The Shallow Bay Formation (Cow Head Group), western Newfoundland, is composed of a series of allocthonous massive limestone conglomerates and autocthonous interbedded limestones and shales. Two faunas recovered from the conglomerates exposed at the Point of Head and Back Cove sections, Cow Head Peninsula are examined herein and are the first Lower Ordovician (Ibexian) trilobites from the Shallow Bay Formation to be comprehensively described. A single boulder recovered from unit 8 on the Point of Head contains a unique olenid-dominated trilobite fauna that is likely earliest Ordovician in age, but a latest Cambrian age cannot be entirely ruled out. The fauna is composed of seven species with the pelturine trilobite Boeckaspis geordii n. sp. dominating the assemblage. A phylogenetic analysis of Boeckaspis and other putatively closely related taxa was conducted herein. The Point of Head assemblage is unique in that it is the only known olenid-dominated fauna from Cambrian-Ordovician boundary sediments in Laurentia and it was recovered from a light grey-brown packstone to grainstone, which is atypical for olenid-dominated faunas. The second fauna consists of specimens recovered from 29 boulders collected by C.H. Kindle and H.B. Whittington from Back Cove and is likely Blackhillsian (upper Ibexian) in age. A total of 73 species from 46 genera representing 20 families were identified from the Back Cove collections. Fifteen species and three genera are new and formally named herein. Phylogenetic relationships of species of Opipeuterella and Apatokephalus respectively were also examined in light of newly described material from Back Cove. An attempt was made to correlate the Back Cove fauna with the Ross/Hintze trilobite-based biostratigraphic zones established in western Laurentia, but this scheme was found to not be directly applicable. The Back Cove data were included in a Q- and R-mode cluster analysis. This is the first analysis to quantitatively examine trilobite biofacies for the upper Ibexian in Laurentia. The Back Cove fauna is representative of a shelf-margin build-up biofacies. Possible earliest occurrences of the Odontopleuridae, Illaenidae, and perhaps the Proetidae or Rorringtoniidae are present in the Back Cove fauna, which lends credence to the hypothesis that the dominant post-Cambrian trilobite groups made their first appearance in shelf-margin build-up environments.

The Dakota Formation (DF) of Iowa (outcrops also in KS, NE, and MN) was deposited along the eastern shore of the Western Interior Seaway during the early Late Cretaceous (112-93.5 Ma). The DF comprises mostly non-marine strata which were deposited in fluvial to estuarine environments. The time interval preserved in this formation marks the early stage of angiosperm evolution, and the macroflora previously described from this formation are predominantly angiospermous. However, biostratigraphic analyses indicate that the palynoflora is dominated by free-sporing palynomorphs. Three localities (one from the lower Nishnabotna Member and two from the upper Woodbury Member) were sampled and eight of the samples were productive. A 300-grain count was conducted for each sample to identify the palynomorphs to a specific morphotype group (free-sporing, gymnosperm-conifer, gymnosperm-other, angiosperm, other, and unidentified). A total of 46 different taxa (genus/species) were also identified. The preservational quality of the samples were also assessed and the preservation does not vary significantly between samples. The morphotype groups, taxonomic identifications, and presence/absence data were used to perform Detrended Correspondence Analyses and k-means and hierarchical cluster analyses in order to test for spatial, temporal, and environmental patterns in vegetation composition. The composition of the palynoflora appears to be primarily driven by differences in the depositional environment, with the highest diversity in taxa occurring in fluvial/estuarine deposits and the lowest diversity in coastal swamp deposits. Additional factors affecting the composition of palynoflora include the preservation of samples and the DF Member, both of which are also strongly correlated with depositional environment.

We conducted EMP and SEM analyses to study the structure, Sr/Ca and Mg/Ca ratios of the Coral Dichocoenia. Both Sr/Ca and Mg/Ca ratios were used to reconstruct the seawater temperature at which the coral grew. The concentrations of Sr and Ca, and Sr/Ca ratio have no significant variations across the alternating narrow-thick bands, but concentrations of Na and Mg, and the Mg/Ca ratio vary significantly across those bands. The uniform distribution of Sr/Ca ratios suggests that this ratio is less sensitive to temperature and biological effects relative to Mg/Ca ratio. Using a Rayleigh-based, multi-element (RBME) coral thermometer, the average temperatures of the thick bands and narrow bands on a Dichocoenia aff. tuberosa longitudinal section were estimated as 25.1 °C with an range between 22.5 °C and 28.3 °C, and 24.9 °C with an range between 21.4 °C and 27.5 °C, respectively. The average temperatures in both thick bands and narrow bands are about 2 °C lower than the current SST level in Costa Rica region. The distinct calculated calcifying fluid Mg/Ca and Sr/Ca ratios of narrow band (Sr/Ca =0.009; Mg/Ca =2.3) and thick band (Sr/Ca =0.010; Mg/Ca =1.2) not only suggests the two types of band are not sharing the same calcifying fluid, but also indicates the two types of bands may utilize distinctive growth mechanisms or may grow in different seasons associated with varying biological effects. The calcifying fluid Mg/Ca and Sr/Ca ratios generated from the thick bands (Sr/Ca=0.010;Mg/Ca=1.2) in coral Dichocoenia afftuberosa (sample 108302) agree with the thick bands in other Dichocoenia corals such as coral Dichocoenia tuberosa (sample 118669), which implies that the thick bands of these corals may share a similar growth mechanism.

Yasur is an active scoria cone volcano in the Siwi Caldera on the island of Tanna, Vanuatu, in the South Pacific. This volcano has been erupting continuously for the last 800 years and is the latest manifestation of episodic volcanic activity in this area dating back to the late Pliocene. Yasur eruptions consist of intermittent Strombolian-style explosions of pyroclastic debris with emissions of volatiles such as SO₂, HCl and HF. Other than CO2 and H2O, the most abundant gas emitted from Yasur is sulfur, and plume monitoring has confirmed the volcano as one of the largest point sources of sulfur on the planet with an average flux of 600-1400 tons/day. Fluorine poses a chronic environmental health risk on Tanna, so understanding long-term exposure rates as well as periodic increases in volcanic intensity will help to better quantify its risk. In this study we gauge compositional variation of magma using fresh pyroclastic bombs collected over a 3-month period from August to November, 2016. Our results suggest long-term broad compositional stability in both the whole-rock and groundmass glass and minerals. Our results show slight variation in volatile phases in both olivine-hosted melt inclusions and groundmass glass over an intensively sampled 3-month period, which suggests that the plumbing beneath Yasur harbors an open-system degassing environment. Volcanic eruptions are usually driven by magma mixing, however, our results show no compositional variation in phenocrysts. We show that Yasur is an excellent example of an inefficiently degassed volcano, and that volcanic activity is controlled by volatile flux. We also use cotectic compositional data to calculate pressure and temperature conditions within the magma chamber and assess fluxes of volatiles from the magma using melt inclusion analyses for S and Cl. Our study places new bounds on the vertical extent of the magma chamber and suggests differentiation from a basaltic trachyandesite at depths of up to 12 km.

The purpose of this study is to constrain the mode and tempo of the processes that generated lavas erupted in 2006 eruption from Augustine Volcano, Alaska. There have been 5 eruptions from Augustine over the last century that ejected andesitic to dacitic lava domes and pyroclastic flows. The short recurrence interval of Augustine, in conjunction with the variety of differentiated magma involved in each eruption makes Augustine an ideal location to study magmatic processes such as magma production, magma mixing, magma differentiation, and shallow degassing occurring over the decadal time-scales in explosive subduction-related volcanoes. Toward this end, 2006 Augustine ejecta were analyzed for abundances of short and long-lived U-series nuclides including 238U, 230Th, 226Ra, and 210Pb as well as the abundances of a complete suite of major and trace elements. Samples from Augustine have nearly constant Th/U rations, but excesses of (230Th) over (238U) that vary more than the analytical error. Based on documentation for basaltic parental magmas (Larsen et al., 2010) and a lack of evidence for garnet fractionation in differentiated magmas, variations in (230Th/232Th) values for Augustine magmas appear to result from mixing melts and crystals, which have average ages as high as 54 Ka. Our most mafic sample (an enclave with 53 wt % SiO2) has (226Ra/230Th) = ~1.2. With increasing concentrations of SiO2, the (226Ra/230Th) values decrease to ~1 at SiO2 ~ 56 wt%, increase to 1.45 at SiO2 ~ 59 wt%, then decrease to ~1 in samples with >61 wt. % SiO2. These data suggest that three magmas mingled and mixed during the 2006 eruption: basaltic andesites with Ra excesses generated by mantle melting; a 59 wt% SiO2 magma with 226Ra excesses generated from incongruent melting of young plutonic materials, and 61-62 wt % SiO2 andesites with relatively long crustal residence times. Excesses of (210Pb) over (226Ra) were measured in the most mafic and silicic samples at Augustine, whereas intermediate samples had either equilibrium (210Pb/226Ra) or small 210Pb deficits. The excesses in the basaltic andesites were likely generated during degassing within a compositional boundary layer. Excesses in high silica samples were likely produced by localized degassing through porous networks of vesicles.

No description available.

The Olympic Mountains, in the cost ranges of northwest Washington, expose a Cenozoic accretionary complex east of the Cascadia Subduction Zone. Accreted material consists of metasedimentary deposits thrust eastward beneath a basaltic terrane (i.e., the basaltic Crescent Formation and the basal Blue Mountain Unit [BMU] turbidite) along a major fault, the Hurricane Ridge Fault (HRF). Recent isotopic dating of zircons from the BMU indicate that it is about 8 my younger than the basalt, implying another major fault may exist east of the HRF, between the BMU and the Crescent Fm. Field observations, data, and samples for microstructural analysis were collected along the Dosewallips River on the eastern side of the mountains beginning just west of the HRF, across the fault and BMU, ending about 4.5 km to the east in Crescent Fm. Evidence for fault-related comminution and frictional melt is present at two locations along the transect: the base of Crescent Fm. and within the Crescent Fm., about 1.6 km from the base. At the contact between the BMU and the Crescent Fm., there is a damage zone that encloses a 4 m wide fault, consisting of an increase then drop in fracture density, progression of comminuted material, and the presence of cataclasite and pseudotachylyte. The structure frequency declines to the east for 0.8 km until our second study site within the Crescent Fm. This outcrop is also notably cut by cataclasite and pseudotachylyte and has a similar increase then drop in fracture density leading to a fault structure, although a fault core has not been identified there. The mineral assemblage in these fault structures includes prehnite, pumpellyite, and epidote, implying that fault deformation occurred at depth along the boundary between the prehnite-pumpellyite and greenschist facies. The fault at the BMU and Crescent Fm. contact, which we name the Ori fault, is a well-developed fault with a mappable damage zone and fault core. This supports isotopic age determined hypothesized thrust fault between the BMU and Crescent Fm. The absence of fault-related deformation between the west and east sites implies two separate fault structures. Overall, evidence from this study suggests primary fault deformation at the contact between the BMU and Crescent Fm. and also within the Crescent Fm. The fault structures documented in this study reveal that along the eastern side of the Olympic Mountains, the Crescent Fm. is more deformed than previously described and that the Siletzia terrane was once seismically active, potentially linked to accretionary processes.

Six major generations of dolomite are present within the Cambrian Langston Formation in the Wellsville Mountains and Bear River Range of northern Utah. Identification of dolomite generations and delineation of their relative sequences are based on normal light petrography, cathodoluminescence, staining, chemistry, inferred burial history, and deformation features. The earliest stage is believed to be Middle to Late Cambrian in age. The presence of dolomite rhombs and dolomitized echinoid fragments and peloids suggests that this stage probably formed under sabkha reflux conditions. Extensive nonferroan, polymodal, nonplanar ("xenotopic") dolomite formed next under confined mixing zone conditions. A succeeding generation of pervasive ferroan, polymodal, nonplanar dolomite formed upon exposure to evolved confined mixing zone waters or fluids derived from basin compaction. Subsequent neomorphism of these two nonplanar stages to nonferroan and ferroan saddle dolomites occurred with increased burial. The final stage of dolomitization is confined to dolomite-filled veins and an orthodolospar probably fanned from fluids associated with Tertiary Basin and Range faulting. Thus, there are at least six major types of dolomite within the Langston Formation. Spatial distribution and intensity of the early-formed dolomite facies, as revealed by fence diagrams, are postulated to be functions of changes in permeability, hydrodynamic dispersion, water chemistry, and concomitant variations in length of the induction ix stages.

The Kasimovian (late Pennsylvanian) to early Roadian (middle Permian) is an interval of Earth history that experienced relatively stable climatic conditions highlighted by significant glaciation, which might represent an analog for current and future climate dynamics. The carbon isotope (δ13C) record during this interval is relatively stable with a few minor but relatively unexplored fluctuations of ~2‰, suggesting stable global OC burial even as peat and/or coal deposits declined at the end of the Permian. This suggests that carbon burial may have increased elsewhere, or changes in the inputs would be required to maintain a constant isotope record. One possibility is that marine OC burial increased to balance the waning peat and/or coal deposits. Enhanced marine OC productivity can possibly lead to increased burial, which would drive a global positive δ13C excursion. For example, the Midland Basin in Texas is characterized by significant Permian hydrocarbon source rocks, which may have affected the global carbon cycle and therefore isotope record. It is possible that there are other substantial marine sinks of OC during this time, but global distributions are not well-constrained. These deposits, however, may have been manifested as organic-rich black shale, or a small but widespread increase of OC globally, which could have accounted for the stability of the carbon isotope record. Resolving the potential mechanisms that may be driving local and global OC burial is imperative for understanding the Earth system feedbacks associated with ancient and potentially future climate perturbations. This research constrains local and potentially global marine redox conditions using a multi-geochemical proxy approach. Total OC contents and isotopes were analyzed to constrain local to global burial, respectively. Iron speciation and δ34Spyr were utilized to constrain local redox conditions – including local anoxic and euxinic (anoxic and sulfidic water-column) conditions and pyrite burial. Redox-sensitive trace metals were measured to interpret local conditions, which are best utilized in combination with Fe speciation, and under certain circumstances can help to decipher basin restriction or global trace metal drawdown due to widespread euxinia. Last, thallium isotopes have been analyzed on anoxic to euxinic samples to determine the global extent of oxic bottom waters and the basin’s connectivity to the open ocean. The combination of these traditional and novel geochemical redox proxies provide new context to interpret the local depositional environment of the Midland Basin. The collected results show that the black shales in the Midland Basin were deposited under low oxygen conditions and at a few points verging on euxinic. The data suggest that eustatic sea levels increased during sediment deposition. Associated with this sea level rise was an increase in bioessential nutrient availability (e.g., trace metals), which led to increased organic carbon drawdown and preservation within the basin. / A Thesis submitted to the Department of Earth, Ocean and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester 2019. / April 8, 2019. / Includes bibliographical references. / Jeremy Owens, Professor Directing Thesis; Seth Young, Committee Member; Yang Wang, Committee Member.

To understand the occurrence and distribution of carbide minerals in ordinary chondrites, thirty meteorites were examined, twenty-eight ordinary chondrites and two iron meteorites. The occurrence of carbide, textures, and chemical compositions were examined in the 7 carbide-bearing meteorites. Two formation methods for carbide have been presented in previous research. These are aqueous alteration and shock heating, and they are examined for validity in this thesis. Additionally, one other formation method for carbide formation through impact and brecciation is put forth and examined. Textural differences between the carbide-magnetite assemblages (CMAs) observed by Krot et al., (1997) and those seen in this study are compared regarding possible evidence for aqueous alteration. Different carbide minerals (haxonite and cohenite) were distinguished using a correction method on linescan data obtained through a scanning election microscope. Cooling rates, formation temperatures, and closure temperatures from carbide associated taenites closely match that of petrographic type 3 material from ordinary chondrites. Carbide is not found in shock melt, and shock blackened areas are less likely to contain carbide. It is unlikely that the heat source that formed carbides exceeded that of petrographic type 3 as too much heat would equilibrate the type 3 material as well as carbide minerals or prevent them from forming.