Cyclostratigraphy and rock‐magnetic investigation of the NRM signal in late Miocene palustrine‐alluvial deposits of the Librilla section (SE Spain)

Abstract

We constructed a high‐resolution time frame for the cyclic continental palustrine‐alluvial section of Librilla (SE Spain) which covers the onset of the Messinian salinity crisis in the marine realm. The section was dated earlier by Garcés et al. [1998] , using magnetostratigraphy. We resampled part of the section that contained a reversed overprint in detail to refine the magnetostratigraphy and to investigate the behavior of the natural remanent magnetization (NRM) signal. The detailed sampling yielded a better constrained position of the upper reversal of Chron C3An.1n. By counting the number of cycles in C3An.1n and taking into account the duration of this Chron, we were able to show that the basic sedimentary cycles in Librilla reflect climatic precession. Subsequently, the sedimentary pattern was tuned to the summer insolation curve, providing a high‐resolution time. Two intervals of complex NRM behavior were identified, showing normal and reversed overprints. The reversed overprints seemed to be restricted mainly to gray palustrine layers. The analysis of coercivity components revealed no difference between samples with overprints or real NRM directions. We performed fuzzy c ‐means cluster analysis on a geochemical data set to link magnetic behavior to geochemical proxies, resulting in a three‐cluster model that roughly describes lithology. Remarkably, all the samples with a normal overprint belong to one particular cluster. The reversed overprints, however, do not show any relation to the cluster partition. We favor the explanation of Garcés et al. [1998] that the reversed overprint would be related to the Messinian salinity crisis.