湘东南茶永盆地白垩纪——古近纪沉积古地理演化

Cretaceous-Paleogene Paleogeographic Evolution of the Chaling-Yongxing Basin in Southeastern Hunan Province

华南中新生代沉积盆地的演化历史记录了区域构造、岩浆和气候事件,对其进行研究可以为揭示区域地貌成因和沉积矿产的找矿勘探提供理论支撑。本文综合分析湘东南茶永盆地的地层对比、沉积相、控盆构造和地质事件等资料,揭示其古地理演化过程。根据茶永盆地的岩石组合、地层序列及古生物组合面貌,自下而上划分为栏垅组(K1l)、神皇山组(K1sh)、罗镜滩组(K2l)、红花套组(K2h)、枣市组(K2E1z)5个地层单元;识别出坡积相、洪积相、三角洲平原相、湖泊相4个沉积相类型,其中湖泊相细分出滨湖亚相和浅湖亚相。古流向、沉积物源和控盆断裂分析认为茶永盆地沉积古地理演化分为三个阶段:在早白垩世,盆地南缘受正断层和走滑断层控制发生断陷开始接受沉积,为近源快速堆积的坡积相和滨湖相,物源来自于南部的栖凤渡—许家洞低山丘陵区和东部的鲤鱼塘低山区;晚白垩世早期,受盆缘两侧逆冲断层控制,沉积中心向西北迁移,东高西低的地貌格局使得盆地西部成为沉降中心,为最大的湖盆扩张期,物源主要来自于盆地东侧的低山区;至晚白垩世晚期—古近纪,盆地沉降中心转移到盆地西缘并收缩形成两个孤立的湖盆,最终受逆冲断层控制萎缩消亡,物源区为西侧和北侧的低山丘陵区。茶永盆地白垩纪-古近纪沉积古地理演化为古太平洋板块和印度板块运动在华南内部的远程响应,构造体制在此期间发生了伸展—挤压—走滑的三次转变,区域发生的沉积、岩浆、火山事件和季风起源与上述板块运动存在耦合关系。

The Meso-Cenozoic sedimentary basins in South China can respond to tectonic,magmatic and climatic events,the evolution process of which can provide support for regional geomorphological genesis research and prospecting and exploration of sedimentary minerals.In this paper,based on comprehensive analysis of stratigraphic comparison,sedimentary facies,basin-controlling fault and geological events of the Chaling-Yongxing Basin (CYB) in southeastern Hunan Province,the sedimentary paleogeographical evolution was revealed.According to rock assemblage,stratigraphic sequence and paleontology of the CYB,it was divided into five stratigraphic units from bottom to top:Lanlong Formation (K_1l),Shenhuangshan Formation(K_1sh),Luojingtan Formation (K_2l),Honghuatao Formation (K_2h),and Zaoshi Formation (K_2E_1z).Four sedimentary facies were identified:deluvial facies,diluvial facies,delta plain facies and lacustrine facies,among which two subfacies were subdivided:shore lake and shallow lake.On the basis of paleocurrent direction provenance analysis and basin-controlling fault,the sedimentary paleogeographical evolution of CYB was divided into three stages:during Early Cretaceous,controlled by normal fault and strike-slip fault,the southern margin of the basin started to collapse and receive sedimentary and turned to deluvial and shore lake with rapid accumulation,and the sedimentary sources were from hills and low mountain area in the southern Qifengdu-Xujiadong and low mountain area in eastern Liyutang.At early Late Cretaceous,the sedimentary center migrated northwest-ward to result in west basin subsidence with high area in the east and low area in the wes controlled by thrust faults on both side of the basin margin,forming the largest lacustrine expansion,and the sources were mainly from the low mountainous area on the eastside of the basin.At late Late Cretaceous-Paleogene,the subsidence center shifted to the western margin of the basin and was contracted to form two isolated basins,which were controlled by thrust faults and disappeared eventually.The source area was from hills and low mountain area in western and northern sides.The sedimentary paleogeographical evolution of the CYB responds to the distant effect of the Pacific plate and Indian plate subduction,and undergoes three shifts of stretching,extrusion and strike-slip.It is a coupling relationship between the sedimentary,magmatic and volcanic events in the region and monsoon origin and above tectonic movement in South China.