@misc{indiciaec8e182e5bbba,
  title = {Controls on porphyrin concentrations of Pennsylvanian organic-rich shales, Western U.S.A.},
  author = {J.L. Clayton and G.E. Michael},
  year = {2002},
  doi = {10.1021/ef00024a004},
  url = {https://pubs.usgs.gov/publication/70015877},
  note = {Source identifier: 70015877}
}