Matching Items (12)
Filtering by
- Genre: Doctoral Dissertation
Description
The present understanding of the formation and evolution of the earliest bodies in the Solar System is based in large part on geochemical and isotopic evidences contained within meteorites. The differentiated meteorites (meteorites originating from bodies that have experienced partial to complete melting) are particularly useful for deciphering magmatic processes occurring in the early Solar System. A rare group of differentiated meteorites, the angrites, are uniquely suited for such work. The angrites have ancient crystallization ages, lack secondary processing, and have been minimally affected by shock metamorphism, thus allowing them to retain their initial geochemical and isotopic characteristics at the time of formation. The scarcity of angrite samples made it difficult to conduct comprehensive investigations into the formation history of this unique meteorite group. However, a dramatic increase in the number of angrites recovered in recent years presents the opportunity to expand our understanding of their petrogenesis, as well as further refine our knowledge of the initial isotopic abundances in the early Solar System as recorded by their isotopic systematics. Using a combination of geochemical tools (radiogenic isotope chronometers and trace element chemistry), I have investigated the petrogenetic history of a group of four angrites that sample a range of formation conditions (cooling histories) and crystallization ages. Through isotope ratio measurements, I have examined a comprehensive set of long- and short-lived radiogenic isotope systems (26Al-26Mg, 87Rb-87Sr, 146Sm-142Nd, 147Sm-143Nd, and 176Lu-176Hf) within these four angrites. The results of these measurements provide information regarding crystallization ages, as well as revised estimates for the initial isotopic abundances of several key elements in the early Solar System. The determination of trace element concentrations in individual mineral phases, as well as bulk rock samples, provides important constraints on magmatic processes occurring on the angrite parent body. The measured trace element abundances are used to estimate the composition of the parent melts of individual angrites, examine crystallization conditions, and investigate possible geochemical affinities between various angrites. The new geochemical and isotopic measurements presented here significantly expand our understanding of the geochemical conditions found on the angrite parent body and the environment in which these meteorites formed.
ContributorsSanborn, Matthew E (Author) / Wadhwa, Meenakshi (Thesis advisor) / Hervig, Richard (Committee member) / Sharp, Thomas (Committee member) / Clarke, Amanda (Committee member) / Williams, Lynda (Committee member) / Carlson, Richard (Committee member) / Arizona State University (Publisher)
Created2012
Description
This dissertation is presented in two sections. First, I explore two methods of using stable isotope analysis to trace environmental and biogeochemical processes. Second, I present two related studies investigating student understanding of the biogeochemical concepts that underlie part one. Fe and Hg are each biogeochemically important elements in their own way. Fe is a critical nutrient for phytoplankton, while Hg is detrimental to nearly all forms of life. Fe is often a limiting factor in marine phytoplankton growth. The largest source, by mass, of Fe to the open ocean is windblown mineral dust, but other more soluble sources are more bioavailable. To look for evidence of these non-soil dust sources of Fe to the open ocean, I measured the isotopic composition of aerosol samples collected on Bermuda. I found clear evidence in the fine size fraction of a non-soil dust Fe source, which I conclude is most likely from biomass burning. Widespread adoption of compact fluorescent lamps (CFL) has increased their importance as a source of environmental Hg. Isotope analysis would be a useful tool in quantifying this impact if the isotopic composition of Hg from CFL were known. My measurements show that CFL-Hg is isotopically fractionated, in a unique pattern, during normal operation. This fractionation is large and has a distinctive, mass-independent signature, such that CFL Hg can be uniquely identified from other sources. Misconceptions research in geology has been a very active area of research, but student thinking regarding the related field of biogeochemistry has not yet been studied in detail. From interviews with 40 undergraduates, I identified over 150 specific misconceptions. I also designed a multiple-choice survey (concept inventory) to measure understanding of these same biogeochemistry concepts. I present statistical evidence, based on the Rasch model, for the reliability and validity of this instrument. This instrument will allow teachers and researchers to easily quantify learning outcomes in biogeochemistry and will complement existing concept inventories in geology, chemistry, and biology.
ContributorsMead, Chris (Author) / Anbar, Ariel (Thesis advisor) / Semken, Steven (Committee member) / Shock, Everett (Committee member) / Herckes, Pierre (Committee member) / Hartnett, Hilairy (Committee member) / Arizona State University (Publisher)
Created2014
Description
Black carbon (BC) is the product of incomplete combustion of biomass and fossil fuels. It is found ubiquitously in nature and is relevant to studies in atmospheric science, soil science, oceanography, and anthropology. Black carbon is best described using a combustion continuum that sub-classifies BC into slightly charred biomass, char, charcoal and soot. These sub-classifications range in particle size, formation temperature, and relative reactivity. Interest in BC has increased because of its role in the long-term storage of organic matter and the biogeochemistry of urban areas. The global BC budget is unbalanced. Production of BC greatly outweighs decomposition of BC. This suggests that there are unknown or underestimated BC removal processes, and it is likely that some of these processes are occurring in soils. However, little is known about BC reactivity in soil and especially in desert soil. This work focuses on soot BC, which is formed at higher temperatures and has a lower relative reactivity than other forms of BC. Here, I assess the contribution of soot BC to central AZ soils and use the isotopic composition of soot BC to identify sources of soot BC. Soot BC is a significant (31%) fraction of the soil organic matter in central AZ and this work suggests that desert and urban soils may be a storage reservoir for soot BC. I further identify previously unknown removal processes of soot BC found naturally in soil and demonstrate that soil soot BC undergoes abiotic (photo-oxidation) and biotic reactions. Not only is soot BC degraded by these processes, but its chemical composition is altered, suggesting that soot BC contains some chemical moieties that are more reactive than others. Because soot BC demonstrates both refractory and reactive character, it is likely that the structure of soot BC; therefore, its interactions in the environment are complex and it is not simply a recalcitrant material.
ContributorsHamilton, George (Author) / Hartnett, Hilairy E (Thesis advisor) / Herckes, Pierre (Committee member) / Hall, Sharon (Committee member) / Arizona State University (Publisher)
Created2013
Description
Historically, uranium has received intense study of its chemical and isotopic properties for use in the nuclear industry, but has been largely ignored by geoscientists despite properties that make it an intriguing target for geochemists and cosmochemists alike. Uranium was long thought to have an invariant 238U/235U ratio in natural samples, making it uninteresting for isotopic work. However, recent advances in mass spectrometry have made it possible to detect slight differences in the 238U/235U ratio, creating many exciting new opportunities for U isotopic research. Using uranium ore samples from diverse depositional settings from around the world, it is shown that the low-temperature redox transition of uranium (U6+ to U4+) causes measurable fractionation of the 238U/235U ratio. Moreover, it is shown experimentally that a coordination change of U can also cause measurable fractionation in the 238U/235U ratio. This improved understanding of the fractionation mechanisms of U allows for the use of the 238U/235U ratio as a paleoredox proxy. The 238U/235U ratios of carbonates deposited spanning the end-Permian extinction horizon provide evidence of pronounced and persistent widespread ocean anoxia at, or immediately preceding, the extinction boundary. Variable 238U/235U ratios correlated with proxies for initial Cm/U in the Solar System's earliest objects demonstrates the existence of 247Cm in the early Solar System. Proof of variable 238U/235U ratios in meteoritic material forces a substantive change in the previously established procedures of Pb-Pb dating, which assumed an invariant 238U/235U ratio. This advancement improves the accuracy of not only the Pb-Pb chronometer that directly utilizes the 238U/235U ratio, but also for short-lived radiometric dating techniques that indirectly use the 238U/235U ratio to calculate ages of Solar System material.
ContributorsBrennecka, Gregory A (Author) / Anbar, Ariel D (Thesis advisor) / Wadhwa, Meenakshi (Thesis advisor) / Herrmann, Achim D (Committee member) / Hervig, Richard (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2011
Description
Molybdenum and uranium isotope variations are potentially powerful tools for reconstructing the paleoredox history of seawater. Reliable application and interpretation of these proxies requires not only detailed knowledge about the fractionation factors that control the distribution of molybdenum and uranium isotopes in the marine system, but also a thorough understanding of the diagenetic processes that may affect molybdenum and uranium isotopes entering the rock record. Using samples from the Black Sea water column, the first water column profile of 238U/235U variations from a modern euxinic basin has been measured. This profile allows the direct determination of the 238U/235U fractionation factor in a euxinic marine setting. More importantly however, these data demonstrate the extent of Rayleigh fractionation of U isotopes that can occur in euxinic restricted basins. Because of this effect, the offset of 238U/235U between global average seawater and coeval black shales deposited in restricted basins is expected to depend on the degree of local uranium drawdown from the water column, potentially complicating the interpretation 238U/235U paleorecords. As an alternative to the black shales typically used for paleoredox reconstructions, molybdenum and uranium isotope variations in bulk carbonate sediments from the Bahamas are examined. The focus of this work was to determine what processes, if any, fractionate molybdenum and uranium isotopes during incorporation into bulk carbonate sediments and their subsequent diagenesis. The results demonstrate that authigenic accumulation of molybdenum and uranium from anoxic and sulfidic pore waters is a dominant process controlling the concentration and isotopic composition of these sediments during early diagenesis. Examination of ODP drill core samples from the Bahamas reveals similar behavior for sediments during the first ~780ka of burial, but provides important examples where isolated cores and samples occasionally demonstrate additional fractionation, the cause of which remains poorly understood.
ContributorsRomaniello, Stephen J. (Author) / Anbar, Ariel (Thesis advisor) / Hartnett, Hilairy (Committee member) / Herrmann, Achim (Committee member) / Shock, Everett (Committee member) / Wadhwa, Meenakshi (Committee member) / Arizona State University (Publisher)
Created2012
Description
Providing an environmental context to early hominins is as important as describing the hominin fossils themselves, because evolutionary processes are tightly linked to everchanging ecosystems that vary across space and through time. An optimal understanding of ecosystems changes is critical to formulate and test hypotheses regarding human evolution and adaptation. Fortunately, the fossil record has yielded abundant remains of mammals which can be used to explore the possible causal relationships between environmental change and mammal – including hominin –evolution. Although many studies have already been conducted on this topic, most of them are framed at large spatial and temporal scales. Instead, this dissertation focuses on the evolution and paleoecology of only one group of mammals (the Suidae) in a specific geographical area (lower Awash Valley in Ethiopia) and within a constrained time frame (3.8–2.6 Ma). Three dissertation papers address: 1) changes in suid taxonomic composition in relation to Late Pliocene faunal turnover ~2.8 Ma in the Lee-Adoyta basin, Ledi-Geraru; 2) comparisons of suid diets from Hadar (~3.45–2.95 Ma) with respect to those of Kanapoi (~4.1 Ma, West Turkana, Kenya); 3) the dietary ecology of the suids from Woranso-Mille (~3.8–3.2 Ma). Results of these papers show that 1) after ~2.8 Ma there is a replacement of suid species that is coupled with low relative abundance of suids. This is compatible with more open and/or arid environments at this time; 2) suid dietary breadth was broader in Hadar than in Kanapoi, but this is mostly driven by the dietary niche space occupied by Kolpochoerus in Hadar, a suid genus absent from Kanapoi; 3) suid diets vary both temporally and geographically within the lower Awash Valley. Kolpochoerus incorporates more C4 resources (e.g., grasses) in its diet after ~3.5 Ma and in general, suids after ~3.5 Ma in Woranso-Mille had C4-enriched diets in comparison with those from nearby Hadar and Dikika. Presumably, the changes in suid communities (relative abundance and taxonomic composition) and dietary shifts observed in suids were triggered by climatic and habitat changes that also contributed to shape the behavioural and morphological evolution of early hominins.
ContributorsAguilar Lazagabaster, Ignacio (Author) / Reed, Kaye E (Thesis advisor) / Kimbel, William H. (Committee member) / Ungar, Peter S. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Migrations, past and present, fundamentally influence human interaction, community building, and social evolution. Studies of contemporary migrations demonstrate that the form and intensity of interaction migrants maintain between homeland and host communities shape social dynamics, innovations, and identities. This dissertation applies a contemporary theoretical framework and biogeochemical analyses to elucidate the scale, processes, and impacts of migration in the hinterland of the pre-Hispanic Tiwanaku polity (ca. AD 500-1100). Social diversity is examined by reconstructing the migration histories and dietary choices of individuals interred at the Tiwanaku-affiliated site of Omo M10 in the Moquegua Valley of southern Peru.
Radiogenic strontium and stable oxygen isotope data from human dental and skeletal elements are used to characterize intra- and inter-individual paleomobility patterns at Omo M10. When contextualized with archaeological evidence, these data reveal multigenerational interaction through migration between communities in the highland Tiwanaku heartland and at Omo M10. The observed greater mobility of females and juveniles at Omo M10 indicates that women and families played an essential role in maintaining social relationships and persistent cultural continuity in Moquegua Tiwanaku life. Contact with the highlands waned over time as disruption in the urban highland centers likely weakened ties to peripheral lowland communities.
Stable carbon and nitrogen data from human dental and skeletal elements are employed to estimate intra- and inter-individual paleodietary patterns. Results indicate diet at Omo M10 varied depending on an individual’s community affiliation, sex, age, and level of mobility; diet broadly changed over time with shifting levels of interaction with highland Tiwanaku communities. Intra-individual biogeochemical analyses of migration and diet at Omo M10 contribute a nuanced perspective on the diverse experiences of multigenerational colonists on the periphery of the Tiwanaku polity.
Radiogenic strontium and stable oxygen isotope data from human dental and skeletal elements are used to characterize intra- and inter-individual paleomobility patterns at Omo M10. When contextualized with archaeological evidence, these data reveal multigenerational interaction through migration between communities in the highland Tiwanaku heartland and at Omo M10. The observed greater mobility of females and juveniles at Omo M10 indicates that women and families played an essential role in maintaining social relationships and persistent cultural continuity in Moquegua Tiwanaku life. Contact with the highlands waned over time as disruption in the urban highland centers likely weakened ties to peripheral lowland communities.
Stable carbon and nitrogen data from human dental and skeletal elements are employed to estimate intra- and inter-individual paleodietary patterns. Results indicate diet at Omo M10 varied depending on an individual’s community affiliation, sex, age, and level of mobility; diet broadly changed over time with shifting levels of interaction with highland Tiwanaku communities. Intra-individual biogeochemical analyses of migration and diet at Omo M10 contribute a nuanced perspective on the diverse experiences of multigenerational colonists on the periphery of the Tiwanaku polity.
ContributorsDahlstedt, Allisen Cecelia (Author) / Knudson, Kelly J. (Thesis advisor) / Buikstra, Jane E. (Committee member) / Goldstein, Paul S (Committee member) / Arizona State University (Publisher)
Created2019
Description
The Middle Stone Age archaeological record from the south coast of South Africa contains significant evidence for early modern human behavior. The south coast is within the modern Greater Cape Floristic Region (GCFR), which in the present-day encompasses the entirety of South Africa’s Winter Rainfall Zone (WRZ) and contains unique vegetation elements that have been hypothesized to be of high utility to hunter-gatherer populations. Extant paleoenvironmental proxy records for the Pleistocene in the region often indicate evidence for more open environments during the past than occur in the area in the present-day, while climate models suggest glacial presence of the WRZ that would support maintenance of C3-predominant GCFR vegetation.
These paleoenvironmental proxies sample past environments at geographic scales that are often regional. The GCFR flora is hyper-diverse, and glacial climate change-driven impacts on local vegetation could have been highly variable over relatively small geographic scales. Proxy records that are circumscribed in their geographic scale are thus key to our understanding of ancient environments at particular MSA archaeological localities.
Micromammal fossil teeth are now recognized as an abundant potential reservoir of paleoenvironmental proxy data at an extremely local scale. This study analyzed modern micromammal teeth obtained from raptor pellets at three locations on the south coast. Stable carbon isotope analysis indicates that the modern micromammals from the taxa sampled consume a wide range of δ13Cplant on the landscape when it is available, and thus stable carbon isotope analysis of micromammal teeth should act as a proxy for the range of available δ13Cdiet in a circumscribed area of vegetation.
Micromammal stable carbon isotope data obtained from specimens from one of the few well-dated MIS6-MIS5 sequences in the region (Pinnacle Point sites 13B, 30, and 9C). δ13Cenamel values for the taxa sampled indicate diets that are primarily C3, and there is almost no evidence for a dietary C4 grass component in any of the sampled specimens. This indicates that, at a minimum, pockets of C3 vegetation associated with the GCFR were likely available to hunter-gatherers at Pinnacle Point throughout the Middle and Late Pleistocene.
These paleoenvironmental proxies sample past environments at geographic scales that are often regional. The GCFR flora is hyper-diverse, and glacial climate change-driven impacts on local vegetation could have been highly variable over relatively small geographic scales. Proxy records that are circumscribed in their geographic scale are thus key to our understanding of ancient environments at particular MSA archaeological localities.
Micromammal fossil teeth are now recognized as an abundant potential reservoir of paleoenvironmental proxy data at an extremely local scale. This study analyzed modern micromammal teeth obtained from raptor pellets at three locations on the south coast. Stable carbon isotope analysis indicates that the modern micromammals from the taxa sampled consume a wide range of δ13Cplant on the landscape when it is available, and thus stable carbon isotope analysis of micromammal teeth should act as a proxy for the range of available δ13Cdiet in a circumscribed area of vegetation.
Micromammal stable carbon isotope data obtained from specimens from one of the few well-dated MIS6-MIS5 sequences in the region (Pinnacle Point sites 13B, 30, and 9C). δ13Cenamel values for the taxa sampled indicate diets that are primarily C3, and there is almost no evidence for a dietary C4 grass component in any of the sampled specimens. This indicates that, at a minimum, pockets of C3 vegetation associated with the GCFR were likely available to hunter-gatherers at Pinnacle Point throughout the Middle and Late Pleistocene.
ContributorsWilliams, Hope Marie (Author) / Marean, Curtis W (Thesis advisor) / Knudson, Kelly J. (Thesis advisor) / Reed, Kaye (Committee member) / Arizona State University (Publisher)
Created2015
Description
The beginning of our Solar System, including events such as the formation of the first solids as well as the accretion and differentiation of planetary bodies, is recorded in meteoritic material. This record can be deciphered using petrographic, geochemical and isotopic investigations of different classes of meteorites and their components. In this dissertation, I have investigated a variety of isotope systematics in chondritic and achondritic meteorites to understand processes that have shaped our Solar System. Specifically, the investigations conducted here are in two main areas: 1) Hydrogen isotope systematics in a meteorite representing the freshest known sample of the martian crust, and 2) Isotopic studies (specifically relating to high resolution chronology, nucleosynthetic anomalies and mass-dependent fractionations) in calcium-aluminum-rich inclusions, which are thought to be the earliest-formed solids in the Solar System. Chapter 1 of this dissertation presents a review of the hydrogen isotopic compositions of various planetary bodies and reservoirs in the Solar System, which could serve as tracers for the volatile sources. Chapter 2 focuses on an investigation of the hydrogen isotopic systematics in the freshest martian meteorite fall, Tissint, using the Cameca IMS-6f secondary ion mass spectrometer (SIMS). These first two chapters comprise the first part of this dissertation. The second part is comprised of chapters 3 through 6 and is focused on isotopic analyses of Calcium-Aluminum-rich Inclusions (CAIs). Chapter 3 is a review of CAIs, which record some of the earliest processes that occurred in the solar nebula. Chapter 4 presents the results of an investigation of the 26Al-26Mg short-lived chronometer (half-life ~0.72 Ma) in two CAIs and their Wark-Lovering (WL) rims from a CV3 carbonaceous chondrite using the Cameca NanoSIMS 50L. Chapter 5 is focused on the results of a study of the Zr isotope compositions of a suite of 15 CAIs from different carbonaceous chondrites using multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), in order to identify nucleosynthetic anomalies in the CAI-forming region. Chapter 6 focuses on the mass-dependent Mg isotopic compositions measured in 11 CAIs from the Allende CV3 carbonaceous chondrite using MC-ICPMS, to evaluate effects of thermal processing on CAIs.
ContributorsMane, Prajkta (Author) / Wadhwa, Meenakshi (Thesis advisor) / Hervig, Richard (Committee member) / Desch, Steven (Committee member) / Garvie, Laurence (Committee member) / Bell, James (Committee member) / Arizona State University (Publisher)
Created2016
Description
Meteorites provide an opportunity to reconstruct the history of the SolarSystem. Differentiated meteorites, also called achondrites, are the result of melting
and differentiation processes on their parent body. Stable isotopic compositions of
differentiated meteorites and their components have added to the understanding of
physical parameters, such as temperature, pressure, and redox conditions relevant
to differentiation processes on planetesimals and planets in the early Solar System.
In particular, Fe and Si isotopes have proven to be useful in advancing the
understanding of physical and chemical processes during planetary accretion and
subsequent evolution.
In this work, I developed a new method to simultaneously purify Fe and Si
from a single aliquot of sample while ensuring consistently high yields and accurate
and precise isotopic measurements. I then measured the Fe isotope compositions
and Si contents of metals from aubrite meteorites to infer the structure and thermal
evolution of their asteroidal parent body. Thereafter, I determined the combined Si
and Fe isotope compositions of aubrite metals and the Horse Creek iron meteorite,
and compared the magnitude of Si and Fe isotope fractionation factors between
metal and silicates for both enstatite chondrites and aubrites to estimate the effect of
high-temperature core formation that occurred on the aubrite parent body. I
additionally assessed whether correlated Si and Fe isotope systematics can be used
to trace core formation and partial melting processes for the aubrite parent body,
angrite parent body, Mars, Vesta, Moon, and Earth. Finally, I measured the combined
Fe and Si isotope composition of a variety of ungrouped achondrites and brachinites
that record different degrees of differentiation under different redox conditions to
evaluate the role of differentiation and oxygen fugacity in controlling their Fe and Si
isotope compositions. Taken together, this comprehensive dataset reveals the
thermal evolution of the aubrite parent body, provides insights into the factors controlling the Fe and Si isotope compositions of various planetary materials, and
helps constrain the bulk starting composition of planets and planetesimals.
ContributorsRay, Soumya (Author) / Wadhwa, Meenakshi (Thesis advisor) / Garvie, Laurence (Committee member) / Till, Christy (Committee member) / Hervig, Richard (Committee member) / Schrader, Devin (Committee member) / Arizona State University (Publisher)
Created2021