Limestone breccia deposits in southern Mexico, Guatemala and Belize have recently been interpreted as proximal to distal ballistic fallout deposits, generated by a bolide impact that struck Yucatan at K/T boundary time. We review the age, lithology and the depositional environment of Þve K/T boundary sections in the South Pete«n area of Guatemala (Caribe, Aserradero, Chisec, Actela, Chemal) in order to evaluate the nature and origin of K/T limestone breccia deposition. The sections are located 500 km south of the proposed impact site at Chicxulub and trend in an eastÐwest direction from the Guatemala/Mexico border to southern Belize. In four of the Þve sections examined, a breccia unit up to 50 m thick overlies reef-bearing shallow-water limestones of late Cretaceous (Campanian-Maastrichtian) age. Rhythmically bedded limestones, marls and siltstones of early Danian age overlie the breccia and were deposited under middle-to outer-neritic conditions. The breccia consists of di¤erently coloured layers of shallow-water limestones. Clast size generally decreases upsection to thin layers of predominantly rounded clasts, and these Þnegrained rudstones grade into grainstones at the top. In at least one section (EI Caribe) diagenetically altered glass spherules are present in the uppermost layers of the grainstone. These glass spherules are of strati- W. Stinnesbeck ( ) Geologisches Institut der Universita¬ t Karlsruhe, Postfach 6980, D-76128 Karlsruhe, Germany Fax:#0721 608 2138 G. Keller Department of Geosciences, Princeton University, Princeton, NJ 08544, USA J. de la Cruz á Carlos de Leo«n Ministerio de Energõ«a y Minas, Direccio«n de Hidrocarburos, Diagonal 17, 29Ð78, Zona 11, Guatemala 01011, Guatemala N. MacLeod á J. E. Whittaker Department of Paleontology, The Natural History Museum, Cromwell Road, London SW7 5BD, UK graphic position and chemical composition similar to black and yellow glass from Beloc, Haiti and Mimbral, Mexico, which some workers have chemically linked to melt glass within the breccia of the Chicxulub cores. We suggest that breccia deposition in Guatemala may have been multi-event, over an extended time period, and related to the collision of the Yucatan and Chortis plates as well as related to a major impact or volcanic event at the end of the Cretaceous.  PDF