UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
4 results
Search Results
Item GEOCHEMICAL INDICATORS OF REDOX AND WEATHERING ACROSS THE EDIACARAN-CAMBRIAN TRANSITION IN SIBERIA(2024) Doerrler, Andrew; Kaufman, Alan Jay; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The transition between the Ediacaran and Cambrian periods witnessed the fall of the enigmatic Ediacara biota. The cause of their extinction is poorly understood, but the timing broadly coincides with a significant negative ẟ13C anomaly, the BAsal Cambrian Carbon isotope Excursion (BACE). These macroscopic organisms were likely tolerant of anoxic conditions, so oceanic oxidation may have been a kill mechanism. This study utilizes uranium isotopes, sulfur isotopes, and cerium anomalies to understand oceanic redox conditions from two BACE sections in Siberia, as well as lithium isotopes to constrain weathering intensity. Reconstruction of seawater ẟ238U values from equivalent evaporite and carbonate-dominated successions indicate a notable increase in oxygen during the event supporting the oxidation hypothesis. Global sea level fall and evaporite formation suggest that seawater salinity increased dramatically along continental margins, which may provide an alternative osmotic kill mechanism for the softbodied Ediacaran biota. Support for the salinity hypothesis comes from profound ẟ7Li and ẟ34S compositions of carbonate and pyrite, respectively, which arguably resulted from the distillation of lithium and sulfate from seawater into evaporite-rich lithologies.Item Development and the Early Animal Fossil Record: Evolution and Phylogenetic Applications(2016) Tweedt, Sarah Maureen; Delwiche, Charles F; Erwin, Douglas H; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Although evolutionary developmental biology and paleontology are linked by the study of morphology, the application of development to paleontological questions has only recently become more prominent. The growth of a robust developmental genetic framework for studying the origin and evolution of morphological features, however, holds great promise for understanding ancient animal life. As paleontology provides the historical record as well as the temporal and environmental context of past morphological evolution, uniting knowledge of developmental genetic systems with this historical record will form a key synthetic approach to understanding the early evolution of developmental processes. Ultimately unraveling the sequence of ancient animal developmental evolution will require combining analysis of comparative developmental data, critical assessment of fossil morphology within a developmental framework, and the targeted exploration of specific geologic periods to fill in the missing record of key times in animal developmental evolution. This study addresses each of these three approaches. First, I provide a new compilation and evaluation of recent comparative and experimental developmental biology data to review the nature of developmental ‘toolkits’ at the origin of the most basal animal clades. I reconstruct early animal developmental capacities and integrate these data within a temporal framework to better understand the context of earliest animal development. Second, I assess longstanding evolutionary hypotheses about the origin of the panarthropod clade and the phylogenetic position of Cambrian ‘lobopod’ fossils by examining signal present within current morphological datasets. I apply new methods to fossil panarthropod phylogeny estimation and suggest strategies for developmentally-informed phylogenetic coding of morphological data. Third, I present the discovery of the oldest spicule-bearing fossil sponges in the rock record, which co-occur in latest Ediacaran strata with classic enigmatic Ediacaran fauna. I provide a formal systematic description of fossil material from localities in both Nevada and southern Namibia. The combined approaches presented herein are a first step towards a deeper integration of developmental principles in the study and discovery of ancient animal life, and contribute to our understanding of the evolution of ancient animal developmental processes.Item Authigenesis, biomineralization, and carbon-sulfur cycling in the Ediacaran ocean(2015) Cui, Huan; Kaufman, Alan J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fossil record of the Ediacaran Period (635-541 Ma) reveals unprecedented rise of early animal life (metazoan) in Earth history. Coupled with this evolutionary milestone, the Earth’s atmosphere and hydrosphere experienced dramatic redox fluctuations. In order to better constrain the redox architecture of the Ediacaran ocean margin, an integrated chemostratigraphic correlation of the Doushantuo Formation in basin scale was conducted (see Chapter 2). The revised redox model suggests that euxinic conditions on the platforms were mainly restricted in lagoonal settings, which helps us to better understand Ediacaran fossil distributions and fluctuated δ13C records in the Ediacaran strata in South China. One of the most distinct features of the Ediacaran chemostratigraphy is the δ13C negative excursion (i.e. Shuram Excursion, or SE) reported globally, which is the largest known C cycle anomaly in Earth history. In order to understand the biogeochemical processes that gave rise to the SE expressed in the upper Doushantuo Formation, systematic petrographic and geochemical investigations were conducted for the outer shelf sections in the Yangtze block (see Chapter 3). Methane-derived authigenic calcite cements and nodules with extreme 13C-depletion were discovered and interpreted as the first empirical evidence of authigenic mineralization associated with the SE. In light of these novel observations, it is proposed that the globally distributed SE may be formed by widespread syndeposition of authigenic carbonates in a sulfate-methane transitional zone positioned at the sediment-water interface in response to a global seawater sulfate increase. Finally, to provide environmental context for the terminal Ediacaran biomineralization of animals, we conducted a high-resolution elemental and isotopic study of the richly fossiliferous Gaojiashan Member (see Chapter 4). Coincident with the first appearance of Cloudina are significant C-S-Ca-Sr cycle anomalies. It is proposed that the onset of calcarious biomineralization of animals may have coincided with an increase in terrestrial weathering fluxes of sulfate, alkalinity, and nutrients to the depositional basin. Enhanced concentration of Ca ion in seawater may have promoted the calcarious biomineralization of the early animals. Integrated chemo-, bio- and litho-stratigraphy of the Doushantuo and Dengying formations presented in this dissertation emphasized intimate co-evolution of Earth-life system during the Ediacaran Period.Item Geochemical and Radiometric Constraints on the Redox History of Late Ediacaran Oceans(2012) Peek, Sara; Kaufman, Alan J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the past decade, significant field and laboratory studies have been devoted to furthering understanding of the chemical conditions that accompanied the origin and diversification of Earth's earliest multicellular animals during the Ediacaran Period (ca. 635-542 Ma). Here, I apply geochemical methods to excellently preserved and exposed sections spanning approximately the last 10 million years of the Ediacaran Period. From Arctic Siberia, hundreds of samples were collected at high stratigraphic resolution, from which carbonate carbon and oxygen profiles have been produced, along with organic carbon and sulfur isotope data. From South China, a carbonate carbon isotope profile has been constructed. Radiometric dates constrain the timing of deposition in our sections. This work uses geochemical data and radiometric dating to inform and improve intra- and inter-basinal correlation, and serves as a preliminary study confirming the suitability of our Siberian sections to the study of oxygenation during the latest Ediacaran Period.