Archaic Period Shell Middens, Sea-Level Fluctuation, and Seasonality: Archaeology along the Northern Gulf of California Littoral, Sonora, Mexico

Abstract

Five recent radiocarbon assays on wood charcoal within archaeological sites from the Puerto Peñasco area, Sonora, Mexico indicate use of the marine resources of the northern Gulf of California area during the Middle Archaic through the Late Archaic periods, ca. 3800 B.C.–A.D. 100. The archaeological shell middens of the region are generally thought of as remains associated with Ceramic period Hohokam marine shell collecting forays with there being little consideration given to the likelihood of an Archaic period component being present. The importance of these age estimates is that they are derived from carbonized botanical remains rather than shell. Because of considerable variability in the carbon reservoir effect, age estimates derived from marine shell from the northern Gulf of California have limited reliability. The seasonality of collection is also considered through a preliminary study of stable oxygen isotope ratios in two shell samples. The results suggests that these shellfish were collected in the late fall, winter, and perhaps very early spring.

14C and Marine Reservoir Effect in Archaeological Samples from the Northeast Gulf of California

“…The ages of middens used in this study range from about 5700 to 1900 yr old (calibrated age before present) and they are located along a 45-km-long reach of the Sonora coast near Puerto Peñasco (Table 1 and Figure 1). The ages of five of these midden layers were originally published in Foster et al (2012) and charcoal from an additional midden layer at Locus 3, Level 1 was added with this study (Figure 2). In order to reduce the chances of dating what was old wood in the landscape at the time of cooking the shell, we dated small individual twigs less than 5 mm in diameter.…”

“…Bulk sediment was collected from the six midden horizons selected for dating and dry-sieved. Charcoal fragments were picked and identified when possible, and single pieces were used for 14 C dating (Foster et al 2012). Shell associated with the midden horizon was also collected and identified.…”

“…Quaternary faulting has been most active along the Baja coast and at the mouth of the Colorado River, whereas the Sonoran coast between Bahia Adair and Puerto Peñasco appears to have been tectonically stable (Ortleib 1991). Midden sites along the Sonoran coast remain close to sea level in elevation and are occasionally buried by sand migration (Foster et al 2008(Foster et al , 2012). Since eustatic sea-level stabilization ~6 ka, geomorphic changes along the far northern gulf coast have been dominated by longshore drift, delta progradation, and migrating dunes, periodically punctuated by powerful eastern Pacific tropical storms that can redistribute large volumes of sediment and significantly alter barrier islands, inlets, and lagoons.…”

“…This suggests that many are temporary use sites, where shellfish were collected live from shallow water, piled on the sand with small local burnable plants (e.g. mesquite and saltbush), and cooked (Foster et al 2012). This cooking method results in small pieces of charcoal associated with shells that are burned and covered with charred carbon.…”

“…The northern end of the Gulf of California has a long history of human activity, much of which was focused on exploitation of marine food, salt, and shell for use in trade (Haury 1976;Foster et al 2012). Because of the frequent exploitation of marine resources, many archaeological sites along the coast of the northern Gulf of California are shell middens that often contain remains of other marine and terrestrial fauna.…”