Both archaeological traditions previously mentioned employed different mobility strategies to satisfy their needs. This work proposes that these strategies can be identified through petrological analysis (stereographic microscope, thin section petrography and X-Ray fluorescence) applied to sediment samples and to the paste of ceramic sherds. 

Figure 2. Trincheras tradition painted pottery sherds: a) Trincheras Purple on Red; b) Trincheras Purple on Brown; c) Altar Polychrome; d) Nogales Polychrome.

Figure 3. Costa Central tradition pottery sherds: a) Tiburón Plain; b) Late Tiburón.

28 thin sections of ceramic sherds and sediment samples were prepared at IG-UNAM. The materials were analyzed in UNISON, in the Mineralogy and Petrology Laboratory of the Department of Civil Engineering and Mining, as well as in the Department of Geology. One of the contributions of this research was the grouping of several samples in a single glass slide, which proved to be quite efficient, cost effective and time saving, as well as allowing easier comparison between samples during analysis under the petrographic microscope.

Figure 4. Thin sections of ceramic sherds.

With the analysis mentioned, it is possible to identify distinct groups belonging to the Trincheras and Costa Central traditions. This study suggests that the presence of both traditions on sites inland and in the coastline is the result of mobility strategies employed by the producers, users and/or carriers of the archaeological materials analyzed. Eight petrographic groups were identified: four belonging to Trincheras (A, B, C, D) and four to Costa Central (E, F, G, H); the characterization of temper in the paste through stereographic microscope allowed the observation of materials not present in the thin sections. XRF analysis also confirmed the presence of distinct geochemical groups between both traditions.

Figure 5. Trincheras tradition petrographic groups.

Figure 6. Costa Central tradition petrographic groups.

By using geological maps of the study area as well as ethnographic analogies of the Tohono O’odham (Fontana et al. 1962) and Comcáac (Bowen & Moser 1968) (both indigenous groups inhabiting the same area as the Trincheras and Costa Central traditions), this work proposes that Trincheras vessels were manufactured in two distinct regions: inland, in the Rio Concepcion Basin, and near the locality of Puerto Libertad along the coastline. It also proposes that Costa Central vessels were manufactured along the Rio San Ignacio Basin.

Figure 7. Proposed provenance of the analyzed ceramic sherds.

Conclusions:

Eight distinct petrographic groups were identified between the Rio Concepcion and Rio San Ignacio basins. The petrological techniques employed enabled the identification of tentative places of origin for the analyzed ceramic sherds. At the level of analysis, it was not possible to identify specific deposits of the materials in the temper of the paste. There is no evidence suggesting that the Trincheras and Costa Central traditions shared raw material sources.

Acknowledgments:

I would like to thank Universidad Nacional Autónoma de México (UNAM), Laboratorio de Mineralogía y Petrología of the Universidad de Sonora (UNISON), and DGAPA-PAPIIT for the grant provided to support the writing of my undergraduate thesis. I also thank my thesis supervisor Dr. César Villalobos and my thesis advisor and guide in petrographic analysis Dra. Alejandra Gomez.