Keller, G., W. Stinnesbeck, T. Adatte, B. Holland, D. Stüben, M. Harting, C.d. Leon, and J.d. Cruz. (2003) 2003. “Spherule Deposits in Cretaceous-Tertiary Boundary Sediments in Belize and Guatemala”. Journal of the Geological Society 160 (5): 783-95. doi:10.1144/0016-764902-119.