New Dating Results

The results of the new dating programme indicate that the human and animal footprints preserved in the upper part of the Xalnene Ash are older than 40,000 years. See figure below:

 

New dates for the Barranca Caulapan and Toluquilla quarry

 

 

 

Barranca Caulapan river sands and gravels,
stratigraphically above the Xalnene ash

 

 

The results derived from different dating methods indicate that the Valsequillo gravels from the Barranca Caulapan area range in age from the Late Pleistocene, around 40,000 years ago, to the early Holocene, around 9,000 years ago. It is important to note that the Barranca Caulapan sands and gravels analysed were taken from strata geologically younger than the Xalnene ash layer in which the footprints were preserved.

 

The mammoth molar was dated at approximately 27,000 years old using ESR; while an organic ball in the gravels was dated at 25,000 years old using C¹⁴. These materials were transported and incorporated into the fluvial sequence of the Barranca Caulapan.

 

However, the mollusc shells are in situ in the deposits and were dated between 27,000 and 39,000 years old using C¹⁴.

Attempts were made to date the Xalnene ash using Argon-Argon dating but the amount of potassium present in the ash was too low for a reliable age determination.

 

More successful was the Optically Stimulated Luminescence (OSL) method to date quartz crystals found in baked lake sediments incorporated into the ash (as xenoliths) and secured an age of around 40,000 years. The sample was taken from the working quarry, 200m south from where the footprints were found.

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