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Magnetostratigraphy of the Lower Cretaceous San Marcos Formation, Coahuila, Mexico

Molina-Garza, R S ; Arvizu, I ; Gonzalez, G

Eos (Washington, D.C.), 2007-06, Vol.88 (25 (2007 Joint Assembly)

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  • Título:
    Magnetostratigraphy of the Lower Cretaceous San Marcos Formation, Coahuila, Mexico
  • Autor: Molina-Garza, R S ; Arvizu, I ; Gonzalez, G
  • É parte de: Eos (Washington, D.C.), 2007-06, Vol.88 (25 (2007 Joint Assembly)
  • Notas: ObjectType-Article-2
    SourceType-Scholarly Journals-1
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    SourceType-Scholarly Journals-2
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    ObjectType-Conference Paper-1
    SourceType-Conference Papers & Proceedings-1
    ObjectType-Article-3
  • Descrição: Continental hematitic strata of the Lower Cretaceous San Marcos Formation, in central Coahuila, were deposited on and along the margins of the Coahuila Island, a prominent paleogeographic element in NE Mexico. It contains the stratigraphic record of activity along the San Marcos fault, the southern margin of the Sabinas basin. It is overlain by marine limestones of the Cupido Formation, and the contact is transitional. It rests on ammonite bearing strata of Tithonian age, but the contact is not well exposed. We sampled the San Marcos Formation at localities in Potrero Colorado and Valle de San Marcos, for a total of 34 paleomagnetic sites in three sections (one site=one bed). The beds dip gently to the north to northwest at all three sections.The characteristic magnetization is a dual-polarity, high coercivity, and high unblocking temperature ( > 650 deg C), northwest directed moderately positive component, overprinted by a north directed magnetization of lower stability. Occasionally, the reverse polarity magnetization (south-southwest to southeast directed) is only revealed by demagnetization trajectories. Dual polarity magnetizations within two sites suggest that the remanence acquisition process is of long duration relative to the duration of reversals. A composite section defines 9 magnetozones, and it is characterized by reversed zones of short duration relative to normal intervals. We thus correlate the magnetic polarity sequence of the San Marcos Formation with the M5 to M0 chron sequence of the Barremian to early Aptian GPTS. Site means are relatively well grouped. Tilt corrected means for each of the sections samples vary from discordant (191.7 deg , -54.9 deg ; k=40.5, alpha95=9.6 deg ; 7 accepted sites) at the base of the section to concordant (333.6 deg , 58.3 deg ; k=28.3, alpha95=12.6 deg ; 7 accepted sites) at the top of the section. The discordance at the base of the section is interpreted in terms of a small clockwise rotation related to activity along the San Marcos fault.
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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