Mercury spikes suggest volcanic driver of the Ordovician-Silurian mass extinction
Qing GongXiangdong WangLaishi ZhaoStephen E. GrasbyZhong‐Qiang ChenLei ZhangYang LiLing CaoZhihong Li
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Abstract The second largest Phanerozoic mass extinction occurred at the Ordovician-Silurian (O-S) boundary. However, unlike the other major mass extinction events, the driver for the O-S extinction remains uncertain. The abundance of mercury (Hg) and total organic carbon (TOC) of Ordovician and early Silurian marine sediments were analyzed from four sections (Huanghuachang, Chenjiahe, Wangjiawan and Dingjiapo) in the Yichang area, South China, as a test for evidence of massive volcanism associated with the O-S event. Our results indicate the Hg concentrations generally vary in parallel with TOC, and that the Hg/TOC ratios remain low and steady state through the Early and Middle Ordovician. However, Hg concentrations and the Hg/TOC ratio increased rapidly in the Late Katian, and have a second peak during the Late Hirnantian (Late Ordovician) that was temporally coincident with two main pulses of mass extinction. Hg isotope data display little to no variation associated with the Hg spikes during the extinction intervals, indicating that the observed Hg spikes are from a volcanic source. These results suggest intense volcanism occurred during the Late Ordovician, and as in other Phanerozoic extinctions, likely played an important role in the O-S event.Keywords:
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The modern loss of species diversity has been labelled the 'sixth extinction' subsequent to the five major mass extinctions widely recognised in the Phanerozoic geologic record – the end-Ordovician (443.8 Ma), the Late Devonian (372.2 Ma), end-Permian (251.9 Ma), end-Triassic (201.4 Ma) and end-Cretaceous (66 Ma) events. Rankings in terms of numbers of genera suffering extinction, and especially in terms of ecological impact, however, put the end-Guadalupian (end-Capitanian) (259.8 Ma) extinction event in the same category with the other major mass extinctions. Thus, there were apparently six major Phanerozoic mass extinctions, and the current loss of species should perhaps be called the 'seventh extinction'.
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The recognition in 1980 of a signature of an extraterrestrial impact at the Cretaceous-Tertiary boundary and its apparent involvement with the mass extinction generated considerable enthusiasm for impacts at other mass extinctions. Numerous claims of impact evidence for the Permo-Triassic mass extinction (251.6 Ma), the largest of the Phanerozoic mass extinctions, have generally been rejected, found wanting, or been difficult to reproduce. Despite this lack of repeatable support, considerable available evidence is consistent with an impact, including the rapidity of extinction, coincident carbon shift, and evident correlation between terrestrial and marine extinctions. However attractive the hypothesis, the coincidence with the Siberian flood basalts and the complex nature of the carbon shift are in conflict with an impact. The most intriguing possibility is that the greatest mass extinction of the Phanerozoic left signals very similar to the end-Cretaceous mass extinction but was produced by entirely Earth-bound processes. If true, this would tell us far more about the nature of ecosystems and how they fail than would identification of another impact.
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O6 - 04 REGIONAL GEOPHYSICS & GEOTECTONICS CRUSTAL STRUCTURE AND PHANEROZOIC (PRE-BLACK SEA OPENING) OROGENIC PROCESSES ON AND NEAR THE SOUTHERN MARGIN OF BALTICA: A EUROPROBE OVERVIEW Randell Stephenson Netherlands Research Centre for Integrated Solid Earth Sciences Vrije Universiteit Faculty of Earth and Life Sciences De Boelelaan 1085 1081 HV Amsterdam The Netherlands Randell Stephenson works at the Vrije Universiteit Amsterdam attached to the Netherlands Research Centre for Integrated Solid Earth Sciences (ISES). His main area of interest in the last decade has been the geology and tectonic history of south-eastern Europe in particular the sedimentary basins overlying the southern
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Abstract The second largest Phanerozoic mass extinction occurred at the Ordovician-Silurian (O-S) boundary. However, unlike the other major mass extinction events, the driver for the O-S extinction remains uncertain. The abundance of mercury (Hg) and total organic carbon (TOC) of Ordovician and early Silurian marine sediments were analyzed from four sections (Huanghuachang, Chenjiahe, Wangjiawan and Dingjiapo) in the Yichang area, South China, as a test for evidence of massive volcanism associated with the O-S event. Our results indicate the Hg concentrations generally vary in parallel with TOC, and that the Hg/TOC ratios remain low and steady state through the Early and Middle Ordovician. However, Hg concentrations and the Hg/TOC ratio increased rapidly in the Late Katian, and have a second peak during the Late Hirnantian (Late Ordovician) that was temporally coincident with two main pulses of mass extinction. Hg isotope data display little to no variation associated with the Hg spikes during the extinction intervals, indicating that the observed Hg spikes are from a volcanic source. These results suggest intense volcanism occurred during the Late Ordovician, and as in other Phanerozoic extinctions, likely played an important role in the O-S event.
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Significance The end of the Triassic Period (∼201.5 million years ago) witnessed one of the largest mass extinctions of animal life known from Earth history. This extinction is suggested to have coincided with and been caused by one of the largest known episodes of volcanic activity in Earth’s history. This study examines mercury concentrations of sediments from around the world that record this extinction. Mercury is emitted in gaseous form during volcanism, and subsequently deposited in sediments. We find numerous pulsed elevations of mercury concentrations in end-Triassic sediments. These peaks show that the mass extinction coincided with large-scale, episodic, volcanism. Such episodic volcanism likely perturbed the global environment over a long period of time and strongly delayed ecological recovery.
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Recent analyses of Sepkoski's genus-level compendium show that only three events form a statistically separate class of high extinction intensities when only post-Early Ordovician intervals are considered, but geologists have called numerous events mass extinctions. Is this a conflict? A review of different methods of tabulating data from the Sepkoski database reveals 18 intervals during the Phanerozoic have peaks of both magnitude and rate of extinction that appear in each tabulating scheme. These intervals all fit Sepkoski's definition of mass extinction. However, they vary widely in timing and effect of extinction, demonstrating that mass extinctions are not a homogeneous group of events. No consensus has been reached on the kill mechanism for any marine mass extinction. In fact, adequate data on timing in ecologic, rather than geologic, time and on geographic and environmental distribution of extinction have not yet been systematically compiled for any extinction event.
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Abstract Climate change is a critical factor affecting biodiversity. However, the quantitative relationship between temperature change and extinction is unclear. Here, we analyze magnitudes and rates of temperature change and extinction rates of marine fossils through the past 450 million years (Myr). The results show that both the rate and magnitude of temperature change are significantly positively correlated with the extinction rate of marine animals. Major mass extinctions in the Phanerozoic can be linked to thresholds in climate change (warming or cooling) that equate to magnitudes >5.2 °C and rates >10 °C/Myr. The significant relationship between temperature change and extinction still exists when we exclude the five largest mass extinctions of the Phanerozoic. Our findings predict that a temperature increase of 5.2 °C above the pre-industrial level at present rates of increase would likely result in mass extinction comparable to that of the major Phanerozoic events, even without other, non-climatic anthropogenic impacts.
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The Kalkarindji continental flood basalt province of Northern Australia is the oldest basaltic LIP in the Phanerozoic having erupted in the mid-Cambrian. At this time, during the Cambrian Explosion, the global environment suffered a series of mass extinctions and biotic turnover. Kalkarindji had the potential to release 1.65 x 106 Tg of CO2, approximately 1.72% of the total Cambrian atmospheric carbon reservoir. It has therefore been implicated as a driver of the environmental changes in the Cambrian Series 2. However, temporal discrepancies between Kalkarindji eruptions and biotic turnover may prevent this LIP from being attributed as the sole cause of the Botomian-Toyonian Extinction, which wiped out up to 45% of all genera in the fossil record; while environmental factors such as sea-level change causing ocean anoxia are implicated in the Redlichiid-Olenellid Extinction. It is certainly possible that Kalkarindji could have played a part in forcing these environmental changes, but further advances in geochronology and sedimentary volcanic proxies are needed to confidently define a direct causational link between these events at the dawn of the Phanerozoic.
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