Paleointensity Estimates Research Articles

Near-collapse of the geomagnetic field may have contributed to atmospheric oxygenation and animal radiation in the Ediacaran Period

Earth’s magnetic field was in a highly unusual state when macroscopic animals of the Ediacara Fauna diversified and thrived. Any connection between these events is tantalizing but unclear. Here, we present single crystal paleointensity data from 2054 and 591 Ma pyroxenites and gabbros that define a dramatic intensity decline, from a strong Proterozoic field like that of today, to an Ediacaran value 30 times weaker. The latter is the weakest time-averaged value known to date and together with other robust paleointensity estimates indicate that Ediacaran ultra-low field strengths lasted for at least 26 million years. This interval of ultra-weak magnetic fields overlaps temporally with atmospheric and oceanic oxygenation inferred from numerous geochemical proxies. This concurrence raises the question of whether enhanced H ion loss in a reduced magnetic field contributed to the oxygenation, ultimately allowing diversification of macroscopic and mobile animals of the Ediacara Fauna.

Planetary Paleomagnetic Intensity Recording Fidelity Test Using a Synthetic Lava

AbstractMeteorite paleomagnetism is fundamental to understanding planetary dynamo processes and the evolution of the early Solar System. However, due to the extraterrestrial and ancient origins of meteorites, their paleomagnetic recording fidelity remains uncertain, which can be tested from a planetary sample formed in a known field. On Earth, historic lavas are used to examine paleomagnetic recording fidelity through the Thellier‐series experiment and other paleointensity methods, which can produce paleointensity estimates to test against the known field strength. But natural terrestrial rocks have different magnetic mineralogy from planetary samples, so they cannot faithfully infer the recording fidelity of meteorites. Here, we used an iron‐particle‐bearing sample from the Syracuse University Lava Project (SULP), which is analogous to the lunar basalts and howardite‐eucrite‐diogenite meteorites and forms in the present‐day Earth's field, to investigate the recording fidelity of these meteorites. No remanence has been identified in the high coercivity range with alternating field (AF) demagnetization due to the sample's low coercivity and AF noise, which produces underestimated paleointensities. Two accurate thermal paleointensities indicate that we may acquire accurate paleointensities from non‐ideal multidomain (MD) iron grains with the Thellier‐Coe and RESET methods, but the success rate is low due to the MD effect and thermal alteration in the experiments. Our results imply that MD iron‐bearing meteorites have the potential to provide accurate paleointensities that can be used to constrain planetary processes.

Establishing a Lunar Origin for Paleomagnetic Records in Apollo Samples

AbstractNumerous paleomagnetic studies attribute the magnetization preserved within Apollo samples to an ancient dynamo. However, other works propose that lunar rocks were instead magnetized by either transient impact‐related magnetic fields on the Moon or by the return spacecraft. To test whether lunar samples could have been magnetized during return to Earth, sample handling, or transport, we exposed lunar rocks to 5–10 mT fields for varying durations. We then determined how easily these magnetic overprints could be removed and how paleointensity estimates are affected by the overprints and their removal. We found that magnetic overprints were cleaned by alternating field (AF) demagnetization to ∼10–30 mT for nearly all samples and that acceptable paleointensities may be obtained from higher AF levels. Therefore, high coercivity (>30 mT) magnetizations observed within lunar rocks are generally not magnetic contamination and were initially acquired on the Moon.

PEAT DEPOSITS AS A NEW SOURCE OF PALEOMAGNETIC RECORDS IN THE HOLOCENE AS EXEMPLIFIED BY THE ETRUSSIA EXCURSION

The paper presents the results of microprobe, paleomagnetic and rock magnetic studies on peats from the Tyapka peat section (Khabarovsk region) formed 4 thousand years. Alternating field demagnetization of peats yielded a horizon of 57–109 cm (1833–3083 cal. BP) with negative inclination values of the magnetization vector, which corresponds to the geomagnetic Etrussia excursion. Obtaining relative paleointensity estimates for peats was pioneered, which are consistent with the literature archeomagnetic data for the western part of Eurasia. It was found that the Etrussia excursion took place against the background of increased values of the Earth’s magnetic field, and its duration was ~ 1200 years.

Changes in Non‐Dipolar Field Structure Over the Plio‐Pleistocene: New Paleointensity Results From Hawai'i Compared to Global Data Sets

AbstractA foundational assumption in paleomagnetism is that the Earth's magnetic field behaves as a geocentric axial dipole (GAD) when averaged over sufficient timescales. Compilations of directional data averaged over the past 5 Ma yield a distribution largely compatible with GAD, but the distribution of paleointensity data over this timescale is incompatible. Reasons for the failure of GAD include: (a) Arbitrary “selection criteria” to eliminate “unreliable” data vary among studies, so the paleointensity database may include biased results. (b) The age distribution of existing paleointensity data varies with latitude, so different latitudinal averages represent different time periods. (c) The time‐averaged field could be truly non‐dipolar. Here, we present a consistent methodology for analyzing paleointensity results and comparing time‐averaged paleointensities from different studies. We apply it to data from Plio/Pleistocene Hawai'ian igneous rocks, sampled from fine‐grained, quickly cooled material (lava flow tops, dike margins and scoria cones) and subjected to the IZZI‐Thellier technique; the data were analyzed using the Bias Corrected Estimation of Paleointensity method of Cych et al. (2021, https://doi.org/10.1029/2021GC009755), which produces accurate paleointensity estimates without arbitrarily excluding specimens from the analysis. We constructed a paleointensity curve for Hawai'i over the Plio/Pleistocene using the method of Livermore et al. (2018, https://doi.org/10.1093/gji/ggy383), which accounts for the age distribution of data. We demonstrate that even with the large uncertainties associated with obtaining a mean field from temporally sparse data, our average paleointensities obtained from Hawai'i and Antarctica (reanalyzed from Asefaw et al., 2021, https://doi.org/10.1029/2020JB020834) are not GAD‐like from 0 to 1.5 Ma but may be prior to that.

Rock Magnetic Characterization of Returned Samples From Asteroid (162173) Ryugu: Implications for Paleomagnetic Interpretation and Paleointensity Estimation

AbstractIn this study, systematic rock magnetic measurements and saturation isothermal remanent magnetization (SIRM) paleointensity calibration experiments were conducted for the returned samples from C‐type asteroid (162173) Ryugu and two carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a paleomagnetic recorder. Our magnetic measurements show that Ryugu samples exhibit signatures for framboidal magnetite, coarse‐grained magnetite, and pyrrhotite, and that framboidal magnetite is the dominant remanence carrier of Ryugu samples in the middle‐coercivity range. The SIRM paleointensity constant was obtained for two Ryugu samples, and the median value was 3,318 ± 1,038 μT, which is close to the literature's value based on the average among magnetite, titanomagnetite, pyrrhotite, and FeNi alloys and is widely used for SIRM paleointensity experiments. The paleointensity values estimated using the obtained SIRM paleointensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that Sun's protoplanetary disk existed at the disk location of Ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.

High geomagnetic field intensity recorded by anorthosite xenoliths requires a strongly powered late Mesoproterozoic geodynamo

Obtaining estimates of Earth's magnetic field strength in deep time is complicated by nonideal rock magnetic behavior in many igneous rocks. In this study, we target anorthosite xenoliths that cooled and acquired their magnetization within ca. 1,092 Ma shallowly emplaced diabase intrusions of the North American Midcontinent Rift. In contrast to the diabase which fails to provide reliable paleointensity estimates, the anorthosite xenoliths are unusually high-fidelity recorders yielding high-quality, single-slope paleointensity results that are consistent at specimen and site levels. An average value of ∼83 ZAm2 for the virtual dipole moment from the anorthosite xenoliths, with the highest site-level values up to ∼129 ZAm2, is higher than that of the dipole component of Earth's magnetic field today and rivals the highest values in the paleointensity database. Such high intensities recorded by the anorthosite xenoliths require the existence of a strongly powered geodynamo at the time. Together with previous paleointensity data from other Midcontinent Rift rocks, these results indicate that a dynamo with strong power sources persisted for more than 14 My ca. 1.1 Ga. These data are inconsistent with there being a progressive monotonic decay of Earth's dynamo strength through the Proterozoic Eon and could challenge the hypothesis of a young inner core. The multiple observed paleointensity transitions from weak to strong in the Paleozoic and the Proterozoic present challenges in identifying the onset of inner core nucleation based on paleointensity records alone.

Absolute Paleointensity Experiments on Aged Thermoremanent Magnetization: Assessment of Reliability of the Tsunakawa‐Shaw and Other Methods With Implications for “Fragile” Curvature

AbstractAbsolute paleointensity (API) of the geomagnetic field can be estimated from volcanic rocks by comparing the natural remanent magnetization (NRM) to a laboratory‐induced thermoremanent magnetization (Lab‐TRM). Plots of NRM unblocking versus Lab‐TRM blocking from API experiments often exhibit nonideal curvature, which can result in biased estimates. Previous work showed that curvature can increase with age; however, selection criteria designed to eliminate such behavior yielded accurate estimates for two‐year‐aged specimens (70.3 ± 3.8 μT;N = 96 specimens out of 120 experiments). API can also be estimated in coercivity space. Here, we use the Tsunakawa‐Shaw (TS) method applied to 20 specimens aged in the laboratory field of 70.0 μT for 4 years, after acquisition of zero‐age (fresh) Lab‐TRM in the same field. Selection criteria for the TS experiment also yielded accurate results (68.5 ± 4.5 μT;N = 17 specimens). In thermal API experiments, curvature is related to internal structure with more single domain‐like behavior having the least curvature. Here we show that the fraction of anhysteretic remanent magnetization demagnetized by low‐temperature treatment was larger for samples with larger thermal curvatures suggesting a magnetocrystalline anisotropy source. We also tested experimental remedies that have been proposed to improve the accuracy of paleointensity estimates. In particular, we test the efficacy of the multi‐specimen approach and a strategy pretreating specimens with low field alternating field demagnetization prior to the paleointensity experiment. Neither yielded accurate results.

Low Paleointensities and Ar/Ar Ages From Saint Helena Provide Evidence for Recurring Magnetic Field Weaknesses in the South Atlantic

AbstractThe South Atlantic Anomaly (SAA) is an area of geomagnetic weakness that represents the most significant anomaly in the present‐day field. Notwithstanding anomalies such as these, a long‐lived hypothesis is that, if averaged over sufficient time (104–106 years), the Earth's magnetic field approximates a geocentric axial dipole (GAD). The question of how significant the non‐GAD features are in the time‐averaged field is an important and unresolved one. The SAA has not always been visible in the historic and paleo‐field models; yet an unstable field was reported in the South Atlantic region on a multimillion‐year timescale. This study presents the first paleointensity study from Saint Helena, a volcanic island in the South Atlantic consisting primarily of lavas emplaced between 10 and 8 Ma. While paleointensity success rates were low, we were able to recover results from five independent lavas that together suggest a low field intensity of 10.5 ± 3.0 μT corresponding to a virtual axial dipole moment (VADM) of 2.4 ± 0.7 × 1022 A m2. These low paleointensity estimates suggest a field in the South Atlantic that was not only unstable in directions, but also substantially weaker than expected. We consider this to constitute further evidence that the SAA is not a single occurrence but rather, the latest in a series of recurring weaknesses in the field in this region, probably caused by Reversed Flux Patches on the Core Mantle Boundary.

ThellierCoolPy: A Cooling‐Rate Correction Tool for Paleointensity Data

AbstractWe report a new approach of implementing cooling‐rate corrections in absolute ancient magnetic field intensity (paleointensity) studies. Nearly all methods of determining paleointensity estimates rely on rocks having recorded a thermoremanent magnetization (TRM), on cooling from above the rock’s constituent minerals’ Curie temperature. Typically paleointensity estimates are made by comparing natural TRM, with a TRM induced in the laboratory; however, TRM intensity has long been reported to be dependent on cooling rate. Natural cooling rates are impractical in laboratories. We have developed a new cooling‐rate correction method and corresponding software (ThellierCoolPy), that directly corrects the unprocessed paleointensity data, using first‐order reversal curve data collected on a sister sample. This site tailored cooling‐rate correction has a unique correction for each temperature step within the paleointensity data set. This new method differs from previous approaches which apply a blanket cooling‐rate correction independent of the material properties of the sample. Paleointensity data from historical lavas from Parícutin, Mexico, are used to demonstrate the new software. For this data set, it is shown that cooling time of 1 million years yields a reduction of the paleointensity of ∼7%. The software is available for download.

Characterizing the Geomagnetic Field at High Southern Latitudes: Evidence From the Antarctic Peninsula

AbstractDue to a dearth of data from high‐latitude paleomagnetic sites, it is not currently clear if the geocentric axial dipole (GAD) hypothesis accurately describes the long‐term behavior of the geomagnetic field at high latitudes. Here we present new paleomagnetic and paleointensity data from the James Ross Island (JRI) volcanic group, located on the Antarctic Peninsula. This data set addresses a notable lack of data from the 60°–70°S latitude bin and includes 251 samples from 31 sites, spanning 0.99–6.8 Ma in age. We also include positive fold, conglomerate, and baked contact tests. Paleointensity data from three methods (Thellier‐Thellier, pseudo‐Thellier, and Tsunakawa‐Shaw) were collected from all sites. The Thellier‐Thellier method had low yields and produced unreliable data, likely due to sample alteration during heating. Results from the Tsunakawa‐Shaw and pseudo‐Thellier methods were more consistent, and we found a bimodal distribution of paleointensity estimates. Most sites yielded either <15 μT or >40 μT, which together span a range of estimates from long‐term geomagnetic field models, but do not favor any model in particular. Alternating‐field demagnetization of these samples, when combined with preexisting data, yields a revised paleomagnetic pole of −87.5°, 025°, α95 = 3.6° for the Antarctic Peninsula over the last ∼5 Ma, which suggests that the current data set is sufficiently large to “average out” secular variation. Finally, the C2r/C2n transition was probably found at a site on JRI, and further geochronological and paleomagnetic study of these units could refine the age of this reversal.

New Paleointensity Data From Aniakchak Volcano, Alaska, USA

AbstractThis study presents the first set of Holocene, high‐quality absolute paleointensity data from Alaska, USA. Existing paleointensity data for the Holocene are generally located at mid‐northern latitudes in North America, Europe, the Middle East, and eastern Asia. Relatively few data are from the Alaska region. IZZI‐modified paleointensity experiments were conducted on glassy volcanic materials from Aniakchak volcano, a mid‐ to high‐latitude composite volcano on the Alaska‐Aleutian arc. The CCRIT selection criteria were applied to the paleointensity results. A total of 30 specimens from six samples with estimated ages ranging from 1931 CE to 2,300 years before present passed all selection criteria. The sample‐mean paleointensities ranged from 49.5 to 68.0 microTesla (μT). The sample‐mean paleointensity results are comparable to modeled intensities, however all except for one sample‐mean paleointensity are lower than those predicted by geomagnetic field models. The paleointensity estimate for the historical 1931 CE eruption was about 15 μT greater than the expected field strength. This overestimate may result from unrecognized alteration or non‐ideal remanence carriers in this sample. Further evaluation of samples from the 1931 CE eruption using a Bayesian estimation method resulted in a paleointensity estimate that encompasses the historical field strength within uncertainty. These new paleointensity results are a valuable contribution to the mid‐ to high‐northern latitude paleomagnetic data set. Incorporation of these data into future geomagnetic field models will improve the predictions of geomagnetic field behavior in the Alaska region.

New Paleointensities From the Skinner Cove Formation, Newfoundland, Suggest a Changing State of the Geomagnetic Field at the Ediacaran‐Cambrian Transition

AbstractThe geomagnetic field in the Ediacaran period appears to be characterized by anomalous directions, high reversal frequencies, and ultra‐low field strength. At the Ediacaran‐Cambrian transition, apparent polar wander paths become less controversial, but hyper‐reversing fields with reversal frequencies similar to earlier in the Ediacaran have been reported until the mid‐Cambrian. To understand the long‐term behavior of the magnetic field during this transitional interval, information about the field strength is vital but currently lacking. To improve the intensity record at that time, samples of volcanic rocks from the 550 Ma Skinner Cove Formation, western Newfoundland, have been used for paleointensity determination. This multi‐method paleointensity study, utilizing thermal and microwave Thellier as well as double‐heating Shaw and pseudo‐Thellier experiments produces paleointensity estimates of 2.6–10.3 μT, corresponding to virtual dipole moments of 0.65–2.25 × 1022 Am2. Analyses using scanning electron microscopy and rock magnetic measurements, as well as a positive intraformational conglomerate test, suggest that the remanence is primary. These intensity estimates are higher than earlier Ediacaran intensities and could point to the geomagnetic field entering into a stronger, more dipole‐dominated state at the Ediacaran‐Cambrian boundary.

Intensity of the Earth's magnetic field: Evidence for a Mid-Paleozoic dipole low

The Mesozoic Dipole Low (MDL) is a period, covering at least ∼80 My, of low dipole moment that ended at the start of the Cretaceous Normal Superchron. Recent studies of Devonian age Siberian localities identified similarly low field values a few tens of million years prior to the Permo-Carboniferous Reverse Superchron (PCRS). To constrain the length and timing of this potential dipole low, this study presents paleointensity estimates from Strathmore (∼411 to 416 Ma) and Kinghorn (∼332 Ma) lava flows, United Kingdom. Both localities have been studied for paleomagnetic poles (Q values of 6 to 7), and the sites were assessed for their suitability for paleointensity from paleodirections, rock magnetic analysis, and microscopy. Thermal and microwave experiments were used to determine site mean paleointensity estimates of ∼3 to 51 μT (6 to 98 ZAm2) and 4 to 11 μT (9 to 27 ZAm2) from the Strathmore and Kinghorn localities, respectively. These, and all the sites from 200 to 500 Ma from the (updated) Paleointensity database (PINT15), were assessed using the Qualitative Paleointensity criteria (QPI). The procurement of reliable (QPI ≥ 5) weak paleointensity estimates from this and other studies indicates a period of low dipole moment (median field strength of 17 ZAm2) from 332 to 416 Ma. This "Mid-Paleozoic Dipole Low (MPDL)" bears a number of similarities to the MDL, including the substantial increase in field strength near the onset of the PCRS. The MPDL also adds support to the inverse relationship between reversal frequency and field strength and a possible ∼200-My cycle in paleomagnetic behavior relating to mantle convection.

Using Meteorite Magnetism to Understand the History of Our Solar System: A Decade of Progress and Upcoming Challenges

Key Points High spatial and magnetic moment sensitivity microscopy techniques have revolutionized meteorite paleomagnetism in the last decade Fu et al. (2021) used quantum diamond microscopy to reinterpret the magnetization of Allende with implications for the protoplanetary disk Further work is required to interpret extraterrestrial paleomagnetic remanences, and how to recover reliable paleointensity estimates

Bias Corrected Estimation of Paleointensity (BiCEP): An Improved Methodology for Obtaining Paleointensity Estimates

AbstractThe assumptions of paleointensity experiments are violated in many natural and archeological materials, leading to Arai plots which do not appear linear and yield inaccurate paleointensity estimates, leading to bias in the result. Recently, paleomagnetists have adopted sets of “selection criteria” that exclude specimens with nonlinear Arai plots from the analysis, but there is little consensus in the paleomagnetic community on which set to use. In this study, we present a statistical method we call Bias Corrected Estimation of Paleointensity (BiCEP), which assumes that the paleointensity recorded by each specimen is biased away from a true answer by an amount that is dependent a single metric of nonlinearity (the curvature parameter) on the Arai plot. We can use this empirical relationship to estimate the recorded paleointensity for a specimen where, that is, a perfectly straight line. We apply the BiCEP method to a collection of 30 sites for which the true value of the original field is well constrained. Our method returns accurate estimates of paleointensity, with similar levels of accuracy and precision to restrictive sets of paleointensity criteria, but accepting as many sites as permissive criteria. The BiCEP method has a significant advantage over using these selection criteria because it achieves these accurate results without excluding large numbers of specimens from the analysis. It yields accurate, albeit imprecise estimates from sites whose specimens all fail traditional criteria. BiCEP combines the accuracy of the strictest selection criteria with the low failure rates of the less reliable “loose” criteria.

Effect of gyroremenance on relative paleointensity estimates applied to ignimbrite

Anhysteretic remanent magnetization (ARM) data serve many applications in the geosciences, such as quantifying the paleomagnetic field intensity, the magnetic grain size distributions in rocks, the degree of particle alignment from flow processes, and the emplacement and strain histories of rocks. However, the use of an alternating field when imparting or removing an ARM may give rise to a gyroremanent magnetization (GRM), which is a spurious signal that can bias ARM data. In this paper, we demonstrate the effect of GRM on ARM acquisition and demagnetization through an example of a relative paleointensity measurement. We describe a method using singular spectrum analysis to remove GRM acquired during static alternating field demagnetization (GRMAF). Another GRM component (GRMARM) is acquired during ARM acquisition. GRMARM is progressively removed during AF demagnetization, which results in a demagnetization spectrum containing two overlapping components (ARM and GRMARM). A second progressive demagnetization of a GRM imparted on the sample using an AF protocol with the same peak field as that used to impart the ARM, should contain the identical GRMARM component as acquired during the original ARM demagnetization. When separately measured, GRMARM can be subtracted from the original ARM demagnetization as a means of isolating a GRM-free ARM. Although we restrict our discussion to relative paleointensity, the methods described herein are applicable to any study involving alternating fields in paleomagnetic laboratory experiments.

Paleointensity and Rock Magnetism of Martian Nakhlite Meteorite Miller Range 03346: Evidence for Intense Small‐Scale Crustal Magnetization on Mars

AbstractThe martian dynamo’s strength and duration are essential for understanding Mars' habitability and deep interior dynamics. Although most northern volcanic terranes were likely emplaced after the martian dynamo ceased, recent data from the InSight mission show stronger than predicted crustal fields. Studying young volcanic martian meteorites offers a precise, complementary method to characterize the strength of the martian crustal field and examine its implications for past dynamo activity. We present the first rock and paleomagnetic study of nine mutually oriented samples from the martian Nakhlite meteorite Miller Range (MIL) 03346, which is well‐suited for paleomagnetic analysis due to its well‐known age (1,368 ± 83 Ma) and lack of significant aqueous, thermal, and shock overprinting. Rock magnetic analysis, including quantum diamond microscope imaging, showed that the natural remanent magnetization (NRM) is carried by Ti‐magnetite crystals containing µm‐scale ilmenite exsolution lamellae, which can accurately record ancient magnetic fields. Demagnetization of the NRM revealed a high coercivity magnetization interpreted to date from the age of eruption based on its intensity, unidirectionality, and a passing fusion crust baked contact test. Paleointensities of four samples reveal a 5.1 ± 1.5 µT paleofield, representing the most reliable martian paleointensity estimates to‐date and stronger than the 2 µT surface fields measured by InSight. Modeling shows that the observed fields can be explained by an older subsurface magnetized layer without a late, active dynamo and support a deeply buried, highly magnetized crust in the northern hemisphere of Mars. These results provide corroborating evidence for strong, small‐scale crustal fields on Mars.

Full‐Vector Paleosecular Variation Curve for the Azores: Enabling Reliable Paleomagnetic Dating for the Past 2 kyr

AbstractFor archeomagnetic dating, high‐quality directional and intensity paleosecular variation curves are needed. The Azores Archipelago in the mid‐Atlantic Ocean provides a wealth of volcanic products erupted during the Holocene, making it an ideal location to (1) gather paleomagnetic data from well dated lava flows and (2) construct a paleosecular variation (PSV) curve that enables paleomagnetic dating of volcanic products with unknown age. Here, we present new full‐vector paleomagnetic data from Pico Island, and combine the new data with existing data from neighboring islands to construct a new full‐vector PSV curve for the Azores Archipelago. An extensive rock‐magnetic study underpins the quality of our paleomagnetic carriers. From Pico Island, we obtained 21 new mean site directions; and 15 paleointensity estimates with the multimethod paleointensity approach from 12 sites, the age was known for 14 and 10 sites, respectively. By bootstrapping the non‐Gaussian uncertainty estimates of the radiocarbon age calibrations and the confidence intervals associated with the direction and paleointensity estimates, we produce the first full‐vector PSV curve with confidence intervals for the Azores covering the past 2 kyr. The PSV curve reveals a period of low inclination between ∼900 and 1560 AD, with minimum values of 32°. The potential of our new full‐vector PSV curve is demonstrated by successfully dating five lava flows from Pico Island.

First archeomagnetic data from Kenya and Chad: Analysis of iron furnaces from Mount Kenya and Guéra Massif

The variation of the Earth's magnetic field over the last millennia is poorly known in Africa, especially in Sub-Saharan Africa that represents less than 1% of the global archeomagnetic dataset. Fourteen iron furnaces from Kenya and Chad have been studied here for archeomagnetic purposes. These structures were dated by 14C from the 14th century in Kenya and from the 18-19th centuries in Chad. Samples, oriented with the plaster cap technique, have been subjected to thermal and alternating field demagnetization, rock magnetic analysis and paleointensity experiment, with the classical Thellier-Thellier technique corrected for anisotropy and cooling rate effects. New directional data (4 from Kenya and 10 from Chad) and one new paleointensity estimate from Kenya (43.5 ± 1.8 μT) were obtained. The Kenyan declinations are in good agreement with the geomagnetic global models, but the inclinations are lower and the intensity higher than predicted. For Chad, the new results prove the efficiency of the archeomagnetic dating, with a precision that is better than radiocarbon for the 18–19th centuries.