The Drill Ancan1 is the only ultra deep Drill in the Hefei basin, Southern margin of the North China Plate. To confirm the preMesozoic strata under the Hefei basin is very useful for the study of tectonics and oil—gas prospecting. Reliable fossils to determine stratigraphic time have not been found in drill samples. Based on the geotectonic, geophysic and geochemical data, and the correlation of lithological natures, thicknesses, geophysic and geochemical indicators, writers consider that the dark colored claystone in Drill Ancan1, below the exposure level of Indosinian movement, is similar to the Neoproterozoic Qingbaikouan System, rather than the Permo—Carboniferous.