scholarly journals Testing the Reliability of Sedimentary Paleomagnetic Datasets for Paleogeographic Reconstructions

2020 ◽  
Vol 8 ◽  
Author(s):  
Edoardo Dallanave ◽  
Uwe Kirscher
Keyword(s):  
Magnetic Susceptibility ◽  
Spatial Distribution ◽  
New Caledonia ◽  
Sedimentary Rocks ◽  
Paleomagnetic Data ◽  
Polar Wander ◽  
Distribution Shape ◽  
Measurement And Analysis ◽  
Temporal Continuity ◽  
Strain Data

Paleogeographic reconstructions largely rely on paleomagnetic data, mostly in the form of paleomagnetic poles. Compilations of poles are used to determine so called apparent polar wander paths (APWPs), which capture the motion through time of a particular location with respect to an absolute reference frame such as the Earth’s spin axis. Paleomagnetic datasets from sedimentary rocks are particularly relevant, because of their spatial distribution and temporal continuity. Several criteria have been proposed through the years to assess the reliability of paleomagnetic datasets. Among these, the latitudinal-dependent elongation of a given paleomagnetic directions distribution, predicted by a widely accepted paleosecular variations model, has been applied so far only to investigate inclination flattening commonly observed in sedimentary rocks. We show in this work that this concept can be generalized to detect “contamination” of paleomagnetic data derived from tectonic strain, which is not always detected by field observation only. After generating different sets of simulated geomagnetic directions at different latitudes, we monitored the variations in the shape of the distributions after applying deformation tensors that replicate the effect of increasing tectonic strain. We show that, in most cases, the “deformation” of the dataset can be detected by elongation vs. inclination ratios not conforming to the values predicted by the paleosecular variations model. Recently acquired paleomagnetic directions and anisotropy of magnetic susceptibility (AMS; a parameter very sensitive to tectonic strain) data from New Caledonia verifies the results of these simulations and highlights the importance of measuring AMS when using sedimentary paleomagnetic data for paleogeographic reconstruction. We suggest to include always AMS measurement and analysis of the distribution shape to assess sedimentary paleomagnetic data used for paleogeographic reconstructions.

scholarly journals 3D lithostratigraphic model of the Paleogene of the onshore part of the Moesian Platform (Northeast Bulgaria)

2018 ◽  
Vol 47 (1) ◽  
pp. 23-36
Author(s):  
Boris Valchev ◽  
Dimitar Sachkov ◽  
Sava Juranov
Keyword(s):  
Spatial Distribution ◽  
Sedimentary Rocks ◽  
Eastern Slope ◽  
The South ◽  
The North ◽  
Lithostratigraphic Units ◽  
Moesian Platform ◽  
Regional Tectonic ◽  
Model Database ◽  
The Individual

The Paleogene sedimentary rocks in the north-easternmost part of the territory of Bulgaria have been penetrated by numerous boreholes. In terms of regional tectonic zonation, the study area is a part of the onshore sector of the Moesian Platform, which partly includes the South Dobrogea Unit and the easternmost part of the North Bulgarian Dome with its eastern slope. The lithostratigraphy of the Paleogene successions consists of six formal units (the Komarevo, Beloslav, Dikilitash, Aladan, Avren, and Ruslar formations) and one informal unit (glauconitic marker). For compiling an overall conception of the regional aspects (lithology, thickness, spatial distribution, and relationships) of the individual lithostratigraphic units and for illustration of their spatial distribution, a 3D lithostratigraphic model based on reinterpretation of individual borehole sections has been created. The model database was compiled by integration of the original lithological data from 338 borehole sections.

scholarly journals GEOLOGICAL AND MAGNETIC SUSCEPTIBILITY MAPPING OF MOUNT GIOUCHTA (CENTRAL CRETE)

2017 ◽  
Vol 43 (1) ◽  
pp. 289 ◽  
Author(s):  
E. Kokinou ◽  
E. Kamberis ◽  
A. Sarris ◽  
I. Tzanaki
Keyword(s):  
Magnetic Susceptibility ◽  
Spatial Distribution ◽  
Stress Field ◽  
Magnetic Measurements ◽  
Strain Analysis ◽  
Geological Structure ◽  
Early Pleistocene ◽  
Middle Pleistocene ◽  
Western Slope ◽  
Strain Pattern

Giouchta Mt. is located south of Heraklion city, in Crete. It is an N-S trending morphological asymmetric ridge, with steep western slope whilst the eastern slope represents a smoother relief, composed of Mesozoic limestone and Eocene- lower Oligocene flysch sediments of the Gavrovo -Tripolis zone. The present study focuses on the geological structure of Mt. Giouchta. Field mapping and tectonic analysis is performed for this purpose. The dominant structures are contractional in nature, deformed by normal faulting related to the extensional episodes initiated in Serravallian times. The strain pattern in the area is revealed from strain analysis. It is inferred that the orientation of the stress field in the area has changed several times: the N-S, stress field which was dominant during Late Serravallian times changed to NE-SW (in Late Serravallian? - Early Tortonian) and subsequently to WNW-ESE (Early to Middle Tortonian) to become NW-SE in Late Tortonian. This orientation changed also during the Quaternary times trending from NW-SE (Early Pleistocene) to ENE-WSW (Middle Pleistocene-Holocene). In addition to the above, surface soil samples were collected in the wider area of mount Giouchta and they were analyzed in order to determine the magnetic susceptibility. GIS techniques were used for mapping the spatial distribution of the geological features and the magnetic measurements on the topographic relief of the area. Statistical analysis techniques were also applied in order to investigate the relation of faulting and magnetic susceptibility. Maps representing the spatial distribution of the above measurements were created by using appropriate interpolation algorithms.

Synthesis of palaeomagnetic datasets suggests that the geomagnetic field was persistently non-uniformitarian in the Devonian

2021 ◽  
Author(s):  
Annique van der Boon ◽  
Andy Biggin ◽  
Daniele Thallner ◽  
Mark Hounslow ◽  
Jerzy Nawrocki ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Weak Field ◽  
Paleomagnetic Data ◽  
Independent Evidence ◽  
Tectonic Plates ◽  
Polar Wander ◽  
Push Forward ◽  
Geomagnetic Polarity ◽  
Life On Earth ◽  
Geomagnetic Polarity Time Scale

<p>The Devonian has long been a problematic era for paleomagnetism. Devonian data are generally difficult to interpret and have complex partial or full overprints. These problems arise from paleomagnetic data obtained from both sedimentary and igneous rocks. As a result, the reconstruction of motions of tectonic plates is often troubling, as these rely on apparent polar wander paths constructed from Devonian paleomagnetic poles. Also the geomagnetic polarity time scale for this time period is poorly constrained. Paleointensity studies suggest that the field was much weaker than the field of today, and it has been hypothesised that this was accompanied by many polarity reversals (a hyperreversing field). We review studies on Devonian paleopoles, magnetostratigraphy and paleointensity. We tentatively suggest that the field during the Devonian might have been so weak and perhaps of a non-dipolar configuration, that obtaining reliable paleomagnetic data from Devonian rocks is extremely difficult.  In order to push forward the understanding of the Devonian field, we emphasise the need for studies to provide fully accessible data down to specimen level demagnetisation diagrams. Incorporating all data, no matter how complex or bad they might seem, is the only way to advance the understanding of the Devonian magnetic field. Recent paleointensity studies appear to suggest that the Devonian and Ediacaran were both extreme weak field intervals. For the Ediacaran, it has been hypothesised that the field had an impact on life on earth. A fundamentally weak and perhaps non-dipolar field during the Devonian might have had an influence on evolution and extinctions. As there is a large number of biological crises in the Devonian, we here pose the question whether the Earth’s magnetic field was a contributing factor to these crises. New independent evidence from the Devonian-Carboniferous boundary suggests that the Hangenberg event was caused by increased UV-B radiation, which is in line with a weak magnetic field.</p>

scholarly journals Application of magnetic susceptibility as a paleoclimatic proxy on Paleozoic sedimentary rocks and characterization of the magnetic signal – IGCP-580 projects and events

Episodes ◽  
2014 ◽  
Vol 37 (2) ◽  
pp. 87-95 ◽  
Author(s):  
Anne-Christine Da Silva ◽  
Michael T. Whalen ◽  
Jindrich Hladil ◽  
Leona Koptikova ◽  
Daizhao Chen ◽  
...  
Keyword(s):  
Magnetic Susceptibility ◽  
Sedimentary Rocks ◽  
Magnetic Signal ◽  
Paleoclimatic Proxy

Paleomagnetism of the Chuar Group and evaluation of the late Tonian Laurentian apparent polar wander path with implications for the makeup and breakup of Rodinia

2019 ◽  
Vol 132 (3-4) ◽  
pp. 710-738 ◽  
Author(s):  
Athena Eyster ◽  
Benjamin P. Weiss ◽  
Karl Karlstrom ◽  
Francis A. Macdonald
Keyword(s):  
Grand Canyon ◽  
Quality Criteria ◽  
Paleomagnetic Data ◽  
Geochronological Data ◽  
Data Set ◽  
Polar Wander ◽  
Apparent Polar Wander Path ◽  
Robust Tests ◽  
Laurentian Margin ◽  
Global Data

AbstractPaleogeographic models commonly assume that the supercontinent Rodinia was long-lived, with a static geometry involving Mesoproterozoic links that developed during assembly and persisted until Neoproterozoic rifting. However, Rodinian paleogeography and dynamics of continental separation around its centerpiece, Laurentia, remain poorly constrained. On the western Laurentian margin, geological and geochronological data suggest that breakup did not occur until after 720 Ma. Thus, late Tonian (ca. 780–720 Ma) paleomagnetic data are critical for reconstructing paleogeography prior to dispersal and assessing the proposed stasis of Rodinia. Here, we report new paleomagnetic data from the late Tonian Chuar Group in the Grand Canyon, Arizona. We combined this new data set with reanalyzed existing data to obtain a new paleopole preserved in hematite, the reliability of which is supported by six of the seven (Q1–Q6) Van der Voo reliability quality criteria. In addition, we identified pervasive mid- to high-temperature overprints. This new paleomagnetic pole was incorporated with recent high-precision geochronological data and existing paleomagnetic data to present a new late Tonian Laurentian apparent polar wander path (APWP). Having examined the paleomagnetic data of other cratons, global reconstructions for 775 Ma, 751 Ma, and 716 Ma are presented. These reconstructions are consistent with Australia located near the present southern margin of Laurentia. However, a stringent analysis of the global data set does not support a good match between any major craton and the rifted conjugate margin to western Laurentia. Breakup on the western Laurentian margin may have involved rifting of a continental fragment or a craton with uncertainties in its late Tonian geochronologic and paleomagnetic constraints. Our revised Laurentian APWP will allow for more robust tests of paleogeography and evaluation of the proposed supercontinent Rodinia.

Magnetic fabric of Devonian and Precambrian dikes from the northeastern Kola Peninsula, Russia

2021 ◽  
Author(s):  
Sofya Fursova ◽  
Roman Veselovskiy
Keyword(s):  
Magnetic Susceptibility ◽  
Spatial Distribution ◽  
Kola Peninsula ◽  
Magnetic Fabric ◽  
Laboratory Studies ◽  
Magma Flow ◽  
Northeastern Part ◽  
Geological Age ◽  
First Results ◽  
Magma Sources

<p>Nowadays, anisotropy of magnetic susceptibility (AMS) is a very widespread method to investigate the magnetic fabric of the rocks. AMS studies provide the information on the magma flow during formation of intrusives (dikes and sills) based on the orientation of the AMS ellipsoid. In this work we present the results of the AMS measurements of Devonian, Paleoproterozoic and Neoarchean dikes, which are located on the northeastern part of the Kola Peninsula. We use these data to reconstruct the direction of magma flow with the final aim to reconstruct the spatial distribution of the magma sources.</p><p>Laboratory studies of AMS were carried out on 1282 samples representing 102 dikes. At this stage, all studied dikes were typified based on their geological age and type of AMS (normal, reversed, intermediate). It is shown that not all the studied intrusive bodies retained the primary magnetic fabric and only a few of them can be used to reconstruct the position of magmatic centers and are promising for obtaining reliable paleomagnetic data. We also present the first results of interpretation of the direction of the magma flow during dike swarms forming.</p><p>The study is supported by the grant of RSF #16-17-10260.</p>

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