STRATIGRAPHY, AGE, NATURE AND ORIGIN OF THE KT BRECCIA FROM NORTH AMERICA TO ARGENTINA

The stratigraphy and age of breccia containing Chicxulub impact glass spherules is documented in late Maastrichtian-early Danian sequences from Texas (USA), northern and southern Mexico, Belize, Guatemala and Haiti. Reworked Chicxulub impact glass spherules are known from all sequences spanning from the latest Maastrichtian to early Danian. The oldest and original ejecta layer is found in the uppermost Maastrichtian of Texas (Brazos), NE Mexico (Loma Cerca, El Penon) and the Chicxulub crater core Yaxcopoil-1. The geochemistry of glass from this layer is identical in all sections and consistent with Chicxulub impact ejecta documented from reworked spherule layers. The K/T boundary, Ir anomaly and mass extinction are stratigraphically well above the oldest ejecta layers, as well as most reworked layers. No Ir anomaly occurs at or near the original Chicxulub spherule ejecta layer. The original spherule ejecta layer was deposited during normal marine sedimentation in the upper Maastrichtian (base of CF1 Zone), ~300'000 prior to the K/T boundary. All younger ejecta layers represent repeated episodes of reworking of the original layer during a sea-level regression and are part of siliciclastic deposition in submarine canyons via mass flows and turbidites (NE Mexico), or incised valleys in shallow environments (e.g. Brazos, Texas, La Popa Basin NE Mexico). The widespread thick microspherule and spheroid deposits in southern Mexico, Belize Guatemala and Haiti are interbedded with breccia, microbreccias and conglomerates resulting from the erosion of shallow carbonate platform sediments. The presence of Maastrichtian and early Danian planktic foraminifera in the matrix of the breccia, as well as within spherule clasts, indicate that redeposition occurred during the early Danian P. eugubina zone. In Brazil (Poty) and Argentina (Neuquen), early Danian (Pla, Plc) microfossils mark the breccias as early Danian age. No evidence of impact origin was detected (e.g., Ir, impact glass spherules, or trace element geochemistry).