Large-scale sill emplacement in Brazil as a trigger for the end-Triassic crisis

Thea H Heimdal,Sara Callegaro,Jahandar Ramezani,René Rodrigues,Henrik H Svensen,Egberto Pereira,Karthik Iyer,Morgan T Jones

doi:10.1038/s41598-017-18629-8

Abstract

The end-Triassic is characterized by one of the largest mass extinctions in the Phanerozoic, coinciding with major carbon cycle perturbations and global warming. It has been suggested that the environmental crisis is linked to widespread sill intrusions during magmatism associated with the Central Atlantic Magmatic Province (CAMP). Sub-volcanic sills are abundant in two of the largest onshore sedimentary basins in Brazil, the Amazonas and Solimões basins, where they comprise up to 20% of the stratigraphy. These basins contain extensive deposits of carbonate and evaporite, in addition to organic-rich shales and major hydrocarbon reservoirs. Here we show that large scale volatile generation followed sill emplacement in these lithologies. Thermal modeling demonstrates that contact metamorphism in the two basins could have generated 88,000 Gt CO2. In order to constrain the timing of gas generation, zircon from two sills has been dated by the U-Pb CA-ID-TIMS method, resulting in 206Pb/238U dates of 201.477 ± 0.062 Ma and 201.470 ± 0.089 Ma. Our findings demonstrate synchronicity between the intrusive phase and the end-Triassic mass extinction, and provide a quantified degassing scenario for one of the most dramatic time periods in the history of Earth.

Highlights

A recent study[15] used high precision U-Pb geochronology to demonstrate that the sub-volcanic phase of Central Atlantic Magmatic Province (CAMP) started 150 ± 38 ky before the oldest basalt flows, and showed that the emplacement of igneous intrusions in Brazil, Spain and Bolivia occurred synchronously with the ETE (201.564 ± 0.015 Ma11)
Basin cross-sections show that CAMP sills in Brazil are widespread in the upper Paleozoic section, extending continuously from the western margin of the Solimões Basin to the eastern margin of the Amazonas Basin (Fig. 1b)
In the Solimões Basin, sills are only present in the upper Paleozoic series, in the Amazonas Basin sills are present in lower Paleozoic sedimentary rocks in the eastern part of the basin (Fig. 1b)

Summary

Introduction

A recent study[15] used high precision U-Pb geochronology to demonstrate that the sub-volcanic phase of CAMP started 150 ± 38 ky before the oldest basalt flows, and showed that the emplacement of igneous intrusions in Brazil, Spain and Bolivia occurred synchronously with the ETE (201.564 ± 0.015 Ma11). This is significant as a large portion of the CAMP is preserved as sills[16], which are widespread in northern Brazil[17,18,19,20,21,22]. The maximum cumulative sill thicknesses are present in the central parts of both basins, with 1038 m in the central Solimões Basin and 915 m in the central Amazonas Basin[20], decreasing towards the margins (Fig. 1a)

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Conclusion