiting a parallel unconformity with the preceding Xianshuihe Formation.On a regional scale,the Neogene Gansu Group’s Xianshuihe and Linxia F

关 键 词：青藏高原东北缘 老龙湾盆地 新近系 咸水河组 临夏组 古地磁 

分 类 号：P61[天文地球—矿床学]