14C AND MARINE RESERVOIR EFFECT IN ARCHAEOLOGICAL SAMPLES FROM THE NORTHEAST GULF OF CALIFORNIA (original) (raw)
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American Antiquity, 2012
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 shel...
Journal of Archaeological Science, 2002
During the Late Holocene, a number of new technologies (single-piece fishhooks, toggling harpoons, plank canoes, etc.) are thought to have significantly enhanced the fishing capabilities of California coastal peoples. The single-piece fishhook, perhaps the most common of these artifacts, appears to correlate with a regional intensification of marine fishing and a period of increased population growth. Determining the antiquity of the single-piece fishhook has been complicated by a variety of taphonomic and methodological factors. Consequently, age estimates for the initial appearance of these artifacts range from about 5500 to 2500 cal-. To help clarify the chronology of this important artifact type, we had eight of the potentially oldest shell fishhooks in the region AMS radiocarbon dated. These dates indicate that the single-piece shell fishhook appeared throughout the southern and central California Coast by at least 2500 cal-. Our data illustrate the utility of direct AMS dating of individual artifacts as a method of documenting site disturbances (bioturbation, historical land use, etc.) and refining artifact, site, and regional chronologies.
American Antiquity, 2004
In many regions, fluctuations have occurred through time in the local 14C activity of seawater. Evaluating these shifts and their effects on 14C age estimates is difficult, and, as a result, archaeologists working in coastal settings tend to preferentially date charcoal samples over shell. Our research on 18 charcoal–shell pairs from Puget Sound and Gulf of Georgia archaeological sites helps elucidate the spatial and temporal dynamics associated with marine reservoir effects in the Pacific Northwest. This analysis suggests that between 0 and 500 B.P. the regional correction value (ΔR) is 400 years, which agrees with the modern value determined by Stuiver and others. Between 500 and 1200 B.P., however, ΔR dips close to zero, possibly reflecting a decrease in offshore upwelling. From 1200 to 3000 B.P., ΔR returns to 400 years. These data are presented as a Puget Sound/Gulf of Georgia regional correction curve for the late Holocene, which local researchers may use to calibrate dates of...
2016
ABSTRACT. Consistently large differences occur in the calibrated 14C ages of stratigraphically associated shell and charcoal samples from Kilometer 4, an Archaic Period archaeological site located on the extreme south coast of Peru. A series of nine shell and charcoal samples were collected from a Late Archaic Period (~6000–4000 BP) sector of the site. After calibration, the intercepts of the charcoal dates were ~100–750 years older than the paired shell samples. Due to the hyper-arid conditions in this region that promote long-term preservation of organic material, we argue that the older charcoal dates are best explained by people using old wood for fuel during the Middle Holocene. Given this “old wood ” problem, marine shell may actually be preferable to wood charcoal for dating archaeological sites in coastal desert environments as in southern Peru and Northern Chile.
HOLOCENE MARINE RESERVOIR TIME SERIES ∆R VALUES FROM CEDROS ISLAND, BAJA CALIFORNIA
∆R values have been calculated based on offsets in radiocarbon values exhibited in a series of stratigraphically paired charcoal and marine shell values, ranging from about 300 to 10,000 BP, excavated from archaeological sites on Cedros Island, Baja California, Mexico. Based on this data, there appears to be the equivalent of about an 800-yr range in inferred ∆R values (-400 to 400 yr) exhibited in Holocene-age marine shells from this portion of the central Baja California coast.
A Radiocarbon Chronology of Hunter-Gatherer Occupation from Bodega Bay, California, USA
Radiocarbon, 2005
We present a Holocene radiocarbon chronology of hunter-gatherer occupation based on contemporaneous samples of charcoal and Mytilus californianus shell recovered from 7 archaeological sites near Bodega Bay, California, USA. A series of 127 14C ages reveals a chronological sequence that spans from 8940–110 cal BP (1 σ). This sequence serves as a foundation for the interpretation of behavioral change along the northern California coast over the last 9000 yr, including the adaptive strategies used by human foragers to colonize and inhabit coastal areas of this region. These 14C ages will also permit us to explore major dimensions of temporal change in Holocene ocean conditions (via marine reservoir corrections) and their potential effect on the resources available to ancient hunter-gatherers.
Archaeologists interested in radiocarbon dating shell midden sites express concern regarding the accuracy of shell dates and how such determinations should be interpreted. This article discusses the problem of dating shells from sites in the southeastern United States. New results are presented comparing shell, bone, and soil-charcoal age determinations from the Crystal River site, located along the west-central Gulf Coast of Florida. Crystal River is a large multimound site whose occupants engaged in long-distance exchange throughout eastern North America during the Woodland period (~1000 BC to AD 1050). In the summer of 2012, test units were excavated in several contexts at the site, including both mounds and occupation areas. Samples were collected for 14 C dating, which were then processed at the University of Georgia Center for Applied Isotope Studies. This article focuses on samples from the stratified shell midden, from which it was hoped to construct a local correction for marine shell that could be used to date other contexts. The soil-charcoal and bone collagen from these samples have very similar ages (bone samples ranging from about 100 cal BC to cal AD 530 and soil-charcoal from cal AD 345 to 560); however, the shell samples collected from the same stratigraphic units are significantly older than the terrestrial dates (ranging from 1300 to 390 cal BC). The difference in calibrated ages between organic materials and the shells ranges between 560 to 1140 yr. This phenomenon cannot be explained solely by the marine reservoir effect. It appears that all the shell samples formed in mixed marine (~50−60%) contexts, as indicated by the stable isotope ratios and the amount of atmospheric carbon remaining in the samples. The age of the shell samples cannot be used to date archaeological events as they are influenced not only by the marine reservoir effect, but also the local hardwater effect, which makes them significantly older.
2008
The dating of historic or protohistoric Pericú Indian skeletons from the Cape Region of Baja California Sur yield radiocarbon results that appear younger than their actual age. This pattern appears to result from problems inherent in all radiocarbon dates of marine origin, including the skeletons of ancient people who derived their food from the sea. This paper is an archaeological case study, showing that marine and terrestrial radiocarbon samples of the same depositional age can lead to confusion about patterns of historic versus prehistoric cultural development. Problems of Coastal Radiocarbon Dating No innovation has done more to revolutionize modern archaeology than the advent of radiocarbon dating shortly after World War II (Fagan 2000; Taylor 1987). Before the introduction of 14C (carbon 14) dating, prehistoric archaeologists could construct regional chronologies of cultural development based only on the study of artifact styles. Aside from limiting the time available for stu...