DISCOVERY OF A PRISTINE CHICXULUB IMPACT GLASS SPHERULE DEPOSIT ON GORGONILLA ISLAND, COLOMBIA, IN THE EASTERN PACIFIC OCEAN
The Gorgonilla spherule layer is approximately 2 cm thick and consists of extraordinarily well-preserved glass spherules up to 1.1 mm in diameter. The size, morphology and chemical composition of these spherules are similar to Chicxulub spherule ejecta from US, Mexico, North and Central America, and the Caribbean, but differ in their unrivaled excellent preservation. About 70-90 % of the spherules are unaltered or only partly altered consisting of colorless or faintly green to yellow glass, and their chemical composition is consistent with other occurrences, e.g. Beloc glasses. The normal size-gradation, presence of delicate spherule textures including welded components quenched from melt, and near absence of bioturbation or traction transport indicate that the basal portion of the Gorgonilla spherule layer represents a nearly unaltered primary air-fall ejecta deposit, not affected by significant reworking.
Age control based on planktic foraminifera indicate a diverse latest Maastrichtian Plummerita hantkeninoides zone CF1 assemblage below the glass spherule layer and an early Danian Parvularugoglobigerina eugubina zone P1a(2) assemblage above including Parasubbotina pseudobulloides and Subbotina triloculinoides, which evolved in the uppermost part of C29r. Maastrichtian planktic foraminifera are present in the spherule layer and clasts with earliest Danian species are present above it marking erosion. These data indicate that spherule deposition could have occurred anytime between the latest Maastrichtian zone CF1 and the early Danian P1a(2), an interval spanning about 200 ky across the K/Pg.