青藏高原东北缘循化盆地渐新世—上新世沉积相分析与沉积演化

位于循化盆地南缘的积石镇羊圈贡拜—西沟上庄剖面发育连续完整的晚渐新世—上新世地层, 从老至新依次出露渐新统—中新统他拉组、中新统咸水河组(中庄段、上庄段、东乡段)和中新统—上新统临夏组(柳树段和何王家段).沉积相分析认为, 他拉组以冲积扇相为主, 咸水河组以富含膏盐层的咸化湖相—三角洲前缘相为主, 临夏组以湖相—三角洲前缘相夹水下扇相为主.通过对沉积序列中古流向的系统测量和分析, 揭示他拉组、咸水河组沉积期的古水流方向多在SE-NW之间, 结合物源分析, 表明当时西秦岭北缘逆冲带和拉脊山逆冲带均已隆起并遭受剥蚀成为循化盆地沉积物的物源供应区; 而在临夏组沉积期, 古水流以NWW为主, 推测循化盆地东部的积石山隆起成为物源的主要供应区.剖面粒度概率累积曲线和C-M图分析结果印证了对剖面沉积相的划分, 并指示盆地沉积时期的三角洲前缘和水下扇发育区存在牵引流. 

Oligocene-Pliocene Sedimentary Facies Analysis and Sedimentary Evolution of Xunhua Basin in Northeastern Margin of Qinghai-Tibet Plateau

The measured section in the southern margin of Xunhua basin located at Yangjuangongbai-Xigoushangzhuang Village, Jishi Town, Xunhua County, Qinghai Province, consists of Miocene to Pliocene strata, named as Tala Fm., Xianshuihe Fm. (consisting of Zhongzhuang Mem., Shangzhuang Mem. and Dongxiang Mem.) and Linxia Fm. (consisting of Liushu Mem. and Hewangjia Mem.). The detailed research of sedimentary facies indicates that the depositional system of the section consists of alluvial fan facies (Tala Fm.), salt water lacustrine facies and delta front facies (Xianshuihe Fm.), lacustrine facies and delta front facies with underwater fan facies (Linxia Fm.) from bottom to top. Paleocurrent measurements obtained from the imbricated structures and cross-beddings show that the paleocurrent direction of section was SE-NW, except the Linxia Fm.. The sedimentary origin analysis demonstrates that the northern margin of the western Qinling thrust belt and the south margin of the Lajishan thrust belt had uplifted as denudation areas and provided deposits to the Xunhua basin. On the contrary, during the depositional stage of the Linxia Fm., the paleocurrent was NWW, indicating that the Jishi Mountain of the eastern edge of Xunhua basin had uplifted as a main denudation area during the Late Miocene-Pliocene. The results of the grain size probability accumulative curves and C-M patterns accord with the division of sedimentary facies mentioned above, and indicate that some tractive current developed in delta front facies and underwater fan facies.