An Unusual Case of Good Charcoal Preservation in Central Texas (Bush and Kibler)

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Pecan (Carya illoinensis) hulls still clinging to the branches in late winter. The nuts dropped in fall and early winter.

Archeologists in central Texas have long been frustrated by poor plant preservation on open-air sites. Even wood charcoal is often sparse due to the alkaline environments on much of the Edwards Plateau (Braadbaart et al. 2009). Conditions in the more acidic Llano Uplift can be slightly better, but wet/dry and freeze/thaw cycles still take their toll on charcoal.

The Jayroe Site (41HM51) provides an example of unusually good charcoal preservation in Central Texas. While located in the Western Crosstimbers region, the Jayroe Site’s riparian locale is similar to alluvial environments found across the more limestone-dominated landscapes of Central Texas, where alluvial deposits and landforms primarily consist of dark loamy to clayey calcareous sediments. The Jayroe artifact and feature assemblages rest on top of a buried cumulic soil formed on such sediments that comprise the first terrace of the Leon River.

The buried soil is similar to the Leon River paleosol identified downstream at Fort Hood (see Mehalchick et al. 1999) in its pedogenic character and geomorphic context. The Leon River paleosol, yielding radiocarbon ages on humates of 1160 ± 40 BP and 1010 ± 70 BP, contains discrete Late Archaic and Austin phase assemblages (Mehalchick et al. 1999:215, 268; Nordt 1992). The stratigraphic position of the Jayroe Site cultural materials on the surface of this buried soil are an indication, along with accompanying radiocarbon ages and temporally diagnostic artifacts (e.g., Perdiz arrow points and Late Caddo ceramics), of the site’s post-Austin phase or Late Prehistoric II age.

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A basin-shaped hearth (Feature 9) atop the paleosol at the Jayroe Site.

What makes the Jayroe Site so noteworthy though is its high degree of contextual integrity and preservation of organic remains (e.g., vertebrate faunal and charred botanical materials). This remarkable degree of integrity and preservation is due in large part to the fact that the site’s surface, the surface of the paleosol, was buried by 60 to 200 cm of interbedded sand and mud deposits that are slightly altered pedogenically. The deposition of this alluvial mantle contributed to the high degree of preservation in three ways.

First, the apparent rapid and deep burial of the occupation surface at the Jayroe Site preserved the spatial integrity of the site’s features and artifacts, largely sealing them off from various biological agents that tend to churned and mix sediments, Secondly, the sand component of the alluvial drape, which consists of fine quartz sands derived from outcrops of lower Cretaceous sands in the surrounding landscape, provide a less alkaline environment that facilitated in the preservation of organic materials, particularly charcoal. And third, the encapsulating sandy deposits are less susceptible to shrinking and swelling under alternating dry and wet conditions, conditions that would have accelerated the mechanical break down of charred botanical remains into smaller, largely unidentifiable particles.  

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Concentration of bison bones and ash lens (upper left) atop the paleosol and below the interbedded sands and muds at the Jayroe Site.

Even the better preservation conditions at Jayroe did not result in the preservation of uncarbonized plant parts. A few uncarbonized seeds were recovered, but these are consisted with modern seed rain expected on the site and are interpreted as such (except possibly the hackberry, whose possible preservation from ancient times on this and other sites deserves a blog post all its own). In terms of botanical preservation, the main difference between Jayroe and less quickly-buried sites lies in the recovery of seeds and pecan nutshell.

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Hawthorn (Crataegus cf. viridis) seed from the Jayroe site. Scale in mm.

The seeds consisted of a sedge and some hawthorn seeds, probably a component of ancient seed rain burned by accident, and hawthorn seeds. Hawthorn trees were part of the riparian forest understory near Jayroe, and hawthorn wood charcoal was recovered in some of the flotation samples. Hawthorns are a crabapple relative and have similar dry, edible fruits.

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Pecan nutshell (Carya illinoinensis) from the Jayroe site. Scale in mm.

Although pecans grow throughout central Texas, pecan nutshell is not terribly common on prehistoric sites. Prior to Jayroe, one of us (Bush) had encountered a total of eleven archaeological pecan shell fragments in the last five years spread over three sites in central Texas (Siren, Herbert Ranch, and Site 41CV947). Pecans are a species of hickory, and they belong to the hickory-walnut botanical family. Not surprisingly, pecans are most similar to hickory nuts in nutritional content (although they have somewhat more fat and less protein), and both are more similar to walnut than to acorn.

Proximate Analysis of Four Edible Tree Nuts and Corn Meal per 100 g Dry Weight (USDA, ARS 2013)

Pecan

Hickory

Walnut

Acorn

Yellow

Cornmeal

Fat (g)

72

64

59

31

4

Protein (g)

9

13

24

8

8

Carbohydrate (g)

14

18

10

53

77

Water (g)

4

2

5

5

4

Energy (kcal)

691

657

618

509

362

Grant Hall points out that the nutrients in pecan and other hickories, especially the linolenic fatty acids, would have been particularly important for hunter-gatherers who relied on lean meat for a portion of the year (Hall 2000).

Traditional hickory processing methods used by Iroquois, Choctaws, Cherokees, and many other tribes involve pounding hickory nuts into small pieces and then heating them in water, where the oil can be skimmed off, the nutmeat retrieved from suspension, and the shells allowed to sink to the bottom (Fritz et al. 2001; Moerman 1998). Experiments by archeologists show that this process yields a much larger number of calories per labor invested than does cracking and picking (Talalay et al. 1984:353). Other common nuts cannot be processed in this manner because either their meats float (acorn, hazelnut) or the nuts become bitter (walnut). These methods also work for pecan nuts.

In Texas today, pecans and other hickories are typically available for collection from mid-October through the first week in December (McEachern et al. 1977). In good years, harvest can begin as early as late September. The earliest possible harvest is best because it minimizes loss to predators such as squirrels.

References Cited

About the Authors

Dr. Leslie L. Bush is a CRHR Research Affiliate, and the proprietor of Macrobotanical Analysis.

Mr. Karl Kibler is an Archeologist/Geomorphologist at Prewitt and Associates, Inc.

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One thought on “An Unusual Case of Good Charcoal Preservation in Central Texas (Bush and Kibler)

  1. I like it; nice article Leslie. You might want to take a look at a shelter collection from Coryell co. Near Mother Neff park donated by Cecil Calhoun. It is the only known collection of perishable assemblages from a shelter along the Leon. HJS

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