EMRP3.3

Throughout its history, the Earth’s magnetic field has undergone changes in its polarity. These changes vary in scale, from millennial (excursions) to hundreds of thousands or millions of years (reversal). Constraining the chronology of these geomagnetic instabilities is fundamental to understanding Earth’s dynamo processes and their surface expressions. Moreover, a detailed geomagnetic instability time scale (GITS) refines its applicability as an accurate correlation and dating tool (magnetostratigraphy) for sedimentary and volcanic sequences and it is fundamental to understanding several aspects of past climate. Indeed, periods of geomagnetic instability are usually associated with a weak field. This in turn weakens the efficiency of the Earth’s magnetic field shielding enhancing the production of cosmogenic isotopes which play a significant role on modulating climate by either directly or indirectly influencing factors such as the total or spectral solar irradiance. In this study, we present a preliminary record of geomagnetic instabilities during the Brunhes (0-0.778 Ma), based on intercorrelation of paleomagnetic data from five marine sedimentary cores collected during the IODP Expeditions 384 and 395C from the North Atlantic Ocean along the Reykjanes ridge. Two of the drilling sites are nearby the ODP Sites 983 and 984 (Channell et al., 2002) providing an opportunity to cross correlate our preliminary results.

How to cite: Di Chiara, A., Satolli, S., Friedman, S., and Expedition 395 Science Party, S. P.: Record of Geomagnetic Instabilities during the Brunhes: preliminary results from IODP Expeditions 384 and 395C from North Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2670, https://doi.org/10.5194/egusphere-egu22-2670, 2022.

Determining Earth’s stability with respect to the spin axis sets boundary conditions for understanding the planet’s deep mantle and interpreting records of past climate. Analyses of global paleomagnetic data sets have suggested very limited polar wander since the Mid-Cretaceous (Cottrell and Tarduno, 2000; Tarduno and Smirnov, 2001). However, this conclusion has been challenged by calls for a Late Cretaceous true polar oscillation whereby the entire solid Earth rotated by 12 degrees, and then rotated back, 86 to 78 million years ago (Mitchell et al., 2021). This posit is based on paleomagnetic data from a dense sampling (approximately 1000 limestone samples) and automated magnetic measurements yielding data from magnetic polarity chrons 34 to 32n in the Italian Apennines. Herein, we analyze these data and find that the oscillation signal across magnetic chrons polarity 33r to 33n exceeds the maximum speed constrained by mantle viscosity (2.4 degrees/myr; Tsai and Stevenson, 2007) and is thus physically implausible. When considered in the light of prior paleomagnetic and rock magnetic studies on these rocks, the data point to an unrecognized overprint magnetization carried by authigenic hematite. This overprint has a differential angular effect on the normal and reversed polarity primary remanences, creating biased magnetic directions and attendant false polar wander. This artifact serves as a cautionary tale with respect to paleomagnetic analyses, but also further highlights the remarkable stability of Earth relative to the axis since at least the mid-Cretaceous which sets the planet apart from smaller planetary bodies which may have experienced polar wander. Principal differences are that external forces since the lunar forming impact are too small to drive such motion, and Earth’s mantle viscosity structure which dampens any potential motion driven by changes in its mass heterogeneities.

How to cite: Cottrell, R., Tarduno, J., and Bono, R.: Late Cretaceous true polar oscillation artifact: further evidence for Earth’s long-term rotational stability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6011, https://doi.org/10.5194/egusphere-egu22-6011, 2022.

The Izu-Bonin-Mariana (IBM) subduction system is a key natural laboratory providing fundamental insights into subduction dynamics and the evolution of associated upper plate magmatism. To investigate the processes associated with subduction initiation and the subsequent evolution of the Philippine Sea plate, International Ocean Discovery Program (IODP) Expedition 351 recovered a complete sedimentary sequence and the top of the underlying volcanic basement at Site U1438 located in a rear-arc position. This offers a unique opportunity to study for the first time and in extreme detail the styles, products, and timing of the volcanic events that marked the emplacement, growth, and demise of the Kyushu-Palau volcanic arc within the IBM system. Here we report a magnetostratigraphy for Site U1438 based on ~60,000 remanence directions isolated from 1063 archive half-core sections and 429 discrete specimens. This identified 112 well-constrained magnetic reversals that may be correlated with the geomagnetic polarity timescale. When combined with additional biostratigraphic and geochronological constraints, this allows construction of a high-resolution age model for Site U1438 and the determination of changes in sedimentation rates during the evolution of the Kyushu-Palau arc. These age constraints show that following subduction initiation at ~52 Ma, diffuse volcanism in both the forearc and rear-arc preceded the initial emplacement of the Kyushu-Palau arc at 44.2 Ma, which then grew through four compositionally distinct eruptive phases until 29.2 Ma. Rollback of the Pacific slab then triggered rifting of the arc (29.2-24.3 Ma), leading to back-arc spreading in the Shikoku and Parece-Vela basins.

How to cite: Maffione, M. and Morris, A.: Timing of Tectonic and Magmatic Events in the Philippine Sea Plate since 50 Ma from High-Resolution Magnetostratigraphy of IODP Site U1438, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8684, https://doi.org/10.5194/egusphere-egu22-8684, 2022.

The question of the total duration of the Siberian Traps magmatic activity in the Siberian platform and its correlation with the Permian-Triassic boundary is still being contentious, remaining essential for a number of studies, especially for the possible links with the end-Permian global biotic crisis.

The aim of this work was to obtain for the first representative and reliable paleomagnetic data on the section of the Samoedsky Formation using the modern instrumental base of paleomagnetic studies to estimate the magmatic activity duration. The Samoedsky Formation lies at the top of the Permian-Triassic volcanic section of the Norilsk region. The major part of the Norilsk tuff-lava pile, except for the lowermost Ivakinsky Formation, corresponds to the normal magnetic polarity interval [1]. Although the paleomagnetic investigation of the Samoedsky Formation basalts was performed previously [1, 2], this interval still remains complicated and the issue of its relation to the normal or reverse polarity interval has not been resolved.

During the field work oriented samples were taken (233 samples from 11 sites) from the lava flows of the Samoedsky Formation in the Verkhnyaya Talovaya river valley (the Norilsk region). At the laboratory stage alternating field and thermal demagnetization were carried out using SQUID SRM, JR-6 (AGICO) magnetometers and MMTD80 thermal furnace.

Based on the results of calculations with the Enkin software package [3], it can be concluded that the three uppermost lava flows of the Samoedsky Formation are magnetized in reversed polarity, which confirms the latest data [1]. Other studied flows demonstrate the normal polarity. Thus, the emplacement of the Samoedsky Formation and consequently the entire lava sequence of the Norilsk region corresponds not only to the LT1n1n chron (the first normal polarity chron of the Lower Triassic), but also to the part of the reverse polarity chron LT1n1r [1], which also affects the correlation of the sections of the Siberian Traps LIP different regions.

References

1. Latyshev A.V., Fetisova A.M., Veselovskiy R.V. Linking Siberian Traps LIP Emplacement and End-Permian Mass Extinction: Evidence from Magnetic Stratigraphy of the Maymecha-Kotuy Volcanic Section // Geosciences. 2020. V. 10. № 8. P. 295.

2. Gurevitch, E.L., Heunemann, C., Rad’ko, V., Westphal, M., Bachtadse, V., Pozzi, J.P., Feinberg, H. Palaeomagnetism and magnetostratigraphy of the Permian-Triassic northwest central Siberian Trap Basalts // Tectonophysics. 2004. V.379. P. 211–226.

3. Enkin R.J. A computer program package for analysis and presentation of paleomagnetic data. Pacific Geoscience Centre, Geol. Surv. Can., 1994. P. 16.

How to cite: Latanova, E. and Latyshev, A.: Magnetic stratigraphy of the Samoedsky Formation, the upper part of the Siberian Traps LIP section in the Norilsk region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10447, https://doi.org/10.5194/egusphere-egu22-10447, 2022.

Magnetostratigraphy is a basic method to provide age constrains when trying to identify paleonvirmental changes in sedimentary successions. This is particularly important in the case of the Middle Eocene Climatic Optimum (MECO), which is a climatic perturbation not exactly coincident with a biostratigraphic boundary and having a peak Ca 40.2 Ma. We introduce the Jaca basin record (Southern Pyrenees) where expanded sedimentary successions record several Eocene climatic episodes. Combined magneto-biostratigraphic dating of these successions is carried out in the Hecho Group (deep clastic systems) and in its vertical successions to the Sabiñánigo and Belsué-Atarés deltaic systems.

New magnetostratigraphic data permit the identification of paleopolarities on the basis of stable demagnetization results from the marls of the deltaic successions. Counting of 32 species of calcareous nanoplankton for biostratigraphic purposes has permitted to identify several biozones throughout the basin. With respect to the MECO, the CNE14/15 biozones boundary has been clearly identified, which is close to c18r/c18n reversal.

A multiproxy study is carried out including mineralogical, elemental and isotopic data from X-ray diffraction, X-ray fluorescence and bulk rock C/O stable isotopes, with the aim to achieve a paleoenvironmental proxy permitting the identification of the MECO.  Ultimately, the integrated chronostratigraphic and multiproxy characterization of the studied sections will permit to understand how deltaic systems reacted the MECO climatic event.

How to cite: Oms, O., Blanchar, H., Dinarès-Turell, J., Ibañez-Insa, J., Verdaguer, J., González-Lanchas, A., Gil-Delgado, A., Flores, J.-A., and Remacha, E.: Magneto-biostratigraphic succession of the Jaca Basin (Southern Pyrenees, Spain): insights on the Middle Eocene Climatic Optimum., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12603, https://doi.org/10.5194/egusphere-egu22-12603, 2022.