T84 A Matter of Time: The Stratigraphic Record of Time and the Future of Timescale Calibration

Tuesday, 27 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

SEDIMENTATION RATES FROM ROCK-MAGNETIC BASED CYCLOSTRATIGRAPHY, PALEOMAGNETIC RESULTS, AND ELECTRON SPIN RESONANCE DATING DISAGREE AT THE BAZA PALEOLAKE, SOUTHERN SPAIN

Paper number: T84-13
Program: Technical Sessions
Time: 4:20 PM – 4:35 PM

Authors

Abstract

New chronologies recovered from Baza paleolake strata confound interpretation of earliest hominin migration through southern Spain. Baza Basin archaeological sites have yielded lithic tools, animal bones, and a hominin molar, the supposed oldest human fossil in Western Europe. Two measured sections near the Barranco León archeological site, Barranco de los Conejos-Barranco de la Losa (BC-L) and La Fuentacica (LF), provide a basis for facies determination, environmental reconstructions, and new chronologies. The sections were sampled for paleomagnetic and rock magnetic investigation every 2-3m and 0.25m, respectively, and for Electron Spin Resonance (ESR) absolute dating. Using comparative sedimentology at each section, the environments of deposition are interpreted to be an embayment of the paleolake and associated ponds, wetlands, and terrestrial environments near the northeastern paleolakeshore. Paleomagnetic data for the ~60m BC-L section recovered a local magnetic polarity stratigraphy of R-N-R-N. The lower N polarity interval has previously been interpreted as the Olduvai subchron and the upper R polarity interval as the Matuyama subchron. The ~47m LF section revealed only reversed polarity specimens in the magnetic stratigraphy. Rock magnetic measurements included low field magnetic susceptibility (MS), Anhysteretic Remanent Magnetization (ARM), and Isothermal Remanent Magnetization (IRM). IRM acquisition experiments confirmed the presence of magnetite in all of the samples. Milankovitch cycles and corresponding accumulation rates were recovered from the MS and ARM data series by determining significant stratigraphic cyclicity. Precession occurs at cycles of ~0.6-0.7m for both the MS and ARM series in the BC-L section and yielded a sediment accumulation rate of ~3cm/kyr. Long eccentricity was recovered from the LF MS data, yielding a sediment accumulation rate of ~5.5cm/kyr. This faster rate could explain the lack of polarity change encoded in the LF section. ESR results at two horizons in the BC-L section revealed ages of ~1Ma, broadly consistent with the accumulation rates, but not the magnetic polarity stratigraphy. Continued disagreement between data sets still prevents an absolute age determination of hominin presence in the region.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357783

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