1. Tonsteins: altered volcanic-ash layers in coal-bearing sequences;Bohor;Geol. Soc. Am., Spec. Pap.,1993
2. Permian–Triassic boundary clay in China is volcanic, not impact ejecta (abst.);Bohor,1989
3. Synsedimentary volcanic ash-derived illitic tonsteins in Late Permian coal-bearing formations of southwestern China;Burger;Int. J. Coal Geol.,1990
4. Petrography and geochemistry of tonsteins from the 4th member of the Upper Triassic Xujiahe Formation in southern Sichuan Province, China;Burger;Coal Geol. Explor.,2000
5. Geochemistry of Trace Elements;Chen,1982