Two LIPs and two Earth-system crises: the impact of the North Atlantic Igneous Province and the Siberian Traps on the Earth-surface carbon cycle

Andrew D Saunders

doi:10.1017/s0016756815000175

Abstract

AbstractThe links between the Siberian Traps and the end-Permian mass extinction, and between the North Atlantic igneous province (NAIP) and the Paleocene–Eocene thermal maximum (PETM), demonstrate a critical role for large igneous provinces (LIPs) in the disruption of the Earth-surface carbon cycle (ESCC). High-precision ages for both volcanic provinces and the associated environmental crises show that, in both cases, the crisis was contemporaneous with the volcanism. The NAIP comprises two phases: the earlier Phase 1 (c. 61 Ma) and the much more voluminous Phase 2 (c. 56 Ma), linked to the opening of the NE Atlantic. The latter triggered the PETM, the largest Cenozoic hyperthermal. The Siberian Traps are significantly more voluminous than the NAIP, and triggered the end-Permian mass extinction. The masses of volcanic CO2emitted from these provinces may have been much greater than previously suggested as substantial gas may come from intrusive bodies deep within the crust. Precursory warming due to the accumulation of volcanic CO2in the atmosphere likely triggered the release of low-δ13C methane hydrate, although the masses of methane hydrate alone may have been insufficient to account for the observed temperature rises. The organic C was likely strongly supplemented by magmatically derived carbon and thermogenic carbon released during emplacement of sills and dykes into C-rich sedimentary units. More data are required on the volcanic flux rates in order to refine the cause–effect relationships between LIPs and the ESCC.

Highlights

The causes of mass extinctions have been debated for over two centuries
There is a growing consensus that mass extinctions are a consequence of catastrophic and rapid changes in the Earth-Surface Carbon Cycle (ESCC). These changes cannot be explained by processes that operate on a geologically long time scale, so attention has turned to more dramatic triggers such as meteorite or comet impacts, flood basalts eruptions, and extra-solar events such as gamma-ray bursts (Thomas et al, 2005)
The Palaeocene-Eocene Thermal Maximum (PETM) is a rapid-onset, short-duration, hyperthermal event with pronounced negative oxygen and carbon isotope isotopic excursions (OIE and CIE) (Kennett & Stott, 1991); a decrease in carbonate productivity associated with shallowing of the carbonate compensation depth and an increase in ocean surface acidification (Zachos et al, 2005; Penman et al, 2014); a major extinction of benthic foraminfera (Thomas, 1989; Thomas & Shackleton, 1996); marine anoxia and/or dysoxia (Dickson, Cohen & Coe, 2012; Dickson et al, 2014) and a major perturbation of global weathering patterns (Ravizza et al, 2001; Wieczorek et al, 2013)

Summary

Introduction

The causes of mass extinctions have been debated for over two centuries. They have been reviewed in innumerable papers and books, including those authored by the honorand of this volume (e.g., Hallam & Wignall, 1997; Hallam, 2005). The PETM is a rapid-onset, short-duration, hyperthermal event with pronounced negative oxygen and carbon isotope isotopic excursions (OIE and CIE) (Kennett & Stott, 1991); a decrease in carbonate productivity associated with shallowing of the carbonate compensation depth and an increase in ocean surface acidification (Zachos et al, 2005; Penman et al, 2014); a major extinction of benthic foraminfera (Thomas, 1989; Thomas & Shackleton, 1996); marine anoxia and/or dysoxia (Dickson, Cohen & Coe, 2012; Dickson et al, 2014) and a major perturbation of global weathering patterns (Ravizza et al, 2001; Wieczorek et al, 2013) It is one of the most studied of the Cenozoic hyperthermals (see, for example, the review by Cohen, Coe & Kemp, 2007), with over 40 high-resolution deep-sea core sets from ocean drilling, abundant terrestrial sections, and good calibration through astronomical cyclicity (Westerhold, Roehl & Laskar, 2012). A detailed review of the dating of the Siberian Traps is given by Ivanov et al (2013) who conclude that the magmatism may have persisted well into the Triassic

Findings

Discussion

Concluding Observations