04/11/2016 – Colóquio - “Cretaceous-Paleogene mass extinction: Asteroid impact, volcanism or both?” Alcides Nóbrega Sial (UFPE)

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Título:

"Cretaceous-Paleogene mass extinction: Asteroid impact, volcanism or both?"

 

Coloquialista:

Alcides Nóbrega Sial (UFPE)

 

Resumo:

We focus here on the bolide impact versus volcanism debate concerning the mass extinction in the Cretaceous‒Paleogene boundary (K–Pg). While the iridium content in the K-Pg layer and He isotopes in fullerenes are regarded as proxies for the Chicxulub asteroid impact, we investigated the use of Hg as a proxy for volcanism straddling this boundary, using distal and proximal sections in relation to the Deccan volcanic center. Notable Hg/TOC spikes have been observed in the studied sections: (a) spike I: in the Meghalaya (India), Gubbio (Italy) and Højerup (Denmark) sections within the CF2 planktic foraminiferal biozone, (b) spike II: large Hg/TOC at the K–Pg boundary in these same sections and (c) spike III: within the P1a planktic foraminiferal subzone in these three and Jhilmili (India) sections. These three Hg/TOC spikes probably resulted from distinct volcanic episodes of Deccan trap main stage (phase-2) and represent true Hg loading to the environment (spike I is probably related to the Poladpur eruptive pulse and spike III, to the Ambenalli one). Besides volcanism, scavenging of Hg by anoxia on seafloor may have contributed Hg to the generation of spike II as stratigraphic record of Mo/Al redox proxy exhibits negative shift in the K‒Pg boundary in most studied sections, suggesting decrease in oxygenation. The Chixulub impact may have triggered the enormous Poladpur, Ambenalli and Mahabaleshwai (Wai Subgroup) lava flows of the Deccan trap main stage. δ202Hgplotted against Δ201Hg values for most of the analyzed samples lie within the box for volcanic emission and some within the box for volcanic emission/chondrite Hg. Most samples show small positive Δ201Hg, in favor of long-term atmospheric transport prior to deposition, supporting volcanic origin for the Hg. This reinforces the potential use of Hg as stratigraphic marker and confirmation of Hg loading to the environment by Deccan phase-2 in three distinct episodes.

 

Data, horário e local:

04 de Novembro de 2016, 16h

Auditório do Departamento de Física – CCEN – UFPE