Sequence stratigraphy of the Late Triassic strata in the Guangyuan region, Sichuan

The exposure sections of the Upper Triassic Xiaotangzi and Xujiahe Formations sedimentary strata in the Guangyuan region, Sichuan are examined in detail with the aid of theory and method of sequence stratigraphy. Two second-order and six third-order sequences have been distinguished. Each of the third-order sequences is age-dated with an average time duration of about 2.9 Ma. The sedimentary facies of the Upper Triassic sedimentary strata in the study area consist of littoral facies, delta facies, facies, braided stream facies, alluvial fan facies. The Triassic strata are considered to be the responses to the formation and evolution of the foreland basins on the Indosinian western Yangtze platform and thrusting of the Longmen mountain area. The Late Triassic sequence stratigraphic framework and four isochronous boundaries are constructed on the basis of the unconformity and other sequence boundaries in combination with the spatio-temporal arrangement of the filling sequences, sedimentary facies and sedimentary systems tracts.