Further Discussion on Water-transgression Delta: Genesis of great thickness large distributed sandstone of Xujiahe Formation in Sichuan Basin

Key words: 
• water-transgression cause filling sand-bodies /
• underwater distributary channel /
• water-transgression delta

Abstract: According to the "water-transgression caused filling sand-bodies" found in Yangtze delta investigation in 1980s, based on the other investigation data and ancient sand-body features, the "water-transgression delta model" has been established. More than 30 years, more and more data have been showen that the model is correct. The modern deposition investigations and satellite pictures from Yangtze delta, Erhai in Yunnan, Daihai in Inner Mongolia et al., have revealed the recent popular model of "underwater distributary channel" is absent, but according to sedimentary theory (such as the cycle stratigraphy and sequence stratigraphy) analysis, the water-transgression deposition is widely developed. The flume simulation experiment has also confirmed that delta is developed in transgression period, so water-transgression sand-body micro-facies should have replaced the underwater distributary channel micro-facies. Great thickness and largely distributed sandstone in member 2 and member 4 of Xujiahe Formation have been caused by the superimposition of multi-channel river mouth progradation (mouth sand bar), retrogradation (water-transgression channel sand-body),channel lateral migration and piecing together with multi-deltas. Water-transgression deltas have formed in transgression period of lake or sea level, and the tectonism, climate changing, particular geological events, topography and depositional rate and so on. could have caused the up and down of water level, and the water-transgression delta has been developed when the water level have went up.