下扬子北缘前陆盆地构造演化及沉积特征

下扬子北缘主要受扬子板块、华北板块和秦岭微板块相互作用控制,自晚二叠世开始,扬子板块向北俯冲于秦岭微板块之下,构造环境由拉伸向挤压转换,于中三叠世形成下扬子北缘前陆盆地。下扬子北缘前陆盆地自萌芽至消亡可划分为3个演化阶段:1)萌芽阶段(P₃—T₁),形成被动大陆边缘盆地,发育深水—半深水复理石建造;2)兴盛阶段(T₂—T₃),由海相前陆盆地向陆相前陆盆地转化,发育海相和陆相磨拉石沉积;3)持续发育—消亡阶段(J_1-2),形成陆内前陆盆地,发育陆相含煤碎屑岩沉积。各演化阶段沉积特征不同,主要体现了由海相沉积向陆相沉积的连续渐进演化,且各阶段的沉积沉降中心基本一致,具有海相—陆相沉积叠合特征。 

TECTONIC EVOLUTION AND SEDIMENTARY CHARACTERISTICS OF THE FORELAND BASIN IN THE NORTHERN PART OF LOWER YANGTZE AREA

The northern part of lower Yangtze area is controlled by the interaction of the Yangtze platform,the North China platform and the Qinling micro-platform.The Yangtze platform starts to dive to the Qinling platform during the late Permian and the northern part of lower Yangtze area accomplishes the tectonic environment conversion from extension to extrusion.The foreland basin in the northern part of lower Yangtze area is formed during the middle Triassic.The evolution of the foreland basin can be divided into 3 stages: 1)sprout and budding stage(P3-T1),during which the passive continental margin basin is formed,characterized by a set of typical deep-water to semideep-water flysch;2)flourishing stage(T2-T3),during which the marine foreland develops to continental foreland,forming marine molasse and continental molasse;3)continued and extinction stage(J1-2),during which the intracontinental foreland is formed,characterized by coal-bearing clastic rock sediments of continental facies.The foreland basin experiences the evolution from marine to continental facies gradually,and the sedimentary characteristics diverge with the different stages.Though the sedimentation and subsidence center migrates continually,it is characterized by continental facies superposed to marine facies.