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The Role of the Siberian Traps in the Permian-Triassic Boundary Crisis: Analysis Through

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The Role of the Siberian Traps in the Permian-Triassic Boundary Crisis: Analysis Through The Role of the Siberian Traps in the Permian-Triassic Boundary Crisis: Analysis through Chemical Fingerprinting of Marine Sediments using Rare Earth Elements A thesis submitted to the Graduate School of the University of Cincinnati in partial fulfillment of the requirement for the degree of Master of Science By Alan Santistevan B.A. University of California, Berkeley December 2018 Committee Chair: T.A. Algeo, Ph.D. Department of Geology, University of Cincinnati, Cincinnati OH 45221-0013 USA 1 Abstract In this study, the question of microenvironmental change related to the overall eruption pattern from the Siberian Traps was examined. Using the unique rare earth element geochemistry that was produced from the successive eruptions, a geological trace that links the Siberian Traps to the environmental collapse from the effects of windblown ash was found in using over 400 marine sediment samples taken from 7 different Permian-Triassic Boundary sections. The following results show values likely indicative of material derived from the lower crust, upper mantle with the Eu/Eu* anomalies from Zal, a microcontinent in the Tethys Ocean, Gujo-Hachiman, an open ocean site in the eastern Panthalassic Ocean, along with Guryul Ravine and Spiti on the northwestern margin of Gondwana. These results represent a global signal, and could reflect a deleterious effect upon marine and terrestrial ecosystems from the possible volcanic ashfall that was produced from the Siberian Traps. 2 3 Table of Contents 1. Introduction 2. Background 2.1. The Permian paleoenvironment 2.2. The Permian-Triassic Boundary crisis 2.3. Potential causes of the Permian-Triassic Boundary crisis 2.4. Rare earth element geochemistry 3. Methods 4. Study Sections 4.1. Gujo Hachiman, Japan 4.2. Ubara, Japan 4.3. Black Ridge West, Greenland 4.4. Spiti, India 4.5. Guryul Ravine, India 4.6. Zal, Iran 4.7. Chaohu, China 5. Results 5.1. Gujo Hachiman, Japan 5.1.1. Al, TOC, and TIC values 5.1.2. REE ratios 5.1.3. Ce/Ce* and Eu/Eu* anomalies 5.2. Ubara, Japan 4 5.2.1. Al, TOC, and TIC values 5.2.2. REE ratios 5.2.3. Ce/Ce* and Eu/Eu* anomalies 5.3. Black Ridge West, Greenland 5.3.1. Al, TOC, and TIC values 5.3.2. REE ratios 5.3.3. Ce/Ce* and Eu/Eu* anomalies 5.4. Spiti, India 5.4.1. Al, TOC, and TIC values 5.4.2. REE ratios 5.4.3. Ce/Ce* and Eu/Eu* anomalies 5.5. Guryul Ravine, India 5.5.1. REE ratios 5.5.2. Ce/Ce* and Eu/Eu* anomalies 5.6. Zal, Iran 5.6.1. TOC, and TIC values 5.6.2. REE ratios 5.6.3. Ce/Ce* and Eu/Eu* anomalies 5.7. Chaohu, China 5.7.1. Al, TOC, and TIC values 5.7.2. REE ratios 5.7.3. Ce/Ce* and Eu/Eu* anomalies 5 6. Discussion 6.1. Significance of Eu/Eu* anomalies for understanding sediment provenance 6.2. Global Patterns of REE variation at the Permian-Triassic Boundary 6.3. Significance of wind blown material emanating from the Siberian Traps 7. Conclusions References Appendices 6 1. INTRODUCTION The Permian-Triassic boundary (PTB) 251.9 million years ago (Burgess et al. 2014) marked the most severe biological cataclysm in the history of life, with up to 95% of all marine species, and 70% of all terrestrial species going extinct (Benton 2005; Sabney and Benton 2008). It was also the only event in Earth’s history when both plants and insects suffered heavy extinction (Labandiera and Sepkowski 1993; Looy et al. 1999). It further took life a full 10 million years through a dynamic multi-step recovery phase to even begin returning the Earth to its pre-existing conditions from the bleak environment that was produced from the near annihilation (Chen and Benton 2012). Dating of the Siberian Traps, the largest aerial flood basalt eruptions of the last 500 million years, has shown that they were effectively coeval with the PTB mass extinction and the respective biozonation (Renne et al. 1995; Kamo et al. 2003, see Figure 1) and thus a potential cause of that event. Climatic effects related to volcanic eruptions have long been documented in relation to environmental disturbances (Rampino et al. 1985) but none to the extent as the Siberian Traps and the PTB Mass Extinction. Contemporary models of volcanic induced climate perturbations are calculated by the total mass of ash output and the height the eruption column rises in the atmosphere in relation to the volcanoes’ latitude, and by how efficiently atmospheric air currents disperse the aerosols worldwide (Courtillot 2002). The rate at which gases are emitted is also a dependent factor and it has been inferred that the gas output from the repeated eruptions (Black et al. 2011, Black et al. 2015) would have been enough to lead to the complete collapse of all normal interactions between the physical world and life (Bond and Wignall 2014). 7 The connections between the flood basalt gas eruptions and the extinction lies within the chemistry of the Cambrian and Ordovician crustal rocks that were laid down before. These Cambrian and Ordovician units contained what would become the greenhouse gases after the magmas extruded through and melted them, thereby mobilizing the gases to release into the atmosphere (Black et al. 2013). Ordovician age gypsum sediments that were melted through produced sulfur while Cambrian age coal deposits produced the carbon dioxide. Therefore, the consecutive link is the magma, the crustal rocks, and the changes within the atmospheric chemistry, which caused a global environmental change bringing about the extinction (Elkins- Tanton 2010, Black et al. 2015). Volcanic units are commonly characterized by unique rare earth element (REE) signatures (Wyman 1996) and published studies have shown that the Siberian Traps had an unusual REE chemistry (Lightfoot et al. 1990, 1993; Arndt et al. 1993, 1995, 1998; Federenko et al. 1997, 2000). With the unique signature that is produced from the REE chemistry, PTB sections from a wide global distribution were analyzed in order to determine the characteristic signature of the Siberian Traps in these successions, and thus, test the relationship between the eruptions of the Siberian Traps to the environmental deterioration of the PTB mass extinction. The signature of the volcanic ash fall provides information regarding the geographic distribution of the windblown ash and the relationship between the regional environmental change and its effects upon marine and terrestrial ecosystems. Furthermore, the importance of the project is that its results will allow Earth Scientists to calculate with a greater precision the rate at which regional environmental degradation happens and the specific effects it has on biological species systems. 8 Figure 1. Geologic Timescale of the Late Permian into the Early Triassic. Includes geomagnetic polarity and associated bio zones from the Late Permian-Early Triassic. Figure created from Time Scale Creator 2014 https://engineering.purdue.edu/Stratigraphy/tscreator/index/index.php 2. BACKGROUND 2.1. The Permian paleoenvironment The Permian was characterized by a major global climate shift, and the changes were witnessed within the compositional and dominance patterns, along with the biogeographical distribution of Permian flora. The Permian was ushered in during ice-house conditions followed by warming patterns that increased global temperatures, likely resulting from the build-up of atmospheric CO2 with interrupting periods of abrupt cooling (Saunders and Reichow 2009). Climate modeling suggests that atmospheric pCO2 rose from values similar to pre-industrial levels in the Early Permian to as much as 10x the pre-industrial levels by the End-Permian, a 9 time when glaciation was completely gone and the Siberian Traps began erupting (Kiehl and Shields 2005). The rise in CO2 is speculated to have resulted from the lack of continental land mass weathering from the absence of extensive mountain belts and increasing aridity (Kiehl and Shields 2005). The buildup of CO2 led to both atmospheric and ocean warming, contributing to the loss of Gondwana polar ice sheets, resulting in decreased latitudinal oceanic circulation and mixing (Kidder and Worsley 2004). In addition to a Permian atmosphere that was already beginning to be characterized by low oxygen conditions, increased oceanic stratification and the spread of oceanic stagnation exacerbated the issue (Kidder and Worsley 2004). Terrestrially, the Permian hosted a rich faunal and floral diversity and as time within the Permian progressed, (from the Early to Middle for example) the proportion of seed plants increased, which reduced the swamp dominant lycopsids and sphenosids (Ziegler 1990). Biome level biogeographical analyses have yielded seven distinct biomes within the Permian, the first being a cold temperate biome between a paleolatitude of 60o and 90o where the Siberian Traps were located (Willis and McElwain 2002). While in the area surrounding the Siberian Craton, the pervasive presence of abundant external water sources from the lagoons, swamps and shallow basins found by Czamanske et al. 1998 would have created intense water-magma interactions leading to phreatomagmatic eruptions (Jerram et al. 2015, Black et al. 2015), see Figure 7. The remaining six biomes include a cool temperate biome that projected relatively greater diversity than the higher colder temperate biome, where the palynological and paleosol data from the latest Permian indicated an abundance of deciduous forests within the higher latitudes (Taylor et al. 1992). The northern hemisphere was composed mainly of cordaites, 10 sphenopsids and ferns, while the southern hemisphere was marked by a high proportion of glossopterids and lycopsids (Willis and McElwain 2002). A warm temperate biome that occupied areas of Greenland, Scandinavia and North America was characterized in the northern hemisphere by a high diversity of cordaites, pteridosperms, gingkoales, sphenopsids and ferns, along with the presence of glossopterids in the south (Willis and McElwain 2002).
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