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Precambrian paleomagnetic studies are critical for testing paleogeographic reconstructions in deep time but rely on the fidelity of the assumption of the geocentric axial dipole (GAD) hypothesis. With high‐reliability data from mafic dykes and volcanic rocks, the scatter of individual virtual geomagnetic poles (VGPs) can be used to test simple GAD models. In order to conduct such a test, the VGPs must be adequate in number and in spatial coverage of the sampling sites. In this study, we targeted the 2.1 Ga Indin dyke swarm of the Slave craton. Building on previous sampling of the Indin dyke swarm in the western and central parts of southern Slave craton, we report results from 9 additional sites in the central and eastern parts of the craton, sites that significantly expand the width of the dyke swarm across the entire craton. The VGPs obtained from 7 of 9 newly identified Indin dykes are broadly similar to previously reported directions, expanding the total of VGPs for individual Indin dykes to n = 28, which is sufficient for a test of the GAD‐based statistical models using VGP scatter. The high VGP scatter of the Indin swarm can be attributed to the relatively high paleolatitude of 56° ± 6° for the Slave craton at the time of dyke emplacement. The Indin data have VGP scatter that is consistent with field models associated with the GAD hypothesis for the indicated paleolatitude, thus confirming the fidelity of the GAD field at ca. 2.1 Ga. Plain Language Summary: A fundamental assumption in paleomagnetism is the geocentric axial dipole (GAD) hypothesis. One feature of GAD that can be used to test it is that paleosecular variation (PSV) under a GAD field varies systematically with latitude, with its scatter being greater at relatively high latitudes than at low latitudes. Lavas and dykes for the past five million years and for various points in Earth's history generally support GAD, but there are some large gaps between these tests. Short‐term departures from GAD and/or intervals of weak fields have been suggested for certain time periods, highlighting the importance of regular tests of the GAD field throughout geological time. We study the ca. 2.1‐billion‐year‐old Indin dykes that fills one of these critical gaps. The Indin dyke swarm intruded across a large swath of the southern Slave craton, allowing us to extensively sample PSV. Our study finds a large VGP scatter for the Indin dykes, but as is to be expected given the relatively high paleolatitude. Thus, the scatter of Indin VGPs aligns with the GAD field model, confirming the reliability of the GAD field at ca. 2.1 Ga. Future studies of paleogeographic reconstruction during this period can confidently utilize paleomagnetism as a reliable quantitative constraint. Key Points: The ca. 2.1 Ga Indin dyke swarm has now been extensively sampled across much of the southern Slave cratonThe age and relatively high paleolatitude of the Indin dyke swarm provides an important constraint on the ancient magnetic fieldThe scatter of the paleomagnetic directions of the Indin dykes statistically supports a typical geomagnetic dipole field at 2.1 Ga [ABSTRACT FROM AUTHOR]

This paper addresses one of the critical questions of scientific inquiry: How do we know when a given data set is representative of the phenomenon being examined? For paleomagnetists, the question is often whether a particular data set sufficiently averaged paleosecular variation (PSV). To this aim, we updated an existing PSV data set that now comprises 2,441 site mean directions from 94 individual studies (PSV10‐24). Minimal filtering for data quality resulted in 1,619 sites from 90 publications. Fitting PSV10‐24 with two newly defined parameters as well as two existing ones form the basis of a Giant Gaussian Process field model (THG24) consistent with the data. Drawing directions from THG24 yields directional distributions predicted for a given latitude allowing a comparison between empirical distributions and the cumulative distribution function generated by the model. This tests whether the observed data adequately averaged out PSV according to THG24. We applied these tests to five data sets from Large Igneous Provinces from the last billion years and find that they are consistent with the THG24 model as well. Sedimentary data sets that may have experienced inclination shallowing can be corrected using an (un)flattening factor that yields directions satisfying THG24 in a newly‐defined, four‐parameter space. This approach builds on the Elongation‐Inclination (E/I) method of Tauxe and Kent (2004), https://doi.org/10.1029/145gm08, so the approach introduced here is called SVEI. We show examples of the use of SVEI and explain how to use this newly developed Python code that is publicly available in the PmagPy GitHub repository. Plain Language Summary: Paleomagnetic vectors recorded by rocks and archeological materials yield information on the structure of the magnetic field through Earth's history. The geomagnetic field mostly resembles a geocentric dipole aligned with the spin axis, but the directions at any given time and place generally deviate from this simple model. Data sets produced over several decades help define global magnetic field behavior. Here, we updated a compilation of paleomagnetic data and used it to establish a new field model representative of the last 10 million years. Prior or emerging data sets can be tested against the model to see whether the two agree in terms of field structure and variability. We tested data sets as old as 1.1 billion years and found them compatible with the model. Moreover, this model can also assess, and potentially correct data from sedimentary rocks that may have suffered from inclination shallowing. Although other correction methods exist, our approach employs a more complete description of the geometry of directional data, thereby allowing a more quantitative comparison of empirical and predicted distributions. Corrected inclinations and their uncertainties define paleolatitudes more accurately, key for plate tectonic and paleoclimatic reconstructions. Key Points: Update of the paleosecular variation database from lava flows (PSV10‐24) for the last 10 MaDefinition of a new Giant Gaussian Process (GGP) model (THG24), compatible with PSV10‐24 matching VGP scatter including data sets as old as 1.1 GaDescription of the SVEI method (an update of E/I) to assess secular variation records and to correct for inclination shallowing in sediments [ABSTRACT FROM AUTHOR]

Paleomagnetic results obtained from 38 Pliocene—Pleistocene volcanic flows from the Knot of the Pastos and surroundings of Puracé volcano and Popayán (southwestern Colombia) are presented. Using stringent quality criteria and excluding sites that classify as representatives of transitional states of Earth's field, a selected group of 27 sites (16 with normal polarity and 11 with reversed polarity) was obtained with a mean direction (Dec = 357.8°, Inc = 6.4°, α95 = 7.5° and κ = 15) that coincides with the geocentric axial dipole field (GAD: Dec = 0o, Inc = 3.2o) and, unlike similar studies at similar latitudes, does not coincide with the GAD plus a 5% axial quadrupolar component (Dec = 0°, Inc = −1.08°). However, when serial correlation (SC) among several sites with high inclination anomalies is taken into consideration, the mean direction of two resulting groups of sites shows greater consistency with a field that includes a quadrupolar component. It is interpreted that the sites treated for SC record states of the field similar to today's field in the area of study, which is being affected by the South Atlantic Anomaly. Plain Language Summary: The only way to study Earth's magnetic field in the geologic past from experimental data is by studying the magnetization of rocks that record Earth's field in a way comparable to the way compasses point close to the geographic north. Earth's magnetic field changes are significant in relatively short time‐scales like years or centuries. In this study the paleomagnetic directions recorded in volcanic products from extinct volcanoes of the Colombian Andes were obtained. Most of the volcanic flows record paleomagnetic directions consistent with the ones obtained from previous studies, which in general differ from the present magnetic directions in the area by being less inclined downwards. However, some of the volcanic flows did record paleomagnetic directions that are similar to the present magnetic directions in the area, which have been linked to an ample low magnetic intensity area in the Atlantic Ocean called the South Atlantic Anomaly. So, as it has been pointed out in other studies, it is possible that this anomaly has acted recurrently during the geologic past. Key Points: The mean paleomagnetic direction among the selected sites from Colombia shows consistency with a geocentric axial dipole (GAD) fieldConsistency with a GAD field with a 5% quadrupolar component is obtained when serial correlation is appliedSerially correlated sites are probably affected by the South Atlantic Anomaly, in a way similar to the present field in the study area [ABSTRACT FROM AUTHOR]

Paleosecular variation analysis is a primary tool for characterizing ancient geomagnetic behavior and its evolution through time. This study presents a new high‐quality directional data set, paleosecular variation of the Paleogene (PSVP), with and without correction for serial correlation, compiled from 1,667 sites from 45 different localities from the Paleogene and late Cretaceous (84–23 Ma). The data set is used to study the variability, structure, and latitude dependence of the geomagnetic field during that period by varying selection criteria and PSV models. Modeled values for the equatorial virtual geomagnetic pole (VGP) dispersion have over‐lapping uncertainty intervals within their uncertainty bounds between 8.3° and 18.6° for the past 250 Ma. We investigate the suitability of two descriptive models of PSV, Model G‐style quadratic fits and covariant Giant Gaussian Process models, and find that both styles of model fail to satisfactorily reproduce the latitude dependent morphology of PSV, but suggest that estimates of the equatorial VGP dispersion may still robustly characterize aspects of Earth's long‐term field morphology. During this time where the PSV behavior has not changed substantially, the reversal frequency has varied widely. The lack of a clear relationship between PSV behavior and reversal frequency is not trivially explained in the context of published findings regarding numerical geodynamo simulations. Plain Language Summary: The geomagnetic field is saved in volcanic rocks, which can be used to study the direction and intensity of this field millions of years later. The magnetic field is formed in the geodynamo in the Earth's outer core. The study of geomagnetic field changes through time gives us information on the changes in the Earth's outer core, lower mantle and inner core. In this study, all the data from the Paleogene and Late Cretaceous were gathered (84–23 million years ago) and studied to see how much the geomagnetic field changed through that time. With this study we now have information on the variability of the field for the entirety of the past 320 million years. We see that during the last 250 million years, the directional variability of the field seems to have varied little, even though the frequency of reversals varied massively. Some numerical simulations of the dynamo process occurring in Earth's core had previously suggested that both of these two things were directly correlated to the magnitude of heat flowing from the outer core to the mantle. Our new results suggest a more complex, nuanced picture. Key Points: A new data set, paleosecular variation of the Paleogene, comprising 1,667 paleomagnetic directions from 45 different localities of volcanics aged between 84 and 23 MaMedian equatorial dispersions of virtual geomagnetic poles have overlapping uncertainty bounds since 250 MaLarge fluctuations in the reversal frequency are not associated with large fluctuations in the inferred median axial dipole dominance [ABSTRACT FROM AUTHOR]

Abstract—To describe secular geomagnetic variation on geological timescales, statistical models have been widely used in recent decades. Currently, the most popular among these is the TK03 model (Tauxe and Kent, 2004). As other statistical models, TK03 numerically characterizes the amplitude of secular geomagnetic variation and the shape of the distribution of paleomagnetic directions which are thought to directly reflect the directions of the geomagnetic field on the considered interval of geological time. For this purpose, three main parameters are used: the scatter Sb (or S) of the virtual geomagnetic poles, the elongation E of the distribution of paleomagnetic directions, and the elongation direction of the distribution of paleomagnetic directions. The correct use of these parameters to describe paleosecular variation requires the fulfillment of certain, sometimes rather strict conditions. These conditions for parameters Sb and E were considered in a number of previous publications, while the limits and conditions of application of have not been studied in detail so far. The results of mathematical modeling presented in this paper allow us to evaluate the stability of the calculated parameter values as a function of sampling latitude, the number of samples used to determine this parameter, the length of the time series from which this parameter is estimated, as well as the inclination shallowing and the degree of averaging if is estimated from sedimentary rocks. We also consider the extent to which the parameter can be sensitive to the presence and characteristics of the equatorial dipole component in the total geomagnetic field. [ABSTRACT FROM AUTHOR]

Previous studies of rapid geomagnetic changes have highlighted the most extreme changes in direction and field strength found in paleomagnetic field models over the past 100 ky. Here we study distributions of rates of change in both time and space. Field models based on direct observations provide the most accurate values for rates of change, but their short duration precludes a complete description of field behavior. Broader representation is provided by time‐varying paleofield models, here including GGF100k, GGFSS70, LSMOD.2, CALS10k.2, HFM.OL1.A1, pfm9k.2, and SHAWQ‐iron age although variability across models and lack of temporal and spatial resolution of fine scale variations make direct comparisons difficult. For the paleofield we define rapid changes as exceeding the peak overall value of 0.4° yr−1 for directional changes and 150 nT yr−1 for intensities as established by the gufm1 model spanning 1590–1990 CE. We find that rapid directional changes are associated with low field strength and can spread across all latitudes during such episodes. Distributions of directional rates of change exhibit high skewness for models that include excursions. Rates of change in field intensity exceeding 150 nT yr−1 arise in brief intervals during the Holocene particularly associated with the strong field Levantine Iron Age Anomaly. Around the Laschamp excursion there are also rare localized occurrences of rapid intensity change. Limitations in current models make it difficult to define absolute rates for past changes, but we see that rapid changes are essential field characteristics not observed in the modern field that should nevertheless be regarded as an essential for Earth‐like dynamo simulations. Plain Language Summary: Earth's magnetic field is generated by fluid motions in its liquid outer core lying deep below the surface. Changes in the modern field are well‐mapped using low earth orbiting satellites and ground observations, but these are very modest. The largest changes over the past hundred thousand years occur on geological time scales predating the era of direct observations. These include geomagnetic excursions, periods characterized by low field strength and unstable directions, and intensity spikes when the field is unusually strong. To study the rates at which field changes occur we use a range of global time‐varying magnetic field models constructed from paleomagnetic and archeomagnetic records. These are much less detailed than modern data, but after accounting for their lesser resolution can still provide key insights into the occurrence of the most rapid changes. We find that high rates of change are an essential characteristic of the geomagnetic field over 0–100 ka that should be reproducible in Earth‐like dynamo simulations. Anomalously large rates of directional change are associated with weak field intensities surrounding geomagnetic excursions. Rapid intensity changes occur in brief intervals associated with the strongest fields found during the past few thousand years. Key Points: Rapid changes are an essential characteristic of the geomagnetic field over 0–100 kaAnomalously large rates of directional change are associated with weak field intensityRapid intensity changes occur in brief intervals associated with strong fields [ABSTRACT FROM AUTHOR]

The documentation and understanding of variations in the Earth's magnetic field through time is fundamental for several disciplines, but current geomagnetic models rely on datasets heavily biased toward the mid‐ and high northern latitudes. The African continent and surrounding islands and oceans are particularly underrepresented. Here, we present a new record of paleo‐secular variation (PSV) of the inclinations over the last 23 ka from Lake Chala, situated at 3°S near Mt Kilimanjaro in eastern equatorial Africa. This groundwater‐fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well‐constrained age model based on 210Pb and 14C dating. The magnetic mineralogy of the sediments is tested with rock magnetic analyses. The Lake Chala inclination record shows four highs and lows over 20 ka and compares well with that of Lake Malawi (10°S) between 20 and 16.2 ka, and from 9.8 to 2.6 ka. This record is linked to PSV records at Lakes Victoria and Malawi using a sequence slotting technique to generate a composite PSV model for east Africa. Analyzed at best‐possible resolutions up to 200 years, the Lake Chala PSV record not only represents an important contribution to improve our understanding of local and global features of the Earth's magnetic field. It also expands the utility of paleomagnetism as a key tool for dating and correlation both for archeological sites throughout East Africa and the many volcanoes, active or dormant, of the East African Rift System. Plain Language Summary: The understanding of the behavior of the Earth's Magnetic field in the geological past is based on an even spatial and temporal distribution of data collections. Nonetheless, data from large areas, such as from the African continent, remain sparse. In this study, we present new data from Lake Chala in equatorial East Africa, near Mount Kilimanjaro. The new inclination data are measured in lacustrine sediments covering the last 23 ka. We combine the data from Lake Chala with other data from Lake Victoria and Lake Malawi to produce a composite record for east African Lakes, using sequence slotting which improves the coherence between the records, whilst still constrained by the sediment age models. The composite record, centered on Lake Chala, improves our understanding of how the Earth's magnetic field changed in the recent past and can serve as an independent tool for dating nearby archeological sites as well as volcanic deposits from the African Rift emplaced in the last 23 ka. Key Points: Lake Chala contains an exceptionally well‐dated paleosecular variation record for east AfricaSequence slotting is used to refine a match to other secular variation records from east African lakesA composite paleosecular variation for equatorial east Africa is produced utilizing the combined set of control dates and magnetic records [ABSTRACT FROM AUTHOR]

Abstract Paleosecular variation analysis is a primary tool for characterizing ancient geomagnetic behavior and its evolution through time. This study presents a new high‐quality directional data set, paleosecular variation of the Paleogene (PSVP), with and without correction for serial correlation, compiled from 1,667 sites from 45 different localities from the Paleogene and late Cretaceous (84–23 Ma). The data set is used to study the variability, structure, and latitude dependence of the geomagnetic field during that period by varying selection criteria and PSV models. Modeled values for the equatorial virtual geomagnetic pole (VGP) dispersion have over‐lapping uncertainty intervals within their uncertainty bounds between 8.3° and 18.6° for the past 250 Ma. We investigate the suitability of two descriptive models of PSV, Model G‐style quadratic fits and covariant Giant Gaussian Process models, and find that both styles of model fail to satisfactorily reproduce the latitude dependent morphology of PSV, but suggest that estimates of the equatorial VGP dispersion may still robustly characterize aspects of Earth's long‐term field morphology. During this time where the PSV behavior has not changed substantially, the reversal frequency has varied widely. The lack of a clear relationship between PSV behavior and reversal frequency is not trivially explained in the context of published findings regarding numerical geodynamo simulations.

Abstract The documentation and understanding of variations in the Earth's magnetic field through time is fundamental for several disciplines, but current geomagnetic models rely on datasets heavily biased toward the mid‐ and high northern latitudes. The African continent and surrounding islands and oceans are particularly underrepresented. Here, we present a new record of paleo‐secular variation (PSV) of the inclinations over the last 23 ka from Lake Chala, situated at 3°S near Mt Kilimanjaro in eastern equatorial Africa. This groundwater‐fed crater lake is characterized by a high sedimentation rate (ca. 1 cm/10 years) and a particularly well‐constrained age model based on 210Pb and 14C dating. The magnetic mineralogy of the sediments is tested with rock magnetic analyses. The Lake Chala inclination record shows four highs and lows over 20 ka and compares well with that of Lake Malawi (10°S) between 20 and 16.2 ka, and from 9.8 to 2.6 ka. This record is linked to PSV records at Lakes Victoria and Malawi using a sequence slotting technique to generate a composite PSV model for east Africa. Analyzed at best‐possible resolutions up to 200 years, the Lake Chala PSV record not only represents an important contribution to improve our understanding of local and global features of the Earth's magnetic field. It also expands the utility of paleomagnetism as a key tool for dating and correlation both for archeological sites throughout East Africa and the many volcanoes, active or dormant, of the East African Rift System.

Abstract Previous studies of rapid geomagnetic changes have highlighted the most extreme changes in direction and field strength found in paleomagnetic field models over the past 100 ky. Here we study distributions of rates of change in both time and space. Field models based on direct observations provide the most accurate values for rates of change, but their short duration precludes a complete description of field behavior. Broader representation is provided by time‐varying paleofield models, here including GGF100k, GGFSS70, LSMOD.2, CALS10k.2, HFM.OL1.A1, pfm9k.2, and SHAWQ‐iron age although variability across models and lack of temporal and spatial resolution of fine scale variations make direct comparisons difficult. For the paleofield we define rapid changes as exceeding the peak overall value of 0.4° yr−1 for directional changes and 150 nT yr−1 for intensities as established by the gufm1 model spanning 1590–1990 CE. We find that rapid directional changes are associated with low field strength and can spread across all latitudes during such episodes. Distributions of directional rates of change exhibit high skewness for models that include excursions. Rates of change in field intensity exceeding 150 nT yr−1 arise in brief intervals during the Holocene particularly associated with the strong field Levantine Iron Age Anomaly. Around the Laschamp excursion there are also rare localized occurrences of rapid intensity change. Limitations in current models make it difficult to define absolute rates for past changes, but we see that rapid changes are essential field characteristics not observed in the modern field that should nevertheless be regarded as an essential for Earth‐like dynamo simulations.

The paleodirection and paleointensity of the geomagnetic field are determined from seven andesibasalt–basalt samples of three lava flows (L1–L3) from the Avachinskii (Avacha) volcano. Based on the sample from the recent lava flow TFE-50 (Tolbachik Fissure Eruption), the reliability of the Thellier–Coe method for geomagnetic field paleointensity determination is demonstrated: the deviation of the calculated Han from the IGRF12 values is at most 3% with a quality factor q > 13. The age of lava flows L1–L3 is refined using paleomagnetic data. Flows L1, L2 of the Molodoi Cone were formed in 1827 and 300–600 years ago, respectively, and the age of flow L3 at the crest of the somma is determined at 30–32 ka, which agrees with the known age estimate of the debris avalanche associated with the catastrophic destruction of the Avachinskii volcano 29 900 ± 37 900 14C years ago. [ABSTRACT FROM AUTHOR]

The Cretaceous Normal Superchron (CNS, 84–121 Ma) is a singular period of the geodynamo's history, identified by a prolonged absence of polarity reversals. To better characterize the paleosecular variation (PSV) of the geomagnetic field at the end of this interval, we sampled seven continuous sequences of lava flows from the Okhotsk‐Chukotka Volcanic Belt, emplaced 84–89 Ma in the vicinity of the Kupol ore deposit (NE Russia). From a collection of 1,024 paleomagnetic cores out of 82 investigated lava flows, we successfully determined the paleodirections of 78 lava flows, which led to 57 directional groups after removing the serial correlations. The resulting paleomagnetic pole is located at 170.0°E, 76.8°N (A95 = 5.2°, N = 57), in good agreement with previous estimates for north‐eastern Eurasia. Aiming at quantifying PSV at a reconstructed paleolatitude (λ) of ∼80°N, we obtained a virtual geomagnetic pole (VGP) scatter Sb=21.5°|19.3°24.0°(N=57) ${{S}_{\mathrm{b}}=21.5{}^{\circ}\vert }_{19.3{}^{\circ}}^{24.0{}^{\circ}}\,(N=57)$, the value of which was corrected for within‐site dispersion and is little dependent on the choice of the selection criteria. Compared to previous paleodirectional data sets characterizing PSV at various paleolatitudes during the CNS, our Sb estimate confirms a relative latitudinal increase Sb(λ = 90°)/Sb(λ = 0°) on the order of 2–2.5. Focusing on PSV at high paleolatitude within the 70°–90° range, we show that Sb was ∼15% lower at the end of the CNS than during the past 10 Myr, confirming that the singular polarity regime of the geodynamo observed during the CNS is likely accompanied with reduced PSV. Plain Language Summary: Compared to the last 10 million years during which Earth's magnetic field stochastically reversed its polarity ∼4 times per million year, the Cretaceous Normal Superchron (CNS, 84–121 Ma) represents an anomalously long period of stable polarity, the understanding of which is crucial to constrain the working of the geodynamo. In this effort to better characterize the paleosecular variation (PSV) of the geodynamo, we investigated the paleomagnetic record of lava flow sequences from the Okhotsk‐Chukotka Volcanic Belt (NE Russia) emplaced 84–89 Ma at high paleolatitude. First, we obtained that the dispersion of virtual paleomagnetic poles (VGP), used as a proxy for PSV, is 2–2.5 times as high at the paleopole as at the paleoequator. Second, we showed that VGP scatter at high paleolatitude was ∼15% lower at the end of the CNS than during the last 10 million years, confirming a potential link between polarity regime and PSV. Key Points: We investigate geomagnetic field behavior at high paleolatitude (∼80°N) at the end of the Cretaceous Normal Superchron (CNS)We present a paleodirectional data set from 78 lava flows (resp. 57 directional groups), emplaced 84–89 Ma in north‐eastern EurasiaWe show that the dispersion of virtual geomagnetic poles at high latitude is ∼15% lower during the CNS than for the past 10 Myr [ABSTRACT FROM AUTHOR]

Magnetostratigraphy has become increasingly popular among geologists worldwide, as evidenced by recent scientific publications. This article reviews the role and place of magnetostratigraphy in general stratigraphic studies. The problem of developing a magnetostratigraphic scale of the Brunhes epoch based on paleosecular variation in the direction or intensity of the geomagnetic field was discussed. Nowadays, the above method has been actively pursued by researchers. Some hitherto little explored problems related to it were considered. Special attention was paid to the applicability range of the local magnetostratigraphic scale on the Earth’s surface. Three methods for estimating this parameter were proposed. Possible causes for the bias of paleomagnetic records in lava flows were analyzed: displacement of a recording medium during the recording process or later, magnetic anisotropy of two types, as well as the distortion of the geomagnetic field due to uneven surface magnetism, unevenly cooling lava magnetism, magnetism of surrounding rocks, or magnetohydrodynamic properties of flowing lava. The issues addressed here are important for improving the quality and reliability of paleomagnetic data.

The Casas Grandes culture in Northern Mexico and Southwest United States has been characterized by its impressive architecture - unique to desert cultures, with houses and constructions of up to four floors built by adobe. In this study, we report an integrated rock-magnetic and archaeomagnetic study from Paquimé archaeological site, considered as an outstanding testimony of the relationship between the cultures of North America and Mesoamerica. The In Situ structures of Paquimé archaeological zone were magnetically analyzed for the first time. Four up to 2.6 m deep Pit Ovens, commonly used for agave cooking, were sampled. 78 specimens were subjected to stepwise alternating field demagnetizations to retrieve characteristic remanence archaeodirections. The great majority of samples yielded evidence of essentially stable, single component remanent magnetization carried by the end members of titanomagnetite solid solutions (almost magnetite phase). Hematite grains apparently also co-exist, but their contribution in total thermoremanence is minor. The archaeomagnetic dating, based on mean declination and inclination, was performed using the global geomagnetic models and the available regional Paleosecular Variation Curves available for Mesoamerica. Additionally, SW United State paleosecular variation patterns from Four Corner region was also considered. The most probable age interval for one of the studied ovens (around 940 AD) is out of Paquimé's main occupation phase between 1200 and 1450 AD. The age estimation for the PH1 pit oven, around 1150 AD, could be located near the limit of the beginning of the Medio Period. Remained two analyzed ovens yielded up to three possible ages distributed around 1100, 1320 and 1480 AD. Pit Ovens studied here, were long time considered to correspond to same time interval, while these new results attest that these combustion structures encompassed almost six centuries in agreement with the historical fact that the city of Paquimé was abandoned before the arrival of the Spaniards. • The Casas Grandes culture in Northern Mexico and Southwest United States. • Deep Pit Ovens of Paquimé, commonly used for agave cooking, were sampled in detail. • Rock-magnetic and archaeomagnetic experiments were performed. • Archaeomagnetic dates based on regional curves and global geomagnetic models. • The ovens persisted over the six centuries. [ABSTRACT FROM AUTHOR]

Statistical studies of paleosecular variation (PSV) are used to infer the structure and behavior of the geomagnetic field. This study presents a new database, paleosecular variation of the Miocene (PSVM), of high‐quality directional data from the Miocene Epoch (5.3–23 Ma), compiled from 1,454 sites from 44 different localities. This database is used to model the latitude dependence of paleosecular variation with varying selection criteria using a quadratic form based on Model G. Our fitted model parameter for latitude‐invariant PSV (Model G a) is 15.6° and the latitude dependent PSV term (Model G b) is 0.23. The latitude invariant term is substantially higher than previously observed for the past 10 Myrs or any other studied ages. We also present a new stochastic model of the time‐average field, BB‐M22, using a covariant giant Gaussian process (GGP) which is constrained using data from PSVM, PINT and Earth‐like geodynamo numerical simulations. BB‐M22 improves the fit to PSVM data relative to prior GGP models, as it reproduces the higher virtual geomagnetic pole (VGP) dispersion observed during the Miocene. Our findings suggest a more variable magnetic field and more active geodynamo in the Miocene Epoch than the past 10 Myrs, perhaps linked to elevated core‐mantle heat flow. Our results suggest that the average axial dipole dominance of the time‐instantaneous field was lower than in more recent times. We note however, that the inclination anomaly estimates, suggest that it cannot be ruled out that the Miocene time averaged field resembles a geocentric axial dipole. Plain Language Summary: The variability of the Earth's magnetic field is dependent on characteristics of the geodynamo in the Earth's outer core. Changes of the geomagnetic field throughout Earth's history are important to study as they give us insight into the evolution of the interior of our planet. We study the changes of the geomagnetic field using data from volcanic rocks that preserved the geomagnetic field direction from when they were formed. In this study, we gathered all the data from the Miocene period (23–5 million years ago) to see how the geomagnetic field was behaving during that time. The database shows that the geomagnetic field in the Miocene Epoch was more variable than in the past 10 million years. Studies that have produced simulations of the geodynamo suggest that when the outer core undergoes stronger convection, this produces a more variable and complicated geomagnetic field at the Earth's surface. The higher variability of the geomagnetic field in the Miocene therefore suggests more vigorous convection in the outer core at that time. Key Points: We compiled a new database, paleosecular variation of the Miocene comprising 1,454 paleomagnetic directions from 44 different localities of Miocene volcanicsVirtual geomagnetic pole dispersions indicate a more variable field during the Miocene compared to the last 10 MyrsThe elevated equatorial virtual geomagnetic pole dispersion suggests more vigorous convection in the outer core during this time [ABSTRACT FROM AUTHOR]

Abstract Statistical studies of paleosecular variation (PSV) are used to infer the structure and behavior of the geomagnetic field. This study presents a new database, paleosecular variation of the Miocene (PSVM), of high‐quality directional data from the Miocene Epoch (5.3–23 Ma), compiled from 1,454 sites from 44 different localities. This database is used to model the latitude dependence of paleosecular variation with varying selection criteria using a quadratic form based on Model G. Our fitted model parameter for latitude‐invariant PSV (Model G a) is 15.6° and the latitude dependent PSV term (Model G b) is 0.23. The latitude invariant term is substantially higher than previously observed for the past 10 Myrs or any other studied ages. We also present a new stochastic model of the time‐average field, BB‐M22, using a covariant giant Gaussian process (GGP) which is constrained using data from PSVM, PINT and Earth‐like geodynamo numerical simulations. BB‐M22 improves the fit to PSVM data relative to prior GGP models, as it reproduces the higher virtual geomagnetic pole (VGP) dispersion observed during the Miocene. Our findings suggest a more variable magnetic field and more active geodynamo in the Miocene Epoch than the past 10 Myrs, perhaps linked to elevated core‐mantle heat flow. Our results suggest that the average axial dipole dominance of the time‐instantaneous field was lower than in more recent times. We note however, that the inclination anomaly estimates, suggest that it cannot be ruled out that the Miocene time averaged field resembles a geocentric axial dipole.

Earth's magnetic field, one of the most enigmatic physical phenomena of the planet, is constantly changing on various time scales, from decades to millennia and longer. The reconstruction of geomagnetic field behavior in periods predating direct observations with modern instrumentation is based on geological and archaeological materials and has the twin challenges of (i) the accuracy of ancient paleomagnetic estimates and (ii) the dating of the archaeological material. Here we address the latter by using a set of storage jar handles (fired clay) stamped by royal seals as part of the ancient administrative system in Judah (Jerusalem and its vicinity). The typology of the stamp impressions, which corresponds to changes in the political entities ruling this area, provides excellent age constraints for the firing event of these artifacts. Together with rigorous paleomagnetic experimental procedures, this study yielded an unparalleled record of the geomagnetic field intensity during the eighth to second centuries BCE. The new record constitutes a substantial advance in our knowledge of past geomagnetic field variations in the southern Levant. Although it demonstrates a relatively stable and gradually declining field during the sixth to second centuries BCE, the new record provides further support for a short interval of extreme high values during the late eighth century BCE. The rate of change during this "geomagnetic spike" [defined as virtual axial dipole moment > 160 ZAm2 (1021 Am2)] is further constrained by the new data, which indicate an extremely rapid weakening of the field (losing ∼27% of its strength over ca. 30 y).

Continuous paleosecular variations reconstructed from sedimentary archives have remarkably deepened our insights into the dynamics of the Earth's magnetic field as well as the chronological purpose. Nevertheless, to construct reliable sedimentary paleomagnetic records in diagenetic reducing sediments is challenging generally due to the pervasive magnetic mineral diagenesis. The relict magnetic minerals are residuals after diagenesis and probably able to record a depositional remanent magnetization, thus it is worthy to explore their paleomagnetic potentials. For this study, two Black Sea sediment cores covering the past 8 ka were subjected to mineralogical and paleo‐ and rock magnetic analyses. Paramagnetic pyrite framboids are pervasive in the studied sediments deposited under anoxic bottom water conditions in the Black Sea. In addition, relict magnetic minerals of ferrous hemoilmenite, Fe‐Mn and Fe‐Cr spinels, and magnetite inclusions are also present in the studied cores. Compared to the previous published paleomagnetic results from the same cores over the last glacial period (20–30 ka) which are dominated by detrital (titano‐)magnetite particles, the studied relict magnetic mineral samples exhibit a similar behavior in recording the depositional remanent magnetization. Furthermore, the obtained paleosecular variations spanning the past 8 ka reproduce the high intensity patterns observed in the regional archeomagnetic and volcanic datasets. Thus, the successful reconstruction of paleomagnetic secular variations from the anoxic Black Sea sediments greatly extend the application of paleomagnetism in sediments deposited in water with a reducing sub‐surface environments from where paleomagnetic data are generally sparse. Plain Language Summary: The Earth's magnetic field can be recorded by magnetic minerals during their deposition within a water column, and are later preserved in sediments. The geomagnetic field signal may be biased if the magnetic minerals are subsequently altered because of changes in bottom water redox conditions. However, relict magnetic minerals are resistant to ambient environmental changes and thus have great potentials to record reliable paleomagnetic signals. To attest this novel idea, we systematically investigated sediments form the Black Sea under strong anoxic bottom water conditions. Our results demonstrate that the relict magnetic minerals survived in the Black Sea sediments covering the past eight thousand years. By comparison with detrital (titano‐)magnetite samples, we found that relict magnetic mineral samples have similar behavior in recording the geomagnetic field. Moreover, the geomagnetic field variations reconstructed from the Black Sea sediments are comparable with other validated regional datasets for the past eight thousand years. Therefore, our new study significantly extends the application of paleomagnetic methods in a wider range of sedimentary redox conditions. Key Points: Relict minerals of hemoilmenite, Fe‐Mn and Fe‐Cr spinels, and magnetic inclusions are magnetic carriers in studied Black Sea sedimentsThe ability in recording the DRM by relict magnetic minerals are comparable with detrital (titano‐)magnetiteThe obtained paleosecular variations resemble reginal field patterns observed in archeomagnetic and volcanic datasets for the past 8 ka [ABSTRACT FROM AUTHOR]

Paleomagnetic poles used to compute apparent polar wander paths (APWPs) are strongly dispersed, which was recently shown to cause a large fraction (>50%) of these poles to be statistically distinct from the APWP to which they contributed, suggesting that current statistical approaches overestimate paleomagnetic resolution. Here, we analyze why coeval paleopoles are so dispersed, using the paleopoles behind the most recent global APWP and a compilation of paleomagnetic data obtained from <10 Ma volcanic rocks (PSV10). We find that paleopoles derived from sedimentary rocks, or from data sets underrepresenting paleosecular variation (PSV), are more dispersed and more frequently displaced. We show that paleopoles based on a smaller number of paleomagnetic sites are more dispersed than poles based on larger data sets, revealing that the degree to which PSV is averaged is an important contributor to the pole dispersion. We identify as a fundamental problem, however, that the number of sites used to calculate a paleopole, and thus the dispersion of coeval paleopoles, is essentially arbitrary. We therefore explore a different approach in which reference poles of APWPs are calculated from site‐level data instead of paleopoles, thereby assigning larger weight to larger data sets. We introduce a bootstrap‐based method for comparing a collection of paleomagnetic data with a reference data set on the same hierarchical level, whereby the uncertainty is weighted against the number of paleomagnetic sites. Finally, our study highlights that demonstrating smaller tectonic displacements requires larger paleomagnetic data sets, and that such data sets can strongly improve future APWPs. Plain Language Summary: Apparent polar wander paths (APWPs) are widely used to reconstruct the position of continents relative to the Earth's rotation axis. These paths are typically calculated by averaging paleomagnetic poles obtained from rocks of similar age. Although these poles are expected to be tightly grouped, they are strongly scattered. Notably, this causes >50% of the poles used in recent APWPs to be statistically different from the APWP itself. Here, we investigate to what extent errors in these poles may explain the observed scatter. We find that poles derived from sedimentary rocks are more scattered than those derived from igneous rocks. Also, poles based on smaller data sets are more dispersed than those based on larger data sets. Our analysis shows that the amount of paleomagnetic data used to determine a pole is often arbitrary. To overcome the subjectivity in pole calculation, we propose a new approach in which an APWP is calculated from individual data points instead of from paleopoles. This allows comparing paleomagnetic data on the same statistical level, and the development of APWPs in which larger data sets have larger weight. Our study thus emphasizes the value of collecting large paleomagnetic data sets, which may improve future APWPs. Key Points: Paleopoles do not average "out" paleosecular variation, which forms a first‐order contributor to the dispersion of coeval paleopolesThe number of sites used to compute a paleopole and the number of paleopoles calculated from a given data set is essentially arbitraryCalculating apparent polar wander paths from site‐level data instead of poles allows the weighting of uncertainties and the amount of data [ABSTRACT FROM AUTHOR]

The Cretaceous Normal Superchron (CNS) was first defined in the 1960s to explain the Cretaceous Quiet Zone in marine magnetic anomaly profiles, which includes no or fewer geomagnetic reversals. This ∼37 million years period is considered the most unique and extreme geomagnetic feature for the last 160 Myr. Superchrons may be caused by the geodynamo operating at peak efficiency with a unique heat flux at the core-mantle boundary (CMB). Previous studies suggest that the CNS is a sign of the connection between Earth’s interior and surface. During the CNS, the geomagnetic intensity may have fluctuated significantly, and the average may have changed with time, and the paleosecular variations had unique features. The warm climate around the CNS may have been caused by volcanic activity associated with active mantle convection. Such mantle convection increases heat flux at the CMB during the CNS, but geodynamo simulations predict small heat flux, which are inconsistent. This discrepancy may be resolved by the growth and collapse of a superplume or by an increase and decrease in the subduction flux.

Abstract Studying paleosecular variation (PSV) can provide unique insights into the average morphology of the geomagnetic field and the operation of the geodynamo. Although recent studies have expanded our knowledge of paleomagnetic field behavior through the late Mesozoic, relatively little is known regarding the Triassic period (ca. 251.9–201.3 Ma). This study compiles the first Triassic virtual geomagnetic pole (VGP) database for the analysis of PSV, as part of a longer Post‐Permo‐Carboniferous Reversed Superchron (PCRS) time interval (265‐198 Ma). VGP angular dispersion and its dependence on apparent paleolatitude are compared against a new PCRS compilation and published PSV compilations for intervals across the last ∼320 Ma. We find that the Post‐PCRS displays near latitudinal invariance of VGP dispersion while the PCRS displays very strong latitudinal dependence. PSV behavior during the Post‐PCRS appears indistinguishable to that previously reported for the interval preceding the Cretaceous Normal Superchron (Pre‐CNS; 126–198 Ma). The near‐constant behavior between time intervals with significantly different apparent average polarity reversal frequencies does not support a suggested relationship between VGP dispersion and reversal frequency. The dispersion observed for the PCRS is consistent with the results of previous studies and represents behavior that is potentially unique over the last ∼320 Ma. A recently published approach to obtain a description of field morphology from equatorial VGP dispersion shows the PCRS geomagnetic field to have been more strongly axial dipole dominated than any interval since. This observation may be causally linked to the PCRS being the longest known superchron in the Phanerozoic geomagnetic polarity timescale.

Abstract Investigations into long‐term geomagnetic variations provide useful information regarding paleomagnetic field behavior. In this study, we assess the latitudinal structure of paleosecular variation (PSV) and the time‐averaged field (TAF) for the Brunhes normal and Matuyama reverse chrons, and for the 0–10 Ma period, from an updated and reviewed paleodirectional database spanning the past 10 Myr. The new database comprises 2,543 paleomagnetic sites from igneous rocks, providing improvements in the geographic and temporal distributions of high‐quality data relative to previous compilations. In addition, the new data collection differs considerably in application of strict selection criteria. Statistical analysis of the virtual geomagnetic pole (VGP) dispersion curve of Model G reveals a low latitudinal dependence of PSV for the last 10 Myr. For this period, we present a zonal TAF model based on the latitudinal distribution of inclination anomaly data. The best estimates found for axial quadrupole and octupole components were about 3% and 1% relative to axial dipole component, respectively. The new statistical models for the Brunhes and Matuyama chrons have different patterns in both PSV and TAF, in compliance with earlier studies. Our quantitative assessments indicate an apparent hemispheric PSV asymmetry, particularly in the Brunhes chron, with a stronger latitudinal signature in the southern hemisphere compared to the north. These findings suggest that equatorial PSV asymmetry, that has previously been found in modern, historical and millennial scale geomagnetic models, has persisted over the past 0.78 Ma.

Investigations into long‐term geomagnetic variations provide useful information regarding paleomagnetic field behavior. In this study, we assess the latitudinal structure of paleosecular variation (PSV) and the time‐averaged field (TAF) for the Brunhes normal and Matuyama reverse chrons, and for the 0–10 Ma period, from an updated and reviewed paleodirectional database spanning the past 10 Myr. The new database comprises 2,543 paleomagnetic sites from igneous rocks, providing improvements in the geographic and temporal distributions of high‐quality data relative to previous compilations. In addition, the new data collection differs considerably in application of strict selection criteria. Statistical analysis of the virtual geomagnetic pole (VGP) dispersion curve of Model G reveals a low latitudinal dependence of PSV for the last 10 Myr. For this period, we present a zonal TAF model based on the latitudinal distribution of inclination anomaly data. The best estimates found for axial quadrupole and octupole components were about 3% and 1% relative to axial dipole component, respectively. The new statistical models for the Brunhes and Matuyama chrons have different patterns in both PSV and TAF, in compliance with earlier studies. Our quantitative assessments indicate an apparent hemispheric PSV asymmetry, particularly in the Brunhes chron, with a stronger latitudinal signature in the southern hemisphere compared to the north. These findings suggest that equatorial PSV asymmetry, that has previously been found in modern, historical and millennial scale geomagnetic models, has persisted over the past 0.78 Ma. Key Points: An updated 0–10 Ma database provides improvements in the geographic and temporal distributions of high‐quality dataWe propose a zonal time‐averaged field model for the past 10 MyrQuantitative analyses suggest equatorial asymmetry of Brunhes chron paleosecular variation [ABSTRACT FROM AUTHOR]

Lake sediments are very useful for providing high-resolution records of geomagnetic field variations, especially for the Holocene period. We present high-resolution paleomagnetic records from three cores (KCL12P1, P2, and P3) recovered from Küçükçekmece Lagoon, located at the northern shoreline of the Sea of Marmara, Turkey. The cores were subjected to a comprehensive paleomagnetic and rock magnetic investigation using oriented samples. According to the age-depth model, based on radiocarbon dating and X-ray fluorescence-derived Ca/Ti element ratios, tuned to available oxygen isotope records based on an absolute calendar-year time-scale, we obtained a new paleomagnetic record for the last 3800 years. Low paleointensities were found during 1500-2000 BP. Stacked paleomagnetic directions from Küçükçekmece Lagoon were correlated to regional geomagnetic field models. This correlation proved that the paleomagnetic records (paleointensity, inclination) obtained from the Küçükçekmece Lagoon sediments considerably agree with the data from the surrounding region over the past 3800 years. [ABSTRACT FROM AUTHOR]

Abstract This work presents an extensive directional paleomagnetic database of the Kiaman reversed superchron. It is composed of 1,459 paleomagnetic directions from igneous rocks corresponding to 91 data sets (or paleomagnetic poles). An almost constant behavior of more concentrated and circular distributions for latitudes higher than 10° was found, which contrasts strongly with predictions of the representative models for the past few million years. We searched for simplified and spatially covariant Giant Gaussian Process (GGP) models that best explain the directional distribution of the Kiaman database. We used the mean strength based on the mean of virtual dipole moment (VDM) results for the period drawn from the available databases. Among the tested models, the one that best explains the directional paleosecular variation of the Kiaman database is the covariant type. According to this model, the correlations between the Gaussian coefficients are valid for the last 10 Myr and the Kiaman superchron. The resulting GGP models have β parameters similar to the 0–10 Ma models, which indicates that the relation between symmetric and antisymmetric families appears unchanged in the geological past. The relative variability of the Kiaman field, as inferred from the ratio αg10¯ from GGP models, is lower than for the past 10 Myr. Thus, as well as the paleointensity, αg10¯ seems to be a proxy that can be used for evaluating the geomagnetic development along the geological time.

This work presents an extensive directional paleomagnetic database of the Kiaman reversed superchron. It is composed of 1,459 paleomagnetic directions from igneous rocks corresponding to 91 data sets (or paleomagnetic poles). An almost constant behavior of more concentrated and circular distributions for latitudes higher than 10° was found, which contrasts strongly with predictions of the representative models for the past few million years. We searched for simplified and spatially covariant Giant Gaussian Process (GGP) models that best explain the directional distribution of the Kiaman database. We used the mean strength based on the mean of virtual dipole moment (VDM) results for the period drawn from the available databases. Among the tested models, the one that best explains the directional paleosecular variation of the Kiaman database is the covariant type. According to this model, the correlations between the Gaussian coefficients are valid for the last 10 Myr and the Kiaman superchron. The resulting GGP models have β parameters similar to the 0–10 Ma models, which indicates that the relation between symmetric and antisymmetric families appears unchanged in the geological past. The relative variability of the Kiaman field, as inferred from the ratio αg10¯ from GGP models, is lower than for the past 10 Myr. Thus, as well as the paleointensity, αg10¯ seems to be a proxy that can be used for evaluating the geomagnetic development along the geological time. Key Points: A new database of paleomagnetic directions of igneous Kiaman sitesThe distributions of the Kiaman directions reveal low paleosecular variationThe first Giant Gaussian Process models for ages older than the last 10 million years are presented [ABSTRACT FROM AUTHOR]

Microbialites–layered, organosedimentary deposits–exist in the geologic record and extend back in deep time, including all estimated times of inner core nucleation. Microbialites may preserve magnetic field variations at high-resolution based on their estimated growth rates. Previous studies have shown that microbialites can have a stable magnetization. However, the timing and origin of microbialite magnetization were not well determined, and no study has attempted to evaluate whether actively growing microbialites record the geomagnetic field. Here, we present centimeter-scale magnetization and magnetic property variations within the structure of modern microbialites from Great Salt Lake (GSL), United States, and Laguna Bacalar, Mexico, Pleistocene microbialites from GSL, and a Cambrian microbialite from Mongolia. All samples record field directions close to the expected value. The dominant magnetic carrier has a coercivity of 35–50 mT and unblocking temperatures are consistent with magnetite. A small proportion of additional high coercivity minerals such as hematite are also present, but do not appear to appreciably contribute to the natural remanent magnetization (NRM). Magnetization is broadly consistent along microbialite layers, and directional variations correlate with the internal slope of the layers. These observations suggest that the documented NRM may be primarily detrital in origin and that the timing of magnetization acquisition can be close to that of sediment deposition.

Paleomagnetic results from globally distributed lava flows have been collected and analyzed under the time-averaged field initiative (TAFI), a multi-institutional collaboration started in 1996 and designed to improve the geographic and temporal coverage of the 0-5 Ma paleomagnetic database for studying both the time-averaged field and its very long-term secular variations. Paleomagnetic samples were collected from 35 volcanic units, either lava flows or ignimbrites, in Costa Rica in December 1998 and February 2000 from the Cordilleras Central and Guanacaste, the underlying Canas, Liberia and Bagaces formations and from Volcano Arenal. Age estimates range from approximately 40 ka to slightly over 6 Ma. Although initial results from these sites were used in a global synthesis of TAFI data by Johnson et al. (2008), a full description of methodology was not presented. This paper documents the definitive collection of results comprising 28 paleomagnetic directions (24 normal, 4 reversed), with enhanced precision and new geological interpretations, adding two paleointensity estimates and 19 correlated 40Ar/39Ar radiometric ages. The average field direction is consistent with that of a geocentric axial dipole and dispersion of virtual geomagnetic poles (17.3 ± 4.6°) is in general agreement with predictions from several statistical paleosecular variation models. Paleointensity estimates from two sites give an average field strength of 26.3 μT and a virtual axial dipole moment of 65 ZAm2. The definitive results provide a useful augmentation of the global database for the longer term goal of developing new statistical descriptions of paleomagnetic field behavior. © 2013. American Geophysical Union. All Rights Reserved.

A full‐vector paleosecular variation (PSV) record (inclination, declination, and relative paleointensity) from the pen‐ultimate glacial (130–180 ka) could be constructed from a total of 12 sediment cores recovered from the Arkhangelsky Ridge in the SE Black Sea. Stacking of the individual partly fragmented records was achieved by a detailed correlation using high‐resolution data records from X‐ray fluorescence scanning, Ca/Ti and K/Ti log‐ratios, as well as magnetic susceptibility. Age constraints are provided by a detailed composite oxygen isotope stratigraphy from three of the cores, correlated to U‐Th‐dated speleothem oxygen isotope records from Hungary and Turkey. The temporal resolution of the stacked paleomagnetic data records is 200 years. Practically, this data set is the first high‐resolution PSV record for SE Europe/SW Asia from marine isotope stage 6, comprising inclination, declination and relative paleointensity. Besides an easterly swing in declination at ∼159 ka and a pronounced intensity low together with low inclinations at ∼148 ka, both not reaching an excursional PSV index of >0.5, the obtained directional variations reflect only normal PSVs, with a PSV index of <0.3. Key Points: Reconstructed geomagnetic field variation record between 180 and 130 ka from Black Sea sedimentsFirst full‐vector paleosecular variation record from marine isotope stage 6 for Southeast Europe/Southwest AsiaIntensity maxima occur at 166.5 ka and at 141.0 ka [ABSTRACT FROM AUTHOR]

[1] This study presents paleomagnetic results from the Snake River Plain (SRP) in southern Idaho as a contribution to the time-averaged field global database. Paleomagnetic samples were measured from 26 sites, 23 of which ( 13 normal, 10 reverse) yielded site mean directions meeting our criteria for acceptable paleomagnetic data. Flow ages (on 21 sites) range from 5 ka to 5.6 Ma on the basis of Ar-40/Ar-39 dating methods. The age and polarity for the 21 dated sites are consistent with the Geomagnetic Reversal Time Scale except for a single reversely magnetized site dated at 0.39 Ma. This is apparently the first documented excursion associated with a period of low paleointensity detected in both sedimentary and igneous records. Combining the new data from the SRP with data published from the northwest United States between the latitudes of 40degrees and 50degreesN, there are 183 sites in all that meet minimum acceptability criteria for legacy and new data. The overall mean direction of 173 normally magnetized sites has a declination of 2.3degrees, inclination of 61.4degrees, a Fisher concentration parameter (kappa) of 58, and a radius of 95% confidence (alpha(95)) of 1.4degrees. Reverse sites have a mean direction of 182.4degrees declination, -58.6degrees inclination, kappa of 50, and alpha(95) of 6.9degrees. Normal and reversed mean directions are antipodal and indistinguishable from a geocentric axial dipole field at the 95% confidence level. Virtual geomagnetic pole dispersion was found to be circularly symmetric, while the directional data were elongate north-south. An updated and corrected database for the northwestern U. S. region has been contributed to the Magnetics Information Consortium (MagIC) database at http://earthref.org.

Maps of virtual geomagnetic poles derived from international geomagnetic reference field models show large lobes with significant departures from the spin axis. These lobes persist in field models for the last few millenia. The anomalous lobes are associated with observation sites at extreme southerly latitudes. To determine whether these features persist for millions of years, paleomagnetic vector data from the continent of Antarctica are essential. We present here new paleomagnetic vector data and Ar-40/Ar-39 ages from lava flows spanning the Brunhes and Matuyama Chrons from the vicinity of McMurdo Sound, Antarctica. Oriented paleomagnetic samples were collected from 50 lava flows by E. Mankinen and A. Cox in the 1965-1966 austral summer season. Preliminary data based largely on the natural remanent magnetization (NRM) directions were published by Mankinen and Cox [1988]. We have performed detailed paleomagnetic investigations of 37 sites with multiple fully oriented core samples to investigate the reliability of results from this unique sample collection. Of these, only one site fails to meet our acceptance criteria for directional data. Seven sites are reversely magnetized. The mean normal and reverse directions are antipodal. The combined mean direction has (D) over bar =12, (I) over bar=-86, alpha=4, kappa=37 and is indistinguishable from that expected from a GAD field. We obtained reproducible absolute paleointensity estimates from 15 lava flows with a mean dipole moment of 49 ZAm(2) and a standard deviation of 28 ZAm(2). Ar-40/Ar-39 age determinations were successfully carried out on samples from 18 of the flows. Our new isotopic ages and paleomagnetic polarities are consistent with the currently accepted geomagnetic reversal timescales.

In small‐volume igneous intrusions, the duration of magmatism can be difficult to determine because assembly of an intrusion from component magma pulses may occur within geochronologic uncertainties. We demonstrate that the paleomagnetic record of short‐term movement of the geomagnetic pole (secular variation) can place constraints on the duration of intrusion assembly over shorter time periods. An analysis of 14C data paired with paleomagnetic data from lava flows illustrates this approach. The flows record paleosecular variation that, when combined with the maximum rate of secular variation from the Holocene, returns a minimum time elapsed between any two flows. Data from an Oligocene laccolith indicate that this system records a minimum of 49° of secular variation and therefore took at least 750 years to be emplaced. High‐precision radiometric geochronology would be unable to resolve this assembly, suggesting that the paleosecular variation record in shallow igneous rocks contains valuable temporal constraints on upper crustal magmatism. Key Points: The record of paleosecular variation of upper crustal intrusions can provide a minimum estimate of the duration of igneous emplacementThis record can potentially constrain the duration of emplacement at a finer resolution than radiometric geochronologyThe technique relies on assuming a rate of paleosecular variation during igneous emplacement [ABSTRACT FROM AUTHOR]

We report comprehensive rock-magnetic and archaeointensity investigations from 21 well-constrained pottery fragments from the Catamarca province of northwest Argentina. The absolute ages of the studied sites are ascertained by several high-quality radiometric ages and range between 1940 to 114014C yr BP. Magnetic mineralogy experiments indicates that the remanence is carried by thermally stable Ti-poor titanomagnetites. Forty-seven samples belonging to 11 out of 98 studied potsherds yielded reliable absolute intensity determinations judging from the quality parameters associated with the Thellier double-heating experiments. Moreover, we analyzed the available absolute geomagnetic intensities associated with the radiometric ages to construct the first intensity paleosecular variation curve (PSVC) for South America using thermoremanent magnetization carried by burned archaeological artifacts obtained in the present investigation and 79 other selected archaeointensities (out of 213 published in the literature). The dataset is used to build the PSVC reference curve by combined bootstrap and temporal P-spline methods. The variation curve shows significant differences with the global prediction model SHA.DIF.14k mainly based on the GEOMAGIA database. This intensity PSVC curve shows reasonably good agreement with paleosecular variation curves for Europe between 850 through 1150 BC and for Asia between 1000 and 1500 BC. This regional curve may be used as most reliable archaeomagnetic dating tool for the major part of South America (Peru, Brazil, Argentina, Chile, and Bolivia) for the last two millennia. [ABSTRACT FROM AUTHOR]

Despite the immense cultural heritage of Mesoamerica, there is still no reference archaeomagnetic curve available for Central Mexico and adjacent areas. The present research has two simultaneous objectives: to obtain finer characteristics of the geomagnetic field elements over archaeological past, and to build up a reliable regional archaeomagnetic dating tool for the time span of 350 BC. to 1500 AD. For these purposes, 72 previous were compiled and analyzed with 40 new data selected from unpublished reports and theses performed in the paleomagnetic laboratories of the Geophysics Institute of UNAM (CDMX and Morelia). Most of the samples carry thermo-remanent magnetization, 31 cases were unburned stuccos, and 3 mural paintings carrying detrital or pictorial remanent magnetization. A total of 112 archaeomagnetic directions constitute the core of the updated catalogue. Special effort should be paid for to the time intervals of 500 BC.--AD. 200 and AD. 1200-325 where there is a major lack of reliable archaeomagnetic results. The present paleosecular variation curve agrees reasonably well with the fluctuation observed in the SW United States area. The differences in the intervals between AD. 600-720, AD. 850 and 1000 and AD. 1200-1325 may be rather attributed to the lack of reliable data than to local non-dipole field. It is urgent to gather a greater number of high-quality data supported by radiometric ages to improve the reference curve in both regions. [ABSTRACT FROM AUTHOR]

We present a paleomagnetic and rock magnetic data set from two long sediment cores collected from Bellsund and Isfjorden contourite drifts located on the eastern side of the Fram Strait (western Spitsbergen margin). The data set gave the opportunity to define the behavior of the past geomagnetic field at high latitude and to constrain the palaeoclimatic events that occurred in a time framework spanning marine isotope stage 3 to the Holocene. A high‐resolution age model was reconstructed by coupling 26 radiocarbon ages and high‐resolution relative paleointensity and paleosecular variation of the geomagnetic field records for the last 60 kyr. We show the variation of the geomagnetic field at high latitudes, pointing out variability during periods of regular paleosecular variation (normal polarity) as well as during the most recent geomagnetic excursions, and we provide a high‐resolution record of the Laschamps excursion. Cross‐cores correlation allowed us to outline major, climate‐related, sedimentary changes in the analyzed stratigraphic sequence that includes the meltwater events MWP‐1a and MWP‐19ky, and the Heinrich‐like events H1, H2, H4, and H6. This contribution confirms that rock magnetic and paleomagnetic analysis can be successfully used as a correlation and dating tool for sedimentary successions at high latitudes, where accelerator mass spectrometry dates and oxygen isotope analyses are often difficult to obtain for the scarcity of calcareous microfossils and the uncertainties related to data calibration may be significant, as well as the complexity of water mass characteristics and dynamics through climate changes. Key Points: Paleomagnetic and rock magnetic analyses of glaciomarine sequencesReconstruction of geomagnetic paleosecular variability at high latitudes (76 degrees to 77 degrees north)High‐resolution correlation along eastern Fram Strait continental margin [ABSTRACT FROM AUTHOR]

Abstract The Mono Lake geomagnetic excursion, characterized by low paleointensity and excursional virtual geomagnetic pole (VGP) positions at about 35 ka, has been cumulatively documented from global sites. However, the geomagnetic field geometry during this short-lived excursion is not conclusively described, since excursional directions are only sporadically reported. A full-vector paleosecular variation (PSV) record between 20 and 40 ka could be reconstructed from seven Black Sea sediment cores. The age models of these cores are based on radiocarbon dating and tephrochronology. Further age constrains were achieved by tuning ice rafted debris (IRD) counts and XRF logs (mainly Ca/Ti ratio) as climate proxies for Dansgaard–Oeschger (D–O) warming events, to the oxygen isotope record from Greenland ice cores (NGRIP). The PSV records of individual Black Sea cores were stacked by using 100-yr bins. At about 34.5 cal. ka BP, the Mono Lake excursion is evidenced in the stacked Black Sea PSV record by both a relative paleointensity (rPI) minimum and directional shifts. Associated VGPs from stacked Black Sea data migrated from Alaska, via the Tibetan Plateau and central Asia, to Greenland, performing a clockwise loop. This agrees with data recorded in the Wilson Creek Formation, USA., and Arctic core PS2644-5 from the Iceland Sea, suggesting a dominant dipole field. On the other hand, the Auckland lava flows, New Zealand, the Summer Lake, USA., and Arctic core ODP-919 yield distinct VGPs located in the central Pacific Ocean due to presumably non-dipole field. Finally, Black Sea sediments younger than the Mono Lake excursion recorded only normal secular variations. Highlights • Paleosecular variation record from 40 to 20 ka obtained from the Black Sea. • Mono Lake excursion evidenced in Black Sea PSV record at about 34.5 ka cal. BP. • Black Sea VGPs exhibit a clockwise loop on Eurasia continent during the Mono Lake excursion. • Black Sea PSV record support dipole dominated field during the Mono Lake excursion. [ABSTRACT FROM AUTHOR]

Nearly three decades ago paleomagnetists suggested that there existed a clear link between latitude dependence of geomagnetic paleosecular variation (PSV) and reversal frequency. Here we compare the latitude behavior of PSV for the Cretaceous Normal Superchron (CNS, 84–126 Ma, stable normal polarity) and the preceding Early Cretaceous‐Jurassic interval (pre‐CNS, 126–198 Ma, average reversal rate of ~4.6 Myr−1). We find that the CNS was characterized by a strong increase in the angular dispersion of virtual geomagnetic poles (VGPs) with latitude, which is consistent with the results of earlier studies, whereas the VGP dispersion for the pre‐CNS period was nearly invariant with latitude. However, the PSV behavior for the last 5 or 10 million years (average reversal frequency of ~4.4–4.8 Myr−1) shows that the latitude invariance of VGP scatter cannot be considered as a characteristic feature of a frequently reversing field and that a strong increase in VGP dispersion with latitude was not restricted to the long periods of stable polarity. We discuss models describing the latitude dependence of PSV and show that their parameters are not reliable proxies for reversal frequency and should not be used to make inferences about the geomagnetic field stability. During the pre‐CNS interval, the geodynamo may have operated in a regime characterized by a high degree of equatorial symmetry. In contrast, more asymmetric geodynamos suggested for 0–10 Ma and the CNS were evidently capable of producing a very wide range of reversal frequencies. Plain Language Summary: In the geologic past, the changes in the Earth's magnetic field have led to numerous polarity reversals, causing the field directions over the entire Earth to be opposite to those observed today. More subtle changes during periods of stable field polarity are referred to as "secular variation." It is widely thought that the manner in which secular variation changes with geographic latitude provides an indirect way of assessing the field stability with regard to its propensity to reverse. Here we derived estimates of paleosecular variation (PSV) for a long interval of stable polarity in the Cretaceous (84–126 Ma) and the preceding Early Cretaceous‐Jurassic interval (126–198 Ma), during which geomagnetic reversals were frequent. We found that the latitude behavior of PSV during these two intervals was significantly different, but the comparison with PSV estimates for the last 5 and 10 million years showed that a strong latitude dependence of PSV, or its invariance with latitude, cannot be considered as a characteristic feature of a stable or frequently reversing field. Our analysis suggests that models describing the latitude dependence of PSV do not provide reliable proxies for reversal frequency and should not be used to make inferences about the geomagnetic field stability. Key Points: Estimates of geomagnetic paleosecular variation (PSV) in Cretaceous and Jurassic time were derived using a new paleomagnetic databaseDifferent PSV latitude patterns were observed for periods of stable geomagnetic polarity (84–126 Ma) and frequent reversals (126–198 Ma)Comparison with the PSV behavior for the last 10 Ma indicates that its latitude dependence is not a reliable proxy for reversal frequency [ABSTRACT FROM AUTHOR]

We provide a high‐resolution and complete paleomagnetic study from a middle‐Holocene (~4,100–3,300 years Before Common Era, BCE) dome‐shaped speleothem (SPAIV) from Algarve, Portugal. Our results show that the SPAIV speleothem carries a primary and stable remanent magnetization, for which directions are similar to other speleothems from the western Alps. Magnetic declination and inclination curves are also comparable to current paleosecular variation models (SHA.DIF.14k, CALS10k.1b, and pfm9k.1a), one of them (SHA.DIF.14k) fitting better with the present data set. Relative paleointensity was estimated using two different methods: conventional normalization of natural remanent magnetization by anhysteretic and isothermal, and the pseudo‐Thellier method, which is being tested here for the first time in a speleothem. Both methods show similar results, with a minimum intensity peak at ~3,850 years BCE. This low relative intensity is observed in all samples pertaining to the same respective calcite laminae. These results suggest that high growth rate speleothems are good high‐resolution recorders of the direction and intensity of the Earth's magnetic field. Key Points: Speleothems constitute reliable magnetic recorders of the Earth's magnetic fieldDirectional paleomagnetic data from the studied speleothem are comparable to paleosecular variation (PSV) models and data from AlpsRelative paleointensity analysis provides primary and reliable records [ABSTRACT FROM AUTHOR]

A comprehensive magnetostratigraphic investigation on sixteen sediment cores from the southeastern Black Sea yielded a very detailed high-quality paleosecular variation (PSV) record spanning from 20 to 15 ka. The age models are based on radiocarbon dating, stratigraphic correlation, and tephrochronology. Further age constraints were obtained by correlating four meltwater events, described from the western Black Sea, ranging in age from about 17 to 15 ka, with maxima in K/Ti ratios, obtained from X-ray fluorescence (XRF) scanning, and minima in S-ratios, reflecting increased hematite content, in the studied cores. Since the sedimentation rates in the investigated time window are up to 50 cm ka −1 , the obtained PSVs records enabled a stacking using 50-yr bins. A directional anomaly at 18.5 ka, associated with pronounced swings in inclination and declination, as well as a low in relative paleointensity (rPI), is probably contemporaneous with the Hilina Pali excursion, originally reported from Hawaiian lava flows. However, virtual geomagnetic poles (VGPs) calculated from Black Sea sediments are not located at latitudes lower than 60°N, which denotes normal, though pronounced secular variations. During the postulated Hilina Pali excursion, the VGPs calculated from Black Sea data migrated clockwise only along the coasts of the Arctic Ocean from NE Canada (20.0 ka), via Alaska (18.6 ka) and NE Siberia (18.0 ka) to Svalbard (17.0 ka), then looping clockwise through the Eastern Arctic Ocean. [ABSTRACT FROM AUTHOR]

Abstract: We report a detailed paleomagnetic study on two Plio‐Pleistocene lava flow sequences from the Djavakheti Highland, Lesser Caucasus. The Korkhi sequence is composed of two volcanic successions of distinct age (1.9 and 3.1 Ma), while the Apnia sequence was emplaced between 3.8 and 3.1 Ma according to available radiometric datings. Normal, reverse and intermediate polarities have been determined from both sequences. Mean directions of the normal and reverse polarity groups for each section do not match the expected field direction, but the possibility of tectonic rotations has been dismissed. A composite analysis of paleomagnetic directions, of virtual geomagnetic pole (VGP) scatter and available paleointensity results from a previous study, allow the interpretation of the observed paleomagnetic results. In the Apnia sequence, both a short recording time unable to average paleosecular variation (PSV) and an anomalous Earth magnetic field (EMF) record are responsible for the observed paleomagnetic directions. According to paleomagnetic results and radiometric ages, this sequence most probably records the reverse to normal polarity transition C2Ar to C2An‐3n. The upper Korkhi subsequence yields an anomalous EMF record, reflecting a transitional time interval. Paleomagnetic results and available absolute ages suggest that this subsequence either records transition C2r‐1r to Olduvai or Olduvai to C1r‐2r. The lower Korkhi subsequence registers a normal polarity interval within the Gauss chron, reflecting a stable stage of the EMF. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the (paleo)latitudinal dependence of angular dispersion sets of virtual geomagnetic poles (VGPs) for the Permian‐Carboniferous Reversed Superchron (PCRS: 262–318 Ma). In order to analyze the paleosecular variation during this period, we prepared different paleomagnetic data sets from scientific databases and recent literature, based on selection criteria which provided high degree of refinement. Model G of McFadden et al. (1988) was fitted to the VGP dispersion data, providing the shape parameters a and b, which were further compared with similar results for the Cretaceous Normal Superchron (CNS) and other periods of different geomagnetic reversal rates throughout the last 3 Ga. Our results indicate high similarity between the angular VGP dispersion from the PCRS and CNS (a low VGP dispersion at low paleolatitudes, and strong paleolatitudinal dependence), in contrasting difference for periods of higher reversal rates (the last 5 Ma). Despite the geodynamic differences related to both Phanerozoic superchrons, such evidence could point out similar heat flux conditions in the CMB, which may favor compatible stability conditions throughout these magnetozones. Notably, two additional observations which arose from the shape parameters relations for both Phanerozoic superchrons and Precambrian data sets demand further investigation: (i) a pattern of increase for the b/a ratio throughout the 0.5–1.6 Ga interval was observed, which could be partially explained by the Maya Superchron, recently proposed by Gallet et al. (2012) and (ii) the b × a relationship for both Phanerozoic superchrons and the 2.45–2.82 Ga interval pointed to the presence of one or more long‐term magnetozones throughout the Paleoproterozoic. [ABSTRACT FROM AUTHOR]

Speleothems are potentially excellent archives of the Earth's magnetic field, capable of recording its past variations. Their characteristics, such as the continuity of the record, the possibility to be easily dated, the almost instantaneous remanence acquisition and the high time-resolution make them potentially unique high-quality Paleosecular Variation (PSV) recorders. Nevertheless, speleothems are commonly characterized by low magnetic intensities, which often limits their resolution. Here we present a paleomagnetic study performed on two cores from a flowstone from the Rio Martino Cave (Western Alps, Italy). U/Th dating indicates that the flowstone's deposition covers almost the entire Holocene, spanning the period ca. 0.5–9.0 ka, while an estimation of its mean growth rate is around 1 mm per 15 years. The flowstone is composed of columnar calcite, characterized by a highly magnetic detrital content from meta-ophiolites in the cave's catchment. This favorable geological context results in an intense magnetic signal that permits the preparation and measurement of thin (∼3 mm depth equivalent) samples, each representing around 45 yr. The Characteristic Remanent Magnetization (ChRM), isolated after systematic stepwise Alternating Field demagnetization, is well defined, with Maximum Angular Deviation (MAD) generally lower than 10°. Paleomagnetic directional data allow the reconstruction of the PSV path during the Holocene for the area. Comparison of the new data with archeomagnetic data from Italian archeological and volcanic records and using the predictions of the SHA.DIF.14k and pfm9k.1a global geomagnetic field models shows that the Rio Martino flowstone represents an excellent recorder of the Earth's magnetic field during the last 9,000 years. Our high resolution paleomagnetic record, anchored by a high-quality chronology, provides promising data both for the detection of short term geomagnetic field variations and for complementing existing regional PSV curves for the prehistoric period, for which well-dated data are still scarce. [ABSTRACT FROM AUTHOR]

A total of nine sediment cores recovered from the Archangelsky Ridge in the SE Black Sea were systematically subjected to intense paleo- and mineral magnetic analyses. Besides 16 accelerator mass spectrometry (AMS) 14 C ages available for another core from this area, dating was accomplished by correlation of short-term warming events during the last glacial monitored by high-resolution X-ray fluorescence (XRF) scanning as maxima in both Ca/Ti and K/Ti ratios in Black Sea sediments to the so-called ‘Dansgaard–Oeschger events’ recognized from Greenland ice cores. Thus, several hiatuses could be identified in the various cores during the last glacial/interglacial cycle. Finally, core sections documenting marine isotope stage (MIS) 4 at high resolution back to 69 ka were selected for detailed analyses. At 64.5 ka, according to obtained results from Black Sea sediments, the second deepest minimum in relative paleointensity during the past 69 ka occurred, with the Laschamp geomagnetic excursion at 41 ka being associated with the lowest field intensities. The field minimum during MIS 4 is associated with large declination swings beginning about 3 ka before the minimum. While a swing to 50°E is associated with steep inclinations (50–60°) according to the coring site at 42°N, the subsequent declination swing to 30°W is associated with shallow inclinations of down to 40°. Nevertheless, these large deviations from the direction of a geocentric axial dipole field ( I = 61 ° , D = 0 ° ) still can not yet be termed as ‘excursional’, since latitudes of corresponding virtual geomagnetic poles (VGP) only reach down to 51.5°N (120°E) and 61.5°N (75°W), respectively. However, these VGP positions at opposite sides of the globe are linked with VGP drift rates of up to 0.2° per year in between. These extreme secular variations might be the mid-latitude expression of a geomagnetic excursion with partly reversed inclinations found at several sites much further North in Arctic marine sediments between 69°N and 81°N. Thus, the pronounced intensity minimum at 64.5 ka and described directional variations might be the effect of a weak geomagnetic field with a multi-polar geometry in the middle of MIS 4. [ABSTRACT FROM AUTHOR]

Paleomagnetic secular variation (PSV) records serve as valuable independent stratigraphic correlation and dating tools for marine and terrestrial sediment sequences, and enhance knowledge of geomagnetic field dynamics. We present a new radiocarbon-dated record (WINPSV-12K) of Holocene geomagnetic secular variation from Windermere, updating the existing 1981 UK master PSV curve. Our analyses used continuous U-channel samples taken from the center of four sediment cores retrieved from Windermere in 2012. The natural remanent magnetization (NRM) of each U-channel was measured before and after stepwise alternating field (AF) demagnetization on a superconducting rock magnetometer at intervals of 0.5-cm or 1-cm. The NRM data reveal a stable and well-defined primary magnetization. Component declinations and inclinations estimated using Principal Component Analysis (PCA) of NRM data from the four Windermere cores correlate well on their independent radiocarbon age models. The four records were stacked using a sliding window bootstrap method, resulting in a composite Holocene PSV record (WINPSV-12K). On millennial timescales WINPSV-12K correlates well with other records from Western Europe and the northern North Atlantic to a resolution of ∼1 kyr, given age uncertainties and spatial variability between records. WINPSV-12K also compares well to the CALS10k.2 and pfm9k.1a model predictions for Windermere. Key regionally-significant PSV inclination features of WINPSV-12K which correlate with other North Atlantic records include peaks at 5–6, 8.5, and 10 cal ka BP, and a trough at 7 cal ka BP. Key PSV declination features include the eastward swing from 5.5–2.3 cal ka BP followed by a major westward excursion at 2.3 cal ka BP, peaks at 1.1 and 7 cal ka BP, and troughs at 5.4 and 8.2 cal ka BP, with the caveat that an estimated magnetic lock-in delay of at least 100–200 yr is present. PSV variations on 1–3 kyr timescales are interpreted to represent strengthening and weakening of the North American versus the Siberian and European–Mediterranean high-latitude flux lobes, based on the close similarities between the North Atlantic regional records and the antiphase existing in the East Asian Stack record and the North East Pacific inclination stack. WINPSV-12K provides a regionally-important new PSV reference curve whose prominent features may serve as stratigraphic markers for North Atlantic paleo-records. [ABSTRACT FROM AUTHOR]

A rock magnetic and paleomagnetic investigation was performed on some selected, radiometrically dated lava flows from the Mascota Volcanic Field (MVF), western Trans- Mexican Volcanic Belt. A set of rock-magnetic experiments and standard paleomagnetic analysis were carried out on 19 sites spanning the time interval from 2268 to 72 kyr. The paleomagnetic directions are anchored to absolute radiometric ages while no such information was available in previous studies. This makes possible to correctly evaluate the fluctuation of Earth's magnetic field from Pliocene to Pleistocene and reveal the firm evidence of possible Levantine excursion. Both Ti-poor and Ti-rich titanomagnetites seem to carry the remanent magnetization with Curie temperatures ranging from 350°C to 537°C. Thirteen flows correspond to the Brunhes chron, one of them exhibits transitional directions, while the remaining six sites belong to the Matuyama chron. New and existing dataset for MVF were used to estimate the paleosecular variation parameters. The selected data include 35 Plio-Quaternary lava flows. After excluding the poor quality data, as well as the transitional directions, the mean paleodeclination is 356.1° and oaleoinclination 39.9°, which agree well with the geocentric axial dipole (GAD) and the expected paleodirections for the Plio-Pleistocene, as derived from the reference poles for the stable North America. The corresponding mean paleomagnetic poles are paleolongitude 226.7° and paleolatitude 86.0°. The virtual geomagnetic pole scatter for the MVF is 15.2°, which is consistent with the value expected from model G at latitude of 20° (this model provides an interpretation of the paleosecular variation at different latitudes for the time of interest). The combined paleomagnetic data, supported by positive reversal test, indicate no paleomagnetically detectable vertical-axis rotations in the study area. The evidence of one transitional directions was detected, which may correspond to the Levantine excursion (360-370 kyr) or unnamed event between 400-420 kyr. [ABSTRACT FROM AUTHOR]

Laguna Melincué is a shallow lake located in Santa Fe Province, Argentina (33°41′27.8″S, 61°31′36.5″W). The catchment area is around 1495 km and it is located in the Pampean Plains. It was reduced to 678 km by the construction of the San Urbano channel in 1941 and reconditioned in 1977, which was built to avoid floods. The floods are related to some El Niño episodes, with high precipitation events. The lake has been previously studied from different approaches, mainly to understand hydrological and climatic variations, but more multidisciplinary studies are needed to understand its complex hydrological situation. Here we present the first paleomagnetic and rock magnetic studies made on a short sediment core collected from the lake in order to contribute to identifying paleoclimatic proxies and to present the first paleomagnetic results for the site. Rock magnetic analyses suggest that the well-preserved magnetic mineralogy is dominated by pseudo single-domain (titano)magnetite and/or maghemite. The results also indicate that a stable characteristic remanent magnetisation can be isolated and thus the directions of the geomagnetic field may be obtained, providing evidence for the use of this lake for paleomagnetic and paleoenvironmental studies. Changes in magnetic grain size and concentration of magnetic minerals suggest environmental variations and changes in the lake level, which are consistent with historical reports. The paleomagnetic results agree well with Cals3k.3 model for inclination and declination of the geomagnetic field except for the dry period probably due to the fact that the core was extracted near the shore. [ABSTRACT FROM AUTHOR]