Abstract:

An integration of high resolution sequence stratigraphic and sequence biostratigraphic analysis ofwell logs allows the recognition of a distinctive sequence biostratigraphic unit from theNeogene Shangyoushashan Formation of the wellXiandong-1and the wellXiandong-8in western Qaidam Basin，NW China.The unit is distinguished from the Xiayoushashan Formation in the samewell of the same area and is used as a boundarymarker.Two comparable sequence biostratigraphic units are also recognized from the lowerPaleogene Xiaganchaigou Formation in the Hongliuquan Yuejin area of the basin.Sequence biostratigraphic correlations show that the top boundary of the remarkable“red bed”in the lowerXiaganchaigou Formation gets younger eastwards，indicating an eastward lake expansion following fluctuations of base-level cycle.In theWunan area of the basin，a sequence biostratigraphic framework is constructed under the constraint of characteristic fossils by integrating sequence biostratigraphic unitswith seism ic stratigraphy，providing standards for regional stratigraphic division and correlations in southwestern Qaidam Basin.Accordingly，the integration of biostratigraphy，seism ic stratigraphy and highˉresolution sequence stratigraphy is a powerful approach in sequence biostratigraphic study and establishing regional isochronous stratigraphic frameworks.

Key words: UpperYoushashan Formation, Lower Youshashan Formation, Lower Ganchaigou Formation, base-level cycle, sequence biostratigraphic unit, Qaidam Basin