Cretaceous-Paleogene Boundary Clays from Spainand New Zealand: Arsenic Anomalies

Abstract

Remarkably high arsenic (As) contents havebeen reported in numerous Cretaceous-Paleogene boundary(KPB) clays worldwide including those from Spain (atCaravaca and Agost) and New (N.) Zealand (at WoodsideCreek). Two interpretations have been offered to explainthis anomaly. The first one suggests that this As was generatedby the combustion of fossil fuels (such as crude oil,coal or oil shales) near the Chicxulub impact site and thesecond interpretation proposes the post-impact combustionof the global biomass at the KPB. Both types of combustionwere presumably triggered by the Chicxulub impactor.This report shows that the estimated surface densitiesof As in Spain and N. Zealand strongly contradict thefossil fuel hydrocarbons/biomass hypotheses. In addition,we also show that previously reported global abundancesof As at KPB are greatly overestimated.The high abundances of iron (Fe) in the ejecta layers fromSpain and N. Zealand lead us to a working hypothesis thata major fraction of their anomalous As was adsorbed fromseawater by the Fe-oxides. These oxides were mainly derivedof Fe from the vaporized carbonaceous chondrite impactor.These were originally deposited on the local (topographicallyhigh) oxic soils in Spain and N. Zealand andthen laterally transported to the KPB sites by the impactinducedsurface waters.

Keywords

• cretaceous-paleogene boundary
• arsenic
• fossilfuel
• crude oil
• wildfire
• iron oxide