(1)
Sawin, R. S.; West, R. R.; Franseen, E. K.; Watney, W. L.; McCauley, J. R. Carboniferous–Permian Boundary in Kansas, Midcontinent, U.S.A. CRES 2006, No. 252, 1-13. https://doi.org/10.17161/cres.v0i252.11838.