Search

Spontaneous reversal of magnetization in rocks and its apparent dependence on the oxidation state of the Fe-Ti oxide minerals is highly significant in view of the overwhelming evidence that exists in support of field reversal. An attempt has been made in this study to classify these "states" of oxidation in terms of characteristic mineral assemblages. The series which has evolved is a texturally progressive series of high temperature origin. The series is supported by known thermal equilibria, by whole rock chemical analysis, and by experimental oxidation of titanomagnetite, ilmenite and olivine. The magnetic and associated mineralogy is discussed in detail and a correlation study with some magnetic properties has been made in controlled sampling of traverses across fourteen single lavas from Iceland. These results show that the degree of oxidation is highly variable throughout a lava and that the maximum degree of oxidation is towards the central part of a lava. Several factors suggest that oxidation takes place deuterically at the time of cooling. The magnetic and petrological implications of this zonation is discussed. In spite of the fact that mixed magnetic polarities and a self reversal mechanism are absent, within single units, a strong positive correlation is nevertheless demonstrated between samples which are highly oxidized and samples which are reversely magnetized. The correlation is well defined but is not fully understood.

Geomagnetic excursions, brief deviations in geomagnetic field behaviour from that expected during 'normal' secular variation, remain some of the most enigmatic features of geomagnetic field behaviour. This thesis presents high-resolution records of geomagnetic excursions recorded at the Blake-Bahama Outer Ridge in the Western North Atlantic. The highest resolution record yet of the Blake geomagnetic excursion (~125 ka) is measured in three cores from Ocean Drilling Program Site 1062 (ODP Leg 172). These cores have sufficiently high sedimentation rates (>10 cm ka-1) to allow detailed reconstruction of the field behaviour at these sites during the excursions. Previous reconstructions of geomagnetic field behaviour during excursions from marine cores have been limited by low-resolution age models. This thesis discusses a new approach, whereby measurements of excess 230Th (230Thxs) are used to constrain relative variations in sedimentation rate. Modifications are suggested to the methods previously used to calculate the concentration of 230Thxs and a new MATLAB® program is developed and described that allows rapid and flexible calculation of 230Thxs. Using this new approach, the duration (6.5±1.3 kyr) and age (129-122 ka) of the Blake excursion are accurately constrained. A palaeomagnetic study is also conducted on two ODP Sites, 1061 and 1062 on the Blake-Bahama Outer Ridge to obtain a high-resolution record of the Laschamp geomagnetic excursion (~41 ka). The Blake excursion is found to be of 'long' duration (6.5±1.3 kyr) whilst the Laschamp excursion is relatively short (<400 years) showing that excursions do not have a characteristic duration, linked to the conductivity of the inner core, but instead occupy a continuous range of durations. The records of both the Blake excursion and the Laschamp excursion from the Blake-Bahama Ridge sites also show rapid transitions to excursional geomagnetic pole positions (less than 500 years), much faster than often quoted for full geomagnetic reversals. Based on current estimates for reversal durations, this would imply that excursions and reversals are controlled by different processes.

In this thesis, I use multiple techniques to investigate the active faulting and deformation of the Altay Mountains, Western Mongolia. The Altay are an intracontinental transpressional mountain range, which are deforming in the far-field of the India-Asia collision. An anastomosing network of dextral faults strikes NNW-SSE, and accommodates NE-SW oriented shortening by rotating anticlockwise about vertical axes. I begin by characterising the Altay faults, and add to what is already known about their surface expression with new observations of active faulting and three previously undescribed ancient earthquake ruptures. I use 10Be cosmogenic dating and uranium-series dating on pedogenic carbonate to estimate the average Quaternary rate of slip for two of the major fault zones in the Altay. The slip rate on the Ölgiy fault is constrained to 0.3-2.1 mm/yr-1. Results from the Hovd fault are ambiguous, demonstrating the complications encountered with application of Quaternary dating techniques. I measure palaeomagnetic directions from Cretaceous to Pliocene-aged sediments in the eastern Altay to constrain the degree of anticlockwise rotation. Results from thermal demagnetisation of specimens indicate that the eastern Altay has not undergone significant rotation, in contrast with previous studies from the Siberian Altay that reveal almost 40 degrees of anticlockwise rotation. This suggests that the eastern-most Altay fault is too young to have experienced significant rotation, or is kinematically different from the Siberian Altay. I apply apatite fission track (AFT) dating and track length modeling to the central Altay. Results from AFT dating show rapid cooling in the late Cretaceous due to the distal assembly of Central Asia, suggesting that there was pre-existing topography at the start of the Late Cenozoic phase of deformation, the timing of which is constrained to have initiated at least 20 Myr ago. My work demonstrates that combining results from techniques that cover a variety of time scales quantifies the evolution of active faulting and deformation in the region.

Magnetic minerals are abundant within our Earth's crust and can retain, through one of a number of processes, a remanent magnetisation induced by the Earth's magnetic field. Analyses of palaeomagnetic samples have been used for the past fifty years to improve our understanding of many of the Earth's major processes. Recent studies utilising newly developed imaging techniques, namely holographic transmission electron microscopy, have for the first time allowed direct observations of the magnetic structure in palaeomagnetic samples on a nanoscale. It is commonly observed that igneous rocks contain closely packed magnetic lamellae with a non-magnetic matrix, a result of the chemical process of exsolution. However, the results of current micromagnetic models, generated to predict the magnetic structure within such samples, are not in agreement with these direct observations. The results do, however, show strong similarities to the direct observations. The discrepancies between the direct observations and micromagnetic models indicate a lack of understanding of the magnetic interactions within such samples. To examine this two distinct hypotheses have been tested. Firstly, the geometry of the system has been altered to examine the effect of this on the magnetic structure of the grains. Secondly, a multiphase model has been produced. This multiphase model allows the simulation of more complicated systems that include more than one magnetic material in direct contact. This multiphase model has allowed us to examine the effect of varying the exchange in these multiphase structures and its effect on the modelled magnetic structure. Further, this multiphase model has allowed us to examine theoretical systems involving combinations of magnetic materials commonly found in palaeomagnetic samples.

If a rock is to retain a geologically meaningful magnetic record of its history, it is essential that it contains magnetic minerals which are capable of carrying stable magnetic remanence. Of the natural occurring magnetic minerals, magnetite is the most important because of its abundance and strong magnetic signature. The stability, i.e., the resistance to demagnetisation or reorientation, of magnetic remanence is related to grain size; in smaller grains the magnetic moments align to have single domain (SD) structures, in larger grains complex magnetic patterns are formed (multidomain (MD)). “Classical” domain theory predicts that SD remanence is stable, whilst MD remanence is not. However experimental evidence has shown that both SD and MD grains can have stable remanences. In this thesis the origin of stable MD remanence is examined. There are two opposing theories; one suggests that the stability is due to independent SD-like structures, the other postulates that the stability is due to metastable MD structure. A series of experiments were designed to examine the stability using a selection of characterised synthetic and natural samples. Low-stress hydrothermal recrystallised samples where grown for this study. For the first time, the stability of thermoremanence induced in hydrothermal crystals to cooling was examined. The results agree with previous observations for crushed and natural magnetites, and support kinematic models. The behaviour of SIRM and thermoremanences in MD magnetite to low-temperature cooling to below the crystallographic Verwey transition at 120-124 K (Tv) and the cubic magnetocrystalline anisotropy isotropic point (Tk) at 130 K was investigated. On cooling through Tv, SIRM was observed to decrease and demagnetise, however thermoremanence was found to display a large increase in the magnetisation at Tv, which was partially re- versible on warming. The size of the anomaly is shown to be dependent on the temperature at which the thermoremanence is acquired, internal stress and grain size. The anomaly is attributed to the large increase in the magnetocrystalline anisotropy which occurs on cooling through Tv . It is postulated that low-temperature cycling demagnetisation is due to kinematic processes which occur on cooling between room temperature and Tk. Characterisation of low-temperature treated remanence and partially alternating field demagnetised remanence, suggest that the stable remanence is multidomain. Low-temperature cooling of remanence in single sub-micron crystals was simulated using micromagnetic models. The models predict the observed anomaly for thermoremanence on cooling through Tv, and also the relative behaviour of SIRM and thermoremanence. The single domain threshold was calculated for the low-temperature phase of magnetite, and was found to be 0.14 microns, compared to 0.07 microns at room temperature.

This dissertation investigates innovative applications of high-resolution magnetic imaging methods to tackle fundamental inquiries in lunar paleomagnetism, paleoclimatology, and environmental science. Through the utilization of cutting-edge imaging technologies, this research introduces advancements in the recently developed magnetometer, the Quantum Diamond Microscope (QDM), and explores techniques for its application. Moreover, it explores enhancements in magnetic sensitivity and novel avenues for leveraging these technologies to deepen our comprehension of rock magnetism in both terrestrial and lunar contexts. The first chapter of this dissertation centers on the development and advancements of the Quantum Diamond Microscope (QDM). It provides an in-depth exploration into the principles underlying the functionality of the QDM, elucidating its operational mechanisms, and detailing its first earth science research applications. Additionally, the chapter delves into recent upgrades aimed at enhancing the QDM's magnetic sensitivity, thus expanding its capabilities for high-resolution imaging and analysis of magnetic materials. Through this investigation, the dissertation aims to contribute to the broader understanding of state-of-the-art imaging technologies and their potential for transformative impacts in various scientific disciplines. The second chapter of the dissertation delves into the realm of paleomagnetic imaging, exploring new avenues for characterizing the magnetic properties of lunar glass spherules. High-resolution paleomagnetic imaging techniques, including alternating field demagnetization, rock magnetic analysis, and magnetic microscopy, are utilized to investigate magnetic mineralogy, magnetic fabric, and paleomagnetic signals preserved in lunar glasses collected during the Apollo 15 mission. We find two primary categories of magnetic signal, one of which has never been explored before in this capacity. The application of these techniques has the potential to shed light on past lunar dynamo magnetic field variations and current space weathering phenomena. The third chapter explores applying the QDM in a paleoclimate and environmental science context by exploring speleothem-based magnetism as a paleoclimate proxy. By using the quantum diamond microscope (QDM) to obtain a sub-annual resolution time series of ferromagnetic content in a Brazilian speleothem from a well-ventilated cave environment covering the period between 1913 and 2016 CE. This high resolution allows us to quantify the correlation between speleothem magnetic properties and an instrumental precipitation record for the first time. We find that ferromagnetic content in the central column displays a modest but significant negative correlation with rainfall (R^2= 0.35; p=0.0027), while magnetism in the speleothem flanks shows a weaker, statistically insignificant relationship. Rock magnetic analyses of the speleothem further reveal ultrafine, pedogenic grains to be the dominant ferromagnetic carriers. Combining QDM and electron microprobe data, we show that these pedogenic grains were likely developed in surface soils and delivered into the cave as part of airborne, 10 to 200 µm silicate-carbonate soil agglomerates. Our results show that speleothem magnetism holds strong potential as a targeted proxy for paleorainfall and demonstrate a method for identifying the mechanism of magnetic enhancement, which sets the necessary foundation for any paleoclimatic interpretations. In summary, this dissertation presents a comprehensive exploration of high-resolution magnetic imaging techniques and their applications across various scientific disciplines. Beginning with the development and advancements of the Quantum Diamond Microscope (QDM), the research delves into its operational principles and recent upgrades aimed at enhancing magnetic sensitivity. The study then transitions into the realm of paleomagnetic imaging, demonstrating novel approaches for characterizing the magnetic properties of lunar glass spherules. Finally, the dissertation explores the application of QDM in paleoclimate and environmental science, showcasing its utility in speleothem-based paleoclimate proxies. Through these investigations, the dissertation contributes to a deeper understanding of rock magnetism, lunar paleomagnetism, and environmental dynamics, highlighting the transformative potential of high-resolution magnetic imaging methods in advancing scientific inquiry and interdisciplinary research.

The igneous and metamorphic rocks which underlie the sedimentary section of an area (colloquially referred to as “basement” rocks) exert substantial influence on the overlying younger rocks. Large structural features are rooted in basement rocks, and additionally the basement usually contains the only available information regarding the pre-sedimentary geological history. Secondary alteration processes in basement rocks can significantly change their mineralogy and mechanical properties. Understanding of geological history and regional structures within a given area therefore requires study of its basement rocks. This dissertation utilizes petrographic, geochemical, structural, and magnetic approaches to study the basement rocks of Oklahoma. New petrographic observations of the Mesoproterozoic Osage Microgranite in northeastern Oklahoma provide evidence of deformation and secondary alteration and suggest a possible extrusive origin for this unit. Geochemical data additionally suggest a subduction-related origin. Study of several cores in northeastern Oklahoma shows that fracturing and hydrothermal alteration are pervasive in the area’s basement rocks, in contrast to common assumptions of intact granite used in modeling studies of induced/triggered seismicity. Magnetic susceptibility measurements of some altered basement rocks and overlying clastic sediments show highly unusual properties, including a strongly negative relationship between susceptibility and the strength of the measuring field. Detailed study shows this is likely due to an unknown magnetic mineral which saturates at very low fields and has a Curie temperature near 85 °C. Paleomagnetic study of the ~1370 Ma Spavinaw Granite yields evidence of remagnetization in the early Cambrian and in the middle Paleozoic. Magnetic fabric data suggests it is either strongly tilted relative to its original emplacement or was emplaced as a dike rather than a horizontal sill. Paleomagnetic data from intermediate and mafic rocks associated with the early Cambrian Glen Mountains Layered Complex in southwestern Oklahoma provide a new constraint on the paleogeography of Laurentia, with implications for various hypotheses relating to early Cambrian geomagnetic behavior. Additionally, some sites show evidence of partial to complete remagnetization in the middle and late Paleozoic.

Earth and Mercury are the only terrestrial planets in our solar system with present-day magnetic dipole fields generated by internal dynamo systems. In contrast, Mars and the Moon show evidence of past dipole fields in the form of crustal magnetic anomalies; to hold measurable magnetizations, crustal materials must have been exposed to an applied field. While the physical principles of magnetic recording are consistent between terrestrial planets, the particular conditions at each planet control the mechanisms by which crustal materials may be magnetized and limit the types of minerals that can retain magnetic remanence. As the suite of magnetic materials used for studies of remanence expands, the need for new methods follows. The integration of rock magnetic techniques with microscopy and chemical analyses enables the reconstruction of increasingly comprehensive narratives of remanence acquisition and alteration, even in materials that are challenging to study using traditional methods. This thesis demonstrates the utility of a materials approach to rock magnetism by applying techniques designed for terrestrial use in a planetary context. The first of two case studies focuses on calcite cave deposits as a means to demonstrate how novel techniques can be used to unlock previously inaccessible archives of magnetic information. Tandem magnetic and microscopic analyses improve our understanding of the rock magnetic properties of weakly magnetic stalagmites and their potential for paleomagnetic research, as well as illuminating the pathways of remanence acquisition in cave systems. The second case study addresses the magnetic anomalies recently detected by the MESSENGER orbiter at Mercury. These anomalies are consistent with remanence acquired in a dipole field. However, in the absence of physical samples, the types of magnetic minerals that could be holding remanence in Mercury’s hot, highly reducing surface environment have not yet been determined. Orbital data is combined with fundamental rock magnetic principles to constrain the magnetic mineralogy of Mercury and to propose mechanisms of magnetization and remagnetization in the lithosphere.

Low-angle normal faults (LANFs) have been mapped in metamorphic core complexes (MCCs) throughout western North America, but dip too shallowly for seismic slip according to Andersonian fault mechanics. Debate over the origin of these structures is split between support for models where normal faults initiate at favorable dips and subsequently rotate to low-angle orientations (e.g. rolling hinge model) and belief that field relationships show that LANFs were active at or near their present orientation. Using paleomagnetic data from pseudotachylyte veins I show conclusively for the first time that LANFs in the South Mountains MCC in Arizona failed seismically at low-angles. Additionally, I detail many of the challenges that I faced using pseudotachylyte in a paleomagnetic study, providing a starting point for future workers seeking to recover remanence directions from similar materials.

Magnetic field intensity is one of Earth's fundamental properties and its temporal behavior has implications in fields ranging from geodynamics to archeology. Thermal remanent magnetization (TRM) has the strongest theoretical basis of all the forms of natural remanent magnetization, and natural and archeological materials have been used to estimate paleointensities for decades. Although founded on sound theory for ideal samples (those that produce linear Arai plots), paleointensity estimation is challenging with non-ideal samples, which are more abundant in nature and widely used in experiments.We examined the behavior of natural samples using both original and laboratory- acquired TRMs during paleointensity experiments and characterized them based on proxies for domain state including curvature, k, and bulk domain stability parameters. We then investigated their capacity to retain a record of the magnetic field. Samples taken from previous experiments were separated into straight and curved groups representing single-domain-like from multi-domain-like remanences, respectively, based on a critical threshold value, k = 0.164.Specimens from the two sets were given a fresh TRM in a 70 μT laboratory field and subjected to an infield-zerofield, zerofield-infield (IZZI)-type paleointensity experiment. Straight specimens recovered the laboratory field with high precision while curved specimens produced more scattered results. However, both sets closely recovered the average laboratory field, which suggests that experiments containing a sufficient number of specimens can avoid large biases in the field estimate.We also found that the dependence of cooling rate on the laboratory TRM was significant in most samples. However, it did not depend on their inferred domain states and should be estimated for all samples whose cooling rates differ from the laboratory field. Our results confirm that while ideally behaved specimens can produce accurate and precise paleofield estimates, non-ideal, or curved, specimens produce more scattered, although unbiased, estimates.

Despite decades of study, the exact cause of the Cretaceous-Paleogene boundary (KPB) mass extinction remains contentious. Hypothesized scenarios center around two main environmental perturbations: voluminous (>10^6 km3) volcanic eruptions from the Deccan Traps in modern-day India, and the large impact recorded by the Chicxulub crater. The impact hypothesis has gained broad support, bolstered by the discoveries of iridium anomalies, shocked quartz, and spherules at the KPB worldwide, which are contemporaneous with the Chicxulub impact structure. However, evidence for protracted extinctions, particularly in non-marine settings, and paleoenvironmental change associated with climatic swings before the KPB, challenge the notion that the impact was the sole cause of the KPB mass extinction. Despite forty years of study, the relative importance of each of these events is unclear, and one key inhibitor is insufficient resolution of existing geochronology.In this dissertation, I present work developing a high-precision global chronologic framework for the KPB that outlines the temporal sequence of biotic changes (both within the terrestrial and marine realms), climatic changes, and proposed perturbations (i.e. impact, volcanic eruptions) using 40Ar/39Ar geochronology and paleomagnetism. This work is focused on two major areas of study: 1) refining the timing and tempo of terrestrial ecosystem change around the KPB, and 2) calibrating the geomagnetic polarity timescale, and particularly the timing and duration of magnetic polarity chron C29r (the KPB falls about halfway into C29r). First I develop a high-precision chronostratigraphic framework for fluvial sediments within the Hell Creek region, in NE Montana, which is one of the best-studied terrestrial KPB sections worldwide. For this work I dated 15 tephra deposits with ± 30 ka precision using 40Ar/39Ar geochronology, ranging in time from ~300 ka before the KPB to 1 Ma after. By tying these results to paleontological records, this work is able to constrain the timing of terrestrial faunal decline and recovery in addition to calibrating late Cretaceous and early Paleocene North American Land Mammal Ages biostratigraphy. To aid in global correlation, I next sought to calibrate the timing and duration of C29r. However, based on discrepancies noticed between a calculated duration for C29r, from new dates collected as part of this dissertation and previously published magnetostratigraphy for the Hell Creek region, and the duration provided within the Geologic Time Scale 2012, it became clear that reliability of sediments from the Hell Creek as paleomagnetic recorders was suspect. To test this claim, a complete characterization of the rock magnetic properties of sediments from the Hell Creek region was undertaken. To aid characterization, a new test to determine the presence of intermediate composition titanohematite (Fe2-yTiyO3; 0.5 ≤ y ≤ 0.7) was developed. Results from rock magnetic characterization show that sediments from the Hell Creek should be reliable paleomagnetic recorders, so long as care is taken to remove goethite (a secondary mineral that previous magnetostratigraphic studies in the Hell Creek did not remove), and to avoid samples that have been heated above ~200ºC. With the knowledge that sediments from the Hell Creek region are reliable magnetic recorders, I collected 14 new magnetostratigraphic sections, and 18 new high-precision 40Ar/39Ar dates which together provide constraints on the timing and duration of chron C29r, at unprecedented precision. This work enables correlation of our record in the Hell Creek to other KPB records around the globe, in addition to providing a test of the Paleocene astrochronologic timescale.

Sheet intrusions provide key pathways for magma transport and storage as it flows through the Earth's crust. Many studies focus on the relationship between the intruding magma and the host rock through which it propagates, however the flow and emplacement processes occurring within the magma are often poorly constrained. Understanding this is vital for understanding the behaviour of active volcanic systems and the development of bodies of economic interest. To address this, I study how magnetic fabrics are preserved in a natural sill and dyke in combination with laboratory experiments using analogue materials to investigate the evolution of intrusion propagation and solidification. The geochemistry and petrology of sills of the Little Minch Sill Complex, Isle of Skye, are well documented, however the physical processes of emplacement, i.e. magma flow and solidification, are relatively understudied. The studied sill was 6 m thick, of crinanite composition and a sheet with evidence of magma fingers. Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM) techniques were combined with petrology, to understand how magnetic fabrics vary across the sill length and thickness. AMS fabrics identified two groupings: Group A at the sill margins showed an initial magma flow aligned with the long-axis of the magma fingers, whereas Group B in the sill interior showed flow reorientation which was inferred to have occurred due to magma finger coalescence. AARM fabrics identified a post-emplacement flow regime, associated with migration of interstitial melt through the solidifying crystal mush. The contrasting fabrics demonstrate that multiple flow regimes were operational within the sill, and that these can be identified using multiple rock magnetism techniques. Within a basaltic dyke from the Skye Dyke Swarm, multiple magnetic fabrics are recorded and originate from contrasting processes. Within the dyke core, magnetic fabrics originate from titanomagnetite, however in margin regions pyrrhotite becomes the dominant source of the fabrics. I identified that within the dyke core a record of lateral magma flow was preserved, however closer to the margins the fabrics were more indicative of magnetite breakdown and growth of pyrrhotite from a sulphide rich hydrothermal fluid which had overprinted any primary flow indicator. There was also variation in fabrics along strike of the dyke, with alteration of the dyke core also evident nearer to branching in dyke strike. This study shows the complexity and variation in magnetic fabrics, how this can vary over short (~13 m) distances and can be affected by post-emplacement alteration. To understand how magnetic fabrics, develop during the propagation of sheet intrusions, a series of laboratory experiments were conducted. In these experiments plaster of Paris (magma analogue) seeded with magnetite particles, a pseudoplastic fluid, was injected into a box filled with flour (host rock analogue), a cohesive granular material. These materials were used to identify the evolution of AMS fabrics across multiple slices of model intrusions. The experimental intrusions formed a range of magma bodies including plutons, dykes, laccoliths and fingers, which indicate a range of processes occurring during initial emplacement and subsequent intrusion growth. AMS analyses of three parallel slices cut perpendicular to the flow axis, identified compressional and shear fabrics closer to the intrusion margins and towards the intrusion leading tips. Magnetic fabrics indicative of flow in the propagation direction were formed closer to the intrusion core and are like those observed in nature, thus demonstrating the potential of laboratory modelling for studying emplacement processes. In combination, these studies of natural intrusions and laboratory experiments investigate the development and evolution of magnetic fabrics across the length and thickness of intrusions. This is important as understanding the evolution of flow during dyke and sill emplacement is vital for determining and improving current emplacement models.

Abstract: Paleomagnetism is a fundamental tool to understand the ancient variations of Earth’s magnetic field through time. Important applications to geochronology and paleography come from interpreting the variations of the planetary magnetic vector. This dissertation explores the different applications of paleomagnetism to uncover important characteristics of the paleointensity magnetic field during the Permo-Triassic boundary and the nature of the apparent polar wander path (APWP) of Siberia, and to create geochronological frameworks for kimberlites in the Siberian platform and for sediments at the Western Canada Sedimentary Basin. Detailed absolute paleointensity measurements from Permo-Triassic sills at the Siberian platform are studied to determine the existence of a low dipole field, which has been previously reported in the area. We found a mean virtual dipolar moment value of 6.01 ± 1.45 × 1022 Am2 which is over 50% higher than the results previously obtained by other authors. Diamondiferous kimberlite pipes are exposed across the north-central part of the Siberian platform. The age of the magmatic activity cannot be clearly determined from isotopic age data – this is the reason why new paleomagnetic poles from four kimberlite pipes are obtained to study their paleomagnetic age. On the basis of a comparison with the Siberian APWP, we estimate the age of the kimberlite magmatism. The acquired paleomagnetic ages span from the Early Silurian to the Middle Late Jurassic. Magnetostratigraphic analysis is used as a dating tool on three deep drilling cores that penetrate Santonian-Campanian strata in southern Alberta, Canada. Chrons 34n and 33r are clearly identified from the studied sections - providing a high-resolution age boundary that creates new age boundaries between adjacent stratigraphic units. In addition, normal polarity zones are observed within C33r, previously described as reverse polarity over its entire length. Siberian APWP contains long unresolved segments; therefore, the nature of the path depends largely on the curve fitting method used. A least square fitting method computed through singular value decomposition is applied to create the path. The method is compared to a smoothing cubic spline fitting and to the most recent version of the Siberian APWP from the literature. For the Mesozoic Era two possible scenarios are explored.

Paleomagnetic data obtained from the Upper Triassic to Lower Jurassic strata of the Moenave Formation, southern Utah and northern Arizona, were used to construct a composite magnetostratigraphy and further refine the position of the base of the Jurassic in the southwest U.S.A. The composite magnetostratigraphy provides a chronostratigraphic framework to tie Triassic-Jurassic sedimentation in the southwest U.S.A to marine strata in the United Kingdom, Turkey, and Italy, and to the Pangean rift history including extrusive igneous rocks, preserved in Morocco, and in the Newark Basin, northeast U.S.A. In addition, paleomagnetic data from the Moenave Formation were used to calculate a pole position for North America for the latest Triassic to earliest Jurassic time. A lesser amount of inclination error, flattening factor of 0.78, is record in Moenave Formation strata compared to observation from coeval Newark Basin strata. The new paleomagnetic pole position for North America, corrected for inclination error and 4° of clockwise Colorado Plateau rotation is located at 62.3° N, 68.0° E (A95 = 7.4°, N = 102). Pole positions from the southwest U.S.A. continue to indicate a westerly pole position for North America at the latest Triassic to earliest Jurassic time. A mid-Pleistocene lake sedimentary record obtained from the Valles Caldera, northern New Mexico was investigated using rock magnetic and paleomagnetic techniques. Lake sediments span three glacial and two interglacial intervals, MIS 14 – 10. Both detrital and diagenetic phases are preserved in sediment throughout the core. Preservation of detrital phases indicates well mixed lake conditions were more common during interglacial intervals. Discrete intervals of diagenetic phases indicate anoxic conditions are more common in sediments deposited during glacial intervals. A series of anoxic intervals are identified in sediment deposited during MIS 12 that are closely related to interstadial events characterized by increased Cyperaceae and Juniper pollen counts and increased mean annual temperatures. Paleomagnetic data are mostly normal polarity consistent with Brunhes normal polarity chron. However, paleomagnetic data combined with relative paleointensity records support the presence of three geomagnetic field phenomena 14±/Calabrian Ridge II at ~536 ka, 11± at ~400 ka, and Levantine at ~360-360 ka.

Quaternary magnetic studies have provided the conceptual framework to bridge magnetic studies into ancient systems. In cases where environmental materials have been subjected to diagenetic alteration two questions come to mind: 1) What part of the magnetic signal is preserved in the rocks; and 2) can the preserved signal be used to infer/identify magnetic patterns that are characteristic of the depositional, post-depositional, and/or diagenetic environment. Analyses of multi-parameter magnetic experiments conducted on upper Mississippian and lower Pennsylvanian continental successions reveal that distinct depositional, pedogenic, and diagenetic magnetic patterns can be separated and identified. Evidence for a primary depositional signal in several of the upper Mississippian lithofacies is identified by a detrital remanence component attributed to source-area-derived magnetite/titanomagnetite. Red and gray vertisols preserve a Mississippian pedogenic signal characterized by magnetic enrichment, depletion, and amalgamation patterns that are associated with the removal and transport of Fe-rich clays as well as vertical mixing by shrink-swell mechanisms. These well-developed vertisols are interpreted to reflect significant hiatuses in sedimentation associated with prolonged exposure on interfluve/floodplain surfaces that may correlative with incised valleys (lowstand surface of erosion). Similarly, in lower Pennsylvanian quartz arenite facies, early siderite cementation zones as well as conglomerate lags with distinctive magnetic characteristics are thought to reflect periods of prolonged exposure and to define unconformities within compound valley fills.

It is a fundamental challenge for geologists to create quantitative estimates of rainfall and temperature in past climates. Yet, records of past climates are integral for understanding the complexities of earth system dynamics. The research presented in this dissertation begins to establish a framework for reconstructing paleoclimates using the magnetic properties of fossilized soils. Magnetic minerals are ubiquitous in soils, and their composition, grain size, and concentration is often directly related to the ambient climatic conditions that were present during soil formation. Using rock magnetic methods, it is possible to sensitively characterize the magnetic mineral assemblages in natural materials - including soils and paleosols. The fundamentals of rock magnetism and many of the common methods used in rock magnetic applications are presented in chapter 2 and chapter 3, respectively. Chapter 4 reviews the physical, chemical, and biological factors that affect magnetic mineral assemblages in soils, the magnetic methods we use to characterize them, and the known relationships between magnetic minerals in soils and climate. A critical component to developing replicable tools for reconstructing paleoclimate is developing analytical and statistical tools that are accessible to the greater community. Chapter 5 introduces a new model, MAX UnMix, that was developed as an open-source, online tool for rock magnetic data processing that is designed to be user-friendly and accessible. Two case studies, on both fossil (Chapter 7) and modern (Chapter 6) soils, are presented and discuss many issues related to applying magnetic paleoprecipitation proxies in deep time. Chapter 7 discusses difficulties in disentangling the effects of pedogenesis, diagenesis, and recent surficial weathering in Paleocene-Eocene (56-55 Ma) paleosols. Chapter 6 explores the relative influence of soil forming factors (vegetation vs. climate) on controlling the pedogenic formation of magnetic minerals in soils developing across the forest-to-prairie ecotone in NW Minnesota. The body of research presented in this dissertation provides many challenges to future workers, while at the same time highlighting that rock magnetism should be a useful tool for researchers interested in deep time paleoclimates moving forward.

Explosive super-eruptions (≥450 km³) are amongst the most catastrophic events at the Earth's surface, with immediate and devastating regional environmental consequences. Recent catastrophic super-eruptions at Yellowstone are well-known, but the previous (Miocene) history of large explosive eruptions from the Yellowstone hotspot is less-well understood, even though some in the central Snake River Plain (cSRP) may have been similar in size, or larger. To test this, local successions of rhyolitic welded ignimbrites in the southern cSRP have been studied to distinguish and characterise individual eruption-units using a combination of fieldwork, whole-rock and mineral chemistry, rock magnetism and geochronology data to correlate them regionally. In the Rogerson Graben, the revised Rogerson Formation comprises five eruption-units, each designated as a member. In the Cassia Hills ~20 km further east, the revised Cassia Formation comprises thirteen eruptionunits, and a new deep drill-hole near Kimberly, reveals three rhyolitic eruption-units. Robust correlations between these sites and to the north of the Snake River Plain have revealed the presence of three new regionally widespread ignimbrite sheets: (1) the Brown’s View Ignimbrite (10.3±0.2 Ma; 2700 km²; 40 km³ DRE); (2) the McMullen Creek Ignimbrite (9.0 ±0.1 Ma; 12,000 km²; 589 km³ DRE); and (3) the Grey’s Landing Ignimbrite (~9.0 Ma; 18,000 km²; 708 km³ DRE).Using standard techniques to calculate eruption magnitudes, two of these record super-eruptions: the McMullen Creek eruption (magnitude 8.4, 1179 km3 DRE) and the Grey’s Landing eruption (magnitude 8.5, 1416 km³ DRE). These represent the largest super-eruptions within the cSRP and are also among the largest eruptions of the entire Snake River-Yellowstone volcanic province. The addition of the three correlations presented here has further reduced the total number of previously inferred eruption-units from 42 to 29. Therefore, mid-Miocene rhyolitic explosive eruptions in the central Snake River Plain were less numerous but significantly larger than previously thought.

This thesis studied 9 sediment cores from the Bohai Sea (JX91-2A and JX91-3B), the Huanghai Sea (JX91-7m and 7G) and the Arabian Sea (cores 1733, 1734a, 1735, 1736 and 1739) through a multi-disciplinary approach including geochemistry, sedimentology, rock magnetism and radiochemistry. The purpose of this study is to retrieve the sedimentary records, characterise and compare the virtually different sedimentation processes in the Chinese and Arabian regions, and to reconstruct regional and trans-continental palaeoenvironmental changes since the Late Pleistocene. The main conclusions drawn from this study concerning A) the China Seas, B) the Arabian Sea and C) palaeoenvironment in the two regions include: A1. The Huanghe River plays a key role in the sedimentation in the Bohai and Huanghai Seas, and its well documented channel switching can be directly correlated with the lithological changes in the sediments; A2. Estuarine turbidity current can be formed in the Bohai Sea in a different way from that in deepwater, owing to the extremely turbid riverwater and highly diluted seawater; but it cannot in the Huanghai Sea; A3. Huanghe estuarine sediment in the Bohai Sea can be linked to the recent soil erosion on the Loess Plateau through geochemical and palaeomagnetic indicators, viz. P, Ti, REE and magnetic susceptibility; B1. Sediments in the Gulf of Oman in the Arabian Sea are generally of aeolian origin, though coarser sands can be found either as saltation population in nearshore cores or as cyclone deposits on the Murray Ridge; B2. Monsoonal variations since the Late Pleistocene in terms of both wind strength and wind direction are responsible for the lithological changes in the Arabian sediments directly, and biogeochemical changes indirectly, through the wind-driven coastal upwelling system in the Arabian Sea.

This study involves the production of arrays of parallelepiped magnetite particles in the size range 0.1 - 1 μm. This was achieved by utilising electron beam lithography techniques which are often employed in the design of semi-conductor devices. These particles are required in order to understand the mechanism of reversal of magnetisation for pseudo-single-domain (PSD) particles important to paleomagnetic studies. The samples used by previous researchers are magnetite powders. In such samples, despite attempts to disperse the particles onto non-magnetic matrix, there is no way of eliminating particle clumping, and magnetostatic interaction. Low temperature magnetic measurements obtained using samples of cubic arrays of magnetite particles shows that the effect of particle clumping is to increase the amount of saturation isothermal remanence (SIRM) lost at the Verwey transition. The dependence of SIRM lost at the Verwey transition on particle size in the PSD size range, is consistent with the vortex domain structure predicted for unconstrained 3-D micromagnetic studies. The results shows that 'true' magnetic memory is a stress related phenomenon. Magnetic properties of cubic arrays of magnetite particles measured at room temperature are not consistent with the mechanism of magnetic reversal of coherent rotation of atomic magnetic moments, but are generally in good agreement with that of vortex nucleation and propagation in general. The method of domain classification using the coercivity ratio often used in rock magnetism, is shown to be not useful in classifying PSD in the submicron size range. Magnetic properties of rectangular parallelepiped magnetite particles are more complex than expected from the simple demagnetisation shape anisotropy contribution.

The Miocene Lost Cabin beds of Cottonwood Valley, Arizona, represent a north-northeasterly fine-grained axial valley basin deposit fed by sediments from the Newberry and Black Mountains to the west and east, respectively. Cottonwood Valley formed within the Colorado River corridor during a period of volcanism and north moving E-W extension spanning the early to middle Miocene. This study uses magnetostratigraphy, rock magnetism, and 40Ar/39Ar dating from detrital sanidine to determine the timing of deposition of the Lost Cabin beds in relation to the arrival of Colorado River sediments. One hundred and seventy samples were used in this study from a total of thirty-nine sites. Magnetite and hematite are identified as predominate carriers of magnetic remanence, with minor contributions from titanomagnetite, titanomaghemite, and pyrrhotite. Rock magnetic measurements were consistent with identifying magnetizations that are held in magnetite and hematite. Normal and reverse polarities yielded a total of three geomagnetic polarity intervals within the Lost Cabin bed sediments. 40Ar/39Ar dating yielded one site with a young sanidine grain that produced an age of 5.49 ± 0.788 Ma. Magnetostratigraphy was correlated to the geomagnetic polarity timescale by using three ash beds with dates that spanned from 5.59 ± 0.05 Ma to 5.35 ± 0.07 Ma. Polarity intervals were identified as Subchrons C3r, and C3n.4n (Thvera), within the Gilbert Chron. Results from this study suggest a post 5.235 Ma arrival date of the Colorado River waters within Cottonwood Valley.

Interpretation of aeromagnetic anomalies to find the subsurface extent and attitudes of multiply deformed stratigraphic units near Roxboro, North Carolina is complicated by effects of regional metamorphism on rock magnetism. Anomaly amplitudes diminish markedly to the WNW near the onset of amphibolite facies. Thus, for similar lithologic mixes in this area, at higher metamorphic grades, magnetic susceptibility contrasts are markedly reduced. Modelling was done to determine the subsurface configuration of a magnetized greenschist facies metasedimentary unit in the faulted core of the Virgilina synclinorium. Magnetic anomalies appear to be caused by the entire fold structure in some locations and by only the upper limbs of the structure in others. Two alternative explanations are proposed: (1) the deeper part of the fold may have been displaced by thrusting, (2) metamorphic grade may increase with depth so that magnetic susceptibility contrasts diminish near the amphibolite facies boundary. The latter explanation is favored because it is consistent with surface data in the region. The study indicates that magnetic modelling has utility in complex metamorphic terrains to determine subsurface structure and subsurface configurations of metamorphic isograds.