Paleomagnetic Measurements Research Articles

Advancing seafloor sampling using submersibles and remotely operated vehicles: The cross-line laser orientation method

Paleomagnetism has played a crucial role in unraveling processes such as plate motion and the emplacement of volcanic products. Despite its significance, a full range of such studies have not been possible for samples from the oceans, primarily due to the technical obstacles associated with obtaining oriented samples from the seafloor. Here we devised a rapid and uncomplicated technique for collecting oriented samples from the seafloor utilizing a cross-line laser system installed on the biaxial pan-tilt unit of the human occupied vehicle (HOV) SHINKAI 6500. This system comprises one laser capable of projecting a vertical line with horizontal mobility, together with a second laser positioned perpendicular to the vertically oriented beam, allowing flexibility to adjust its projection both upward and downward. The center of the cross-line laser is focused on a target rock or sediment corer. Orientation of the cross-line laser is calculated from the positions of SHINKAI 6500 and the pan-tilt unit, which are recorded every second. An accurate restoration of the collected sample to its original orientation can be achieved based on the laser path marked on the rock surface and the laser orientation data. We collected rocks and sediments from the seafloor of the Okinawa Trough in order to test our new orientation method and conducted paleomagnetic measurements on them. Paleomagnetic directions of the rocks are roughly consistent with the Earth's current magnetic field direction, proving validity of the method. This innovative method has the potential to become widely adopted for collecting oriented samples from seafloor using a HOV and remotely operated vehicle (ROV).

The Impact of Grain‐Size Distributions of Iron‐Oxides on Paleomagnetic Measurements

AbstractMagnetic signals in igneous rocks arise from assemblages of iron‐oxide bearing minerals that differ in for example, size, shape, and chemistry. Paleomagnetic measurements on bulk samples measure millions of such grains simultaneously, producing a statistical ensemble of the magnetic moments of the individual grains. Scanning magnetometry techniques such as the Quantum Diamond Microscope (QDM) measure magnetic signals on micrometer scales, allowing the identification of magnetic moments of individual grains in a sample using for example, Micromagnetic Tomography (MMT). Here we produce a grain‐size distribution of iron‐oxides in a typical Hawaiian basalt from the superparamagnetic threshold (∼40 nm) to grains with a diameter of 10 µm. This grain‐size distribution is obtained by combining FIB‐SEM and MicroCT data from sister specimens, and normalizing them to the mineral surface area of non‐magnetic minerals. Then we use this grain‐size distribution to determine the contributions of individual magnetic carriers to bulk magnetic measurements and surface magnetometry. We found that measurements on bulk samples are sensitive to relatively small grain sizes in the realm of single domain or vortex states (<200 nm), while signals in surface magnetometry arise mainly from larger grains with diameters >1 µm. This implies that bulk measurements cannot be compared straightforwardly to signals from surface magnetometry from the same sample. Moreover, our observations explain why MMT results are insensitive to the presence of many small grains in a sample that intuitively should hamper their outcome.

Paleomagnetic secular variation and revised chronostratigraphy of Bering Sea (IODP expedition 323) deep-sea sediments (MIS 5)

This study presents new high-resolution, full-vector paleomagnetic secular variation (PSV) records from IODP Expedition 323 Sites U1339, U1343, U1344, and U1345 in the Bering Sea (51°N-60°N) during Marine Isotope Stage 5 (71–130 ka). The chronology of the records has been determined by oxygen isotope stratigraphy with an age uncertainty of ∼±2000 years. The data come from shipboard paleomagnetic measurements of deep-sea sediments with accumulation rates of 26–54 cm/ky. The sample interval in the composite records is 5 cm with a time resolution of ±100–200 years. The composite PSV records for each site were developed by correlation and analysis of 3–4 paleomagnetic records from individual holes at each site. The composite records are a combination of the best correlatable PSV data from each site. We have been able to significantly correlate the PSV records from all four sites. We have identified 56 inclination features (highs/lows) and 54 declination features (east/west extremes) in all the records. Relative paleointensity has been determined by normalizing the sediment natural remanence, after 20-mT af demagnetization, to magnetic susceptibility. This normalization process is complicated by environmental variability, thus our relative paleointensity records are limited to large-scale correlations among the four sites. We correlated our relative paleointensity records to the global PISO-1500 paleointensity record that is itself dated by oxygen isotope stratigraphy. We can identify 6 key intensity highs/lows in our composite records and the PISO-1500 record that provide additional dating isochrons for our records. There are three short magnetic field excursions recorded with replication at these four sites – The youngest excursion occurred at 100 ± 2 ka and is associated with the Fram Strait Excursion. Two older excursions occurred at 116 ± 2 ka and 119.5 ± 2 ka. We associate both of these with the Blake Event. All three of the excursions have very short time intervals (∼200–400 yrs) with somewhat out-of-phase inclination and declination variability. All three of these are Class I excursions. We have studied the statistical characteristics our composite records by calculating the 3ky and 9ky averaged inclinations, declinations, unit vectors, and relative paleointensity over 71–130 ka after removing all excursional directions. The averaged inclinations and declinations are consistent among the four sites. The averaged angular dispersion is bimodal in its overall pattern. Most of the time angular dispersion is low (∼±10°–12°) except for three shorter intervals that have significantly higher angular dispersion (∼±24–30°) and lower paleointensities. The high angular dispersion intervals are associated with the three short excursional intervals. The timing and pattern of interrelated high angular dispersion, low paleointensity, and excursions is synchronous with the PSV pattern recorded during MIS 5 in the central North Atlantic Ocean. We think this defines a distinctive low-intensity/low-energy state for the geomagnetic field.

Preliminary Characterization of Submarine Basalt Magnetic Mineralogy Using Amplitude‐Dependence of Magnetic Susceptibility

AbstractThe past ∼200 million years of Earth's geomagnetic field behavior have been recorded within oceanic basalts, many of which are only accessible via scientific ocean drilling. Obtaining the best possible paleomagnetic measurements from such valuable samples requires an a priori understanding of their magnetic mineralogies when choosing the most appropriate protocol for stepwise demagnetization experiments (either alternating field or thermal). Here, we present a quick, and non‐destructive method that utilizes the amplitude‐dependence of magnetic susceptibility to screen submarine basalts prior to choosing a demagnetization protocol, whenever conducting a pilot study or other detailed rock‐magnetic characterization is not possible. We demonstrate this method using samples acquired during International Ocean Discovery Program Expedition 391. Our approach is rooted in the observation that amplitude‐dependent magnetic susceptibility is observed in basalt samples whose dominant magnetic carrier is multidomain titanomagnetite (∼TM60–65, (Ti0.60–0.65Fe0.35–0.40)Fe2O4). Samples with low Ti contents within titanomagnetite or samples that have experienced a high degree of oxidative weathering do not display appreciable amplitude dependence. Due to their low Curie temperatures, basalts that possess amplitude‐dependence should ideally be demagnetized either using alternating fields or via finely‐spaced thermal demagnetization heating steps below 300°C. Our screening method can enhance the success rate of paleomagnetic studies of oceanic basalt samples.

A unified intensity of the magnetic field in the protoplanetary disk from the Winchcombe meteorite

AbstractOne key feature of our protoplanetary disk that shaped its transformation into a system of planetary bodies was its vast magnetic field. Unique constraints on the properties of this field can be gleaned from paleomagnetic measurements of certain meteorites. Here, we apply this approach to the recent CM chondrite fall Winchcombe with the aim of constructing the most complete and reliable record to date of the behavior of the disk field in the outer solar system. We find that the interior of Winchcombe carries a stable, pre‐terrestrial magnetization that likely dates from the period of aqueous alteration of the CM chondrite parent body. This remanence corresponds to a paleointensity of 31 ± 17 μT accounting for the average effect of parent body rotation. Winchcombe is rich in framboids and plaquettes of magnetite, which formed via precipitation following the dissolution of iron sulfide. This contrasts with most other CM chondrites, where magnetite formed predominantly via pseudomorphic replacement of FeNi metal. Accounting for the potential differences in recording fidelities of these types of magnetite, we find that the reported paleointensities from all CM chondrites to date are likely underestimates of the disk field intensity in the outer solar system, and use our measurements to calculate a unified intensity estimate of ~78 μT. This paleointensity is consistent with two independent values from recent studies, which collectively argue that the disk field could have played a larger role in shaping the behavior of the disk in the outer solar system than previously considered.

New 40Ar/39Ar radiometric ages of lamproites indicate latest Tortonian marine restriction of the Fortuna Basin, Eastern Betics, southern Spain

Exposures of lamproitic volcanic rocks have been used to constrain the age of the evaporitic basin-fill in the Fortuna Basin of southern Spain. K/Ar dates initially suggested a Messinian age assignment for these deposits; however, subsequent 40Ar/39Ar dates indicated a Tortonian age, implying the early onset of evaporite formation in the eastern Betic Cordillera, in an event termed the “Tortonian Salinity Crisis”. In this paper, we critically review the published chronology of the key igneous outcrops and provide new 40Ar/39Ar ages, which show that the Cabezos Negros lamproites lie close to the Tortonian-Messinian boundary (c. 7.25 ​Ma). We also provide new paleomagnetic measurements from each of the three lamproitic outcrops (Cabezos Negros, Derramadores, and El Tale), which demonstrate normal magnetic polarity coincident with episodes of volcanic and subvolcanic activity. The presence of peperites and pillow structures indicate that volcanism at Cabezos Negros was coeval with deposition of the lower part of Rambla Salada Gypsum Member. Therefore, the normal polarity identified in this unit should be equivalent to the normal polarity on the Cabezos Negros lamproites. These results indicate that the initial marine restriction and evaporitic deposition of Fortuna Basin occurred more than a million years before the Messinian Salinity Crisis.

PRELIMINARY PALEOMAGNETIC INVESTIGATIONS ON PLEISTOCENE SEQUENCES IN LOMBARDY NORTHERN ITALY

Paleomagnetic measurements have been carried out in continental sediments of Northern ltaly. The loess deposits of Copreno, the loess and paleosols of Cascina Lina and Barlassina, and the la­custrine sediments of Pontida all belong to the Brunhes Normal Polarity Epoch, in agreement with their previous chronostratigraphic classification. The lower lacustrine sediments of Bagaggera, previously attributed to the antepenultimate glaciation, belong to the Matuyama Reversed Polarity Epoch, whilee the overlying sandy-loamy sequence belongs to the Brunhes. At Leffe the entire sequence up to the top of the lacustrine sediments belongs to the Matuyama Epoch, being in such way older than previously admit­ted. These paleomagnetic results prove that the "ferretto" is a complex of paleosols of different age, ranging from Lower to Middle Pleistocene.

Effects of Hydrothermal Alteration and Mineralization on the Paleomagnetic Properties of Rocks from IODP Expedition 376 at Brothers Volcano

AbstractThe 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.

10Be Indicator for the Matuyama‐Gauss Magnetic Polarity Reversal From Chinese Loess

AbstractThe Matuyama‐Gauss (M‐G) magnetic polarity reversal is regarded as a fundamental time marker in the stratigraphic division of the Quaternary‐Neogene. However, previous paleomagnetic studies have shown that the M‐G is mainly recorded in the Chinese loess unit L33—a glacial stage (corresponding to marine isotope stage 104, i.e., MIS 104)—which is asynchronous with the timing recorded in marine sediments. Here, we solve this long‐standing debate by exploiting a method to extract reproducible records of paleomagnetic field intensity from Xifeng and Lantian loess profiles with meteoric 10Be. The results showed that for both loess profiles, the 10Be‐derived M‐G boundary is located in paleosol S32 ca. 2,589 ± 3 ka, which corresponds to MIS 103. This is synchronous with that seen in marine sediments, though it is, on average, ∼19 ka younger than the boundary inferred from paleomagnetic measurements from the two profiles, which demonstrates that magnetic overprinting has occurred.

Assessment of the radiation risk at flight altitudes for an extreme solar particle storm of 774 AD

Intense solar activity can lead to an acceleration of solar energetic particles and accordingly increase in the complex radiation field at commercial aviation flight altitudes. We considered here the strongest ever reported event, namely that of 774 AD registered on the basis of cosmogenic-isotope measurements, and computed the ambient dose at aviation altitude(s). Since the spectrum of solar protons during the 774 AD event cannot be directly obtained, as a first step, we derived the spectra of the solar protons during the ground level enhancement (GLE) #5 on 23 February 1956, the strongest event observed by direct measurements, which was subsequently scaled to the size of the 774 AD event and eventually used as input to the corresponding radiation model. The GLE #5 was considered a conservative approach because it revealed the hardest-ever derived energy spectrum. The global map of the ambient dose was computed under realistic data-based reconstruction of the geomagnetic field during the 774 AD epoch, based on paleomagnetic measurements. A realistic approach on the basis of a GLE #45 on 24 October 1989 was also considered, that is by scaling an event with softer spectra and lower particle fluxes compared to the GLE #5. The altitude dependence of the event-integrated dose at altitudes from 30 kft to 50 kft (9.1–15.2 km) was also computed for both scenarios. Our study of the radiation effects during the extreme event of 774 AD gives the necessary basis to be used as a reference to assess the worst-case scenario for a specific threat, that is radiation dose at flight altitudes.

Paleomagnetism and paleolatitude of igneous drill core samples from the Izu-Bonin forearc and implications for Philippine Sea plate motion

The Philippine Sea plate is an integral part of the east Asian plate mosaic but its past motions can only be reconstructed from paleomagnetic data. Moreover, because the plate is largely submarine, few fully-oriented paleomagnetic data are available. International Ocean Discovery Program (IODP) Expedition 352 cored at four sites on the Izu-Bonin forearc, penetrating ∼1170 m of forearc igneous crust radiometrically dated at ∼51 Ma. Paleomagnetic measurements on 361 samples produced paleo-inclination data that were used to estimate paleolatitude. Twenty five independent magnetic units give a paleocolatitude of 90.1° ±4.4° (2σ uncertainty), implying a paleolatitude exactly on the equator. Unit variance agrees with global paleosecular variation models, implying that these variations have been properly sampled and averaged. The paleolatitude implies northward drift of ∼28°, which agrees with other Izu-Bonin forearc sites of similar age. A slight difference in northward drift with southern Philippine Sea plate sites is consistent with plate rotation. Certain parts of the cored sections yield samples that were remagnetized to the present geocentric axial dipole inclination after ∼30 Ma, implying a tectonic event of unclear origin.

New 40Ar/39Ar age of the full vector Upper Mammoth geomagnetic polarity transition recorded in the Pu’u Kualakauila volcanic sequence, Hawaii

Paleomagnetic measurements, coupled with 40Ar/39Ar dating, are improving our understanding of the geodynamo by providing detailed terrestrial lava records of the short-term behavior of the Earth's magnetic field. As part of an investigation of the Wai'anae Volcano, Oahu, and the short-term behavior of the geomagnetic field, we sampled a long volcanic section located on the volcano's collapsed flank at a locality known as Pu’u Kaulakauila. Prior paleomagnetic investigations of the Kamaile'unu Volcanic Series (i.e. Herrero-Bervera and Coe, 1999, Herrero-Bervera and Valet, 1999, 2005) revealed transitional directions. The fresh lava flows, easy access, and close geographical proximity to KAr dated flows made this ~215-m thick sequence of flows an excellent candidate for detailed paleomagnetic analysis. At least eight samples, collected from each of 47 successive flow sites, were stepwise demagnetized by both alternating field and thermal methods. Magnetostratigraphic results indicate the existence of four excursions or aborted reversals occurring at approximately ~36, ~75, ~130, and ~ 151 m above flow#1. The mean directions of magnetization of the entire section sampled indicate a reversed polarity, with ∼10 m of the section characterized by truly excursional/Cryptochron directions (~7 lava flows). Paleointensity (P.I.) determinations indicate a steady decreasing of the PI values from 75 μ-T to ~12.2 μ-T reaching a minimum of 7.1 μ-T. These very low PI values are within the transitional/excursional part of the record. The corresponding VGPs are located on the western part of Australia. 40Ar/39Ar incremental heating experiments on groundmass from transitional flow sites at different stratigraphic levels yield a weighted mean plateau age of 3.201 ± 0.041 Ma, which, combined with the overall reversed polarity and two older polarity reversals, strongly suggests that the transitional lavas correspond to the Upper Mammoth polarity transition.

QDM[formula omitted]: A MATLAB toolbox for analyzing quantum diamond microscope (QDM) magnetic field maps

Paleomagnetic measurements of rock magnetizations are typically performed using classical net moment rock magnetometers on bulk, millimeter- to centimeter-sized samples. In this case, the limited spatial resolution effectively averages across the signal of multiple populations of magnetic grains, each of which may have a distinct geological history. Magnetic field imaging with the quantum diamond microscope (QDM) allows for the measurement of weakly magnetic (10−16 Am2) samples at micrometer spatial resolution, potentially isolating the signal of magnetic grain populations and resolving ambiguities from bulk sample analyses. To achieve such high resolution, the QDM retrieves the energy spectrum of nitrogen–vacancy (NV) color centers within micrometer-scale pixels across a millimeter-scale field of view. Therefore, large amounts of data need to be processed to generate a magnetic field map, which itself often requires further specialized analysis. Until now, no freely-available, comprehensive, open-source software package existed that was able to process this type of data. Here we give an overview of the most important features of QDMlab, our open-source MATLAB toolbox for generating and analyzing QDM magnetic field maps of geologic samples. QDMlab utilizes modern computational techniques like graphics processing unit (GPU) and spectral fitting routines as well as automated image alignment algorithms. QDMlab contains easy-to-use functions for (1) generating magnetic field maps from raw QDM data, (2) map editing, and (3) quantifying the net magnetic moment and rock magnetic properties of rock and mineral samples.

Lifetime of the Outer Solar System Nebula From Carbonaceous Chondrites

AbstractThe evolution and lifetime of protoplanetary disks (PPDs) play a central role in the formation and architecture of planetary systems. Astronomical observations suggest that PPDs evolve in two timescales, accreting onto the star for up to several million years (Myr) followed by gas dissipation within ≲1 Myr. Because solar nebula magnetic fields are sustained by the gas of the protoplanetary disk, we can use paleomagnetic measurements to infer the lifetime of the solar nebula. Here, we use paleomagnetic measurements of meteorites to constrain this lifetime and investigate whether the solar nebula had a two‐timescale evolution. We report on paleomagnetic measurements of bulk subsamples of two CO carbonaceous chondrites: Allan Hills A77307 and Dominion Range 08006. If magnetite in these meteorites can acquire a crystallization remanent magnetization that recorded the ambient field during aqueous alteration, our measurements suggest that the local magnetic field strength at the CO parent body location was <0.9 μT at some time between 2.7 and 5.1 Myr after the formation of calcium‐aluminum‐rich inclusions. Coupled with previous paleomagnetic studies, we conclude that the dissipation of the solar nebula in the 3–7 AU region occurred <1.5 Myr after the dissipation of the nebula in the 1–3 AU region, suggesting that protoplanetary disks go through a two‐timescale evolution in their lifetime, consistent with dissipation by photoevaporation and/or magnetohydrodynamic winds. We also discuss future directions necessary to obtain robust records of solar nebula fields using bulk chondrites, including obtaining ages from meteorites and experimental work to determine how magnetite acquires magnetization during chondrite parent body alteration.

Middle Miocene-Pleistocene Magneto-Cyclostratigraphy from IODP Site U1501 in the Northern South China Sea

Site U1501 of International Ocean Discovery Program (IODP) Expedition 368 locates on a broad regional basement high in the northern margin of the South China Sea (SCS). This study refines the chronostratigraphy of the upper 160 m sedimentary succession from Hole U1501C using paleomagnetic measurements and cyclostratigraphic analysis on the Natural Gamma Radiation (NGR) data. Rock magnetic analysis displays that the magnetic signal of the sediments is mainly carried by single-domain (SD) and multi-domain (MD) magnetite. A total of 12 geomagnetic reversals are identified and correlated to the geomagnetic polarity time scale (GPTS) in Geologic Time Scale 2020 (GTS 2020), combining biostratigraphic data and planktonic foraminiferal oxygen records. The Milankovitch cycles of 405-kyr long orbital eccentricity, ∼100-kyr short orbital eccentricity, and obliquity cycles are identified in the NGR profile. A 15.54 Myr astronomical time scale is constructed by tuning the short eccentricity cycles filtered from the NGR profiles to the La2010 astronomical solution with the constraints of the magnetostratigraphic results, biostratigraphic age datum and planktonic foraminiferal oxygen records. This new high-resolution age model provides a new temporal constraint on the tectonic and paleoenvironmental evolution in the South China Sea.

Late Holocene Paleomagnetic Secular Variation in the Chukchi Sea, Arctic Ocean

AbstractThe geomagnetic field behavior in polar regions remains poorly understood and documented. Although a number of Late Holocene paleomagnetic secular variation (PSV) records exist from marginal settings of the Amerasian Basin in the Arctic Ocean, their age control often relies on a handful of radiocarbon dates to constrain ages over the past 4,200 years. Here we present well‐dated Late Holocene PSV records from two sediment cores recovered from the Chukchi Sea, Arctic Ocean. The records are dated using 26 14C measurements, with local marine reservoir corrections calibrated using tephra layers from the 3.6 cal ka BP Aniakchak eruption in Northern Alaska. These 14C‐based chronologies are extended into the post‐bomb era using caesium‐137 dating, and mercury isochrons. Paleomagnetic measurements and rock magnetic analyses reveal stable characteristic remanent magnetization directions, and a magnetic mineralogy dominated by low‐coercivity minerals. The PSV records conform well to global spherical harmonic field model outputs. Centennial to millennial scale directional features are synchronous between the cores and other Western Arctic records from the area. Due to the robust chronology, these new high‐resolution PSV records provide a valuable contribution to the characterization of geomagnetic field behavior in the Arctic over the past few thousand years, and can aid in developing age models for suitable sediments found in this region.

Eocene relative paleointensity of the geomagnetic field from Integrated Ocean Drilling Program Site U1403 and U1408 sediments in the northwest Atlantic

Published relative paleointensity (RPI) records older than ∼3Ma are extremely limited in time and space. To develop a more robust understanding of RPI variations, we have conducted rock magnetic and paleomagnetic measurements on Eocene marine sediments recovered at Integrated Ocean Drilling Program (IODP) Sites U1403 and U1408 in the northwest Atlantic. A series of rock magnetic measurements indicate that the main remanence carrier is single domain biogenic magnetite. Paleomagnetic measurements yielded RPI records for Chrons C18–C21 and C22n, which correlates to ∼38.4–49.6Ma. The record is compromised in a few short intervals by inhomogeneous rock magnetic properties. RPI minima always occur at chron boundaries and RPI fluctuates between highs and lows within each chron. This record is the first to show that these characteristics persist at least since the onset of Chron C22n at ∼49.3Ma. We conclude that these are intrinsic and fundamental features of the geomagnetic field regardless of the polarity reversal rate. We produce a stacked RPI curve for Chron 18, named PIS-C18, on the basis of the RPI records obtained in this study and those from IODP Sites U1331 and U1332 in the equatorial Pacific that are matched by visual inspection. The PIS-C18 RPI of the stack is generally high with no prominent lows during Chron C18n.2n, whereas it is not as high and has several prominent lows almost equivalent to the RPI minima at the chron boundaries during Chrons C18n.1n and C18r. A histogram of RPI during Chron 18 is slightly skewed to the right, and the ratio of the standard deviation to the mean paleointensity is 0.38. These characteristics are similar to a histogram of the RPI stack for the last 1.5 million years. We interpret this to imply that character of the geodynamo for 104–106 years timescales has been unchanged since the Eocene.

Statistical Analysis of Small Faults in Rotated Blocks of Crust Near the Húsavík‐Flatey Transform Fault, Northern Iceland

AbstractThe dextral Húsavík‐Flatey fault, in northern Iceland, provides a unique opportunity to observe an oceanic transform fault on land. Structural and paleomagnetic measurements from lavas and dikes on Flateyjarskagi peninsula indicate that rocks adjacent to the fault have rotated clockwise more than 100°. We examine the effect of this rotation on the orientations of small faults that developed in rocks adjacent to the transform fault. We also use patterns in small‐scale data to build on models of the style of deformation surrounding the fault. We apply statistical tools including spatial regressions to structural data to estimate the amount of distributed shearing around the transform fault, and to predict the orientations of rotated structures. Some small faults are consistent with predicted rotations, while others are consistent with the modern kinematics, suggesting that they postdate block rotation. This protracted temporal history for small faults complicates paleostress interpretations from rocks adjacent to the Húsavík‐Flatey fault. Previous studies assumed the small faults formed in their modern orientations and attributed their variability to stress variations, whereas we identify populations of faults that have likely rotated to their present‐day attitudes.

Assessment of the Influence of Astronomical Cyclicity on Sedimentation Processes in the Eastern Paratethys Based on Paleomagnetic Measurements Using Discrete Mathematical Analysis

The introduction of modern methods for the mathematical processing of geological data is one of the promising areas of study and development in the field of geosciences. For example, today mathematical geology makes it possible to reliably identify astronomical cycles by measuring the scalar magnetic parameters of rocks (magnetic susceptibility). The main aim of this study is to develop a mathematical tool for identifying stable oscillation cycles (periods) in the dataset of the magnetic susceptibility of rocks in a geological section. The author’s method (algorithm) is based on the concept of discrete mathematical analysis—an innovative mathematical approach to the analysis of discrete geological and geophysical data. Its reliability is also demonstrated, by comparison with the results obtained by classical methods: Fourier analysis, Lomb periodogram, and REDFIT. The proposed algorithm was applied by the authors to analyze the material of field geological studies of the Zhelezny Rog section (Taman Peninsula). As a result, stable cycles were determined for the Pontian and Lower Maeotian sedimentary strata of the Black Sea Basin (Paratethys).

Diamonds Are a Paleomagnetist’s Best Friend

Typical paleomagnetic measurements average a sample’s signal. The quantum diamond microscope helps scientists make micrometer-scale maps of magnetism, showing where a sample locked in its magnetic signatures.