PB ISOTOPES IN VALANGINIAN WEISSERT EVENT SEDIMENTS AT ODP SITE 1149B LINKED TO LARGE-VOLUME SILICIC ERUPTIONS IN THE PARANá-ETENDEKA LARGE IGNEOUS PROVINCE

Volcanism from large igneous provinces is inferred to have had significant global environmental impact, but demonstrating synchronicity between the volcanism and sedimentary records of environmental change is not straightforward. The Valanginian Weissert event (Erba et al., 2004) has been linked to the effects of the Paraná-Etendeka volcanism, but this interval of the geological time scale is poorly calibrated. Several studies have used sediment Pb isotopes to fingerprint the timing of input of volcanic Pb from a particular large igneous province. For example, sediments spanning the Weissert event at ODP Site 1149B require input of radiogenic Pb that Chavagnac et al. (2008) attributed to degassing of aerosols from the Paraná-Etendeka flood basalts.

A re-evaluation of Pb isotope data on Paraná-Etendeka lavas shows that, if the radiogenic Pb in the ODP Site 1149B sediments is linked to the Paraná-Etendeka volcanism, then it is uniquely associated with the large-volume silicic eruptions rather than the effusive basaltic lavas. Another possibility is continental-derived Pb, but sediment trace element data show limited input of aeolian dust (Chavagnac et al., 2008), and Pb released by enhanced continental weathering would not be expected to be transported efficiently to the deep oceans given its short residence time. This strengthens the case for a temporal link between the Paraná-Etendeka volcanism and the Weissert event. Although basaltic magmatism dominates the province, there is no evidence for Pb associated with basalt eruptions in the Site 1149B sediments on the other side of the globe, suggesting that eruption columns produced by the basaltic eruptions did not reach the stratosphere. Whether this is a general feature of flood basalt eruptions could be tested by measuring Pb isotopes in well-dated globally-dispersed sedimentary sequences that are contemporaneous with other major basaltic provinces. The arid environment and lack of hydromagmatic deposits might have limited the explosiveness of basaltic eruptions in the case of the Paraná-Etendeka province, and here the widespread global dispersal of Pb is apparently linked to the ability of large-volume (>1,000 km³) silicic eruptions to loft aerosols into the upper stratosphere.

References:

Erba et al. (2004), Geology, 32, 149-152.

Chavagnac et al. (2008), JGR, 113, B06201.