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Keywords:

  • magnetostratigraphy;
  • Rio Sacuz;
  • Latemar;
  • cyclostratigraphy

Abstract

[1] A new magnetostratigraphy and magnetic susceptibility cyclostratigraphy from Middle Triassic basinal sediments at Rio Sacuz, northern Italy, suggests a depositional duration of ~1 myr for most of the 670 m carbonate Latemar Platform, giving a high-resolution estimate for the duration for the Latemar's deposition. The new magnetostratigraphy from Rio Sacuz clarifies the ambiguities in a previous magnetostratigraphic study of the Latemar caused by lightning strike remagnetizations. Our Rio Sacuz study was unaffected by lightning. Using thermal demagnetization, we show a Normal-Reversed-Normal-Reversed sequence at the Latemar-correlated locality of Rio Sacuz. With a polarity interval duration of ~0.25–0.5 myr for the Middle Triassic, this gives a depositional duration of ~1–2 myr. Rock magnetic experiments show that the magnetic carrier is magnetite, suggesting a primary, depositional-age remanence. Measurement of magnetic susceptibility at 1 m intervals from Rio Sacuz reveals eight short eccentricity cycles (~95–125 kyr) bundled into slightly more than two 405 kyr long eccentricity cycles indicating a more precise duration for the Rio Sacuz section of 0.8 to 1 myr. The shorter depositional duration required by this study forces a sub-Milankovitch time scale of 1–2 kyr for the Latemar platform's meter-scale rhythmic bedding and provides strong evidence for nonorbitally driven climate change in the Middle Triassic.