Dating of the Valsequillo volcanic deposits: Resolution of an ongoing

archaeological controversy in Central Mexico

Darren F. Mark, Silvia Gonzalez, David Huddart, Harald Böhnel

“…Perhaps the most spectacular challenge to the ‘Clovis First’

model was the reported presence of human footprints within

a basaltic ash (Xalnene Ash, Valsequillo Basin, Central Mexico),

dated to 38.04 _ 8.57 ka using optically stimulated luminescence

(OSL; Gonzalez et al., 2006a). However, Renne et al. (2005) challenged

the validity of the footprints by dating lapilli from the Xalnene

Ash using 40Ar/39Ar and reported an age of 1.30 _ 0.03 Ma

(2s). Renne et al. (2005) also reported a reversed palaeomagnetic

polarity for the ash, consistent with deposition during chron C1r.2r

(Cande and Kent, 1995). Such antiquity casts considerable doubt on

the interpretation of the impressions as human footprints…”

“…In attempt to resolve the controversy surrounding the age of the

Xalnene Ash, we report new 40Ar/39Ar data for the volcanic rocks of

the Valsequillo Basin (Fig. 1A). We sampled basaltic lava flows and

alkaline tuffs from the Valsequillo stratigraphic sequence to

• anthropology
• geology
• geoarchaeology
• migration