Study on Sedimentary Facies of Jialingjiang Formation of Early Triassic at Changyuanba Structure

Changyuanba structure belt in Southern Sichuan area was carbonate platform at Jialingjiang period of Lowe Triassic, open-platforms, localized mesa and evaporation-mesa were well developed. The first and third Jialingjiang periods are the open-platform developing periods, and the second and the fourth Jialingjiang period are localization-mesa and evaporation-mesa developing periods. Lime-mud or lime-lagoon microfacies are widely developed from the first Jialingjiang Group to the first subsegment of the second Jialingjiang Formation. Localized lagoon microfacies with gypsum pool/ plateau and dolomite pool/ plateau in east of the belt along the structure axis and limestone at both sides are developed at the second and third subsegments of the second Jialingjiang Formation from the third subsegment of the third Jialingjiang Formation to the first subsegment of the fourth Jialingjiang Formation , the range of granule beach is reduced but the dolomite lagune is obviously extended. From the second to fourth subsegments of the fourth Jialingjiang Formation, the gypsum evaporation lagoon in southern part and dolomite lagoon in the northern part are developed.