The Research Of Sedimentary System And Sequence Stratigraphy Of Yangchang Formation (Triassic) In The South Of Ordos Basin

On the tectonic evolvement, the south of ordos basin inherited the whole basin characteristic that pale-tectonical movements resembled in the early-middle Trias period and the Permain period. Late Triassic-Middle Jurassic epoch, Indosinian movement tethys plate moved to northward or north-northeast. Under the right lateral shear force, Jingchuan area of the west of basin appeared a north-northeast doming, but Tongchuan - huangling area appeared a north-south depression. The circumstance was half-humidity weather when Yangchang formation began to sediment. The sediment of south Ordos basin was formed in this regional geological background.In the south of Ordos basin, the thickness of Yangchang formation changed from 400m to 1400m, which generally had appeared that the western was thin but the eastern was chick, and that the northern was thin but the southern was chick. However, the partition and contrast of Yanchang formation followed and searched 5 pieces of primary markers and one pieces of assistant marker where the Yangchang formation distributing was more steady in research area, and the stratum could be divided into ten pieces of member following the principles that firstly contrasting the bag segments, then contrasting the small segments, being controlled by cycle and consulting the thickness, etc.The hypsography was low and plain in the south of Ordos basin when Yangchang formation began to deposit. The process of sediment come through three processes that was plain-river environment in the early lake basin development era, lake environment in the metaphase era and the delta and the flood plain-river plain environment in the late era. The main was river and delta facies environment sediment. In the middle and east district where the depression was bag and the environment was deep lake that frequently broke out turbidity current. This thesis identified the upper Triassic be composed mainly by alluvial fan, river, lake and delta sedimentary system, and farther distinguished those sedimentary system, then divided carefully them into 14 types sediment subfacies and 24 types sediment microfacies. After carefully researched the subfacies like deep lake turbidity current and delta sediment, those modes had been put forward.Based on using the borderline between the delta plain and the delta front facies, and analyzing Kaolinite content that was enriched in bank zone to confirm the situation of lake strandline, had carefully confirmed the ichnographic lake strandline distributing and sedimentary facies zone in different period.In the south of Ordos, the basin heavy mineral association mainly was divided into two types.The southwest and the northeast provenance was the important provenance district that had good inheriting characters and affected for a long time. But in Huachi, Heshui and Guchengchuan, the heavy mineral association was various and changed extraordinarily great, and in a long time, there obviously was a commixing belt that had been synthetically affected by all other various provenances. The upper Triassic in Fuxian area, the geochemistry characters and the distributing mode of REE curve was consistented with the Archaean and the early Proterozoicmetamorphic rock. But in Zhenjing area, the REE distributing mode of REE curve also resembled the metamorphic rock in the northeast of Ordos area, which indicated that the Ordos area was a unitive basement in the Archaean and the early Proterozoic era. The only difference was the process of the tectonic evolvement of the southwest and the northeast part of Ordos area. Accordingly, these proved all their provenances inherited the characters of the original mother roch, then discussed the provenance evolvement.Based on utilizing the stratum touching relations, the characters of facies cycle, the abrupt interface of facies, the regional characteristic interface (the maximum lake flooding surface), and the river channels sand's overlapping fashion and the regional good contrasting markers, the sequence interfaces had been identified after researching the...