Evidence of wildfires and elevated atmospheric oxygen at the Frasnian−Famennian boundary in New York (USA): Implications for the Late Devonian mass extinction

The Devonian Period experienced significant fluctuations of atmospheric oxygen (O2) levels (∼25−13%), for which the extent and timing are debated. Also characteristic of the Devonian Period, at the Frasnian−Famennian (F−F) boundary, is one of the “big five” mass extinction events of the Phanerozoic. Fossilized charcoal (inertinite) provides a record of wildfire events, which in turn can provide insight into the evolution of terrestrial ecosystems and the atmospheric composition. Here, we report organic petrology, programmed pyrolysis analysis, major and trace element analyses, and initial osmium isotope (Osi) stratigraphy from five sections of Upper Devonian (F−F interval) from western New York, USA. These data are discussed to infer evidence of a wildfire event at the F−F boundary. Based on the evidence for a wildfire at the F−F boundary we also provide an estimate of atmospheric O2 levels of ∼23−25% at this interval, which is in agreement with the models that predict elevated pO2 levels during the Late Devonian. This, coupled with our Os isotope records, support the currently published Osi data that lacks any evidence for an extra-terrestrial impact or volcanic event at the F−F interval, and therefore to act as a trigger for the F−F mass extinction. The elevated O2 level at the F−F interval inferred from this study supports the hypothesis that pCO2 drawdown and associated climate cooling may have acted as a driving mechanism of the F−F mass extinction

A 50-year record of NOx and SO2 sources in precipitation in the Northern Rocky Mountains, USA

Ice-core samples from Upper Fremont Glacier (UFG), Wyoming, were used as proxy records for the chemical composition of atmospheric deposition. Results of analysis of the ice-core samples for stable isotopes of nitrogen (δ15N, ) and sulfur (δ34S, ), as well as and deposition rates from the late-1940s thru the early-1990s, were used to enhance and extend existing National Atmospheric Deposition Program/National Trends Network (NADP/NTN) data in western Wyoming. The most enriched δ34S value in the UFG ice-core samples coincided with snow deposited during the 1980 eruption of Mt. St. Helens, Washington. The remaining δ34S values were similar to the isotopic composition of coal from southern Wyoming. The δ15N values in ice-core samples representing a similar period of snow deposition were negative, ranging from -5.9 to -3.2 ‰ and all fall within the δ15N values expected from vehicle emissions. Ice-core nitrate and sulfate deposition data reflect the sharply increasing U.S. emissions data from 1950 to the mid-1970s

Using Hydrous Pyrolysis, Organic Petrography and Micro-Spectrometry to Understand Solid Bitumen and Kerogen Evolution in the Early Oil Window

This dissertation describes applications of hydrous pyrolysis, organic petrography and micro-spectrometry to understanding visual and chemical evolution of solid bitumen (a solid hydrocarbon) and kerogen (insoluble sedimentary organic matter) with thermal advance. The properties investigated occur from immature to early-mid oil window conditions of petroleum generation. The dissertation is divided into four chapters. The introductory chapter describes the general problem that is addressed by the dissertation research—mechanism and thermal regimes of kerogen conversion to petroleum. The second chapter describes and characterizes how thermal stress causes changes to the chemistry and visual appearance of Tasmanites, a marine alga. The third chapter uses the experimental method of hydrous pyrolysis to characterize the response of vitrinite and solid bitumen to thermal stress. The final chapter explores unanswered questions, discusses limitations, and presents some ideas for future research. Collectively, the results presented herein have application to better understanding of the conditions and processes of hydrocarbon generation in the early oil window and can be used to better predict the locations where the conditions of the early oil window can be expected in sedimentary basins

Petrologic and geochronologic evolution of the Grenville orogen, northern Blue Ridge Province, Virginia.

Basement rocks in the northern Virginia Blue Ridge include petrologically diverse granitoids and granitic gneisses that collectively record over 100 m.y. of Grenville orogenic history. New U-Pb sensitive high-resolution ion microprobe (SHRIMP) isotopic analyses of zircon indicate igneous crystallization ages of 1159 ± 14 Ma (high-silica charnockite), 1078 ± 9 Ma (leucogranite gneiss), 1060 ± 5 Ma (Old Rag magmatic series), and 1050 ± 8 Ma (low-silica charnockite). These ages, together with SHRIMP and thermal ionization mass spectrometry (TIMS) ages from previous studies, define three intervals of Grenville-age magmatic activity: Ca. 1160-1140 Ma (Magmatic Interval I), ca. 1112 Ma (Magmatic Interval II), and ca. 1080-1050 Ma (Magmatic Interval III). Field relations and ages of crosscutting igneous units indicate that a high-grade deformation event, likely associated with Ottawan orogenesis, occurred between 1078 and 1050 Ma. All rocks display tholeiitic affinity and trace-element concentrations indicative of derivation from heterogenous sources. The low-silica charnockite exhibits A-type geochemical affinity; however, all other meta-igneous rocks are compositionally transitional between A-types and fractionated I-types. Similar ages of magmatism in the Blue Ridge and Adirondacks indicate that meta-igneous rocks in both massifs define age clusters that both predate and postdate the main pulse of local Ottawan orogenesis. Late- to postorogenic A-type magmatism is represented by the 1050 Ma low-silica charnockite in the Blue Ridge and the 1060-1045 Ma Lyon Mountain granitic gneiss in the Adirondacks. Zircons from Blue Ridge granitoids emplaced during Magmatic Interval III preserve evidence of thermal effects associated with waning stages of Ottawan orogenesis at ca. 1020 Ma and 980 Ma

Mesoproterozoic magmatism and deformation in the northern Blue Ridge, Virginia and Maryland: Application of SHRIMP U-Pb geochronology and integrated field studies in the definition of Grenvillian tectonic history

Geologic mapping of Mesoproterozoic lithologies and foliations, and sensitive high-resolution ion microprobe (SHRIMP) U-Pb crystallization ages of 43 samples of orthogneisses and metagranitoids from the northern Blue Ridge establish new subdivisions: group 1 (1183-1144 Ma), group 2 (1143-1111 Ma), and group 3 (1078-1028 Ma). Protoliths of group 1 were metamorphosed at amphibolite- to granulite-facies conditions and strongly deformed between ca. 1153 and ca. 1144 Ma. Metagranitoids of groups 2 and 3 were emplaced continually for another 115 m.y. and display only local effects of diminishing deformation events. Ages of zircon overgrowths overlap temporally with igneous crystallization ages of group 3, but continued until ca. 960 Ma.The geochronologic sequence defined by rocks in the allochthonous Blue Ridge corresponds temporally with events documented elsewhere in eastern North America. Here, magmatism and the main deformation event occurred at the same time as the Shawinigan orogeny; magmatism with lesser deformation occurred at the same time as the Ottawan orogenic phase of the Grenvillian orogeny. The Neoproterozoic Robert son River batholith separates distinct orthogneisses and metagranitoids geographically. This plutonic body is interpreted to have intruded a Mesoproterozoic boundary that was reactivated during extension from 760 to 700 Ma. Despite the overprinting effects of Neoproterozoic extensional and Paleozoic contractional deformation events, which characteristically impart northeasterly trends to structural features, the majority of the group 1 rocks display prominent, high-grade foliations that trend to the northwest, reflecting the typical Mesoproterozoic tectonic grain observed in massifs from New Jersey to Vermont, as well as in the Adirondacks