Paleomagnetism: Continents and Oceans
... Magnetostratigraphy is a valuable tool for both local and global correlations (Opdyke and Channell, 1996;McElhinny and McFadden, 2000;Ogg et al., 2016). Globally correlative magnetostratigraphic patterns within Karoo sedimentary rocks span the late Triassic to early Jurassic Upper Elliot Formation, the biostratigraphic Permian-Triassic boundary in the Beaufort Group, as well as the Permian mid to Upper Ecca Group and its contact interval with the Beaufort Group (Kirschvink and Ward, 1998;De Kock and Kirschvink, 2004;Ward et al., 2005;Lanci et al., 2013;Sciscio et al., 2017;Tohver et al., 2015;Belica et al., 2017). ...
... The results for the ARM version of the Lowrie-Fuller test (Johnson et al., 1975) shows that in all samples, the ARM progressive AF demagnetization curve lies above that of IRM (Fig. 5b). This is indicative of Single-Domain (SD) or Pseudo-Single-Domain (PSD) magnetic grains (McElhinny and McFadden, 2000;Kirschvink et al., 2015). The relative separation between the two curves indicates that magnetic clumping occurred when exposed to the applied field. ...
... Our Fuller test of NRM origin (Fig. 5c) shows NRM values that are about three orders of magnitude less than the corresponding IRM level and two orders of magnitude below the ARM values. This suggests that the NRM signal is a Depositional or post-depositional Remanent Magnetization (DRM or pDRM), rather than a Chemical Remanent Magnetization (CRM) or Thermal Remanent Magnetization (TRM; McElhinny and McFadden, 2000). ...
We present results of rock and paleomagnetic magnetic analyses of a ~671 m-thick continuous vertical drill core(KZF-1) that intersect the lower Ecca Group (early-mid Permian) of the southwestern Karoo Basin, South Africa. Rock magnetic and optic microscopy experiments indicate monoclinic pyrrhotite and single-domain magnetite in the mudstones, shales, and siltstones as carriers of characteristic remanent magnetization (ChRM), which is likely a post-detrital remanent magnetization. Stepwise demagnetization and removal of low-coercivity and thermally less stable magnetizations reveal the preservation of a dual polarity ChRM in 90 samples. These are used to construct a magnetostratigraphic profile for the core that is dominantly reversed polarity with four short normal polarity subchrons. Correlation with published U-Pb SHRIMP and CA TIMS ages and the proposed composite reference section for the Early Permian allows us to propose an Artinskian (281 Ma) to Kungurian (276 Ma) age for the lower Ecca Group rocks. Our magnetostratigraphic profile can be tied in with published profiles from the mid to Upper Ecca Group to produce the first composite profile that spans all of the Ecca Group in the southwestern region of the Karoo Basin.
... (Tauxe et al., 2010). A rock's natural remanent magnetization (NRM) can be measured using a magnetometer or through the process of demagnetization and be compared to Earth's current magnetic field to determine changes in Earth's geological history (McElhinny & McFadden, 2000). Human use of magnetics dates back thousands of years, from the mystification surrounding lodestones, to the utilization of naturally magnetic materials in navigation (Prothero, 2018). ...
... The given data set's results, found through deconstructing the formulas used in paleomagnetism and analyzing the sample data using statistical analysis, revealed that the original site was once located near the coast of modern day Mauritania and Western Sahara during the Late Mesoproterozoic Era (1.105 Gya). When compared to literature surrounding this time, this information reveals that this was the location of southwest Africa during the preliminary formation of Rodinia, a supercontinent (McElhinny & McFadden, 2000). ...
... This process successfully fulfilled its original objective as the values of the magnetic information (location, declination, inclination) were able to be explained through trigonometry and partial derivatives, the derived equations were applied to collect more information on the sample site, a statistical analysis (using R, , and α−95 0 ) was performed to analyze the data, and the role of the calculations was illustrated in Figure 20. These results, which showed the movement of the rock sample over the past billion years, were expected due to extensive evidence supporting continental drift and past data surrounding supercontinents dating back to the Late Mesoproterozoic Era (McElhinny & McFadden, 2000). Although the original objectives were met, these results show how difficult the answer to this problem is -constructing past geographic formations requires many data points, across various locations on Earth to be relevant. ...
Rocks have the ability to preserve magnetic information used in determining past geographic formations. The purpose of this report is to determine the past location of a site from a given data set’s magnetic information and the calculations found through their application to paleomagnetism. Magnetic information includes the rock sample’s location and concentration of trace magnetic particles which were used to find declination and inclination on site. The sample’s paleolatitude and paleolongitude are calculated using trigonometric equations that are derived using calculus. After a statistical analysis, these results are compared to the present day’s magnetic poles to determine the past location of the site. This location, along with the magnetic information, is combined to construct a past geographic formation that existed a billion years ago. This process reveals that the site currently found in southwest Namibia, was located near the coast of modern-day northwest Africa during the late Mesoproterozoic Era within a 95% certainty. When compared to past literature these results show the reliability and role of paleomagnetism, as well as the importance of collaboration across the geosciences.
... This statistical framework is simple to apply and has been the foundation of paleomagnetic statistical analysis for over 60 years (Fisher, 1953;McElhinny & McFadden, 2000;Watson & Irving, 1957). What happens, however, when individual directions employed in the maximum likelihood estimation of , R, and also carry uncertainties? ...
... This allows specimen ChRM uncertainty, which is represented traditionally by a MAD value, to be propagated. Furthermore, an ability to quantify and propagate ChRM uncertainty negates the need for specimen selection/rejection based on arbitrary MAD cutoffs (McElhinny & McFadden, 2000). Rather, specimens with larger uncertainties will be appropriately downweighted, which reduces their influence on the estimated mean direction. ...
... Processing paleomagnetic data in a fully hierarchical fashion from the specimen to pole level is not possible when using VGPs (McElhinny & McFadden, 2000). For example, a site mean direction represented by a Fisher (1953) distribution no longer conforms to a Fisher (1953) distribution after VGP transformation. ...
Estimation of paleomagnetic directions plays a crucial role in magnetostratigaphy, paleogeographic reconstruction, and constraining past geomagnetic field behavior. While analysis and aggregation of paleomagnetic directional data are performed in a hierarchical fashion, the standard statistical framework employed by paleomagnetists does not consider uncertainty propagation through each level of the hierarchy. With this limitation, inferences drawn from paleomagnetic data will be affected by underestimated uncertainties. We provide here an approximate directional uncertainty propagation scheme that applies to Fisher distributions and, thus, to a number of paleomagnetic data processing tasks. The scheme is a straightforward addition to the existing paleomagnetic statistical framework and is demonstrated using case studies to show how uncertainties can be propagated through different stages of the paleomagnetic data processing chain. Furthermore, we discuss situations, such as the transformation into virtual geomagnetic poles, where this simple form of uncertainty propagation cannot be employed because the data are not Fisher distributed.
... I will integrate the results with geochronological data, and review the Permian magnetostratigraphic and paleomagnetic database. McElhinny and McFadden, 2000). AUS = Australia, PAK = Pakistan. ...
... If non-dipole fields are considered, then the assumption that the Geocentric Axial Dipole (GAD) can be applied to Phanerozoic paleomagnetic data is no longer valid (Briden et al., 1971;Torsvik and Van der Voo, 2002;Van der Voo and Torsvik, 2001). Furthermore, global compilations of paleomagnetic data demonstrate that if Eastern Gondwana is excluded from APWP calculations, a better longitudinal fit is seen between the APWPs of Laurussia and Western Gondwana McElhinny and McFadden, 2000;Torsvik et al., 2012;Van der Voo, 1993). ...
... The majority of available Early−Late Permian paleomagnetic results from Eastern Gondwana are from the New England Orogen (NEO) of eastern Australia (Clark, 1994;Irving and Parry, 1963;Klootwijk, 2003;Pisarevsky et al., 2016;Shaanan et al., 2015a). This orogen records several complex structural episodes of orocline formation and significant compression and folding associated with the Permian−Triassic Hunter Bowen Orogeny (McElhinny and McFadden, 2000;McElhinny et al., 2003;Pisarevsky et al., 2016;Van der Voo, 1993). Uncertainty regarding whether the NEO results were consistent with cratonic Gondwana, as well as the poor age control, led to the exclusion of Australian paleomagnetic results from 321−183 Ma in the calculation of the Gondwana APWP . ...
The Early Permian—Triassic time interval includes several major mass extinctions, global tectonic and climatic events, as well as major volcanism. The calibration of these events with the Geologic Time Scale is difficult due to the lack of a robust and globally correlative Permian chronostratigraphic reference frame. This thesis applies the technique of magnetostratigraphy to two foreland basin fills located along the southern Panthalassan margin of Gondwana at ca 290-250 Ma: the Sydney Basin of eastern Australia; and the Karoo Basin of South Africa. The sedimentary rocks contain two key stratigraphic boundaries: the end of the Kiaman Reverse Superchron (ca 265 Ma) and the Permian-Triassic Boundary (ca 252 Ma). The Kiaman Reverse Superchron represents a unique ca 50 Ma geomagnetic interval of reverse polarity, whereas the Permian-Triassic Boundary is associated with the largest mass extinction of the Phanerozoic aeon.
Paleomagnetic and 40Ar-39Ar isotopic data from the Gerringong Volcanics and magnetostratigraphic data from the overlying Narrabeen Group in the southern Sydney Basin provide new terrestrial global chronostratigraphic constraints for Australia. The end of the Kiaman Reverse Superchron is represented by the first appearance of normal polarity at the type section near Kiama, Australia. A corresponding 40Ar-39Ar (plagioclase) age of 265.05 ± 0.46 Ma, and a comprehensive review of reported middle Permian normal polarities, supports an age of ca 265 Ma for the end of the superchron, and the transition to a reversing geodynamo. Comparison between the Gerringong Volcanics and Western Gondwanan paleomagnetic data is consistent with the Pangea A configuration for the Middle Permian. Additionally, six magnetozones (three normal, three reverse) are reported from a ~60 m section in the overlying Narrabeen Group near Clifton, Australia. Comparison with the Geomagnetic Polarity Time Scale and published carbon isotope data gives an approximate location of the Permian-Triassic Boundary in the lower Wombarra Claystone, within a zone of normal polarity ca 200,000 years earlier than the conodont-defined Permian-Triassic Boundary at the GSSP in Meishan, China.
A ~1500 m magnetostratigraphic composite reported from the Ecca Group in the Tanqua Sub-basin (southwest Karoo Basin) is restricted to reverse polarity, placing it within the ca 318 to 265 Ma Kiaman Reverse Superchron, resolving a decade-long controversy over the age of the Ecca Group. A reported U-Pb (zircon) SHRIMP age of 269.5 ± 1.2 Ma from the upper Tierberg Formation is interpreted as a minimum constraint due to a proposed episode of regional Pb-loss or lack of co-eruptive zircon. Additionally, magnetostratigraphic data are reported from a 91 m section of the overlying Permian-Triassic Beaufort Group, and results show a much higher degree of magnetic overprinting. A comparison with published overprint directions and the Gondwana APWP supports a west to east propagation of remagnetization intensity associated with Jurassic emplacement of the Karoo Large Igneous Province.
A global magnetostratigraphic composite of late Kiaman reversals suggests a slow restart mechanism for the transition to the reversing geodynamo at 265.05 ± 0.46 Ma. The paleomagnetic results reported here indicate the potential use of Permian sedimentary rocks for refining the various superchron models involving paleosecular variation, multipolar fields, and the relationship between major geomagnetic field transitions and massive surface volcanism.
... For instance, Likhoele sample LIK29 shows a strong present field component (northeast and up-directed) in addition to a stable (up to 625 °C) R-component that demagnetizes along a great circle path. For palaeomagnetic stability and to establish if the LEF and UEF samples have one true mean for reversed and normal samples, the comparison of the antipode of the mean of the reversed-polarity samples is taken against the mean of the normal polarity samples, in a reversals test (see Supplementary material; McElhinny and McFadden, 2000). It was based on the positive overall reversals tests that the ChRM N-and R-components are interpreted to be primary Late Triassic-Early Jurassic directions for the Elliot Formation in addition to the regionally consistent magnetic polarity patterns. ...
... The overall Elliot Formation (EF) palaeopole position is indicated at latitude 60.5°S. The palaeopole calculated here for the EF is comparable to that of McElhinny and McFadden (2000) for the Early Jurassic of Africa, i.e. EF (this study): 60.5°S, 082.6°E vs. African Early Jurassic: 68°S, 247°E and De Kock (2003) Elliot Formation pole of 68.9°S, 265.6°E. ...
... EF (this study): 60.5°S, 082.6°E vs. African Early Jurassic: 68°S, 247°E and De Kock (2003) Elliot Formation pole of 68.9°S, 265.6°E. The Late Triassic African palaeopole sits at 65.8°S and 259.7°E ( McElhinny and McFadden, 2000). Fig. 3 illustrates the geographical setting of the mean palaeomagnetic pole calculated in this study for the combined Elliot Formation (EF), LEF and UEF. ...
The end-Triassic mass extinction and the transition and explosive diversification of fauna over the Triassic-Jurassic boundary is poorly understood and poorly represented in the rock record of the Southern Hemisphere. This is despite the rich diversity in both body and trace fossils of Triassic-Jurassic age in southern Africa, which is not found in coeval Northern hemisphere localities. We report here the first palaeomagnetic polarity zonation of the Upper Triassic-Lower Jurassic continental red-bed succession (Elliot Formation; Stormberg Group) in southern Africa. The results from 10 partially overlapping sections, with a composite thickness of ~ 280 m, provide a magnetic polarity chronology of the main Karoo Basin in South Africa and Lesotho. Palaeomagnetic analyses reveal that heating samples to between 150 °C and ~ 300 °C removes the secondary, moderately inclined (~ 48°) normal-polarity component of remanent magnetization. This component overlaps with the present-day field and is comparable to the overprint direction expected from Lower Jurassic Karoo dolerite intrusions. In contrast, a likely primary, high unblocking temperature component, of dual polarity, consistently is of steeper inclination (~ 63°). This characteristic remanence passes the reversals test, except where means are based on small sample populations. There are only two resulting polarity zones for the ~ 200 m thick lower Elliot Formation (LEF) with potential for a thin 3rd magnetozone in the uppermost part. The upper Elliot Formation (UEF), in contrast, which was sampled over ~ 80 m thickness, has five polarity zones. The failure of the reversal test for the UEF and combined Elliot Formation (LEF + UEF) indicates that the normal polarity samples may be biased by a younger overprint of either the Jurassic normal polarity of the Karoo Large Igneous Province or present day field. The separate poles calculated for the four sites in the lower and ten sites in the UEF overlap with the Late Triassic and Early to Middle Jurassic Gondwana poles, respectively. The combined Elliot Formation and UEF pole positions are better constrained than the LEF and therefore considered more reliable. Overall the LEF shows considerable overlap with the Late Triassic Apparent Polar Wander Paths (APWP) poles.
... In turn, the reference plate may be reconstructed together with the other plates, to another reference frame. This can be Earth's magnetic field, as determined from paleomagnetic measurements of rocks of known age (McElhinny and McFadden, 2000). ...
... Under ideal circumstances, when rocks are formed, they acquire a remnant magnetization that records a declination and inclination, which record the local Earth magnetic field at that site at that geologic time. The inclination varies with latitude and is the main feature of interest in palaeomagnetic reconstructions (Butler, 1992;McElhinny and McFadden, 2000). ...
Literature survey, knowledge accretion and writing assignment as a prerequisite for doctoral degree. This is a synthesis for all the literature survey results.
... PSV10 includes 2401 sites globally, with the vast majority of sites (93%) falling in the age range 0-5 Ma and most (1753 sites or 73%) being of normal polarity. Iceland has produced many data from 5-10 Ma (and of reverse polarity), but they appear to have been excluded from PSV10 due to the requirements for the application of modern magnetic cleaning methods or, more specifically, that 'principal component analysis' (PCA) was applied to determine specimen directions, i.e. the 'DC-4' or 'DC-5' protocol, using the classification of McElhinny and McFadden (2000). Studies were also excluded from the compilation if 'demagnetization methods were not clearly stated' or they specifically targeted transitional events (Cromwell et al. 2018). ...
... A number of reliability criteria have been suggested for various purposes (e.g. McElhinny and McFadden 2000;Johnson et al. 2008;Cromwell et al. 2018), and we encourage the reader to think about the applicability of these criteria when using Icelandic data. There may be uses for the data in ICEPMAG that have not been envisioned and blanket application of such criteria may hinder research in some direction. ...
Abstract The extensive lava piles of Iceland contain a unique record of geomagnetic field variations spanning the past ~ 16 Ma. Since the 1950s, palaeomagnetic data have been obtained from over 9400 Icelandic lavas. We have compiled all palaeomagnetic data currently available and developed a publicly accessible database (http://www.icepmag.org). The data within the database are primarily palaeodirections, with a relatively smaller number of palaeointensity data (8936 entries contain direction only, 218 intensity only, and 337 both direction and intensity). In addition, the database contains a wide range of metadata, including geochronological information, site details, and laboratory methods. The search interface of the database allows users to search for data using a range of customisable filters (e.g. by publication, geological age, location, laboratory method, palaeomagnetic statistics) and to quickly visualise and download the matching search results. The data within the database have significant potential for understanding long-term palaeomagnetic field variations at high latitude, the behaviour of excursions and reversals, and geological mapping on Iceland.
... The tectonic evolution of the primordial continental crust can be well understood with the study of the Neoarchean dyke swarms (Hunt et al. 1995;French and Heman 2010;Dash et al. 2013;Samal et al. 2019). An integrated palaeomagnetic and geochronological study of the basaltic dykes is a suitable approach to place constraints on the paleogeographic reconstructions and could establish various models for the breakup and assembly of paleo supercontinents (McFadden 1990(McFadden , 1998Butler 1992;Joseph 1994;McElhinny and McFadden 2000;Pradhan et al. 2010;Dash et al. 2013). Various crustal elements from the Indian subcontinent also contribute a significant role in paleogeographic reconstructions for every supercontinent (Rogers and Santosh 2003;Halls et al. 2007;Meert et al. 2010;Pradhan et al. 2010;Meert 2012Meert , 2014Dash et al. 2013;Pivarunas et al. 2018). ...
... The Carboniferous pole path for Gondwana is recognised as historically poorly defined Smith, 1999;McElhinny and McFadden, 2000;Edel et al., 2018). This may reflect among other the widespread presence across Gondwana of pre-latest Carboniferous lacunae and consequent paucity of paleomagnetically-informative stratigraphic successions (e.g. ...
A long and detailed pole path has been defined from ignimbritic successions across the Tamworth Belt forearc basin of a Carboniferous continental arc in the southern New England Orogen (SNEO) of eastern Australia. Stratigraphic successions spanning about 50 myr have been studied paleomagnetically in 400 sites covering 4500 samples. The Carboniferous SNEO path is thought representative for Australia and Gondwana. Its prominent from-south-over-east-to-north loop with a mid Carboniferous apex differs fundamentally from conventional Australian and Gondwanan Carboniferous pole paths featuring from-south-over-west-to-north loops. The eastern loop of the SNEO path is supported by poles from other workers on the Tamworth Belt. The western loop of conventional paths may reflect unrecognised overprinting and alternative polarity interpretation. Mid-to-latest Carboniferous segments of the SNEO path and of a Carboniferous-to-Permian pole path for the northern Variscan massifs of Armorica (AR) are comparable in shape and length, each spanning more than a hundred degrees of arc. Visual matching of the two pole path segments by rotation around an Euler pole, with the SNEO segment taken as representative for Gondwana and representation of the AR segment tentatively extended to Laurussia, locates Armorica off northwestern Gondwana, and with it Laurussia, in a mid-to-latest Carboniferous Pangea-B configuration. The two mid-to-latest-Carboniferous pole path segments are each bounded by prominent mid Carboniferous and latest Carboniferous-to-earliest/early Permian loops, likely reflecting global tectonic events, dating the Pangea-B configuration as extending from the Sudetic phase to the Asturian phase of the Variscan Orogeny, with transformation to Pangea-A starting likely therefrom. Such a Pangean evolution offers new insights in location of a northern Gondwanan Armorican Spur, causes of the late Carboniferous Hercynian Unconformity and early Permian Pangea-wide extension, and drivers for contemporaneous oroclinal deformation of the Ibero-Armorican Arc and the SNEO. Global movements described by the SNEO and AR pole paths suggest causality between a Visean northern excursion of Gondwana that likely disturbed the earth’s moment-of-inertia, a latest Visean-to-Serpukhovian inertial interchange true polar wander (IITPW) event that led to the Serpukhovian biodiversity crisis and latest Visean-Serpukhovian onset of continental glaciation consolidating the Late Paleozoic Ice Age (LPIA), and the Bashkirian start of the Permo-Carboniferous Reverse Superchron (PCRS).
... Matrix calculations 25 based on Euler angles had replaced the traditionally used graphical rotations on stereonets. Currently 26 routine calculations such as transforming from the sample coordinate system to the geographic coordinate 27 system or performing tilt correction are customarily executed by existing software (e.g., Tauxe et al. (VGP) can also be found by rotating on a stereonet, but the calculation has traditionally relied on 30 spherical trigonometry requiring case separation (e.g., McElhinny and McFadden 1999). Representing 31 demagnetization paths on stereonets needs spherical linear interpolation, but the paths are drawn using a 32 linear combination of vectors. ...
A variety of rotation operations are needed in paleomagnetism. These include transformations to the geographic coordinate system, tilt correction, finding virtual geomagnetic poles, and drawing demagnetization paths. Different methods have been used for each rotation operation - graphical manipulations on a stereonet, matrix calculations, and spherical trigonometry - and computer software has been developed based on these methods. Quaternions, which are commonly used in three-dimensional computer graphics, can handle rotations about arbitrary axes and provide descriptions of various rotation operations in paleomagnetism in a unified manner. Conversion from a sample coordinate system to the geographic coordinate system depends on orientation methods that vary by sample type and laboratory. Conventionally, coordinate transformations have been calculated using rotation matrices by Euler angles based on stereonet manipulations, but quaternions can flexibly accommodate samples oriented by different conventions. Tilt correction can be expressed as a single rotation about the strike direction of the formation. Virtual geomagnetic poles can be obtained by two-step rotations using quaternions. Furthermore, spherical linear interpolation for drawing demagnetization paths can be performed using quaternion rotation. Python functions are included for all of the rotation operations discussed in this paper; therefore the readers can incorporate these functions into their own programs to perform rotations using quaternions.
... Each paleomagnetic direction represents a paleomagnetic component determined with the principal component analysis of Kirschvink (1980) that is interpreted by the expert as the characteristic remanent magnetization (ChRM). Each of these components comes with a maximum angular deviation (MAD) value that describes component uncertainty, and MAD values of 15° are typically used as reliability filter (McElhinny & McFadden, 2000), although smaller angles (e.g., 5°, Asefaw et al. (2021)) are also used. The total scatter in a paleomagnetic dataset then consists of within-site and between-site scatter (McElhinny & McFadden, 1997), whereby the uncertainties ...
To determine a paleopole, the paleomagnetic community commonly applies a loosely defined set of quantitative data filters that were established for studies of geomagnetic field behavior. These filters require costly and time-consuming sampling procedures, but whether they improve the precision and influence the position of paleopoles has not yet been systematically analyzed. In this study, we performed a series of experiments on four datasets which consist of 73-125 lava sites with 6-7 samples per lava. The datasets are from different regions and ages, and are large enough to represent paleosecular variation, yet include demonstrably unreliable paleomagnetic directions. We show that the systematic application of data filters based on within-site scatter (a maximum angular deviation filter on individual directions, a k-cutoff, a minimum number of samples per site, and eliminating the farthest outliers per site) cannot identify unreliable directions. We find instead that excluding unreliable directions relies on the subjective interpretation of the expert, highlighting the importance of making all data available following the FAIR principles. In addition, data filters that decrease the number of sites even have an adverse effect; they decrease the precision of the paleopole. Between-site scatter often outweighs within-site scatter, and when collecting paleomagnetic poles, the extra efforts put into collecting multiple samples per site are more effectively spent on collecting more single-sample sites.
... Alteration CRM constitutes one class of magnetic overprint. Overprints can also be acquired without modification of the depositional magnetic mineralogy (McElhinny & McFadden, 1999), by the acquisition of a partial thermoremanent magnetisation (pTRM) during cooling following a heating event, which may be either protracted (uplift and exposure after deep burial) or comparatively rapid (cooling after local heating, for example in the contact zone around an intrusion). Both processes may be active during and in the wake of post-depositional deformation events. ...
Paleomagnetic studies in the Lachlan Orogen have indicated rotation of elements within it, but the evidence for rotation is limited and has significant statistical uncertainty. This study presents a detailed paleomagnetic investigation, assisted by X-ray analysis of magnetic mineralogy of middle Cambrian to lower Silurian sedimentary and igneous rocks in Victoria and New South Wales. Four demagnetisation behaviours (types A, B, C and D) have been recognised. Type A is characterised by a single component, resulting in an approximately linear path over the magnetite unblocking temperature range. Type B specimens exhibit slow progressive demagnetisation over a wide temperature range, with clustering of demagnetised directions above the magnetite Curie temperature, indicating hematite. Behaviour C is also characterised by clustering of directions, but this extends over a wider temperature range. Samples with behaviour D show noisy and non-informative demagnetisation, indicating very low magnetic stability. Hysteresis data confirm that samples with behaviour B and C have high coercivities and remain unsaturated above 300 mT. Mineral liberation analysis of selected samples indicates presence of iron oxides, magnetite, titanomagnetite, botryoidal hematite and iron hydroxides. Only three sites yielded specimens with type A primary magnetisation, with a poorly defined pole from the Dookie Volcanics on the central limb of the orocline, which does match a previous result from the same district. Two paleopoles, of type B and C specimens from the rocks in Tabberabbera Zone and the Rockley Volcanics, plot within the confidence limit of poles defining the late Silurian to Early Devonian Australian apparent polar wander path. These poles match other poles representing Devonian overprints around the margins of the Lachlan Orogen that have been interpreted to be the result of alteration mineralisation produced by fluids driven by tectonic compression during events in the Bindian (420–410 Ma) or early Tabberabberan (405–380 Ma) orogenies.
• KEY POINTS
• Paleomagnetic techniques have been used to test the rotation within the elements of the Lachlan Orocline in southeast Australia.
• Results suggest that the original remanence in the rocks is obscured owing to post-deformation overprint.
• This overprint is widespread in the Lachlan Orogen and is associated with the deformation during Bindian/Tabberabberan orogenic events.
... Afanasyev et al., 2014). A mathematical model (Afanasyev et al., 2014) has shown that depending on olivine fraction in the kimberlite matrix, a cone-shaped intrusion (with a near-surface width of 540 m) undergoes complete serpentinization during a time interval of ~380 to 2000 years, which is generally not sufficient to average out PSV (McElhinny and McFadden, 2000). Laboratory oxidation of synthetic olivine over a course of several days (Hoye and Evans, 1975) resulted in crystallization of magnetite capable of acquiring and retaining a stable CRM, further indicating that magnetite crystallization associated with olivine alteration is a relatively rapid process. ...
A selective compilation of paleomagnetic data from North America indicates that a vast amount of rapid polar motion occurred in Late Jurassic time. The over 30° polar shift that accumulated during a relatively short time interval (∼160-145 Ma) suggests an episode of fast true polar wander (TPW) and was referred to as the Jurassic “monster polar shift” by some workers. However, this rapid TPW event is not supported by paleomagnetic data on a global scale. Here, we scrutinize the Jurassic apparent polar wander path (APWP) by virtue of a new paleomagnetic and ⁴⁰Ar/³⁹Ar geochronology study of Mesozoic coast-parallel dykes exposed in southwest Greenland. Combined with existing geochronological data, our results show that the dykes were emplaced during a prolonged period centered at 147.6 ± 3.4 Ma (2σ). A primary nature of the characteristic remanent magnetization is supported by multiple positive baked contact tests and a reversal test. The paleomagnetic pole calculated from 40 site-mean paleomagnetic directions is located at Plat=69.3°S, Plong=5.0°E (A95=4.6°), or at Plat =73.9°S and Plong= 0.4°E when reconstructed to North America. Our new high-quality paleomagnetic pole and an updated global APWP do not support the fast Jurassic polar shift but instead indicate steady polar motion with moderate rates of about 0.7°/Myr. The new pole effectively reduces the mismatch between the APWPs for Laurentia and Europe. Our critical reassessment of the monster polar shift indicates that it may be an artifact of paleomagnetic and geochronological data that were previously used to argue for its existence.
... The presence of either titanomagnetite or greigite is equally probable; titanomagnetite is generally detrital, whereas greigite is a product of early diagenesis (e.g., Roberts & Weaver, 2005;Ron et al., 2006). Additionally, the results for carbonate concretions show a demagnetization temperature of 400°C, which can be attributed to maghemite and either iron sulfides or titanomagnetite (e.g., Bilardello & Kodama, 2009;Jackson & Bowles, 2014;Kobayashi & Nomura, 1972;Kodama et al., 2010;McElhinny & McFadden, 2000). The results of the IRM analysis also suggest the occurrence of some high-coercivity mineral, likely hematite. ...
Analysis of anisotropy of magnetic susceptibility (AMS) and anhysteretic remanent magnetization (AARM) was conducted on unconventional gas‐bearing Silurian shale rocks from northern Poland. Samples of these rocks were collected from depths greater than 3,500 m from two drill cores. The aim was to investigate magnetic fabrics to verify current models of depositional conditions, current direction, and/or tectonic evolution. To obtain an in‐depth interpretation, rock magnetic studies, microscopic analyses, and graptolite orientation measurements were performed. The results indicate that the magnetic susceptibility is mainly governed by paramagnetic minerals (phyllosilicates) with a small contribution of ferromagnetic minerals, mostly magnetite. Typically, in the studied mudstones, the AMS and AARM fabrics are characterized by strong bedding‐parallel foliation, resulting mostly from compaction. The foliation is much weaker in the associated early‐diagenetic calcareous concretions. Although the mudstones are almost isotropic in the bedding plane, there is a slight tendency for grouping of magnetic lineation axes with an orientation of approximately NNW‐SSE. The corresponding orientation of the AMS lineation is preserved in the concretions, and the same trend also prevails in the preferred orientation of graptolites. Thus, we interpret this orientation to be related to paleocurrents. The observed directions show that during the Wenlock (Silurian) in the studied part of the Baltic Basin, the dominant currents had an orientation of circa NNW‐SSE along the margin of Baltica. Our results confirm that even in such fine‐grained sediments, in which there are no other unequivocal directional sedimentary indicators, paleocurrent directions can be determined by applying AMS and AARM methodology.
... While the concept of seafloor spreading provided a qualitative explanation for the mechanism of continental drift, identifications of marine magnetic anomalies allowed quantitative estimates of displacements between continents through geologic time, paving the way for the development of the modern theory of plate tectonics. The geomagnetic field averaged over a sufficiently long time interval (tens to hundreds of thousands of years) is closely approximated by the field of a geocentric dipole aligned parallel to the Earth's rotation axis (Merrill et al., 1996;McElhinny and McFadden, 2000). The dipolar geometry of the time-averaged field allows paleomagnetists to estimate positions of geographic poles relative to the studied locations by analyzing directions of remanent magnetization, provided that these magnetizations were acquired over a time interval that was sufficiently long to average out short-term deviations of the geomagnetic field from that of a geocentric axial dipole (paleosecular variation). ...
Since the beginning of the 1990s, chronological frameworks of terrestrial records are mostly based on accelerator mass spectrometry (AMS) radiocarbon dating on plant macrofossils. In contrast to the previous use of bulk organic matter, plant macrofossils are inherently more reliable since the source of their carbon is known and should not be composed of heterogeneous material that could be of different ages. Nevertheless, inconsistencies even within the plant macrofossils chronologies are still common. This article aims to review the most common plant macrofossils and to consider their suitability and reliability for ¹⁴C-AMS dating.
... Numbers indicate the more likely age of the pole and the arrows show the APWP inferred from the poles' distribution. Details of poles in Table 1.1 This pole falls far away from the Adma Diorite and Planalto da Serra lavas poles suggesting either a very fast displace- ment between 630 and 615 Ma or a Late Paleozoic remag- netization, when the reference poles for Gondwana fall over Antarctica (e.g., McElhinny and McFadden 2000). Note that in Fig. 1.5, if an opposite polarity is chosen for the Tin Dioulaf sedimentary rocks pole, a fast but nearly rectilinear path can be defined between Tin Dioulaf sedimentary rocks, Planalto da Serra and Adma diorite poles. ...
In the last two decades some consensus has been reached with regard to the assembly of Gondwana being a long and complex process. Reliable paleomagnetic data are essential to determine the paleogeographic and kinematic evolution of each Gondwana-forming block during its assembly as well as to place chronological constraints on such a process. A review of paleomagnetic data from Western Gondwana blocks indicates that the available Ediacaran to Cambrian database is still scarce and uneven for different cratons, despite clear improvement in the quantity and quality of paleomagnetic information in recent decades. The main constraints placed by the available information are as follows: The Río de la Plata and Congo–Sao Francisco cratons were likely already attached by mid-Ediacaran times (c. 575 Ma) and not part of Rodinia. The Arabian-Nubian Shield was part of proto-Gondwana by 550 Ma and probably even earlier. Paleomagnetic constraints are virtually absent for the Kalahari craton. Amazonia and West Africa were probably still part of Rodinia and attached to eastern Laurentia by the Early Ediacaran (c. 615 Ma), suggesting that a large Ediacaran Clymene Ocean existed between Amazonia and the Congo–Sao Francisco–Río de la Plata block. The age of Amazonia amalgamation is poorly constrained by paleomagnetic data as ≥525 Ma. The accretion of Eastern Gondwana blocks probably occurred in the latest Ediacaran-Cambrian times as suggested by the apparent polar wander path of Australia.
... There are other reliable data for the Kara microcontinent: this includes three paleomagnetic poles for 500, 450 and 420 Ma (Metelkin et al., 2000;. It is these data that are placed at the core of our paleotectonic reconstructions along with the extensive paleomagnetic database for the Laurentia, Baltica, Siberia and Gondwana cratons (Pechersky and Didenko, 1995;Torsvik et al., 1996;Smethurst et al., 1998;McElhinny and MacFadden, 2000;Wingate and Giddings, 2000;Pavlov et al., 2002;Torsvik and Van der Voo, 2002;Metelkin et al., 2007Metelkin et al., , 2012Li et al., 2008). The paleogeographic position of the cratons is corrected (within confidence limits for paleopoles) in accordance with the general model and available global reconstructions, including structures of the Arctic sector (Scotese, 1997;Lawver et al., 2002Lawver et al., , 2011Golonka et al., 2003Golonka et al., , 2006Kurenkov et al., 2005;Torsvik, 2002, 2007). ...
In this paper we offer paleoreconstructions
for key structures of the Arctic based on the synthesis of geostructural, geochronological and new paleomagnetic data bearing upon the Late Neoproterozoic and the Paleozoic histories of the Taimyr fold belt and Kara microcontinent. These tectonic features are part of a greater continental mass that we term “Arctida”, with an interesting history of breakup and reassembly that is constrained by our new data and synthesis. In the Central Taimyr accretionary belt fragments of an ancient island arc (960 Ma) have been discovered, and the paleomagnetic pole for the arc approximates the synchronous (950 Ma) pole for the Siberian paleocontinent. For the Kara microcontinent we demonstrate its evolution in the Early Paleozoic and its collision with Siberia in the Late Paleozoic. These data along with an extensive published paleomagnetic database for the cratons of Laurentia, Baltica, Siberia, and Gondwana are the basis for the presented paleotectonic reconstructions. The migrations of those Arctida tectonic blocks that lack paleomagnetic data are reconstructed based on geologic information.
... Furt- hermore, AMS and remanence are related so that if the anisotropy degree is more than 10 % it is likely that the direction of remanence is deflected and does not reflect the ambient field correctly (e.g. McElhinny & McFadden, 2000). Hence, the locally ext- reme anisotropy degree (up to 2.5; Fig. 10a, Table 3) in Satulinmäki apparently affected the remanen- ce and contributed to its overall direction. ...
Palaeomagnetic and anisotropy of magnetic susceptibility (AMS) studies were carried out on a orogenic gold deposit in Jokisivu, located in the western part of the Pirkanmaa Belt in the Svecofennian domain of southern Finland. These results are compared with previous studies obtained from Satulinmäki, belonging to the Forssa Group in the western part of the Häme Belt, southern Finland and also results from the Central Lapland Greenstone Belt in northern Finland. The main aim of the studies was to test the capability of palaeomagnetic and AMS methods to provide relative age constraints about the structurally controlled gold formation processes. Palaeomagnetic data were used to obtain timing for the emplacement of hydrothermal fluids relative to geological structures. AMS was used to delineate the magnetic fabric. Petrophysical measurements and rock magnetic tests were carried out to define the magnetic minerals and their magnetic domain states as they have importance in preservation of the ancient remanent magnetization. Both the magnetic carriers and the remanence directions of the gold deposits in southern Finland deviate from those previously reported from the Central Lapland Greenstone Belt. The main magnetic mineral in the southern Finland deposits is coarse- to fine-grained monoclinic pyrrhotite whereas in the Central Lapland Greenstone Belt the magnetization is carried by fine-grained magnetite/titanomagnetite. The remanence directions in the southern Finland deposits are rotated and deflected so that no Svecofennian directions have been preserved. This, coupled with correlations between the orientation and orientation distribution of the magnetic and the rock fabric elements imply that the hydrothermal fluids were injected pre/syntectonically during the late stages of Svecofennian orogeny. This is contrasting to the Central Lapland Greenstone Belt, where previous works inferred that the well-preserved 1.88–1.84 Ga Svecofennian palaeomagnetic directions indicate that the gold-bearing hydrothermal fluids were emplaced in existing fractures during the late- or post-deformational stage of the orogeny.
... West Avalonia includes parts of Newfoundland and Nova Scotia, whereas East Avalonia includes southern England, Wales, and Ireland. Paleomagnetic data indicate that both the East and West Avalonian terranes belonged to Gondwana or Laurentia during the Paleozoic (Torsvik et al., 1993;McElhinny and McFadden, 1999). The endemic fauna in Avalonia were progressively replaced in the Llandeilo-Ashgill by those with Baltica and Laurentia affinities (Fortey and Cocks, 2003), suggesting increasing proximity to those continents and a widening gap with Gondwana (Nance and Linnemann, 2008). ...
The Mona Complex in Anglesey-Lleyn, Wales formed by Avalonian subduction and accretion from the latest Neoproterozoic to early Paleozoic. It comprises an ophiolite, high-pressure metamorphic rocks, volcaniclastic sediments and mélanges. However, understanding of the tectonic evolution has been held back by the paucity of age constraints, thus only a major geochronological study will be sufficient to decipher the subduction, accretion and exhumation history of this significant Avalonian orogen. We conducted U-Pb dating of detrital zircons in the Monian Supergroup in order to constrain the maximum depositional ages, and undertook K-Ar dating of phengites and U-Pb dating of detrital zircons in the Blueschist unit, the Central Shear Zone (CSZ), and the New Harbour Group to estimate the timing and duration of the metamorphic events, and to constrain the minimum depositional age of the Gwna Group.
The tectonics, geography, and climate of the Cretaceous world was a very different from the modern world. At the start of the Cretaceous, the supercontinent of Pangea had just begun to break apart and only a few small ocean basins separated Laurasia, West Gondwana, and East Gondwana. Unlike the modern world, there were no significant continent-continent collisions during the Cretaceous and the continents were low-lying and easily flooded. The transition from a Pangea-like configuration to a more dispersed continental arrangement had important effects on global sea level and climate. During the Early Cretaceous, as the continents rifted apart, the new continental rifts were transformed into young ocean basins. The oceanic lithosphere in these young ocean basins was thermally elevated, which boosted sea level. Sea level, on average, was ∼70 m higher than the present-day. Sea level was highest during the mid-Cretaceous (90 Ma – 80 Ma), with a subsidiary peak ∼ 120 million years ago (early Aptian). Overall, the Cretaceous was much warmer than the present-day (> 10˚C warmer). These very warm times produced oceanic anoxic events (OAEs) and high temperatures in equatorial regions sometimes made terrestrial and shallow marine ecosystems uninhabitable (temperatures > 40˚C). This is unlike anything we have seen in the last 35 million years and may presage the eventual results of man-made global warming. This mostly stable, hot climate regime endured for nearly 80 million years before dramatically terminating with the Chicxulub bolide impact 66 million years ago. Temperatures plummeted to icehouse levels in the “impact winter” resulting from sunlight-absorbing dust and aerosols. As a consequence of the collapse of the food chain, ∼75% of all species were wiped out (Sepkoski, 1996). The effect of this extinction event on global ecosystems was second only to the great Permo-Triassic Extinction (McGhee et al., 2013).
The Powell Basin is a small oceanic basin bounded by continental blocks that fragmented during break up of Antarctica from South America. This basin bounds the South Orkney Microcontinent to the east, the South Scotia Ridge to the north, and the Antarctic Peninsula to the west. The timing of its opening is poorly constrained due to the low amplitude of the oceanic spreading magnetic anomalies which hampers their identification and interpretation causing large uncertainties in proposed ages that range from the Late Eocene to Early Miocene. This basin has been extensively studied using a variety of geophysical methods including seismic, gravity and magnetics surveys intended to unveil the tectonic domains, the particularities of its magnetic anomalies and the understanding of the thermal regime in this area. Here, we show new magnetic and heat flow data integrated with other geophysical data from international databases (multichannel seismic data, bathymetry and free-air gravity), to analyze the thermal structure of the lithosphere of Powell Basin and the upper mantle dynamics as well as to discuss the probable causes of the abnormally small amplitudes of its magnetic anomalies. Our results show that the low magnetic anomaly amplitudes are not widespread but concentrate in the eastern and southwestern part of the basin. We propose that these small amplitudes result from the thermal dependency of magnetic rocks caused by an asthenospheric branch flow that penetrates the Powell Basin through the northern area.
Sampling strategies used in paleomagnetic studies play a crucial role in dictating the accuracy of our estimates of properties of the ancient geomagnetic field. However, there has been little quantitative analysis of optimal paleomagnetic sampling strategies and the community has instead defaulted to traditional practices that vary between laboratories. In this paper, we quantitatively evaluate the accuracy of alternative paleomagnetic sampling strategies through numerical experiments and an associated analytical framework. Our findings demonstrate a strong correspondence between the accuracy of an estimated paleopole position and the number of sites or independent readings of the time‐varying paleomagnetic field, whereas larger numbers of in‐site samples have a dwindling effect. This remains true even when a large proportion of the sample directions are spurious. This approach can be readily achieved in sedimentary sequences by distributing samples stratigraphically, considering each sample as an individual site. However, where the number of potential independent sites is inherently limited the collection of additional in‐site samples can improve the accuracy of the paleopole estimate (although with diminishing returns with increasing samples per site). Where an estimate of the magnitude of paleosecular variation is sought, multiple in‐site samples should be taken, but the optimal number is dependent on the expected fraction of outliers. The use of filters based on angular distance helps the accuracy of paleopole estimation, but leads to inaccurate estimates of paleosecular variation. We provide both analytical formulas and a series of interactive Jupyter notebooks allowing optimal sampling strategies to be developed from user‐informed expectations.
Various rotation operations are required in paleomagnetism. These include transformations to the geographic coordinate system, tilt correction, and finding virtual geomagnetic poles. Different methods have been used for each rotation operation—graphical manipulation on stereonet, matrix calculation, and spherical trigonometry—and computer software has been developed based on these methods. Quaternions, which are commonly used in three-dimensional computer graphics, can handle rotations about arbitrary axes and provide a unified description of the various rotation operations in paleomagnetism. The conversion from a sample coordinate system to the geographic coordinate system depends on orientation methods that vary by sample type and laboratory. Traditionally, coordinate transformations have been computed using rotation matrices of Euler angles based on stereonet manipulation, but quaternions can flexibly accommodate samples oriented by different conventions. Tilt correction can be expressed as a single rotation around the strike direction of the formation. Virtual geomagnetic poles can be obtained by a single quaternion rotation instead of complicated spherical trigonometry. Python functions are provided for all of the rotation operations discussed in this paper, so the readers can incorporate these functions into their own programs to perform rotations using quaternions.
The Late Roman Antiquity walls of Le Mans in northwest France are one of the most representative and preserved examples of the urban fortifications that developed in the Roman provinces of Gaul and Germany at this period. Because of a lack of reliable chronological data, the construction of the walls was poorly dated, which made unclear its historical context. The main objective of this study was to reassess the date of construction using several methods on a well-preserved sector (sector 11) of the Late Roman Antiquity walls. The dated masonries, thoroughly studied in building archaeology beforehand, are characterized by an alternating of stone and brick courses. Sampling focused on one hand on mortars with four radiocarbon dates (14C) and six single-grain optically stimulated luminescence (SG-OSL) dates, and on the other hand on bricks with two OSL dates (quartz fine grain technique) and one archaeomagnetic date on a set of 104 bricks. The consistency between the dates on the two types of materials discards a possible reuse of the bricks from former Roman buildings. They were produced for the construction of the walls with the presence of several types of bricks likely reflecting a supply from at least two workshops. The dating program in the sector 11 also included 21 14C dates and six SG- OSL on protohistoric structures, Early Empire masonries and large medieval buildings, in order to investigate the evolution of the area over the long-term and to better constrain the chronology of the Late Roman Antiquity walls in Bayesian modelling. The chronological model (Chronomodel software) dates this construction between 301 and 423 CE at 95% of confidence. This date clearly excludes that the Late Roman Antiquity walls were built during the crises of the 3rd century, as previously thought, but rather in the stable political and economic context of the 4th century.
Este livro aborda praticamente todos os temas mais importantes da Oceanografia moderna, com a finalidade de possibilitar a apreciação de um grande número de áreas de atuação desta ciência. Os leitores encontrarão textos muito bem elaborados e ilustrados sobre o início e o desenvolvimento da Ciência Oceanográfica, a composição do interior da Terra, o relevo oceânico, sedimentos no assoalho marinho, Geofísica marinha, a dinâmica de fluidos e a circulação marinha, ondas e marés, características físicas do Oceano Austral, a composição da água do mar, a poluição orgânica e por metais, a bioluminescência marinha, a vida no mar, seus habitantes e ecossistemas, o perfil e a atuação do oceanógrafo, dentre outros. O livro contempla 37 capítulos, totalizando mais de 900 páginas, distribuídos em: Histórico da Oceanografia, Oceanografia Geológica, Oceanografia Física, Oceanografia Química, Oceanografia Biológica, Oceanografia na Prática e o Profissional Oceanógrafo. Esta obra também representa os 75 anos – "Jubileu de Brilhante" do IOUSP comemorado neste ano de 2017. Outro marco importante é a "Década das Nações Unidas de Ciência Oceânica para o Desenvolvimento Sustentável", também conhecida como Década do Oceano, declarada pelas Nações Unidas em 2017, que está em curso entre 2021 e 2030.
The 3-D subseafloor architecture of submarine hydrothermal systems is largely unknown, particularly at arc volcanoes. The alteration of volcanic rocks in these systems produces dramatic changes in their magnetic properties. Here, we present the first comprehensive study of paleomagnetic measurements from oriented samples of hydrothermally altered dacites from Brothers volcano (Kermadec arc), drilled during International Ocean Discovery Program (IODP) Expedition 376. These data have enabled insight into the progressive evolution of magnetic minerals in subseafloor volcanic rocks affected by variable types and degrees of hydrothermal alteration in response to varying fluid temperatures, chemistry, and associated mineralization; from initial chloritization typical of relatively low-temperature interaction with seawater to extremely altered rocks affected by higher-temperature, very acidic magmatic fluids.
Hydrothermally altered samples show a significant reduction in natural remanent magnetization intensity (10–4 to 10–2 A/m) compared with unaltered samples (1–10 A/m), suggesting that primary titanomagnetite grains are destroyed during the hydrothermal alteration process. Except for a small region in proximity to the mineralized stockwork zone, no chemical remanent magnetization is observed in association with hydrothermal alteration, consistent with the widespread formation of diamagnetic and/or paramagnetic minerals such as pyrite, rutile, and leucoxene, which do not carry any natural remanent magnetization.
Demagnetization experiments show that most of the oriented samples possess a stable characteristic remanent magnetization induced by the residual primary magnetic minerals formed at the time the rocks cooled on the sea floor. Partially chloritized dacites, however, are characterized by large magnetic susceptibilities, low Koenigsberger ratios, and very low magnetic coercivities, consistent with initial dissolution of smaller, singledomain magnetic grains, indicating that intensely hydrothermally altered rocks are better paleomagnetic indicators than initially chloritized samples at the periphery of the hydrothermal systems.
The significant magnetic contrast between fresh and hydrothermally altered rocks, in addition to a thick layer (>300 m) of demagnetized rocks observed at Brothers volcano, confirms the empirical results that magnetic anomalies are important geophysical tools to determine the geometry of hydrothermal systems at submarine arc volcanoes.
The scaling up of wireless operating microelectronics for upcoming Internet of Things (IoT) applications demands high-performance micro-supercapacitors (MSCs) with corresponding high-energy and power capabilities. Indeed, this necessitates the quest for MSC’s electrode materials capable of delivering high energy density at high charge/discharge rates. Many multicationic oxides, such as spinel manganese-iron compounds, demonstrate good pseudocapacitive properties as positive electrodes in conventional supercapacitors. However, fulfilling the required fabrication techniques is a challenge for their applications in MSCs. Hence, this study, for the first time, demonstrates the successful deposition of spinel Mn-Fe thin films on a functional platinum-based current collector. The deposition is achieved in a reactive oxygen environment via reactive DC magnetron sputtering techniques and subsequently annealed ex-situ at 600°C in a nitrogen environment. The electrochemical signature in neutral 1 M Na2SO4 aqueous electrolyte is comparable to those reported for spinel type Mn-Fe bulk counterparts. The areal capacitance at 10.0 mV.s-1 is 15.5 mF.cm-2 for 1 µm thick film, exhibiting excellent coulombic efficiency (close to 100%) and long-term cycle stability after 10,000 cycles. Thus, the synthesis of the multicationic pseudocapacitive oxides via compatible microelectronic deposition methods has set a prospective path to achieve very high-performance MSCs for future IoT applications.
The Sa'al Metamorphic Complex (SMC; southern Sinai) encompasses the oldest arc rocks in the Arabian-Nubian Shield, comprising two non-consanguineous metavolcanic successions (Agramiya Group and Post-Ra'ayan Formation) separated by the Ra'ayan metasedimentary Formation. It experienced three distinct deformational events (D1-D3), and two low- medium-grade regional metamorphic events (M1-M2). The Agramiya Group and Ra'ayan Formation experienced all tectonometamorphic events (D1–D3 and M1–M2), whereas the Post-Ra'ayan volcanic rocks were only affected by the D3 and M2 events. The D1 is an extensional event and linked with the late Rodinia break-up (~Tonian; 900–870 Ma). The M1 metamorphism variably affected the older Agramiya Group, the rhyolitic tuffs in lower to upper greenschist facies conditions and the basic and intermediate volcanic rocks underwent amphibolites facies metamorphism. The Ra'ayan metasedimentary Formation experienced upper greenschist to amphibolite facies metamorphism. The upper greenschist facies M2 affected the youngest Post-Ra'ayan volcanic rocks and other stratigraphic successions. The compressive D2 and D3 events were coeval with the accretion of dismembered terranes in the Gondwana assembly. The D2 can be linked with the Tonian–Cryogenian arc-arc assembly (~880–760 Ma; in Elat and Sinai), whereas the D3 and the accompanied M2 is constrained at 622–600 Ma (Ediacaran).
As the largest and most diverse vertebrate group on the planet, fishes have evolved an impressive array of sensory abilities to overcome the challenges associated with navigating the aquatic realm. Among these, the ability to detect Earth’s magnetic field, or magnetoreception, is phylogenetically widespread and used by fish to guide movements over a wide range of spatial scales ranging from local movements to transoceanic migrations. A proliferation of recent studies, particularly in salmonids, has revealed that fish can exploit Earth’s magnetic field not only as a source of directional information for maintaining consistent headings, but also as a kind of map for determining location at sea and for returning to natal areas. Despite significant advances, much about magnetoreception in fishes remains enigmatic. How fish detect magnetic fields remains unknown and our understanding of the evolutionary origins of vertebrate magnetoreception would benefit greatly from studies that include a wider array of fish taxa. The rich diversity of life-history characteristics that fishes exhibit, the wide variety of environments they inhabit, and their suitability for manipulative studies, make fishes promising subjects for magnetoreception studies.
Most modern articles in the palaeomagnetism literature are based on statistics developed by Fisher's 1953 paper ‘Dispersion on a sphere’, which assumes independent and identically distributed (iid) spherical data. However, palaeomagnetic sample designs are usually hierarchical, where specimens are collected within sites and the data are then combined across sites to calculate an overall mean direction for a geological formation. The specimens within sites are typically more similar than specimens between different sites, and so the iid assumptions fail. This article has three principal goals. The first is to review, contrast and compare both the statistics and geophysics literature on the topic of analysis methods for clustered data on spheres. The second is to present a new hierarchical parametric model, which avoids the unrealistic assumption of rotational symmetry in Fisher's 1953 paper ‘Dispersion on a sphere’ and may be broadly useful in the analysis of many palaeomagnetic datasets. To help develop the model, we use publicly available data as a case study collected from the Golan Heights volcanic plateau. The third goal is to explore different methods for constructing confidence regions for the overall mean direction based on clustered data. Two bootstrap confidence regions that we propose perform well and will be especially useful to geophysics practitioners.
Este livro foi concebido a partir do Curso de Difusão Cultural Noções de Oceanografia, ministrado semestralmente desde 1993, por docentes, pós-graduandos, pós-doutorandos e técnicos do Instituto Oceanográfico da Universidade de São Paulo (IOUSP), de forma voluntária, nas manhãs de domingo. Mesmo durante a pandemia o curso foi mantido e ministrado por via remota de modo que, em 2021, foi ultrapassada a marca de 10.000 alunos participantes, com um público abrangendo desde alunos do ensino médio até profissionais de diversas áreas, relacionadas ou não às ciências marinhas.
O curso visa a divulgação da Oceanografia, contemplando suas grandes áreas: Física, Química, Geológica e Biológica, além de tratar sobre Instrumentação Oceanográfica e as atividades do Museu do IOUSP; o propósito do curso tem sido muito bem cumprido ao longo de todos esses anos. Contudo, havia a necessidade crescente de fornecer aos alunos um material com conteúdo mais amplo e detalhado, do que o oferecido nas aulas e apostilas do curso.
Após esforços consideráveis ao longo de vários anos e a participação de mais de 70 profissionais do IOUSP, que se empenharam com esforço e entusiasmo, a composição deste e-book foi finalizada, e ele poderá ser acessado gratuitamente no site do IOUSP.
O livro contempla 37 capítulos, totalizando mais de 900 páginas, distribuídos em: Histórico da Oceanografia, Oceanografia Geológica, Oceanografia Física, Oceanografia Química, Oceanografia Biológica, Oceanografia na Prática e o Profissional Oceanógrafo. Portanto, o livro aborda praticamente todos os temas mais importantes da Oceanografia moderna, com a finalidade de possibilitar a apreciação de um grande número de áreas de atuação desta ciência. Os leitores encontrarão textos muito bem elaborados e ilustrados sobre o início e o desenvolvimento da Ciência Oceanográfica, a composição do interior da Terra, o relevo oceânico, sedimentos no assoalho marinho, Geofísica marinha, a dinâmica de fluidos e a circulação marinha, ondas e marés, características físicas do Oceano Austral, a composição da água do mar, a poluição orgânica e por metais, a bioluminescência marinha, a vida no mar, seus habitantes e ecossistemas, o perfil e a atuação do oceanógrafo, dentre outros.
Neste ano de lançamento do livro, o IOUSP está completando 75 anos – "Jubileu de Brilhante". Outro marco importante é a "Década das Nações Unidas de Ciência Oceânica para o Desenvolvimento Sustentável", também conhecida como Década do Oceano, declarada pelas Nações Unidas em 2017, que está em curso entre 2021 e 2030. O lançamento deste livro, durante essas comemorações de suma relevância, há de contribuir para difundir e complementar o conhecimento acadêmico / científico / social em Oceanografia.
Os autores dos capítulos, editores e o Instituto Oceanográfico da Universidade de São Paulo se sentem extremamente honrados por vosso interesse na Oceanografia e neste livro. Em nome de todos, recebam os nossos melhores votos da mais elevada estima e consideração.
Palaeomagnetic poles form the building blocks of apparent polar wander paths and are used as primary input for quantitative palaeogeographic reconstructions. The calculation of such poles requires that the short-term, palaeosecular variation (PSV) of the geomagnetic field is adequately sampled and averaged by a palaeomagnetic dataset. Assessing to what extent PSV is recorded is relatively straightforward for rocks that are known to provide spot readings of the geomagnetic field, such as lavas. But it is unknown whether and when palaeomagnetic directions derived from sedimentary rocks represent spot readings of the geomagnetic field and sediments are moreover suffering from inclination shallowing, making it challenging to assess the reliability of poles derived from these rocks. Here, we explore whether a widely used technique to correct for inclination shallowing, known as the elongation-inclination (E/I) method, allows us to formulate a set of quality criteria for (inclination shallowing-corrected) palaeomagnetic poles from sedimentary rocks. The E/I method explicitly assumes that a sediment-derived dataset provides, besides flattening, an accurate representation of PSV. We evaluate the effect of perceived pitfalls for this assumption using a recently published dataset of 1275 individual palaeomagnetic directions of a >3 km-thick succession of ~69-41.5 Ma red beds from the Gonjo Basin (eastern Tibet), as well as synthetic data generated with the TK03.GAD field model. The inclinations derived from the uncorrected dataset are significantly lower than previous estimates for the basin, obtained using coeval lavas, by correcting inclination shallowing using anisotropy-based techniques, and by predictions from tectonic reconstructions. We find that the E/I correction successfully restores the inclination to values predicted by these independent datasets if the following conditions are met: the number of directions N is at least 100, the A95 cone of confidence falls within a previously defined A95min-max reliability envelope, no negative reversal test is obtained and vertical-axis rotation differences within the dataset do not exceed 15°. We propose a classification of three levels (A, B, and C) that should be applied after commonly applied quality criteria for palaeomagnetic poles are met. For poles with classification ‘A’, we find no reasons to assume insufficient quality for tectonic interpretation. Poles with classification ‘B’ could be useful, but have to be carefully assessed, and poles with classification ‘C’ provide unreliable palaeolatitudes. We show that application of these criteria for datasets of other sedimentary rock types classifies datasets whose reliability is independently confirmed as ‘A’ or ‘B’, and that demonstrably unreliable datasets are classified as ‘C’, confirming that our criteria are useful, and conservative. The implication of our analysis is that sediment-based datasets of quality ‘A’ may be considered statistically equivalent to datasets of site-mean directions from rapidly cooled igneous rocks like lavas and provide high-quality palaeomagnetic poles.
Anthropogenic eutrophication and spreading anoxia in freshwater systems is a global concern. Little is known about anoxia in earlier historic times under weaker human impact, or under prehistoric natural conditions with different trophic, land cover and climatic regimes. We use a novel approach that combines high‐resolution hyperspectral imaging with µ‐XRF and HPLC‐pigment data, which allows us to assess chloropigments (productivity) and bacteriopigments (anoxia) at seasonal subvarve‐scale resolution. Our ~9700 cal a bp varved sediment record from NE Poland suggests that productivity increased stepwise from oligotrophic Early Holocene conditions (until ~9200 cal a bp) to mesotrophic conditions in the Mid‐ and Late Holocene. Natural eutrophication was mainly a function of progressing landscape evolution with intense weathering under dense forest and warm‐moist climatic conditions. Generally, anoxia increased with increasing productivity. Seasonal anoxia and some multi‐decadal periods of meromixis were the common mixing patterns throughout the Holocene except for a period of persisting meromixis between ~5200 and 2000 cal a bp. Anthropogenic deforestation around 400 cal a bp resulted in substantially better lake oxygenation despite high productivity. In this small lake, aquatic productivity and lakeshore forest cover (wind shield) were more important factors controlling oxic/anoxic conditions than Holocene temperature variability.
There are hundreds, perhaps thousands of sites of archaeological importance throughout the world. In this study the alignments of over twohundred ancient sites were measured and analyzed. Sites are organized into eight geographic regions: South America, Mesoamerica, North America, Europe, the Middle East, Africa, Asia and the Pacific Ocean. Google Earth imagery and measurement tools were used to estimate the alignment of linear and rectilinear structures at these sites with respect to true (geographic) north. In considering standard celestial and geographic reasons for the alignments, many were found to be oriented to the cardinal directions, in the directions of solstices and other solar events, to lunar standstills, and certain stars. A number of sites in China and Thailand were likely aligned to magnetic north at the time of construction using a compass. Some sites appear to have been aligned to “sacred directions” that include Islamic qibla and Quechua ceques. Site alignment statistics reveal similarities and differences between geographical regions in terms of how sites within regions are aligned. Perhaps the most unexpected finding is that the alignment of about half of the sites could not be explained in terms of any of the reasons considered.
There are hundreds, perhaps thousands, of sites of archaeological importance throughout the world. In this study, the alignments of more than two hundred ancient sites were measured and analyzed. Sites are organized into eight geographic regions: South America, Mesoamerica, North America, Europe, the Middle East, Africa, Asia, and the Pacific Ocean. Google Earth imagery and measurement tools were used to estimate the alignment of linear and rectilinear structures at these sites with respect to true (geographic) north. In considering standard celestial and geographic reasons for the alignments, many were found to be oriented to the cardinal directions, in the directions of solstices and other solar events, to lunar standstills, and to certain stars. A number of sites in China and Thailand were likely aligned to magnetic north at the time of construction using a compass. Some sites appear to have been aligned to "sacred directions" that include Islamic qibla and Quechua ceques. Site-alignment statistics reveal similarities and differences between geographical regions in terms of how sites within regions are aligned. Perhaps the most unexpected finding is that the alignment of about half of the sites could not be explained in terms of any of the explanations considered.
We present the first thermal model for the lithosphere in Turkey, which shows a highly heterogeneous pattern associated with mosaics of the Tethyan and modern subduction systems. We calculate a regionally average crustal density of 2.90 g/cm³ consistent with the presence of large volumes of mafic material. The Moho temperature with a regionally average value of 650–850 °C shows strong short‐wavelength variations. Lithosphere thinning to 50–75 km in most of western Anatolia may have developed in response to the Hellenic slab rollback, while the Neoproterozoic block in the Menderes Massif preserves a 150 km deep lithosphere root. In central Anatolia, the lithosphere thickness decreases southward from 100–150 to 50–60 km along a linear belt of young basaltic volcanism, followed by a belt of a 150 km thick lithosphere. We interpret this characteristic pattern by a SE dipping paleoslab beneath the western Taurides, which may cause the Cyprus subduction melting zone to deviate toward NW and NE. The Eastern Pontides‐Lesser Caucasus have 150–200 km thick lithosphere roots caused by collisional tectonics. The East Anatolian Plateau is underlain by a 80–140 km thick lithosphere, which suggests the presence of significant continental fragments; the patchy pattern of its thermal heterogeneity may be explained by teared and fragmented Tethyan slabs. A poor correlation between the lithosphere thermal structure, heat flux, the Neogene volcanic regions, and mantle seismic velocities implies that seismic anomalies are essentially controlled by heterogeneous mantle hydration by subduction systems of different ages and cannot be explained by temperature variations alone.
Paleomagnetism is a technique very useful in structural geology providing that the rocks keep a stable record of the paleoearth magnetic field information. Paleomagnetism has been used in deciphering the evolution and geometry of orogens and extensional basins. The evolution of an orogen has many points of view, but the use of paleomagnetism allows (i) calculating vertical and/or horizontal rotations during basin and orogen evolution and hence providing actual data to calculate out-of-plane movements particularly important when constructing cross-sections to calculate shortening, (ii) dating syntectonic sediments at foreland basins, which in combination with exhumation rates, for example, allow for a complete reconstruction of the evolution of the orogen, and (iii) deducing chemical interactions when remagnetization occurs. At larger scale, paleomagnetism has been fundamental for paleogeographic reconstructions and evolution of tectonic plates.
The Ramgarh structure of SE Rajasthan, central India, situated within an almost undeformed, flat-lying Vindhyan Supergroup of sedimentary rocks of Meso- to Neoproterozoic age, is a potential candidate of asteroid impact crater for last many decades. A fresh observation on remote sensing images (ASTER, Landsat and Google Earth Imageries) along with structural analyses in field show that this rectangular structure has a rim-to rim diameter of ~<2.5 km with a present diameter/depth ratio of ~12, a small central conical peak (~6 m high), and quaquaversal dips of rim crest sandstones with average dips between 21° and 50°. Unlike the surrounding sedimentary rocks, which only show two sets of wide-spaced (~2 m) vertical fractures trending NE-SW and NW-SE, the country rocks within the structure show extreme brittle deformation including vertical fractures in numerous directions, moderately dipping fractures trending mostly NE-SW and NW-SE, and moderate fault planes with N-S and E-W trends. The geometry of the Ramgarh structure is very similar to those of asteroid impact craters, where the profound brittle deformation of the sedimentary country rocks within the structure could have been resulted due to sudden shock during the impact. Reactivation of fractures existing within the pre-impact country rocks inside and adjacent to the Ramgarh structure by the shock effect is also possible. Our present observation on sub-samples from a cm-sized glassy silicate piece and our previous study on mm-sized particles, recovered from this structure, show that these magnetic materials have very high Natural Remanent Magnetization (NRM) (~2–19 Am⁻¹) and NRM to saturation isothermal remanent magnetization ratio (REM) (~7–145%) indicating the presence of a high magnetic field during their formation, much higher than the ambient Earth’s magnetic field. A natural phenomenon that could generate a unique ring-shaped deformation structure on a monotonously flat-lying, undeformed sedimentary country rock as well as a high magnetic field in and around this structure is a hypervelocity asteroid impact. The rectangular shape of the Ramgarh structure, which resembles the Arizona Crater, USA, was resulted due to post-impact dextral slip along a NW-SE unnamed fault, followed by dextral NE-SW faulting and minor sinistral slip along E-W fracture. These fractures reactivated perhaps during the modification stage of evolution of the Ramgarh structure. Our remote sensing observation further confirms that the impact took place on the palaeo-channel of Parvati River, which is now displaced towards W due to impact.
Globally distributed paleomagnetic data from discrete volcanic sites have previously been used for statistical studies of paleosecular variation and the structure of the time‐averaged field. We present a new data compilation, PSV10, selected from high quality paleodirections recorded over the past 10 Ma and comprising 2,401 sites from 81 studies. We require the use of modern laboratory and processing methods, a minimum of 4 samples per site, and within site Fisher precision parameter, kw, ≥ 50. Studies that identify significant tectonic effects or explicitly target transitional field states are excluded, thereby reducing over‐sampling of transitional time intervals. Additionally, we apply two approaches using geological evidence to minimize effects of short‐term serial correlation. PSV10 is suitable for use in new global geomagnetic and paleomagnetic studies as it has greatly improved spatial coverage of sites, especially at equatorial and high latitudes. VGP dispersion is latitudinally dependent, with substantially higher values in the southern hemisphere than at corresponding northern latitudes when no VGP cutoff is imposed. Average inclination anomalies for 10° latitude bins range from about + 3 ± 2° to ‐7.5 ± 2° for the entire dataset, with the largest negative values occurring at equatorial and mid‐northern latitudes. New 0–5 Ma TAF models (LN3 and LN3‐SC) based on selections of normal polarity data from PSV10 indicate a term that is 3.0% of . Non‐zonal variations in field structure are observed near the magnetic equator and in regions of increased radial flux at high latitudes over the Americas, the Indian Ocean, and Asia.
Poles from continental redbeds are a large fraction of the world's palaeomagnetic database. Nonetheless, the time of acquisition and origin of the remanent magnetization of redbeds has been long debated. We report palaeomagnetic data, rock magnetic data, and microscope observations for Lower Cretaceous redbeds in southern Mexico. These data allow us to discriminate between the hysteresis properties of remanent magnetizations of detrital and chemical origin, and to establish the early origin of a chemical remanence. Red sandstones of the Zicapa Formation contain a multi-component remanence revealed by thermal demagnetization, and consisting of three stable components with partially overlapping laboratory unblocking-temperatures of < 250°C, ∼300°C to ∼500°C, and > 600°C, (low, intermediate, and high temperature, respectively). They are interpreted as a viscous remanence residing in detrital magnetite, a chemical remanence residing in authigenic hematite, and a depositional remanence residing in detrital hematite, respectively. The low-temperature component is nearly parallel to the recent dipole field. The tilt-corrected overall site means of the intermediate (chemical) and high temperature (depositional) components are indistinguishable (Dec = 282.0°, Inc = 12.4°, k = 13.33, α95 = 10.1°, N = 17, for the intermediate temperature; and Dec = 272.5°, Inc = 16.5°, k = 14.04, α95 = 11, N = 14, for the high temperature). Elongation/inclination analysis suggests that depositional and chemical components require applying a f = factor of approximately 0.4. Both of these components define a magnetic polarity zonation, but the polarity of the chemical and detrital components may or may not be the same. The chemical remanence coincides, more often than not, with the polarity of the depositional remanence of the overlying (younger) strata, suggesting a delay in remanence acquisition of tens to a few hundred ka for the chemical component. Pigmentary and detrital haematite were recognized with microscopic observations. The particle size of haematite ranges from approximately 10 to 300 μm for detrital haematite (martite, specularite, and laterite), and from ca. 0.2 to 1 μm for pigmentary haematite flakes. The IRM of these rocks can be modeled with components of low coercivity (H1/2 between 5–10 mT interpreted as detrital magnetite), and components of a wide coercivity range (prevailing H1/2 from ∼400 to 600 mT interpreted as haematite). Hysteresis ratios show a systematic correlation with demagnetization behavior, with lower Hcr/Hc values and higher Mrs/Ms values for samples with a dominant chemical component, than form samples with a significant ( > 40%) depositional component.
The conglomerate test has served the paleomagnetic community for over 60 years as a means to detect remagnetizations. The test states that if a suite of clasts within a bed have uniformly random paleomagnetic directions then the conglomerate cannot have experienced a pervasive event that remagnetized the clasts in the same direction. The current form of the conglomerate test is based on null hypothesis testing, which results in a binary “pass” (uniformly random directions) or “fail” (non-random directions) outcome. We have recast the conglomerate test in a Bayesian framework with the aim of providing more information concerning the level of support a given data set provides for a hypotheses of uniformly random paleomagnetic directions. Using this approach we place the conglomerate test in a fully probabilistic framework that allows for inconclusive results when insufficient information is available to draw firm conclusions concerning the randomness or non-randomness of directions. With our method, sample sets larger than those typically employed in paleomagnetism may be required to achieve strong support for a hypothesis of random directions. Given the potentially detrimental effect of unrecognized remagnetizations on paleomagnetic reconstructions it is important to provide a means to draw statistically-robust data-driven inferences. Our Bayesian analysis provides a means to do this for the conglomerate test.
Even in times preceding the worldwide acceptation of the plate tectonics paradigm, paleomagnetic data have furnished the most striking evidence of Wegener’s continental drift theory. In this chapter, I present selected topics from paleomagnetism, which are essential for using paleomagnetic data in plate kinematics modelling. First, I introduce Neel’s theory of thermo–remanent magnetization, which represents the form of primary remanent magnetism acquired by most igneous rocks. Then, the basics of paleomagnetic sampling and statistics are discussed. Finally, the chapter presents some advanced applications, such as the construction of apparent polar wander paths and true polar wander, as well as a global plate motions model since the Triassic.
The Earth’s magnetic field represents the ultimate cause of rock magnetization. Here I describe the main internal source, or geodynamo, associated with convective currents in the external core, as well as the crustal field, generated by magnetized rocks, and the external magnetospheric and ionospheric sources. The concepts discussed in this chapter are essential for the correct use of magnetic data in plate kinematics. In particular, it is considered the secular variation of the core field, which represents the ultimate cause of most difficulties in collecting and analysing paleomagnetic data on continents. Furthermore, the concepts of polarity inversion and chron are introduced, along with the techniques used to build geomagnetic timescales. These topics are particularly important for the analysis of marine magnetic anomalies, a major source of data in plate kinematics. Finally, this chapter introduces the potential field technique, which represents the fundamental mathematical tool for describing the Earth’s magnetic field.
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