The Cretaceous–Tertiary (K/T) boundary transition at Coxquihui, state of Veracruz, Mexico: evidence for an early Danian impact event?

The Cretaceous–Tertiary (K/T) transition at Coxquihui, State of Veracruz, Mexico, differs from all other Mexican sections by the presence of two spherule-rich layers interbedded with pelagic marls, but lacking the characteristic siliciclastic deposit. A 1-cm-thick spherule layer is located at or near the K/T boundary and contains a small Ir enrichment of 0.2 ng/g (background values <0.1 ng/g). The precise stratigraphic position of this spherule layer with respect to the K/T boundary is uncertain due to a hiatus that spans from to the lower Parvularugoglobigerina eugubina Zone (Pla) to the upper part of the latest Maastrichtian Plummerita hantkeninoides Zone. A 20-cm-thick marl layer separates the first spherule layer from a 60-cm-thick second spherule layer, which is also within Zone Pla. An Ir enrichment of 0.5 ng/g is present in the overlying 10-cm-thick marl layer. The stratigraphic positions of these two spherule layers and Ir enrichments are strikingly similar to those found at two other localities, Beloc in Haiti and Caribe in Guatemala, and suggest the possibility of an early Danian impact event.