ASWT Radiocarbon Update #2

ASWT-C14 Updates-Logo

In this post you will find an update on Emily McCuistion’s progress in her radiocarbon dating learning curve, and “First Dates,” a history of the invention of radiocarbon dating excerpted from Emily’s thesis draft.

Footprints  Carbon Footprints

Since the previous update I’ve had some great opportunities to further my knowledge of radiocarbon dating.  Here are the highlights:

In the Fall of 2017, I worked with Dr. Raymond Mauldin at the Center for Archaeological Research (CAR) at the University of Texas at San Antonio, to learn how samples are chemically pretreated, or cleaned, prior to being radiocarbon dated.

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Bison hair undergoing pretreatment at CAR.

This process generally consists of an acid-base-acid sequence to eliminate external contaminants such as humic substances found in soil. We treated one unusual sample—bison hair from a Lower Pecos rockshelter—which required a little research and experimentation to determine the best pretreatment method. Prior to treating the archaeological sample, we practiced on modern bison hair, donated to us by Thunder Heart Bison for that purpose.

During Spring break 2018 I had the rare opportunity of touring DirectAMS’s radiocarbon facilities in Seattle and Bothell, Washington. Over two days I witnessed the radiocarbon dating process, from pretreatment and graphitization through measurement by AMS. The staff at DirectAMS were incredibly generous in sharing their knowledge and time with me.

Direct AMS

At DirectAMS’s lab in Bothell, WA: (left to right) Director of Laboratory Operations Alyssa Tate, Emily McCuistion, and Brittany Hundman, Director of Archaeological Services.

Also during the Spring 2018 semester, I attended a Bayesian modeling workshop held in advance of the Society for American Archaeology (SAA) conference in Washington D.C.  The workshop was located in the bowels of the Smithsonian Institution! It was put on by Drs. Tony Krus and Derek Hamilton from the University of Glasgow. It was a great, and challenging, workshop, and I’d recommend it to anyone interested in using Bayesian statistics for radiocarbon analysis—this year the workshop is again coinciding with the SAAs. For the 2018 SAAs, I presented a poster on my preliminary thesis data and proposed work. I had a lot of interest and good conversations with people from around the world who have undertaken similar projects, who shared advice and articles with me—a fruitful trip to D.C. all around!

This past fall, Dr. Black and I were invited to participate in a Texas Archeological Society poster symposium on radiocarbon dating across Texas. Participants were asked to chart radiocarbon dates for their region (ours was the Lower Pecos Canyonlands) using summed probability distributions (SPDs). 000479For our poster we investigated patterns in an SPD of all dates from Lower Pecos rockshelter sites—open sites were excluded to avoid preservation biases encountered at open sites—and an SPD of directly-dated desert succulents (i.e., sotol, agaves, prickly pear, and yucca).

I would like to thank Texas State University and the Texas Archeological Society for financially supporting my thesis trips and research, the staff at DirectAMS, and many people in the Texas archaeology community who have helped me on this long learning curve. I’ve still got a distance to go.

If you’d like to get in touch, please email me at: erm63@txstate.edu. Thanks for reading!

 

First Dates: A review of the early history of 14C

The radiocarbon dating method was published a week before calendar pages turned to January 1950 (Arnold and Libby 1949). January 1, 1950 would, in time, become a significant placeholder on the Western time scale: day-zero Before Present (BP). The year 1950 was elected to divide radiocarbon time because global atmospheric carbon levels were, by then, drastically altered by human activities. Fossil fuel emissions decreased quantities of 14C (the Suess Effect) while atomic testing resulted in increases in the production of 14C (known as bomb carbon) (Taylor and Bar-Yosef 2014:23). It has also been proposed that “BP” stand for “Before Physics,” meaning before atomic testing, to avoid the confusion of “present” (Flint and Deevey 1962). The year A.D. 1950 represents a turning point in chronometrics and is an homage to Willard Libby and his colleagues’ accomplishment. Arguably, “BP” is also a symbol of an increasingly secular world, one in which scientific breakthroughs such as the atom bomb were rippling across the world.

The roots of radiocarbon science predate Libby’s 1949 accomplishment. Many others’ work laid the foundation upon which radiocarbon dating was born. Just 15 years before, it was not known that 14C existed at all. Physicist Franz Kurie was the first to publish suspicions that 14C may be artificially created (Kurie 1934), based on anomalous particle behavior (recoil tracks) seen when 14N was bombarded with “fast neutrons” in a particle accelerator; if the recoil tracks were from a proton being ejected, and not from an alpha-particle, 14N must transform into 14C. Imagery of the recoil tracks led Kurie to posit that it was a proton being ejected, though additional work was needed to confirm this possibility (Kamen 1963:235). The next year, two parties independently reported that the same particle behavior could be created with “slow neutrons,” though it was still uncertain whether the particle was a proton.

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“Wild Bill” Libby. Photo Credit: Columbia University.

In 1936, further support for Kurie’s supposition came from a study by Burcham and Goldhaber, which showed that the particle emission produced in this interaction was almost certainly a proton. Also in 1936, physical chemist Martin Kamen completed a doctoral dissertation for which he examined 730 recoil tracks; his observations were the same as those made by Kurie (Kamen 1963:236). In 1937, Kamen and Kurie began working together at the Berkley Radiation Laboratory with the aim of investigating neutron-nuclear interactions. At this point the existence of 14C was sufficiently proved, at least in a laboratory setting, though little was known about the isotope. It was believed that 14C was an unstable, radioactive, isotope, and that the half-life was short—mere hours or days, or at most, months. However, this was yet to be confirmed.

The late 1930s were a time of burgeoning research into the use of isotopes as biological tracers. It was hoped that a radioactive-isotope of one of the abundant biological elements—Hydrogen, Oxygen, Carbon, or Nitrogen—would be found to have a long-enough half-life to be used for biological tracer studies (Kamen 1963:239). Thus, research into 14C during this time was focused on its possible utility in such applications. Technological advances in cyclotrons made by Ernest Orlando Lawrence, and internal-target preparation advances by Kamen, set the stage for the future of radioactive-isotope research.

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Interview with Dr. Martin D. Kamen (left). Photo credit: (an2_a30_11_11), University Communications. Public Relations Materials. RSS 6020. Special Collections & Archives, UC San Diego

Finally, in 1940, Kamen and Samuel Ruben, a student of Willard Libby, found that 14C had a much longer half-life than previously believed (Kamen 1963:241); however, Kamen and Ruben believed the half-life of 14C was 25,000 years (AIP 1979b)!  The inaccuracy of their half-life calculation aside, Kamen and Ruben are credited for “discovering” 14C (AIP 1979b), at least as a tool for biological and chemical research.

Not only was the 14C created in labs artificial, so were the neutrons that produced 14C through bombardment of 14N. In the 1930s it was unknown whether either neutrons or 14C occurred naturally. In the late 1930s, cosmic-ray physicist Serge A. Korff at the Bartol Research Foundation was trying to detect neutrons in natural radiation by sending Geiger counters to various levels of the atmosphere with balloons (Schuur et al. 2016:26). Eventually Korff and Danforth (1939) found increasing neutron intensity with elevation. They suggested that this was the result of cosmic radiation interacting with the atmosphere. It followed that if neutrons could be identified in the atmosphere, 14C must also be present. This study was, according to Libby, the catalyst for his radiocarbon dating work (AIP 1979b).

Willard “Wild Bill” Libby [1908-1980] graduated from University of California, Berkley with his undergraduate degree in 1931. He triple-majored in chemistry, math, and physics, and built the first Geiger counter in the United States for his senior project (AIP 1979a). In 1933, Libby was awarded his doctoral degree from Berkeley (Schuur et al. 2016:23). After receiving his PhD., Libby continued at Berkley as faculty; he is regarded as Berkley’s first nuclear chemist (Marlowe 1999:10).

It would be five years between reading Korff and Damforth’s article and Libby taking time to develop the radiocarbon method; in 1940, Libby obtained a Guggenheim Fellowship and took sabbatical from Berkley to conduct research at Princeton University. Soon thereafter, the United States’ entered World War II, and Libby went to work on the Manhattan Project at Columbia University to develop atomic bombs. In 1945, after the war, Libby began working at the University of Chicago, which was then becoming the leading institution in atomic sciences. It was there, at Chicago’s Department of Chemistry and Institute for Nuclear Studies, that Libby would develop radiocarbon dating. Thirty years later, when asked why he was the person to come up with the method and not someone else, Libby answered that the obstacle for others was the idea of global mixing: “Here I was talking about the ocean, I mean the entire ocean mass, the entire biosphere, the entire atmosphere, as though it were in my test tube…Once you get over that, the whole carbon dating thing falls into place” (AIP 1979b).

Libby’s early work with radiocarbon dating was conducted in total secrecy, for fear that funding would be withheld from him because of the outlandish-nature of this project (AIP 1979b).

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Ph.D. student Ernest C. Anderson (left) and Willard F. Libby (right). Photo credit: University of Chicago Photographic Archive, [apf1-03868], Special Collections Research Center, University of Chicago Library.

Without breaching his secrecy, Libby put a student and an assistant to researching 14C; graduate student Ernest Anderson was applied to the task of identifying the natural abundance of 14C, and James Arnold was tasked with isolating and measuring 14C. Anderson was able to complete his project by obtaining samples of modern wood from around the world, and thereby also solved the aforementioned obstacle of worldwide mixing.

The radiocarbon dating method, though conceptually straight-forward, faced several practical challenges. Libby still needed to determine if it was practicable given the costs of access to equipment, sample sizes, and time— it often took four days of round-the-clock counting to get the measurement for a single sample. In addition, Libby and his colleagues needed access to a detector that was sensitive enough to count 14C. Obtaining samples of historical materials to date was not easy, and required the assistance of archaeologists. Libby stated, “Those museum dogs were not going to give it [samples] to a bunch of physical chemists to burn up, no way” (AIP 1979b). Once samples were obtained, they required cleaning of contaminants, another step Libby cites as critical in the development of radiocarbon dating.

The shared history of radiocarbon dating and archaeology begins in 1947. At this point Libby is certain radiocarbon dating is feasible, but needs funding and access to equipment to test the method. Libby first discloses his plans for radiocarbon dating to those close to him in 1946, and in 1947 James Arnold’s father provides unsolicited Egyptian specimens to Libby, obtained from Ambrose Lansing at the Department of Egyptian Art at New York’s Metropolitan Museum of Art (Marlow 1999:11-12). The year 1947 also saw the informal creation of a University of Chicago seminar club to discuss the role of social science in the atomic age, spearheaded by Chicago researchers Harold Urey (a 1934 Nobel laureate in chemistry, and an ally of Libby’s), associate professor Harrison Brown, and anthropologist and dean of social sciences, Robert Redfield (Marlow 1999:13). That same year, radiocarbon dating was for the first time presented to an audience outside Chicago, at a Viking Fund Supper Conference. Though two-dozen anthropologists and archaeologists were in attendance, it was asked that the development of radiocarbon dating not yet be made public (Marlow 1999:19). Soon after the conference, the Viking Fund financially backed Libby’s radiocarbon dating project.

Though communication about the radiocarbon method was slow and fraught with misunderstandings, Libby’s project had well-connected advocates and plenty of interest, as well as controversy, among archaeologists. Debate swirled around who should oversee the integration of the new method into archaeology before the method was even shown to be practicable. Organizations proposed for this task included the Society for American Archaeology, the American Anthropological Association, the Committee for the Recovery of Archaeological Remains, the National Research Council, and the Viking Fund, among others (Marlow 1999). In great part the calls to delegate an organization came from fears that the radiocarbon method was going to be controlled by the University of Chicago or the Viking Fund, and that the tool would not be made available to all who sought to use it (Marlow 1999:22). There were other concerns as well, such as whether old-world archaeologists would have representation in discussions of radiocarbon dating. A historic meeting occurred in January 1948 at a Viking Fund Supper Conference with a presentation by Libby, which was well attended by archaeologists. Here, the dispute over who should represent archaeologists was settled—the American Anthropological Association was chosen as the representative body, “to collaborate with Libby’s group, coach its brethren to be scrupulous in fulfilling their reciprocal responsibilities, and mediate the inevitable disputes and misunderstandings that arose” (Marlow 1999:25).

For many archaeologists at the time, radiocarbon dating was intimidating. In part this was due to its association with the atom bomb; while radiocarbon dating was not directly related to the development of the bomb, it was developed by atomic scientists and in a social climate of fear and awe of the power of the atom (Marlow 1999:23). Additionally, most archaeologists lacked the necessary background to understand how radiocarbon dating worked, and thus were reluctant to adopt the technology. Radiocarbon dating was also viewed as a threat to established dating methods and chronologies. Some even postulated that it could render obsolete their job as an archaeologist, as all the questions could now be easily answered (Marlow 1999:22-23).

The first published radiocarbon-dated samples were run on wood with known or assumed dates (Arnold and Libby 1949). These samples consisted of two dendrochronological samples, a floor fragment from a Syrian palace, two ancient Egyptian wood fragments (from a coffin and a funerary boat), and two samples from Egyptian tombs which were assayed as one sample. The measured ages were found to be satisfactory in comparison to expected dates of the samples. The half-life used to calculate the ages was 5720 ± 47 years. The study established that the radiocarbon method was useful for up to 4600 year ago and expressed the author’s hope that future research could evaluate the accuracy of the method up to 20,000 years ago. This article was radiocarbon’s seminal unveiling to the wider scientific public.

Though the new technology was discomfiting to many archaeologists at the time of its development, by the end of the 1950s it was widely accepted in archaeology as well as in other fields of study (e.g., geology); by then twenty radiocarbon labs had been established around the world, and the journal Radiocarbon was in circulation to consolidate radiocarbon date lists from the labs and ensure sufficient information was being published (Taylor and Bar-Yosef 2014:288). Most of these early radiocarbon labs were established at universities or research institutions, though one commercial lab was opened in the United States as well. In 1960, Libby won the Nobel Prize in Chemistry for the radiocarbon dating method. Taylor and Bar-Yosef point out that archaeology has only been mentioned once in a Nobel award citation, and that was for Libby’s Nobel (2014:289).

References Cited

AIP
1979a       Interview of Willard Libby by Greg Marlowe on 1979 April 12, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA. Electronic document, www.aip.org/history-programs/niels-bohr-library/oral-histories/4743-1, accessed February 9, 2019.

1979b      Interview of Willard Libby by Greg Marlowe on 1979 April 16, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA. Electronic document, http://www.aip.org/history-programs/niels-bohr-library/oral-histories/4743-2, accessed February 9, 2019.

Arnold, J. R., and W. F. Libby
1949    Age Determinations by Radiocarbon Content: Checks with Samples of Known Age. Science 110(2869):678–680.

Flint, Richard Foster and Edward S. Deevey
1962    Editorial statement. Radiocarbon 4(1):i–ii.

Kamen, Martin D.
1963    The early history of carbon-14. Journal of Chemical Education 40(5):234.

Korff, S. A., and W. E. Danforth
1939    Neutron Measurements with Boron-Trifluoride Counters. Physical Review 55(10):980–980.

Kurie, Franz N.D.
1934    A new mode of disintegration induced by neutrons. Physical Review 45(12):904.

Marlowe, Greg
1999    Year One: Radiocarbon Dating and American Archaeology, 1947-1948. American Antiquity 64(01):9–32.

Schuur, Edward A.G., Ellen Druffel, and Susan E. Trumbore (editors)
2016    Radiocarbon and Climate Change. Springer International Publishing.

Taylor, R.E., and Ofer Bar-Yosef
2014    Radiocarbon Dating: An Archaeological Perspective. Left Coast Press, Inc. Walnut, California.

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The Developing Tales of Sayles Adobe

By Victoria Pagano

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E.B. Sayles 1932 sketch map of Eagle Nest Canyon.  Note the area labeled “Sandy Adobe.” Courtesy Texas Archeological Research Laboratory, UT Austin.

Tori here, former 2015 ASWT intern and current Texas State anthropology graduate student. This season I am back leading excavations at the Sayles Adobe site as I collect data for my master’s thesis.

The terrace site of Sayles Adobe (41VV2239) sits just within the mouth of Eagle Nest Canyon (ENC), a short distance up the canyon from its confluence  with the Rio Grande. On E.B. Sayles’ 1932 sketch map of the canyon the site area is indicated as “sandy adobe,” with no mention of cultural material. Apparently, it was considered to be just a natural terrace formation.

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1958 photographs showing the site area looking toward the mouth of the canyon (above);  Skiles Shelter as viewed while standing on Sayles’ “sandy adobe” (below). Courtesy Texas Archeological Research Laboratory, UT-Austin.

 

 

During the Ancient Southwest Texas Project’s 2014 field season, the massive June 21st flood (see The Canyon Runs Deep) deposited a thick layer of flotsam atop the back dirt pile for the Skiles Shelter excavations. In order to finish filling in the open excavation units, the crew decided to take fill  from the alluvial terrace deposit nearby. This seemed like a good choice until the crew encountered fire-cracked rocks (FCR) about a meter below a thick bed of sandy Rio Grande alluvium. Digging stopped immediately and the area remained untouched (by archaeologists) until late 2015.

 

 

And so it begins..

In December 2015, a crew of five: Drs. Steve Black and Charles Frederick, Charles Koenig, Amanda Castaneda, and myself, carried out a three-day reconnaissance of the alluvial terrace and 2014 borrow pit with the idea that this as-yet-unrecorded site might make a good thesis research project.

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Discovery borrow pit, pre-clearing and post-clearing, December, 2015.

My initial observations were limited.  It was clear that the locality was an alluvial terrace and that the burned rocks that the 2014 crew had encountered were not likely just discard washing down from Skiles Shelter. But vegetation across the terrace made any sort of determination on the full extent of the site difficult. We cleared just enough vegetation to get a better idea about the morphology of the terrace. The most promising formation model is that large limestone boulders in the canyon bottom and the canyon wall created a catchment for alluvial sediment during back flooding from the Rio Grande. Repeat flood deposits created an open terrace just a few meters downstream from

IntroSayles

Current views of Sayles Adobe from the canyon rim looking toward the mouth of the canyon (above) and (below) the large boulders in the canyon bottom that seem to have formed a massive sediment trap. Skiles Shelter that could be used for certain activities between deposition events. This formation process would make Sayles Adobe a bit different in comparison to other investigated terraces in the Lower Pecos.

During this visit we worked to clear vegetation from and around the initial exposure to facilitate testing at the site. A quick surface reconnaissance (mostly on hands and knees) revealed scattered FCR on the surface at multiple locations across the terrace. Frederick and I cleaned and squared off two exposed faces of the borrow pit to examine the stratigraphy. I soon discovered a thin, compact layer of very fine silt, directly above (covering) several burned rocks amid carbon-stained matrix. Frederick recognized the silt layer as a flood (mud) drape.  The stratigraphic sequence looked very promising.

 

 

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Extent of the flood drape exposure at the end of the December 2015 visit. You can clearly see the color and textural changes.  From top to bottom: light brown sandy loam, tan silt flood drape, and burned rock and carbon-stained matrix below.

 

Understanding the Geoarcheaology of the Canyon

The excavation and analysis of Sayles Adobe is being conducted as part of my Master’s thesis research in order to reconstruct and understand the natural formation of the terrace and document the prehistoric uses of the locale. I hope to be able to address four main research questions:

  • What is the nature and timing of flood events during the human history at Sayles Adobe?
  • What can the Sayles Adobe terrace deposits tell us about the climatic and environmental conditions at the time the formed?
  • Do flood deposits at Sayles Adobe correlate to other flood deposits seen in shelters in the canyon?
  • How do site use behaviors seen at Sayles Adobe relate to other sites in the canyon?

The primary focus of our excavations will be to collect data aimed towards the cultural and natural formation processes witnessed at the Sayles Adobe terrace. This will form the foundation for my interpretation and analysis of behavioral patterns witnessed at the site.  The cultural materials and geoarchaeological samples will be analyzed and compared to the other sites within Eagle Nest Canyon.

2016 Sayles Adobe Investigations

Our first session focused on testing the Borrow Pit area that was exposed in 2014 and cleaned up in December 2015. During this time myself, Spencer Lodge, and Kelton Meyer, worked to carefully peel away the mud drape in the north to south profile (PS01) and reveal as much stratigraphy as we could.

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The mud drape could easily be “peeled” off in chunks from the charcoal stained sediment below.

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Annotated Profile Section 01 (PS01).

 

 

 

 

 

 

 

 

 

To add greater resolution to the Sayles Adobe tale, Tiffany Osburn of the Texas Historical Commission visited Sayles and carried out a ground penetrating radar (GPR) survey across the terrace. Using two different range antennas, she made multiple passes in a grid and in transects to provide us with an idea of what might be under the surface that we wouldn’t know without completely excavating the site. The GPR results  will aid in the interpretation of (and guide) further excavations at the site.

A priority of our second session at the site was to continue work in the Borrow Pit area. The ultimate goal of the work here is to create a deep profile that can be used to document and sample the natural and cultural stratigraphy of the site.

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Partially annotated results of the 270Hz GPR survey. Courtesy of Tiffany Osburn.

Using GPR data, we began working to ground-truth these results by conducting bucket auger tests that reach up to 3m deep along the East-West and North-South axis of the site.  (More on our auger testing in a few weeks, when intern Justin Ayers takes on the Sayles auger survey).

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Ongoing investigations at Sayles Adobe.

Some readers might ask, why even bother with a site like Sayles Adobe in a canyon that has such culturally rich rockshelters?  In comparison to those sites, Sayles may seem like a pipsqueak with not much to offer.  But, in truth Sayles is no less exciting or enriching than the sheltered sites. Sayles provides an opportunity to see what other activities were taking place in Eagle Nest Canyon that we can’t see in the shelters or along the canyon rim.  Our initial work shows that we have at least one sealed cultural layer that has not been disturbed by later occupation. In contrast, hunter-gatherers returned to the rockshelters time and time again, with the remains of each visit co-mingled with that of the last and mixed through pit digging, plant baking, and many other activities. As ASWT has documented in high resolution, the rockshelters have palimpsest deposits with complicated stratigraphy and few, if any, expansive areas of sealed cultural deposits.  Sayles Adobe has the potential to add a new level of understanding to human behaviors and natural formation processes of deposits in the canyon.

Our goal isn’t just to put together a chronology of the use of the canyon over the past few thousand years, it is to weave together an understanding of the people and the natural world in which they lived.  Stay tuned for further developments.

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A Sabinal arrow point has just come to light about 10 cm below the flood drape.

Rocky Midden High

By Bryan Heisinger

There is no denying that fire cracked rock (FCR) has a heavy presence in the research of the Ancient Southwest Texas Project. On a day to day basis, we sit on, trowel through, trip over, and often smell (strange.. I know) the enormous pile of FCR that fills Eagle Cave. Anyone who has worked with us long enough knows that we take our rocks seriously — and for good reason! By studying the FCR from our excavations we hope to address research questions about earth oven use and intensification in and around Eagle Nest Canyon.

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Charles loves his burned rocks.

FCR is the by-product of rocks that have been used for cooking and heating purposes. A rock becomes “fire cracked” after it is exposed to intense heating/cooling and reuse in an earth oven or other thermal environments. Continuous episodes of thermal cycling cause the rocks to fracture into smaller, angular shaped pieces and once the rocks become too small to retain heat for cooking they are discarded in favor of newer/larger rocks. The accumulation of tossed FCR typically form in the shape of ring around the oven pit and in the case of rock shelters, they begin to form talus slopes. Ultimately, this ring or discard zone is categorized archaeologically as a burned rock midden.

Rocksort

In order to effectively study FCR and burned rock middens, reliable methods needed to be established for quantifying and categorizing the rock that we find during excavations. The Rocksort recording procedure was created as a way to document FCR using known size and attribute divisions that are common among earth oven literature and experimental studies. The size of FCR can tell us some information about the use-life of that rock and approximately how many times it was used for cooking purposes before it was discarded. The attributes of that particular rock (e.g. pitted limestone, roof spall, igneous/metamorphic rock) can help us determine the general source of the rock (e.g., uplands vs. canyon bottoms vs. within rockshelters).

It is important to note that we do not collect and record every rock that we encounter during excavation. Such a process would be extremely time consuming and would produce lots of repetitive data. Rather, we have been collecting and weighing FCR through selective column samples along our exposed profiles and other areas that we deem necessary or informative at our excavation sites. Through this selective Rocksort documentation, we will gain a representative sample of the varying densities and sizes of rock that are occurring at the sites we are investigating in and around Eagle Nest Canyon.

During the Rocksort process we split the FCR from a particular layer/strat or feature on a grid board (lines at 7.5 cm) into the following categories based on the maximum dimension : < 7.5 cm, between 7.5 -11 cm, between 11-15 cm, and > 15 cm (Fig. 1.). These rock size categories are based on the 20,000-odd FCR that were counted and measured as part of excavations at the Higgins site in San Antonio, directed by our very own Dr. Steve Black (see Higgins BRM).

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Bryan and ASWT volunteer Kris Bobbit rocksorting an excavation layer in Eagle Cave.

Furthermore, this separation allows us to identify the stages of thermal fracture in the FCR and whether or not that particular layer/strat or feature being excavated is related to a discard event (e.g., small rocks <11 cm), a cooking event (e.g., larger rocks >11 cm), or some combination thereof.

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A.) Predominately larger FCR >11  cm were found within cooking features; B.) Predominately smaller FCR 11< cm were found within discard zones.

 

Each square on the Rocksort board measures 7.5 cm and provides a speedy method for quickly measuring and grouping the hundreds of rocks that need to be sorted. After the rocks are sorted, they are photographed on the board and weighed according to their size and attribute class (Fig 2.).  This data is then entered on the excavation form and the sorted FCR is dumped into the back dirt piles.

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Fig. 2: The ASWT Rocksort table (above) and the always famous Rocksort board (below).

 

The Big Picture

As mentioned earlier, the ultimate goal of our FCR documentation is to measure the amount of earth oven cooking that took place in Eagle Nest Canyon and other rockshelters and open sites in the Lower Pecos Region. However, you may be wondering how in the name of Einstein do we siphon our Rocksort data into something understandable?

Sparing you the math, we can take this data and calculate the approximate volume, FCR mass, and FCR density  of the burned rock middens in and around Eagle Nest Canyon. This data – with the help of radiocarbon dating – can tell us when and how much earth oven cooking took place at each site in the canyon over time. Additionally, we can compare the Eagle Nest Canyon FCR data with that from previous ASWT projects along the Devils River to give us an idea of the amount of earth oven intensification that occurred across the Lower Pecos landscape over time. Pretty cool right?

What it all boils down to is having the ability in the future to be able to estimate the number of earth ovens at different sites with minimal excavation. We hope to be able to not only compare earth oven features across the Lower Pecos but possibly North America.

 

 

 

 

 

 

 

 

ENC Take Three: A Look Ahead at the 2016 Season

By Charles Koenig and Steve Black

The 2016 season is planned as the penultimate major field season in Eagle Nest Canyon. We are have a larger field crew, 10 of us full time joined periodically by returning veteran collaborators (e.g., Ken Lawrence), new collaborators (e.g., Karl Reinhard and Isabel Teixeira-Santos), and volunteers, most of whom are also ENC veterans. We will be working at two main locations within Eagle Nest Canyon: Eagle Cave and Sayles Adobe, a new locality.

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The 2016 ENC core crew (from left to right): Charles Koenig, Amanda Castaneda, Victoria Pagano, Justin Ayers, Spencer Lodge, Bryan Heisinger, Emily McCuistion, Kelton Meyer, and Stephanie Mueller. 

2016 Eagle Cave Excavations

The 2016 Eagle Cave work will continue exposing, documenting, and sampling the south wall of the main trench (see 2015 Investigations of Eagle Cave). We are off to a running start because several profile sections were exposed at the end of the 2015 season that we documented but did not sample.

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Bryan Heisinger cleans off the profile while other crew members look on.

We will finish exposing the south wall of the main trench down to the large spall layer, and towards the mouth of the site take a large unit down to test the Collins’ Hypothesis that Paleoindian occupation layers may be deeply buried closer towards the dripline than UT or the Witte Museum excavated. We will continue to use SfM as our primary documentation method, and will maintain our sampling strategy of collecting 100% of the matrix from sampling columns.

We will follow our 2014-2015 excavation strategy focused on a vertical approach, but as we get deeper into the deposits we will be able to open up a horizontal block several meters across. Taking a horizontal approach to sampling the lower deposits will allow us to look at artifact and feature distribution across the earliest site deposits within the confines of the main trench, something that we could not do with the upper deposits. The methods we will use for the lower deposits will likely be a modification to our vertical methods, but still rely primarily on TDS and SfM mapping of artifacts and samples.

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The view from the total data station (TDS) while work continues on the south wall of the main trench.

Backfilling and Stabilizing the South Wall of the Eagle Cave Main Trench. 

After excavations are complete near the end of 2016 season we will begin the process of stabilizing and backfilling the trench wall to protect it from collapse.  This will likely not be the “final” backfill event (this will occur during the concluding winter/spring 2017 field season), but we will cover the deposits enough to protect them from damage.  We have not yet solidified a plan, but we anticipate using some combination of gravel from the canyon bottom, clean fill brought in from elsewhere, large plastic bins, and backdirt from our Eagle Cave excavations.  We want to be sure whatever we use to backfill can be removed without damaging the intact deposits.

Toward this end, during the 2016 season we will consult engineers and archaeologists who have rockshelter stabilization experience to help us design a plan to carefully stabilize and fully backfill both Eagle Cave and Bonfire Shelter in 2017.

2016 Investigations of Sayles Adobe

As our ENC excavations have progressed, it has become more and more apparent flooding down the Rio Grande has impacted the sites and the natural history of the canyon more than we realized.  Therefore, to address new research questions relating to flooding and the human use of the lower canyon’s alluvial terrace, Texas State graduate student Victoria Pagano will lead excavations into newly named and recorded Sayles Adobe site, located immediately in front and downstream of Skiles Shelter.

41VV2239_GENERAL_1608.JPG

Sayles Adobe as initially recorded in December 2015. Tools staged for the subsequent clearing.

41VV2239_CREW_0018.JPG

Sayles Adobe after clearing was completed this past week (January 12th).

The results of this excavation will be reported in Victoria’s Master’s thesis. The research objectives and questions for Victoria’s project are still in development, but it will involve geoarchaeological analysis of the terrace to gain a better understanding of the frequency, magnitude, and impact of Rio Grande flooding, as well as sample what we hope are well-stratified cultural deposits.  Our ideal would be to find alternating alluvial and cultural deposits, the latter dating the former and the former sealing and protecting the later.

The site is hereby named in honor of pioneering Texas archaeologist E.B. Sayles who first recorded the presence of archaeological sites in Eagle Nest Canyon in the winter of 1932. Sayle’s sketch map of the canyon depicts a dashed in area in front of Skiles Shelter and Kelley Cave that is labeled “Sandy Adobe” but otherwise not described.

Sayles-1932-Langtry-A-B-map-cleaned

E.B. Sayles sketch map of Eagle Nest Canyon. Sayles Adobe is located where Sayles outlined a “Sandy Adobe” towards the confluence of the Rio Grande.

We believe this is how he noted the alluvial terrace knoll which is composed of fine sandy loam (Rio Grande alluvium) that has the same color as dried adobe.  Pagano formally recording the site a few weeks ago and it is officially 41VV2239, meaning the two thousandth, two hundredth and thirty ninth archaeological site recorded in Val Verde County – wow!

In mid-December, 2015 Pagano and ENC co-principal investigator Charles Frederick exposed a small portion of the burned rock layer encountered approximately 1 m below the surface in the borrow pit dug in 2014 during the backfilling of Skiles Shelter.

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Victoria and Charles Frederick discuss Sayles Adobe.

Pagano recognized and exposed a thin mud drape several centimeters thick that lies directly atop the burned rock deposit.  We think it highly likely that additional cultural deposits will be encountered, minimally representing materials eroding down from Skiles Shelter, but more likely representing primary open-campsite deposits, likely of a short-term nature.

41VV2239_CREW_1704.JPG

Victoria exposing the “mud drape” covering several large fire-cracked rocks.

The 2016 excavation methodology will be based on initial sampling of the borrow pit (Unit A) and just-conducted ground penetrating radar work by Tiffany Osburn of the Texas Historical Commission.  The Sayles Adobe excavation will be stepped as it gets deeper to ensure safety and stability. Victoria will be fleshing out the strategic details as she pulls together her thesis proposal, due in early February, 2016.  Black and Frederick will serve on Pagano’s thesis committee (along with TxState professor Britt Bousman) and will work closely with Victoria to plan and conduct the Sayles Adobe research.

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As Justin Ayers looks on, Tiffany Osburn of the Texas Historical Commission runs Ground Penetrating Radar (GPR) over the surface of Sayles Adobe looking for sub-surface indicators of cultural features. We eagerly await the results!

            We may be able to carry out limited and special-purpose investigations elsewhere in the Canyon during the 2016 season, but finishing our Eagle Cave excavations and gaining a substantive deep sample of Sayles Adobe are our main goals. We anticipate an excellent 2016 season!

Eagle Cave South Trench 2015: Profile Section 12

By Emily McCuistion

**This is the third of four blog posts showcasing a different Profile Section that was documented and sampled during the 2015 field season. Each of these Profile Sections has different sediment characteristics, artifacts, and ecofacts. Profile Section 12 is located further towards the dripline than Profile Sections 9 or 17 For a location map see 2015 Investigations at Eagle Cave.**

IMG_5961

Emily standing next to her poster at TAS.

Profile Overview

Profile Section 12 (PS12) is located centrally in the south trench wall of Eagle Cave at a point of transition from superior preservation (just behind the shelter’s dripline) to increasingly fragmented organics and compacted sediments near the back of the shelter. The profile is characterized by dense fire cracked rock (FCR) from earth oven cooking capping alternating deposits of fibers (plant remains), FCR, and latrine deposits.

PS12

Profile Section 12 prior to sampling.

PS12_strats

Stratigraphic boundaries of Profile Section 12

Strat Descriptions

(Listed top to bottom)

  • S174: Disturbed, dominated by dense FCR.
  • S177: Dense FCR with ash and some fiber.
  • S229: Thin lens of burned fiber.
  • S230: Thin lens of “ashy” silt with little FCR.
  • S231: Thin lens of FCR in loose, “ashy” silt.
  • S232: Charcoal stained “ashy” silt; few FCR.
  • S233: Decomposed fibers in a silty matrix.
  • S234: Fiberous; possibly urine compacted.
  • S235: Lens of fiber and coprolites in silt matrix, extends only ~40cm into exposure. S272: Compact with irregular topography and some fibers; possibly urine compacted; overlaying or intermixed with FCR.
  • S236: Semi-compact “ashy” silt with few FCR, some fibers likely intrusive from S234.
  • S241: Small patch of fiber and coprolites.
  • S237: Dense FCR in a loose “ashy” silt.
  • S238: Thick fiber layer with scattered FCR.
  • S239: Originally thought to be intact but found to be disturbed during excavation.
  • S240: Originally thought to be intact but found to be disturbed during excavation.
  • S285: White “ashy” silt with crumbly limestone and FCR

 

Profile Sampling

Two sampling columns (Units 57 and 64) were excavated by stratigraphic layer (strat) in the eastern 2/3rd of the profile. When sampling strats individually was not feasible, several strats were combined into a unit-layer.

PS012

Layers excavated in sampling column units 57 and 64, re-projected onto PS12. Layer boundaries are based on the east-west midline of the units.

Data Summary

The graphs below present data from the sampling columns (Units 57 and 64). Note that data correlate imperfectly in the sampling columns as some strats were lumped together into layers during excavation, and other strats were not present in both sampling columns. An asterisk indicates that a strat was sampled individually in one unit, but was not sampled individually in the unit-layer listed in parenthesis. For instance, within Matrix volume, S229 and S232 were collected individually in Unit 64, but S230 was not present in Unit 64. In Unit 57, S229, S232, and S230 were collected as part of Layer 2.

PS12_MatrixVolume

Matrix Volume does not include FCR >1 inch. No Matrix collected from S174, S177, or S239.

PS12_FiberMass

Fiber mass is from ½” sieve.

PS12_FCRMass

FCR mass includes only FCR >1 inch. FCR data was not taken for S174.

PS12_Debitage

Lithic debitage count is from ½” sieve.

Artifacts

Artifacts found in sampling PS12 include a bone tool, a groundstone fragment, a wooden artifact with cut marks, 6 fiber knots and 2 strands of cordage, 2 biface fragments, 2 cores, 8 modified flakes, 3 painted pebbles, 19 manuports, 2 quids, 45 paleofeces or fragments of paleofece, and abundant faunal and botanical remains.

PS12_Artifacts

The Future of PS12!

Anticipated data and study includes radiocarbon dating, faunal, botanical, coprolite, pXRF, micromorph, residue and artifact analysis. PS12 has an important role to play in understanding site use, formation and preservation processes at Eagle Cave.

PS12_Excavators

Dr. Kevin Hanselka (left) annotates PS12 and Emily (right) excavating one of the two sampling columns in PS12.

**A PDF version of the poster is available here: McCuistion_TAS2015_PS012_FINAL

Graduate Project on Archaeology Blogs

ASWT Project blog readers:

Our blog is participating in a graduate student research project looking at blogs and social media in Archaeology.  This project is designed by Fleur Schinning at Leiden University in the Netherlands.  If you have a few spare minutes, please take her survey by following this link: http://goo.gl/forms/z3BAUTyYUL.

From Fleur:
I am currently writing my master’s thesis as a part of my specialisation in Heritage Management at Leiden University in the Netherlands, in which I am supervised by Monique van den Dries. My research will focus on the use of blogs and social media and how they contribute to the accessibility of archaeology in the Netherlands.
 
Public archaeology has been developing considerably in the Netherlands for the last couple of years, but much can still be improved concerning public outreach activities. This is why I have decided to focus my research on communication methods that are favourable in our current digital age and might make archaeology more accessible for a wider public.
 
For my research I will be looking at several blogs from both the UK and USA; in these countries blogging seems widely accepted and used a lot as a tool in creating support for archaeology, and I have come across some very interesting blogs, of which your blog is one.
 
To be able to explore how blogging in archaeology contributes to public archaeology, I would like to question the bloggers and blog readers of these blogs. This is where my request comes in. I have set up a questionnaire in which I ask the visitors of your blog several questions regarding their motives for visiting the blog and so on.
Thanks,
ASWT Project Team

2015 Eagle Nest Canyon Expedition – Call for Interns

Preparations for the 2015 field season are underway, and once again we are offering 3 competitive internship positions!  Click the link at the bottom of the page to download a PDF for more information.  To apply, please send CV (with references and contact) along with a 500 word statement of interest to Charles Koenig (ck1286@txstate.edu) by November 15, 2014.  We had three fantastic interns this past spring, and we look forward to another successful field season!

From left to right: Jacob Sullivan, Brooke Bonorden, and Bryan Heisinger were the three interns this past spring.  They all exceeded expectations, and we look forward to this year's applicants!

(Pictured from left to right) Jacob Sullivan, Brooke Bonorden, and Bryan Heisinger were the ENC interns this past spring.  All three of them played integral roles in the success of the 2014 expedition, and we look forward to working with a new group of interns.

2015 Call for Interns

Link to PDF version of 2015 ENC Expedition Call for Interns:

2015 Eagle Nest Intern-call