Anatomy of a Half Graben, Northwestern China Wan Yang, Geology Dept., Wichita State University Fluvial-lacustrine sediment fill in rift basins are important petroleum source and reservoir rocks. Our investigation revealed the complex events and controlling processes of sedimentation in a half-graben ~260 million years ago. Fluvial & eolian deposits The sequence of events, from bottom/old to top/young, in the field photo include: Shallow lake carbonate deposition; Lake withdrawal & erosion, forming Unconformity 1; River peneplanation and deposits; Landscape stabilization and soil formation under arid climate over a long period of Unconformity 2; Renewed river and loess deposition under a dry and windy climate. Unconformity 2 Ancient calcareous soil Fluvial sandstone Unconformity 1 Lacustrine limestone