Abstract:

According to the theory and approach of the sequence stratigraphy, we have investigated the meandering river delta outcrops of the Upper Triassic Yanchang Formation along the eastern margin of Ordos Basin, and identified LST, TST, and HST. Four types of distributary channel depositional systems, including sheetlike subsurface distributary channel, meandering channel and braided channel, which built delta sand body framework, have been identified from the Chang 7 Member to Chang 4+5 Member in Yanchang Formation. Sequence stratigraphic framework and sand body architecture have been illustrated; furthermore, stratigraphic architecture and delta sandbody framework model and sandbody framework related to the relative lacustrine level change have been established. The study demonstrated that the sandbody architecture should have evolved regularly in response to relative lacustrine level change in Ordos Basin; the sand body may have eroded in early LST, and amalgamated channelfilled sandbody was  expected in late LST; isolated channelfilled sandbody occurred in TST; during early HST sand body was absent, and sheetlike sand body took place during late HST.

Key words: sequence stratigraphic framework, sandbody architecture, relative lacustrine level change, Yanchang Formation, meandering river delta, Ordos Basin