pXRF – Tree Time Archaeology

Top 10 Sites of 2019!

We are heading into the fall of 2020 and the season crunch is in full swing! We have been pretty busy, despite the challenges of COVID-19, and have found quite a few new and exciting sites. This makes us recall the sites of 2019! It was hard to make time to write up what we found in 2019. Although we find over 100 sites every year, these sites stand out either because we found interesting artifacts or the site is unique in some way.

GgPs-6: Found while assessing a proposed cutblock for Vanderwell Contractors near Swan Hills, AB. The site is located on an irregular ridge surrounded by muskeg and set back from a small lake. At this site we found an asymmetrical projectile point made of quartzite. The projectile point doesn’t fit any of the established diagnostic styles known in Alberta, but could possibly be a hafted knife similar to this knife we found back in 2014.

GgPs-6 – Irregular shaped projectile point found at the site

FgPw-21: Found while assessing a proposed cutblock for Weyerhaeuser Pembina Timberlands near the Brazeau Reservoir. The site is located on prominent hill surrounded by muskeg. At this site we found a small biface made of purple quartzite and a utilized Knife River Flint flake. The biface appears to have been resharpened in the past and was likely once much larger. The tool was likely discarded once the flintknapper felt the tool became exhausted and unusable. The flake of Knife River Flint, is an exotic material that comes from a source in the Dakotas. Along the sharp edges of the flake, small chips we call utilization scars or wear was observed. Sometimes all a person needs is a sharp flake to get the job done!

FgPw-21 – Left : Utilized Knife River Flint flake. Right: Quartzite biface

GgPs-10: Found while assessing a proposed cutblock for Vanderwell Contractors near Swan Hills, AB. The site is located on an irregular knoll overlooking muskeg to the south. Usually we find 1-10 flakes in shovel test, which we interpret as hitting the periphery of a flintknapping scatter likely associated with a single tool production event. Sometimes we get a positive test with 30-50 flakes in a shovel test and feel we hit the knapping area dead-on. If multiple lithic materials are present it likely represents various tool production events. But at this site we hit a full-on lithic workshop! We recovered four hammerstones, five cores, and a total of 7888 flakes!

GgPs-10 – View of the site location and a small sample of the 7,888 flakes recovered!

GiPk-3: Found while assessing a proposed cutblock for Vanderwell Contractors near the Fawcett River. The site is located on a small knoll located southwest of the river and overlooking a wetland to the south. Although we only found one artifact at this site, it is a very interesting tool. The tool is a portion of an obsidian flake made using microblade core technology. The blade has some utilization wear along the lateral edges, as indicated in the picture above. As we have discussed before, obsidian is a volcanic glass and each volcano has a unique chemical signature that allows us to trace where the artifact material came from. We were able to zap this specimen with the pXRF and discovered this obsidian came from over 1700 km from Mount Edziza in British Columbia!

GiPk-3 – Brian holding up the Obsidian microblade after discovery!

FiPx-5: Found while assessing a proposed cutblock for Blue Ridge Lumber near Niton Junction, AB. The site is located on a long ridge that comes to a high point in the southeast. At this site we found a 90 m long site with flakes, cores, and one ugly projectile point. The projectile point might represent an aborted point that the flintknapper discarded. One of the lateral edges and the one of the notches are broken off, which may represent an error during tool production which resulted in the tool being discarded.

FiPx-5 – Left: Projectile point found at site. Right: View west across the site from where the point was found.

FiPx-2: Found while assessing a proposed cutblock for Blue Ridge Lumber near Niton Junction, AB. At this site we found lithic debitage, two cores and one bone awl. The bone awl is somewhat degraded and the point is not very sharp, but it appears to have been sharpened into a point at one end. The awl would have been used to pierce and mark materials such as leather and wood.

FiPx-2 – Bone awl and core found at site.

GdPu-19: Found while assessing a proposed cutblock for Blue Ridge Lumber near Swan Hills, AB. The site is located on a low southeast facing edge overlooking a relict oxbow. Although we didn’t find much lithic debitage at this site, we found two hearths (old campfires), 54 pieces of faunal remains (animal bones), and lots of charcoal. Two of the animal bones have indicators of human modification in the form of cutmarks, polish, and spiral fractures. The charcoal from both hearths and the calcined bone were all sent away for radiocarbon testing and received dates of: Charcoal Calibrated AD (1495-1650 AD); calcined bone Calibrated AD (1681-1937 AD). While not very old, this site is interesting in that it was occupied just prior to European Contact in Alberta!

GdPu-19 – Left: One of the hearths identified from which several pieces of calcined bone and charcoal were recovered from. Right: Large bone with cutmarks.

FcPx-39: Found while assessing a proposed cutblock for Sundre Forest Products near Nordegg, AB. The site is located on a west-facing terrace overlooking Dutch Creek. At this site, we found a beautiful siltstone biface preform. Much like GiPk-3 and other sites where we only find one formed tool, these sites likely represent a tool being dropped or lost by hunter or flintknapper.

FcPx-39 – Siltstone biface found at the site, marked by red flagging.

FcPx-50: Found while assessing a proposed cutblock for Sundre Forest Products near Nordegg, AB. This site is located on a series of rolling hills overlooking the North Saskatchewan River. At this site we found one biface and 15 pieces of lithic debitage. The biface is made from Red Deer Mudstone, also known as Paskapoo Chert, is a material we do not find often. Additionally, we also found one piece of obsidian which was sourced to Bear Gulch, Idaho.

FcPx-50 – Left: Red Deer Mudstone biface. Right: Obsidian flake.

FcPx-49: Found while assessing a proposed cutblock for Sundre Forest Products near Nordegg, AB. This site is located on a large prominent ridge located back from a deeply-incised stream. At this site we had 12 positive tests over 170 x 75 m area. In these positive tests, we found one siltstone biface, two cores, one animal bone, and over 1000+ flakes. Several of the flakes also showed signs of utilization wear.

FcPx-49 – Left: Siltstone biface. Right: Siltstone utilized flake.

No volcanoes in Alberta, so where does the Obsidian come from?

When working close to an obsidian source (i.e. volcanoes), archaeologist will regularely find obsidian tools and debitage. However, in the boreal forests of northern Alberta, obsidian is a rare find indeed. So to find any evidence of it at all is pretty significant. Volcanic glass, or obsidian, is one of the sharpest naturally occurring materials on earth. It is sometimes used by surgeons who require a cutting edge that is much thinner and sharper than a stainless steel scalpel. Not only is obsidian extremely sharp, but it is also relatively easy to flint knap and is used by many beginners trying to learn this ancient skill. These features made obsidian a highly valued knapping material.

Pre-contact peoples fashioned various tool types from it, such as knives, projectile points, or composite tools. One method of knapping obsidian was blade core technology. This method involves preparing an obsidian core so that a series of small blades can be removed. This method minimizes the amount of material that is wasted and allowed people to quickly reproduce blades that were a similar size and shape. These blades were then hafted to a bone or stick to create a cutting utensil. To create larger tools, obsidian would have been knapped using normal methods as well.

Obsidian blade and core — Photo credit: B. Bernard

Last summer, Tim and I were surveying some forestry cutblocks at the base of the southern slopes of the Marten Hills, east Slave Lake. During the screening process, I had targeted a series of small knolls that overlooked a muskeg. These knolls were close to the headwaters of the Fawcett River, where a natural pass would have allowed people to easily traverse through the hills. Tim and I walked to the top of the highest knoll and started digging test pits.

Brian at GiPk-3 - Copy — Brian at the GiPk-3 hill top

We were completely shocked when my first test contained an obsidian blade. At this point we were extremely excited, and were sure that we had just found a crazy site. However, even though we dug 40+ test pits, we never found another artifact. The site turned out to be an isolated find. Nuts!

So if there are no volcanoes in Alberta, where did this obsidian blade come from? Luckily, advances in technology allowed us to quickly solve this question. During his Master’s degree, Tim obtained a license to operate a pXFR analyzer (portable X-Ray Fluorescence), so Tree Time Services Inc. rented one of these devices. Other obsidian artifacts recovered by Tree Time services were all found to come from south of the U.S. border. However, the results of Tim’s analysis suggests that the blade was made of obsidian from Mt. Edziza, British Columbia.

Results of pXRF, showing range for various volcanic sources.

That means that this piece of stone had been transported/traded by Pre-contact peoples over a distance of 1700 km! At 10 km travelling distance in a day (on foot), that is 170 days, or almost 6 months. Mt. Edziza obsidian has never been found in the Lesser Slave Lake region, however is is somewhat common in the Peace Region in northwest Alberta. GiPk-3 represents one of the furthest known Mt Edziza obsidian finds from its source. Although Tim and I were disappointed that we didn’t find more artifacts, this single find provided evidence for trade networks that spanned vast distances long before European contact.

Edziza to GiPk-3 — Image Credit: Todd Kristensen

Sourcing with pXRF (portable X-Ray Fluorescence)

“Sourcing” is the study of associating artifacts with their geologic origin in order to infer human transport of materials. This field of research has revealed networks of trade and exchange among indigenous peoples in pre-contact times. But how do researchers figure out the actual source?

One method is with Portable X-Ray Fluorescence (pXRF) analysis. These instruments are used by geologists, archaeologists, and other specialists to gather chemical data of materials in a non-destructive manner. When the results are compared to known sample locations, archaeologists can infer how far the material an artifact was made from has traveled from its geological source. Take obsidian, for example. Obsidian has been found at archaeological sites thousands of kilometers from any volcano. Since there are several volcanoes in North America, identifying which artifact comes from which source affects the interpretation of trade networks.

The analyzers themselves are a very intricate piece of technology that use radiation to gather chemical data of samples. The two main components are the X-Ray tube and the detector. Radiation is emitted down the X-Ray tube towards the sample object and interacts with its surface atoms. This interaction consists of radiation knocking an electron from the atom out of place, creating a vacancy in the electron cloud. This vacancy is filled by other electrons in the atom. The electrons shed energy in the form of X-Rays as they fill that vacancy, which is emitted out and collected by the detector.

The spacing between the orbital shells of electrons in the atom is unique to that element. An atom of potassium for instance, has different spacing between the electron shells than gold or iron. So, when an electron fills the vacancy and emits X-Rays, the emitted X-Rays are equivalent to the distance that is unique to that element. The detector collects these x-rays which are diagnostic of the elements present in the sample. Internal software then calibrates the readings into proportions of all elements in the sample.

How XRF works — Simplified diagram of an XRF. Left, an X-Ray tube emits radiation onto a sample, which interacts with the surface. The emitted X-Ray data is collected by a detector. Right, The radiation ejects an inner electron from the atom. This vacancy is filled by a 2^nd (a) or 3^rd (b) layer electron. This movement of the electrons emits X-Rays.

pXRF analyzers are useful tools for archaeologists since we study culturally significant objects, and do not want to alter or destroy the artifacts we wish to analyze. They are also relatively easy to use. Although users require a certification, they are safe when operated correctly, and the data can be downloaded and interpreted quickly.

A recent study of 750 obsidian artifacts has showed that indigenous trading networks spanned thousands of kilometers. Archaeological sites in Alberta contain obsidian which originated from north, central, and coastal British Columbia, Wyoming, Idaho, and Oregon, spanning a trade network almost 2,000 km across.