Features and Chronology
At archaeological sites, features represent locations of concentrated activity. Imagine your house as an archaeological site: your kitchen, discovered by future archaeologists, would be a feature, but so would your oven and sink. Features can have a variety of sizes, shapes, and functions, and they are apparent at different scales, depending upon how well a site is preserved. Comparable to your oven, prehistoric inhabitants used hot rocks to cook. These features are called hearths, and the result of re-using hearths over-and-over are burned rock middens. These and many other features will be described below.
Also discussed below is how we determined chronology: what resources were being used during what time. Today, past time is determined by a number of complex lab tests. These tests are less important to understand at this moment, and the results of these tests, the chronology of Zatopec, will be described in detail.
A total of 27 deposits originally identified as features were recorded at Zatopec; this number includes both the 1980s Southwest Texas State field schools as well as the CAS excavations. These features were classified based on form and perceived function into concentrations of burned rock (such as from cooking fires), storage/trash pits, hearths (pits), lithic concentrations, post holes, and human burials. Generally, the site's uneven depositional condition leaves the interpretations of many of these features open to question. After full excavation and documentation, some features were clearly the result of prehistoric human activities while others, unfortunately, were the products of burrowing animals.
Below are samples of features excavated during field schools (top row) and during 2007 excavations (bottom row). Burned rock concentrations are simply a cluster of burned rock and are the product of cooking with fire and heated stones. Storage/trash pits are features that intrude into lower sediment, but their exact function remains something of a mystery. Hearth pits are also intrusive, but were presumably related to smaller cooking episodes involving burned rock. Lithic concentrations are clusters of debris left over from manufacturing stone tools. Post holes are small intrusive features that are thought to have contained and supported posts for a structure. Burials are self explanatory, but they are omitted from illustration here due to their sensitive nature. Click on the photographs below to learn about the selected features.
Many of the artifacts and features recovered from Zatopec were placed in time by their association with diagnostic projectile points, those with a unique style that archaeologists know from work elsewhere to date to a certain period. But an important part of our analyses included radiometric dating. Radiometric dating (also called radiocarbon) is the analysis of radioactive isotopes present in archaeological material. Radiocarbon, or carbon-14, was the particular isotope used to obtain dates from Zatopec. Carbon 14 is consumed and turned into tissue by both plants and animals while they are living. The moment the plant or animal dies, radiocarbon begins to decay at a predictable rate. As a result, scientists and specialized machinery can measure the amount of radiocarbon remaining and calculate the amount of time that has passed since it began to decay (since the organism died). Samples selected for radiocarbon dating from Zatopec's artifacts included bison remains, human remains, and charcoal recovered from features.
Twenty-six total dates were obtained through radiometric analysis of organic remains recovered from Zatopec. All dates fell approximately within the last 2300 years before present; to us, this figure indicates the poor preservation of older organic components at the site since stone tools suggested a much longer history. Additionally, many charcoal samples taken from features, such as the large burned rock midden and Burial 1, revealed that a good portion of the site's sediment was mixed (this was to be expected based on the geoarchaeological work described elsewhere). Analyzed bison bones show that site occupants were bison hunting prolifically during Toyah times and also, to lesser degrees, during the Late Archaic period and colonial era. Radiocarbon analysis of the human remains indicated that two of the individuals perished quite close together in time, approximately 1300-1305 years ago. The third individual died perhaps 50 to 100 years later. The fact that the three dates are so close together clearly shows that people returned to this particular location to bury their dead.
In addition to directly dating crucial components of the site, radiometric analysis provided some answers to long-addressed archaeological questions in Texas. For example, the presence and absence of bison during particular time periods has been a topic of research by archaeologists for decades. Our study of bison remains shows the usefulness of analyzing bison remains directly in order to clearly define periods of use. Theoretically, this method could be used on any of a number of animal and plant remains, as long as the species could be identified by specialists and archaeologists can positively associate these remains with past human behavior.