High resolution chronology using rock magnetic cyclostratigraphy in the Baza basin, Southern Spain

Abstract

The Baza Basin in Southern Spain contained the largest paleolake in Europe (>600km2) and recorded Plio-Pleistocene paleoclimate and paleoenvironmental changes. A measured stratigraphic section, Barranco de los Conejos, provides a basis for facies determination, environmental reconstructions, and new chronologies. Based on comparative sedimentology, we determined the depositional environment of the section to be an embayment of the Baza paleolake and associated paludal ponds and wetlands and terrestrial environments near the northeastern lakeshore. We also developed new magnetic polarity stratigraphy and rock magnetic cyclostratigraphy on the 60m-thick section, using an oriented sample interval of 2-3m for paleomagnetic analyses and an unoriented sample interval of 0.25m for rock magnetic studies, including low field magnetic susceptibility, Anhysteretic Remnant Magnetization (ARM), and Isotropic Remnant Magnetization (IRM). IRM acquisition experiments confirmed the presence of fine-grained magnetite in the collected samples. We recovered the precessional and eccentricity Milankovitch frequencies above the 99% confidence limit encoded in the stratigraphic section with ARM data series and calibrated these results with age constraints from the magnetic polarity stratigraphy. Taken together, these data allow for higher-resolution and greater confidence in the chronology of the stratigraphic section. Precessional cyclicity occurred at significant cycles of 0.6-0.7m for both the ARM and susceptibility data series in the Barranco de los Conejos section and is correlated with the nearby, hominin-bearing Barranco León site. Based on the cyclostratigraphy, our favored sediment accumulation rate is 3.6±0.4cm/kyrs, consistent with the range of published paludal lake sedimentation rates. A new, 47m-thick section, La Fuentacica, was sampled similarly to the Barranco de los Conejos section. The same magnetic polarity stratigraphy and rock magnetic cyclostratigraphy and comparative sedimentology analyses will be applied to the new data, which will yield a more comprehensive reconciliation of the absolute ages of the archaeological sites around the Baza Basin and the reconstruction of its paleo-shoreline.