1,081 results on '"Palaeomagnetism"'
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2. Reliability of the palaeomagnetic signal recorded in a lava flow erupted on 4 December 2021 in La Palma (Canary Islands, Spain).
- Author
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Calvo-Rathert, Manuel, Vernet, Eva, Parés, Josep M, Soler, Vicente, Sánchez-Moreno, Elisa-María, Bógalo, María-Felicidad, Carrancho, Ángel, Yamamoto, Yuhji, and Rodríguez-Méndez, Lidia
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GEOMAGNETISM , *INTRAPLATE volcanism , *LAVA flows , *REMANENCE , *VOLCANOES - Abstract
A basaltic lava flow erupted from the Tajogaite volcano on 4 December 2021, in La Palma (Canary Islands, Spain) was sampled to find out to what extent reliable and correct information on both intensity and direction of the Earth's magnetic field can be obtained from the palaeomagnetic signal recorded in a lava flow which erupted under known conditions. Samples were taken every few centimetres across a flow up to a total of 27 oriented cores. Palaeomagnetic experiments showed a strong viscous overprint in many samples. Nevertheless, the mean palaeomagnetic direction obtained agrees well with the actual value from IGRF-13. Rock magnetic experiments were performed to obtain additional information about the quality and reliability of the results and the reasons for unsuccessful determinations. Analysis of mostly irreversible thermomagnetic curves showed that the carriers of remanence were magnetite and titanomagnetite of low and/or intermediate Curie-temperature. Hysteresis parameter ratios showed a pronounced variability across the flow. Analyses of frequency dependent susceptibility, IRM acquisition coercivity spectra and FORCs showed a noticeably presence of very low coercivity grains (multidomain and superparamagnetic-single domain boundary). Multimethod palaeointensity experiments were performed with the Thellier-Coe, multispecimen and Tsunakawa-Shaw methods. Only three of 25 cores from the flow yielded successful Thellier-Coe determinations, in agreement with the expected field value of 38.7 μT (IGRF-13). However, palaeointensities of 60 per cent of the specimens agree with the expected value performing an informal analysis without considering criteria thresholds. Four of six Tsunakawa-Shaw determinations performed on samples from the flow yielded correct results, but three multispecimen determinations providing apparently successful determinations largely underestimate the expected field intensity. Combination of three Thellier-Coe and four Tsunakawa-Shaw successful determinations yields a multimethod palaeointensity result B = (36.9 ± 2.0) μT in good agreement with the expected field intensity. [ABSTRACT FROM AUTHOR] more...
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- 2024
- Full Text
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3. A lunar core dynamo limited to the Moons first ~140 million years.
- Author
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Zhou, Tinghong, Tarduno, John, Cottrell, Rory, Neal, Clive, Nimmo, Francis, Blackman, Eric, and Ibañez-Mejia, Mauricio
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Atmospheric chemistry ,Core processes ,Early solar system ,Palaeomagnetism ,Rings and moons - Abstract
Single crystal paleointensity (SCP) reveals that the Moon lacked a long-lived core dynamo, though mysteries remain. An episodic dynamo, seemingly recorded by some Apollo basalts, is temporally and energetically problematic. We evaluate this enigma through study of ~3.7 billion-year-old (Ga) Apollo basalts 70035 and 75035. Whole rock analyses show unrealistically high nominal magnetizations, whereas SCP indicate null fields, illustrating that the former do not record an episodic dynamo. However, deep crustal magnetic anomalies might record an early lunar dynamo. SCP studies of 3.97 Ga Apollo breccia 61016 and 4.36 Ga ferroan anorthosite 60025 also yield null values, constraining any core dynamo to the Moons first 140 million years. These findings suggest that traces of Earths Hadean atmosphere, transferred to the Moon lacking a magnetosphere, could be trapped in the buried lunar regolith, presenting an exceptional target for future exploration. more...
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- 2024
4. The palaeomagnetic field recorded in Eyjafjarðardalur basalts (2.6–8.0 Ma), Iceland: are inclination-shallowing corrections necessary in time-averaged field analysis?
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Muxworthy, Adrian R, Riishuus, Morten S, Supakulopas, Radchagrit, Niocaill, Conall Mac, Barfod, Dan N, Døssing, Arne, Turner, Kathryn, and Cych, Brendan
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REMANENCE , *MAGNETIC declination , *MAGNETIC fields , *PALEOMAGNETISM , *BASALT - Abstract
SUMMARY: The geocentric axial dipole (GAD) hypothesis is key to many palaeomagnetic applications, for example plate-tectonic reconstructions; however, the validity of this hypothesis at high latitudes is not fully resolved. To address this, in this paper we determined the palaeomagnetic directional data of 156 lava units in Eyjafjarðardalur, Iceland, with the aim of determining the validity of the GAD hypothesis at high latitudes using time-averaged field (TAF) analysis. In addition to the palaeomagnetic directional data, we constructed an age model for the sequences using new 40Ar/39Ar dates, magnetostratigraphy and field data. The sequence age range is 2.6–8.0 Ma. We show that the mean virtual geomagnetic pole (VGP) for our data does not agree with the GAD theory at 95 per cent confidence, when only the standard tilt and tectonic corrections are made; however, when inclination-shallowing processes are accounted for, for example thermoremanence (TRM) anisotropy and refraction effects, the mean VGP can align with GAD at 95 per cent confidence. These inclination-shallowing processes are shown to reduce the inclination by up to 14° for some of the basaltic units. Applying the inclination-shallowing correction also reduces VGP dispersion to levels that agree with global model predictions. We propose that much of the scatter within the palaeomagnetic directional databases are due to inclination-shallowing process effects, which become more important as the natural remanent magnetization (NRM) intensity is high, for example >2 A m−1. We propose that inclination-shallowing processes can be identified and corrected for by examining the NRM intensity and dispersion. [ABSTRACT FROM AUTHOR] more...
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- 2024
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5. The last gasp of the Rogaland Igneous Complex, Norway: a palaeopole for the 920 Ma Tellnes intrusion.
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Brown, Laurie L, McEnroe, Suzanne A, and Robinson, Peter
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REMANENCE , *ANORTHOSITE , *MINERALOGY , *GRANULITE , *MAGNETITE - Abstract
The Rogaland Igneous Complex (RIC) in southern Norway intruded into Sveconorwegian granulite crust beginning ∼930 Ma. Three massif anorthosite bodies, Egersund–Ogna, Helleren and Åna-Sira, were intruded some 10 Myr later by the Bjerkreim–Sokndal layered intrusion. The Garsaknatt leuconorite and the ilmenite-rich Tellnes norite, one of the youngest rock in the complex at ∼920 Ma, intrude the anorthosite or nearby country rock. Magnetic mineralogy and palaeomagnetic studies carried out on the Tellnes norite, the Garsaknatt leuconorite and the surrounding Åna-Sira anorthosite, indicate the magnetization of all three bodies are dominated by hemo-ilmenite carrying the remanence as a thermochemical remanent magnetization, although magnetite is present in some samples. The three bodies yield steep negative inclinations with northwesterly declinations (Tellnes, I = −71.9°, D = 305.0°, α95 = 10.6°; Garsaknatt, I = −73.1°, D = 312.7°, α95 = 4.7°; and Åna-Sira, I = −81.2°, D = 326.3°, α95 = 6.7°). When combined with data from other bodies in the RIC, the older anorthosites have steeper inclinations, and higher palaeolatitudes, while the younger units have less steep inclinations and shallower palaeolatitudes by nearly 10°, indicating northward plate motion during cooling of the intrusions. Age of the remanence is difficult to determine precisely, however, best estimates are ∼910 Ma for the older anorthosites and ∼900 Ma for the younger intrusions. Although these differences are significant, a unified pole position (35.6° N, 215.1° E), combining all the 111 sites from the RIC, strongly supports the assumed position of southern Baltica in Rodinia at ∼900 MA. [ABSTRACT FROM AUTHOR] more...
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- 2024
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6. Combined uranium-series and electron spin resonance dating from the Pliocene fossil sites of Aves and Milo's palaeocaves, Bolt's Farm, Cradle of Humankind, South Africa.
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Yu, Wenjing, Herries, Andy I. R., Edwards, Tara, Armstrong, Brian, and Joannes-Boyau, Renaud
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ELECTRON paramagnetic resonance ,FOSSIL teeth ,PALEONTOLOGICAL excavations ,GEOCHRONOMETRY ,DENTAL enamel ,ELECTRON spin resonance dating - Abstract
Bolt's Farm is the name given to a series of non-hominin bearing fossil sites that have often been suggested to be some of the oldest Pliocene sites in the Cradle of Humankind, South Africa. This article reports the results of the first combined Uranium-Series and Electron Spin Resonance (US-ESR) dating of bovid teeth at Milo's Cave and Aves Cave at Bolt's Farm. Both tooth enamel fragments and tooth enamel powder ages were presented for comparison. US-ESR, EU and LU models are calculated. Overall, the powder ages are consistent with previous uranium-lead and palaeomagnetic age estimates for the Aves Cave deposit, which suggest an age between ~3.15 and 2.61 Ma and provide the first ages for Milo's Cave dates to between ~3.1 and 2.7 Ma. The final ages were not overly dependent on the models used (US-ESR, LU or EU), which all overlap within error. These ages are all consistent with the biochronological age estimate (<3.4–>2.6 Ma) based on the occurrence of Stage I Metridiochoerus andrewsi. Preliminary palaeomagnetic analysis from Milo's Cave indicates a reversal takes place at the site with predominantly intermediate directions, suggesting the deposit may date to the period between ~3.03 and 3.11 Ma within error of the ESR ages. This further suggests that there are no definitive examples of palaeocave deposits at Bolt's Farm older than 3.2 Ma. This research indicates that US-ESR dating has the potential to date fossil sites in the Cradle of Humankind to over 3 Ma. However, bulk sample analysis for US-ESR dating is recommended for sites over 3 Ma. [ABSTRACT FROM AUTHOR] more...
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- 2024
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7. Remagnetization of the Upper Permian–Lower Triassic limestones in the western Lhasa Terrane and its tectonic implications.
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Bian, Weiwei, Jiao, Xianwei, Wang, Suo, Liang, Jiacheng, Ma, Jiahui, Ding, Jikai, Zhao, Hanqing, Yang, Tianshui, Zhang, Shihong, Wu, Huaichun, Li, Haiyan, and Deng, Chenglong
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LIMESTONE , *CALCITE , *IRON sulfides , *REMANENCE , *OZONE layer , *IRON oxidation , *IRON oxides , *PYRITES , *MINERALS - Abstract
The drift history of the Lhasa terrane plays an essential role in understanding the tectonic evolution of the Bangong-Nujiang Tethyan Ocean and the Neo-Tethyan Ocean, as well as the evolutionary history of the Tibetan Plateau. Here, a combined rock magnetic, petrographic, and palaeomagnetic study is performed on the Upper Permian–Lower Triassic limestones (∼259–251 Ma) in the western Lhasa terrane. The site-mean direction for the 28 sites is D g = 32.1°, I g = 50.3°, k g = 47.9 and α 95 = 4.0° in situ and D s = 342.9°, I s = 32.7°, k s = 43.2 and α 95 = 4.2° after tilt-correction, yielding a palaeopole at 68.9°N, 314.4°E with A 95 = 4.3°, corresponding to a palaeolatitude of 18.0° ± 4.3°N. The fold tests are not significant because the sampling section shows monoclinic features with minor variations in their bedding attitudes. The palaeopoles for the directions before and after tilt-correction are compared with reliable Late Permian–Palaeogene palaeopoles obtained from the Lhasa terrane. Based on these comparisons, the studied limestones were remagnetized prior to tilting and this remagnetization most likely occurred during the Early Cretaceous. The depositional environment of the limestones may have changed from anoxic to suboxic and oxic during the Early Cretaceous, leading to the oxidation of iron sulphide to authigenic magnetite. Meanwhile, the Late Jurassic–Early Cretaceous convergence between the western Lhasa and Qiangtang terranes may have resulted in tectonic fluid migration and the formation of calcite veins and stylolites in the limestones. This is supported by the presence of small calcite veins and stylolites in some samples, as well as the fact that the framboidal oxides were formerly sulphides (mostly pyrite), implying that the majority of the iron oxides observed in the limestones were authigenic. These processes indicate that chemical remanent magnetization caused by the growth of magnetic minerals related to tectonic fluid migration was most likely the mechanism for the limestone remagnetization. [ABSTRACT FROM AUTHOR] more...
- Published
- 2024
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8. Matuyama/Brunhes magnetic reversal recorded in flowstone from the Račiška pečina Cave (Slovenia).
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Pawlak, Jacek, Hercman, Helena, Gąsiorowski, Michał, Pruner, Petr, Błaszczyk, Marcin, Sierpień, Paula, Matoušková, Šárka, Kdýr, Šimon, Schnabl, Petr, Zupan Hajna, Nadja, Mihevc, Andrej, and Bosák, Pavel more...
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CLAY minerals , *KARST , *TRACE elements , *SEQUENCE analysis , *SPELEOTHEMS - Abstract
A flowstone section in the Račiška pečina Cave (Classical Karst, SW Slovenia) records multiple chronostratigraphic and palaeoclimatic proxies that can be correlated with other records on the global scale (Mediterranean region, Japan). Its upper part has an excellent record of the Matuyama/Brunhes (M/B) magnetic reversal. The M/B reversal zone, which is 6 mm in thickness, was detected by a high-resolution palaeomagnetic analysis of the sequence. An age model based on oxygen isotopic stratigraphy locates this quick transition in mid-MIS 19, between 777.9 and 777.2 ka, with the midpoint at 777.7 ka. The transition is marked by abrupt changes in stable isotopic compositions, trace element concentrations and flowstone fabrics that point to temperature and precipitation changes. Two distinct maxima in trace element concentrations at the beginning and the end of the M/B transition indicate two periods of higher precipitation, with increased washes of clay minerals into the cave. In addition, the stable isotopic (δ13C and δ18O) compositions indicate that significant cooling and high precipitation occurred during the M/B reversal within the generally warm MIS 19. [ABSTRACT FROM AUTHOR] more...
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- 2024
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9. Palaeomagnetic results from Early Mesozoic strata in the Qaidam Basin and their implications for the formation of the Northern China Domain.
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Wang, Bin, Huang, Baochun, Yang, Zhenyu, Zhang, Guowei, Liu, Xiaoming, Duan, Liang, Armstrong, Richard A, and Meng, Qingren
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The Northern China Domain is located between the Central Asian Orogenic Belts to the north and the Kunlun–Qinling belt to the south, and it comprises the North China, Alxa and Tarim blocks. The relationships among the Northern China domain and the southern tectonic elements such as the Qaidam Basin/Terrane are debated because of the major modification by crustal deformation in the late Mesozoic–Cenozoic. To address this issue, we conducted a palaeomagnetic and high-precision radiometric dating study of Triassic volcanic rocks and Middle Jurassic strata in the Qaidam Terrane. Our objective was to determine the relationship between the Qaidam Terrane with the Tarim Block and the North China Block (NCB) during the late Palaeozoic and early Mesozoic. Four volcanic samples yielded zircon U-Pb ages of 236–243 Ma. The characteristic remanent magnetizations (Middle Triassic: D = 40.2°, I = 54.6°, α95 = 3.4°; Middle Jurassic: D = 27.4°, I = 48.0°, α95 = 7.9°) passed the fold and reversal tests, and yielded Middle Triassic and Middle Jurassic palaeopole positions at 57.6° N, 178.2° E, A 95 = 4.0° and 65.8° N, 197.6° E, A 95 = 7.8°, respectively. Based on these new poles, combined with other reliable data, we compared the apparent polar wander path (APWP) of the Qaidam Terrane with those of the NCB and Tarim Block. The results show that, from the Carboniferous through Early Cretaceous, the APWP of the Qaidam Terrane resembles that of the Tarim Block, but it is quite different from that of the NCB. Combined with other reported evidence, we conclude that the Qaidam Terrane was an independent dynamic unit during the late Palaeozoic until its connection with the Tarim Block, which was followed by continuous eastward motion. During this process, the connection between the Qaidam Terrane and the NCB–Alxa blocks occurred in the Middle Triassic, and subsequently the Qaidam Terrane underwent multiple tectonic responses to collisions with the Qiangtang Terrane, Lhasa Terrane and the India Plate, before the formation of its modern tectonic configuration. [ABSTRACT FROM AUTHOR] more...
- Published
- 2024
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10. Using Palaeomagnetic Techniques to Date Indigenous Archaeological Sites in New Zealand
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Shefali Poojary, Fergus Robinson, and Gillian Turner
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Palaeomagnetism ,archaeomagnetic dating ,Aotearoa/New Zealand ,Māori ,earth ovens (hāngī) ,hāngī stones ,Archaeology ,CC1-960 - Abstract
Aotearoa/New Zealand was first settled by the Māori people some 800–1000 years ago. Archaeomagnetism provides one of the few means of dating early sites of Māori occupation, particularly when radiocarbon dating is not feasible. This involves dating the thermoremanent magnetization imparted to the heat-retaining stones used in traditional Māori earth ovens, hāngī or umu, at the time of their last cooling. The direction of this magnetization is correlated with the reference curve of the changes in the geomagnetic field direction in New Zealand over the past 1000 years, NZPSV1k.2023. Here, we describe the application of archaeomagnetic dating to indigenous hāngī sampled at two sites in the North Island of New Zealand. The first, in the present-day city of Napier on the east coast, has been studied in detail and is shown to have been occupied, possibly intermittently, over 400–600 years, while the second, in present-day Waikanae on the west coast, is tentatively dated to ca. 1760 AD, just decades before the first European arrival in New Zealand. more...
- Published
- 2023
- Full Text
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11. Palaeomagnetic field intensity measurements from the 2.6 Ga Yandinilling dyke swarm (Western Australia).
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Hawkins, Louise M, Biggin, Andrew J, Liu, Yebo, Grappone, J Michael, and Li, Zheng-Xiang
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DIPOLE moments , *DIKES (Geology) , *PHANEROZOIC Eon , *SCANNING electron microscopy , *MAGNETIC fields , *ARCHAEAN - Abstract
Precambrian palaeointensity measurements provide fundamental constraints on the evolution of the deep Earth. Core evolution models predict trends in dipole moment on billion-year timescales that can be tested by palaeomagnetic records. Here, we report new palaeointensity results from the recently identified ∼2.62 Ga Yandinilling dyke swarm of the Yilgarn Craton, Western Australia, and consider them alongside published measurements spanning 500 Myr across the late Archaean to earliest Proterozoic. Rock magnetic and scanning electron microscopy analysis confirm that the magnetic mineralogy is fine-grained magnetite, appearing mostly as exsolved lamellae with ilmenite. Six sites produced acceptable palaeointensity estimates from thermal and microwave IZZI protocol Thellier experiments and from double-heating technique Shaw experiments. These site mean values of 9–26 µT translate to virtual dipole moments of 11–44 ZAm2 that are considerably lower than today's dipole moment of ∼80 ZAm2 and the value predicted for this time period by some thermal evolution models. Their average (median = 41 ZAm2) is, however, similar to the long-term average during both of the intervals 2300–2800 Ma (median = 44 ZAm2; N = 103) and 10–500 Ma (median 41 ZAm2; N = 997). While there is little evidence for a substantial net change in average dipole moment between the late Archaean and Phanerozoic, there is preliminary evidence that its variance has increased between the two intervals. This lower variance more than two billion years ago supports the idea that the geodynamo, even while not producing a stronger magnetic field, was more stable on average at the Archaean–Proterozoic transition than it is today. [ABSTRACT FROM AUTHOR] more...
- Published
- 2024
- Full Text
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12. An end-member modelling approach to pseudo-Thellier palaeointensity data.
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van Grinsven, Liz, van Leeuwen, Tristan, and de Groot, Lennart V
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REMANENCE , *NONNEGATIVE matrices , *MAGNETIC fields , *MATRIX decomposition , *VOLCANIC ash, tuff, etc. , *GEOMAGNETISM , *MAGNETIC entropy - Abstract
Absolute palaeointensities are notoriously hard to obtain, because conventional thermal Thellier palaeointensity experiments often have low success rates for volcanic samples. The thermal treatments necessary for these experiments potentially induce (magnetic) alteration in the samples, preventing a reliable palaeointensity estimate. These heating steps can be avoided by pseudo-Thellier measurements, where samples are demagnetized and remagnetized with alternating fields. However, pseudo-Thellier experiments intrinsically produce relative palaeointensities. Over the past years, attempts were made to calibrate pseudo-Thellier results into absolute palaeointensities for lavas by mapping laboratory induced anhysteretic remanent magnetizations (ARMs) to the thermally acquired natural remanent magnetizations (NRMs). Naturally occurring volcanic rocks, however, are assemblages of minerals differing in grain size, shape and chemistry. These different minerals all have their own characteristic mapping between ARMs and thermal NRMs. Here, we show that it is possible to find these characteristic mappings by unmixing the NRM demagnetization and the ARM acquisition curves into end-members, with an iterative method of non-negative matrix factorization. In turn, this end-member modelling approach (EMMA) allows for the calculation of absolute palaeointensities from pseudo-Thellier measurements. We tested our EMMA using a noise-free numerical data set, yielding a perfect reconstruction of the palaeointensities. When adding noise up to levels beyond what is expected in natural samples, the end-member model still produces the known palaeointensities well. In addition, we made a synthetic data set with natural volcanic samples from different volcanic edifices that were given a magnetization by heating and cooling them in a controlled magnetic field in the lab. The applied fields ranged between 10 and 70 µT. The average absolute difference between the calculated palaeointensity and the known lab field is around 10 µT for the models with 2–4 end-members, while the palaeointensity of almost all flows can be retrieved within a deviation of ±20 µT. The deviations between the palaeointensities and the known lab fields are almost Gaussian distributed around the expected values. Although the two data sets in our study show that there is potential for using this end-member modelling technique for finding absolute palaeointensities from pseudo-Thellier data, these synthetic data sets cannot be directly related to natural samples. Therefore, it is necessary to compile a data set of known palaeointensities from different volcanic sites that recently cooled in a known magnetic field to find the universal end-members in future studies. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
13. A stacked record of relative palaeointensity for past 500 ka from western equatorial Indian Ocean sediments.
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Chen, Liang, Zhou, Liang, Liu, Jiabo, Yin, Zhengxin, Zhang, Jianli, Guan, Yulong, Chen, Long, Zhang, Yuzhen, Hu, Yuewei, Liu, Yang, and Jiang, Zhaoxia
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REMANENCE , *OCEAN , *STRATIGRAPHIC correlation , *SEDIMENTS - Abstract
Relative palaeointensity (RPI) records can reflect the evolution of the Earth's axial dipole field and provide a suitable template for global stratigraphic correlation. Current RPI records are primarily obtained from the Atlantic and Pacific Oceans, particularly in the mid-latitudes of the Northern Hemisphere. Fewer RPI records originate from the Indian Ocean, particularly in low latitude areas, which limits sediment dating and geomagnetic evolution studies in these regions. In this study, we conduct a palaeomagnetic study on four sediment cores recovered from the western equatorial Indian Ocean (WEIO) to establish a new regional RPI stack from the past 500 ka for the global coverage of palaeointensity data, as well as a regional reference for palaeointensity-assisted stratigraphy. To estimate the RPI, the isothermal remanent magnetization is used as a normalizer. A chronological framework is constructed by correlating RPI records and environmental magnetic parameters (anhysteretic remanent magnetizationsaturation/isothermal remanent magnetization, ARM/SIRM) with PISO-1500 and LR04 δ18O curves, respectively. Our RPI stacked curve (WEIO-500) varies according to global and other regional high-resolution records. The five lows in the obtained RPI curve can be correlated with previously reported excursions. In addition, the mean inclination direction of each core is similar to the expected hypothetical geocentric axial dipole direction, with a negative inclination anomaly (mean Δ I) of −2.18° to −4.86°. The low mean Δ I and its reproducibility reflect the reliability of our chronological framework and stacked curve, thereby providing a new reference for correlating and calibrating RPI records from WEIO as well as other equatorial areas. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
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14. New palaeoproterozoic palaeomagnetic data from Central and Northern Finland indicate a long-lived stable position for Fennoscandia.
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Luoto, T, Salminen, J, Mertanen, S, Elming, S-Å, and Pesonen, L J
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POLAR wandering , *GEOMAGNETISM , *CRATONS , *OROGENIC belts , *GABBRO , *LATITUDE - Abstract
The Svecofennian gabbro intrusions coincide temporally with the global 2100–1800 Ma orogens related to the amalgamation of the Mesoproterozoic supercontinent Nuna. We provide a new reliable 1891–1875 Ma palaeomagnetic pole for Fennoscandia based on rock magnetic and palaeomagnetic studies on the Svecofennian intrusions in central Finland to fill gaps in the Palaeoproterozoic palaeomagnetic record. By using the new pole together with other global high-quality data, we propose a new palaeogeographic reconstruction at 1885 Ma. This, together with previous data, supports a long-lived relatively stable position of Fennoscandia at low to moderate latitudes at 1890–1790 Ma. Similar stable pole positions have also been obtained for Kalahari at 1880–1830 Ma, Siberia at 1880–1850 Ma, and possibly India at 1980–1775 Ma. A new reconstruction at the beginning of this period indicates the convergence of several cratons at 1885 Ma in the initial stages of the amalgamation of the Nuna supercontinent at low to moderate latitudes. The close proximity of cratons at low to moderate latitudes is further supported by global and regional palaeoclimatic indicators. Stable position of several cratons could indicate a global period of minimal apparent drift at ca. 1880–1830 Ma. Before this period, the global palaeomagnetic record indicates large back-and-forth swings, most prominently seen in the high-resolution 2020–1870 Ma Coronation loops of the Slave craton. These large back-and-forth movements have been explained as resulting from an unstable geomagnetic field or basin- or local-scale vertical-axis rotations. However, the most likely explanation is inertial interchange true polar wander (IITPW) events, which is in line with the suggestion of large amplitude true polar wander events during the formation of the supercontinent. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
15. Using Palaeomagnetic Techniques to Date Indigenous Archaeological Sites in New Zealand.
- Author
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Poojary, Shefali, Robinson, Fergus, and Turner, Gillian
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ARCHAEOLOGICAL excavations ,MAORI (New Zealand people) ,ARCHAEOLOGICAL dating ,THERMOREMANENT magnetization ,GEOMAGNETISM ,RADIOCARBON dating ,PALEOMAGNETISM - Abstract
Aotearoa/New Zealand was first settled by the Māori people some 800–1000 years ago. Archaeomagnetism provides one of the few means of dating early sites of Māori occupation, particularly when radiocarbon dating is not feasible. This involves dating the thermoremanent magnetization imparted to the heat-retaining stones used in traditional Māori earth ovens, hāngī or umu, at the time of their last cooling. The direction of this magnetization is correlated with the reference curve of the changes in the geomagnetic field direction in New Zealand over the past 1000 years, NZPSV1k.2023. Here, we describe the application of archaeomagnetic dating to indigenous hāngī sampled at two sites in the North Island of New Zealand. The first, in the present-day city of Napier on the east coast, has been studied in detail and is shown to have been occupied, possibly intermittently, over 400–600 years, while the second, in present-day Waikanae on the west coast, is tentatively dated to ca. 1760 AD, just decades before the first European arrival in New Zealand. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
- View/download PDF
16. Palaeosecular variation in Northern Patagonia recorded by 0–5 Ma Caviahue–Copahue lava flows.
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Moncinhatto, Thiago R, de Oliveira, Wellington P, Haag, Mauricio B, Hartmann, Gelvam A, Savian, Jairo F, Poletti, Wilbor, Brandt, Daniele, Sommer, Carlos A, Caselli, Alberto T, and Trindade, Ricardo I F more...
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LAVA flows , *REMANENCE , *MAGNETIC domain , *MAGNETIC structure , *MAGNETIC fields , *GEOMAGNETISM , *MAGNETIC entropy - Abstract
Palaeosecular variation (PSV) determinations and studies of the geometry of the Earth's main magnetic field provide important information about the field evolution, and to constrain numerical geodynamo models. Palaeomagnetic directional data from lava flows over the last few million years is of particular interest because the regional and global tectonic effects are minimal. However, the distribution of this type of palaeomagnetic data is uneven where the Southern Hemisphere is the destitute side. Therefore, the better knowledge of the geomagnetic field behaviour depends on the increased availability of high-quality data, especially in the Southern Hemisphere. A PSV and the time-averaged field (TAF) study was then performed in 0–5 Ma lava flows from the Caviahue–Copahue Volcanic Complex located in Northern Patagonia, Argentina (37°0′S, 71°10′W). The magnetic mineralogy of lava flows was investigated through thermomagnetic susceptibility curves, isothermal remanent magnetization (IRM) acquisition curves, hysteresis loops and first-order reversal curves (FORCs). Samples are essentially comprised of titanomagnetite with different Ti contents and magnetic domain structures typical of vortex state particles. A total of 50 volcanic sites were sampled, which provided 42 reliable palaeomagnetic site-mean directions after alternating field and thermal demagnetization. From these 42 sites, 36 are of normal and 6 are of reversed polarity. The mean direction from normal (reversed) sites is D = 356.2°, I = −50.1°, α95 = 4.0° and N = 36 (D = 176.5°, I = 59.5°, α95 = 14.1° and N = 6). Using only site-level data with the precision parameter k ≥ 100, we obtain 26 palaeomagnetic sites for PSV and TAF investigations in the study region. The filtered data set has a mean direction (D = 354.4°, I = −53.2° and α95 = 5.1°) close to the expected direction for a geocentric axial dipole (GAD) field (I GAD = −57.3°). The palaeopole (Plat = 84.4°, Plon = 229.1° and A 95 = 5.7°) coincides with the Earth's spin axis within the 95 per cent confidence interval. Virtual geomagnetic pole scatter (|$S_{B} = {15.8^{18.9}_{11.8}}^{\circ }$|) and the inclination anomaly (|$\Delta I = 4.1_{-1.0}^{{9.2}^{\circ }}$|) are both consistent at the 95 per cent confidence level with recent PSV and TAF models, respectively. Our results support the presence of small non-dipole field contributions (<3 per cent) superimposed on the GAD term, as reported by South American studies at mid southern latitudes. [ABSTRACT FROM AUTHOR] more...
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- 2023
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17. Palaeomagnetic evidence of the deformation of the Pontides during the closure of the Intra-Pontide Ocean in the early Cretaceous.
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Cengiz, Mualla
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CRETACEOUS Period , *SEDIMENTARY rocks , *VOLCANIC ash, tuff, etc. , *EOCENE Epoch , *MIOCENE Epoch - Abstract
Several models exist concerning the deformation history of the Pontides in North Anatolia during the Cretaceous period, which vary depending on the positions of the Istanbul and Sakarya zones, the consumption of the northern branches of the Neotethys ocean and the rifting of several sub-basins. Notably, the early Cretaceous tectonic history of the Pontides involved the closure of the northern Neotethys ocean (Intra-Pontide ocean), and the collision between the Istanbul and Sakarya zones, producing thrust structures along the collisional front. The lack of palaeomagnetic data providing evidence for this deformation pattern demonstrates that further investigation is required, particularly focusing on the Lower Cretaceous strata in the Pontides. Thus, this study aimed to examine samples from a total of 78 sites from the Lower–Upper Cretaceous sedimentary rocks, and Middle Eocene to Middle Miocene sedimentary and volcanic rocks. Results of this study indicated large counterclockwise rotations up to R ±Δ R = −73.9°±9.1°, and small clockwise rotations of R ±Δ R = 14.2°±12.2° in the Istanbul and Sakarya zones, during the Early Cretaceous and Late Cretaceous periods. These rotation patterns are accompanied by the closure of the Intra-Pontide ocean, and the collision between the Istanbul and Sakarya zones during the Early and Late Cretaceous periods. On the other hand, in the Middle Eocene, small counterclockwise rotations of R ±Δ R = −6.4°±13.9° and 4.6°±12.9° along the western coastline of the Pontides indicated that the northern margin of the Pontides was stable during this period. [ABSTRACT FROM AUTHOR] more...
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- 2023
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18. Late Cretaceous stratigraphic division in the northwestern Songliao Basin, Northeast China: Evidence from palaeontology and palaeomagnetism.
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Wang, Wendong, He, Fubing, Guo, Hongyu, Xu, Jianxin, Zhao, Jiaqi, Chen, Hongpeng, Chen, Yang, Zhou, Long, Wang, Zhenjie, and Zhou, Zhiguang
- Subjects
- *
PETROLEUM prospecting , *PALEONTOLOGY , *NATURAL gas prospecting , *STRATIGRAPHIC correlation , *SEDIMENTATION analysis , *PETROLOGY - Abstract
This paper combines new palaeomagnetic studies, palaeontological dating, and sedimentary analyses to propose a modified stratigraphic classification scheme in the northwestern Songliao Basin, which is of great significance for stratigraphic correlation, sedimentation analysis, basinal subsidence, and oil and gas exploration. New palaeontological and palaeomagnetic evidence redefined a group of semi‐consolidated lacustrine strata, buried beneath the Quaternary Yaluhe Formation on the Western Slope of the Songliao Basin, as Late Cretaceous, not the Middle Pleistocene. The chronostratigraphic framework re‐evaluates its stratigraphic age as late Coniacian to early Campanian (Late Cretaceous), between 83 and 85 Ma. Sedimentation research from 17 boreholes on the Western Slope of the Songliao Basin displays that the semi‐consolidated strata successively experienced lacustrine and delta facies deposits. Comparison of this new stratigraphy with the Late Cretaceous sequences on the adjacent Central Depression of the Songliao Basin reveals significant variations in lithology and palynological assemblages. Three new palynological assemblages are also reported from the Late Cretaceous sequences of the Songliao Basin. [ABSTRACT FROM AUTHOR] more...
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- 2023
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19. Weak palaeointensity results over a Pliocene volcanic sequence from Lesser Caucasus (Georgia): transitional record or time averaged field?
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Sanchez-Moreno, Elisa M, Calvo-Rathert, Manuel, Goguitchaichvili, Avto, Tauxe, Lisa, Vashakidze, George T, and Lebedev, Vladimir A
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Palaeointensity ,Magnetic field variations through time ,Palaeomagnetism ,Geochemistry & Geophysics ,Geology ,Geophysics ,Geomatic Engineering - Abstract
SUMMARY A palaeointensity study has been carried out on a Pliocene sequence of 20 consecutive lava flows where previous directional results seem to reflect anomalous behaviour of the Earth's magnetic field (EMF), which can be explained by a polarity transition record or non-averaged palaeosecular variation or both. Here, we perform a total of 55 palaeointensity determinations using the original Thellier–Thellier (TT) method and 100 with the IZZI method. We assess the performance of our selection criteria using a set of strict threshold values applied to a set of test data whose TRMs were acquired in known fields. Absolute palaeointensity determinations that passed our selection criteria were obtained on four specimens with the TT method and on 41 specimens with the IZZI method. Application of reliability criteria at a site level yielded palaeointensity results in 8 of 20 studied lava flows. We obtained median values of VADM between 28.9 and 45.6 ZAm2 for the reverse polarity lower Apnia section, while the normal polarity upper section displayed a single value of 54.6 ZAm2. The low palaeointensity values before a transitional direction lava flow and the higher value after it, suggest the common behaviour at the start of a polarity reversal and the recovery after it. However, an isolated record of a stable EMF, where the intensity is lower than the current for the same location (83.7 ZAm2), cannot be discarded. Consequently, this interpretation would support a weak time-averaged field. more...
- Published
- 2020
20. The sheeted dyke-gabbro transition zone : the key to unravelling the palaeomagnetic record of the Oman ophiolite
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Koornneef, Louise Maria Theresia
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552 ,palaeomagnetism ,remagnetization ,ophiolite - Abstract
The Oman ophiolite is a natural laboratory for the study of processes operating above a nascent subduction zone. It formed in the Late Cretaceous by supra-subduction zone spreading and shortly afterwards was emplaced onto the Arabian continental margin. Twelve massifs in the ophiolite expose complete sections of the Neotethyan oceanic lithosphere, including upper mantle peridotites, lower crustal gabbros, and upper crustal sheeted dykes and lava flows. Previous palaeomagnetic studies have suggested that the southern massifs of the ophiolite were affected by a large-scale remagnetization event during emplacement, which completely replaced original remanences acquired during crustal accretion. In contrast, primary magnetizations are preserved throughout its northern massifs. This study therefore aims to: (i) apply palaeomagnetic, magnetic fabric and rock magnetic techniques to analyse systematically crustal sections through the southern massifs of the Oman ophiolite to investigate the extent and nature of this remagnetization event; and (ii) to use any primary magnetizations that survived this event to document intraoceanic rotation of the ophiolite prior to emplacement. Results demonstrate that remagnetization occurred from the base of the ophiolite upwards, and involved the acquisition of a chemical remanence that decreases in intensity up-section, related to upwards expulsion of orogenic fluids during obduction onto the Arabian continent. Magnetic fabrics in layered gabbros and dykes are aligned with macroscopic magmatic structures (layering and dyke margins), indicating that the distribution of new magnetic phases during remagnetization was controlled by existing silicate fabrics. Remagnetization appears to have been pervasive throughout the southern massifs, except at one locality (Wadi Abyad) where primary magnetizations are inferred to be preserved in the sheeted dyke complex at the top of the exposed section. Similar primary remanences were isolated at a control locality in the Salahi massif, outside of the region of remagnetization. Net tectonic rotation analysis at these non-remagnetised sites shows an initial NNE-SSW strike for the supra-subduction zone ridge during spreading, comparable with recently published models for the regional evolution of the ophiolite. more...
- Published
- 2020
21. New palaeomagnetic results of Permian tectonic blocks in the western segment of the Yarlung Zangbo Suture Zone and their tectonic implications.
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Li, Zijian, Li, Yalin, Tan, Xiaodong, Li, Shuai, Ma, Xingduo, Huang, Song, Xiao, Siqi, Cheng, Jianbo, and Zhang, Jiawei
- Subjects
- *
SUTURE zones (Structural geology) , *REMANENCE , *GEOMAGNETISM , *VOLCANIC ash, tuff, etc. , *FOSSILS , *ZIRCON , *PALEOSEISMOLOGY , *LATITUDE - Abstract
The composition and structure of the Yarlung Zangbo Suture Zone (YZSZ) provide important constraints on long‐standing disputes about the evolution of the Neo‐Tethys Ocean and continental collision. The Permian tectonic blocks (mainly composed of limestones and volcanic rocks) are widely distributed in the YZSZ. There are still different understandings about the origin of these blocks and their relationship with the evolution of the Neo‐Tethys Ocean. Here, we report the first reliable palaeomagnetic results of the Permian tectonic blocks in the Gyanyima and Mayum areas, the western segment of the YZSZ. Fossil records and our new zircon U–Pb results provide 254–252 Ma and 249 ± 2 Ma age constraints for the strata in the Gyanyima and Mayum sections, respectively. A total of 109 specimens were subjected to stepwise thermal demagnetizations. Among them, 83 specimens yielded interpretable results. After removing a recent geomagnetic field direction at low to intermediate temperature ranges, characteristic remanent magnetization (ChRM) directions can be isolated from the upper Permian–lower Triassic Gyanyima Formation (Fm). Unblocking temperature spectra of the ChRM indicate magnetite and haematite as the main carriers in the basalt and limestone/andesitic‐basalt samples, respectively. The ChRM passed the fold tests and a reversal test at 95% confidence level, indicating that it is most likely a primary remanence. The tilt‐corrected mean direction for 14 sites is D = 18.0°, I = −14.4°, k = 20.5, and α95 = 9.0°, which corresponds to a palaeolatitude of 7.3°S and a palaeopole at 48.3°N, 233.3°E with A95 = 8.1°. Combining the rock assemblage, palaeomagnetic, palaeontological, and geochronologic data, we conclude that these blocks were most likely seamounts formed in the low‐latitude area of the Neo‐Tethys Ocean. The palaeolatitude and origin of these blocks indicate that the evolution of the Neo‐Tethys Ocean was a complex process interspersed with the development of a series of seamounts and microblocks. [ABSTRACT FROM AUTHOR] more...
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- 2023
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22. variation of geomagnetic field intensity in Central Anatolia during the Neogene-Quaternary period.
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Kaya, Nurcan, Hisarlı, Z Mümtaz, Nowaczyk, Norbert R, and Makaroğlu, Özlem
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- *
GEOMAGNETISM , *GEOMAGNETIC variations , *PLEISTOCENE Epoch , *DATA libraries , *LAVA , *NEOGENE Period - Abstract
A detailed palaeointensity study was performed using the modified Thellier method on 18 Quaternary and Neogene volcanic units, ages ranging from 0.08 to 5.98 Ma, in Central Anatolia, Turkey. Robust data, which were estimated from 12 lava units in the study area, significantly increase the database of palaeomagnetic data, directions and absolute palaeointensity for the Anatolian region covering the time window back to ∼6 Ma. Previous studies sensitively dated the samples, except for one site dated in this study. The palaeointensity (VDM) value from the upper Miocene site estimated as 48.6 ± 9.2 μT (10.1 × 1022 ± 1.9 Am2) fits well into the Neogene VDM range in the data archives. For Pliocene samples with an age of 4.7 Ma, the palaeointensity was calculated to be 21.0 ± 4.7 μT. For these samples, an inclination of +42.9° was determined, and together with the results of low palaeointensity and normal polarity, this corresponds to the Nunivak or Sidufjall subchrons. These are normal polarity chrons within the Gilbert Chron which predominantly has reversed polarity. Palaeodirectional data and field strength with age between 0.08 and 2.57 Ma clearly showed the Brunhes and Matuyama Chrons in the Pleistocene. Three new data with 25.0 ± 7.9 μT (age 1.84 Ma), 59.7 ± 8.2 μT (age 2.15 Ma) and 79.6 ± 19.3 μT (age 2.57 Ma) from the early Pleistocene period significantly contribute to global data archives, which lack palaeointensity data from similar latitude range. The average VDM values for nine Pleistocene sites were calculated to be 51.5 ± 16.4 μT (10.3 × 1022 ± 3.7 Am2). According to the comparison of our data with the palaeointensity database, field model record and previous studies of the Pleistocene, significantly high field strength obtained from Central Anatolia, located in the Northern Hemisphere, could have occurred due to asymmetry between the Northern and Southern Hemispheres during the Pleistocene. [ABSTRACT FROM AUTHOR] more...
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- 2023
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23. Vector unmixing of multicomponent palaeomagnetic data.
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Tonti-Filippini, Justin A D and Gilder, Stuart A
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- *
REMANENCE , *PRINCIPAL components analysis , *HEMODILUTION , *DEMAGNETIZATION , *HEMATITE , *MAGNETIZATION - Abstract
Palaeomagnetic investigations often encounter multiple magnetization components, where secondary processes have obscured, partially overprinted or completely replaced the original (primary) remanent magnetization. Identification and separation of primary and secondary magnetizations are generally carried out with principal component analysis of stepwise demagnetization data. However, rocks may contain multiple generations of magnetic minerals with overlapping unblocking ranges that complicate the discrimination of components when applying best-fitting line procedures. Developing a method to differentiate and quantify contributions of overlapping magnetic components using directional data is therefore highly desirable. This paper presents a method to unmix stepwise demagnetization data using an inverse modelling approach. We show that the method is capable of accurately resolving two or three magnetic components with overlapping or superimposed unblocking spectra as well as quantifying absolute component contributions. The method depends on accurate identification and selection of end-member components prior to analysis; in doing so, the method can help palaeomagnetists understand how magnetization components combine to explain their data. We show that the dilution of one component by more than ca. 25 per cent from another component can result in linear demagnetization curves that decay to the origin on orthogonal plots, but whose best-fitting direction can significantly deviate from both end-members. The efficacy of the method is demonstrated through examples of demagnetization data from hematite and/or magnetite-bearing sandstones from China. This method can be broadly applied to all multicomponent magnetization problems in palaeomagnetism. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
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24. Assessing inclination flattening in the Holocene: insights from sediment data and global models.
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Liu, Pengfei, Panovska, Sanja, Zhang, Keke, and Hirt, Ann M
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- *
HOLOCENE Epoch , *GEOMAGNETISM , *MARINE sediments , *SEDIMENT compaction , *SEDIMENTS - Abstract
Lacustrine and marine sediments are one of the main sources of information in constructing Holocene global geomagnetic field models. The use of sediment records, however, leads to the question whether the compaction of sediments leads to a systematic biasing of inclination. We evaluate 78 sedimentary records worldwide for inclination flattening using the Elongation–Inclination (E/I) method; 20 records indicate flattening. The uncorrected and corrected values for inclination are compared to global geomagnetic field models. The results suggest that the uncorrected values agree better with the predictions from global geomagnetic field models based on sediment and archaeomagnetic data, but also with a model independent of sediment data. The 20 sites are located in mid-latitudes where inclination anomalies are predicted both in the Holocene and throughout the Brunhes epoch. Our results demonstrate that shallow inclination may not only result from compaction but may reflect the structure of the geomagnetic field on short timescales. This suggests that secular variation is not averaged out over a time period that covers the Holocene. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
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25. Improved anisotropy of magnetic remanence results from vectorial readings using novel refinement method.
- Author
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Wack, Michael R
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- *
MAGNETIC anisotropy , *REMANENCE , *MAGNETIC measurements , *MAGNETIC moments , *INFORMATION measurement - Abstract
Anisotropy of magnetic remanence (AMR) is typically obtained by imparting a remanence through a sequence of reference directions and subsequent measurement of the remanent magnetic moment with a separate device. This gives rise to potential misalignments which can affect the resultant anisotropy tensor. Vectorial measurements from rock magnetometers are favourable to obtain the best estimate of the anisotropy tensor but make the results highly dependent on the exact knowledge of the reference directions. This can be partly overcome by using the projection of the remanence vector on the reference direction instead of using the full vector in the calculation of the best-fitting anisotropy tensor. Since AMR experiments are laborious, it is troublesome to compensate the loss in information with additional measurements. This paper demonstrates an iterative refinement method to recover the original reference directions and therefore to improve the results of AMR experiments by using full vectorial readings. The method works well with a six-axis protocol for misalignment of the reference directions up to 25° and for degrees of anisotropy up to 250 per cent, which covers most experimental and geological cases. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
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26. New palaeomagnetic data for Palaeoproterozoic AMCG complexes of the Ukrainian Shield
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V.G. Bakhmutov, O.V. Mytrokhyn, I.B. Poliachenko, and S.I. Cherkes
- Subjects
ukrainian shield ,proterozoic ,palaeomagnetism ,amcg complexes ,tectonic reconstruction ,Geography (General) ,G1-922 ,Geology ,QE1-996.5 - Abstract
A palaeomagnetic study of rocks for two Palaeoproterozoic anorthosite-mangerite-charnockite-granite (AMCG) complexes in the Ukrainian Shield was done to put additional constraints on the interpretation of palaeogeography of Fennoscandia and Volgo-Sarmatia in the Palaeoproterozoic. With this study, 5 sites of Korsun-Novomyrhorod and 3 sites of Korosten AMCG complexes in central and north-western parts of the shield, respectively, were chosen for palaeomagnetic sampling given the geological, modern geochronological and previous palaeomagnetic data. Primary remanent magnetization was isolated on samples of anorthosites, Gabbro, and monzonites within a narrow time interval of U-Pb geochronology dataset of 1.76—1.75 Ga. The palaeomagnetic poles calculated for Korosten and Korsun-Novomyrhorod complexes are almost identical, which indicates that the Volyn and Ingul Domains developed within a single structure of the Ukrainian Shield since at least 1.75 Ga. The new palaeomagnetic pole calculated for all 8 sites (Plat=22.7 °N, Plon=167.4 °E, A95=3.3°) agrees well with previous studies by Elming et al. [2001, 2010]. The selection of the most reliable palaeomagnetic poles for Fennoscandia and Volgo-Sarmatia of this time indicates that the present position of the Ukrainian Shield relative to Fennoscandia is not the same as for about 1.75 Ga, when Fennoscandia occupied a subequatorial position within palaeolatitudes of 5—20 °N, and Volgo-Sarmatia was located close to the equator and rotated relative to Fennoscandia counterclockwise by about 40° compared to its present position. more...
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- 2023
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27. The use of high frequency microwaves in absolute palaeomagnetic intensity experiments
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Simon Lloyd, Andy Biggin, Mimi Hill, Lennart De Groot, Neil Suttie, Joseph Morris, Harald Boehnel, and John Shaw
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palaeomagnetism ,geomagnetism ,palaeointensity ,microwave system ,rock magnetism ,Science - Abstract
The Microwave Palaeointensity System at the University of Liverpool has developed, over 30 years, into the current third generation version; a combined 14 GHz microwave resonant cavity and superconducting quantum interference device magnetometer integrated microwave system. The use of microwave energy minimises the bulk temperatures required to demagnetise and remagnetise palaeomagnetic material, thereby limiting the significant problem of thermo-chemical alteration of magnetic minerals. Here we review the microwave palaeointensity approach, including its development, technical details, modern usage and results. We have carried out a comprehensive analysis of 20 palaeointensity studies, published between 2008 and 2022, where data collected using the microwave system may be compared with various other methods at the site level. An assessment of microwave results revealed no statistical bias compared to thermal, and known field data. We also present results from a new controlled experiment which tests the ability of the microwave to accurately recover weak, ancient palaeointensities when strongly overprinted. We conclude that the microwave system can be used for the primary method of determining accurate absolute palaeointensities or as part of a multi-method approach, and is well suited to a wide range of material from archaeomagnetic samples to ancient rocks. more...
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- 2023
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28. Early Eocene magnetostratigraphy and tectonic evolution of the Xining Basin, NE Tibet.
- Author
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Meijer, Niels, Dupont‐Nivet, Guillaume, Licht, Alexis, Roperch, Pierrick, Rohrmann, Alexander, Sun, Aijun, Lu, Shengcheng, Woutersen, Amber, and Nowaczyk, Norbert
- Subjects
- *
PALEOMAGNETISM , *PALEOGENE , *NEOGENE Period , *EOCENE Epoch , *CENOZOIC Era , *LAND subsidence - Abstract
The Cenozoic strata of the Xining Basin, NE Tibet, have provided crucial records for understanding the tectonic and palaeo‐environmental evolution of the region. Yet, the age of the lower part of the sedimentary stratigraphy and, consequently, the early tectonic evolution of the basin remain debated. Here, we present the litho‐ and magnetostratigraphy of various early Eocene sections throughout the Xining Basin independently constrained by the U–Pb radiometric age of a carbonate bed. Our study extends the dated stratigraphy down to 53.0 Ma (C24n.1r) and reveals highly variable accumulation rates during the early Eocene ranging from 0.5 to 8 cm/ka. This is in stark contrast to the low but stable accumulation rates (2–3 cm/ka) observed throughout the overlying Palaeogene and Neogene strata. Such a pattern of basin infill is not characteristic of flexural subsidence as previously proposed, but rather supports an extensional origin of the Xining Basin with multiple depocentres, which subsequently coalesced into a more stable and slowly subsiding basin. Whether this extension was related to the far‐field effects of the subducting Pacific Plate or the India–Asia collision remains to be confirmed by future studies. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
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29. Palaeomagnetic constraints on a Late Permian to Early Triassic final closure of the Palaeo‐Asian Ocean.
- Author
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Zhang, Donghai, Zhao, Guochun, Huang, Baochun, Zhao, Jie, and Zhao, Qian
- Subjects
- *
OCEAN , *SUTURE zones (Structural geology) , *MAGNETITE , *AMALGAMATION , *OROGENIC belts ,PANGAEA (Supercontinent) - Abstract
Final closure of the Palaeo‐Asian Ocean signifies the ultimate amalgamation of the North China, Tarim, Mongolia, Songliao, Xilinhot and other Central Asian blocks, and therefore, is critical in reconstructing the configuration of the Pangea supercontinent during the late Palaeozoic to early Mesozoic. However, the final closure time remains contentious. Here, we present a systematic palaeomagnetic study on the Upper Permian sedimentary sequences of the Xilinhot Block, located to the north of the Solonker Suture Zone. Rock magnetic results indicate stable pseudo‐domain magnetite is the dominant magnetic carrier. The characteristic components isolated between ~350 and 590°C display the existence of dual polarities. Combined with previous results, the merged site‐mean directions yield a negative reversal test and inconclusive fold tests. By comparing with coeval and posterior data, and correlating with stitching plutons that intruded the sampling sections, we argue for a remagnetization origin for the newly obtained data, which is most likely acquired during the thermal event when the stitching granitic plutons intruded at 242.0 ± 3.7 Ma. Then we synthesized available palaeomagnetic data from the Central Asian Orogenic Belt and adjacent blocks, and propose a Late Permian to Early Triassic final closure of the Palaeo‐Asian Ocean. Our reconstruction of Pangea in the Early Triassic negates the existence of a cut‐through seaway between the Mongol‐Okhotsk and Palaeo‐Asian Oceans. The Mongol‐Okhotsk Ocean was an extension of Panthalassa, in trumpet‐shaped and faced to the east, rather than an individual oceanic basin separating Siberia from the Cinamuria Block. [ABSTRACT FROM AUTHOR] more...
- Published
- 2023
- Full Text
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30. Reconstruction of the geomagnetic field during the Late Quaternary in Scotland using lacustrine sedimentary records
- Author
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Rada Torres, Myriam Andrea, Tait, Jennifer, and Whaler, Kathy
- Subjects
Palaeosecular Variations ,Palaeomagnetism ,Palaeoenvironments ,Tephrochronology ,Geochronology ,climate change ,Late Pleistocene ,Holocene ,Geomagnetic excursions ,Pompeii Tephra ,Avellino Tephra - Abstract
At about 2900km deep beneath our planet surface, there is a sharp boundary where solid rock from the Earth's mantle gives way to the molten iron-nickel alloy comprising the Earth's outer core, with temperatures over 2000ºC. Further 2200km deeper into the Earth, very high pressure turns the core into solid iron, with temperatures exceeding 5000ºC. The interaction and heat transfer between the solid and liquid cores combined with the Earth's rotation movements generates the Earth's magnetic or geomagnetic field, in a process known as the geodynamo. Direct observations through navigation records, geomagnetic observatories and satellites have taught us that the geomagnetic field constantly changes at the Earth's surface and sometimes deviates considerably from the theoretical models, in non-cyclical fluctuations called secular variations. To study the geomagnetic field in the geological past, we rely on magnetic minerals such as magnetite and haematite present in rocks at the Earth's cold crust, which have the ability to preserve the orientation (described as declination and inclination) and sometimes the strength (called palaeointensity) of the ancient geomagnetic field at the time the rock was formed. In this sense, lake and marine sediments are valuable stratified archives since they can provide high-resolution and continuous records of the Earth's magnetic field fluctuations that have occurred through time, known as palaeosecular variations (PSV). Recent numerical and computational models of the geodynamo indicate that secular variations respond to localized changes at the 2900km depth core-mantle boundary, which means that PSV records can potentially give us insight into the evolution and dynamics of the Earth's core and lower mantle through geological time and for specific regions. The present PhD project produced the first PSV record for Scotland and the UK covering the last 19,000 years from the Late Pleistocene and throughout The Holocene (Late Quaternary), using lake sediment cores from Bardowie Loch in the Central Belt of Scotland. This is also one of the few studies that describes the variations of the geomagnetic field in direction and intensity during The Holocene in the UK, making the hereby results a valuable piece in the puzzle of the geodynamo behaviour in the northern North Atlantic region, which has been particularly distinctive during the Late Holocene. PSV records of North America, Greenland, Iceland, Fennoscandia (Norway, Sweden, Finland and Russia), most recently Lake Windermere (England) and now Bardowie Loch (Scotland) are consistent with direct observations and computational models of two regions of concentrated geomagnetic flux (called flux lobes) at the core-mantle boundary beneath Canada and Siberia. The declination and palaeointensity patterns of the mentioned PSV records agree with significant oscillations in strength between both flux lobes for the last 5000 years. These are especially evident in the records from Bardowie Loch, Lake Windermere and the northern North Atlantic (Greenland and Iceland marine-cores), which suggest that the Canadian flux lobe has been weakening while the Siberian flux lobe has considerably increased in strength for the last 2000 years. The Late Pleistocene section of the Bardowie Loch PSV record shows two intervals of exceptional deviation in direction at ca 18.3ka to ca 16.2ka and ca 15ka to ca 12.8ka. The deepest interval displays rare shallow inclinations (~20º) for Scotland's latitude joined by large oscillations in the declination (a maximum of 70-degree deviation). Such substantial variations in the geomagnetic field orientation agree with the poorly known Hilina Palli Excursion, dated between 22ka and 17ka and observed globally in volcanic rocks, marine and lake cores from Hawaii and California to Lake Baikal and China. The upper interval of anomalous geomagnetic field behaviour, close to the end of The Pleistocene, exhibits the largest drop of inclination from present-day values (about 70º) to negative inclinations (-12º), while the declination presents oscillations over 50-degrees. These dramatic variations in orientation are consistent with the controversial Gothenburg Excursion (ca 12.3 to ca 13.8ka), which were originally reported in sediments from the Scandinavian Glacial Interstadial and also observed in North American glacial lakes, with poorly constrained ages from 7.6ka to 14ka. Arguments against this event are based on the large climatic changes taking place at the end of The Pleistocene, which could have affected the preservation process of the geomagnetic field in such sediments. Numerical models have indicated that excursions are caused by magnetic field reversals taking place only in the Earth's outer liquid core, unlike complete reversals where the geomagnetic field changes polarity throughout the outer and inner core. This could explain why geomagnetic reversals usually last hundreds of thousands to millions of years, while geomagnetic excursions only have from few thousand years of duration, like the events observed in the Bardowie Loch PSV record, to a maximum of ten thousand years. Bardowie Loch was selected as the study site based on its small-size basin, which is part of a glacial landscape, and limited catchment area without any sizeable river system. This ensures a low energy environment, which is necessary for the magnetic minerals to align with the Earth's magnetic field at the sediment/water interface during deposition. Our geological analyses suggest that Bardowie Loch originally formed as consequence of the movement of large glaciers, possibly at the time of the last glacial maximum about twenty thousand years ago. Then from ~19ka to ca 11.5ka, the Bardowie Loch basin was part of a Proglacial Environment, a lake fed with sediments transported by glacial melt-water. We carried out rock magnetic characterisation studies based on the magnetic properties of the glacial lake-sediments, which were supported by microscopic and geochemical analyses. The results show that there are pulses of substantial deposition into the lake basin of sediments eroded from nearby Palaeozoic volcanic rocks, rich in magnetic mineral grains. Additionally, there are layers made of very fine sediments (clay and fine silt) that present large concentrations of chemical elements associated to biological productivity in the lake-water ecosystem, joined by abundant quantities of microscopic-algae fossils (diatoms). These layers also give indications of anoxic conditions at the lake-bottom and strong evidence of magnetite produced by a remarkable type of bacteria, called magnetotactic bacteria (MTB). The results from these glacial lake-sediments analyses were correlated with published data from Greenland ice-cores. We found that the largest deposition pulses occurred when temperatures abruptly increased at the end of two distinctive periods of colder glacial conditions called Stadials, at ca 14.8Ka for Stadial 2 and ca 11.6Ka for Stadial 1 (in Bardowie Loch chronology), which implies that these high detrital input events might be the result of significant melting of glaciers close to the Bardowie Loch basin. We also found that two different warming climate events produced the fine-sediments layers containing diatoms and possible MTBs. The first was a period of mild environmental conditions in the North Atlantic region known as the Last Glacial Interstadial, between ca 14.8ka and ca 13.2ka (Bardowie chronology), and the second event was the global warming that marked the onset of The Holocene, dated between 11.7ka and 11.3ka for these layers in the Bardowie Loch sequence. A thousand percent surge in organic matter content combined with a substantial decrease of sediment input from the Palaeozoic volcanic rocks and significantly lower concentration of magnetic minerals characterised the Holocene sediments of the Bardowie Loch sequence. Results from geological, geochemical and rock magnetic studies of these layers indicate that Bardowie Loch has been through three very different stages. Between ca 11.5ka and ca 8ka Bardowie was a thermally stratified lake, denoted by laminated muds and alternation of oxic and anoxic phases, with strong indications of MTBs at the lake bottom. These observations imply first that the Bardowie basin was larger and considerable deeper at that stage than today and second, large temperature contrasts from winters to summers during this time., From ca 8ka to ca 4ka we found the largest concentrations of organic matter joined by rapid increments of elements related to biological productivity and abundant accumulation of insects remains, all of which imply significant climate warming at this time. We also found compelling evidence for basin shallowing at this stage combined with strong indications of soil formation at ~4.5ka. This shallowing could be the result of the Earth's crust rising to adjust for the deformation caused by the large ice sheet loads during the Pleistocene. more...
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- 2019
31. Chronology of the Hominin Sites of Southern Africa
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Herries, Andy I.R.
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- 2022
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32. A Holocene palaeomagnetic secular variation record from Lake Pupuke, New Zealand.
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Corkill, Ruth M. and Turner, Gillian M.
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TEPHROCHRONOLOGY , *REMANENCE , *HOLOCENE Epoch , *EARTH'S core , *GEOMAGNETIC variations , *EXPLOSIVE volcanic eruptions - Abstract
Palaeomagnetic records from three cores of lake sediment have been merged, producing a new Holocene geomagnetic secular variation record for northern New Zealand. The cores are from Lake Pupuke, a maar lake in Auckland Volcanic Field (AVF). They contain tephra from Rangitoto Volcano (530 ± 10 yr BP), Taupō (1718 ± 10 yr BP), Tūhua/Mayor Island (7637 ± 100 yr BP) and Rotomā tephra from Ōkataina Volcanic Centre (9423 ± 120 yr BP). These tephra dates are supplemented by selected radiocarbon age estimates. The cores were correlated using tephra and fine-scale variations in magnetic susceptibility. The natural remanent magnetisation is strong, stable and carried by fine-grained titanomagnetite from AVF's basaltic volcanoes. The resulting palaeosecular variation (PSV) record spans from 10,000 to 1500 yr BP. It shows well-defined, millennial-scale swings in direction between 10,000 and 8000 yr BP and between 4000 and 1500 yr BP, while between 8000 and 4000 yr BP variations are of higher frequency and lower amplitude and centre on the geocentric axial dipole field direction. This is in excellent agreement with published PSV records from Mavora Lakes, 1000 km further south, indicating the regional nature of PSV – resulting from broad-scale changes in the circulation of conducting iron-rich fluid of Earth's outer core. [ABSTRACT FROM AUTHOR] more...
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- 2022
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33. Palaeomagnetic data from the late Cenozoic Tagay section (Olkhon Island, Baikal region, Eastern Siberia).
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Kazansky, Alexey Yu., Shchetnikov, Alexander A., Matasova, Galina G., Filinov, Ivan A., Erbajeva, Margarita A., Daxner-Höck, Gudrun, and Mörs, Thomas
- Abstract
One of the most important fossil fauna localities in the Baikal region is the Tagay section. It is located on the shore of Tagay bay at the northwestern coast of Olkhon Island in the Baikal Lake and consists of two different exposures, Tagay-1 and Tagay-2. The Tagay-1 section exposes predominantly lake sediments of Miocene age and contains a faunal complex. The Tagay-2 section is composed of slope wash and subaerial sediments of Early Pleistocene (Calabrian?) age with remains of small mammals. A total of 95 samples for palaeomagnetic studies were taken in both sections. Magnetic susceptibility (MS), its frequency dependence (Fd) and anisotropy were measured from all samples. The stable component of the natural remanent magnetization (NRM) was obtained using stepwise alternating field (AF) demagnetization. The magnetic polarity pattern was constrained for the Tagay-1 section. It includes an extended zone of reversed polarity, complicated by three normal subzones of minor rank. Palaeontological data allow correlation of the Tagay-1 pattern with the magnetic chrons C5Dn to C5Cn.1n (late Burdigalian – early Langhian). Palaeomagnetic directions in the upper part of the Tagay-2 section are randomly distributed due to intensive slope-wash processes resulted in mechanical perturbation of the sediments. The lower part of Tagay-2 section demonstrates only reversed polarity, although the scatter of directions is quite large due to landsliding. This reversed interval may be correlated with the Matuyama chron between Cobb Mountain and Olduvai subchrons. Synchronous increase of MS and Fd values in palaeosols suggests a pedogenic (or "Chinese") mechanism influencing magnetic properties of the Tagay-2 section under warm palaeoclimatic conditions. [ABSTRACT FROM AUTHOR] more...
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- 2022
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34. 3-D modelling and analysis of superparamagnetic effects in ATEM based on the FDFD.
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Ji, Yanju, Liu, Huaishi, Yu, Yibing, and Zhao, Xuejiao
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MAGNETIC permeability , *MAGNETIC fields , *MAGNETIC flux density , *MAGNETIC susceptibility , *ELECTRIC transients , *POWER law (Mathematics) , *ELECTRICAL conductivity measurement , *ELECTROMAGNETIC pulses - Abstract
SUMMARY: Superparamagnetic (SPM) effects lead to 1/ t power-law delay approximately during the middle and late periods of transient electromagnetic responses. Ignoring SPM effects can produce large errors and cause incorrect data interpretation. Furthermore, because of the non-linearity of the Chikazumi magnetic susceptibility model, it is difficult to discretize the model in the time domain. Therefore, developing an algorithm for 3-D modelling of SPM effects in the time domain directly is difficult. In view of the above problems, we propose a 3-D modelling method of SPM effects for airborne transient electromagnetic (ATEM) data. We also introduce the widely used Chikazumi magnetic susceptibility model into the finite-difference frequency-domain (FDFD) method. According to the mapping relations between the magnetic field intensity and the magnetic permeability on the grid after discretization, we re-establish the scientific matrix of the magnetic permeability. And we adopt arithmetic averaging of the two adjacent cubes' magnetic permeability as the magnetic permeability in boundary, which is a different setting method with the electrical conductivity. The 3-D modelling of SPM effects is successfully realized, and its maximum relative error is less than 7 per cent. We subsequently analyse the intrinsic properties of the abnormal magnetic medium, as well as the effect of the SPM unit's parameters, such as the depth, thickness, electrical conductivity, zero-frequency magnetic susceptibility, and the height of the receiver, on the response. Then, we calculate the SPM responses of 3-D magnetic bodies and analyse the influence of magnetic susceptibility and electrical conductivity on magnetite responses. The present study can provide theoretical guidance for ATEM detection in magnetic media and lay a foundation for 3-D inversion of SPM effects. [ABSTRACT FROM AUTHOR] more...
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- 2022
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35. Palaeomagnetic inclination anomaly in the Deccan traps and its geodynamic implications over the Indian plate.
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Sangode, S J, Dongre, Ashish, Bhagat, Amarjeet, and Meshram, Dhananjay
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Rapid northward drift of the Indian plate during Deccan volcanism assumes a gradual equatorward shallowing of the paleomagnetic inclinations amongst subsequently younger lava flows. Compilation of palaeomagnetic database and using 1062 statistically significant site mean directions from the Deccan Volcanic Province discovered an inclination anomaly of +10 degrees during the Deccan main phase eruptions (DEM within Chron C29r at 66.398–65.688 Ma). The anomaly represents northward tilt during C29r followed by its restoration in C29n (~65 Ma). This anomaly is explained here by the Indian lithospheric response to Réunion plume head during DEM. A sequence of coincident geodynamic instances including: (i) biostratigraphically constrained ‘the brief inland seaway’, (ii) development of a regional southward dip for the lava flows, (iii) major drop in sea level at the southern tip of peninsula, and (iv) accelerated spreading and convergence rates during C29r to 29n transitions; substantiate the effect of lithospheric tilt and its restoration. We present a plume-lithosphere evolutionary model to explain the anomaly and its wider implications over the Indian lithospheric plate. [ABSTRACT FROM AUTHOR] more...
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- 2022
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36. Directions Old and New: Palaeomagnetism and Fisher (1953) Meet Modern Statistics.
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Scealy, Janice L., Heslop, David, Liu, Jia, and Wood, Andrew T. A.
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CONFIDENCE regions (Mathematics) , *CONFIDENCE intervals , *ROTATIONAL symmetry , *GEOLOGICAL formations , *PARAMETRIC modeling - Abstract
Summary: Most modern articles in the palaeomagnetism literature are based on statistics developed by Fisher's 1953 paper 'Dispersion on a sphere', which assumes independent and identically distributed (iid) spherical data. However, palaeomagnetic sample designs are usually hierarchical, where specimens are collected within sites and the data are then combined across sites to calculate an overall mean direction for a geological formation. The specimens within sites are typically more similar than specimens between different sites, and so the iid assumptions fail. This article has three principal goals. The first is to review, contrast and compare both the statistics and geophysics literature on the topic of analysis methods for clustered data on spheres. The second is to present a new hierarchical parametric model, which avoids the unrealistic assumption of rotational symmetry in Fisher's 1953 paper 'Dispersion on a sphere' and may be broadly useful in the analysis of many palaeomagnetic datasets. To help develop the model, we use publicly available data as a case study collected from the Golan Heights volcanic plateau. The third goal is to explore different methods for constructing confidence regions for the overall mean direction based on clustered data. Two bootstrap confidence regions that we propose perform well and will be especially useful to geophysics practitioners. [ABSTRACT FROM AUTHOR] more...
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- 2022
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37. Do changes in geomagnetic secular variation, dipole moment and polarity reversal frequency correlate over the past 155 Myr?
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Eid, B, Lhuillier, F, Shcherbakov, V P, and Shcherbakova, V V
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DIPOLE moments , *GEOMAGNETIC variations , *GEOMAGNETISM , *APPLICATION program interfaces , *SOLAR cycle - Abstract
Changes in palaeosecular variation, dipole moment and polarity reversal frequency are salient features of the Earth's magnetic field over the geological past, yet how these changes are linked by the geodynamo remains controversial. To further understand this issue, we provide new absolute (API) and relative (RPI) palaeointensities from the ∼1-km-thick basaltic sequence of Waja (North Ethiopia) emplaced around 31 Ma, yielding an instantaneous virtual dipole moment of 57 ± 9 ZAm2 (1 σ, N = 18) and a relative variability in intensity ε F = 0.39 ± 0.07 (1 σ, N = 19). Our analysis of the API database with strict selection criteria (inclusion of Thellier-style determinations with pTRM checks only, at least five determinations per cooling unit, and within-unit relative standard error lower than 10 per cent) fails to identify any robust correlation between changes in dipole moment and reversal frequency over the past 155 Myr. More convincingly, the available RPI results are consistent with an increase of the palaeosecular-variation proxy εF with reversal rate, as predicted by numerical dynamo simulations. We also find that the API-based estimate ε F = 0.40 ± 0.03 (1 σ, N = 104), computed from the filtered version of the World Palaeointensity Database for the 0.77–31 Ma interval, is consistent with the scaling rule, suggesting that the API record has been sufficiently sampled over the past 31 Ma. We thus speculate that the absence of negative correlation between changes in dipole moment and reversal frequency in the API database over the past 155 Myr may be the result of insufficient sampling prior to 31 Ma rather than the signature of an intrinsic geomagnetic feature. [ABSTRACT FROM AUTHOR] more...
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- 2022
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38. Geochronology of Laterites
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Ghosh, Sandipan, Guchhait, Sanat Kumar, Ghosh, Sandipan, and Guchhait, Sanat Kumar
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- 2020
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39. Temporal evolution of crustal rotation in the Aegean region based on primary geodetically-derived results and palaeomagnetism.
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Lazos, Ilias, Sboras, Sotirios, Chousianitis, Konstantinos, Kondopoulou, Despina, Pikridas, Christos, Bitharis, Stylianos, and Pavlides, Spyros
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SATELLITE geodesy , *ROTATIONAL motion , *KINEMATICS - Abstract
The Aegean is tectonically the most active and complex area in the Mediterranean region, including numerous active structures of all types of kinematics, often related to destructive seismic events. In such a tectonic environment, the estimation of rotational regime is decisive in the determination of the geodynamic and geotectonic evolution of this region. Satellite geodesy is a reliable way of estimating the rotation rate, while its comparison with palaeomagnetic data can lead to the identification of well-established patterns. To this direction, we use geodetic datasets recorded by permanent GPS/GNSS stations and we apply the triangulation methodology by combining three stations each time. Consequently, for each and every point of the 4733 extracted ones, the rotation rate and its pattern are calculated. Using the above results, two rotation models are proposed: one for the past 1 Myr and one for the past 5 Myr. In addition, the geostatistical analysis of the geodetically extracted results was carried out, in order to determine their spatial distribution. The comparison and combination of these two geodetically induced models with palaeomagnetic data, led to the delineation of distinct upper crust areas of uniform rotation within the Aegean region. [ABSTRACT FROM AUTHOR] more...
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- 2022
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40. Palaeomagnetic indication for India–Asia collision at 12°N and maximum 810 km Greater India extent in the western suture zone.
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Dannemann, Sven, Appel, Erwin, Rösler, Wolfgang, Neumann, Udo, Liebke, Ursina, and Nag, Debarati
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SUTURE zones (Structural geology) , *OROGENIC belts , *PALEOGENE , *MAGNETIC properties , *CRETACEOUS Period , *REMANENCE , *EOCENE Epoch - Abstract
Knowing the pre-collisional extent of the northern Indian Plate margin ('Greater India') is vital to understanding the tectonic evolution of the India–Asia collision and the formation of the Himalayan–Tibetan orogen. However, suitable geological units for palaeomagnetic investigations along the Himalayan belt are limited, which makes it difficult to reconstruct Greater India during the pre-collisional period in Late Cretaceous to Palaeogene. Often the palaeomagnetic results from the Zongpu Formation at Gamba in southern Tibet (∼88.5°E) were used for estimates of Greater India, but their validity was recently questioned. As a contribution to closing the data gap, we performed a palaeomagnetic study of the Palaeocene/Lower Eocene Dibling limestone (DL) in the western Tethyan Himalaya of Zanskar (34.0°N/76.6°E). The results from 27 sites revealed a well grouping (k = 71.7) syntectonic magnetization with best grouping at 52 per cent unfolding. The remagnetization of the DL was acquired shortly after ∼54 Ma, at the latest at ∼49 Ma, and is probably carried by fine-grained magnetite formed during the early orogenic phase. Assuming proportional tilting of the fold limbs, the corresponding palaeolatitude of 11.8 ± 2.4°N suggests a maximum Greater India extent of 810 ± 420 km and a first continental contact with the southern Eurasian margin at ∼12°N in the western part of the suture zone. The tectonostratigraphic equivalence of the DL with the Zongpu Formation at Gamba and a great similarity in their magnetic properties supports a secondary origin of the Gamba results. Through understanding the mechanism of remagnetization in the DL, an early orogenic remanence acquisition is also indicated for the Zongpu Formation, and thus the Gamba results deserve further credit for Greater India reconstructions. However, we note a large inconsistency of the available Late Cretaceous and Palaeogene palaeolatitude data from the Tethyan Himalaya by up to ∼20°, corresponding to differences of up to ∼2000 km in the size of Greater India. These discrepancies require further palaeomagnetic work in the Tethyan Himalaya, and in particular we recommend comparative studies at same locations and of same units. [ABSTRACT FROM AUTHOR] more...
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- 2022
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41. How to make continental reconstructions: the importance of the knowledge of high strain along former plate boundaries
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Şengör, A. M. Celâl, Natal’in, Boris A., Lom, Nalan, Zabcı, Cengiz, and Sunal, Gürsel
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- 2023
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42. Magnetic Susceptibility of Ferrimagnetic Minerals and its Connection with Fe-Metabolising Microbial Community
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Bajić, Maja and Bajić, Maja
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Interaction between minerals and bacteria represents an abundant natural phenomenon depictingnature's complexity and how abiotic and biotic components are intertwined. This interaction is evidentin modern-day ecosystems, and it significantly shaped the early stage of life on Earth by influencinggeochemical processes. Evidence of this interaction includes microbialites. In the first part, this master's thesis explores the impact of iron-redox bacteria on the magneticproperties of synthetic and natural magnetic materials, with significant implications for understandingearly Earth conditions and paleoenvironments. In the second part, the magnetic signal recorded in thesediment core from the Baltic Sea is examined to identify the ferrimagnetic minerals responsible for itand their origin (biotic versus abiotic). A better understanding of the origin of ferrimagnetic mineralsallows for a more conclusive interpretation of palaeomagnetism and palaeoenvironmental history of theBaltic Sea. In both parts, the change in magnetic susceptibility was used as the main method to depictmechanisms of mineral-bacteria interaction. Experiment with iron-oxidising bacteria (Leptothrix mobilis) showed a decrease in magneticsusceptibility over time, consistent with the oxidation of solid iron/magnetic materials. However, asmall difference between bacteria culture and control samples points out that the decrease is caused byabiotic oxidation rather than bacterial. Supporting evidence is the absence of viable cells in all bacterialsamples, suggesting that L. mobilis did not grow in these experiments. In experiments with iron-reducing bacteria (Geobacter sulfurreducens), magnetic susceptibility increased by 7%. Controlsamples with the same reducing media did not show a change in magnetic susceptibility, indicating thatthe susceptibility change is caused by bacterial reduction of iron oxides. Magnetic susceptibility signal obtained in the sediment core from the Baltic Sea indicates rapidlyoxidis more...
- Published
- 2024
43. Late miocene silicic subvolcanic plumbing system related to oblique rifting in the Pacific-North American plate boundary, Sonora, Mexico: geodynamic implication in a regional context.
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Velderrain-Rojas, L.A., Vidal-Solano, J.R., Alva-Valdivia, L.M., and Vega-Granillo, R.
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IGNEOUS intrusions , *MIOCENE Epoch , *PLUMBING , *MAGNETIC anisotropy , *MAGNETIC declination , *RIFTS (Geology) - Abstract
Rocks from subvolcanic silicic magmatism (SSM) are exposed intermittently over a wide area along the Sonora coast, NW Mexico. This region is characterized by syn-rift volcanism related to the development of the Pacific-North America transform plate boundary during the Late Miocene (~12.5-~6 Ma). The ca. 11 Ma U-Pb age obtained from the SSM in the study area makes this magmatism part of the first stages of this tectonic event. Variations in magnetic mineralogy and textural relationships of the SSM suggest that they are a hypabyssal suite emplaced at distinctive depths. The anisotropy of magnetic susceptibility used for the petrofabric analysis reveals that, generally, the magnetic lineation is subparallel to the magnetic foliation and both are subhorizontal, suggesting a lateral emplacement. Palaeomagnetic analysis of 31 sites on the intrusive bodies indicates clockwise vertical axis rotations up to 90° related to dextral strike-slip faults. The fieldwork observations, magnetic fabric orientation, and the distribution of the SSM suggest that the magmas were propagated in a transtensional setting ascending probably through tension gashes from a deep main magma body, and emplaced as sheet intrusions in the syn-rift volcanic sequence. We propose that the vertical axis rotations of the SSM bodies are part of a unique transtensional-type deformation system of the oblique-divergent plate boundary, which it gradually changed. The SSM rocks are distinguished from other plutonic rocks forming most of the basement of NW Mexico by their age, distribution, emplacement environment, and deformation style. Finally, this study provides compelling evidence of igneous plumbing system within rift zones and a valuable contribution to the history of magmatism and tectonic control related to the development of the oblique rifting in the Gulf of California plate boundary. [ABSTRACT FROM AUTHOR] more...
- Published
- 2022
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44. Das Rotliegend in der Stratigraphischen Tabelle von Deutschland 2016 (STD 2016).
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Menning, Manfred, Glodny, Johannes, Boy, Jürgen, Gast, Reinhard, Kowalczyk, Gotthard, Martens, Thomas, Rößler, Ronny, Schindler, Thomas, von Seckendorff, Volker, and Voigt, Sebastian
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GEOMAGNETISM , *GEOLOGICAL time scales , *SEQUENCE stratigraphy , *VOLCANIC ash, tuff, etc. , *CONFIDENCE intervals , *MAGNETIC susceptibility , *CHEMOSTRATIGRAPHY , *PERMIAN-Triassic boundary , *CYCLOSTRATIGRAPHY - Abstract
Time indications for the correlation and calibration of the Rotliegend of Germany are integrated and presented in a new way. The correlations are based on the visual balance of bio- and ecostratigraphic indications and radio-isotopic age determinations (RIA), whereby confidence limits, equivalent to those of the RIA, are applied also for other time indications (conchostracans, aquatic tetrapods, fishes, insects, macroflora, and ecostratigraphic indications). In contrast, terrestrial tetrapods and their tracks, chemo- and sequence stratigraphy, and magnetic susceptibility did not contribute to correlations in the Rotliegend in Central Europe. The Illawarra Reversal of the Earth' magnetic field (≈ 265 Ma) is fundamental for correlation and calibration. In general, however, the Regional Stratigraphic Scale is calibrated using U-Pb CA-ID-TIMS-RIA on zircon, Ar-Ar- and Rb-Sr-based RIA and, in addition, in the Early and Late Rotliegend using orbital-climatically controlled eccentricity cycles (≈ 100 ka, ≈ 400 ka). The boundary ages of the subgroups and of most formations are rounded to 0.5 Ma to avoid overinterpretation. Because of some inconsistent time indications alternative interpretations are also offered. The hitherto differing ages for the global Carboniferous-Permian boundary are the result of different dating methods: The ≈ 296 Ma in the Stratigraphic Tables of Germany 2002 and 2016 A (STG 2002; STG 2016 A) is an integrative age based on RIA from Central Europe, whereas the ≈ 299 Ma in the Global Stratigraphic Scales 2004 ff. and the STG 2016 B is based on a CA-ID-TIMS RIA on zircon from the southern Ural area. The age of ≈ 299 Ma is plausible from the perspective of the current Rotliegend RIA because the Rb-Sr age of 290.7 ± 0.9 Ma for the Donnersberg Formation (Lippolt & Hess 1989) has been replaced by the age of 294.5 ± 2.2 Ma, as recalculated in the present work. The updated time scale developed here will be integrated in the Stratigraphische Tabelle von Deutschland Kompakt 2022 (STDK 2022) and into the Stratigraphic Table of Germany Compact 2022 (STGC 2022). The age of the base of the Rotliegend in the Saar-Nahe Basin (SN, base Remigiusberg Formation and Glan Subgroup) is ≈ 299 Ma (U-Pb CA-ID-TIMS, zircon) resp. ≈ 300 Ma (Ar-Ar); the balanced compromise age of both is ≈ 299.5 Ma. In the Thüringer Wald (TW), the Rotliegend begins with the Ilmenau Formation (Subkommission Perm-Trias 2011) at ≈ 299.5 Ma (U-Pb CA-ID-TIMS). On the Flechtingen Block, at the southern margin of the Central European Basin, the oldest volcanic rock of the Altmark Subgroup is dated at 302 ± 3 Ma (U-Pb SHRIMP data). Accordingly, the Rotliegend in the STG 2002 and STG 2016 A starts at ≈ 302 Ma. However, the mean age calculated in the present work for the SHRIMP data of Breitkreuz & Kennedy (1999) is 298.6 ± 1.9 Ma, so that the base of the Altmark volcanic succession is here re-dated as ≈ 300.5 Ma. Thus, the ages of the present lithostratigraphic lower limits of the Rotliegend in northern Germany (CEB), in the TW and in the SN are, with ≈ 300.5 Ma to ≈ 299.5 Ma, only weakly diachronous if the nominal (face) values, which are both in the latest Carboniferous, are compared without the confidence intervals. For the first time, the Rotliegend of Germany is geochronologically subdivided into Early (≈ 300.5-295.5/294 Ma), Middle (≈ 295.5/294-266 Ma) and Late Rotliegend (≈ 266-257.5 Ma). The very long lasting Middle Rotliegend includes numerous and also extremely long stratigraphic gaps as a result of the amalgamation and the associated immense uplift of Pangaea in the area of Central and Western Europe. A very large stratigraphic gap in the Central European Basin (CEB) of ≈ 15 Ma (≈ 281-266 Ma, here called the Pangaea Gap) is supported by conchostracans, the Illawarra Reversal and the different palaeomagnetic properties of the sediments below and above the gap, which are discussed here for the first time. The Middle Rotliegend (duration of ≈ 29.5/28 Ma) is approx. twice as long as the Early (≈ 5.5/7 Ma) and Late Rotliegend (≈ 8.5 Ma) combined. The latter, however, contain the thickest successions in the Saar-Nahe Basin and the Central European Basin, respectively, which are free of gaps in the basin centre, with 'gaps' being defined in this context as time spans of ≤ 100 ka and ≤ 400 ka, respectively. In the CEB, the Elbe Subgroup is cyclostratigraphically calibrated to 5.6 Ma. A gapless area in the Saar-Nahe Basin is the Glan Subgroup, which covers only 4 Ma and 3 Ma, respectively; correspondingly, its subunits G1 to G10 (Glan 1 to Glan 10), introduced here, last on average 0.4 Ma and 0.3 Ma, respectively. This results in a maximum accumulation rate of 870 Bubnoff (Bub, m/Ma, mm/ka) and of 1150 Bub, respectively, which can be explained by a maximum of tectonic activity along the Hunsrück Southern Border Fault. For the lower Nahe Subgroup (N1 to N5, Nahe 1 to Nahe 5), the maximum accumulation rates are ≈ 450-200 Bub and for the upper Nahe Subgroup (N6-N8), at an estimated duration of 12 Ma ≈ 125 Bub and ≈ 50 Bub at a duration of 30 Ma, respectively. In the Central European Basin the maximum accumulation rates are much lower compared to the Glan Subgroup, with 200 Bub in the Elbe Subgroup and ≈ 360 Bub in the Havel Subgroup (Fig. 27), although here the subsidence rate may have been higher than the accumulation rate, as the basin was ≈ 130 m below sea level at the end of Folge ro4 (Top of the Hannover Formation; this paper). We recommend (1) Bubnoff (Bub) as unit of measure of the accumulation rate and (2) the stratigraphic terminology of the Subkommission Perm-Trias (2011) and the STG 2016 A. We here propose that numerous tuffs of the Glan Subgroup could originate from volcanic centres of the TW, whereas so far only source areas south of the SN were discussed: On the one hand, the tuff-rich time of the upper Jeckenbach Subformation - Odernheim Formation (= Glan units 7 and 8 = G7/G8) seems to correlate with the volcanogenic Oberhof time in the TW and, on the other hand, the tuff-poor time of the Wahnwegen Formation - middle Jeckenbach Subformation (G2/G6) seems to correlate with the upper Ilmenau, Manebach, Goldlauter and lowest Oberhof formations, which are devoid of volcanic rocks in the TW. Should causality exist here, an additional and also precise criterion for correlation would be established. At present there are two variants: On the one hand, volcanism in the Oberhof Formation, according to RIA (U-Pb CA-ID-TIMS on zircon), begins ≈ 1.8 Ma earlier and ends ≈ 0.8 Ma earlier than in the Donnersberg Formation (Ar-Ar, Rb- Sr recalculated). On the other hand, the conchostracan Lioestheria pseudotenella in the TW, if considered equivalent to L. cf. pseudotenella in the SN, the ecostratigraphic and lithofacial indications and the aquatic tetrapod D. pulcherrimus, point to for a similar age of these magmatites. The Sobernheim Lens (SN, Nahe units N4/N5) with its fossils so important for correlations is here assigned to the Jakobsweiler Member (N4, upper Donnersberg Formation), to the Quartzite-Conglomerate (N5, in literature often Wadern) and to the lowermost Standenbühl Formation (N4/N5). The youngest time indication Co13, the conchostracan Lioestheria arroyoensis sp. nov. correlates the upper Standenbühl Formation (N8, Martens 2020, where N8 may be extremely long), roughly with the Arroyo Formation in Texas (≈ early Kungurian). The here favoured age of the Tambach Formation of ≈ 294-292 Ma is significantly higher than the ≈ 286-283 Ma of STG 2016 A and the ≈ 284-281 Ma of STG 2016 B. It is based on RIA R25 (Table 9; lower Rotterode Formation, 295.8 ± 0.4 Ma; Lützner et al. 2021), which is the youngest CA-ID-TIMS RIA in the TW, and the duration estimate of the Rotterode - Tambach gap. In the SN, the youngest RIA R29 (Rb/Sr) is from the Donnersberg Formation (294.5 ± 2.2 Ma, this paper). From here on until ≈ 265 Ma (Illawarra Reversal), the numerical ages of all Rotliegend units and their connection to the Global Stratigraphic Scale (GSS) are uncertain and therefore correlations between Central Europe and the global reference section in the southern Ural area, partly biostratigraphically via North America, vary greatly. In this contect, the „series“ Wolfcampian and Leonardian (standard Permian units of the USA) played an important role. However, these lithostratigraphic units are at least unsuitabel as a reference system for large parts of North America, because they represent very variable time spans from region to region, similar with the "Lower Rotliegend" ("Autun") and "Upper Rotliegend" ("Saxon") of Central and Western Europe and therefore their assignement to the GSS is also very variable. This is due, among other things, to the fact that the Wolfcampian is often still understood as "lower Lower Permian", although considerable parts of it are now placed in the Carboniferous, because as a result of the introduction of the Global Stratigraphic Section and Point (GSSP) for the base of the Asselian Stage (= global base of the Permian in the southern Ural area), the conventional regional Carboniferous-Permian boundaries shifted to an higher stratigraphic level and thus to a younger age in the USA, China and the Donbass (Fig. 14). If the 57 sedimentary cycles in the Ottweiler and Glan subgroups (Königer & Stollhofen 2001: mean duration 245 ka each) in the SN are orbital-climatically induced, these cycles can only be 100 ka cycles (short eccentricity). This is also supported by the 6 cycles in units G7 and G8 that have been described in detail in the literature, which are consistent with the duration of the Glan Subgroup of 3 Ma and (preferred) 4 Ma, respectively. The total duration to be expected from 57 cycles à ≈ 100 ka is ≈ 5.7 Ma in contrast to the duration determined here according to RIA of ≤ 8 Ma. One reason for the difference could be that in the Ottweiler und Glan subgroups there are cycles that have not been recorded so far. The time span of ≤ 8 Ma is also an outcome of the new estimate for the duration of the Cantabrian Gap (early Stephanian) in the Saar-Nahe Basin of ≈ 3.6 Ma that is clearly longer than proposed in the STG 2002 and STG 2016. [ABSTRACT FROM AUTHOR] more...
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- 2022
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45. record of the lower Mammoth geomagnetic polarity reversal from a marine succession in the Boso Peninsula, central Japan.
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Haneda, Yuki and Okada, Makoto
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GEOMAGNETIC reversals , *MAMMOTHS , *GEOMAGNETISM , *PENINSULAS , *MARINE sediments , *DEMAGNETIZATION - Abstract
Palaeomagnetic records from geological archives provide significant information about the nature of geomagnetic polarity reversals; however, there are few detailed palaeomagnetic records of pre-Pleistocene reversals. The lower Mammoth Subchron boundary (late Pliocene) is recorded in a 10-m interval of a marine succession deposited at high accumulation rates (9–66 cm kyr–1) in the Boso Peninsula, central Japan. Here, we report a continuous palaeomagnetic record of the lower, normal to reverse boundary interval of the Mammoth Subchron, including the geomagnetic field direction and relative palaeointensity, with an average temporal resolution of ca. 800 yr. A hybrid method of thermal demagnetization at 200 °C and progressive alternating field demagnetization were used to effectively extract the primary palaeomagnetic component, which is carried by magnetite. The lower Mammoth transition is characterized by palaeomagnetic direction of instability and decay of the relative palaeointensity, and occurred from late Marine Isotope Stage MG3 (3351 ka) to MG2 (3336 ka) or MG1 (3331 ka), spanning 15–20 kyr. Virtual geomagnetic poles (VGPs), calculated from primary palaeomagnetic directions, rapidly rebounded twice from southern latitudes to northern latitudes within the transition. In contrast to the complex lower Mammoth reversal behaviour recorded in the Boso Peninsula succession, records from a lava sequence in O'ahu (Hawai'i) reveal a rebound following a 180° directional change, and those from a marl succession in Sicily (Italy) indicate a single rapid directional change. Diverse geomagnetic field evolution among these three sections is reflected resolution difference among the records likely in combination with an influence of non-axial dipole field. [ABSTRACT FROM AUTHOR] more...
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- 2022
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46. Laschamps geomagnetic excursion recorded in continental sediments from southern Germany.
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Kirscher, U, Dallanave, E, Weissbrodt, V, Stojakowits, P, Grau, M, Bachtadse, V, and Mayr, C
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MAGNETIC measurements , *HEMATITE , *MINERALOGY , *PLEISTOCENE Epoch , *DEPTH profiling , *GEOMAGNETISM - Abstract
We present palaeo- and rock magnetic results from a well-dated, 21 m-thick, Late Pleistocene continental sedimentary section located in southern Germany. Rock magnetic measurements reveal a complex magnetic mineralogy dominated by low coercivity minerals likely related to single domain biogenic magnetite and biogenic or early diagenetic greigite. In the lower part of the section also detrital haematite is present. The stable remanence shows predominantly normal polarity with two marked deviations at ∼1280-1200 cm and at 886 cm profile depth. Whereas the lower excursion is well established by several samples and documented also by detrital haematite, the upper one is only represented by a single sample and revealed by magnetite and greigite. Using the radiocarbon-based age model for the section, the lower excursion yields an age of 42.8–41.3 ka cal BP and is interpreted to represent the Laschamps geomagnetic excursion. The increased abundance of greigite in the upper part of the section, especially in the sample responsible for the upper anomalous direction, renders the interpretation of an actual excursion problematic due to the reducing environment necessary for the greigite formation. [ABSTRACT FROM AUTHOR] more...
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- 2021
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47. The Iceland Palaeomagnetism Database (ICEPMAG)
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Justin A. D. Tonti-Filippini and Maxwell C. Brown
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Palaeomagnetism ,Geomagnetism ,Database ,Iceland ,ICEPMAG ,Geography. Anthropology. Recreation ,Geodesy ,QB275-343 ,Geology ,QE1-996.5 - Abstract
Abstract The extensive lava piles of Iceland contain a unique record of geomagnetic field variations spanning the past ~ 16 Ma. Since the 1950s, palaeomagnetic data have been obtained from over 9400 Icelandic lavas. We have compiled all palaeomagnetic data currently available and developed a publicly accessible database (http://www.icepmag.org). The data within the database are primarily palaeodirections, with a relatively smaller number of palaeointensity data (8936 entries contain direction only, 218 intensity only, and 337 both direction and intensity). In addition, the database contains a wide range of metadata, including geochronological information, site details, and laboratory methods. The search interface of the database allows users to search for data using a range of customisable filters (e.g. by publication, geological age, location, laboratory method, palaeomagnetic statistics) and to quickly visualise and download the matching search results. The data within the database have significant potential for understanding long-term palaeomagnetic field variations at high latitude, the behaviour of excursions and reversals, and geological mapping on Iceland. more...
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- 2019
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48. Improvements to the Shaw-Type Absolute Palaeointensity Method
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Simon J. Lloyd, Greig A. Paterson, Daniele Thallner, and Andrew J. Biggin
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palaeointensity ,palaeomagnetism ,geomagnetism ,thermal remanence ,methodology ,Science - Abstract
Palaeointensity information enables us to define the strength of Earth’s magnetic field over geological time, providing a window into Earth’s deep interior. The difficulties in acquiring reliable measurements are substantial, particularly from older rocks. Two of the most significant causes of experimental failure are laboratory induced alteration of the magnetic remanence carriers and effects relating to multidomain magnetic carriers. One method that has been claimed to overcome both of these problems is the Shaw method. Here we detail and evaluate the method, comparing various selection criteria in a controlled experiment performed on a large, non-ideal dataset of mainly Precambrian rocks. Monte Carlo analyses are used to determine an optimal set of selection criteria; the end result is a new, improved experimental protocol that lends itself very well to the automated Rapid 2G magnetometer system enabling experiments to be carried out expeditiously and with greater accuracy. more...
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- 2021
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49. First palaeointensity data from the cryogenian and their potential implications for inner core nucleation age.
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Lloyd, Simon J, Biggin, Andrew J, Halls, Henry, and Hill, Mimi J
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NUCLEATION , *IGNEOUS provinces , *DIPOLE moments , *DIABASE , *ELECTRIC generators - Abstract
The timing of inner core nucleation is a hugely significant event in Earth's evolution and has been the subject of intense debate. Some of the most recent theoretical estimates for the age of nucleation fall throughout the Neoproterozoic era; much younger than previously thought. A young inner core requires faster recent core cooling rates and a likely hotter early core; knowledge of its age would be invaluable in understanding Earth's thermal history and total energy budget. Predictions generated by numerical dynamo models need to be tested against such data, but records are currently much too sparse to constrain the event to a precise period of time. Here, we present results from 720 Ma dolerite dykes (and one sill) from the Franklin Large Igneous Province, which fall within a crucial 300 Myr gap in palaeointensity records. This study uses three independent techniques on whole rocks from 11 sites spread across High Arctic Canada and Greenland to produce virtual dipole moments ranging from 5 to 20 ZAm2 (mean 11 ZAm2); almost one order of magnitude lower than the present-day field. These weak-field results agree with recent ultralow palaeointensity data obtained from Ediacaran rocks formed ∼150 Myr later and may support that the dynamo was on the brink of collapse in the Neoproterozoic prior to a young inner core formation date. [ABSTRACT FROM AUTHOR] more...
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- 2021
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50. Remagnetization of Jutal dykes in Gilgit area of the Kohistan Island Arc: Perspectives from the India–Asia collision.
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Jadoon, Umar Farooq, Huang, Baochun, Zhao, Qian, Shah, Syed Anjum, and Rahim, Yasin
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ISLAND arcs , *REMANENCE , *MAGNETITE , *DISTRIBUTION (Probability theory) , *PYRRHOTITE , *SCANNING electron microscopy - Abstract
The Kohistan Island Arc (KIA) occupies the northwestern region of the Himalayan Mountains, sandwiched between Asia and India plates. Its formation, collision with plate boundaries, and evolution has been controversially discussed for a couple of decades. To better understand this, a palaeomagnetic study has been conducted on the Jutal dykes (ca. 75 Ma), intruded in the northeastern part of the KIA. Comprehensive rock magnetic investigations reveal that the magnetic carrier minerals are pyrrhotite and magnetite. An intermediate temperature component (ITC) predominates the natural remanent magnetization and shows good coincidence within-site; it is carried by pyrrhotite and is considered reliable, yielding a mean direction at D g/ I g = 11.5°/39.9° (k g = 28.4, α 95 = 3.5°) before and D s/ I s = 8.6°/12.1° (k s = 5.1, α 95 = 9.1°) after tilt correction. A high-temperature component that is carried by magnetite exhibits random distribution within-site. The fold test for the ITC is negative, indicating a post-folding origin. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy indicates that the magnetic carrier minerals were influenced by metamorphism or thermochemical fluids. The comparison of mean palaeolatitude (22.6 ± 3.5°N) of the ITC with the collisional settings and thermal history of the study area implies that the remagnetization occurred at ∼50–35 Ma, consistent with the previous reported palaeomagnetic data of the KIA. We propose a tectonic model that shows the evolution of the Jutal dykes, supporting the concept that India collided with the KIA first, followed by a later collision with Asia. [ABSTRACT FROM AUTHOR] more...
- Published
- 2021
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