四川盆地白垩纪构造层序、岩相古地理及演化

CRETACEOUS TECTONIC SEQUENCE AND LITHO-PALEOGEOGRAPHIC EVOLUTION IN THE SICHUAN BASIN

四川盆地白垩系可划分为2个构造层序,构造层序内部以最大湖泛面为界分为湖盆扩张期的沉积层序和湖盆收缩期的沉积层序。以沉积层序为编图单元,编制了四川盆地白垩纪的4张岩相古地理图,反映了四川盆地白垩纪的古地理特征及盆地演化,在早白垩世(TS1)期间沉积相主要沿着龙门山系呈东北向展布,发育有冲积扇、冲积平原、河流、湖泊等沉积相;到了晚白垩世(TS2)由于燕山运动第Ⅲ幕的影响,使盆地的沉积格局发生大角度偏转,变为北西—南东向,除了发育冲积扇、扇三角洲、盐湖以外,还发育砾漠和沙漠等沉积相。四川盆地主要发育了两种沉积模式,分别为冲积扇—河流—湖泊和冲积扇—扇三角洲—盐湖—河流。四川盆地白垩纪构造层序、岩相古地理的演化到构造运动的控制。

The Cretaceous System in the Sichuan Basin includes 2 tectonic sequences,each of which can be further divided by the maximum flood surface into a sedimentary sequence representing basin expansion period and one representing basin contraction period.Using sedimentary sequences as mapping units,we constructed four Cretaceous litho-paleogeographic maps of the Sichuan Basin,and discussed the characteristics of Cretaceous paleogeography and basin evolution of the Sichuan Basin.Our analysis shows that during the Early Cretaceous（TS1 period） sedimentation occurred along the Longmenshan Mountain in the direction of NE-SW,and was dominated by alluvial fan,alluvial plain,and lacustrine facies.During the Late Cretaceous（TS2 period）,due to third episode of the Yanshan orogeny,the distribution of sedimentary pattern was changed to follow a NW-SE diretion,and sedimentation was dominated by alluvial fan and salt lake,gravel desert and desert facies.The two main depositional systems during the Cretaceous Period were alluvial fan-fluvial-lacustrine system and alluvial fan-fan delta-salt lake-river system.The development and distribution of Cretaceous tectonic sequences and litho-paleogeography of the Sichuan Basin were controlled by tectonic activities.