Adatte, T., G. Keller, S. Burns, K. Stoykova, M. Ivanov, D. Vangelov, Utz Kramar, and Doris Stüben. 2002. “Paleoenvironment across the Cretaceous-Tertiary Transition in Eastern Bulgaria”. In Catastrophic Events and Mass Extinctions: Impacts and Beyond: Boulder, Colorado. Boulder: Geological Society of America Special Paper 356.