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

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.