restricted access 7. Geochemistry and Provenance of Archaeological Ceramics from West-Central Chihuahua, Mexico
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120 7 Geochemistry and Provenance of Archaeological Ceramics from West-­ Central Chihuahua, Mexico Philip Fralick, Pete Hollings, and Joe D. Stewart From 1989 to 2000, the Proyecto Arqueológico Chihuahua (PAC) conducted several seasons of reconnaissance and excavation in west-­ central Chihuahua (Figure 7.1) (Kelley et al. 1999, 2004). The project identified two distinct regional manifestations involving Ceramic period agricultural habitation sites: the Casas Grandes (or Chihuahua ) culture and the La Cruz culture (Larkin et al. 2004; MacWilliams 2001; MacWilliams and Kelley 2004; MacWilliams et al. 2002; Stewart et al. 2005). Chronologies for both cultures are based primarily on radiocarbon dating (Stewart et al. 2004). In the Babícora Basin and upper Río Casas Grandes, the middle Santa María Valley, and the middle Santa Clara Valley, the Viejo period (ca. AD 800–1200) featured hamlets or villages of individual houses, the latter mostly built in pits of varying depths, with a variety of pottery: undecorated, textured, painted, and textured-­ and-painted. The Medio period (ca. AD 1200– 1450; see Dean and Ravesloot 1993) included larger surface structures with contiguous rooms (­pueblos) and more elaborately painted pottery. Both periods of the Casas Grandes culture are also found north of the PAC study area (e.g., Cruz Antillón and Maxwell 1999; Di Peso 1974; Di Peso et al. 1974; Douglas and Quijada 2004; Whalen and Minnis 2001b). The La Cruz culture (ca. AD 700–1200), in the Laguna Bustillos Basin south of the Casas Grandes culture area, manifests as hamlets of individual pit and surface houses with brown pottery, undecorated except for the rare use of red paint. No later Ceramic period sites are known in the La Cruz region except for one very different cerro de trincheras (terraced hill) with undecorated pottery. One PAC research goal was to investigate regional interactions such as resource procurement and exchange, as indicated by artifact styles or the geological provenance of raw materials. In a study of obsidian artifacts (Fralick et al. 1998), we used ICP-­AES (inductively coupled plasma– atomic emission spectroscopy) and other techniques to determine the multielement geochemistry of the artifacts. This study identified four obsidian groups correlated with fractional crystallization histories of four different magma chambers. Only one-­ tenth of the 77 samples appeared to derive from more than 1 km from local sources of marekanites (nodules), which are almost ubiquitous in drainages throughout the study area (there being no known bedrock sources). The study results suggested little long-­ distance procurement or exchange of either marekanites or obsidian artifacts. Raw materials for pottery are also widely available, and we assume that there was no reason to travel long distances to obtain these bulky, heavy materials. However, there might have been social or economic motivations for the transport of finished ceramics. This chapter presents results from a geochemical study of Figure 7.1. Map of the study area showing sites where sherds and sediment samples were collected. The study area was divided into southern, western, central, and northern subareas based on the geochemistry of rhyolite samples from each (see Fralick et al. 1998 and Figure 7.2). In places, the boundary between areas was inferred due to a lack of obsidian sample locations. Figure 7.2. Experimental mixing diagrams showing the effect of adding various amounts of temper to potter’s clay. (A) Here the clay and two possible temper types form a linear array, and the pot compositions must fall along this trend line. This is the simplest scenario and the easiest to interpret when conducting provenance studies. (B) More commonly, three or more points will scatter on the diagram (here three such points are shown). If the pot includes temper from one source rock, the points will still fall on a mixing line, but if two or more source rocks contributed to the temper, the points will occupy the two-dimensional space enclosed by the source rock and clay points. (C) In A and B, the points representing pot compositions plotted near the clay composition because clay dominates the samples. This will be the case unless the temper composition has at least an order of magnitude more of a plotted element than the clay composition. By choosing appropriate elements, ratio plots can result in pot compositions being more equally distributed and visually more spread out, as shown in this diagram. 123 Geochemistry and Provenance of Ceramics potsherds and potential ceramic raw materials (Fralick et al. 2016:Table 1) from Casas Grandes and La Cruz archaeological sites...


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