Clovis and Folsom Age Estimates: Stratigraphic Context and Radiocarbon Calibration

Article excerpt

The events to do with peopling the New World archaeologically represented by 'Clovis' and 'Folsom' have been - tantalizingly - beyond the range of radiocarbon calibration. Now calibration extends further, one can ask if the abruptness of Clovis, of Folsom, and of the transition between them are realities. A calibrated chronology for those sites where the stratigraphic security is best shows these in truth are rapid human affairs.

Introduction

In the late 1920s, the discovery of several fluted projectile points associated with skeletons of an extinct species of bison convinced the archaeological profession that human populations had entered the New World sometime between 10,000 and 25,000 years ago (Wormington 1957). This age was at least twice that previously accepted by the professional community. These fluted projectile points - given the name Folsom points after the nearest New Mexico town - had not previously been known (Meltzer 1989).

In 1932-33, larger and more robust fluted points were found in situ at the Dent site in Colorado. Their association with the skeletons of a dozen mammoths led to the idea that these Folsom-like points (they were not as yet called Clovis) were used to kill mammoths, while the more delicate Folsom points were used to kill smaller game, like bison (Wormington 1957). In 1936 and 1937, near Clovis, New Mexico, a robust fluted point was found again with mammoth bones. However, these materials were in sediments stratigraphically below a deposit containing Folsom points associated with bison skeletons. This resulted in the robust form being recognized as older than Folsom and being named Clovis points.

For over half a century, the stratigraphic separation of Clovis and Folsom has persisted, while nearly a dozen stratified Clovis sites and several dozen stratified Folsom sites have been scientifically excavated. Since the early 1950s, 14C age determinations have been obtained on a variety of materials associated with, or purported to be associated with, Clovis and Folsom materials. In addition, using primarily dendrochronologically dated wood to provide known age controls, systematic anomalies in the 14C time scale over the Holocene were documented. Unfortunately, Clovis 14C and most of the Folsom 14C values lay beyond the reach of the dendrochronologically based calibration database. However, from time to time, questions were posed as to the possible effect of calibration on the Clovis and Folsom 14C values if the calibration database was ever extended (e.g. Haynes 1971; Taylor 1987; 1991; Meltzer 1995; Batt & Pollard 1996). With the availability of paired uranium/thorium (234U/230Th) and 14C samples from cores drilled into coral formations, a pre-dendrochronological calibration 14C data base has now been developed (Bard et al. 1993a; 1993b; Edwards et al. 1993).

The purpose of this discussion is to consider the corpus of 14C values in light of the stratigraphic contexts of Clovis and Folsom and the physiochemical characteristics of the sample materials, to address issues associated with the extension of the 14C time frame for which calibration data has been made available using uranium-series/14C paired values, and to address what can and cannot now be confidently asserted concerning the chronological overlap between Clovis and Folsom.

Stratigraphic contexts

This discussion of Clovis/Folsom 14C data is based on the premise that the stratigraphy of most of the sites considered here can be correlated to the generalized sequence summarized in FIGURE 1 (Haynes 1984; n.d.), a view based upon the consistent stratigraphic position of fauna, flora, and archaeology from site to site (Haynes 1971; 1991; n.d.).

In FIGURE 1, alluvial unit [Alpha] represents Pleistocene streams with discharges several times greater than modern streams. Unit [[Beta].sub.1] represents terminal Pleistocene channel sedimentation following a pronounced interval of degradation represented by unconformity [Z. …