--> Abstract: Magnetostratigraphy of Mesozoic Shallow-Water Carbonates: Preliminary Results from the Middle Jurassic of the Paris Basin, by D. M. Aissaoui and J. L. Kirschvink; #91004 (1991)

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Magnetostratigraphy of Mesozoic Shallow-Water Carbonates: Preliminary Results from the Middle Jurassic of the Paris Basin

AISSAOUI, DJAFAR M., and JOSEPH L. KIRSCHVINK, California Institute of Technology, Pasadena, CA

The use of sedimentary paleomagnetism has enhanced greatly our understanding of the timing of deposition and diagenesis of Cenozoic platform and reefal carbonates. Its application to similar but older deposits will have direct implications for economic exploration and development. We report here preliminary paleomagnetic results from the Middle Jurassic limestones of the Paris basin (France). The samples consist mainly of bioclastic and oolitic limestones deposited in ancient counterpart of the shallow-water environments of the Bahama platform.

The Jurassic samples are stable to progressive, incremental demagnetization and exhibit magnetization patterns identical to Cenozoic rocks from the Bahama platform or Mururoa Atoll. The natural remanent magnetization of these limestones is weak and comprised between 7.7 * 10x9 to 1.8 * 10x8 AM(2)/kg. Magnetic components of both normal and reversed polarity are observed. Paired isothermal remanent magnetization (IRM) and alternating field demagnetization experiments show that most of the remanence is lost between 20 and 45 mT, which is typical of single-domain biogenic magnetite or maghemite. The ratio of IRM at Hrc to the saturation IRM ranges from 35 to 42% indicating a moderate to low interparticle interaction. This is confirmed by the anhysteretic remanent magnetization as compared with intact, freeze-dried cells of magnetotactic bacteria and chiton teeth.

Magnetic minerals extracted from the Jurassic samples are examined to further confirm the occurrence of SD magnetite within the Middle Jurassic limestones of the Paris basin. These preliminary results suggest that these strata should be good for the paleomagnetic investigation of Mesozoic shallow-water carbonates.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)