@misc{indiciaeb5244ec3187b,
  title = {A modern vs. Permian black shale - the hydrography, primary productivity, and water-column chemistry of deposition},
  author = {D.Z. Piper and R.B. Perkins},
  year = {2004},
  doi = {10.1016/j.chemgeo.2003.12.006},
  url = {https://pubs.usgs.gov/publication/70027040},
  note = {Source identifier: 70027040}
}