Obsidian Hydration Research Articles

Archaeology in Eastern Africa: Recent Developments and More Dates

Obsidian hydration dating has been successfully applied to East African archaeological sites. Chemical sourcing of obsidian artefacts has documented long-distance movement of obsidian from the Central Rift valley. A date in the ninth or eighth century b.c. has been obtained for iron objects in the Er Renk District of the Southern Sudan. Tentative culture-historical sequences are available from excavations around the Sudd and in the Lake Besaka region of Ethiopia. Archaeological research has begun in the interior of Somalia. In northern Kenya, claims that Namoratunga II is an archaeo-astronomical site have been challenged. Excavations at Mumba-Höhle and Nasera have shed new light on the transition from the Middle to Later Stone Age in northern Tanzania perhaps 20,000 to 30,000 years ago. Knowledge of the Elmenteitan Tradition has been considerably advanced by excavations in south-western Kenya. Iron-smelting furnaces with finger-decorated bricks have been discovered in south-eastern Kenya, though not yet dated. New dates falling in the last few centuries have caused first millennium a.d. dates obtained previously for Engaruka to be rejected. Excavations at several sites on the East African coast indicate that the beginnings of coastal occupation from the Lamu archipelago to Mozambique fall in the ninth century a.d. In Malawi the Shire Highlands seem to have been settled around the tenth century a.d. Investigations of large smelting-furnaces in central Malawi indicate that they were used as concentrators of poor-quality iron ore. Excavations in rock-shelters on the southern edge of the Copperbelt have produced a culture-historical sequence spanning the last 18,000 years. The western stream of the Early Iron Age was established in the Upper Zambezi valley by about the mid fifth century a.d.

Geological Age Determinations by Non-Radiometric Methods

Because no one was around to chronicle most of the geological events which occurred during the earth's history, it is necessary to rely upon somewhat less direct (but no less useful) methods to place these events in the proper time frame. The basic assumptions used are 1) we live in an ordered universe, and 2) physical laws have not changed through time. The assigning of an age (in years) to a particular event requires that some process having a predictable rate be utilized. Various radioactive nuclides are commonly used but a number of other methods provide supplementary or complementary chronologic information. These other methods include tree-ring counting, varve counting, thermoluminescence, amino acid racemization, obsidian hydration, and magnetic reversals. Because of the cross testing of methods and the interlocking nature of the age data, the geologic time scale rests upon a very firm foundation.

Some Practical Applications of Obsidian Hydration Dating in the Subarctic

Eight case studies of obsidian hydration dating in the Koyukuk River region of northwestern interior Alaska are discussed. Historiographic conclusions include recognition of late and early microblade industries, apparent verification of the hypothesis that northern fluted points date within a Paleo-Indian time frame, and validation of a Tuktu-like first millennium A.D. Northern Archaic phase. However, variance in the data and lack of firm hydration rates render the results less precise than is desired. Methodological conclusions have ramifications that should apply throughout the subarctic region and well beyond. These are: 1) Hydration measurements may be unreliable for dating individual specimens; 2) Lack of closely controlled hydration rates or dependence on 14-C dates with large errors for calibration can be crippling; 3) The average of a series of specimens can be used to date components which were formed during a brief period of occupation, though high variance of the data may be disconcerting; 4) Variance was low in one case for specimens all derived from the same piece of raw material, but for dating it may be necessary to find, through induced hydration or other means, the precise hydration rate applicable to each different piece of raw material (from a single component); and 5) Many variables may be responsible for results which render some sample sets unreliable or unusable, especially those from surface sites. Some of these variables require further technical investigation - loss of the hydration layer and recommencement of hydration after exposure to forest and tundra fires, for instance. Other factors are reasonably well understood by researchers, but it would be desirable to have computer simulations of site contexts in order to assess the magnitude, correlations, and cumulative results of their effects.Key words: archaeology, western Subarctic, Alaska, dating, obsidian, obsidian hydration

Obsidian Hydration Dating Update

The obsidian hydration dating technique has been refined since its invention in 1960. The hydration process slows down as it proceeds and appears to follow the relation: hydration thickness is proportional to the square root of time. The variables that influence the hydration rate are mainly the temperature experienced by the object to be dated and its chemical composition.Methods of estimating effective integrated field temperatures and composition variables of obsidians are discussed.

Obsidian Dating in California: Theory and Practice

A review of the obsidian hydration rates proposed for California obsidian sources raises questions of both practical and theoretical nature about the use of obsidian dating. Obsidian hydration rates so far proposed (primarily but not exclusively by Jonathon Ericson) require careful evaluation and checking against empirical data; routine use of the preliminary rates ignores cautions raised by the investigators and can lead to inaccurate chronological determinations. Used with discrimination, however, obsidian dating does yield chronological ages in which there can be a reasonable degree of confidence.

UCLA Radiocarbon Dates X

The measurements reported in this date list form the chronometric framework for obsidian hydration and trade studies in California (Ericson, 1975; 1977; 1978; 1981; Ericson et al, 1975; Singer and Ericson, 1977). All samples were analyzed as CO2 gas at close to 1 atm in a 7.5L proportional counter with three energy channels. Radiocarbon ages are based by convention on the 5568 ± 30 yr half-life. The biospheric standard is 95% the count rate of NBS oxalic acid for radiocarbon laboratories. Background is based on CO2 obtained from marble. Counter operation is checked against a historically dated wood sample from the funerary boat of Sesostris III, 1872 +4−8 BC (Hayes, 1962). All samples were subjected to accepted NaOH, HCl or other special chemical treatments to exclude contamination. No tree-ring calibration was applied to any of the samples listed.

Obsidian hydration dating of volcanic events

Obsidian hydration dating of volcanic events had been compared with ages of the same events determined by the 14C and KAr methods at several localities. The localities, ranging in age from 1200 to over 1 million yr, include Newberry Craters, Oregon; Coso Hot Springs, California; Salton Sea, California; Yellowstone National Park, Wyoming; and Mineral Range, Utah. In most cases the agreement is quite good. A number of factors including volcanic glass composition and exposuretemperature history must be known in order to relate hydration thickness to age. The effect of composition can be determined from chemical analysis or the refractive index of the glass. Exposure-temperature history requires a number of considerations enumerated in this paper.

A New Obsidian Hydration Rate in the Greater Southwest

A new obsidian hydration rate is proposed for archaeological obsidian derived from the Antelope Wells source area located along the international boundary between the United States and Mexico near the Antelope Wells border crossing in Hidalgo County, New Mexico. Prehistorically, obsidian from this source was used extensively in the region lying between Casas Grandes, Chihuahua and Lordsburg, New Mexico. As the Antelope Wells source is the only one occurring within this area the new rate should provide archaeologists working in the region with an accurate and reliable absolute dating method.

Buffalo Jump Complexes in Owyhee County, Idaho

(1978). Buffalo Jump Complexes in Owyhee County, Idaho. Plains Anthropologist: Vol. 23, No. 82, pp. 213-221.

Obsidian Hydration Profiles Measured by Sputter-Induced Optical Emission

The variation of concentrations of hydrogen, sodium, potassium, lithium, calcium, magnesium, silicon, and aluminum as a function of depth in the hydration layer of obsidian artifacts has been determined by sputter-induced optical emission. The surface hydration is accompanied by dealkalization, and there is a buildup of alkaline earths, calcium and magnesium in the outermost layers. These results have clarified the phenomena underlying the obsidian hydration dating technique.

Obsidian Sources in Guatemala: A Regional Approach

Geologic sources of obsidian are frequently treated in the archaeological literature as single, discrete flows, each being recognized as a different source as long as it can be geographically isolated. However, some recent studies show a tendency toward the correction of this misconception, and toward defining operationally the obsidian source concept on a regional basis. This work is intended to help achieve such definition for a number of obsidian sources in the central highlands of Guatemala. Geochemical characterization of samples from diverse source localities, attained by means of neutron activation analysis, is utilized for this purpose. The information thus obtained has importance to a number of fields of research in archaeology. To the now-routine studies on prehistoric trade routes, other lines of investigation can be added, namely the determination of source-specific obsidian hydration rates for dating purposes, and the reconstruction of structural features in sociocultural systems.

Summary of the 1978 Northwestern Wyoming Archeological Project

Only a brief summary of the results can be presented at this time as the data are still being analyzed. Mitigation was completed on the reconstruction of the Mammoth Water System, Yellowstone National Park. The system begins at the intake at the confluence of Indian Creek and the Gardner River. The pipeline runs into Mammoth Hot Springs. Our field research consisted of the recording of cultural resources, test excavations at 50 meter intervals along the pipeline, and the excavation of the Bear Claw site (48YE504). The latter produced a range of projectile point types suggesting intermittent occupations of the site back to at least 7000 B.P. Also recovered were parts of a butchered elk (Cervus canadensis) in association with obsidian tools. Eventually, we will be able to obtain obsidian hydration dates from these tools and hence some minimal data concerning the temporal duration of elk in northern Yellowstone Park.

An Obsidian Hydration Rate for the Lower Columbia River Valley

AbstractA hydration rate for obsidian of 1.3 μm2 per 1,000 radiocarbon years has been calculated for the lower Columbia River Valley of Oregon and Washington. The rate provides a means for dating prehistoric archaeological sites containing obsidian in terms of their radiocarbon age.

A Revision in the Government Mountain-Sitgreaves Peak, Arizona, Obsidian Hydration Rate

ABSTRACTA revised hydration rate for obsidian from the central Arizona Government Mountain-Sitgreaves Peak source area is presented. Data obtained since 1975 suggest that the hydration characteristics of obsidian from 1 to 6,000 years B.P. can best be predicted using a simple squared diffusion model. This new rate improves the accuracy of previously reported rates and, consequently, will increase the usefulness of obsidian hydration dating throughout central and northern Arizona.

Obsidian Hydration Studies in Highland Ecuador

A total of 383 obsidian hydration measurements are reported for highland Ecuador. Specifically, hydration rim measurements have been used to test the reliability of five radiocarbon dates from the site of El Inga, and three of them are shown to be too young.

Obsidian hydration dating and correlation of Bull Lake and Pinedale Glaciations near West Yellowstone, Montana

The ages of the last two glaciations near West Yellowstone, Montana, can be calculated by obsidian hydration techniques that are calibrated by K-Ar dating of obsidian-bearing lava flows. The average age of glacial abrasion of obsidian in the Pinedale terminal moraines is about 30,000 yr, with most age measurements between 20,000 and 35,000 yr. For the Bull Lake moraines, it is about 140,000 yr, with most measurements between 130,000 and 155,000 yr. This age for the Bull Lake moraines is also supported by geologic relations that show that the moraines are older than a rhyolite flow dated by K-Ar as 114,500 ± 7,300 yr old (lσ). These obsidian hydration ages of the Pinedale and Bull Lake Glaciations correlate well with the last two cold intervals of the marine record. The age determined for the Bull Lake Glaciation near West Yellowstone antedates the last interglaciation of the marine record, which is commonly correlated with the Sangamon Interglaciation. Our results suggest correlation of the Pinedale Glaciation near West Yellowstone with much or all of the Wisconsin Glaciation and of the Bull Lake with the late Illinoian. This differs with the commonly accepted correlation of the Pinedale with the late (“classical”) Wisconsin and of the Bull Lake with the early Wisconsin. The correlation of Bull Lake with late Illinoian appears equally or more compatible with traditional criteria for correlation, namely comparative soil development and degree of preservation of morainal morphology.

New results in obsidian hydration dating

Abstract A number of source‐specific obsidian hydration rates are proposed for California obsidian sources. Based on these findings, two major modifications are suggested as refinements of the present obsidian hydration dating technique: (1) source‐specific obsidian hydration rates should be determined for individual obsidian sources within a given geographic region, and (2) which will necessitate the identification of the source of each obsidian artefact for greater precision of obsidian hydration dating results.

A New Obsidian Hydration Rate for Certain Obsidians in the American Southwest

A new hydration rate is presented for the Government Mountain-Sitgreaves Peak obsidian source in Arizona. It is based on an analysis of hydration measurements from a series of independently dated obsidian artifacts from that source. Since obsidian obtained from Government Mountain-Sitgreaves Peak was widely traded in the prehistoric Southwest, the new hydration rate should provide archaeologists working in many parts of the Southwest with a reliable and inexpensive absolute dating technique.

Obsidian hydration profile measurements using a nuclear reaction technique

Ambient water diffuses into the exposed surfaces of obsidian, forming a hydration layer which increases in thickness with time to a maximum depth of 20-40 μm (ref. 1), this layer being the basic foundation of obsidian dating. We have used the resonance at a ^(19)F energy of 16.45 MeV (0.83 MeV centre-of-mass energy) (ref. 4) in the nuclear reaction ^1H(^(19)F,ɑy)^(16)O to measure directly the hydration profiles of obsidian samples. This technique has already been used to measure the hydrogen concentration profiles in lunar samples and other solids to depths up to 0.4 μm with a resolution of 0.02 μm (refs 5 and 6). A second strong resonance at 17.64 MeV is encountered in extending these measurements to greater depths but its contribution can be unfolded from the data.

TEMPORAL ORDERING OF SURFACE‐COLLECTED OBSIDIAN ARTIFACTS BY HYDRATION MEASUREMENT

ABSTRACTSTwo samples of obsidian projectile points from northwestern Nevada, one surface collected and the other excavated, were subjected to obsidian hydration measurement. The temporal ordering of the three projectile‐point types in each of the two samples was demonstrated to be the same on the basis of their hydration measurements. The validity of this temporal ordering of the projectile‐point types in the two samples was confirmed by the stratigraphic sequence of the types in the excavated sample.We have found that surface‐collected obsidian artifacts can be relatively dated by hydration measurement. In northwestern Nevada they hydrate at a rate almost double that of their excavated typological counterparts, but their relative ordering remains the same.