Volume 6 - 2018 | https://doi.org/10.3389/feart.2018.00182 Paleomagnetism of South American Jurassic/Cretaceous rocks has been troubled by elongated distributions of poles which has led to contrasting interpretations many discordant paleomagnetic poles from the Carboniferous to the Triassic have also been recognized and systematically explained by a variety of processes but this portion of the South American apparent polar wonder path (APWP) still remains problematic we have conducted a paleomagnetic study of the sedimentary Permo-Carboniferous Itararé Group rocks and three intruding mafic sills of likely Cretaceous age within the state of São Paulo The site-mean VGP distributions obtained from the sedimentary rocks define elongations that include the VGPs of the mafic intrusions We interpret these distributions as remagnetization paths toward the directions characteristic of the sills we show that the remanence directions of the sills are partially overprinted by the present time-averaged and current Earth's magnetic field Our interpretations are supported by extensive rock-magnetic data that provides a viable mechanism for the secondary magnetizations The current study focuses on the paleomagnetism and rock-magnetism of the mafic intrusions and how they affected the paleomagnetic recording of the sedimentary rocks careful analysis of the paleomagnetic data of the Itararé sedimentary rocks enables isolation of a primary VGP distribution that is consistent with the reference Carboniferous pole position Extending our study to other Carboniferous to Triassic South American paleomagnetic records reveals that the majority of these data are elongated similarly to the Itararé Group rocks the elongations systematically intersect at the location of the Late Cretaceous reference pole and at a long- recognized “problematic” location observed in some Jurassic and Cretaceous rock formations we interpret the elongations to reflect remagnetizations from the primary VGP positions toward Jurassic-Cretaceous pole locations that occurred as a result of the widespread magmatic events associated with the opening of the South Atlantic We suggest that the extent of the remagnetizations is formation-specific and that other rock-formations should be carefully re-evaluated As of today no convincing argument has been put forward to justify such widespread observations they demonstrated that inclination corrections of South American paleopoles had the potential of eliminating the continental overlap and determine that in this region the igneous activity lasted from 133 to 130 Ma confirming the Early Cretaceous age for the magmatism in the area also sampled in the present study) and Santa Catarina (Rio do Sul) While for the Rio do Sul rhythmites they claimed to have isolated a primary Permo-Carboniferous magnetization for the Itu quarry rhythmites a strongly elongated distribution was obtained which the authors vaguely dismissed as anomalous The current study thus focuses on the paleomagnetic and rock-magnetic results of the igneous rocks and how these likely affected the paleomagnetic recording of the sedimentary rocks A more detailed rock-magnetic study of the sedimentary rocks will be the topic of a dedicated article A comparison to paleomagnetic results from other South American rock formations indicates that the discordant results are related consequently challenging the validity of many paleopoles from South America and bearing important implications for the continent's APWP at large The Campo Mourão and Taciba formations instead comprise fining-upward cycles composed of subglacial tillites overlain by resedimented diamictites or conglomerates and sandstones In the northern part of the Paraná Basin the Itararé Group strata are red in color and are referred to as the Aquidauana Formation. However, subsurface data suggest that the two are equivalent (Milani et al., 1994, 1998). The correlation between outcrops and subsurface sections is not fully established (Rocha-Campos et al., 2008) Because of these reasons and the lack of a formal stratigraphy paleomagnetic investigations of the Itararé Group in the State of Sao Paulo are particularly challenging No magnetic stratigraphy exists for the Itararé Group within the northern Paraná Basin mean paleomagnetic directions and VGPs isolated from each sampling site: N and k are number of specimens and precision parameter respectively; a95 and A95 are the 95% confidence circles for the directions and VGPs respectively; for the sedimentary rocks it is also specified whether they are included in the NS or both distributions for the great circle analysis Study area: (A) location of the study area within the Paraná Basin; (B) Site locations and outcropping geological formations within the state of Sao Paulo Note that three sites of the Itararé Group rocks (II12 and II19) were collected in the neighboring state of Minas Gerais All sampled strata are flat-lying except for site IT5 which displays complex folding resulting from slumping who determined an Early Cretaceous age (133–130 Ma) and refer to these as the Northern Paraná Basin (NPB) igneous intrusions and flows In our study we refer to these results for comparison Rock cores were drilled using a gasoline powered portable drill and oriented using a Pomeroy orienting fixture Whenever possible both magnetic and sun-compass readings were taken to orient the cores Most cores were large enough for ~3–4 standard-sized (2.5 × 2.2 cm) cylinders to be cut yet for the more sandy lithologies shorter Rock-magnetic and paleomagnetic measurements were initiated at the Instituto de Geociencias Brazil (IGc-USP) and continued at the Institute for Rock Magnetism Specimens from sites IT-1 through IT-5 and the three igneous sites were measured at the IGc-USP Magnetic moments were measured on an AGICO (Brno Czech Republic) JR-6a spinning magnetometer in conjunction with thermal demagnetization conducted on an TD-48 ASC Scientific (Carlsbad or in conjunction with alternating field (AF) demagnetization conducted on a Molspin (Oxon Magnetization results are volume-normalized and reported in units of A/m Magnetic remanence and frequency dependent susceptibility were also measured as a function of temperature on Quantum Design (San Diego USA) Magnetic Properties Measurement Systems (MPMSs) to evaluate magnetic mineralogy and grain size Experiments included measuring magnetic remanence upon heating from 10 K to room temperature after cooling in a 2.5 T field (field cooled remanence and after cooling in zero field but applying a saturation isothermal remanent magnetization (SIRM) of 2.5 T at 10 K (zero-field cooled remanence A room temperature (RT) 2.5 T SIRM was also applied and the remanence measured upon cooling to 10 K and warming back to room temperature (RTSIRM) AC susceptibility as a function of temperature and frequency was also measured on the MPMS on specimens from the three mafic sills Paleomagnetic directions obtained from this study are compared to the present day geomagnetic field direction determined using the Magnetic Field Calculator available at the NOAA website https://www.ngdc.noaa.gov/geomag/magfield.shtml The present-day field (at the time the sampling was conducted) obtained for São Paulo The time-averaged dipole field direction calculated for the study area is oriented 360 whereas the critical value of V (Vcrit) is 7.5 while for the sill at IT14 V is 63.4 and Vcrit is 6.7 In both cases the two components can be statistically considered distinct Zijderveld diagrams for selected specimens from the mafic sills: (A,D,G) intermediate temperature component of magnetization typically isolated between 400 and 525°C; (B,E,H) high temperature component isolated in the same specimens as in (A,D,G) typically between 525 and 600°C; (C,F,I) AF demagnetization revealing one component of magnetization only Site IT15 shows linear demagnetization behavior and in certain specimens two components can be isolated. The first component is isolated between ~100 and 300°C (Figure 2G), and has an orientation of opposite polarity to the Earth's magnetic field (Figure 2B). The high temperature component direction at site IT15 is isolated between ~300 and 580–600°C (Figure 2H) when performing Watson's V test to determine whether the two distributions share a common mean indicating that the two directions are statistically indistinguishable We can therefore disregard the lower temperature component for this sill On a stereonet, the intermediate temperature magnetization component directions of IT9 and IT14 are indistinguishable from the present-day field direction. In particular the individual directions of IT9 are somewhat elongated between the present-day field direction and the time averaged field (Figure 3A), however the mean directions are indistinguishable from that of the present field (Figure 3B) Directions isolated from the mafic sills: (A) intermediate temperature component directions isolated from sills at IT9 (red) and IT14 (blue) the present-day field direction (PF) and the time-averaged dipole field (DF) are the black square and diamond open (closed) symbols are for upper (lower) hemisphere projections respectively; (B) site-mean directions for the intermediate temperature-component magnetizations symbols as in (A); (C) high-temperature component directions isolated from the mafic sills site IT15 (purple); (D) site-mean directions for the high temperature-component magnetizations The demagnetization patterns of the sills are consistent with the directional changes observed (Figures 4A,B). Thermal demagnetization of specimens from sites IT9 and IT14, possess a first decrease in NRM around 350–400°C (Figure 4A) Above this temperature the first stable direction coincident with the present day magnetic field the high temperature component is isolated up to ~580°C (magnetite's Curie temperature) at which point the specimens are completely demagnetized (A) Thermal demagnetization of the NRM of the mafic sills respectively; vertical dashed lines indicate the temperature ranges at which the intermediate and high temperature components were isolated; (B) AF demagnetization of the mafic sills colors as in (A); the mean median destructive fields are reported with 1 standard deviation error bars Specimens from site IT15 instead show a rather monotonic decrease in magnetization with temperature and only one specimen shows a break in slope at 300°C. Specimens from this site are also completely demagnetized by ~580°C, but the one specimen with the 300°C inflection point still carries 3.5% of the total remanence by 600°C (Figure 4A) The RTSIRM curves are similar to those from the previous site The sill at site IT15 has ZFC remanence curve higher than the FC curve Cooling of the RTSIRM has a monotonic decrease until the TV and upon heating only 31% of the remanence is recovered Susceptibility curves measured while heating to 650°C and cooling back to room temperature show a prominent drop of susceptibility at 570°C (IT9), 560°C(IT14), 555°C (IT15), which is consistent with the Curie temperature of magnetite, possibly lowered by some Ti-substitution (Supplementary Figures 5A,C,D) Specimens from IT9 and IT14 also show an increase and decrease of susceptibility near ~150–300°C Cooling curves reveal lowered Curie temperatures with respect to the heating curves and the appearance of a second Curie temperature possibly as a result of exsolution during heating The prominent peaks of IT9 and IT14 below the Curie temperatures are broadened and shifted to lower temperatures IT15 does not show such a pronounced behavior but instead possesses a constant increase of susceptibility with temperature until the Curie point is reached Room temperature hysteresis loops of representative specimens reveal higher coercivities for IT9 and IT14, than IT15 (Supplementary Figure 6), but heightened magnetization for the latter. The inverse relationship of remanent and in-field magnetizations (cf. Supplementary Figures 3, 6) is consistent with overall increasing grain size from IT9 and 14 to IT15 Unmixing of backfield demagnetization and IRM acquisition curves acquired on a VSM (Figure 5) demonstrate that while the dominant coercivities for IT9 and IT14 are centered ~60 mT lower coercivity distributions are also present The coercivity distributions are shifted toward lower coercivities for the backfield curves and toward higher coercivities for IRM acquisition Curves for IT15 also possess two coercivity distributions but centered at lower fields ~5 and 15 mT IT15 also demagnetizes more easily (lower fields) than it magnetizes Unmixing of backfield DC demagnetization and IRM acquisition curves: (A,B) specimen from sill at IT9; (C,D) specimen from sill at IT14; (E,F) specimen from sill at IT15 Note how the coercivity distributions are systematically revealed at lower fields during demagnetization than acquisition Results show a very similar FORC distribution to that obtained at room temperature yet somewhat shifted toward lower values of BC An initial pilot study of the Itararé Group sedimentary rocks was conducted by performing both thermal and AF demagnetization experiments on select specimens from each site collected Both techniques isolated the same components of magnetization whenever possible AF demagnetization was preferred because of its rapidity AF demagnetization was unable to fully demagnetize the remanence and therefore the specimens were subject to subsequent thermal treatment The red sedimentary rocks and other sites with a pink coloration were thermally demagnetized directly under the assumption that the characteristic remanent magnetization (ChRM) resided in hematite The sedimentary rock specimens of the Itararé Group typically have weak NRM intensity between 10−5 and 10−7 Am2/kg despite an overall broad range of magnetization intensities (10−3–10−8 Am2/kg) II14A1) and is well-defined up to ~100 mT though not always fully demagnetizing (e.g. Different styles of demagnetization can be observed within the same site and maintain consistent directions of magnetization indicating that the sedimentary rocks are heterogeneous in terms of the grain size (e.g. It is noteworthy that the ChRM of the competent claystones is consistently isolated in the ~20–80 mT AF range (e.g. Orthogonal alternating field demagnetization diagrams of representative specimens from the sedimentary rocks of the Itararé Group Solid (open) symbols represent projections on the horizontal (vertical) plane; red symbols are the demagnetization steps used for principal component analysis (PCA); blue lines are the PCA line-fits Thermal demagnetization behavior also varies by site and specimen The ChRM is isolated in variable laboratory unblocking temperature ranges similarly to the results of the AF demagnetization experiments confirming the heterogeneity of magnetic grain-sizes and thus coercivity spectra which is responsible for the variable laboratory unblocking temperatures The gray and tan rhythmites (e.g., IT2C1, II20A2), brown diamictites (e.g., II10A1), yellow sandstones (e.g., II11D3) and the red (sometimes silty) mudstones (e.g., II13A1, II19E1) possess remanences that are not fully unblocked until ~675–680°C, indicating higher coercivity hematite as the ChRM carrier (Figure 7) Orthogonal thermal demagnetization diagrams of representative specimens from the sedimentary rocks of the Itararé Group indicating that both magnetite and hematite carry the same component of magnetization In other sites that are also not red in color II10) the stable ChRM direction is only isolated through thermal demagnetization starting at laboratory unblocking temperatures higher than ~500°C and is fully unblocked by 675–685°C Specimens from site II18 lost over 90% of the remanence by 600°C and the ChRM was isolated between ~350 and 600°C (e.g. thus the ChRM of site II18 is interpreted to reside in magnetite The red coloration of the sediments from II18 is due to hematite pigment but the hematite is not an important remanence carrier The dominant groups of site-mean directions are oriented north and upward or southeast and downward ChRM directions isolated from certain sites (II4 and II9) define multiple and distinct groups of directions Site-mean directions of the Itararé Group rocks plotted on a stereonet: solid (open) symbols are projections on the lower (upper) hemisphere; black and red symbols are for sedimentary and igneous rocks Because the intermediate temperature component is identical to the present-day field direction for the study area at the time the field work was performed this VGP provides a useful reference for the discussion presented below The VGPs calculated from the igneous rocks confirm the results obtained by Ernesto et al. (1999), who calculated VPGs from paleomagnetic data derived from dykes, sills, and lava flows, that follow an elongated distribution that includes the VGPs from the three sills collected in this study. For a direct comparison we have plotted the results of Ernesto et al. (1999) in Figure 9B Note that each VGP is calculated from an individual igneous unit (sill dyke or flow) with a mean sample number of ~8 therefore these are comparable to the VGPs calculated in our study Table 2. South paleopoles, as reported in the literature, utilized in this study and separated by age: Identifiers correspond to the labels used in Figure 9; Ages are reported in Ma; degrees latitude degrees longitude; A95 is 95% circle of confidence around the mean of the VGPs; *A95 was recalculated because not reported in the original study [either the α95 (La Tabla or the csd (Piaui) of the directions were reported] The site-mean VGPs calculated for the sedimentary rocks are plotted in Figure 9C together with the VGPs calculated for the mafic sills. All VGPs appear to form elongated distributions, highlighted in Figure 9C. Arguably, such distribution of VGPs are not Fisherian and should not be averaged using Fisher (1953) statistics to calculate a mean paleopole that the VGPs of many sedimentary rocks cluster around those of the igneous sills Low temperature remanence measurements of the three mafic sills that intrude the Itararé Group reveal SD-PSD behavior for the sill at IT9 and somewhat larger grains for the sill at IT14, whereas the remanence of the sill at IT15 indicates MD grains (FC-ZFC curves in Supplementary Figure 3) High temperature susceptibility experiments (Supplementary Figure 5) indicate oxidized maghemite rims on magnetite grains for sills IT9 and IT14, and one dominant magnetite grain size for IT15 (Supplementary Figure 5) Room and 400°C temperature FORC diagrams (Supplementary Figure 7) show interacting SD distributions for the sills at IT9 and IT14 and dominant MD distributions for IT15 with relatively narrow unblocking temperature ranges suggest that these particles carry the same remanent component as the larger grains a common event responsible for the growth of the SD particle would have likely resulted in a magnetic overprint of the softer MD (and possibly PSD) particles These larger grains are of likely primary origin and formed during slow cooling of the intrusions however their magnetization is probably secondary yet these particles retain high unblocking temperatures for the particularly high unblocking temperatures observed in their study a low temperature thermoviscous magnetization alone would likely not be sufficient to explain the data They propose a combination of thermoviscous magnetization and superimposed chemical weathering as responsible for the observed unblocking temperatures This model agrees with the presence of interacting SD and MD grains within the mafic sills that intrude the Itararé Group that both carry the same remanence components These interpretations are also consistent with the paleomagnetic analysis presented below These observations suggest that the larger PSD-MD grains are the dominant remanence carriers for these sills It follows that the directions isolated must either be an ancient magnetization mostly residing in larger PSD- MD particles that is coincidentally close to the time-averaged field directions or a recent overprint recorded by the same grains which protracted over enough time to capture the time-averaged field the elongation attests to very recent overprints toward the present-day field that cannot be fully removed by either thermal or AF treatment and likely resides in the high-coercivity interacting SD grains the harder SD grains carry a very recent magnetic overprint that is visco-chemical in origin and cannot be fully erased whereas the dominant distribution of PSD-MD grains carries the high-temperature component which is either a primary magnetization coincidentally close to the time-averaged dipole field direction or a secondary thermo-viscous remagnetization Determining the magnetic carrier of the components isolated in the sill at IT15 using both AF and thermal demagnetization is more straightforward as indicated by all rock-magnetic measurements performed and more specifically in two overlapping grain size distributions The magnetization isolated here is distinct and has opposite polarity to that of the other sills This magnetization also resides in MD magnetite it does not appear to be overprinted by the present-day field It must therefore represent a stable primary direction or an ancient overprint that is resistant to laboratory cleaning in which case it would likely be a thermo-viscous remagnetization The sills likely intruded the Carboniferous sedimentary sequence during the post-Jurassic extensional events that are responsible for the widespread magmatism in the Paraná/Chaco-Paraná basins. The three sills collected in this study crop out proximally to some igneous rocks reported on by Ernesto et al. (1999) and are surrounded by other outcrops on all sides the VGPs derived from these units follow the same distribution that approximately follows the 30 and 210° E meridians It is therefore reasonable to assume that these rocks are related providing a precise age constraint (133–130 Ma) for these intrusions It was previously determined that the directions isolated from the three sills have been overprinted by the present-day magnetic field. The elongation of the VGPs derived from the sills, dykes and flows sampled in our and Ernesto et al.'s (1999) studies may therefore be a consequence of either incomplete removal of the remagnetization component or an anomalous geomagnetic field behavior during the Cretaceous Discriminating between the two possibilities would be speculative because both datasets are derived from dual-polarity data we prefer to interpret these magnetizations as primary but with incomplete removal of the present-day field overprint in some sites The VGPs of the Itararé Group sedimentary rocks appear to define distinct trends A first trend follows the distribution of the VGPs from the three mafic sills and is defined by the cluster of many VGPs around them, and is highlighted with a dashed line in Figure 9C. It is reasonable to assume that these sedimentary rocks were remagnetized by the intrusive rocks, and this distributions is further explained by comparison with the VGPs obtained from igneous rocks by Ernesto et al. (1999) (Figure 9B) It is apparent that many VGPs obtained from Permo-Carboniferous sedimentary rocks are distributed along the same elongated trend of the Early Cretaceous igneous rocks providing solid evidence for remagnetization of these rocks Two other trends are highlighted in Figure 9C and also include the VGPs obtained from the three mafic sills One distribution (denoted E-W) extends from the VGP of site II8 into the opposite hemisphere toward II4su These VGPs appear to “pin” the distribution eliminating them from the analysis results in a great circle-fit with similar orientation (strike 164.8° The similarity of the fits suggests that the elongation is a real feature and the high scatter of certain VGPs is an effect of remagnetizations possibly associated with other unrecognized igneous bodies or migration of fluids associated with the magmatic events Interestingly, if one disregards the VGPs east of the intersection of the distributions (i.e., VGPs II4su, II4nd, II5nd, II6su, II9nd) under the assumption that these represent spurious magnetizations and/or based of their higher scatter, then the remaining VGPs define a loop that is remarkably similar to the classic South American APWP (e.g., Tomezzoli et al., 2013, highlighted in yellow in Figure 9D) Such high velocity is in stark contrast with the average 1–8 cm year plate motion based on current sea floor spreading rates and assumed to have been valid through geologic history and implicitly the Pangea B reconstruction are unrealistic under multiple lines of evidence warranting an in-depth investigation of the remagnetization and data quality postulations intermediate and minimum principal components (τ1 respectively) of the VGP great-circle fits and calculated shape (g) and strength (z) parameters We analyzed the elongation of the distributions of South VGP from each rock Formation and their mean intersections. Similarly to the analysis of remagnetization circles (McFadden and McElhinny, 1988) it is assumed that if the magnetizations are primary the elongations of VGPs intersect at the mean paleopole position for the corresponding age of the magnetizations the great circles intersect at a position consistent with the pole for the time of the secondary magnetization For the purpose of determining whether Carboniferous including the Itararé Group sedimentary rocks have been remagnetized by a common Jurassic/Cretaceous event rock formations of these ages are analyzed together The mafic sills that intrude the Itararé Group in the Early Cretaceous are analyzed with the Late Jurassic/Early Cretaceous formations The expectation is that if the magnetizations are primary the formations would intersect at distinct positions according to their ages Stereonet projections of great circle-fits through the VGPs of the rock formations studied The South pole is in the center and the prime meridian is vertical through the plots light blue and green data are for Carboniferous (and intruding sills) Intersections of great circles and bootstrap 95% confidence ellipses are black symbols (A) “Late Cretaceous” distribution; (B) “X” distribution; (C) “JK-Sills” distribution The Carboniferous through Triassic formations define two distinct groups with intersections in the NW and NE quadrants of a stereonet (upper hemisphere), irrespective of the age of the rocks (Figures 10A,B The intersection of the first group (Lat −71.7° Long 337.8°; confidence ellipse: Lat range −79.2 to −63.5°; Long range 318.6–347.3°) coincides with the mean Late Cretaceous reference pole will be referred to as “Late K.” The second group has a mean intersection that does not coincide to any Cretaceous reference pole and is referred to as “X” (Lat −75.5° Long 44.5°; confidence ellipse: Lat range −79.4 to −71.4°; Long range 25.9–66.7°) We note that three Permian and one Triassic rock formations have distributions that fit equally well the “Late K” and the “X” groups It is perfectly acceptable for a rock to record multiple magnetizations and therefore have a distribution of VGPs that is elongated between the two latest magnetizations the two intersection positions are located 18.1° apart and therefore it is not unreasonable that certain formations will have distributions of VGPs that are close to both intersections the distribution of the Tepuel Formation has a different orientation from the other formations and its τ3 does not fit a common great circle In virtue of this it has not been included in the two groups and possibly represents a primary and distinct magnetization It follows that magnetizations “JK-Sills” (indistinguishable from magnetization “X”) is either somewhat overprinted by the present-day field direction or is a primary Late Jurassic/Early Cretaceous magnetization and its elongation reflects the geomagnetic field behavior and coincidentally overlaps with the present-day field direction Figure 11. Woodcock (1977) diagram Shape and strength of the VGP distributions plotted as ln (τ1/τ3) vs Additionally, for each Fm. we have also calculated the angular VGP scatter (S) (e.g., McFadden et al., 1988) of all VGPs, and after applying a variable cut-off angle (SV, Vandamme, 1994). These values are reported in Table 3 We note that the variable cut-off angle only makes a difference to eight of the VGP distributions we point out that to fully evaluate the shape and strengths of the distributions cut-off angles should not be applied as these will inevitably modify the shape parameters and outliers should be removed based on the paleomagnetist's experience It is apparent that the majority of the data analyzed in this study do not fit either the PCRS or CNS models, suggesting that the scatter of these data may be the result of unremoved secondary magnetizations, which increased the elongation and/or the strength of the distributions (see Figure 11) we must stress that while a large (or too small) S value may be an indication of remagnetization in general S cannot be used as a tool alone to identify remagnetizations the observations that the data used in this study are highly elongated and/or possess strong distributions the observation that the VGP distributions have common intersections regardless of the rock ages together with the observation that the VGP scatter generally does not agree with global models of VGP scatter for similar aged-rocks make a valid case for widespread remagnetizations in South America That task is beyond the scope of this study We do realize that the possible mechanism for remagnetization suggested here for the igneous rocks, thermo-viscous remagnetization of larger PSD-MD grains, may not appear convincing to many, partly due to the still relatively poor understanding of MD grains. However, the evidence compiled for Jurassic/Cretaceous remagnetizations of older rocks appears overwhelming. Very similarly, Veselevskiy et al. (2016) reported convincing evidence for widespread Early Jurassic remagnetizations in Fennoscandia that affected 500 Ma to ~2 Ga rocks with significant consequences for the APWP of Baltica The authors of that study were not able to provide convincing petrographic or magnetic evidence or mechanisms for the remagnetizations and speculate that migration of low-temperature fluids resulted in chemical remagnetization may help better constrain the magnetization history of this Fm The Hoyada Verde Fm VGPs show the most pronounced elongation and VGP scatter of all the studied formations suggesting that these VGPs may likely have been dragged toward a younger paleopole position and away from the expected Carboniferous pole position We have conducted a detailed paleo and rock-magnetic investigation of the Permo-Carboniferous Itararé Group sedimentary rocks and three intruding mafic sills that were encountered during field work Paleomagnetic analysis revealed that many of the sedimentary rock sites have paleomagnetic directions that are grouped around those of the intrusive rocks from our and published studies which have been precisely dated as Early Cretaceous The intrusive rocks instead have stable magnetization directions that do not agree with the Cretaceous reference poles but such discordant directions are also encountered in other South American Late Jurassic/Early Cretaceous rocks and have been deemed “problematic” by previous workers the intrusive rocks have magnetic overprints that are stable up to high temperatures that record the present-day field direction A detailed rock-magnetic investigation of the remanence-carrying minerals of the intrusive rocks reveals that the present-day overprint is carried by interacting SD magnetite particles The more stable component is instead carried by a population of PSD-MD magnetite grains A great circle analysis performed on VGPs from Carboniferous through Triassic rocks as well as the “problematic” Late Jurassic/Early Cretaceous rocks from South America clearly reveals two common intersecting positions one corresponding to the Late Cretaceous and one of a different age This observation suggests that all Carboniferous to Triassic rocks have been somewhat overprinted by either a Late Cretaceous magnetization and/or a different magnetization likely associated with a short lived geomagnetic field behavior during the Late Jurassic/Early Cretaceous and possibly overprinted by the present-day magnetic field The cause of the secondary magnetizations resides with the well-documented extensional processes that affected South America during the opening of the South Atlantic and responsible for the widespread magmatism that occurred at that time We note that many of the South American paleopoles are inconsistent with the classic Pangea A reconstruction We have calculated a displacement rate of ~18 cm/yr from the currently-accepted APWP for South America highlighting how this is unrealistic from a plate motion standpoint These lines of evidence provide further support for widespread remagnetizations The extent of the remagnetizations is formation-specific but a careful evaluation of the Itararé Group sedimentary rocks allows discriminating sites that are likely unaffected that enabled calculating a reliable paleomagnetic pole this paleomagnetic pole was corrected for inclination shallowing Details of the paleomagnetism of the Itararé sedimentary rocks and inclination correction will be presented in a separate study together with a comparison to other coeval paleopoles and associated paleogeographic implications We echo Veselevskiy et al. (2016) in suggesting that the implications of unidentified remagnetization throughout the geologic record may be profound We find the evidence presented in this study compelling despite the fact that a solid theoretical background for the remagnetization mechanism is still lacking and we suggest it should be investigated further DB contributed conception and design of the study data acquisition and analysis and writing of the manuscript WC performed data acquisition and analysis JD performed statistical analysis on a section of the manuscript All authors contributed to manuscript revision The research was funded by the Sao Paulo Research Foundation (FAPESP) grants 2011/51204-0 and 2011/51228-6 The National Science Foundation Instrument and Facilities grants NSF/EAR 1028690 and 1339505 to the Institute for Rock Magnetism allowed the continuation of the project and partially supporting WC Additional support for WC was provided by the University of Minnesota's Undergraduate Research Opportunity Program The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest We thank the two reviewers for the detailed comments and suggestions and the editor John Geissmann for handling the manuscript We wish to thank Irene Raposo for applying for funding and contributing to sampling and data acquisition Paulo Roberto dos Santos is cordially thanked for providing a detailed overview of the Itararé Group rocks during two field trips and Samuel Pedro Egidio for field-assistance Mike Jackson and Bruce Moskowitz are kindly thanked for careful proofreading of the manuscript and providing useful comments and suggestions This article is IRM publication number 1702 The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/feart.2018.00182/full#supplementary-material and duration of the superplume events and eras over geological time CrossRef Full Text Grupo Itararé (P-C da Bacia do Paraná) nas regiões de Limeira e Piracicaba – SP: contribuição ao estudo das litofácies Google Scholar The atypical Permian petroleum system of the Paraná Basin Tar sandstones in the Paraná basin of Brazil: structural and magmatic controls of hydrocarbon charge Paraná flood basalt volcanism primarily limited to ~ 1 Myr beginning at 135 Ma: new 40Ar/39Ar ages for rocks from Rio Grande do Sul and critical evaluation of published radiometric data A tale of two continents: some tectonic contrast between the Central Andes and the North American Cordillera as illustrated by their paleomagnetic signatures Analysis of Late Jurassic-recent paleomagnetic data from active margins of South America CrossRef Full Text | Google Scholar Geomagnetic secular variation in the cretaceous normal superchron and in the Jurassic A new inclination shallowing correction of the Mauch Chunk Formation of Pennsylvania based on high field-AIR results: implications for the Carboniferous North American APW path and Pangea reconstructions “Next-generation plate-tectonic reconstructions using GPlates,” in Geoinformatics: Cyberinfrastructure for the Solid Earth Sciences (Cambridge: Cambridge University Press) Google Scholar central Brazil: Implications for the late Paleozoic apparent polar wander path for South America The geomagnetic field in Permo-Triassic time CrossRef Full Text | Google Scholar CrossRef Full Text | Google Scholar “A tectonic approach to continental drift,” in Continental Drift-A Symposium Paleomagnetic results from Mesozoic strata in the Merida Andes CrossRef Full Text | Google Scholar Paleomagnetism of lower cretaceous rocks from east of the liquine-ofqui fault zone southern Chile: evidence of small in-situ clockwise rotations non-interacting single domain behavior in natural and synthetic samples CrossRef Full Text | Google Scholar The Kiaman reversed polarity superchron at Kiama: toward a field strength estimate based on single silicate crystals CrossRef Full Text | Google Scholar Studies on rock formations from Northeast Brazil CrossRef Full Text | Google Scholar Davis, J. 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This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) distribution or reproduction in other forums is permitted provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited in accordance with accepted academic practice distribution or reproduction is permitted which does not comply with these terms *Correspondence: Dario Bilardello, ZGFyaW8uYmlsYXJkZWxsb0BnbWFpbC5jb20= Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher 94% of researchers rate our articles as excellent or goodLearn more about the work of our research integrity team to safeguard the quality of each article we publish A project of Journalists and media professionals can attend this hybrid seminar The Barão de Itararé Center for Alternative Media Studies and the Inter Press Service (IPS) agency are hosting the first edition of the International Seminar on Communication and Latin American Integration Sessions will discuss topics such as challenges for democracy in Latin America lessons and challenges for public and grassroots communication initiatives for strengthening independent media platforms regulation and fighting disinformation Registration fee is BRL150 for in-person attendance and BRL60 for remote participants Judas actor in Easter play dies from accidental hangingThe Columbus DispatchAn actor portraying Judas in an Easter Passion play in Brazil has died after accidentally hanging himself during the performance was enacting the suicide of Judas during the performance on Good Friday in the city of Itarare Klimeck was hanging for four minutes before fellow performers realized something was wrong where he died on Sunday from the effects of a lack of oxygen to the brain Itarare is about 200 miles west of Sao Paulo HOT: » What kind of news would you like to see more of? A Brazilian actor died after accidentally hanging himself during the play "The Passion of the Christ," CNN reported was one of the actors from a local theater company taking part in an independent production of the play April 6 in the city of Itarare Klimeck died Sunday after spending more than two weeks in a medically induced coma due to extensive brain injuries from a prolonged lack of oxygen after accidentally hanging himself according to the Hospital Santa Casa de Misericordia The cause of death was not immediately available Photos taken by a local photographer show the final moments of the play as Klimeck hangs himself as described in the Bible in the book of Matthew Klimeck wore a harness under his robe during the play Police investigator Jose Victor Bassetti told the news station this was the third year the local fire department let the theater company borrow the harness for the play and that Klimeck was not supervised because he knew how to use the equipment are now being analyzed at the Criminal Institute of Sorocaba Luiz Carlos Rosner owns a sandwich cart next to the city square where the play was taking place He described the anxiety after cast members realized Klimeck was unconscious explaining there was someone unconscious hanging from the rope and that he wanted to cut it," Rosner told TV Record "I was a little worried about giving him a knife in the middle of the crowd." We need your support so Novinite.com can keep delivering news and information about Bulgaria a day dedicated to honoring the Holy Virgin Mary regarded as the most significant Christian holiday is celebrated annually in Bulgarian homes with great joy Holy Saturday marks the final day of Holy Week positioned between the sadness of Christ’s entombment and the joy of His anticipated resurrection A 12-meter cross featuring a crucified Jesus Christ has been installed at a roundabout in the Bulgarian town of Elin Peli Good Friday falls on the Friday preceding Easter Sunday is marked by the themes of humility and spiritual instruction The European Commission is proposing significant changes to EU regulations concerning road safety and vehicle registration According to preliminary data from Eurostat the eurozone economy grew by 0.4% in the first quarter of the year compared to the previous three months doubling the 0.2% increase recorded at the end of 2024 The European Commission has announced a €910 million investment under the European Defence Fund (EDF) to enhance defence manufacturing capabilities across the European Union The European Commission has strongly condemned the circumstances surrounding the death of Ukrainian journalist Viktoriia Roshchyna Friedrich Merz is poised to become Germany's next chancellor following the approval of a coalition agreement between his CDU/CSU bloc European countries are struggling to mobilize even 25,000 troops to Ukraine for a potential peacekeeping mission Google Street View Cars Return to Bulgaria for Major Mapping Update Housing Prices Soar in Bulgaria’s Major Cities as Demand and Supply Strain Increase