CORRELATION OF CRETACEOUS-PALEOGENE ("KT") BOUNDARY SECTIONS, NORTHERN BELIZE

During the Chicxulub impact (or "KT" boundary) event, direct ejecta covered part of the Yucatan peninsula, including Belize. In northern Belize, these ejecta consisted of vapor plume deposits with accretionary lapilli and debris-flow deposits that formed as the ejecta curtain collapsed. These ejecta deposits are preserved today in fault-bounded graben fills that crop out at several places in northern Belize. At Albion Island, Belize (~ 400 km from impact), about 15 m of direct ejecta crops out at a local quarry. The stratigraphy of this deposit, from base upward, is 1 meter of clay (resting on the eroded surface of the Maastrichtian Barton Creek formation) that has a minor component of carbonate spherules (formerly accretionary lapilli?), which is followed upward by 14 m or more of impact breccia (carbonate clasts with a wide range of sizes within a fine clay, pulverized carbonate, and glass-fragment matrix). The glass (vesicular, irregular fragments) in the matrix is now largely altered to green clay. At Armenia, Belize (~ 450 km from impact), about 10 m of direct ejecta and related KT boundary deposits crop out on a main highway. These deposits include a boulder-bearing paleosol (atop the Barton Creek formation), a vapor plume deposit with accretionary lapilli and irregular, vesicular glass fragments, and a polished pebble bed. It is likely that the vapor plume deposits at Armenia is the lateral equivalent of the impact breccia layer at Albion Island. The polished pebble bed is likely a secondary (reworked) deposit of ballistically emplaced pebbles that washed from the land surface into the low-lying area of the small graben basin at Armenia. A similar pebble deposit, over 10 m thick, occurs at a site that is east of Albion Island and north of Armenia. This site, called Progresso Lagoon, is an important location for preservation of the ballistically emplaced pebbles because their preservation at this site is much better than others in the area (especially regarding their surface textures, which included polish, pits, and striations).