Early Indosinian movement character in the LowerMiddle Yangtze
region from gypsumsalt characters in LowerMiddle Triassic
Hu Guangming1 Zhang Yajin2 Zhou Yan3
1.School of Geoscience|Yangtze University|Jingzhou|Hubei 434023； |2.Daqing Oilfield Exploration and Development Research Institute|Daqing|Helongjiang 163712； |3.Petroleum Exploration and Development Institute of SINOPEC|Beijing 100083
The gypsumsalt deposition is the sedimentary response to early Indosinian movement. The author analyses the characters of early Indosinian movement from origin of gypsumsalt，the gypsumsalt vertical layer difference in Lower and Middle Yangtze region，the gypsumsalt characters in thickness and attitude，the distribution of sediment center and subsidence center. Shelf and platform(carbonatite)，lagoontidal flat(dolomite and gypsumsalt)and coast(clastic rock)appear one by one，which indicates largescale regressive from the tectonic uplift of early Indosinian movement. During the tectonic uplifting，the rudimental sea water in LowerMiddle Yangtze region is being evaporated to form gypsumsalt layers by the hot dry climate. And the gypsumsalt layers in Middle Yangtze are lower than that ones in Lower Yangtze. So，the author deduces that the collision between Middle Yangtze and Huabei Block was earlier than that between Lower Yangtze and Huabei Block. The current tectonic framework comes from the middle Indosinian movement and early Yanshan movement. But the thick gypsumsalt layers that are mainly dolomitegypsum interbed，gypsum containing dolomite，dolomitic gypsum and so on，are distributing in current depression，and the thin gypsumsalt layers that are mainly pseudocrystals of gypsum，gypsum dolomite，dolomite containing gypsum and so on，are distributing in transition zone between current depression and uplift. And the gypsumsalt thickness and attitude is relating to the deep of water and topography. In addition，the stratum contour maps show that the gypsumsalt mainly distributes at the subsidence center. All those plane characters of gypsumsalt show that the topography during gypsumsalt depositing is in line with the current tectonic framework，and that slight fold deformation(no angular uncomformity or lostrecord)occurred during gypsumsalt depositing.