PhD Degree Culminating Works
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This is a collection of dissertations produced by University of Minnesota Duluth (UMD) doctoral students as a requirement for receiving their PhD degrees from programs based at UMD.
Please note, this collection contains only some of the dissertations produced by UMD doctoral students, and none from after 2011. Additional dissertations, including anything from after 2011, can be found in the University of Minnesota Twin Cities Dissertations and Theses collection.
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Item Development of Archean Lode-Gold and Massive Sulfide Deposit Exploration Models using Geographic Information System Applications: Targeting Mineral Exploration in Northeastern Minnesota from Analysis of Analog Canadian Mining Camps (Volumes I-III)(2001-12) Peterson, Dean MDetailed lode-gold (LG) and volcanogenic massive sulfide (VMS) deposit mineral potential maps have been developed from new mapping and compilation of a 2270 mi2 area of the Late Archean Wawa Subprovince of the Superior Province in northern Minnesota. The mineral potential maps have been developed by the integration of ore deposit models for lode-gold and volcanogenic massive sulfide deposits into an exhaustive geological, geochemical, and geophysical Geographical Information System (GIS) data compilation of the study area. In addition, detailed GIS geological compilations from the three largest lodegold mining camps of the Superior Province of Canada (the Hemlo, Timmins, and Kirkland Lake mining camps) have been completed, and are incorporated in the lode-gold mineral potential model. Methods used to predict mineral potential include both knowledge-driven (LG and VMS models) and data-driven (LG only) analysis of information derived from the new GIS geologic map compilations, and from databases of geochemical and geophysical data for the Minnesota study area. The mineral potential analysis includes the use of fuzzy logic techniques in ranking the importance of specific types of information derived from the ore deposit models. In addition, fuzzy logic techniques have been used in the digital overlay of hundreds of maps portraying specific geologic data, into the final LG and VMS maps showing base- and precious-metal mineral potential of the Minnesota study area.Item Palynological Investigations Related to Archaeological Sites and the Expansion of Wild Rice (Zizania Aquatica L.) in Northeast Minnesota(2001-01) Huber, James KennethFour pollen sequences, from Big Rice, Cloquet, Gegoka, and East Bearskin lakes in northeast Minnesota indicate that postglacial vegetation progressed from tundra to a shrub parkland or forest-tundra to a conifer-hardwood forest to a mixed conifer-hardwood forest and to an uppermost ragweed zone that indicates Euro-American settlement and deforestation beginning about 1890. Based on the abundance of Gramineae pollen in the Big Rice Lake pollen sequence, wild rice (Zizania aquatica) is present in harvestable quantities approximately 1,600 years before its known use in a Laurel occupation at the Big Rice archaeological site. Pollen data from the uppermost sediment of Shannon Lake suggest that Gramineae abundance data may not indicate the presence of substantial wild rice beds in bays and shallows of lakes with large areas of deep open water. The Gramineae pollen profile from Gegoka Lake, which now supports wild rice over most of its surface, indicates that the current presence of wild rice in some lakes may be a relatively recent event. Nonsiliceous algae recovered in conjunction with pollen from Big Rice, Cloquet, Gegoka, and East Bearskin lakes indicate that each lake has undergone cycles of nutrient enrichment. Changing environmental or limnologic competition, or both, as well as competition by macrophytic vegetation, is indicated by oscillations in nonsiliceous algae abundance. Gramineae abundance data and Gramineae pollen grain size distribution data indicate that wild rice was probably present in harvestable quantities in northeast Minnesota in late Paleoindian times and has persisted up to the present. Gramineae pollen grain size distribution data was especially useful in identifying the probable presence of prehistoric wild rice in lakes that have Gramineae pollen profiles with low to moderate abundances. The advantages of using both palynological methods to determine prehistoric wild rice lakes is demonstrated by the Wild Rice Lake Reservoir pollen sequence. Preliminary data indicate a much greater association of Woodland sites and historic wild rice lakes than of Paleoindian/ Archaic sites and wild rice lakes. This suggests that wild rice became a more important food resource in the Woodland Period.Item Late Quaternary Climate History on the Northeast Tibetan Plateau: Multiproxy Investigation of Lake Qinghai Sediments, China(2011-09) Liu, XiujuThe objective of this dissertation is to reconstruct the history of the Asian monsoon and to examine the controls of the climate system on the Tibetan Plateau, using lake sediment cores from Lake Qinghai, China. Lake Qinghai is the largest inland water body in China, situated on the northeastern margin of the Tibetan Plateau, where the climate conditions are mainly controlled by the interaction of the East Asian monsoon and the Westerlies. It lies near the limit of penetration of the Asian summer monsoon, and is thus sensitive to climate changes. Yet the climate history in this region is not fully understood. This dissertation contributes to our understanding of a detailed Holocene and late glacial climate history in western China. A set of Lake Qinghai sediment cores, including a 18.6-m-long drill core (LQDP05-1F), a 3.5-m-long Uwitec sediment core (QH07-1A), and a 0.85-m-long mini-Mackereth core (QH07-1B-1MM), provide a record of climate that extends further back in time than that from any other records for Lake Qinghai. Results from multiple proxies derived from the composite 2007 core (QH07) are internally consistent and reveal a distinct Holocene and Late Pleistocene climate record. Carbonate content and total organic carbon in sediments are interpreted as proxies for the strength of the Asian summer monsoon. During the glacial period (~14,600 to ~20,000 yrs), the summer monsoon intensity remained low and relatively constant, suggesting cool, dry, and relatively stable climatic conditions. The Holocene (~11,500 yrs to present) was a time of enhanced summer monsoon strength and greater variability, indicating relatively wetter but more unstable climatic conditions than those of the Late Pleistocene. The warmest, wettest part of the Holocene occurred from ~9,000 to ~11,500 yrs. The transition between the Holocene and the Late Pleistocene, about 11,500 years ago, was abrupt. A cool Younger Dryas appears to be recorded in the record, but its onset is not as distinct as it is in cave records from Dongge and Sanbao. Evidence of a warm interval correlative with the Bølling–Allerød oscillation is weak in the QH07 record. We propose that changes in the contrast of summer insolation between the continent and the ocean are the primary control on the Asian monsoon system over the glacial/interglacial time scales. Secondary influences may include ice sheet size (albedo) and sea level (distance from moisture source). A climate threshold for arrival of monsoonal rainfall is suggested at the northeastern Tibetan Plateau. Magnetic properties and geochemistry of sediments were determined for an 18.6 m uchannel sample of core LQDP05-1F and several selected discrete samples. These results provide clues to changes in magnetic mineral concentration, grain-size distribution, mineralogy, and geochemical composition, as well as having implications for paleoclimatology. The relative abundances of iron and concentration-dependent magnetic parameters reflect higher concentrations of magnetic minerals during glacial times than the Holocene. Hysteresis measurements of the discrete samples show larger proportions of single domain (SD) minerals relative to multiple domain (MD) particles in Late Pleistocene sediment compared to Holocene sediment, suggesting that the glacial period was dominated by deposition of fine-grained aeolian materials, whereas the Holocene was characterized by increased riverine transport of coarse materials to the lake. Furthermore, greater variability of magnetic parameters and geochemical composition during the Holocene suggests complex and multiple sediment sources. Magnetite has been identified as the primary ferrimagnetic mineral throughout the core, suggesting relatively constant mineralogy. Relatively low magnetite concentration during the Holocene is mainly due to dilution by increased authigenic carbonate that is strongly associated with riverine Ca delivery. The presence of monoclinic pyrrhotite implies reducing depositional environment associated with remineralization of organic matter in the lake. Several lines of evidence suggest the occurrence of greigite, which may indicate relatively dry climate conditions during the glacial period. Results from the elemental composition and magnetic properties of the Lake Qinghai sediments are consistent with records derived from lithological and sedimentological proxies. Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Fluorescence (XRF) scanning techniques were evaluated, using sediments from Lake Qinghai and Lake Malawi (Africa). The results show statistically significant correlations between conventionally measured concentrations of carbonate (%CaCO3), total organic carbon (%TOC), and biogenic silica (%BSi), and absorbance in the corresponding FTIR spectral regions, as well as between conventional measurements and XRF elemental ratios including calcium: titanium (Ca/Ti), incoherent: coherent X-ray scatter intensities (Inc/Coh), and silicon: titanium (Si/Ti). Both FTIR and XRF techniques exhibit great potential to quantitatively assess concentrations of inorganic and organic components of lacustrine sediments. These results provide evidence that climate on the Tibetan Plateau has varied considerably, suggesting a relatively stable, cold, and dry Late Pleistocene along with a weak Asian summer monsoon, versus a relatively unstable, warm, and wet Holocene with a relatively strong summer monsoon. The results also highlight that the Asian monsoon system is driven by changes in the contrast of summer insolation between the continent and the ocean over the glacial/interglacial time scales.Item Trace Element Geochemistry and Geochronology of Early Precambrian Granulite Facies Metamorphic Rocks near Granite Falls in the Minnesota River Valley(1976-12) Wilson, Wendell EugeneThe Sr isotopic composition and the trace element contents of K, Rb, Sr and Ba have been measured for 27 whole-rock samples and 18 mineral separates taken from four rock units in the Minnesota River Valley near Granite Falls, Minnesota. In addition, 4 whole-rock samples and 1 mineral separate were analyzed from samples of amphibolite xenoliths from the Morton-Sacred Heart area southeast of Granite Falls. The isochron ages obtained from the Rb-Sr data are given below in AE (billions of years); ages determined for metamorphic events are given in brackets. The initial ratios (Ri) given refer to the whole-rock isochrons. Garnet-Biotite Gneiss: 3.54 ± .14 [1.81], Ri=.7008 ±.0009 Hornblende-Pyroxene Gneiss (Outer Unit): 3.31 ± .26 [1.78], Ri=.7011 +.0012 Hornblende-Pyroxene Gneiss (Inner Unit): Geochemical disequilibrium precludes dating but suggests an age greater than 3.8. Metagabbro of Himmelberg: 2.68 +.20 [l.80, 2.41], Ri=.7037 +.0001 Amphibolite xenoliths: 3.52 + .15, R.=.7094 +.0013 The trace element distribution patterns suggest the following interpretations. The hornblende-pyroxene gneiss (inner unit) is older than the Montevideo gneiss (which has been previously dated at 3.7 AE); the closest analog is probably a metamorphosed island arc basalt. The hornblende-pyroxene gneiss (outer unit) is probably analogous to a metamorphosed oceanic alkali basalt. The metagabbro is probably analogous to a metamorphosed ocean floor basalt or low-K tholeiite and the age of 2.68 AE is only a minimum. The garnet-biotite gneiss is probably analogous to a metamorphosed graywacke and the age of 3.54 AE is only a minimum. The amphibolite inclusions analyzed are probably analogous to metamorphosed graywackes and are older than the Morton gneiss, which has been previously dated as being 3.55 AE old. The rocks at Granite Falls therefore probably represent a very old (3.7 AE) layered sequence of basaltic rocks and graywackes which was intruded by the Montevideo gneiss 3.7 AE ago. The rock types are analogous to those of the less metamorphosed. Archean greenstone-granite complexes, and are compatible with formation in an ancient island arc tectonic environment. They are probably the remnants of the original continental nucleus of the North American Craton.Item Stratigraphy, Physical Volcanology, and Hydrothermal Alteration of the Footwall Rocks to the Winston Lake Massive Sulfide Deposit, Northwestern Ontario(1993-09) Osterberg, Steven ArvidThe Winston Lake Zn-Cu-Ag massive sulfide deposit is situated above a sequence of metamorphosed Archean calc-alkaline volcanic and volcaniclastic rocks. A detailed mapping, petrographic, and chemical study was undertaken to evaluate the stratigraphic and hydrothermal development of the footwall rocks with regard to depositional environment and spatial controls on metasomatism and mineralization. The footwall rocks are dominated by interlayered successions of metamorphosed volcaniclastic and volcanic rocks that have been extensively intruded and block faulted. Volcaniclastic-sediments were deposited at the base of the stratigraphy where they were interlayered with felsic pyroclastic deposits and/or their turbiditic equivalents. Locally massive sulfide and cherty exhalative beds were deposited. A relatively thick section of interlayered felsic and mafic lava flows were erupted and deposited above the basal volcaniclastic rocks; minor interflow elastic and base metal-poor exhalative sediments accumulated during pauses in mafic volcanism. An upper elastic succession accumulated above the lava flows; basinal volcaniclastic-sediments were deposited and were overlain in part by felsic pyroclastic material that was erupted from a distant, extraneous source. Interlayered mafic lava flows and volcaniclastic rocks cap the footwall stratigraphy and host the Winston Lake deposit and stratigraphically equivalent mineralized occurrences. Facies analysis of lava flows, along with the basinal distribution of volcaniclastic-sediments indicates the Winston Lake footwall stratigraphy developed in a subsiding, subaqueous rift environment. Subsidence was focussed in the rift axis; associated stresses resulted in development of synvolcanic faults within and distal to the rift axis. The dominance of passive eruption products indicates volcanism occurred in relatively deep water beneath the volatile fragmentation depth. Approximately 50% of the footwall stratigraphy has been hydrothermally altered in subconcordant to cross-stratal zones. Interaction of the rocks with metasomatic fluids, followed by isochemical metamorphism has resulted in unusual modal abundances of tremolite/actinolite, biotite, sillimanite, staurolite, anthophyllite/gedrite, chlorite, and quartz relative to metamorphosed primary compositions. Microprobe analyses indicate extreme Fe/Mg enrichment offerromagnesian silicates near the base of the stratigraphy. Mass balance analysis indicates variable enrichment of MgO, Fe2O3T, and K2O, and depletion of CaO and Na2O in altered rocks; TiO2 and Al2O3 were relatively immobile. Overall mass losses, indicative of metasomatic leaching, dominate alteration towards the base of the stratigraphy, whereas both gains and losses occurred in the upper portions of the section. Mg enrichment occurred in stratiform zones through shallow circulation of seawater-based hydrothermal fluids during progressive stratigraphic growth. Minor associated base metal-poor exhalites developed during intermittent pauses in volcanism and sedimentation. Substratiform zones of iron-aluminous-potassic alteration developed as chemically evolved fluids, which originated at depth, interacted with permeable lithologic units through which they buoyantly migrated. The distribution of alteration indicates that chemically-evolved fluids rarely reached the sea floor environment but were generally confined beneath impermeable stratigraphic units. Metalliferous fluids periodically passed through the footwall rocks to the sea floor; no distinct chemical or mineralogical fingerprint of their passage is evident in the rocks, suggesting the metalliferous fluids were similar to chemically-evolved fluids except in metal content. The metalliferous fluids reached the sea floor during at least two stages of stratigraphic growth in which metals were deposited as massive sulfides. The first stage was at the Pick Lake deposit, near the base of the stratigraphy and the second stage was at the Winston Lake deposit at the top of the section. The distribution and composition of alteration and associated base metal sulfide and cherty exhalative occurrences indicates the Winston Lake hydrothermal system was multistaged and involved multiple hydrothermal fluids. Stratigraphic development in a subsiding rift environment spatially controlled the movement of buoyant hydrothermal fluids through permeable lithologic units. Periodic synvolcanic faulting released metalliferous fluids to the sea floor where base metal sulfides were deposited.Item The Petrology and Geochemistry of Archean Volcanics, Western Vermilion District, Northeastern Minnesota(1977-12) Schulz, Klaus JurgenThe Archean Vermilion greenstone belt in northeastern Minnesota was sampled stratigraphically for petrologic and geochemical study. The oldest unit, the Ely Greenstone, is divided into three members: lower, Soudan Iron-formation and upper members. The lower member consists of calc-alkaline pillowed flows of basalt and andesite composition and mafic to felsic tuffs and breccias. The majority of flows and breccia fragments are highly amygdaloidal suggesting shallow deposition. Geochemically, the lower Ely volcanic rocks are similar to recent island-arc calc-alkaline rocks, but have lower Al2o3 and Y contents. A model involving partial melting of amphibolite or garnet amphibolite is proposed for these rocks. The upper Ely member consists largely (>90%) of pillowed to massive tholeiitic basalt. Two distinct chemical types are recognized in the upper Ely; a low TiO2 , low FeOT/MgO, and a high TiO2 high FeOT/MgO group. Very few intermediate compositions have been found. Mass balance calculations using both major and trace elements suggests that these two basalt groups can be related by low pressure fractional crystallization of olivine, plagioclase and pyroxene in the ratios 5:50:45. The apparent abundance of high TiO2 basalts with few intermediate compositions suggests that the tholeiitic magmas fractionated in shallow chambers isolated from the main magma reservoir and were only periodically tapped. The upper basalts are compositionally similar to other Archean basalts and have characteristics in common with ocean floor and island arc tholeiites. The Newton Lake Formation consists of a mafic member and a felsic member. The felsic member consists of calc-alkaline andesites and dacites mainly of fragmental nature which are chemically similar to the lower Ely member calc-alkaline rocks and probably had a similar origin. The mafic member consists of pillowed flows and layered to nonlayered mafic-ultramafic sills. The basalts are distinguished by a wide variety of crystal morphologies and textural types with many having skeletal pyroxene phenocrysts in a spherulitic matrix. A model involving supercooling and changing rates of coolings can account for the range in observed textures. Two major chemical basalt types have been identified. One is characterized by high MgO, varying Al2O3/TiO2 ratios and marked iron enrichment with decreasing Al2o3. These are similar both texturally and compositionally to basaltic komatiites from Australia and Canada. A model involving fractionation in the shallow layered sills is proposed to explain the range of flow compositions. The other basalt group is distinguished by having high NgO, FeOT, CaO and incompatible elements (except Y) with low but constant Al2o3/TiO2 ratios and marked iron enrichment with increasing Al2o3. These basalts share similarities to South African komatiites and to the so called high iron tholeiite suite in Munro Township, Canada. It is suggested, based on textural and chemical characteristics, that these basalts may represent a chemically distinct komatiite type. Petrologic modeling has been largely unsuccessfull in relating the two Newton Lake basalt types. Varying degrees of partial melting of distinct mantle sources seem necessary for these two types. Geologic and petrologic observations suggest that the Vermilion greenstone belt developed through the coalescence of petrologically distinct volcanic centers. Calk-alkaline volcanism appears to have been more or less continuous while basaltic volcanism was intermittent in nature. Mass balance considerations imposed by the geologic and petrologic conclusions require rapid recylcling and replenishment of source material to generate the calc-alkaline volcanic rocks which in turn provided sediment to form the source for the intrusive "granitic" batholiths. In terms of modern analogs, a marginal-basin-island-arc setting seems most compatible with the available data. However, for a better understanding of early crustal evolution, further attention should be directed at determining the unique interaction of tectonic-igneous processes during the Archean.Item Paleoenvironmental Reconstruction Using Laminated Sediments Containing Authigenic Carbonate Minerals: Case Studies from the Great Lakes Region of North America(2004-10) Wittkop, Chad AndrewSediment cores from twelve lakes in lower Michigan and one in southern Ontario were examined in search of annual laminations containing authigenic carbonate minerals. Nine lakes contained some degree of such laminations, but lamination quality and mineral abundance varied considerably due to localized hydro logic effects. The exceptional nature of sediment records from three lakes made them subject to detailed study. All three were supersaturated with respect to calcite in their epilimnetic waters, though carbonate minerals were not detected in surface sediments of the lake with undersaturated hypolimnetic waters. Empirical and model evidence suggests that calcite dissolution in hypolimnetic waters acts as a primary control on sediment calcite abundance. The Holocene varves of Derby Lake, MI, record high- and low-frequency variability in sediment calcite and organic carbon abundance through the Holocene to 8700 calendar years before present. These data exhibit many low-carbonate intervals that generally persist for less than a century in but increase in frequency through the latter part of the record. Some intervals occur in concordance with known Holocene paleoclimatic events, including the globally recognized 8200 cal yr BP event. In sediments that have accumulated since 1890 AD, periods of high carbonate abundance correspond to intervals of below-normal temperature and aboveaverage precipitation. This climatic regime favors limnologic conditions conducive to calcite preservation. Authigenic siderite occurs in isolated intervals of high abundance (up to 80%) in the Holocene varves of Otter Lake, MI. Iron concentrations at present are an order of magnitude lower than required for siderite saturation. The stable-isotopic composition of siderite carbon in high-abundance intervals is enriched several per mille relative to lake inorganic carbon values, which may indicate a dissolved inorganic carbon input from methanogenic sediments. Siderite likely precipitated at or near the lake bottom during periods of enhanced iron supply and incomplete lake circulation. Geochemical indicators of human disturbance occur in sediments of Crawford Lake, Ontario coincident with periods of documented Iroquois and European activity in the watershed. Elemental indicators of landscape erosion and chronology are sensitive enough to detect a three-decade abandonment of an Iroquois village near the turn of the 15th century.Item Paleoenvironmental Variability in the Southeast African Tropics Since the Last Glacial Maximum: Molecular and Isotopic Records from Lake Malawi(2007-04) Castañeda, Isla SaritaThis study utilizes molecular and isotopic techniques to examine past variability in terrestrial and aquatic tropical ecosystems from southeast Africa. Two different timescales are investigated, the past 23 cal ka to examine glacial-interglacial climate variability, and the past 730 years to examine decadal to centennial scale climate variability. Carbon isotope measurements of plant leaf waxes provide a sensitive indicator of aridity and document dry conditions in southeast Africa during the Last Glacial Maximum, the Younger Dryas cold period, and during the Little Ice Age. Peak wet conditions are observed at 13.6 and 5 cal ka, and a shift to wetter conditions is also noted from 1800 AD to the present. Arid conditions in southeast Africa are associated with southward migrations of the mean latitudinal position of the Intertropical Convergence Zone (ITCZ) during Northern Hemisphere cold periods. In contrast to studies that have suggested Holocene climates were relatively stable, the Holocene in southeast Africa was characterized by extreme and abrupt changes in moisture availability, which likely affected human and faunal migrations as well as the development and collapse of human civilizations. In addition to affecting aridity in southeast Africa, southward migrations of the ITCZ also influenced algal productivity in Lake Malawi. Lipids of aquatic algae indicate a major increase in the primary productivity at the Pleistocene/Holocene boundary, which is likely related to a northward migration of the ITCZ over Africa at this time. The Younger Dryas stands out as a major feature in the records of nearly all algal lipids and is marked by an abrupt increase in algal productivity, which can be attributed to increased northerly winds over Lake Malawi. During the past 730 years there is also evidence for changes in algal productivity with decreasing abundances of diatom lipids and increasing abundances of dinoflagellate lipids noted over the past few centuries.Item Calibration and Application of a New Paleotemperature Tool in Lacustrine Systems: TEX86 for Continental Paleoclimate Reconstruction(2005-11) Powers, LindsayThe calibration of the TEX86 (TetraEther indeX of tetraethers with 86 carbon atoms) paleotemperature proxy in lacustrine systems provides a new hydrologically independent paleothermometer, enabling high-resolution lake surface temperature reconstructions from large lakes. TEX86 is based on the relative abundance of cyclopentane containing membrane lipids (glycerol dialkyl glycerol tetraethers or GDGTs) of aquatic Crenarchaeota, a non-thermophilic Archaea. I have developed a calibration for the TEX86 paleotemperature proxy from a climatically diverse suite of globally distributed lacustrine systems (N=15). The results of this calibration show a strong linear relationship between TEX86 values and published mean annual and mean winter lake surface temperature. The TEX86 index appears to work best in large lakes, which are typically the best integrators of regional climate variability. Methanogenic/methanotrophic and hydrothermal Archaea are capable of producing some of the same isoprenoid tetraethers, and in certain cases can confuse the TEX86 signal. I have applied TEXs6 to lacustrine sediments from Lake Malawi, East Africa, to develop high-resolution paleotemperature records from the Last Glacial Maximum (LGM) to the present. I find a ~4 °C overall warming since the LGM, with temperature reversals of more than 2 °C during the Younger Dryas (12.5 ka BP) and in the early Holocene (Fig.1), possibly associated with the 8.2 ka climate event. The onset of warming in the Lake Malawi basin coincides with the BYRD oxygen isotope record of warming in Antarctica. While the range of temperatures observed in this record is not surprising, the timing of post-glacial warming, the thermal response to the YD, and the Holocene history of warming and cooling trends are providing important new insights into tropical climate dynamics on centennial to millennial scales. Additionally I have produced a temperature record from Lake Malawi spanning the past 700 years at ~50 year sampling resolution. This record shows an anti-phase relationship with solar forcing and primary productivity records ii through much of the record. In the past 100 years there is a strong coherence with solar irradiance and atmospheric CO2 concentrations with the temperature record indicating a possible shift in tropical climate response to external forcing.