ASWT Radiocarbon Update #2

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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.

Blog-Bison-hair

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.

Kamen

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).

Anderson

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.

ASWT Radiocarbon Update #1

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Editor’s Note:  This blog piece is based on an email newsletter sent out earlier this fall to supporters of the successful 2016 Dating Eagle Cave crowdfunding campaign.  Author Emily McCuistion is a veteran of the 2015 and 2016 ASWT Eagle Nest Canyon Expeditions. She is a graduate student at Texas State University and is studying radiocarbon dating in the Lower Pecos Canyonlands for her thesis under Dr. Steve Black.  Emily can be contacted at: erm63@txstate.edu

By Emily McCuistion

ERM

Practicing the Texas State Bobcat growl at Sayles Adobe, 2016.

I am a child of Austin, Texas, and I’ve had a lifelong interest in the outdoors and in old things. After graduating from the University of Texas at Austin with a BA in anthropology, I moved west for archaeology work; I called the Great Basin and Mojave Desert home for several years as I worked in Death Valley National Park and in southern Nevada. I also worked in the pine forests of the western Sierra Nevada Mountains, on the Texas Gulf coast on a nautical excavation of a Civil War gunboat, and across that great big Pacific Ocean, in New South Wales, Australia, where I worked on archaeology contract projects in advance of mining developments, mostly. For the past four years, I have spent summers with the National Park Service in Denali, Alaska and winters in Texas. Dr. Black has rightly described me as an itinerant archaeologist, and I describe myself as a generalist—one who is interested in learning about ancient hunter-gatherer people worldwide. This interest meshes well with the thesis research path I have embarked on—learning how the radiocarbon record can be used to inform our understanding of the past, both in broad strokes and fine details.

These updates are part of my education—an exercise in articulating what I am learning, and an opportunity to share what I am learning with the archaeology community and invested public. I hope that the newsletters will provoke you to ask questions about radiocarbon dating and how it shapes our understanding of the prehistory of the Lower Pecos Canyonlands. Some of this material will likely appear in an expanded form in my thesis.

Radiocarbon Basics

roasted hearts

Hearts of sotol and lechuguilla roasted in an experimental earth oven. Were they to preserve for 5730 years, they would have half the 14C they had in 2015 when the ASWT team harvested them. In twice that time, 11,460 years, they would have 1/4th the 14C from 2015, and so on.

Radiocarbon (14C) is an unstable isotope of carbon which makes up only a tiny fraction of the carbon in our atmosphere. Most 14C is created in the earth’s upper atmosphere, when thermal neutrons from cosmic rays react with nitrogen. After that, radiocarbon, and the other naturally occurring carbon isotopes (12C and 13C), react with oxygen to become carbon dioxide (CO2), and become distributed throughout the atmosphere.

 

Photosynthesis is the primary mechanism by which carbon is incorporated into terrestrial plants. Animals intake carbon through the food chain. Fungi, that often overlooked kingdom, takes in carbon through decomposition of its host. Aquatic organisms are more complex; they take in dissolved carbon in ocean, lakes, and rivers. Therefore, aquatic organisms, and the terrestrial animals that derive a large part of their diet from aquatic resources, often date to older than their contemporaneous terrestrial counterparts. These differences in carbon levels in various environments are called reservoir effects; there are ways to adjust assay results to account for these effects. The important thing to grasp here is that radiocarbon dating rests on the idea that CO2, and therefore 14C, is evenly distributed in the atmosphere; aquatic environments aside, relative quantities of atmospheric carbon should be consistent around the planet at any given time.

Though atmospheric carbon is assumed to be consistent across the planet at any given time, it is known that levels of 14C in the atmosphere vary through time. Amounts of 14C are effected by the earth’s magnetic field, by solar flares, by major volcanic eruptions, and, in more recent centuries, by the burning of fossil-fuels and by nuclear detonations. How are these variations through time accounted for? Dendrochronology (tree ring counting; annual growth in trees reflect environmental conditions through time, and tree ring sequences can be accurately dated by simple counting), and more recently, elemental measurements from corals, are used to establish calibration curves. Calibration curves correlate radiocarbon years with calendar or solar years, which is necessary for relating sample ages to most chronologies. Calibration will be discussed in greater depth in a future update.

Essential Terms and Symbols

PricklyP

Prickly pear cactus incorporating carbon from the atmosphere through photosynthesis.

  • Sample: the organic material which undergoes laboratory processing (e.g., preserved plant material, charcoal, bone, a fragment of a perishable artifact, even residues from artifacts).
  • Assay: the laboratory process performed on the sample which extracts and measures the carbon. “Assay” is a noun and a verb.
  • Date: a term often used loosely; a sample is not technically “dated,” it is assayed. The assay results are reported as a statistical estimate range of possible dates, in radiocarbon years before present (RCYBP, or often simply as BP) .
  • δ (delta): indicates isotopic fractionation differences, and is reported with the conventional age [I’m still learning about this topic; it has to do with the ratio of isotopes and loss of lighter isotopes with time—it will be discussed in the future].
  • σ  (sigma): associated with the statistical age range (the standard deviation from the estimated mean age). Standard deviation is expressed by a “±” followed by a number, which, when added or subtracted from the mean, indicates the upper and lower limits of the estimated age range. The σ will be given as 1σ or 2σ, which indicates the confidence level of an estimated date range: 1σ deviation means that the actual age of the dated material has an approximately 68% probability of dating anywhere in that range. A 2σ deviation means that there is an approximately 95% probability; 2σ will always have a larger range of possible dates than 1σ.

Delta Sigma What?  Reading Radiocarbon Ages

There are several types of radiocarbon ages that archaeologists report:

  • Conventional: normalized for isotopic fractionation (δ 13C) but uncalibrated. Reported as BP (before present, “present” being 1950 AD) which is actually radiocarbon years before present (RCYBP). In these updates I will use RCYBP when discussing conventional dates, for clarity.
  • Reservoir Corrected: adjusted age to account for variation in the carbon reservoir (e.g., aquatic environments).
  • Calibrated: accounts for variation in quantity of 14C through time, and translates radiocarbon years into solar or calendar years. Reported as cal BP, cal AD, or cal BC.

In sum, there are several ways to express an age (e.g., RCYBP, BP, AD, BC, cal BP, etc.). These suffixes are critical to indicating what type radiocarbon data is being presented. The conventional age is generally regarded as the most essential age to report, as it reflects the 14C measurements of the sample, without which reservoir correction and calibration would not be possible. A corrected and calibrated assay, however, is integral to establishing chronologies, and for simply grasping how old something is relative to our own calendar system.

For Example, radiocarbon assay TX-107 (wood charcoal), from excavations at Eagle Cave (Stratum V, Hearth 1) by the University of Texas in 1963, was reported in 1965 by Pearson et al. and by Richard Ross thusly:

8760±150 BP (1σ)
6810 BC
6510-7110 BC (2σ)

This notation indicates that the actual age of the materials has a 68% confidence of dating between 8910-8610 RCYBP (150 added to and subtracted from 8760). The 6810 BC date is the mean conventional age estimate (it has been converted to BC from BP by subtracting 1950 from 8760). Finally, there is a 95% probability the sample age falls in the 2σ range, in this case expressed in BC. The 2σ range of possible ages is several hundred years larger.

Several pieces of information considered key today were not reported in the 1950s and 1960s. Calibration curves were not yet established when this date was published. Additionally, isotopic fractionation was not always reported. The TX-107 assay was neither corrected for isotopic fractionation nor calibrated when reported in 1965. As the sample was run on charcoal, a reservoir corrected age is not applicable. Previously reported Lower Pecos assays such as this one will be recalibrated, or in this case, calibrated and corrected for isotopic fractionation for what is likely the first time, as part of my thesis.

FootprintsCarbon Footprints

In this section I share my everyday experiences of learning about radiocarbon dating so that the reader can walk in my metaphorical radiocarbon footsteps. My journey began last winter, and was propelled forward by a couple of key experiences.

One of these experiences was being invited by Dr. Raymond Mauldin and his colleagues at the University of Texas at San Antonio’s Center for Archaeological Research (CAR) to assist with a poster for the Society for American Archaeology’s (SAA) 2017 annual meeting. The poster presented an investigation of population patterns in Central Texas and the Lower Pecos Canyonlands, using large radiocarbon data sets from each region and comparing the abundance and distribution of dates through time. To this end, I contributed an initial compilation of 490 radiocarbon dates from the Lower Pecos. The bulk of these, 268 assays, had been assembled by Solveig Turpin and published in the 1991 study she edited Papers on Lower Pecos Prehistory. The remaining data, 222 assays, came from project reports and articles from the 1990s and 2000s, and from the Ancient Southwest Texas Project’s 2010-2017 excavations. The data were then vetted to eliminate dates with large standard deviations, because such dates are too imprecise for the requirements of the study. Data were also divided between samples from open sites (upland and terrace) and those from rockshelter sites, because preservation of organic materials differ enormously between these site types. In April, 2017 I attended the SAAs in Vancouver, BC, to help present the poster, and enjoyed my first SAA conference experience very much.

The other milestone in my Spring 2017 semester was writing and defending my thesis proposal. This was my first opportunity to explore the application of the large Lower Pecos dataset to address archaeological questions. Potential research problems include increased use of earth ovens as a response to environmental change, spatial change in earth oven facilities through time, differential preference for sotol and lechuguilla, the uses of plants associated with earth ovens for non-comestible purposes (e.g., sandals, basketry, cordage), bison presence, and population fluctuations and settlement through time. I suspect that there will be insuffcient data to meaningfully address certain of these topics, in which case I will highlight the need for further research. The Lower Pecos radiocarbon data set I assemble will be made available to other researchers through an online database.

Several steps must be taken to prepare the dataset for analyses, including compiling the data needed, and correcting and calibrating the conventional ages. In addition, the archaeological context, laboratory treatments, and sample material will be critically evaluated to understand how the assay can (or can’t) be applied to addressing the aforementioned topics. In addition, I am rolling up my sleeves at CAR this autumn, where I am learning sample preparation methods from Dr. Mauldin. Some of the samples I will be assaying come from Eagle Cave, thanks to the generous contributions of the crowdfunding campaign! After initial processing at CAR, the samples will go to radiocarbon lab DirectAMS, where I hope to follow the samples through their final carbon measurements.

My present focus is on collecting and assessing contextual data at the Texas Archeological Research Lab (TARL), selecting additional samples from the ASWT excavations at Eagle Cave and Kelley Cave for assaying at CAR, and acing my statistics class so that I can do the analysis next spring. I am also working with the Center for Archaeological Studies at Texas State, where I am rehousing and cataloguing the spectacular Skiles family collection— an opportunity indirectly related to my thesis work, but which increases my knowledge of the material culture of the Lower Pecos, in particular the fiber industries. In the coming months I hope to relate to you my experiences in CAR’s radiocarbon lab. Thanks for your interest in my studies!

Fire on the Mountain: Earth Oven Features in Nevada

IMG_0178

Sheep Range roasting pit with banana yucca (foreground) and Joshua trees (background) growing around it.

Editor’s Note: This blog piece was written in 2016, but is only now being posted owing to …  the distractions of ASWT research.  Spencer, a stalwart member of the 2016 ENC crew, has returned to southern Nevada where he is again working on the Desert National Wildlife Refuge.

By Spencer Lodge

Hello everyone, this blog is a little different than previous posts.  Instead of focusing on work we accomplished in Eagle Nest Canyon, I will highlight what I have learned about the earth oven facilities I recorded in southern Nevada as part of my 2016 M.A. thesis at Texas State University, “Fire on the Mountain: Roasting Pits in the Sheep Range on Desert National Wildlife Refuge.” (Google the title if you would like to read my thesis.) My study area represents an interesting contrast with the Lower Pecos Canyonlands, a contrast I appreciate all the more after spending six months (Jan-June 2016) helping to excavate and document the copious evidence of earth oven cookery at Eagle Cave and Sayles Adobe.

Before moving to Texas for grad school, I worked on the Desert National Wildlife Refuge located some 20 miles north of Las Vegas. While working there I recorded nearly 200 roasting pits (i.e., ring middens) throughout the Sheep Range, the primary mountain range on the Refuge. When researching graduate programs, I was attracted to Texas State University due to the focus on earth oven technology by Dr. Black. Even though 1,000 miles separate southern Nevada and southwest Texas, I find the similarities in earth oven technology between both areas to be quite interesting.

My Study Area

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Satellite image of the Sheep Range within the Desert National Wildlife Refuge (red) where my research was conducted.

My study focused on the Sheep Range, located roughly 20 miles north of Las Vegas in southern Nevada, in the fuzzy boundary between the Great Basin to the north and Mojave Desert to the south. The Great Basin, known for its internal draining system which resulted in pluvial large lakes during the Late Pleistocene and Early Holocene, is evidenced by the Desert Dry Lake located directly northwest of the Sheep Range. Flora associated with the Mojave Desert is located at various ecoregions spread across the Sheep Range, including Utah agave, Joshua Trees, Banana Yucca, and Mojave Yucca.

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Utah agave (left) and banana yucca (right), two of the plants that were likely baked in Sheep Range roasting pits.

The extremes are very apparent in southern Nevada, from the bone dry playa beds up to pinion covered mountains. This region is dry, receiving 2-7 inches of rain per year in the lowlands, and up to 16-25 inches in in upper elevations (Mayer et al. 2012:30). Reliable water sources in the immediate area consisted of springs scattered throughout the Sheep Range. Due to the aridity and extreme nature of the landscape, prehistoric peoples in the region were highly mobile with relatively low population density. In fact, the Southern Paiute (or Nuwuvi) who inhabited southern Nevada at the time of Euroamerican contact had the lowest population density of any group in the Great Basin.

Ethnographic accounts for the use of roasting pits by Southern Paiute suggest this method of cooking was used for numerous plant foods, including agave, various species of yucca, and green pinyon pine cones.

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View of a roasting pit (foreground) surrounded by Joshua trees and black brush with the Desert Dry Lake in the background.

Recording and Studying Roasting Pits

While conducting a survey on the Desert National Wildlife Refuge where the Sheep Range is found, I documented my first roasting pit. These earth oven facilities are comprised of rock, carbon-stained sediment, and charcoal, all by-products of hot-rock cooking. A typical roasting pit has a circular shape with a sunken central depression where the oven was built. To my surprise, a significant amount of the thermally-altered rocks were white, allowing us to spot the features several hundred meters away even with a pinyon tree growing from the center.

Even more surprising, the density of white rock allowed me to find more than 250 roasting pits using aerial imagery. The process I used to find these sites was rather straight-forward. Using Google Earth, I scanned the canyons and alluvial fans extending from the Sheep Range, staying at an average eye elevation of 7,000 ft. Potential roasting pits were marked to be verified in the field.

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A volunteer writes the photo log as I (background) search for associated artifacts.

In the field, roasting pits were measured, photographed, and the surrounding landscape was surveyed for associated material culture or additional roasting pits initially unidentified. Three primary types of measurements were taken: the diameter of the midden, the diameter of the sunken depression, and the size of the cooking pit when identifiable. Height measurement were taken as well, but deemed unreliable as I was unable to know exactly where the roasting pit midden ended and the topography underneath began.

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Schematic model of roasting pit showing the terminology used by Lodge (2016).

Observations focused on the type of vegetative zone and topographical setting in which the feature was constructed, as well as how one roasting pit differed from those around it. (For example: Was it smaller? Did it appear more eroded or infilled? Was it located closer to resources?) Once a roasting pit was recorded, we either hiked or flew to the next one on my list. I was fortunate to have the aid of a helicopter to access the more isolated roasting pits, which was terrific given the rugged and generally undeveloped nature of the Sheep Range. In total, 193 roasting pits were recorded and another 30 potential cooking features were identified. After the end of this field project, I recorded an additional 10 roasting pits.

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Example of a roasting pit that is smaller, more ephemeral than most, and partially filled in with sediment. Visible in the background is the helicopter that allowed me to access remote features.

Analyzing Roasting Pits

I was unable to excavate or perform any destructive forms of analysis to the feature or cultural materials found in association. Instead I decided to analyze roasting pit distribution and size measurements throughout the Sheep Range using a combination of statistics and ArcGIS. Statistical tests were used to see if roasting pit size varied significantly according on the vegetative zone it was built in, and to test the usefulness of my identification method in areas with poor visibility (tree cover). ArcGIS was used to see if roasting pits were more often built in clusters or equally distributed, and if clustered, whether “hot spots” of use could be identified. I also conducted thermal testing on rock samples and used X-Ray Defraction (XRD) to determine the material type as well as the reason why thermally-altered rocks turn and remain white.

For both statistical and GIS analysis, I looked at midden size as an indication of use. That is to say, since each cooking event results in additional waste in the form of spent rock, charcoal, carbon stained sediment, etc., I infer that roasting pits with larger middens were used more often than those with smaller middens. I measured the length and width of each midden (Exterior), as well as the interior depressions.

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Example of a well-defined roasting pit with the central cooking depression covered in vegetation.

 

Both methods of analysis taught me several things. First, roasting pits built in lower elevation vegetative communities (such as the Creosote Brush Community) were smaller on average than those built in higher elevation communities (such as Mixed Shrub or Pinion/Juniper Communities). Since both fuel and food resources diminish along with elevation, higher elevation sites allowed people to revisit locations more frequently, increasing midden size more quickly in the process.

Second, GIS analysis indicates roasting pits were more often built in groups, as opposed to constructed evenly throughout the Sheep Range. Hot-Spot GIS analysis also highlighted certain portions of the Sheep Range where larger roasting pits were concentrated, suggesting these locations were more often frequented for baking foods.

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Scatter plot showing the relationship between roasting pit size and elevation.

Cooking Features in Nevada and Texas

Like the burned rock middens of the Lower Pecos, the roasting pits of southern Nevada are synonymous with earth oven facilities. The term earth oven facility refers both to the cooking pit where foods are baked and to the associated debris created from cooking (spent rocks, charcoal, etc.). Roasting pits are comprised of a central depression where foods were baked and a surrounding ring midden.

One critical difference between earth oven features in southern Nevada and southwest Texas is the amount of excavation they have received. Here in Nevada, roasting pit excavation has been minimal compared to the extensive work done in Texas. Recovered botanical remains from several roasting pits suggest agave, yucca, and meat were all cooked within. Just over 60 radiocarbon dates have been obtained from southern Nevada roasting pits, mostly dating to the past 2,000 years and as far back as 3,800 B.P. In comparison, there are now hundreds of radiocarbon dates from earth oven facilities in southwest and central Texas! Ring middens are also present in Texas, however they tend to have larger accumulations of fire-cracked rock and occur in both open air and rockshelter settings. While earth ovens have been found in rockshelters in Nevada, roasting pits are found only in open settings.

Color Change

Perhaps the most striking difference between the earth oven facilities of the Lower Pecos Canyonlands and those of southern Nevada is how visible they are on the landscape. Roasting pits in the Sheep Range are overall much easier to spot due in part to their color. When heated to temperatures exceeding 875° C, dolomite and limestone, the preferred material type for pit roasting in the Sheep Range, changes color from gray to white. Roasting pit middens are not entirely comprised of white rocks, but rather a mixture of bleached and natural colored rocks. However, even a relatively minimal amount of white rocks intermixed within a midden allows roasting pits to stand out against the otherwise drab landscape.

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An up close example showing the mixture of white and natural colored rock found with a roasting pit.

Limestone was also commonly used in earth ovens in southwest Texas, but in contrast to southern Nevada, burned white rocks are not commonly found. For example, while excavating in Eagle Cave in 2016 I encountered less than ten white limestone rocks among the many hundreds of fire-cracked rocks I handled. Instead, the burned limestone rocks in the Lower Pecos are typically dark gray in color after use, sometimes exhibiting a pinkish hue.

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Nevada dolomite before (left) and after (right) being heated to 900 C.

Size Variation

Another reason why the Sheep Range roasting are apparent on the landscape is due to their size. On average, roasting pits were nearly a meter in height at their peak with a maximum recorded height of over two and a half meters! When you consider that roasting pits were commonly built in areas lacking tall vegetation, they simply had nowhere to hide.

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A very impressive two and a half meter tall roasting pit in the Sheep Range.

Conclusion

Since wrapping up the 2016 field season at Eagle Nest Canyon, I have returned to southern Nevada to work once again at the Desert Refuge. Using what I’ve learned researching earth ovens in Eagle Nest Canyon, I intend to continue investigating roasting pits throughout the Range (I’ve already recorded another ten features, bringing my total to 203!).  I also hope to explore the experimental use of earth ovens and perhaps one day I’ll have the opportunity to excavate one of the roasting pits of southern Nevada.   Until then I’ll keep looking up at the Sheep Range and thinking about times not so long ago when the Chemehuevi, a Southern Paiute group, frequented the area.

“One could tell from great distances when people gathered mescal [and] see fires on all the mountains.”

 

Lodge, Spencer N.
2016    Fire on the Mountain: Roasting Pits in the Sheep Range on Desert National Wildlife Refuge. M.A. thesis, Anthropology, Texas State University.

 

 

2017 ENC Expedition: The Final Chapter

By Charles Koenig

Five years ago this past January, Steve and his graduate students Dan Rodriguez and Matt Basham launched the ASWT investigations within Eagle Nest Canyon. At the time Steve was helping Dan and Matt plan their thesis research, and Steve and Carolyn Boyd were just beginning to discuss having a joint dirt and rock art archaeological field school. Looking back it is hard to conceptualize, but that short 10-day trip in January 2013 launched arguably the most locally-intensive archaeological study ever conducted within the Lower Pecos Canyonlands.

Since 2013, ASWT has carried out signficant excavations at Skiles Shelter, Kelley Cave, Horse Trail Shelter, Eagle Cave,  and Sayles Adobe, as well as smaller scale testing at 41VV890 and Lonestar Bridge. Each one of these sites has yielded an incredible amount of archaeological data, and we are slowly beginning the long process of analysis and publication. We have wrapped up our work at all but Eagle Cave and Sayles Adobe and this season (2017) marks the final chapter of ASWT field work in Eagle Nest Canyon. (Not really, ASWT will be helping Texas State’s newest archaeology professor, Dr. David Kilby, get to a running start in Bonfire Shelter this summer…but that is for another blog post.)

Backfill or Bust

When we were planning for the ENC work, we established three overarching and ambitious research goals that we would strive to meet over the span of our research. These goals are: 1) understand the natural and cultural history of the canyon; 2) share what we learn with the professional archaeological community and the general public; and 3) preserve the sites and archaeological records for future generations. We are well on our way to accomplishing point one, and as field work wraps up we will continue to learn more about the natural and cultural history of the canyon. For point two, over the past five years we have given dozens of talks at local and regional archaeological meetings; we keep our work (mostly) current on social media; and we already have several theses and publications written about ENC with more on the way. The third point is in some ways the most difficult to achieve, and is one we are spending most of our time pursuing during the 2017 field season.

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A crew member dumps excavated sediment back into a unit in Skiles Shelter.

In order to preserve the sites for future generations, after excavations are complete we stabilize and backfill our units. Backfilling prevents damage that would occur from natural forces (erosion, plants, and animals) and visitors to the sites. At most of the sites our backfilling task is made “easier” by virtue of simply putting the stockpiled fill (i.e., backdirt) we excavated and screened back into the holes. At Sayles Adobe, for instance, once Tori finishes her final sampling in a few weeks we can easily move the piles of screened dirt back into the open excavation units. However, unlike the rest of  the sites, there is no “easy” backfilling at Eagle Cave.

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Steve Black cleans up wall-fall at Sayles Adobe. The massive pile of sediment in the background is the excavated sediment Tori will be able to use to backfill Sayles Adobe.

As we have discussed in several other blog posts, the main trench in Eagle Cave was not backfilled by the Witte Museum in the 1930’s or by the University of Texas in the 1960’s. Since the 1960’s, the once vertical profiles within Eagle Cave slumped and collapsed into a massive depression (see Where Context is Crucial), destroying all intact deposits immediately surrounding the trench. Further, both the Witte and UT archaeologists screened their excavated dirt out near the dripline, and now nearly all of the sediment they removed has been lost down the talus slope. In other words, past Eagle Cave archaeologists left us a massive hole in the center of Eagle Cave without the backdirt to fill it back in.

Witte to UT to 2003

The trench as excavated by the Witte Museum (left) was about 6 feet wide. When the University of Texas Amistad Salvage Project cleaned out the trench in 1963 (center) it was somewhat wider. Fifty years later the once vertical excavation walls had collapsed into a massive depression (right, circa 2003). Yellow arrows point to a unique spall.

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The Eagle trench towards the end of ASWT work (Fall 2016). The same spall is visible on the rear wall  that is pointed out in the above Witte and UT photographs.

Reinforcements Arrive: Eagle Cave Restoration Archaeologists

Prior to the start of the 2017 field season, we were fortunate to apply for and receive a Texas Preservation Trust Fund Grant from the Texas Historical Commission. We applied for this grant as a way to help fund the backfilling efforts at Eagle Cave. As a part of the grant, we had to calculate how much fill was missing from the main trench prior to the start of ASWT excavations in 2014. Based on our calculations, we estimated nearly 225 cubic yards of fill needed to be imported into the site just to re-fill the old Witte-UT trench. 225 cubic yards is nearly 20 dump trucks! This 225 cubic yards is in addition to our own excavated fill from Eagle that we needed to put back. We knew we had to move a lot of dirt, and we knew we needed help.

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Amanda Castañeda

We were fortunate to once again be jointed by ASWT veteran Amanda Castañeda. Amanda completed her Master’s thesis research on bedrock features in the Lower Pecos (see Mortar She Wrote), and was with us for the entire 2016 field season. We also posted job opportunities for two “Restoration Archaeologists,” whose main duty would be helping to move 225 cubic yards of fill into Eagle Cave. We are very pleased to be joined in the field this spring by Juan “Kiko” Morlock and Michelle Poteet.

Kiko Morlock

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Juan “Kiko” Morlock

Hey there! Juan Diego Morlock here, but y’all can call me Kiko! I spent my childhood roaming the wilds of Big Bend National Park and Far West Texas. After graduating high school, I worked for the National Park Service as a Wildland Firefighter and Fire Ecologist, as well as an Archaeology Intern at the Center for Big Bend Studies at Sul Ross State University. I graduated with my B.S. in Anthropology from Texas State University in May of 2015, and continued working for the CBBS and NPS for a while. When the opportunity arose to work with the 2017 Eagle Nest Canyon Expedition, I jumped at the chance. I had fallen in love with the Lower Pecos Canyonlands after several childhood canoe trips on the Devils and Pecos rivers. I knew it would be an adventure steeped in the rich archaeological history of the LPC as well as a means to improve my abilities and knowledge of the technology and techniques used in my field. I’m excited to expand my archaeological horizons as a Rockshelter Restoration Archaeologist with the 2017 Expedition!

Michelle Poteet

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Michelle Poteet

Hello everybody. I was born and raised in Oklahoma, but I have roamed around quite a bit throughout my lifetime. I even spent several years studying in Japan before I came back to my home state to pursue my higher education. At the University of Oklahoma I earned my B.A in Anthropology while focusing on archaeology and paleoethnobotany. For more hands-on experience I worked at the Oklahoma Archaeological Survey for three years as well as both volunteered and worked on field projects in the state.

A beautiful new environment, high levels of preservation, use of new technologies, and the chance to work on a preservation project much larger in scale than anything I had yet to take on are what drew me to the 2017 Eagle Nest Expedition. Getting to join in on an archaeological field academy and hiking and bouldering in such a scenic area on a daily basis have been an unexpected bonus. I look forward to the rest of the project, logistical challenges and all!

Eagle Cave 2017: Where We Stand

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The 2017 ENC Core Crew

During the first four weeks of the 2017 season the crew carried out last minute sampling within Eagle Cave, focusing predominantly on collecting matrix samples for archaeoentomology (bugs) samples (see Archaeoentomology?). Once we finished collecting our final few samples (including helping Charles Frederick collect nighttime OSL samples), it was time to begin the Eagle Cave Refill Challenge. We began backfilling operations last week, and have thus far moved about 1/6 of the imported fill (7 dump trucks worth). While the previous sentence sounds simple enough, we have been on a roller coaster ride of highs and lows, complex logistical problems, and hard labor.

We are excited to share our backfilling adventure with you this spring, stay tuned for more blog posts detailing the backfilling operation.  You can follow the action on the ASWT  Facebook page.

 

ENC Summer Interns

At the end of our last session, three of our core team members left ENC and headed to cooler climes and new archaeology. Bryan Heisinger returned to Sequoia Kings Canyon National Park, Emily McCuistion returned to Denali National Park, and Kelton Meyer went home to Colorado to assist on a Colorado State University field school. As sad as we were to see Bryan, Emily, and Kelton go, we are equally happy to welcome our two new summer interns to the crew: Lindsay Vermillion and Kate Richey. Both Lindsay and Kate have worked in ENC before. Lindsay was a summer intern in 2014, and has volunteered on the project over several occasions. Kate was one of our field school students in 2015.

Lindsay Vermillion

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Hi everyone! I’m from Big Bear Lake (a tiny mountain town in Southern California) and am currently an upper-division undergraduate student at Texas State working towards my BA in anthropology, with a focus in archaeology. I have done some work on California’s Channel Islands through Humboldt State University, particularly regarding sea mammal exploitation on San Miguel. This past year I interned with Shumla Archaeological Research and Education Center studying the rock art of the Lower Pecos. I am also involved with the Experimental Archaeology Club at Texas State where I first became acquainted with the Ancient Southwest Texas Project. I have previously volunteered for ASWT and am happy to be back as an intern.

Other Useless Information: I am a classically-trained cook dedicated to sustainability. In my spare time I like to garden, poetry slam, salsa (though I’m not very good at it,) and bask in the sun as much as possible.

 

Kate Richey

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Hi my name is Kate Richey I am from British Columbia, Canada and am entering into my final year of archaeology at the University of Calgary. I participated in the 2015 field school in Eagle Nest canyon where we excavated at Horse Trail shelter. It was my first time out in the field and I had very little idea of what we would be doing or where we would be working and I was amazed when I saw the canyon that we would be working in every day. Last year’s field school was a great experience and so when I found out there was an opportunity to come back and work in the canyon again I had to say yes. Despite the many poisonous animals, the very warm temperatures and the liberal use of jalapenos (none of which we have much of in Canada) I am very happy to be back! So far it has been a steep learning curve but every day brings new finds and things to discuss and I am looking forward to the rest of time I get to spend down here.

 

We are happy to have both of them on the crew and look forward to a successful finish of our field season!

Pigmented Artifacts of Eagle Nest Canyon

By Emily McCuistion

The sheltered limestone walls of the Lower Pecos Canyonlands are known for their complex and well-preserved pictographs, or painted images on rock. Here in Eagle Nest Canyon several of the rockshelters hold within them both pictographic murals on their walls and portable rock art in the ground in the form of painted pebbles. The focus of this blog piece, however, is neither. Rather, pigmented artifacts without clear intentional design, those having a splotch, wash, or stain of paint or pigment, are the primary subject at hand. These artifacts have the potential to relate the rock art on the walls and in the ground to the technologies of pigment and paint manufacture and use, as well as to the other activities of the canyon’s inhabitants. What follows is a preliminary introduction to the pigmented artifacts we have found in the last three years of the Eagle Nest Canyon Expedition, as well as a partial overview of pigment and paint studies undertaken in the Lower Pecos Canyonlands.

Pigment and Paint

Paint recipes in this region are believed to be comprised of three ingredients: pigment, a binder, and an emulsifier. Pigment is the ingredient that supplies color. The binder is the vehicle for the pigment, giving paint various qualities when drying into a film on whatever canvas is chosen. The emulsifier is a suspension agent. Though it is not known with scientific certainty the exact binding and emulsifying ingredients in the rock art paints of the Lower Pecos, Dr. Carolyn Boyd’s replicative experiments with paint-making from local ingredients may point in the right direction. She successfully used red and yellow ochers as pigments, bone marrow from deer as a binder (compare to oil in oil paint), and yucca root (which contains saponins) pounded and mixed with water as an emulsifier.

Austrailia

An ocher source in the West McDonnell Range of central Australia. Ocher (mineral pigment, derived from earth) is important to many native groups around the world, and it features in the native place names of several place I have lived: Death Valley, California has an indigenous name of Tumpisa (and variations of that name), which is translated as rock ocher.  Similarly, Dubbo, a country town in New South Wales, Australia, is translated as “red earth” and is said to refer to ocher used in body paint

DNA studies aiming to reveal what species of animals may have been used in making the binder in rock art in this area have been undertaken on samples from local pictographs. Unfortunately, the studies thus far have not yielded satisfactory and replicable results. On the pigment front, however, our own Charles Koenig and Amanda Castaneda, in conjunction with Carolyn Boyd, Karen Steelman, and Marvin Rowe, have made strong headway in elucidating what some of the pigments used in this region are. More on that below.

Local Rock Art Styles and Canvases

As many of readers of this blog know or have gathered by now, the Lower Pecos Canyonlands is known for its pictographs. Actually, that is quite an understatement- the region is becoming world-renowned for its pictographs. There are four defined styles of pictographs: Red Linear, Pecos River Style, Bold Line Geometric, and Red Monochrome. The styles are believed to be chronologically separated and reflect the culture of different (though perhaps related) groups of people. (For more on rock art of the Lower Pecos see http://www.texasbeyondhistory.net/pecos/art.html and check out SHUMLA’s  pioneering rock art studies).

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Amistad National Recreation Area archaeologist Jack Johnson at White Shaman, one of the classic Pecos River style pictograph sites in the Lower Pecos.

As mentioned, there are also decorated portable artifacts found in excavated contexts. These include the relatively common painted pebbles, rare painted woven items such as burial mats, and rarer-still painted faunal remain such as deer bones, mussel shell and snail shell. Paint would have been applied to other ephemeral canvases as well, such as human skin.

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An “early” style painted pebble recovered from Eagle Cave in 2015. Notice the black, fine-line design. Pebble is about 6 cm long.

Pigmented Artifacts from Eagle Nest Canyon

During the Ancient Southwest Texas project’s three years of excavation in Eagle Cave, six pigmented artifacts have been identified. Several of these have small splotches of red pigment or paint on them, such as the fire cracked rock and flake below.

Flake&FCR

Left: FN33079, found near the center of the rockshelter in a layer dominated by fire cracked rock and ash. A piece of red ocher was found in the same strat. Right: FN33960: This piece of fire cracked rock with pigment on it was found in the same general part of site (PS016) as painted limestone below.

Other artifacts have better defined pigmentation and I believe would lend themselves to an interesting study of possible pigment and paint-making technologies. These include a tabular limestone rock with thick paint coating one surface and dripping over the edges…

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FN32916 was found in a fiber-rich (botanical) layer with excellent preservation, near the front of the rock shelter. The strat also contained coprolites, debitage, a core, flake tool, and a quid (chewed fibrous succulent leaf). The reverse side is unpigmented but appears to be pecked, as is typical of a stone surface being prepared as a grinding implement. This artifact is unusual in that it appears to be covered in opaque paint rather than just pigment.

And a second broken limestone rock with pigment along one margin.

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This limestone fragment (FN32955) was found in the same sampling column but slightly lower than FN32916 above, and seems to be the same rock type. Pigment runs along one margin, and is splotchy on the back side. It was also found in a fiber-rich layer with other artifacts, including coprolites, knotted fibers, and a burned antler fragment.

…a flake with a heavily pigmented margin….

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This chert flake with pigment along one margin was found near the back of the rockshelter in a layer with scattered fire cracked rock and charcoal. Numerous other artifacts were also found in the layer from which this artifact came, including hundreds of animal bone fragments, stone tools including a dart point, and, interestingly, a crumbly piece of ocher.

A final pigmented artifact from Eagle Cave was found as we were removing slumping and disturbed sediments from the trench floor. The artifact is unfortunately without stratigraphic provenience. It is an interesting artifact nonetheless, a broken oval mano with clear evidence of grinding on several sides. A vertical break through the ground stone artifact has edges/margins that have been trimmed or beveled all the way around the break, resulting in a raised surface. Red pigment is evident on the ground surfaces, and on the raised broken surface it appears that there is faint yellow pigment!

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The same fragment of ground stone with red pigment (left) and yellow pigment (right) collected from disturbed deposits in Eagle Cave.

Three pigmented artifacts were also found in Kelley Cave and are described by Dan Rodriguez in his 2015 thesis:

“One bifacial and one unifacial scraper were observed to have red pigment on a single side. The pigment on the bifacial scraper appears to be a congealed paint while the unifacial scraper pigment appears to be an applied powder. Also found in Feature 3 was a burned rock fragment with a red brush mark.”

Other pigmented artifacts have been found in the general region as well illustrated by the online TBH exhibit by Susan Dial on Kincaid  Shelter (see Ancient Art: Mysterious Stones and Pigments). This rockshelter located about 50 miles northeast of the Lower Pecos Canyonlands shares strikingly similar painted and incised pebble designs, as well as a number of pigmented limestone cobbles which may have been used to process pigment.

Progress in Pigment and Paint Research

With the exception of the aforementioned ground stone with likely yellow pigment, all pigmented artifacts thus far identified in Eagle Nest Canyon are pigmented red. Paint colors found in the rock art in the Lower Pecos Canyonlands are white, black, yellow, and a spectrum of reds to oranges. Past studies using X-ray diffraction (XRD) on Lower Pecos murals detected specific iron minerals in the pictographs, such as hematite. All pictographs on which XRD was conducted contained a combination of iron minerals. A recent portable X-ray florescence (pXRF) study by ASWT’s Charles Koenig and Amanda Castaneda, in conjunction with other researchers, has yielded interesting insight into what type of mineral pigments these colors are typically associated with. pXRF is a tool for analyzing elements, is non-destructive, and as the name indicates—portable! For these reasons it is a useful tool in identifying elemental similarities and differences in rock art. Koenig et al. found that manganese is the usual pigment in black paints in the Lower Pecos, though charcoal was also used. Red and yellow paints are made with iron-rich minerals, pXRF shows, but may be combined with manganese (either by a natural mixing in the ocher source or intentionally by the artist.) A result of this study was to elucidate the use of manganese in black paints in Pecos River style pictographs, and infer by the absence of manganese in black colored Red Linear style pictographs and un-typed styles, that charcoal was the pigment. Charcoal presence in pictographs also has potential for radiocarbon dating, a method which Dr. Karen Steelman, a collaborating researcher of ours, is currently exploring.

It is an exciting time to be studying Lower Pecos archaeology, as so much interest is being garnered by local research, and as we have many new technologies available which can help us better understand our human past. I feel that we are on the brink of linking the rock art on the walls to the archaeology in the ground, and it will be fascinating to better understand the relationship these pigmented artifacts had to the rock art created here.

Zone VI: Into the Eagle Cave Unknown

Zone VI: Into the Eagle Cave Unknown

By Charles Koenig

Since we began excavating the main trench in Eagle Cave in 2014, we have always had some idea of what to expect thanks to the previous work by the 1963 University of Texas excavations.  In 1963, Mark Parsons and Richard Ross spent three days illustrating the north wall of the “Old Witte Trench.”

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Digitized and colorized field illustration of the 1963 Eagle Cave profile drawn by Mark Parsons and Richard Ross. The deep column in the center was added several months after the upper profile was annotated. Many more lenses, layers, and levels were noted on this profile than made it into the simplified, published version below. Original scan courtesy of the Texas Archeological Research Laboratory.

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Version of the profile that appeared in Ross’s 1965 Eagle Cave report. Only the major stratigraphic zones are noted.

Even though they did not record nearly as many “zones” and “lenses” as we have documented strats (units of stratification), we can correlate some of the 1963 stratigraphic zones to 2015/2016 strats because they took the time to illustrate and describe the different layers. Broadly speaking, UT recorded 6 major stratigraphic zones (1-6), in addition to many other lenses and layers within zones. In Zones 1-5, UT recovered a variety of cultural debris (chipped-stone tools, plant and animal remains, and our favorite – burned rock), and the earliest deposits in Zone 5 were dated to 6500-7000 B.C. (Ross 1965). However, they stopped excavating at the top of Zone 6 because it was considered a “sterile layer of yellowish limestone spalls and dust.”

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One of the 1963 Eagle Cave crew members beginning to dig the deep test through “sterile” fill. The white sediment at the man’s feet is Zone 6. View is looking west. Image courtesy Texas Archeological Research Laboratory.

From the outset of our work in Eagle, we have been guardedly optimistic the deposits from Zone 6 and deeper might not be sterile, but simply UT did not excavate far enough to find the next layer of cultural material. In reading the site journal for the 1963 work, we realized the UT crew stopped excavating at Zone 6 not only because they interpreted it as being sterile, but also because they simply ran out of time to excavate any deeper. They did sink a deep test to bedrock at the end of their work, but this was quickly excavated, and from what we can gather, they did no detailed recording or screening of materials that came out of this test. So, as we began excavating into the top of Zone 6 at the end of our last session (the last week in March) we were excited because we knew from that point down we would be excavating into the unknown – the oldest (>9000 years), minimally explored deposits within Eagle.

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South trench in Eagle Cave profile as of 4/17/2016. Top image is just of the orthophoto of the trench, and the bottom is the same image superimposed with our interpretation of UT Zones 1-6 .

First Contact

The first place we excavated into Zone 6 was towards the rear wall in the site. Several of us (Kelton, Justin, and myself) were excavating units to expose a profile section, when Justin uncovered a most surprising artifact: a thick fragment of what appeared to be bison long bone.

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Justin working in Zone 6 (white/yellow in profile).

In addition to the bison bone fragment, Justin also recovered two chunky biface fragments. After the months of anticipation, wondering what we may or may not find, and then to find artifacts and bison bone in one of our first units … we were excited, to put it mildly! As most things go on an archaeological site the bison bone find occurred on almost the last day of the field session, so we had to wait two full weeks before we could investigate Zone 6 again.

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The two biface fragments (top) and sizable bison bone fragment (bottom) recovered in Zone 6 towards the rear wall.

The Trench Floor

Even though we all wanted to jump right in to excavating Zone 6 and seeing what was there, the first thing we did when we got back to work was to devote several days to removing disturbed fill from the bottom of the trench. After completing this dusty, hot, exhausting job we had exposed intact stratigraphy across the entire bottom of the trench. And, by removing the disturbed fill, we exposed more or less exactly the floor of the 1963 excavations into Zone 6.

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The crew removing disturbed fill from the bottom of the trench (left), and the top of Zone 6 exposed in the bottom of the trench (right).

Once we had the top of Zone 6 exposed across the trench floor, we laid out several units with the goal of excavating down in the trench floor to give us room to work as well as expose profiles on the south wall. However, after only excavating about 10 centimeters below where the UT excavations stopped our excavations slowed dramatically when we started finding bison bone fragments; lots of them.

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The scatter of bison bones as originally photographed in Unit 109.

Unlike the single bone fragment Justin found in the upper Zone 6 towards the rear of the site, Emily, Spencer, and Bryan began exposing dozens of fractured bison bones scattered over a 5 meter area. We knew we had something really cool, and that Zone 6 was definitely not sterile!

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The top surface of Feature 14 (fragmented bison bone scatter) as initially exposed in the Eagle Cave trench floor. The bison bones are slightly more yellow than the surrounding white/yellow rockshelter sediments.

Feature 14

As we continued to expose more and more bone, we realized these bone fragments were all related to one another and likely represent a single behavioral episode. Because of our working interpretation that the bones were fractured and strewn across the extant surface of the shelter in a single event, we gave the bone scatter the designation Feature 14 (the 14th formally designated feature recorded in Eagle Cave since 2014). The feature designation also means we wanted to take special care in how we went about recording the provenience of the bones. To do this we took a series of SfM models and shot in with the TDS many of the bones.

41VV0167_Feature14_108-114

Intermediate map showing Units 108 and 114 with additional bison bones exposed.

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Intermediate map showing Units 109 and 115 with additional bones exposed. The cluster of rock in the center of the image is Feature 15, a likely hot-rock thermal feature.

We were also very fortunate to have Art Tawater on hand that week as one of our volunteers. Art is a longtime member of the Texas Archeological Society and the Tarrant County Archeological Society, and one of his passions and areas of expertise is zooarchaeology. After the bones were mapped in (piece-plotted with TDS shots) and photographed, Art made a preliminary field ID for the various bones. This was a huge help because none of us (except Black) had any experience with excavating bison bones, let alone trying to figure out what element each bone fragment might be from!

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Art (left) helping Spencer (right) ID and package up bison bone for transport out of the site.

Mapping in the bones and collecting field observations slowed down the removal process, but we wanted to collect as much data in the field as we could so that when our collaborating zooarchaeologists Chris Jurgens and Haley Rush finally get to see the bones they will be well armed for the analysis to begin!  Plus, while the bones were well preserved, they had been purposefully fragmented originally  and some were crushed and cracked by the overlying deposits and did not remain intact upon careful removal.   Our detailed photographic record and Art’s field observations will allow a more complete analysis of the butchering and processing activities that took place on this surface over 9,000 years ago.

41VV01678_BisonMandible

One of the few diagnostic bones we recovered: a proximal left mandible (jaw) fragment from a juvenile bison with deep cut marks on the posterior side. This bone is visible in the Unit 109-115 image above.

Not Just Bone

In addition to the scattering of bison bone, we also found a modest amount of associated lithic debitage and stone tools. If you look closely several of the tools are visible in the above maps. It is telling that most of the chert artifacts appear to be made of only two or three cobbles judging from the matching colors and textures.  This bespeaks a short-term occupation during which only a few cobbles were knapped.

F14_Stonetools

Two bifacial tools found in direct association with the bison bone of Feature 14. Some of the debitage recovered appears to be the same raw material.

And although there is not the dense concentration of fiber within Feature 14 as in other areas of Eagle, we did recover some very badly decomposing organics.

41VV0167_TS6_U114_L2_FN34411_0674

A decomposing piece of wood recovered during excavation of Feature 14.

And I also can’t forget to mention the possible hot-rock thermal feature (Feature 15) found at the east edge of the bison scatter, with bones above and below rocks that appear burned!

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Chalkboard shot of Feature 15, a likely hot-rock thermal feature in direct association with the scattered bison bones.

So What Does it All Mean?

We just finished excavating the main portion of Feature 14 earlier this week, so it is really too early to even say the analysis has begun, but we can at least offer up some of our preliminary observations and working ideas. Based on the how fragmented the bones are, we hypothesize Feature 14 represents a bison butchering and processing locale/event within Eagle Cave; possibly that of a single juvenile bison (portions thereof).

41VV0167_Feature14_bonescatter

The outline of all mapped bison bones (in black) superimposed onto the initial Feature 14 exposure. The most complete bone–a rib–was recovered at the boundary between Units 114 and 109. All the other bones are fragmentary.

Not only were most of the bones fragmentary, but very few had diagnostic (articular) ends left. In most cases, the field ID was either “medial rib fragment” (~90% of bones) or “long bone shaft fragment” (~8%) of the bones. The fragmented nature of the bones suggests that the people may have been trying to extract bone marrow or render grease from the bones after the meat was removed.

We also have some interesting horizontal distributions of certain artifacts and bones. The areas where we found the highest number of bones with cut marks overlaps with where most of the debitage is clustered. Bones with cut marks plus many flakes indicates this location was where people were cutting bone and/or meat and needing to resharpen their tools. It was also telling to find the relatively few burned bone fragments we found appear to have been concentrated around several thermally altered rocks and scattered charcoal!

41VV0167_Feature14_interpretation

Distribution/highest concentrations of burned bone, bones with cut marks, and debitage overlaid against the bone scatter.

We were also fortunate to recover a projectile point from the same layer as the bison bone. Although not directly associated, this dart point fragment was recovered just to the west of the majority of the bison bones and is made of a very similar dark chert material as much of the debitage.

41VV0167_Feature14_DartPoint

From top left: photograph of dart point fragment in situ; both sides of the dart point in the lab; map showing the location where the dart point was recovered in relation to the bison bone.

At the moment we are not ready to officially type the point, but it is a lanceolate, contracting stem dart point fragment that shares several attributes of Angostura points.

Where to from Here?

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Myself, Jack Skiles, and Steve ponder Feature 14 when it was first exposed.

The fact that we encountered Feature 14 as quickly as we did after beginning into the “sterile” deposits of Eagle Cave gives us hope for additional, older, cultural deposits below. We do not know how old the bison bones are at the moment, but we will be sending out radiocarbon samples soon. We have had a lot of fun excavating this intriguing feature, and we look forward to sharing new findings as we make them!

41VV0167_Feature14_Profile

The location of the Feature 14 bone scatter (linear cluster of yellow dots) and the original bison long bone fragment discovered towards the rear wall. We are excited by the prospects of what we may find as we go deeper into unknown Eagle Cave!