Published:March 06, 2020
Over the past 30 years, considerable research efforts have been directed toward understanding the context and nature of environmental changes that occurred immediately prior to, at, and after the five major Phanerozoic mass extinctions. Earth’s volcanic activity linked to large igneous provinces (LIPS) has been the leading scenario explaining the pattern in four of the five major Phanerozoic mass extinctions, with an asteroid impact ruling the fifth. Today, new revelations about Deccan LIP volcanism also take center stage for the fifth, calling for reinterpretation of the cause of this mass extinction. The major triggering mechanisms for these catastrophes appear to be continental flood basalt volcanism and silicic magmatism, which also appear to have ended Neoproterozoic glaciations.
This volume focuses on new developments for identifying global proxies of environmental change, including rates and tempo of volcanic eruptions and their expressions in marine and terrestrial sediments globally, rapid and extreme climate changes, ocean acidification, and ecosystem responses to these catastrophes.
This is the second GSA Special Paper devoted to this broad topic concentrating on the role of LIP volcanism in mass extinctions, the first being published in 2014: Volcanism, Impacts, and Mass Extinctions: Causes and Effects (Keller and Kerr, 2004). Following a topical session organized at the 2016 Geological Society of America Annual Meeting, this present volume includes nine papers that assess the state of research into the causes of mass extinction events and decipher the respective roles of volcanism, bolide impacts, sea-level fluctuations, and associated climate and environmental changes in major episodes of species extinction.
In Chapter 1, Grzegorz Racki reviews historical hypotheses and latest discussions on the link between volcanism and extinctions. Notwithstanding the particularity of each major biodiversity crisis in the Phanerozoic, he suggests that volcanic cataclysm is thought to be the key to their explanation within a variety of time scales and forms of feedback in the context of the press-pulse model. The volcanism ecosystem interactions are specific to each igneous province and numerical simulations must be assessed on a case-by-case basis. In order to understand the extinction risk related to particular volcanic and/or impact events, all vulnerability agents, especially target/host substratum features controlling calamitous thermogenic degassing, should be taken into account for future macroevolutionary analyses.
In Chapter 2, Nasrrddine Youbi and others review the link between the Central Iapetus magmatic province and the ca. 580 Ma Gaskiers glaciation. Based on an impressive and seemingly complete outline of the literature, they summarize the known chronology of the Gaskiers glaciation and volcanic rocks of the Central Iapetus magmatic province, and suggest that this volcanism caused both the beginning and end of the glaciation at ca. 581–579 Ma.
Next, Henrik H. Svensen and others explore the venting structures formed by the interaction of igneous intrusions with sedimentary basins, using hydrothermal breccia pipes formed in the Karoo Basin of South Africa during emplacement of igneous sills in the Karoo LIP. They conclude that the pipes formed following sill emplacement and pressure increase in the organic-rich shale, and were followed by rapid carbon degassing, which emphasized their important role in the Early Jurassic climate change and oceanic anoxic event.
In Chapter 4, Guillaume Charbonnier and others demonstrate the presence of a global Hg peak at the onset of the Weissert episode and suggest that the Paraná-Etendeka LIP activity was the origin of the major environmental change observed at the early-late Valanginian transition.
In Chapter 5, Brahimsamba Bomou and others review the Guerrero-Morelos carbonate platform response to the Caribbean-Colombian Cretaceous LIP during the Cenomanian–Turonian oceanic anoxic event (OAE) 2. They demonstrate the persistence of oligotrophic to mesotrophic conditions throughout the OAE 2 on the Central Mexico carbonate platform despite the proximity to the Caribbean-Colombian oceanic plateau. They also show that the correlation with the pelagic environment of the Eastbourne section (UK) reveals a synchronicity of biotic responses between basin and platform environments. Low oxygen conditions are marked by multiple blooms of Heterohelix species in the basin, corresponding to an assemblage dominated by ?Decastronema, Thaumatoporella, and Istriloculina on the carbonate platforms.
Next, in Chapter 6, Diethard Sanders and others explore the rarely observed shallow-water carbonate platform in Austria across the Cretaceous-Paleogene (K/P) boundary, and compare it with similar platform sequences from Croatia, Oman, Madagascar, Tunisia, Belize, and Guatemala. They observed surprisingly similar deposition and erosion patterns in near-shore siliciclastic environments of southern Tunisia, Texas, and Argentina across the K/P boundary transition correlative with sea-level falls and repeated subaerial exposure forming hardgrounds. Correlation with deep-sea depositional patterns reveals coeval but shorter intervals of erosion. This reveals a uniform response to the K/P boundary transition linked to climate and sea-level changes, whether in shallow nearshore or deep-sea environments, with climate change tied to Deccan volcanism in magnetochrons C29r-C29n.
In Chapter 7, Sucharita Pal and others present a high-resolution organo-molecular study in the marine Um-Sohryngkew river K/P boundary succession of Meghalaya, India. They interpret that the dominance of high-molecular-weight aromatic hydrocarbon markers suggests regional fire induced by the heat supplied by Deccan volcanism across the K/P boundary transition. They conclude that regional wildfire played a significant role in affecting ecosystem deterioration.
In the penultimate chapter, Eric Font and others investigate rock magnetic susceptibility and mineralogy of bole beds from the Deccan magmatic province, India. They observed the increase in the magnetic signal is mainly due to increasing phyllosilicate and goethite, whereas magnetite and hematite remain constant. They attribute the variation in the magnetic mineral assemblage to contrasting humid and dry environments during weathering, leading to the preferential formation of goethite or hematite, respectively. Their analyses suggest a single weathering profile led to soil formation in two studied red boles, with few or no contribution by an external source.
In Chapter 9, Guillaume Le Hir and others investigate how abiotic factors (temperature, pH, and calcite saturation state) act on various marine organisms to determine primary productivity and biodiversity changes in response to drastic environmental changes. Their model results show that the combination of Deccan volcanism with a 10-km-diameter impact would lead to global warming (3.5 °C) caused by rising carbon dioxide (CO2) concentration (+470 ppmv), interrupted by a succession of short-term cooling events due to the formation of sulfate aerosols. Resulting consequences include decreased surface ocean pH by 0.2 (from 8.0 to 7.8), and deep ocean pH by 0.4 (from 7.8 to 7.4), which would lead to decreased biomass of calcifying species and their biodiversity by ~80%, while noncalcifying species reduced by ~60%. These results may explain the severity of the extinction among pelagic calcifying species.
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Mass Extinctions, Volcanism, and Impacts: New Developments
This volume covers new developments and research on mass extinctions, volcanism, and impacts, ranging from the ancient Central Iapetus magmatic province linked with the Gaskiers glaciation to thermogenic degassing in large igneous provinces, the global mercury enrichment in Valanginian sediments, and the Guerrero-Morelos carbonate platform response to the Caribbean-Colombian Cretaceous large igneous province. This section is followed by a series of end-Cretaceous studies, including the implications for the Cretaceous-Paleogene boundary event in shallow platform environments and correlation to the deep sea; the role of wildfires linked to Deccan volcanism on ecosystems from the Indian subcontinent; rock magnetic and mineralogical study of Deccan red boles; and factors leading to the collapse of producers during Deccan Traps eruptions and the Chicxulub impact.