@misc{indiciae5d511582e12a,
  title = {Permian chronostratigraphic subdivisions},
  author = {Jin Yugan and Bruce R. Wardlaw and Brian F. Glenister and Galina V. Kotlyar},
  year = {1997},
  url = {https://pubs.usgs.gov/publication/70073403},
  note = {Source identifier: 70073403}
}