Impact did not trigger Deccan volcanism: evidence from Anjar K/T boundary intertrappean sediments

Abstract

Many hypotheses including asteroidal and cometary impacts, Deccan volcanism, impact induced volcanism and coincidental impact and volcanism have been put forth to explain the observed enhancement of iridium and mass extinction at the K/T boundary (KTB). The identification of KTB layer within the Deccan intertrappean sediments at Anjar, about half way between Flow III and Flow IV provides new constraints on some of these hypotheses. The chemical characteristics of this layer show high concentrations of Ir, Os and other siderophiles accompanied by enrichment of chalcophiles and depletion of lithophiles. The Os/Ir ^~1.1, close to the meteoritic value and other chemical and stratigraphic criteria indicate that it may be the ejecta fallout layer, resulting from a bolide impact at the KTB. Presence of three basalt flows below this layer implies that the volcanism was already active when this layer was deposited and impact of the K/T bolide did not trigger Deccan volcanism.