Remagnetization of the pyeongan supergroup in the yeongwol

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Abstract

Paleomagnetic and rock magnetic investigations have been carried out for the late CarboniferousPermian Pyeongan Supergroup, exposed in the Yeongwol area in eastern South Korea. A total of 228 independently oriented core samples was drilled from thirteen sites for the study. The mean direction after bedding correction (D/I = 202.7°/-24.6°, k = 2.4, 095 = 36.9°) is more dispersed than the in-situ mean direction (D/I = 175.3°/-58.9°, k = 69.0, 95 = 5.3°), indicating that the fold test is negative at 95% confidence level. In addition, the stepwise unfolding of the characteristic rémanent magnetization (ChRM) reveals a maximum value of £at 0% unfolding. Furthermore, authigenic magnetite and hematite grains are identified by the electron microscope observations. These results collectively imply that the ChRM directions were acquired after tilting of the strata by a chemical rémanent magnetization when the secondary authigenic magnetic minerals formed. The ChRM directions of the Supergroup, however, pass the reversal test at 95% confidence level suggesting that the remagnetization occurred during the period including both normal and reversed polarity intervals. Because the paleomagnetic pole position (39.4°E, 85.6°N, Acs = 8.9°) of the Pyeongan Supergroup calculated from the mean site directions of the ChRMs is close to that of the Tertiary period of the Korean Peninsula, it is interpreted that the remagnetization in this area occurred during the Tertiary. However, it is also plausible that the study area might be rotated about 30° anticlockwise after the remagnetization at the end of the Daebo Orogeny, in the beginning of the Cretaceous period.

Original languageEnglish
Pages (from-to)1217-1232
Number of pages16
JournalJournal of Geomagnetism and Geoelectricity
Volume49
Issue number10
Publication statusPublished - 1997 Dec 1

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remagnetization
magnetization
authigenic mineral
magnetic mineral
Tertiary Period
confidence
orogeny
Cretaceous Period
hematite
magnetite
South Korea
fold
Cretaceous
electron
peninsulas
strata
polarity
rock
poles
electron microscopes

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

Cite this

Remagnetization of the pyeongan supergroup in the yeongwol. / Doh, Seong-Jae.

In: Journal of Geomagnetism and Geoelectricity, Vol. 49, No. 10, 01.12.1997, p. 1217-1232.

Research output: Contribution to journalArticle

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abstract = "Paleomagnetic and rock magnetic investigations have been carried out for the late CarboniferousPermian Pyeongan Supergroup, exposed in the Yeongwol area in eastern South Korea. A total of 228 independently oriented core samples was drilled from thirteen sites for the study. The mean direction after bedding correction (D/I = 202.7°/-24.6°, k = 2.4, 095 = 36.9°) is more dispersed than the in-situ mean direction (D/I = 175.3°/-58.9°, k = 69.0, 95 = 5.3°), indicating that the fold test is negative at 95{\%} confidence level. In addition, the stepwise unfolding of the characteristic r{\'e}manent magnetization (ChRM) reveals a maximum value of £at 0{\%} unfolding. Furthermore, authigenic magnetite and hematite grains are identified by the electron microscope observations. These results collectively imply that the ChRM directions were acquired after tilting of the strata by a chemical r{\'e}manent magnetization when the secondary authigenic magnetic minerals formed. The ChRM directions of the Supergroup, however, pass the reversal test at 95{\%} confidence level suggesting that the remagnetization occurred during the period including both normal and reversed polarity intervals. Because the paleomagnetic pole position (39.4°E, 85.6°N, Acs = 8.9°) of the Pyeongan Supergroup calculated from the mean site directions of the ChRMs is close to that of the Tertiary period of the Korean Peninsula, it is interpreted that the remagnetization in this area occurred during the Tertiary. However, it is also plausible that the study area might be rotated about 30° anticlockwise after the remagnetization at the end of the Daebo Orogeny, in the beginning of the Cretaceous period.",
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