Cyclicity and NRM acquisition in the Armantes section (Miocene, Spain): Potential for an astronomical polarity time scale for the continental record

Abstract

The results are presented of a detailed study of a short (250 kyr) interval from a cyclically bedded continental sequence that is composed of alternating reddish silts and whitish limestones (Armantes section, Central Spain). The lithology as well as the carbonate and gamma-ray records indicate that five small-scale cycles are developed in one large-scale cycle, implying that the small-scale cyclicity is related to precession and thus caused by climate forcing. Rock magnetic experiments show that the NRM is carried by hematite and magnetite/maghemite and that the relative contribution of hematite is related to lithology. The positions of the reversal boundaries can reliably be determined, even though reversals of the magnetite and hematite components appear to be recorded at slightly different levels. We conclude that the well-developed cyclicity and the good paleomagnetic properties of the sediments will enable the construction of an astronomical polarity time scale (APTS) for the continental realm. Copyright 1997 by the American Geophysical Union.