Mathematics – Logic
Scientific paper
May 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010e%26psl.294...58m&link_type=abstract
Earth and Planetary Science Letters, Volume 294, Issue 1-2, p. 58-68.
Mathematics
Logic
Scientific paper
Rock- and paleomagnetic investigations were performed on the late Pleistocene reef sequence of Tahiti, and take part of a multidisciplinary study of the Holocene and Pleistocene reef sequences, carried out by the IODP (Integrated Ocean Drilling Program) Expedition 310. The objectives were to characterize the natural remanent magnetization and its mineral carriers, in order to identify high-resolution magnetostratigraphic markers of the late Brunhes chron. A series of 85 specimens subsampled within a 79 m-thick silty-carbonate sequence cored at the Maraa site (SW of Tahiti) display a strong and stable natural remanent magnetization (NRM) carried by titanomagnetite inherited from the basalts which form the bulk of the island. The average negative inclination is assignable to the field generated by the normal polarity axial dipole field at the site latitude. A few specimens (103-119 m below modern sea level) carry a reversed primary magnetization acquired in a weak excursional field. Based on subsidence rate estimates ranging from 0.25 to 0.4 m/kyr, this suggests the identification either the Laschamp excursion (˜ 40 ka) or the Blake event (115-120 ka). Radiometric dates of ˜ 131 to ˜ 134 ka at 117 m below modern sea level confirm that these layers were deposited during the marine isotope stage 5.5 and recorded the direction and intensity anomaly associated with the Blake event. Another sea-level highstand reef unit, occurring deeper in the Pleistocene sequence has seemingly recorded another paleomagnetic intensity anomaly which is not yet definitely identified. Reef systems, which developed around volcanic islands, contain geological records of excursions. But, it is necessary to improve the understanding of NRM acquisition and the role of carbonate diagenesis in order to establish radiometrically dated records of geomagnetic excursions.
Camoin Gilbert
Lund Steven P.
Ménabréaz Lucie
Thouveny Nicolas
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