Experimental Development of Transport Percussion Marks on Obsidian Clasts, Pilauco Site, Chilean Northwestern Patagonia
Experimental Development of Transport Percussion Marks on Obsidian Clasts, Pilauco Site, Chilean Northwestern Patagonia
Authors
Madrigal, Catalina
Lledo, Haroldo
Fritte, Daniel
Pino, Mario
Lledo, Haroldo
Fritte, Daniel
Pino, Mario
Authors
Date
Datos de publicaciĆ³n:
MINERALS,Vol.12,,2022
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Abstract
In the Pilauco site (40 degrees 34 ' 11 '' S, 73 degrees 06 ' 17 '' W; 13,570 +/- 70-12,540 +/- 90 14C year BP), a previous geochemical trace analysis suggested that the Puyehue-Cordon Caulle Volcanic Complex is the most likely source for obsidian and dacitic glass artifacts at Pilauco. It was hypothesized that the glassy rocks were probably collected from a pebble beach deposit, as deduced by the presence of crescentic percussion marks on the artefact cortexes. An experimental study was designed using pebble obsidian clasts. Bidirectional transport produced by the waves on a beach was imitated by an oscillating table, using time lapses equivalent to a transport of 0.7 to 20 km. One hundred clasts were randomly selected and marked. The morphological changes were registered, measured and photographed after seven sequential runs. At the end of the experiment at 20 km, the mass loss of rounded and fractured clasts was 5% and 11%, respectively. Crescent, circular, pseudo-circular and irregular percussion marks occurred in both types of clasts. In all cases, the crescent marks developed a pseudo-frosted surface appearance, giving a whiter tone that masks the black color of the obsidian, exactly as observed in the cortex of the artifacts knapped in dacitic glass at the Pilauco site. Thus, it is highly probable that the vitreous material was obtained from a beach sourced by the Puyehue-Cordon Caulle Volcanic Complex.