The Next Layer, A Sampling Column Story

The Next Layer, A Sampling Column Story

By Kelton Meyer

The inherently destructive process of excavation means that archaeologists must devise effective measures to capture as much useful data as possible as deposits are destroyed. One of the most important aspects of our excavations in Eagle Cave is the process by which we sample intact stratigraphy. By carefully exposing intact layers in profile, spending much needed time defining strats and sampling with diligence, we are able to gain high resolution views into the lives of the prehistoric Native Americans who frequented Eagle Cave.

I’m Kelton Meyer, an intern with the ASWT project and soon-to-be graduate student at Colorado State University. I’m writing this post to share my experience in excavating Profile Section 25 (PS025), and to take you into the trench where we are working hard to tell Eagle Cave’s stratigraphic story.

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Excavating my sampling column, PS025

Exposing Profile Section 25

The first step in the process of sampling intact stratigraphy is to create a clean profile to clearly expose the layering. We do this by excavating in fairly traditional excavation units to create a “wall” (AKA profile) in an undisturbed context. In the case of PS025, two units were excavated to create the profile, Units 76 and 85. The unit configurations are not necessarily governed by size, shape, or grid orientation, but are dependent on identifying the dividing line between intact and disturbed deposits. When we first started excavating in the main trench last spring, we had to remove lots of disturbed fill from the face of the trench prior to placing an excavation unit. However, as we have continued deeper this season, we have been able to trace the intact deposits easier and more confidently as we have worked our way down into the trench.

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Unit 76 (left) excavated in May 2015 and Unit 85 excavated in February 2016. The south walls of these two units combine to create PS025.

Our excavation units typically consist of anywhere from 1-10 layers, and these layers are defined by factors like changes in sediment color, consistency, artifact density, or the indication of a possible cultural feature. Without a profile to guide our excavation, it is often very difficult to excavate these layers following natural stratigraphy. To aid us in assigning stratigraphic provenience to any artifacts, we take sets of SfM photos (see Archaeology in a Whole New Dimension)  to build 3D models of our units each night in our digital field lab. Using these 3D models we can link our “traditional” units with the stratigraphy we record in profile. Once the necessary excavation units have been completed the newly created profile wall is ready for cleaning, SfM photogrammetry, and field annotations.

Profile Section 25

PS025 is one of the larger profiles, located towards the rear of the rockshelter and in the approximate middle of the overall vertical stratigraphy of the site. It is representative of different occupational zones, and varying episodes of earth oven dismantling and refuse.

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An orthomosaic of the south trench and profile sections with PS025 highlighted in red.

 

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Orthomosaic of Profile Section 25

What We Can See

After we’ve built a 3D model of the profile in the lab we print out an orthomosaic (a profile view) into the field for annotation. With a conveniently sized paper copy of the profile in hand, we can sketch stratigraphic changes, assign numbers to the strats, and take any other notes that we deem necessary. For PS025, the field copy was especially handy due to the varying effects of sunlight upon the lightly colored sediment, and the broken characteristics of the strats.  Once again, the Eagle Cave stratigraphy bears little resemblance to textbook layer cake simplicity.

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My PS025 field annotation.  The numerous hatchered areas are rodent bioturbated.

When determining stratigraphic changes in profile, several factors are taken into consideration. We first identify any visible disturbed contexts, such as rodent burrows. In  PS025, evidence of rodent bioturbation was obvious. Large pockets of mottled sediment intruded into most of the intact stratigraphic layers (strats), bringing fecal matter, grasses, and other debris into the profile wall. We then assign strats from top to bottom,  according to the superposition of the layers. Strats can vary in color, texture, and consistency of sediment. Some strats extend across fairly large zones, while others are small, thin, and broken in profile view. Once the profile has been fully annotated and the strat information has been entered into the database, each individual strat is ready for direct sampling.

I found the annotation of PS025 to be an enjoyable experience, and it allowed for some artistic expression. Bioturbation often presents annotation challenge, but it sharpened my archaeological skills as I traced and separated the intact from the disturbed.

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Here I am concentrating on my profile annotation

Taking from the Wall

In Eagle Cave it is important to record the provenience of all aspects in excavation, and especially in sampling. A midpoint for each strat is “shot in” using a TDS (Total Data Station) and the precise location of each subsequent sample we take from the profile must also be shot in as well. We collect spot samples, geo-matrix samples, and 14C samples. A spot sample is a small bag of undisturbed strat sediment. A geo-matrix sample is a somewhat larger bag of sediment that includes rock and pebble constituents to allow the geoarchaeologists to characterize sediment size and texture.  A 14C sample can be a collective variety of botanical remains like charcoal, seeds, or leaves that come from unquestionably intact areas within each strat. These point-provenienced samples will allow the analytical team to review sediment characteristics, analyze the geo-archaeological properties of individual strat matrix, and, potentially, to obtain a targeted date from each strat.

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TDS points of all samples and strat definitions taken from PS025

The collection process from the wall requires expert troweling and methodical strategy. A reduction in the size of trowels, pans, and brushes is absolutely necessary! When choosing to collect samples from a profile, it is best to begin from the bottom and move upwards so that the next strat is not contaminated by sediment spills. Sometimes, the strats in profile are so small or intermittent that it is not possible to collect all three sample types. Priority is given to spot samples where adequately sized geo-matrix sampling is not possible, and 14C samples are collected when the appropriate material is visible in the profile (e.g., a charred cut leaf base). Additionally, artifacts that have been left in situ  as the profile wall is cleaned and examined are shot in, photographed, and collected. When samples of each strat have been removed, it is time to choose where to place a sampling column.

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Collecting samples from the profile

Collecting from PS025 was at first a heartbreaking experience. Much time was expended in making the wall an appealing example of visual stratigraphy.  I’m trying to say it was tedious work and often frustrating when seemingly intact proved to be rodent-churned. However, understanding the importance of the samples I was taking made it all worthwhile.

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Distal portion of a chert biface in profile

The Sampling Column

A sampling column is a specific type of unit used in our excavations at Eagle Cave. The principle goal of these units is to provide an in-depth look into the stratigraphy of a profile section by isolating intact strats and collecting sizable matrix samples. Choosing where to place sampling columns depends entirely on the characteristics of individual profiles and factors like stratigraphic density, artifact density, feature locations, etc. The evolving research goals of the project dictate where columns are placed. Eagle Cave field director Charles Koenig consults with the excavator(s) most familiar with each profile section and makes the call. Sampling columns may be placed in areas of the profile that favor exposed features, and this may result in some relatively minor strats not being sampled. This is why it is important to collect the initial samples before the sampling column is placed! Some profile sections receive more than one sampling column, for instance exposures with nicely intact stratigraphy and excellent organic preservation like latrine deposits.

The columns are typically small rectangular areas measuring 20 to 40 cm in each dimension.  Sampling columns are excavated strat by strat, and in the more dense stratigraphic areas of the site they can be consist of 20 plus strats. The proper excavation of a sampling column is very detailed and careful work. All of the undisturbed strat matrix is collected for later processing and curation, and all artifacts encountered during excavation are shot in, photographed, and collected. Additionally, we carryout Rock Sort data collection for each strat. The crew must constantly refer to their field annotations to ensure that the excavated strat layers do not cut into new strats, or involve previously sampled strats as sediment is removed.

At the end of each completed strat, SfM photogrammetry is performed. In many cases, new stratigraphic layers are encountered and identified as the sampling column comes down in the profile. These new strats must be annotated, sampled, plotted, and collected. Sometimes, strats that existed in profile may not continue far behind the profile wall, and thus must be sampled even more carefully to preserve at least some data given the paucity of sediment matrix.

The column for PS025 was strategically placed to sample a feature visible in profile.  The defining characteristics of Feature 11 were the large boulder-like burned rock protruding from the wall and the surrounding pattern of compacted ash, charcoal, and fire-cracked rock. In total, the sampling column consisted of 14 excavated strats, with one being identified mid-excavation. Most of the strats consisted of ashy gray/white sediment having a very fine texture and containing compacted charcoal.  Some strats produced burned and unburned fiber, other botanical remains (e.g., charred seeds), animal bone, chipped stone tools, and other types of artifacts shot in with the TDS.

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Location of sampling column

 

Lab Processing

After each strat is sampled and collected, matrix is brought back to the field lab for processing. The collected matrix from each strat is weighed and quantified, and then screened through a 1/2” sieve to remove large artifacts and rocks. Artifacts collected from the screen are cleaned, weighed, analyzed, and set aside for curation. The remainder of the matrix is bagged and cataloged, awaiting further analysis. The screened matrix is also curated and given a specimen number for our database, so that the provenience of each sample is thoroughly recorded in our system.

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Justin Ayers sieving dusty matrix

As work continues in Eagle Cave and more data is collected, the process of curation becomes increasingly important. The variety of artifacts and samples we collect will provide answers to many of our research questions regarding the lifeways of the prehistoric occupants of Eagle Cave. Samples for macrobotanical data, faunal identification, lithic reduction strategies, tool analysis, archaeoentomology of human fecal matter, and even phytoliths, are awaiting for the analytical team to decipher as we work towards understanding natural and cultural formation processes, ecology, climatic conditions, cultural patterns and much more from this awe-inspiring rockshelter in the Lower Pecos Canyonlands.  I’m proud to be able to contribute the next layer in the Eagle Cave sampling column story.

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Elton Prewitt and I examine an artifact I exposed while excavating my sampling column.

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Experimental Gauntlet: Replicate This!

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“Butted knife”  41VV2239  FN50156

By Steve Black

As the principal investigator of Ancient Southwest Texas (ASWT) and as faculty sponsor of the Texas State Experimental Archaeology Club, I hereby challenge the 2016 ASWT crew and Club members to convincingly replicate the use wear pattern(s) apparent on the recently recovered biface pictured above.

This distinctive artifact was found in situ on 3/28/2016 at Sayles Adobe (41VV2239) by ASWT 2016 Intern Kelton Meyer working under Victoria Pagano who is directing the Sayles investigation for her thesis research. The artifact was found about a meter below the surface of this terrace site amid scattered FCR (fire-cracked rocks) that I would guess represent the upper and outer part of an earth oven facility where desert succulents like sotol and lechuguilla were baked. (It could be the edge of a buried burned rock midden, perhaps an incipient one?)

In our previous six seasons in the Lower Pecos Canyonlands (LPC), ASWT has found no other example of this quite formal artifact type, but several were found during the Amistad salvage era at the Nopal Terrace and Devil’s Mouth sites.  They occur fairly often in the Kerrville area and in the western Balcones Canyonlands.

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What kind of a “fist axe” would have such a delicate blade, a butter axe?

These unusual artifacts have been given many names.  What is in a name? Some have called them fist axes or hand axes because of their somewhat similar appearance to Old World artifacts, most of which date tens or hundreds of thousands of years earlier.  There is a simple morphological reason why these Old World terms seem functionally inappropriate – what kind of axe would have such a delicate cutting edge? (A butter axe?)  The latest edition of Turner and Hester (but cf. earlier editions) uses the type name Kerrville biface, which is geographically appropriate, if dissatisfying to some. Typological maven Elton Prewitt prefers the descriptively appropriate term butted biface. I prefer the functionally appropriate term butted knife; that these are some sort of cutting/slicing tool seems obvious.  Consensus, however, has yet to emerge on either the name or the specific purpose(s) of these tools.

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Even though I pride myself on not being “artifact-oriented,” this unexpected new find in excellent context has me in a dither. When I initially looked at the artifact in our field lab the evening it was found, it set my intellectual juices flowing and I harkened back several decades ago.  Then, as is still true, I was convinced that I knew exactly what butted knives were characteristically used as: sotol trimming knives (plus Agave lechuguilla in Lower Pecos?).

I recall that I once envisioned experimentally replicating the striking use wear that most butted knives display:  remarkably bright “silica polish” rather evenly distributed across both faces of almost the entire blade of intact examples. I even took several modest steps in the experimental direction.  For instance, Glenn Goode kindly made a fine replica to be used experimentally.  But alas, I failed to follow through with the hard work that a rigorous replication project would entail and my Goode-made biface sits gathering dust in my TxState office on my show-and-tell shelf.

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Butted biface replica made by Glenn Goode out of Georgetown flint.

Within an hour of seeing the Sayles Adobe specimen, I took several pictures of it and sent one to my former mentor and long-time boss, Dr. Thomas R. Hester, UT-Austin professor emeritus and former director of both the Texas Archeological Research Laboratory at UT-Austin and the Center for Archaeological Research at UTSA.  I also sent one to Elton, who most of us Texan archaeologists regard as a stone-tool typological guru of the first water (most of us think the same about Tom Hester). The subject line of my email was “Butted agave knife” and I closed both email messages with “I knew you would appreciate!”  Sure enough, they both replied right away and here are tidbits.

Hester:  “We call them Kerrville “bifaces” because the polish/wear has never been satisfactorily replicated.  But, I’ve long thought they were plant-working tools, not necessarily slicing and dicing, but mebbe chopping/hacking into an agave or some other soft plant where the distal got “imbedded” and the polish eventually appeared.”

Prewitt: “Nice butted biface. I do not like the term “Kerrville Biface” since it has never been appropriately defined as far as I am aware (I could very well be wrong, but …). And, yes, we do have good ideas about their uses.”

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These are called “butted” because the thick, proximal end of the tool is typically the outer cortex-covered surface of the original chert nodule. It was obviously made this way so the usually rounded butt fits in your hand with the blade tip (distal end) pointing out ready for action. The Sayles Adobe artifact seems to lean to the right in this photo because it is resting on its rather flat butt.  This artifact appears to be made on ledge chert, thus the flat, thin cortex rind you can glimpse.  High quality ledge chert is rare in the Lower Pecos, but often occurs in  in the Kerrville area.

Intrigued?  So here is my challenge.  I think it would be a most worthy project to (1) design a rigorous experimental program to convincingly replicate the telling use wear pattern(s) of a call-it-what-you-will; and (2) successfully follow through with such a program.  Here are some considerations and suggestions.

Before picking up the gauntlet, you will want to do your homework and do your best to read everything ever written about the subject.  These butted things have been admired by many, often speculated and reasoned about in print, studied under the microscope, and studied experimentally (if inconclusively). Doubtlessly more so than I can recall.

This will not be easy.  If the use wear could have been easily and convincingly replicated it would have already been done. And it is entirely possible these artifacts were sometimes used on more than one material and/or in more than one motion. I venture to say that such a project will almost certainly take many months of concerted replicative effort and likely several years to see through to peer-reviewed publication, which should be the end goal.

With that in mind, I recommend that the ASWT crew and the Club talk amongst yourselves and consider forming a leadership team of three to guide the effort.  You will need competent, motivated decision makers and with three, you would always have a tie-breaker (as Dan Potter, Kevin Jolly and I learned on the Higgins Experiment in 1993).  And you will need diverse skills and continuity.  I recommend that the three project leaders include TxState students or former students of varying levels of experience including several who aren’t graduating anytime soon.

But it will likely take far more than three of you to get it done.  You will likely want to try more than one contact material (sotol/lechuguilla, meat, and grass all come to mind).  You will likely need many hundreds of strokes in said materials to create patterned wear.  You will want to properly document each step, photographically, metrically, and so on.  I’d think it would make a fine experimental project.

You would be wise to consult others.  I would put Professor Hester at the top of your list.  I’ll bet he has seen more than one student paper on the subject, he has sure as heck seen many more of things than me, he has published on them, and I know he shares my abiding curiosity.  Elton is always a go-to source for informed typological opinion regarding lithics.   Professor Britt Bousman teaches the graduate seminar in lithic technology at TxState, and he might even let you look at and document butted things (perhaps before and after replication?) using TxState’s fancy use wear microscope. Dr. Mike Collins of TxState is unsurpassed in his knowledge of lithic technology and he once dug a site near Kerrville.  Dr. Marilyn Shoberg (of Austin) might well have looked at some of these things under a scope. Dr. Todd Alhman might have archaeological examples at CAS (ask about the Tom Miller Collection).  Chris Ringstaff or Glenn Goode might be willing to make several freshly chipped stone replicas to be used in experiments.  Ken Lawrence would certainly approve of experimental work of this sort being done out at Professor Grady Early’s place in the phosphate-sampled area.  I’m certain inquiry will lead you to others who would be worth consulting and might lend a hand.

But do not make the common mistake of uncritically accepting dogma.  Challenge assumption, question authority, and think for yourselves.  I, for one, could well be wrong about some of my claims in this piece as well as those I make in classes and in print. (Say it ain’t so, Shoeless Blackie, say it ain’t so.)

Should a group of you rise to the occasion and accept the challenge, don’t do so lightly.  I won’t hold it against you if you don’t pick up the gauntlet.  But I might if you accept the challenge and fail to follow through.  If I’ve piqued your interest, start with doing your homework and decide whether to go forward.  Then craft a proper research design.  If I approve your plan I will endeavor to support your effort in multiple ways. I think this could be fun learning exercise and make a useful contribution to Texas archaeology.

Yours in the experimental cause, SLB

Dating Eagle Cave

As followers of this blog know well, the Ancient Southwest Texas research team has been investigating this Eagle Nest Canyon and Eagle Cave since 2013.   Following a cutting-edge “High Resolution, Low Impact” excavation strategy, we have carefully exposed, documented, and sampled literally hundreds of stratigraphic layers at Eagle Cave, some pencil-thin and some thick and massive.  The deposits in this dry rockshelter are complex – nothing like the flat, layer-cake examples found in archaeology textbooks.

Instead we encounter twisting and turning layer upon layer often cutting through one another.  This intricate layering is the result of daily life in the shelter on and off over thousands of years as the ancient inhabitants dug cooking pits, baked desert plants in earth-covered ovens, and carried out myriad other activities.  They often used their abandoned cooking pits as convenient trash dumps where spent cooking debris, worn-out fiber sandals, fire-cracked cooking rocks, and much more were discarded. The Eagle Cave deposits may be complicated, but the preservation is incredible, and we are recovering an amazing variety of scientific data from uncharred plant remains, wooden artifacts, and woven mats to animal bones, insects and human coprolites.

To allow us to properly and thoroughly date the Eagle Cave deposits and critical analytic samples, we have embarked on a crowdfunding campaign and are Texas State University’s inaugural guinea pig.  Most of this post is taken from our Dating Eagle Cave campaign page.  Check it out and be sure and see the video as you consider helping support our goal of making Eagle Cave the best dated and most thoroughly studied site in the Lower Pecos Canyonlands of southwest Texas.

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Eagle Cave Main Trench Section as it looked at end of 2015 season showing mid-points of calibrated radiocarbon dates (yellow) and lots of questions about as-yet undated deposits.

Eagle Cave Challenge

The last major excavation of a dry rockshelter in the Lower Pecos Canyonlands took place back in the 1970s, when archaeologists from Texas A&M investigated Hinds Cave about 10 miles from here.  The ecologically oriented Hinds Cave dig recovered hundreds of coprolites which have been studied by graduate students and specialists ever since.  Truly, Hinds Cave has proven to be a scientific treasure (see http://www.texasbeyondhistory.net/hinds/.  We believe that Eagle Cave has the potential to build on and expand this legacy in many important ways.  Herein lies the challenge.

Major archaeological investigations of dry rockshelters with outstanding organic preservation, like Hinds and Eagle Caves, take many years of concerted research effort.  The actual digging is completed in a few years, but thoroughly analyzing the resulting data and fully realizing its scientific potential takes considerable research time and funding.  And it takes numerous carbon-dated, stratigraphically controlled samples.   We have already collected many more samples at Eagle Cave than were obtained at Hinds Cave and we have much better scientific control.

Because we are taking advantage of 21st century digital technologies, our documentation system at Eagle Cave is sophisticated and precise.  Every sample is assigned a unique code linked to a database that tells us precisely where it came from, usually within a few centimeters.  For every surface we expose – horizontal and vertical – we systematically take dozens of overlapping photograph.  Each night in our digital field lab we use special software to “stitch” these images together to form seamless three-dimensional models.  In other words, we can digitally reconstruct almost everything we excavate.  Scientifically speaking, this makes our samples extremely valuable.

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UT-North profiles from 2014 excavations being studied by Tina Nielsen for her M.A. thesis. In yellow are the calibrated midpoints of radiocarbon dates we obtained last year and the red question marks highlight yet-to-be dated areas.

Radiocarbon Dating

For us to achieve the scientific potential of such materials we must precisely date the Eagle Cave layers and special samples. Knowing exactly where something came from and what it was found with is only part of the challenge – we also need excellent chronological control – how long ago was a given layer created?  To figure this out, archaeologists use a combination of understanding the stratigraphy (layering), formation processes (how layers formed), and (radio)carbon dating (how old it is).  Any organic material can be used for carbon dating, and Eagle Cave has an abundance of organic material in virtually all of the layers. We prefer to date plant remains: charred wood, uncharred plant leaves, seeds, fiber artifacts and so on.   Using modern radiocarbon dating techniques all that is needed is a very small sample.  Specially equipped labs can measure the ratio of carbon isotopes, and calculate age based on the ratio of carbon-12 to radioactive carbon-14 (which has a half-life of 5730 years).  Do the math, and you can determine about how long ago the once-living plants died and ceased to accumulate carbon-14.

To confidently date a site with complex stratitgraphy, many dates are needed.  For instance, over fifty radiocarbon dates have been obtained on samples from Hinds Cave.  Thus far we have less than half that many for Eagle Cave. This isn’t a matter of one-upmanship, it’s a matter of scientific need.  We must know the absolute dates of key stratigraphic layers and critical samples through a concerted, multiphase program of radiocarbon dating in order to make our hundreds of samples scientifically valuable.  Securely dating key layers will in turn give us approximate (relative) dates for the many more “in between” layers.

What We Need

So far we have 18 radiocarbon dates from our 2014-2015 work.  For the next phase of dating we are seeking funding for 20 more dates.  Dating a complex site like Eagle Cave is an “iterative” process, meaning that the results from one round of dating helps us see the gaps and fine-tune the next round.  Radiocarbon dating is expensive with the going commercial rate for the most precise dating method (AMS dating) is $600 per sample.  Fortunately, we are working with a radiocarbon scientist at another university in a collaborative arrangement that allows us to get dates for less than half that rate.  Add in the need to get expert identification of the plant remains we are dating and 20 more dates will cost us about $300 each for a total of $6000, our campaign goal.  If we are very fortunate and exceed our goal, we will be able to get started on the following phase.

 Please consider helping to support our Dating Eagle Cave campaign!