Geology
Permanent URI for this communityhttp://hdl.handle.net/1903/2243
Browse
8 results
Search Results
Item SULFUR ISOTOPE RECORDS IN NEOARCHEAN CARBONATES: IMPLICATIONS FOR THE EARLY PRECAMBRIAN SULFUR CYCLE(2017) Zhelezinskaia, Iadviga; Farquhar, James; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mass-independent fractionation of sulfur isotopes found in Early Precambrian records is the main evidence supporting an oxygen-poor atmosphere before ~2.4 Ga when ancient sulfur cycling was different than today. In previous studies, shale facies formed in deep-water environments have been the main target that were used to constraint the ancient sulfur cycle using sulfur isotopes, even though, among sedimentary Neoarchean strata, carbonate rocks are found to be more abundant. In order to follow previous observations and reveal processes operating in shallow water environments, I conducted a series of systematic studies of Neoarchean carbonate archives. Elemental and isotope measurements of sulfur and carbon in carbonate (and some shale) facies were obtained from multiple cores drilled through ~2.7 to 2.5 Ga successions of South Africa (GKF01, GKP01, and BH1-Sacha), Western Australia (AIDP-2, AIDP-3, BB, PR, RP, and RG) and Brazil (GDR-117). This study demonstrates that carbonate facies preserve distinctive MIF-S compositions relative to shale facies. Drilled pyrites in carbonate formations mostly preserved negative Δ33S values suggesting that the major sulfur source to shallow environments was atmospheric sulfate that also was isotopically redistributed through microbial sulfate reduction producing δ34S > 35‰ isotope fractionation. Atmospheric sulfate was the main source for seawater sulfate making its concentration in the Neoarchean ocean of less than 10µM/l. At this low concentration, reservoir effects would be pronounced leading to the formation of carbonate associated pyrites with highly positive δ34S compositions ranging to > +30‰. The bulk pyrites in most carbonate formations from South African and Western Australian cores possess small positive Δ33S signals (<+3.0‰) suggesting the incorporation of 20-35% of photolytic elemental sulfur. Photolytic sulfate with Δ36S/Δ33S deviations found in macroscopic pyrites with negative Δ33S from the Carawine Formation provide evidence for changes in atmospheric reactions during periods of an organic hazy atmosphere. My study of Δ36S/Δ33S in contemporaneous Jeerinah shale indicates the possible temporal decoupling of the MIF-S signal on a basinal scale implying heterogeneous haze structure. Integration of sulfur and carbon isotopes measured in carbonate facies suggests that sulfur-metabolizing microbes such as sulfur phototrophs and sulfate reducers were actively recycling these elements in shallow marine environments.Item HYDROLOGICAL, BIOLOGICAL, AND GEOCHEMICAL RELATIONSHIPS AMONG CARBON, NITROGEN, AND BASE CATIONS IN RESTORED AND UNRESTORED URBAN STREAMS(2017) Doody, Thomas Rossiter; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Urban infrastructure changes hydrologic flowpaths of water into streams and alters ecosystem function. Geomorphic stream restoration is commonly implemented to stabilize channels, while ecosystem function, and nutrient retention are of secondary concern. This research investigated whether restoration alone significantly influences N uptake in streams and if significant hydrological, biological, and geochemical relationships exist between coupled biogeochemical cycles that should be considered when evaluating restorations. Carbon, nitrogen, base cations, and stream metabolism dynamics were investigated in six urban streams in Baltimore,MD. Nitrate tracer injections were used to quantify nitrogen uptake dynamics. Results did not show significant differences in nitrogen uptake based on restoration. Organic carbon, inorganic carbon, and nitrogen each have distinct but interrelated hydrological, biological, and geochemical relationships across all sites. These dynamic relationships may also significantly affect nitrogen uptake, but more spatiotemporal data are needed to quantify and understand variability among restored and unrestored sites.Item DISSOLVED AND GASEOUS FLUXES OF CARBON AND NITROGEN FROM URBAN WATERSHEDS OF THE CHESAPEAKE BAY(2016) Smith, Rose Marie; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon and nitrogen loading to streams and rivers contributes to eutrophication as well as greenhouse gas (GHG) production in streams, rivers and estuaries. My dissertation consists of three research chapters, which examine interactions and potential trade-offs between water quality and greenhouse gas production in urban streams of the Chesapeake Bay watershed. My first research project focused on drivers of carbon export and quality in an urbanized river. I found that watershed carbon sources (soils and leaves) contributed more than in-stream production to overall carbon export, but that periods of high in-stream productivity were important over seasonal and daily timescales. My second research chapter examined the influence of urban storm-water and sanitary infrastructure on dissolved and gaseous carbon and nitrogen concentrations in headwater streams. Gases (CO2, CH4, and N2O) were consistently super-saturated throughout the course of a year. N2O concentrations in streams draining septic systems were within the high range of previously published values. Total dissolved nitrogen concentration was positively correlated with CO2 and N2O and negatively correlated with CH4. My third research chapter examined a long-term (15-year) record of GHG emissions from soils in rural forests, urban forest, and urban lawns in Baltimore, MD. CO2, CH4, and N2O emissions showed positive correlations with temperature at each site. Lawns were a net source of CH4 + N2O, whereas forests were net sinks. Gross CO2 fluxes were also highest in lawns, in part due to elevated growing-season temperatures. While land cover influences GHG emissions from soils, the overall role of land cover on this flux is very small (< 0.5%) compared with gases released from anthropogenic sources, according to a recent GHG budget of the Baltimore metropolitan area, where this study took place.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 A Time-Series Geochemical Study of the ca. 2.5 Ga Batatal Formation in Brazil: Sulfur and Carbon Isotopic Insights into Environmental Conditions before the Great Oxidation Event(2013) Zhelezinskaia, Iadviga; Kaufman, Alan J; Farquhar, James; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Neoarchean metasedimentary rocks from the Batatal Formation, Brazil were studied using petrographic, elemental and stable isotopic techniques to provide a better understanding of coupling between the atmosphere-ocean system and biogeochemical cycles prior to the Great Oxidation Event. Multiple sulfur isotope data from both shale and carbonate lithofacies confirms global preservation of mass-independent fractionations, thought to be produced through photochemical reactions in an oxygen-free Neoarchean atmosphere. Isotopic differences between lithofacies within the shallow marine Batatal Formation, and beyond in deeper subtidal environments from correlative successions in Western Australia and South Africa, suggest a strong influence of environmental conditions on the preservation of distinct &Delta33S signatures. To explain the novel isotopic data, it is proposed the Batatal Formation was deposited in a shallow water evaporitic environment, which resulted in higher sulfate concentrations and greater sulfur isotope fractionation associated with the activity of sulfate-reducing bacteria. Higher temperatures associated with such environments may have also promoted carbon dioxide limitation resulting in lesser carbon isotopic fractionation by photoautotrophs.Item Geomorphic, hydraulic, and biogeochemical controls on nitrate retention in tidal freshwater marshes(2012) Seldomridge, Emily; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal freshwater wetlands are ideal sites for nitrate retention because of their position within the landscape (near the head of tide); they receive water, discharge, nutrients (N and P), and sediment loads directly from contributing watersheds. Nitrate retention (the difference between nitrate inputs and outputs in an ecosystem), however, is difficult to predict due to the complex interactions between flow processes and the multiple retention processes. The goal of the study was to evaluate both external and internal controls on nitrate retention, and to determine whether scaling procedures could be identified to estimate nitrate retention for an entire ecosystem. The external controls included temperature, dissolved oxygen concentrations, and incoming nitrate concentrations. Internal controls are the interactions among geomorphic, hydrologic, and biological systems within individual marshes that influence nitrate retention. This study was conducted in the upper Patuxent River Estuary where the ecosystem is composed of hundreds of individual marshes that are connected to the estuary through tidal inlets; marsh inlet geomorphology governs water and nitrate fluxes into the marshes. This study therefore took a mass balance approach to determine geomorphic, hydrologic, and biological influences on nitrate retention. Nitrate retention was measured over a 4-year period in three tidal freshwater wetlands, selected to represent a range of marsh sizes. An examination of the mass balance data suggest that nitrate retention is an outcome of complex interactions among inlet geomorphic characteristics, hydrologic flux, and biogeochemical processes. In cases where nitrate concentrations and temperatures are greater than critical (limiting) values, an emergent behavior in which nitrate retention is a simple function of water volume is observed. The wetland ecosystem is composed of numerous, small wetlands that process a small percentage of total nitrate; approximately 50% of retention is processed by the large marshes that comprise only 4% of the total population, but over 80% of the marsh area; therefore, any processes that affect tidal water volumes in large marshes is likely to affect net nitrate retention. The growth of vegetation in these large channels reduced ecosystem nitrate retention.Item A carbon and nitrogen isotopic analysis of Pleistocene food webs in North America: implications for paleoecology and extinction(2008-05-05) France, Christine Ann Missell; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon and nitrogen isotopic reconstructions of North American Pleistocene trophic relationships were used to examine the extinction within terrestrial mammals ~10,000 years ago and distinguish between two potential causal mechanisms - human over-hunting and climate change. Additionally, individual animals were examined for unique isotopic signatures associated with feeding specializations, digestive strategies, and juveniles. Bones representing a comprehensive set of Pleistocene mammalian genera were obtained from three fossil localities: McKittrick Brea, California; Saltville, Virginia; and several sites in Florida. Collagen, a durable bone protein whose carbon and nitrogen isotopic composition reflects dietary input, was extracted from specimens and analyzed for delta-13C, delta-15N, % collagen, %C, %N, and C:N. Radiocarbon dating and amino acid analyses were performed on select sample sets. Results indicated that several specimens contained well preserved collagen, the isotopic values of which indicated both trophic position and vegetation preference. Those samples that contained residual diagenetic proteinaceous material exhibited increased hydrolysis of collagen with time and leaching of disassociated amino acids. Trophic relationships were reconstructed from well preserved specimens for Aucilla River, Florida and the herbivores of Saltville, Virginia, with a less complete reconstruction established for McKittrick Brea, California. The following notable trends emerged: 1) absence of nitrogen isotopic distinction between ruminants and non-ruminants, 2) enriched juvenile nitrogen isotopic signature, 3) distinction of giant ground sloths as omnivores, 4) C4 grass grazers and open C4 grasslands restricted to southern North American latitudes, 5) generalized and opportunistic feeding habits of herbivores, 6) potential prey specializations of carnivores. A noticeable lack of competition and feeding specialists among herbivores suggested a stable base to these late Pleistocene ecosystems, which argues against climatically induced stress on plants. While carnivore specimens were fewer, the apex trophic levels appeared to exhibit a similar lack of competition, which would be expected in a human-driven extinction where carnivores were stressed due to rapidly over-hunted herbivores. The ultimate cause of the late Pleistocene mammalian extinction in North America can not be exclusively attributed to either of these two mechanisms at this point in time; rather, a combination of factors should be considered.Item Isotope and Organic Geochemistry of a Unique Proterozoic, Postglacial Succession: The Lapa Formation, Vazante Group, Brazil(2007-05-09) Brody, Kristina; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study is the second to investigate biological characteristics associated with Proterozoic glaciation via molecular fossils from organic matter preserved in shale. In the Vazante Group, Minas Gerais, Brazil, the Serra da Lapa Formation unconformably overlies a formation recently dated to ca. 1.13 Ga. Lithologic and isotopic data suggest the Lapa represents deposition immediately after either an early Neoproterozoic "snowball Earth" ice age or a possible regional, but still low-latitude, late Mesoproterozoic ice age. The relative abundances of biomarkers and other organic molecules show variations that match lithologic and isotopic changes observed in 40 meters of exploration drill core studied. Inconsistencies among biomarker abundances as well as differences between the organic matter of the Lapa Formation and that of the underlying formation hint at heterogeneity among and within formations. A more complete picture of the Vazante Group is warranted before characteristics of preserved organic matter can be interpreted in the context of depositional environments or postdepositional processes.