Using Geoarchaeology to Find the Sources of Raw Materials

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This article examines how archaeologists can use geoarchaeology to help determine the sources for the raw materials of artifacts.

Figuring out where ancient people got the raw materials for the tools and artifacts that they produced has historically been something of a guessing game in archaeology. Sure there were times when it was possible to conclude where the materials came from just by sight, if an obsidian blade was a certain color with flecks of another color, and there was only one source of obsidian colored thusly with in a wide area for instance, but more often than not obsidian is simply black and shiny, and could come from many different possible sources nearby.

Geoarchaeology is changing this, and it is now becoming much easier for archaeologists to trace the sources of these raw materials. This article will look at how archaeologists are using geoarchaeology to address this issue in general and also will look more closely at Sherwin Summit in California, the Kuril Islands, both of which talk about the origin points of obsidian flakes and tools.
Archaeology Tools: Using Geoarchaeology to Find the Sources of Raw Materials

Geoarchaeology is being used in many ways, with Firestone et. al. (2007) and Kennet et. al. (2009) using it to argue for the idea that an extraterrestrial impact wiped out the North American mega fauna as well as Clovis, and started the Younger Dryas cooling event 12,900 years ago and, Collard, Buchanan, and Edinborough (2009) as well as Marlon et al. (2009) using the same geoarchaeological methods to argue against the same hypothesis.

Geoarchaeology has been used to show changes in population density over time by Marwick (2005), and Linderholm (2007). When compared to such as these using geoarchaeology to find the source of raw artifact material might seem dull by comparison, but in actuality can be very important for any archaeologist that wants to draw anthropological conclusions from artifact assemblages. Sherwin Summit in central eastern California is a good example of this.

Sherwin Summit

Sherwin Summit is described by Eerkens, Ferguson, Glascock, Skinner, and Waechter (2007), their research focused primarily on finding out where the smaller obsidian flakes found at the site came from, and if there were any differences between small flakes, large flakes, and formal tools in terms of origin source. Sherwin Summit consists of 14 archaeological sites set in an 18km line between 1400 meters and 2100 meters in elevation, and nearly all the artifacts found were between 1000 and 2500 years old.

In all 406 flakes and tools were analyzed from these sites for this research, the large flakes and formal tools were analyzed using X-ray fluorescence (XRF), while the small flakes were analyzed via instrumental neutron activation analysis (INAA). The authors went into this research with the idea that smaller flakes, larger flakes, and formal tools would all have different providences. This is because smaller flakes often come from reworking of existing tools, and formal tools are only discarded when they are no longer useful, while the larger flakes are indicative of new tools being made on the site.

The authors felt that new tools would likely be coming from the nearest sources of obsidian, while the remains of older tools in the form of small flakes and formal tools would be coming from further away, as the people carried the tools which were discarded or which produced the smaller flakes during reworking with them for longer periods of time and thus transported them further from their original sources.

Comparing the data they collected on the samples from Sherwin Summit with a map of the area around Sherwin Summit shows that the author’s seem to be on the correct track in their reasoning. The two closest origin points account for 88% of the large flakes at the site, but only 77% of the small flakes and formal tools.

Encouraged by these results the authors went on to test two more areas, Mohawk Valley in northern California and Bone Cave in Oregon. At Mohawk Valley they found that the data turned out much the same way, small flakes and formal tools were more likely to be from obsidian sources that were further way, although the percentages were even more dispirit. At Bone Cave the model held good for large flakes vs. small flakes, where small flakes were 25% more likely to have come from further away then large flakes, but did not hold true for formal tools, which were statistically more likely to come from closer sources then either large or small flakes according to the data.

This anomaly of the formal tools not adhering to the model probably has more to do with small sample size (only 5 samples) then it has to do with a reflection of ancient reality, but more research is called for. Eerkens et. al.’s research at Sherwin Summit has shown that obsidian tended to travel further in ancient California then had been previously thought, and research from the Kuril Islands in the Russian Far East is showing much the same thing.

Kuril Islands

The Kuril Islands are an island chain stretching from the Kamchatka peninsula down toward the northern Japanese island of Hokkaido. Although the Kuril Islands have a volcanic history stretching back to the late cretaceous (Chudaev et al., 2006) the volcanoes there do not produce obsidian, yet obsidian artifacts are often found there. Phillips and Speakman (2009) set out to analyze this obsidian and determine where it was coming from, they determined that possible sources were several sites on Hokkaido and the Kamchatka peninsula, and began testing obsidian from archaeological sites in the Kurils using a portable XRF device.

The results show that obsidian from both places is found throughout the Kuril Islands, but that, perhaps unsurprisingly, the southern islands have more obsidian from Hokkaido, while the northern islands have more obsidian from Kamchatka. The situation on the central islands was a bit surprising, however, in that more of the obsidian there comes from Kamchatka to the north then from Hokkaido to the south. This is somewhat unexpected given that the central islands are separated from the northern islands by a very deep straight that is frequently lashed by foul weather, while getting from the southern Kurils to the central islands would be relatively easier for ancient peoples.

Both the Sherwin Summit and Kuril Island studies show that least cost path models of procurement do not always work, although Taliaferro, Schriever, and Shackley (2010) have shown them to be of some merit in the cases they looked at in New Mexico. Thus far we have been looking at using geoarchaeology to trace the source of the raw material used in making obsidian tools, but it can be put to use as a way of finding the raw materials behind other products as well.

The two examples given above are not the only instances of archaeologists using geoarchaeological techniques to help determine the source of raw materials; of course, there are many other cases out there, such as the study of roman to modern age archaeological glass done by Silvestri, Longinelli, and Molin (2010). The three examples provided are good accounts of this use of geoarchaeology in action. Finding the sources of raw materials may be one of the more pedestrian uses that archaeologists are putting geoarchaeology to, but while it might not be flashy it is interesting and very important in helping to develop an understanding of past peoples and cultures.