SINGLE K/PG IMPACT AT CHICXULUB: NEW EVIDENCE FROM THE GULF OF MEXICO BASIN FLOOR

A massive, previously unreported K/Pg boundary deposit has been identified in the basinal Gulf of Mexico in 15 industry wells with penetrated thicknesses ranging from 10 m (bathyal) to 200 m (basinal). Microfossils found within the deposit are predominantly lower Maastrichtian to upper Campanian in age with rare uppermost Maastrichtian species, including Micula prinsii, and sparse Coniacian to Aptian species, consistent with the Cretaceous / Tertiary "cocktail" assemblage associated with the Chicxulub impact deposit in Gulf of Mexico and Caribbean DSDP cores. The basinal deposit is a relatively uniform micrite with an overall fining upwards character, similar to the tsunami-derived "homogenites" of the Mediterranean and the K/Pg boundary Penalver and Cacarajicara formations of Cuba. Seismically, the deposit is found throughout the basin floor, typified by a concordant, parallel couplet of high-amplitude reflectors with little interior character, which is also typical of the Mediterranean “homogenites”. It thickens to over 1000 m in paleo-lows, while on paleo-highs it is relatively thin and often truncates older horizons. An unconformity is found at the base of the deposit at all locations, removing the Maastrichtian and Upper Campanian in the basin, and down to as old as the Jurassic on the paleo-slope, suggesting substantial slope instability induced by earthquakes and tsunami waves produced by the Chicxulub impact. This basinal deposit is interpreted to represent locally-derived mass transport deposits overlain by a single, thick, graded bed produced by the settling of pelagic components resuspended into the water column. This new evidence indicates a single K/Pg boundary impact that caused unprecedented devastation to the Gulf of Mexico, and does not support assertions that the Chicxulub impact preceded the K/Pg boundary, that the impact had little effect outside of the direct vicinity of the crater on the Yucatan Platform, or that there were multiple impacts.