Sedimentary Filling Characteristics Within Tectonic Sequence Of Coupling Between The Western Sichuan Foreland Basin And Longmenshan Orogenisc Belt From Late Triassic To Jurassic

Guided by sedimentology, sequence stratigraphy, paleobiology, geochemistry, geophysics and so on, Integrated researhed the outcrops, cores ,logging data ,seismic data and geochemistry data from the late Triassic to Jurassic in the western Sichuan foreland Basin, realized the charaters of depositional system, sequence stratigraphy, depositional charaters within Tectonic Sequence, discussion the realationship between the western Sichuan foreland basin and Longmenshan orogenisc belt from late Triassic to Jurassic. The main achievements as follow were obtained:1.According to the petrofabric, depositional fabric , sedimentary sequence, life assemblage and so on, combined with predecessor's research, 3 sedimentary system groups and 8 sedimentary system were recognized. Continental sedimentary system group contain alluvial fan sedimentary system, fluvial sedimentary system and lake sedimentary system; transition sedimentary system group contain delta sedimentary system and gulf sedimentary system; marine sedimentary system group contain beach sedimentary system and mixed shelf sedimentary system.2.According to the outcrops and cores ,combined with logging data and seismic figures ,7sequence typical surfaces were found,which were surface of unconformity, surface of ancient karst, surface of erosion, surface of weather crust, surface of onlap,transition surface of rock character and facies and flooding transgressive surface. And then 6 tectonic sequence and 14 sedimentary sequence were recognized,the characters of eace tectonic sequence and sedimentary sequence detailed researched, and the elements which controled or impacted the development of tectonic sequence and sedimentary sequence were discussed at the same time.3.sedimentary-filling graphs within tectonic sequence system tract from late Triassic to Jurassic built up, found that:①From late Triassic to Jurassic, the environment of western Sichuan foreland basin was difference ,at the beginning ,the setting was marine, then changed to transition ,finally changed to continental environment, and the key stage was Anxian tectonic movement. ②The tectonic movement of Longmenshan orogenisc belt was eposide, the movement of each part of Longmenshan orogenisc belt was different form late Triassic to Jurassic, and the adjacent area's setting was different too.So the sedimentary models built up in different place or at the different time was difference.③During the Ma'antang Stage(TS1BE), tectonic movement of Longmenshan orogenisc belt was weak and entire underwater ,mixed shelf is the mainly setting of the western Sichuan foreland baisn and sponge reefs found in the Anxian district. During the Xiaotangzi Stage(TS1BW), the north part of Longmenshan orogenisc belt uplifted firstly and marine delta found in the corresponding place of western Sichuan foreland basin.During the stage of TS2BE, tectonic movement of the north part of Longmenshan orogenisc belt rivived , which led sedimentary structures with rapid filling characters forming in the north-west part of western Sichuan foreland basin, and tectonic movement of the middle part and the south part of Longmenshan orogenisc belt remainly quiet. In this situation ,form west to east, marine delta to coastal-shallow sea setting formed in the north-west Sichuan foreland baisn ,and coastal-shallow sea to marine delta setting formed in the other place. During the stage of TS2BW, the south part of Longmenshan orogenisc belt uplifted ,too. The fragmentary material stripped form the south part and the north part of Longmenshan orogenisc belt were transported into the western Sichuan foreland basin. During this time ,tectonic movement of the middle part of Longmenshan orogenisc belt was not obvious, the environment of western Sichuan foreland basin remain transition.When the time come to the end of TS2BW and the begin of TS3BE, the middle part of Longmenshan orogenisc belt uplifted ,and the sea water dismiss form the western Sichuan foreland basin.After that, fluvial delta and lake were the mainly setting of western Sichuan foreland basin.④During the stage of Jurassic,the tectonic movement mainly occurred at the stage of basin expansion(BE) ,and the stage of basin withdrawal(BW) is quiet. So we could find alluvial fan sedimentary system in the stage of BE and delta fan sedimentary system in the stage of BW.⑤The RST system tract occurred during the stage of tectonic movement happened, which lead to alluvial fan sedimentary system, PST system tract occurred during the stage of tectonic movement quiet , and mainly developed delta fan sedimentary system , alluvial fan sedimentary system hardly found.