Wednesday, October 27, 2010

Coring & Augering

Generally, my opinion of the Park Safari and its excavators is that we are all a rugged bunch. We dutifully and energetically attend to our trench as we did our first test pits.

But say we were not able to dig our systematic test pits and were unaware of the basic stratigraphy of the site- what then? There are a variety of other methods used to examine the innards of a site without actual excavation, saving both cost and time.

First and most simply are the techniques of augering and coring. These methods originated in the geology when it was used to understand the fluvial deposits in the Mississippian Delta region in 1935 (Stein 1986, 506). Once applied to archaeology in the same region, it was used to discern cultural from non-cultural deposits in an area of interest as well as compared to the geological findings to establish a relative chronology. Following the advent of radiocarbon dating, coring and augering became more of a resource for gathering testable material below the surface.

Augering is the more destructive of the two, requiring a drill of varying sizes bored into the ground and returning the soils from below. It can pull up in bucket sized increments the layers which it has disturbed, but they are by no means intact and sufficient for accurate study. To penetrate to large depths of several meters a motorized drill is often used to power the auger.

Alternatively coring involves small tubes- about 3cm in diameter- to be pushed into the ground at predetermined depth intervals and shaken forth to pull up a sliver, albeit a compacted one, of earth representing the stratigraphy of the ground below. It is officially defined by Stein as “a continuous section of sediment or rock obtained by using a hollow cylinder called a corer” (1986, 505). If to be used with radiocarbon or chemical testing, this sample preserves more accurately the layers below.

Similarly, soil testing is common practice in locating indications of human activity; phosphate testing is used to locate where the original chemistry of an area has been disturbed by either fire pits or concentrations of human activity, as when nutrients are removed from the soil by activity, or added in with refuse decomposition (Roskams, 55). At Park Safari we based the site of the trench (PS2010TR-1) on readings taken from the methane peepers set up by the McGill Geology department.

If we were completely unaware of the stratigraphy at the Park Safari graveyard, coring would act as an inexpensive and expedient method for understanding the layers we would encounter upon digging: these would be the organic layer, the mineral layer, and then the yellowish clay layer indicating artifact sterility. Were we to come upon a deposited layer, or animal remains, it would indicate a ‘cultural’ layer, which would then be plotted to a map for overall reference. Our overall picture of the graveyard, however, is severely lacking; there are no known burial sites except for those which have already been uncovered and in the middle of the western field stands what believed to be an old structure and our only indications are from the methane emission readings. A systematized augering test done at intervals through the mounds and vegetation would illuminate concentrations of articulated or non-articulated bones, therefore grave sites (like of lions).

In the last few decades a range of machines have been developed that create images of the sub-surface, blasting far beyond the WWII era aerial photography techniques of mapping. As they lay far beyond our budget, I include only a most special machine in this short post: Ground Penetrating Radar (GPR). The cause of a local stir both within and without the department of Anthropology, a newly acquired (or currently being acquired, depending on tense implications, and $$ allocations) GPR machine. In simple terms, GPR functions by sending microwave pulses (300-500MHz) below the surface, and creates an image based on velocity reduction of the wave once it has passed through a denser object (Kvamme 2005, 436-7). This method is highly depended on soil types and water content; our flooded trench, for example, would indicate we stand upon a rocky pond. On some days, indeed this is what I’ve come to believe too. But there is a lion in there somewhere.

Kvamme, K. 2005. Terrestrial Remote Sensing in Archaeology. In: Maschner, H.D.G., Chippindale, C. (Eds.), Handbook of Archaeological Methods. Lanham, MD: AltaMira Press, pp. 423-77.

Roskams, S. 2001. Excavation. Cambridge: Cambridge University Press.

Stein, J.K., 1986. Coring Archaeological Sites. American Antiquity 51, 505-527.

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