@misc{indiciae83337bc16ad5,
  title = {Sturgis Formation (Upper Pennsylvanian), a new map unit in the western Kentucky coal field},
  author = {Thomas M. Kehn},
  year = {1973},
  doi = {10.3133/b1394b},
  url = {https://pubs.usgs.gov/publication/b1394B},
  note = {Source identifier: b1394B}
}