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- All Subjects: Planetology
- All Subjects: Molybdenum
- Creators: Whipple, Kelin X
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
Olympus Mons is the largest volcano on Mars. Previous studies have focused on large scale features on Olympus Mons, such as the basal escarpment, summit caldera complex and aureole deposits. My objective was to identify and characterize previously unrecognized and unmapped small scale features to understand the volcanotectonic evolution of this enormous volcano. For this study I investigated flank vents and arcuate graben. Flank vents are a common feature on composite volcanoes on Earth. They provide information on the volatile content of magmas, the propagation of magma in the subsurface and the tectonic stresses acting on the volcano. Graben are found at a variety of scales in close proximity to Martian volcanoes. They can indicate flexure of the lithosphere in response to the load of the volcano or gravitation spreading of the edifice. Using Context Camera (CTX), High Resolution Imaging Science Experiment (HiRISE), Thermal Emission Imaging System (THEMIS), High Resolution Stereo Camera Digital Terrain Model (HRSC DTM) and Mars Orbiter Laser Altimeter (MOLA) data, I have identified and characterized the morphology and distribution of 60 flank vents and 84 arcuate graben on Olympus Mons. Based on the observed vent morphologies, I conclude that effusive eruptions have dominated on Olympus Mons in the Late Amazonian, with flank vents playing a limited role. The spatial distribution of flank vents suggests shallow source depths and radial dike propagation. Arcuate graben, not previously observed in lower resolution datasets, occur on the lower flanks of Olympus Mons and indicate a recent extensional state of stress. Based on spatial and superposition relationships, I have constructed a developmental sequence for the construction of Olympus Mons: 1) Construction of the shield via effusive lava flows.; 2) Formation of the near summit thrust faults (flank terraces); 3) Flank failure leading to scarp formation and aureole deposition; 4) Late Amazonian effusive resurfacing and formation of flank vents; 5) Subsidence of the caldera, waning volcanism and graben formation. This volcanotectonic evolution closely resembles that proposed on Ascraeus Mons. Extensional tectonism may continue to affect the lower flanks of Olympus Mons today.
ContributorsPeters, Sean I. (Author) / Christensen, Philip R. (Thesis advisor) / Clarke, Amanda B (Committee member) / Whipple, Kelin X (Committee member) / Arizona State University (Publisher)
Created2015
Description
Planetary surface studies across a range of spatial scales are key to interpreting modern and ancient operative processes and to meeting strategic mission objectives for robotic planetary science exploration. At the meter-scale and below, planetary regolith conducts heat at a rate that depends on the physical properties of the regolith particles, such as particle size, sorting, composition, and shape. Radiometric temperature measurements thus provide the means to determine regolith properties and rock abundance from afar. However, heat conduction through a matrix of irregular particles is a complicated physical system that is strongly influenced by temperature and atmospheric gas pressure. A series of new regolith thermal conductivity experiments were conducted under realistic planetary surface pressure and temperature conditions. A new model is put forth to describe the radiative, solid, and gaseous conduction terms of regolith on Earth, Mars, and airless bodies. These results will be used to infer particle size distribution from temperature measurements of the primitive asteroid Bennu to aid in OSIRIS-REx sampling site selection. Moving up in scale, fluvial processes are extremely influential in shaping Earth's surface and likely played an influential role on ancient Mars. Amphitheater-headed canyons are found on both planets, but conditions necessary for their development have been debated for many years. A spatial analysis of canyon form distribution with respect to local stratigraphy at the Escalante River and on Tarantula Mesa, Utah, indicates that canyon distribution is most closely related to variations in local rock strata, rather than groundwater spring intensity or climate variations. This implies that amphitheater-headed canyons are not simple markers of groundwater seepage erosion or megaflooding. Finally, at the largest scale, volcanism has significantly altered the surface characteristics of Earth and Mars. A field campaign was conducted in Hawaii to investigate the December 1974 Kilauea lava flow, where it was found that lava coils formed in an analogous manner to those found in Athabasca Valles, Mars. The location and size of the coils may be used as indicators of local effusion rate, viscosity, and crustal thickness.
ContributorsRyan, Andrew J (Author) / Christensen, Philip R. (Thesis advisor) / Bell, James F. (Committee member) / Whipple, Kelin X (Committee member) / Ruff, Steven W (Committee member) / Asphaug, Erik I (Committee member) / Arizona State University (Publisher)
Created2018
Description
Biochemical reactions underlie all living processes. Their complex web of interactions is difficult to fully capture and quantify with simple mathematical objects. Applying network science to biology has advanced our understanding of the metabolisms of individual organisms and the organization of ecosystems, but has scarcely been applied to life at a planetary scale. To characterize planetary-scale biochemistry, I constructed biochemical networks using global databases of annotated genomes and metagenomes, and biochemical reactions. I uncover scaling laws governing biochemical diversity and network structure shared across levels of organization from individuals to ecosystems, to the biosphere as a whole. Comparing real biochemical reaction networks to random reaction networks reveals the observed biological scaling is not a product of chemistry alone, but instead emerges due to the particular structure of selected reactions commonly participating in living processes. I perform distinguishability tests across properties of individual and ecosystem-level biochemical networks to determine whether or not they share common structure, indicative of common generative mechanisms across levels. My results indicate there is no sharp transition in the organization of biochemistry across distinct levels of the biological hierarchy—a result that holds across different network projections.
Finally, I leverage these large biochemical datasets, in conjunction with planetary observations and computational tools, to provide a methodological foundation for the quantitative assessment of biology’s viability amongst other geospheres. Investigating a case study of alkaliphilic prokaryotes in the context of Enceladus, I find that the chemical compounds observed on Enceladus thus far would be insufficient to allow even these extremophiles to produce the compounds necessary to sustain a viable metabolism. The environmental precursors required by these organisms provides a reference for the compounds which should be prioritized for detection in future planetary exploration missions. The results of this framework have further consequences in the context of planetary protection, and hint that forward contamination may prove infeasible without meticulous intent. Taken together these results point to a deeper level of organization in biochemical networks than what has been understood so far, and suggests the existence of common organizing principles operating across different levels of biology and planetary chemistry.
Finally, I leverage these large biochemical datasets, in conjunction with planetary observations and computational tools, to provide a methodological foundation for the quantitative assessment of biology’s viability amongst other geospheres. Investigating a case study of alkaliphilic prokaryotes in the context of Enceladus, I find that the chemical compounds observed on Enceladus thus far would be insufficient to allow even these extremophiles to produce the compounds necessary to sustain a viable metabolism. The environmental precursors required by these organisms provides a reference for the compounds which should be prioritized for detection in future planetary exploration missions. The results of this framework have further consequences in the context of planetary protection, and hint that forward contamination may prove infeasible without meticulous intent. Taken together these results point to a deeper level of organization in biochemical networks than what has been understood so far, and suggests the existence of common organizing principles operating across different levels of biology and planetary chemistry.
ContributorsSmith, Harrison Brodsky (Author) / Walker, Sara I (Thesis advisor) / Anbar, Ariel D (Committee member) / Line, Michael R (Committee member) / Okie, Jordan G. (Committee member) / Romaniello, Stephen J. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Previous workers hypothesized that lunar Localized Pyroclastic Deposits (LPDs) represent products of vulcanian-style eruptions, since some have low proportions of juvenile material. The objective of the first study is to determine how juvenile composition, calculated using deposit and vent volumes, varies among LPDs. I used Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (LROC NAC) digital terrain models (DTMs) to generate models of pre-eruption surfaces for 23 LPDs and subtracted them from the NAC DTMs to calculate deposit and vent volumes. Results show that LPDs have a wide range of juvenile compositions and thinning profiles, and that there is a positive relationship between juvenile material proportion and deposit size. These findings indicate there is greater diversity among LPDs than previously understood, and that a simple vulcanian eruption model may only apply to the smallest deposits.
There is consensus that martian outflow channels were formed by catastrophic flooding events, yet many of these channels exhibit lava flow features issuing from the same source as the eroded channels, leading some authors to suggest that lava may have served as their sole agent of erosion. This debate is addressed in two studies that use Context Camera images for photogeologic analysis, geomorphic mapping, and cratering statistics: (1) A study of Mangala Valles showing that it underwent at least two episodes of fluvial activity and at least three episodes of volcanic activity during the Late Amazonian, consistent with alternating episodes of flooding and volcanism. (2) A study of Maja Valles finds that it is thinly draped in lava flows sourced from Lunae Planum to the west, rendering it analogous to the lava-coated Elysium outflow systems. However, the source of eroded channels in Maja Valles is not the source of the its lava flows, which instead issue from south Lunae Planum. The failure of these lava flows to generate any major channels along their path suggests that the channels of Maja Valles are not lava-eroded.
Finally, I describe a method of locating sharp edges in out-of-focus images for application to automated trajectory control systems that use images from fixed-focus cameras to determine proximity to a target.
There is consensus that martian outflow channels were formed by catastrophic flooding events, yet many of these channels exhibit lava flow features issuing from the same source as the eroded channels, leading some authors to suggest that lava may have served as their sole agent of erosion. This debate is addressed in two studies that use Context Camera images for photogeologic analysis, geomorphic mapping, and cratering statistics: (1) A study of Mangala Valles showing that it underwent at least two episodes of fluvial activity and at least three episodes of volcanic activity during the Late Amazonian, consistent with alternating episodes of flooding and volcanism. (2) A study of Maja Valles finds that it is thinly draped in lava flows sourced from Lunae Planum to the west, rendering it analogous to the lava-coated Elysium outflow systems. However, the source of eroded channels in Maja Valles is not the source of the its lava flows, which instead issue from south Lunae Planum. The failure of these lava flows to generate any major channels along their path suggests that the channels of Maja Valles are not lava-eroded.
Finally, I describe a method of locating sharp edges in out-of-focus images for application to automated trajectory control systems that use images from fixed-focus cameras to determine proximity to a target.
ContributorsKeske, Amber (Author) / Christensen, Philip R. (Thesis advisor) / Robinson, Mark S (Committee member) / Clarke, Amanda B (Committee member) / Whipple, Kelin X (Committee member) / Bell, James F. (Committee member) / Arizona State University (Publisher)
Created2018
Description
Both volcanic and tectonic landforms are surface expressions of the inner workings of a planet. On Earth, volcanism and crustal deformation are primarily surface expressions of plate tectonics. In contrast, the lunar crust has been deformed by solely endogenic processes following large impact events.The Procellarum KREEP (potassium (K), rare earth elements (REE), and phosphorus (P)) Terrane (PKT) is a thermally and chemically distinct geologic province on the Moon. Despite the wealth of remote sensing data, the origin and evolution of the PKT is poorly understood. This study focuses on floor-fractured craters and silicic magma genesis within the PKT.
First, I present a detailed study of floor-fractured craters, including morphometric measurements using topographic datasets from the Lunar Reconnaissance Orbiter Camera (LROC), variations in temporal heat flow, lithospheric rheology and the locations of floor-fractured craters relative to impact basins. The overarching conclusion is viscous relaxation and magmatic intrusion are not necessarily mutually exclusive, as has been argued in earlier studies. This work also provides new evidence for the existence of the putative Procellarum basin.
Next, with rhyolite-MELTS modeling, I demonstrate that fractional crystallization of KREEP basalt magmas is a plausible mechanism for generating silicic melts. The results suggest that following crystallization, the composition of the remaining ~30 wt.% liquids are consistent with returned lunar silicic fragments.
Finally, using crater counting methods I tested the stratigraphic relationship between the floor-fractured crater, Hansteen, and the silicic volcanic landform, Mons Hansteen. Absolute model ages (AMAs) suggest that the basalts on the floor of Hansteen crater formed contemporaneously with Mons Hansteen, implying that bimodal volcanism might have played a role in silicic magma genesis on the Moon.
ContributorsRavi, Srinidhi (Author) / Robinson, Mark S (Thesis advisor) / Till, Christy B (Committee member) / Watters, Thomas R (Committee member) / Whipple, Kelin X (Committee member) / O'Rourke, Joseph G (Committee member) / Arizona State University (Publisher)
Created2023
Description
Archean oxidative weathering reactions were likely important O2 sinks that delayed the oxygenation of Earth’s atmosphere, as well as sources of bio-essential trace metals such as Mo to the biosphere. However, the rates of these reactions are difficult to quantify experimentally at relevantly low concentrations of O2. With newly developed O2 sensors, weathering experiments were conducted to measure the rate of sulfide oxidation at Archean levels of O2, a level three orders of magnitude lower than previous experiments. The rate laws produced, combined with weathering models, indicate that crustal sulfide oxidation by O2 was possible even in a low O2 Archean atmosphere.
Given the experimental results, it is expected that crustal delivery of bio-essential trace metals (such as Mo) from sulfide weathering was active even prior to the oxygenation of Earth’s atmosphere. Mo is a key metal for biological N2 fixation and its ancient use is evidenced by N isotopes in ancient sedimentary rocks. However, it is typically thought that Mo was too low to be effectively bioavailable early in Earth’s history, given the low abundances of Mo found in ancient sediments. To reconcile these observations, a computational model was built that leverages isotopic constraints to calculate the range of seawater concentrations possible in ancient oceans. Under several scenarios, bioavailable concentrations of seawater Mo were attainable and compatible with the geologic record. These results imply that Mo may not have been limiting for early metabolisms.
Titanium (Ti) isotopes were recently proposed to trace the evolution of the ancient continental crust, and have the potential to trace the distribution of other trace metals during magmatic differentiation. However, significant work remains to understand fully Ti isotope fractionation during crust formation. To calibrate this proxy, I carried out the first direct measurement of mineral-melt fractionation factors for Ti isotopes in Kilauea Iki lava lake and built a multi-variate fractionation law for Ti isotopes during magmatic differentiation. This study allows more accurate forward-modeling of isotope fractionation during crust differentiation, which can now be paired with weathering models and ocean mass balance to further reconstruct the composition of Earth’s early continental crust, atmosphere, and oceans.
Given the experimental results, it is expected that crustal delivery of bio-essential trace metals (such as Mo) from sulfide weathering was active even prior to the oxygenation of Earth’s atmosphere. Mo is a key metal for biological N2 fixation and its ancient use is evidenced by N isotopes in ancient sedimentary rocks. However, it is typically thought that Mo was too low to be effectively bioavailable early in Earth’s history, given the low abundances of Mo found in ancient sediments. To reconcile these observations, a computational model was built that leverages isotopic constraints to calculate the range of seawater concentrations possible in ancient oceans. Under several scenarios, bioavailable concentrations of seawater Mo were attainable and compatible with the geologic record. These results imply that Mo may not have been limiting for early metabolisms.
Titanium (Ti) isotopes were recently proposed to trace the evolution of the ancient continental crust, and have the potential to trace the distribution of other trace metals during magmatic differentiation. However, significant work remains to understand fully Ti isotope fractionation during crust formation. To calibrate this proxy, I carried out the first direct measurement of mineral-melt fractionation factors for Ti isotopes in Kilauea Iki lava lake and built a multi-variate fractionation law for Ti isotopes during magmatic differentiation. This study allows more accurate forward-modeling of isotope fractionation during crust differentiation, which can now be paired with weathering models and ocean mass balance to further reconstruct the composition of Earth’s early continental crust, atmosphere, and oceans.
ContributorsJohnson, Aleisha (Author) / Anbar, Ariel D. (Thesis advisor) / Till, Christy (Committee member) / Hartnett, Hilairy (Committee member) / Romaniello, Stephen J. (Committee member) / Sharp, Thomas (Committee member) / Arizona State University (Publisher)
Created2020