Ceramic petrography of the Bacabal phase (sambaqui Monte Castelo): one of the oldest uses of freshwater sponge spicules in the Amazon

Abstract

This paper contains the results of petrographic analysis on 22 ceramic fragments from the Bacabal phase of the Monte Castelo shell mound (Rondônia), one of the oldest Amazonian potteries dating up to 4,000 years BP. The petrographic analysis confirmed the high frequency of freshwater sponge spicules (cauixi) as a non-plastic, with novel data on the distribution of spicules that allow us to infer the process of ceramic paste preparation and vessel manufacture. The same proportion between clay matrix and sponge spicules was maintained throughout all Bacabal layers, independent of individual variations for each element. This allows us to infer the existence of a pottery recipe maintained throughout the Bacabal occupation of the site. The same type of sponge spicule described in the ceramic paste was identified in clayey sediments surveyed in the region, although at a lower frequency. Thus, the manufacture of Bacabal ceramics could have involved a combination of: selection of spicule-rich clays; and intentionally added sponge spicules. Sponge spicules in the Bacabal pottery represent an exceptional case for research into the development of ceramic technologies supported by the use of these non-plastics, which became popular during the Upper Holocene in the lowlands of South America.