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Paleomagnetic Records: Discovery and Correlation

This overview delves into paleomagnetic records, exploring the discovery and origin of Earth's magnetic field, its properties, and its significance. Key figures such as Hans Christian Oersted and Andre-Marie Ampere are highlighted for their contributions. Various types of paleomagnetic records are discussed, including volcanic, archaeomagnetic, and marine sedimentary records, shedding light on how these studies provide insights into the Earth's magnetic history. The implications of these records enhance our understanding of geological and environmental processes over time.

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Paleomagnetic Records: Discovery and Correlation

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  1. Paleomagnetic Records:Discovery and Correlation Jeannie Bryson

  2. Outline • Discovery of Magnetic Field • Origin of Magnetic Field • Properties of Magnetic Field • Types of Paleomagnetic Records • Volcanic • Seafloor magnetic anomalies • Archaeomagnetic • Marine Sedimentary Sequences • Use and Implications of Magnetic Records Source: http://geomag.usgs.gov/program.html

  3. Discovery of Magnetic Field • Hans Christian Oersted-1821 • Accidentally discovered that passing an electric current over a compass caused the arrow to move • Andre-Marie Ampere • Further concluded that magnetism was “ a force between electric currents”; parallel currents attract and opposite currents repel

  4. Origin of Earth’s Magnetic Field • Source: “motion of electrical charges” • Magnetic field produced by electrical currents but it is not fully understood how • “dynamo effect”- One possibility • electrical currents produced by the coupling of convective effects • rotation in the spinning liquid metallic outer core of iron and nickel Source:http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html

  5. Properties of Earth’s Magnetic Field • Magnetosphere: • Earth’s Surface: Neutral • ~100km above surface: Solar Rays cause charged ions • Hinders the ability of solar rays to enter atmosphere, i.e. “bow shock” Source: http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html

  6. Properties of Earth’s Magnetic Field • Field Lines and Van Allen Radiation Belts Source:http://csep10.phys.utk.edu/astr161/lect/earth/magnetic.html

  7. Properties of Earth’s Magnetic Field • Magnetic Field Components • Declination: angle between horizontal component of magnetic-field vector in relation to true north • Inclination: angle between horizontal plane and total field vector

  8. Properties of Earth’s Magnetic Field • Dipole Component • Magnetic field lines come out of south pole and converge at north pole • Non-Dipole Component • Poles are not antipodal-asymmetrical • Axis is tilted ~ 11 degrees relative to the rotational axis

  9. Properties of Earth’s Magnetic Field • Geodynamo: a “dynamo” in core generates electrical currents • “self-sustaining” : electrically-conducting fluid flow across magnetic-field lines and generate electrical current to support existing field • Earth’s Magnetic Field ~ 3.5 billion years old • Rocks dated by paleomagnetic methods • Proves that Earth’s magnetic field must be regenerative

  10. Properties of Earth’s Magnetic Field • Geodynamo: alpha-omega dynamo cycle Source:http://geomag.usgs.gov/intro.html

  11. Types of Paleomagnetic Records • Magnetization • Thermoremnant Magnetization: • Lava and clays contain small amounts of iron and when heated obtain magnetization that is parallel to Earth’s magnetic field after cooling (unless reheated) • Depositional Remnant Magnetization: • Lake and ocean sediments are deposited and settle, iron particles record Earth’s magnetic field (unless disturbed) Source: http://www.archserve.id.ucsb.edu/anth3/Courseware/Chronology/11_Paleomag_Archaeomag.html

  12. Types of Paleomagnetic Records • Volcanic Records • Thermoremnant magnetization • 50 kyr record • Lava cools and iron in lava obtains magnetization of the time and place of cooling • Magnetization can then be measured and dated • Lava records are not continuous

  13. Types of Paleomagnetic Records • Archaeomagnetic Records • Remnant magnetism: heating above Curie point sets magnetization • Virtual Geomagnetic Pole (VGP): measures location of magnetic north at a certain time • Uses magnetization of object and another dating tool; i.e. 14C or dendrochronology • VGP’s can be used to create a curve representing paleomagnetic variations

  14. Types of Paleomagnetic Records • Marine Sediment Records • Yohan Guyodo-1996,1999: 200 kyr and 800 kyr • 800 kyr: 33 marine records stacked to create a composite curve • Sediments provide continuous record with few disturbances • Shows non-dipole moments • Does not support periodicity thought to be caused by Earth’s orbital influence • Data correlated with O18 reference curves

  15. Sint-800: 800 kyr marine sediment record

  16. Types of Paleomagnetic Records • Sea-Floor anomalies • 780 kyr record • East Pacific Rise • Supported by seafloor glass paleomagnetic record for past 50 kyr • Similar to marine sedimentary record • Can be used to understand both ridge crest accretion and geomagnetic field behavior

  17. Concluding Thoughts • Variations in geomagnetic intensity do not appear to show any signs of periodicity • Due to non-dipole component • Mean fluctuations in amplitude appear to be constant

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