Management of ambiguities in magnetostratigraphic correlation.

Florent Lallier and Christophe Antoine and Julien Charreau and Guillaume Caumon. ( 2011 )
in: Proc. 31st Gocad Meeting, Nancy

Abstract

Magnetostratigraphy is a powerful tool to access absolute dating of sediments enabling good and detailed chronostratigraphic correlation. It is based on the correlation of a magnetic polarity column, observed and measured in a given sediment section, to a magnetic polarity reference scale where polarity changes are well dated via other independent methods. However, magnetostratigraphic correlations are loose for they are only constrained by the binary magnetic chrons (i.e normal or reversal) and their thickness, wich are both defined from depth variations of the magnetic remanent directions. Yet, the thickness of a given magnetic chron is a function of time and sediment preservation rate, which may not be stationary, leading to ambiguities when performing the correlations. To better address these ambiguities and to provide a more objective approach, a new numerical method based on the Dynamic Time Warping algorithm is proposed. Correlation likelihood between two magnetic chrons is computed as a function of ratios between the thickness of the considered chron and the thickness of the chrons above and below. Thus, the likelihood correlation computation method does not depend on the sediment preservation rate but assumes it as locally constant. Moreover, in order to manage nonrecorded magnetic polarity inversions (because of non-deposition or erosion) the DTW algorithm is improved to allow multiple gaps. In the case of absolute dating of sections, i.e. correlation between the studied section and the reference scale additional rules are used: (i) gaps are not allowed on the reference scale, which assumes that all inversions observed on the studied section exist on the reference scale; (ii) extremities of the studied section are considered as free into the DTW algorithm. This method is applied to the Subei section (Gansu Province, western China) and allows an objective evaluation of three conflicting interpretations proposed in the literature.

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BibTeX Reference

@INPROCEEDINGS{Lallier2GM2011,
    author = { Lallier, Florent and Antoine, Christophe and Charreau, Julien and Caumon, Guillaume },
     title = { Management of ambiguities in magnetostratigraphic correlation. },
 booktitle = { Proc. 31st Gocad Meeting, Nancy },
      year = { 2011 },
  abstract = { Magnetostratigraphy is a powerful tool to access absolute dating of sediments enabling good and detailed chronostratigraphic correlation. It is based on the correlation of a magnetic polarity column, observed and measured in a given sediment section, to a magnetic polarity reference scale where polarity changes are well dated via other independent methods. However, magnetostratigraphic correlations are loose for they are only constrained by the binary magnetic chrons (i.e normal or reversal) and their thickness, wich are both defined from depth variations of the magnetic remanent directions. Yet, the thickness of a given magnetic chron is a function of time and sediment preservation rate, which may not be stationary, leading to ambiguities when performing the correlations.
To better address these ambiguities and to provide a more objective approach, a new numerical method based on the Dynamic Time Warping algorithm is proposed. Correlation likelihood between two magnetic chrons is computed as a function of ratios between the thickness of the considered chron and the thickness of the chrons above and below. Thus, the likelihood correlation computation method does not depend on the sediment preservation rate but assumes it as locally constant. Moreover, in order to manage nonrecorded magnetic polarity inversions (because of non-deposition or erosion) the DTW algorithm is improved to allow multiple gaps. In the case of absolute dating of sections, i.e. correlation between the studied section and the reference scale additional rules are used: (i) gaps are not allowed on the reference scale, which assumes that all inversions observed on the studied section exist on the reference scale; (ii) extremities of the studied section are considered as free into the DTW algorithm.
This method is applied to the Subei section (Gansu Province, western China) and allows an objective evaluation of three conflicting interpretations proposed in the literature. }
}