Early and Middle Holocene Archaeology in the Northern Great Basin: Dynamic Natural and Cultural Ecologies
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Early and Middle Holocene Archaeology in the Northern Great Basin: Dynamic Natural and Cultural Ecologies by Dennis L. Jenkins, Thomas J. Connolly, and C. Melvin Aikens The primary questions addressed in this chapter— begin to address even the most basic issues. Yet, here and in the volume as a whole—include: “were humans at the very foundation of our research, archaeologists present in the Northern Great Basin during Terminal have often made too little effort to be consistent Pleistocene times?” and “what is our current within the discipline. In this volume, we attempt to understanding of changing cultural and ecological add impetus to an important change in the reporting regimes in the Northern Great Basin during Early and and use of radiocarbon dates in Northern Great Basin Middle Holocene times?” This introductory chapter research that is long overdue. We advocate the addresses the first question in methodological terms at primary use of calibrated radiocarbon ages when the outset, and later we offer in more substantive discussing time, a convention used throughout this terms our current understanding of the key issues volume, rather than continuing to employ presented in the following papers. To deal with the conventional radiocarbon ages. second question, which is much broader, we Radiocarbon dating has undoubtedly been the summarize in a general way the contributions of the single most important method of age determination volume as a whole. It is necessary to begin, however, employed in the field of archaeology since its with preparatory discussions of the radiocarbon dating invention in 1950. But in the Northern Great Basin, as and obsidian hydration research methods and elsewhere, the radiocarbon chronology generally reporting protocols employed throughout this initial employed in regional synthetic and comparative chapter, and throughout the volume as a whole. research has lagged well behind important improvements in the dating method itself. Although it has long been clear that “radiocarbon years” do not Preliminary Notes on Radiocarbon and precisely equal calendar years, many archaeologists Obsidian Hydration Dating have continued to report their findings in terms of radiocarbon years, even though a method for Refining culture and environmental history calibrating ages in actual calendar years has been remains a primary archaeological concern in the available for some time (e.g., Stuiver and Reimer Northern Great Basin (Figure 1). Without a 1993, 2000). This poses a number of problems, both chronologic framework for each site or set of sites for the general public that “consumes” archaeological investigated, questions about the nature of settlement knowledge, and for the professionals who seek to and subsistence systems, inter- and intra-regional advance and refine that knowledge (cf. Minckley et population movements, trade, and paleoclimatic or al., this volume; Skinner 1995a; Bartlein et al. 1995). paleoecological change cannot be adequately Archaeologists’ continued discussion of ages addressed. We must, therefore, begin by clearly expressed in radiocarbon years creates confusion in stating how we are going to deal with time in our cases where written histories expressed in terms of the efforts to order the events of the past. modern Gregorian calendar do not properly match up with archaeological histories. It is also true that the Radiocarbon Dating variance of radiocarbon ages from calendar years generally (but unevenly) increases with samples The accurate depiction of past lifeways and greater than about 3000 years old, so that dates paleoecological events from the archaeological record expressed in radiocarbon years may be 1000 to 2000 requires establishing the relative ages of specimens, years or more “too young” for the Terminal features, and strata. The question “how old is it?” Pleistocene/Early Holocene times considered in this strongly affects most aspects of archaeology. If we volume, as compared to true calendar years. In don’t first think about the age of things we cannot addition, uncalibrated radiocarbon determinations may Early and Middle Holocene Archaeology of the Northern Great Basin Edited by D. L. Jenkins, T. J. Connolly, and C. M. Aikens, pp. 1-20, University of Oregon Anthropological Papers 62, 2004 1 2 Dennis L. Jenkins, Thomas J. Connolly, and C. Melvin Aikens Figure 1. Physiographic features and archaeological sites in the Northern Great Basin. appear to cluster significantly along a time-line, while determinations are the means of translating measured in reality the clustering is due to causes such as thicknesses of obsidian hydration rinds into years. fluctuating solar activity, variance in the amount of Thus, any investigative reporting involving ages atmospheric insolation from cosmic ray activity, or the determined by the radiocarbon method should begin so called “atom bomb” effect which caused an with the calibration of the radiocarbon determinations. artificial enrichment of the earth’s atmosphere with The use of dates expressed in radiocarbon years radioactive isotopes of carbon after 1945. There are has persisted despite these problems for the very good other possible anomalies as well. reason that while new calibration methods were being It is absolutely vital to employ calibrated ages of developed and improved, archaeologists felt it prudent radiocarbon dates to the application of the obsidian to continue reporting in terms of established methods. hydration dating method (see below), as radiocarbon For some years therefore, many archaeologists have Early and Middle Holocene Archaeology in the Northern Great Basin: Dynamic Natural and Cultural Ecologies 3 been careful to specify whether ages they presented Indeed, it was at Newberry Volcano on the were in radiocarbon years before present (RCYBP) or northwest edge of the Fort Rock Basin that important calendar years before present (cal. BP). We believe pioneering efforts were made by Irving Friedman the time is now upon us to shift the chronological (1968, 1977; Friedman and Long 1976). Friedman discussion over in a thoroughgoing way to calendar and Smith (1960) recognized that establishing reliable years. At the same time, we recognize the need for rates of obsidian hydration requires prior obsidian many to refer back and forth between the old and new source characterization of the dated specimens and a formats. working knowledge of the thermal history of those To this end, therefore, reported radiocarbon dates, specimens (Friedman and Long 1976; Friedman and sample numbers, the material dated (to species level, Smith 1960; Friedman and Trembour 1983). if known), sample weights or volumes (if known), and Individual volcanic sources exhibit unique chemical corresponding calibrated ages, are provided in the compositions which may affect the rate of hydration. texts and tables of the following chapters. Calibration Thus, in theory at least, each source hydrates at its has been provided by application of the CALIB own rate. However, it is encouraging to note that computer routine developed by the University of regionally clustered subgroups of obsidian sources Washington Quaternary Isotope Laboratory (Hughes 1986:290)—such as those in and around the Radiocarbon Calibration Program (Stuiver and Reimer Fort Rock Basin—apparently hydrate at similar rates. 1993; Stuiver et al. 1998). The resulting calibrated Consequently, with careful documentation of ages are designated throughout this volume as “cal. specimen associations, proper application of sampling BP.” Radiocarbon years are designated “RCYBP.” methods, and appropriate expectations directing the Readers will observe, therefore, somewhat different interpretation of the resulting data, it has been possible ages for known events than those commonly seen in to develop a robust, broadly applicable, and relatively older literature. For example, the age of the climactic accurate obsidian hydration dating protocol for eruption of Mount Mazama, previously placed about particular subgroups of obsidian sources in the 6850 radiocarbon years before present (RCYBP), is Northern Great Basin. now calculated at about 7600 years ago (cal. BP). The Theoretically, obsidian hydration offers a method age of the famed Fort Rock type sagebrush sandals, of directly addressing the age of individual obsidian previously placed at about 9000 RCYBP, is now specimens. The sample of obsidian hydration calculated at ca. 10,000 cal. BP. The controversial readings currently available for the Fort Rock Basin earliest date of 13,200 RCYBP from Fort Rock Cave offers good evidence that the method works well at is now calculated at ca. 15,800 cal. BP. many sites, though certainly not all, since some sites seem to generate more than their fair share of Obsidian Hydration Dating incomprehensible hydration measurements. For instance, obsidian hydration measurements taken on Obsidian hydration is a weathering process, specimens recovered from subsurface contexts at two involving the adsorption of molecular water on Early Holocene sites located on Buffalo Flat near obsidian surfaces, producing hydration bands that Fossil Lake in the eastern end of the Fort Rock Basin thicken with time. Production of chipped stone tools exhibit hydration thicknesses more typical of post- exposes fresh obsidian surfaces to this process, Mazama Middle Holocene sites (Oetting, this effectively setting the hydration clock of each volume). The same is true of some hydration rims on specimen. Hydration bands are visible on thin sections