The stratigraphy and age of altered impact glass (microtektites,
microkrystites) ejecta layers from the Chicxulub crater are documented
in Late Maastrichtian and Early Danian sediments in Mexico, Guatemala,
Belize and Haiti. In northeastern Mexico, two to four ejecta layers are
present in zone CF1, which spans the last 300 ky of the Maastrichtian.
The oldest ejecta layer is dated at 65.27 +/- 0.03 Ma based on sediment
accumulation rates and extrapolated magnetostratigraphy. All younger
ejecta layers from the Maastrichtian and Early Danian
Parvularugoglobigerina eugubina zone Pla(1) may represent repeated
episodes of reworking of the oldest layer at times of sea level changes
and tectonic activity. The K/T boundary impact event (65.0 Ma) is not
well represented in this area due to widespread erosion. An Early Danian
Pla(1) Ir anomaly is present in five localities (Bochil, Actela,
Coxquihui, Trinitaria and Haiti) and is tentatively identified as a
third impact event at about 64.9 Ma. A multiimpact scenario is most
consistent with the impact ejecta evidence. The first impact is
associated with major Deccan volcanism and likely contributed to the
rapid global warming of 3-4 degreesC in intermediate waters between 65.4
and 65.2 Ma, decrease in primary productivity and onset of terminal
decline in planktic foraminiferal populations. The K/T boundary impact
marks a major drop in primary productivity and the extinction of all
tropical and subtropical species. The Early Danian impact may have
contributed to the delayed recovery in productivity and evolutionary
diversity. (C) 2003 Elsevier Science B.V. All rights reserved.