A global apparent polar wander path for the last 320 Ma calculated from site-level paleomagnetic data

Apparent polar wander paths (APWPs) calculated from paleomagnetic data describe the motion of tectonic plates relative to the Earth's rotation axis through geological time, providing a quantitative paleogeographic framework for studying the evolution of Earth's interior, surface, and atmosphere. Previous APWPs were typically calculated from collections of paleomagnetic poles, with each pole computed from collections of paleomagnetic sites, and each site representing a spot reading of the paleomagnetic field. It was recently shown that the choice of how sites are distributed over poles strongly determines the confidence region around APWPs and possibly the APWP itself, and that the number of paleomagnetic data used to compute a single paleomagnetic pole varies widely and is essentially arbitrary. Here, we use a recently proposed method to overcome this problem and provide a new global APWP for the last 320 million years that is calculated from simulated site-level paleomagnetic data instead of from paleopoles, in which spatial and temporal uncertainties of the original datasets are incorporated. We provide an updated global paleomagnetic database scrutinized against quantitative, stringent quality criteria, and use an updated global plate motion model. The new global APWP follows the same trend as the most recent pole-based APWP but has smaller uncertainties. This demonstrates that the first-order geometry of the global APWP is robust and reproducible. Moreover, we find that previously identified peaks in APW rate disappear when calculating the APWP from site-level data and correcting for a temporal bias in the underlying data. Finally, we show that a higher-resolution global APWP frame may be determined for time intervals with high data density, but that this is not yet feasible for the entire 320–0 Ma time span. Calculating polar wander from site-level data provides opportunities to significantly improve the quality and resolution of the global APWP by collecting large and well-dated paleomagnetic datasets from stable plate interiors, which may contribute to solving detailed Earth scientific problems that rely on a paleomagnetic reference frame

Rotations of Normal Fault Blocks Quantify Extension in the Central Tauride Intramontane Basins, SW Turkey

Quantifying the amount of stretching in extensional basin systems is often challenging in the absence of seismic profiles or boreholes. However, when fault spacing and orientation as well as vertical axis rotation patterns are known, map-view restoration may provide a good estimate of total extension. This integrated structural and paleomagnetic approach provides a relatively straightforward tool in extensional basin restoration and fault zone kinematic analysis. Here we provide results of an extensive paleomagnetic survey of the Neogene Central Tauride intramontane basins (SW Turkey), where previous work revealed a complex array of basin-bounding normal faults and relay ramps. In total, 437 oriented cores were sampled at 43 sites distributed within Miocene-Pliocene continental sedimentary rocks from the Ilgın, Altınapa, Yalvaç, and Beyşehir basins. Despite the more or less coherent overall strike of the mountain belt and basins, rotations vary from ~42° clockwise (Yalvaç) to ~10° (Beyşehir), ~21° (Ilgın), and ~30° (Altınapa) counterclockwise. We show that the rotation pattern is related to normal faults and lateral variations in fault displacement superimposed on regional rotation patterns. We restore these to estimate a minimum NE-SW horizontal extension of ~30–35 km across the basin system. As a consequence of our reconstruction, it appears that the Sultandağları range that exposes low-grade metamorphic Paleozoic and Mesozoic rocks of the Geyikdağı and Bolkardağ nappes of the Taurides represents a Miocene extensional core complex

Rotations of Normal Fault Blocks Quantify Extension in the Central Tauride Intramontane Basins, SW Turkey

Quantifying the amount of stretching in extensional basin systems is often challenging in the absence of seismic profiles or boreholes. However, when fault spacing and orientation as well as vertical axis rotation patterns are known, map-view restoration may provide a good estimate of total extension. This integrated structural and paleomagnetic approach provides a relatively straightforward tool in extensional basin restoration and fault zone kinematic analysis. Here we provide results of an extensive paleomagnetic survey of the Neogene Central Tauride intramontane basins (SW Turkey), where previous work revealed a complex array of basin-bounding normal faults and relay ramps. In total, 437 oriented cores were sampled at 43 sites distributed within Miocene-Pliocene continental sedimentary rocks from the Ilgın, Altınapa, Yalvaç, and Beyşehir basins. Despite the more or less coherent overall strike of the mountain belt and basins, rotations vary from ~42° clockwise (Yalvaç) to ~10° (Beyşehir), ~21° (Ilgın), and ~30° (Altınapa) counterclockwise. We show that the rotation pattern is related to normal faults and lateral variations in fault displacement superimposed on regional rotation patterns. We restore these to estimate a minimum NE-SW horizontal extension of ~30–35 km across the basin system. As a consequence of our reconstruction, it appears that the Sultandağları range that exposes low-grade metamorphic Paleozoic and Mesozoic rocks of the Geyikdağı and Bolkardağ nappes of the Taurides represents a Miocene extensional core complex

Reliability of palaeomagnetic poles from sedimentary rocks

Palaeomagnetic poles form the building blocks of apparent polar wander paths and are used as primary input for quantitative palaeogeographic reconstructions. The calculation of such poles requires that the short-term, palaeosecular variation (PSV) of the geomagnetic field is adequately sampled and averaged by a palaeomagnetic data set. Assessing to what extent PSV is recorded is relatively straightforward for rocks that are known to provide spot readings of the geomagnetic field, such as lavas. But it is unknown whether and when palaeomagnetic directions derived from sedimentary rocks represent spot readings of the geomagnetic field and sediments are moreover suffering from inclination shallowing, making it challenging to assess the reliability of poles derived from these rocks. Here, we explore whether a widely used technique to correct for inclination shallowing, known as the elongation–inclination (E/I) method, allows us to formulate a set of quality criteria for (inclination shallowing-corrected) palaeomagnetic poles from sedimentary rocks. The E/I method explicitly assumes that a sediment-derived data set provides, besides flattening, an accurate representation of PSV. We evaluate the effect of perceived pitfalls for this assumption using a recently published data set of 1275 individual palaeomagnetic directions of a >3-km-thick succession of ∼69–41.5 Ma red beds from the Gonjo Basin (eastern Tibet), as well as synthetic data generated with the TK03.GAD field model. The inclinations derived from the uncorrected data set are significantly lower than previous estimates for the basin, obtained using coeval lavas, by correcting inclination shallowing using anisotropy-based techniques, and by predictions from tectonic reconstructions. We find that the E/I correction successfully restores the inclination to values predicted by these independent data sets if the following conditions are met: the number of directions N is at least 100, the A95 cone of confidence falls within a previously defined A95min-max reliability envelope, no negative reversal test is obtained and vertical-axis rotation differences within the data set do not exceed 15°. We propose a classification of three levels (A, B and C) that should be applied after commonly applied quality criteria for palaeomagnetic poles are met. For poles with classification ‘A’, we find no reasons to assume insufficient quality for tectonic interpretation. Poles with classification ‘B’ could be useful, but have to be carefully assessed, and poles with classification ‘C’ provide unreliable palaeolatitudes. We show that application of these criteria for data sets of other sedimentary rock types classifies data sets whose reliability is independently confirmed as ‘A’ or ‘B’, and that demonstrably unreliable data sets are classified as ‘C’, confirming that our criteria are useful, and conservative. The implication of our analysis is that sediment-based data sets of quality ‘A’ may be considered statistically equivalent to data sets of site-mean directions from rapidly cooled igneous rocks like lavas and provide high-quality palaeomagnetic poles

Reliability of palaeomagnetic poles from sedimentary rocks

Palaeomagnetic poles form the building blocks of apparent polar wander paths and are used as primary input for quantitative palaeogeographic reconstructions. The calculation of such poles requires that the short-term, palaeosecular variation (PSV) of the geomagnetic field is adequately sampled and averaged by a palaeomagnetic data set. Assessing to what extent PSV is recorded is relatively straightforward for rocks that are known to provide spot readings of the geomagnetic field, such as lavas. But it is unknown whether and when palaeomagnetic directions derived from sedimentary rocks represent spot readings of the geomagnetic field and sediments are moreover suffering from inclination shallowing, making it challenging to assess the reliability of poles derived from these rocks. Here, we explore whether a widely used technique to correct for inclination shallowing, known as the elongation–inclination (E/I) method, allows us to formulate a set of quality criteria for (inclination shallowing-corrected) palaeomagnetic poles from sedimentary rocks. The E/I method explicitly assumes that a sediment-derived data set provides, besides flattening, an accurate representation of PSV. We evaluate the effect of perceived pitfalls for this assumption using a recently published data set of 1275 individual palaeomagnetic directions of a >3-km-thick succession of ∼69–41.5 Ma red beds from the Gonjo Basin (eastern Tibet), as well as synthetic data generated with the TK03.GAD field model. The inclinations derived from the uncorrected data set are significantly lower than previous estimates for the basin, obtained using coeval lavas, by correcting inclination shallowing using anisotropy-based techniques, and by predictions from tectonic reconstructions. We find that the E/I correction successfully restores the inclination to values predicted by these independent data sets if the following conditions are met: the number of directions N is at least 100, the A95 cone of confidence falls within a previously defined A95min-max reliability envelope, no negative reversal test is obtained and vertical-axis rotation differences within the data set do not exceed 15°. We propose a classification of three levels (A, B and C) that should be applied after commonly applied quality criteria for palaeomagnetic poles are met. For poles with classification ‘A’, we find no reasons to assume insufficient quality for tectonic interpretation. Poles with classification ‘B’ could be useful, but have to be carefully assessed, and poles with classification ‘C’ provide unreliable palaeolatitudes. We show that application of these criteria for data sets of other sedimentary rock types classifies data sets whose reliability is independently confirmed as ‘A’ or ‘B’, and that demonstrably unreliable data sets are classified as ‘C’, confirming that our criteria are useful, and conservative. The implication of our analysis is that sediment-based data sets of quality ‘A’ may be considered statistically equivalent to data sets of site-mean directions from rapidly cooled igneous rocks like lavas and provide high-quality palaeomagnetic poles

Discovery of Holocene millennial climate cycles in the Asian continental interior: Has the sun been governing the continental climate?

We conducted a high-resolution study of a unique Holocene sequence of wind-blown sediments and buried soils in Southern Siberia, far from marine environment influences. This was accomplished in order to assess the difference between North Atlantic marine and in-land climate variations. Relative wind strength was determined by grain size analyses of different stratigraphic units. Petromagnetic measurements were performed to provide a proxy for the relative extent of pedogenesis. An age model for the sections was built using the radiocarbon dating method. The windy periods are associated with the absence of soil formation and relatively low values of frequency dependence of magnetic susceptibility (FD), which appeared to be a valuable quantitative marker of pedogenic activity. These events correspond to colder intervals which registered reduced solar modulation and sun spot number. Events, where wind strength was lower, are characterized by soil formation with high FD values. Spectral analysis of our results demonstrates periodic changes of 1500, 1000 and 500 years of relatively warm and cold intervals during the Holocene of Siberia. We presume that the 1000 and 500 year climatic cycles are driven by increased solar insolation reaching the Earth surface and amplified by other still controversial mechanisms. The 1500 year cycle associated with the North Atlantic circulation appears only in the Late Holocene. Three time periods — 8400–9300 years BP, 3600–5100 years BP, and the last ~ 250 years BP — correspond to both the highest sun spot number and the most developed soil horizons in the studied sections

Putative greigite magnetofossils from the Pliocene epoch

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