Keller, Gerta, Wolfgang Stinnesbeck, Thierry Adatte, Norman MacLeod, and Donald Lowe. 1994. Field Guide to Cretaceous-Tertiary Boundary Sections in Northeastern Mexico. LPI Contribution No 827. Houston: Lunar and Planetary Institute. Referenced from www.researchgate.net: Field guide to Cretaceous-tertiary boundary sections in northeastern Mexico.