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Upper and lower Jaramillo polarity transitions recorded in IODP Expedition 303 North Atlantic sediments: implications for transitional field geometry

Upper and lower Jaramillo polarity transitions recorded in IODP Expedition 303 North Atlantic sediments: implications for transitional field geometry
Upper and lower Jaramillo polarity transitions recorded in IODP Expedition 303 North Atlantic sediments: implications for transitional field geometry
Sediments collected during the Integrated Ocean Drilling Program (IODP) Expedition 303 in the North Atlantic provide records of polarity transitions and geomagnetic excursions at a high resolution. Here we investigate polarity transitions at the upper and lower boundaries of the Jaramillo subchronozone at Sites U1305, U1304, and U1306. The sediments carry strong natural remanent magnetizations (NRM) with median destructive fields consistent with magnetite as the dominant magnetic carrier. Both polarity transitions are characterized by low values of relative paleointensity. The U1305 record of the lower Jaramillo reversal exhibits a marked cluster of virtual geomagnetic poles (VGPs) over southern South America, and a secondary accumulation in the region of NE Asia/North Pacific. The main South American VGP cluster is also visible at Site U1304, which documents a less complex pattern, possibly because of a higher degree of smoothing. Records of the upper Jaramillo polarity transition document a VGP loop over the Americas, followed by north to south motion including a secondary VGP accumulation near India. The similarity between several records of the upper Jaramillo transition obtained at various sites in the North Atlantic is a strong indication that geomagnetic field changes have been faithfully captured. Results suggest that a transverse, possibly dipolar, field component has fluctuated during these polarity reversals, and that these fluctuations combined with a reduced axial dipole component yielded the observed field at the Earth’s surface during the polarity transitions. The lower Jaramillo transition also exhibits VGP clusters in the vicinity of South America and eastern Asia but these clusters are shifted relative to the upper Jaramillo VGP clusters, implying a memory exerted by the upper mantle on polarity transition geometry.
geomagnetic, reversals, geometry, jaramillo, marine, sediments
0031-9201
131-140
Mazaud, A.
3127d8d6-5892-477b-ad1f-7147bc7b84ca
Channell, J.E.T.
f37676da-640c-4bdc-8f9f-e2ffa43fe449
Xuan, C.
3f3cad12-b17b-46ae-957a-b362def5b837
Stoner, J.S.
7470dbc1-c6ff-4c08-b98c-3be4d1d43c2a
Mazaud, A.
3127d8d6-5892-477b-ad1f-7147bc7b84ca
Channell, J.E.T.
f37676da-640c-4bdc-8f9f-e2ffa43fe449
Xuan, C.
3f3cad12-b17b-46ae-957a-b362def5b837
Stoner, J.S.
7470dbc1-c6ff-4c08-b98c-3be4d1d43c2a

Mazaud, A., Channell, J.E.T., Xuan, C. and Stoner, J.S. (2009) Upper and lower Jaramillo polarity transitions recorded in IODP Expedition 303 North Atlantic sediments: implications for transitional field geometry. Physics of the Earth and Planetary Interiors, 172 (3-4), 131-140. (doi:10.1016/j.pepi.2008.08.012).

Record type: Article

Abstract

Sediments collected during the Integrated Ocean Drilling Program (IODP) Expedition 303 in the North Atlantic provide records of polarity transitions and geomagnetic excursions at a high resolution. Here we investigate polarity transitions at the upper and lower boundaries of the Jaramillo subchronozone at Sites U1305, U1304, and U1306. The sediments carry strong natural remanent magnetizations (NRM) with median destructive fields consistent with magnetite as the dominant magnetic carrier. Both polarity transitions are characterized by low values of relative paleointensity. The U1305 record of the lower Jaramillo reversal exhibits a marked cluster of virtual geomagnetic poles (VGPs) over southern South America, and a secondary accumulation in the region of NE Asia/North Pacific. The main South American VGP cluster is also visible at Site U1304, which documents a less complex pattern, possibly because of a higher degree of smoothing. Records of the upper Jaramillo polarity transition document a VGP loop over the Americas, followed by north to south motion including a secondary VGP accumulation near India. The similarity between several records of the upper Jaramillo transition obtained at various sites in the North Atlantic is a strong indication that geomagnetic field changes have been faithfully captured. Results suggest that a transverse, possibly dipolar, field component has fluctuated during these polarity reversals, and that these fluctuations combined with a reduced axial dipole component yielded the observed field at the Earth’s surface during the polarity transitions. The lower Jaramillo transition also exhibits VGP clusters in the vicinity of South America and eastern Asia but these clusters are shifted relative to the upper Jaramillo VGP clusters, implying a memory exerted by the upper mantle on polarity transition geometry.

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More information

Published date: February 2009
Keywords: geomagnetic, reversals, geometry, jaramillo, marine, sediments
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 351194
URI: http://eprints.soton.ac.uk/id/eprint/351194
ISSN: 0031-9201
PURE UUID: 8e262d60-2621-4de9-8604-405cc46f6dda
ORCID for C. Xuan: ORCID iD orcid.org/0000-0003-4043-3073

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Date deposited: 16 Apr 2013 10:03
Last modified: 08 Jan 2022 03:20

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Contributors

Author: A. Mazaud
Author: J.E.T. Channell
Author: C. Xuan ORCID iD
Author: J.S. Stoner

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