Representational Bias in Phytoliths from Modern Soils of Central North America: Implications for Paleovegetation Reconstructions

Thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology or Earth and Environmental Sciences, Department of Earth and Environmental SciencesUnderstanding localized patterns and community compositions of vegetation in an environment is critical to the reconstruction of climatic and ecological conditions across all spatiotemporal scales. One of the most accurate and useful ways to characterize vegetation, and therefore to describe the climatic and ecological conditions of a location, is through the plant fossil record. Phytoliths (plant silica microfossils) are often preserved in the absence of other paleobotanical data and are becoming more widely used for deep-time vegetation reconstructions. Significant work has been done to standardize the analytical methodology of phytolith extraction, statistical analysis, and interpretation, but more detailed investigations are needed to understand how well a given phytolith assemblage represents the aboveground plant biomass for a given ecosystem. We present results from paired soil phytolith assemblages and local vegetation assemblages across the central United States, from temperate forest, grassland, and rangeland/scrubland ecosystems. Phytolith assemblages from soil A-horizons were compared to percent cover of species and plant biomass estimates obtained via field observations and aerial estimates of tree cover to analyze differences in the relative abundance of forest or woody vegetation versus grasses. Soil phytolith assemblages from all sites average a 32% bias toward the grass morphotypes as compared to actual aboveground biomass observations, and comparisons to percent cover yielded broadly comparable bias figures. Percent bias estimates do not show significant correlations to most environmental factors (temperature, precipitation, local elevation), however, an extremely strong correlation (p< 0.001) was observed with soil order type. As a result, we suggest further research into the development of correction factors between phytolith sample assemblages and their inferred past counterpart ecosystems based on estimates derived from modern analyses of each major soil order type. Such corrections are essential to the continued use of phytoliths as a proxy for past vegetation and ecological reconstructions throughout the Phanerozoic record.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98093/1/Hyland_Ethan_MS_2012.pdf1

Rise of the Colorado Plateau: A Synthesis of Paleoelevation Constraints From the Region and a Path Forward Using Temperature-Based Elevation Proxies

The Colorado Plateau’s complex landscape has motivated over a century of debate, key to which is understanding the timing and processes of surface uplift of the greater Colorado Plateau region, and its interactions with erosion, drainage reorganization, and landscape evolution. Here, we evaluate what is known about the surface uplift history from prior paleoelevation estimates from the region by synthesizing and evaluating estimates 1) in context inferred from geologic, geomorphic, and thermochronologic constraints, and 2) in light of recent isotopic and paleobotanical proxy method advancements. Altogether, existing data and estimates suggest that half-modern surface elevations were attained by the end of the Laramide orogeny (∼40 Ma), and near-modern surface elevations by the mid-Miocene (∼16 Ma). However, our analysis of paleoelevation proxy methods highlights the need to improve proxy estimates from carbonate and floral archives including the ∼6–16 Ma Bidahochi and ∼34 Ma Florissant Formations and explore understudied (with respect to paleoelevation) Laramide basin deposits to fill knowledge gaps. We argue that there are opportunities to leverage recent advancements in temperature-based paleoaltimetry to refine the surface uplift history; for instance, via systematic comparison of clumped isotope and paleobotanical thermometry methods applied to lacustrine carbonates that span the region in both space and time, and by use of paleoclimate model mediated lapse rates in paleoelevation reconstruction

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M&gt;70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0&lt;e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Did increasing seasonality and fire frequency cause the c4 grassland transition in South America (SA)? Investigations from two paleosol sites in NW Argentina using δ13c isotopes, molecular biomarkers, phytoliths, and X-ray fluorescence (XRF)

Recent advances in molecular biomarkers along with traditional bulk δ13C isotopic analysis, phytolith assemblages, and XRF analysis allow for the detailed reconstruction of continental paleoecological and paleoclimatic conditions. We use these methods to reconstruct conditions during the expansion of C4 grasses, considered one of the most important biological events during the Cenozoic. We hypothesize that in SA, the spread of C4 grasses was driven by the intensification of the SA Summer Monsoon and that this increase in C4 vegetation caused an intensification of fire regimes, due to both seasonality fire and fireC4 expansion feedbacks, that has long been suspected but poorly documented and never studied in this context in SA. This study presents resultsfrom welldated paleosols from two sites in N.W. Argentina: La Viña (LV) and Palo Pintado (PP) in the Salta Province. The LV site includes the Jesus Maria Formations, Guanaco and Piquete (~15 4Ma), while the PP site includes the Palo Pintado Formation (~7.5 6 Ma). Previous studies have interpreted these sites as foreland basin sediments deposited in a meandering stream tolacustrine environment. Shifts in the δ13C obtained from bulk organic matter and phytolith assemblages in these paleosols are used to identify vegetation transitions from C3dominatedgrasslands and forests, to C4dominated grasslands. Leaf wax biomarkers include higher order nalkanes (C20 to C36), and are used to independently determine vegetation composition and changes to aridity and seasonality. XRF analysis is carried out to determine the chemical index of alteration in paleosols, which is a comparable proxy for precipitation seasonality. Polycyclic aromatic hydrocarbons (PAH) are used to determine fire regimes, in order to verify whether C4 expansion promoted fires. δ13C analysis of LV reveals a steady change from a C3dominatedecosystem at 15 Ma to a C3C4 intermediary ecosystem by 7.5 Ma. The PP site does not show any directional change in vegetation type during the investigated period between 7.2 Ma to 6 Ma, though δ13C values indicate a mixed C3C4 ecosystem throughout this period. However, results from the PP site show that increasing C4 cover, determined from bulk organic matter δ13C, is positively correlated with an increased fire frequency, determined from increasing PAH concentrations. Ultimately, these data contribute to constraining the causes of C4 expansion in NW Argentina, including the most important climatic controls and feedbacks from fire regimes, in continental SA.Fil: Ghosh, Adit. California State University; Estados UnidosFil: Cotton, Jennifer M.. California State University; Estados UnidosFil: Hyland, Ethan G.. North Carolina State University; Estados UnidosFil: Hauswirth, Scott C.. California State University; Estados UnidosFil: Raigemborn, María Sol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Tineo, David. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaThe Geological Society of America Connects 2021PasadenaEstados UnidosGeological Society of Americ

Timing of the Greenhorn Transgression and OAE2 in Central Utah Using CA-TIMS U-Pb Zircon Dating

Contextualizing subbasinal influences on accommodation and pace of the rapid landscape evolution during the base-level rise of the Upper Cretaceous (upper Cenomanian–lower Turonian) Greenhorn Cycle within the Western Interior of North America requires refined stratigraphic controls of key sediment successions. Herein, a blended analysis of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), chemical abrasion thermal ionization mass spectrometry (CA-TIMS), and δ13C isotopic data is utilized to identify two regionally significant ash-fall marker beds southeast of the Wasatch Plateau, specifically the TT1 and TT4, which bracket the Cenomanian–Turonian boundary and the Greenhorn Cycle transgression in the Western Interior Seaway (WIS). Based on our analysis of the recovered ash-fall zircons, a meaningful depositional age (DA) for the TT1 is 94.616 Ma ± 0.027 and 94.010 Ma ± 0.017 for the TT4 bentonite of the Tununk Shale. When coupled with the pre-existing biostratigraphic framework, correlation potential greatly increases with the (TT1) Naturita falling within the Sciponoceras gracile Assemblage Zone. Common molluscs associated with this biozone within the southern and central regions of Utah include Inoceramus pictus, Euomphaloceras spp., and Pycnodonte newberryi. The (TT4) Tununk within the upper portion of the Watinoceras coloradoense Assemblage Zone is commonly associated with the following mollusc genus within the areas to the south and north of the study area: Mytiloides and Morrowites. Furthermore, these dates constrain the Cenomanian–Turonian boundary, provide accurate chronostratigraphic markers for intra and interbasinal correlation and serve to strengthen global linkages to Ocean Anoxic Event 2 (OAE2) during the Greenhorn Cycle transgression

Age, depositional history, and paleoclimatic setting of Early Cretaceous dinosaur assemblages from the Sao Khua Formation (Khorat Group), Thailand

We describe the sedimentology, geochronology, and geochemistry of the Early Cretaceus Sao Khua Formation of the Khorat Basin, northeastern Thailand, and report a temporal range adjustment for its dinosaurian assemblage. Facies analysis and architectural studies reveal that sedimentation occurred within a floodplain setting fed by large meandering bedload-rich channels. Interfluve areas comprised freshwater lakes and emergent areas subject to pedogenic modification. Multiple paleosol types are identified and geochemistry is indicative of a stable humid subtropical climate regime. Based on radiometric dating of detrital zircons (via LA-ICP-MS), we interpret that the middle part of the Sao Khua Formation was deposited no later than 133.8 (+/- 1.8) Ma (late Valanginian), and grain ages collected from the overlying lowermost Phu Phan Fm constrain sedimentation of the upper part of the Sao Khua Formation to no earlier than 132.4 (+/- 2.0) Ma (early Hauterivian). In consideration of the Early Cretaceous regional tectonic framework, we interpret that youthful igneous zircon grains are derived from the adjacent South China-Vietnam South Borneo Volcanic Arc. We establish that the entombed dinosaur biota (including members of the Ornithomimosauria, Spinosauridae, Megaraptora, and Somphospondylia) is ~5-9 million years older than previously recognized and that these records are among the oldest known globally for these clades. Constraining the age of the Sao Khua Formation indicates that the shift from sauropod-dominated, ornithischian depauperate ecosystems of the Sao Khua Formation to iguanodontian-rich ecosystems of the Khok Kruat Formation occurred sometime between the early Hauterivian and Aptian on the Khorat Plateau

InterCarb: A Community Effort to Improve Interlaboratory Standardization of the Carbonate Clumped Isotope Thermometer Using Carbonate Standards

International audienceIncreased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth-system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I-CDES) values for Intercarb-Carbon Dioxide Equilibrium Scale

Toward a Cenozoic history of atmospheric CO2

The geological record encodes the relationship between climate and atmospheric carbon dioxide (CO2) over long and short timescales, as well as potential drivers of evolutionary transitions. However, reconstructing CO2 beyond direct measurements requires the use of paleoproxies and herein lies the challenge, as proxies differ in their assumptions, degree of understanding, and even reconstructed values. In this study, we critically evaluated, categorized, and integrated available proxies to create a high-fidelity and transparently constructed atmospheric CO2 record spanning the past 66 million years. This newly constructed record provides clearer evidence for higher Earth system sensitivity in the past and for the role of CO2 thresholds in biological and cryosphere evolution