Obsidian Hydration Research Articles

Obsidian hydration dating by infrared transmission spectroscopy

AbstractThe obsidian dating method converts the quantity of diffused molecular water within a near‐surface hydration layer to elapsed time using an experimentally derived diffusion coefficient predicted from the structural water content of the glass. Infrared spectroscopic transmission measurements on transparent archaeological samples record vibrational responses of water bands in the near‐infrared region, permitting determination of structural water content (OH), and the amount of diffused ambient water (H2O). In this application, the H2O water band at 5200 cm−1 is measured directly. The accuracy of the approach is assessed by an evaluation of the precision of each contributing variable. The new protocol is evaluated using obsidian artifacts from radiocarbon‐dated deposits at Salamanca Cave in Argentina.

A novel approach to documenting water diffusion in ancient obsidian artifacts via the complexity analysis of microscope images

The diffusion of water through the surface of archaeological obsidian is mainly a temperature-dependent and concentration driven phenomenon that forms the basis of the hydration dating (OHD) method. For the first time, we apply a novel fractal approach, which explores the various attributes of images linked to the variation in water concentration and structural deficiencies within the hydrated layer. The microscopic images of hydrated layers on two obsidian specimens from Africa spanning thousands of years have been investigated. Seven complexity measures of fractal dimension (succolarity, lacunarity, correlation dimension, local connected fractal dimension (LCFD), fractal fragmented index (FFI), entropy and normalized Kolmogorov complexity (TIFF-LZW)), were applied to the hydration layer images. It was found that the effective determination of diffusion depth mainly comes from the application of succolarity, FFI and LCFD fractal indices, plus the structural deficiencies at the surface and the misconnected lacunas at the interface of the water diffusion layer and unaltered obsidian. The difference between fractal dimensions of the hydrated area and the non-hydrated images turned out to be a crucial quantitative parameter. Accordingly, we found that especially the succolarity, which is based on the capacity of a water fluid to percolate through the obsidian area in a given direction, was critical to determine the characteristics of the obsidian hydration layer. The FFI and LCFD estimate the compaction/fragmentation and connectivity, respectively. Therefore, the fractals play an important role in understanding the general diffusion in solids theory and the study aims at providing a new direction in the OHD and diffusion fields concerning the complex dynamic systems and structures which display a fractal pattern.

Obsidian hydration dating helps understand pre-hispanic land use on the volcanic island of Tenerife, Canary Islands, Spain

Critical to the survival of island-based human societies is their resilience and adaptation to volcanic hazards. We here evaluate pre-Hispanic (before 15th century AD) land use patterns on the volcanic island of Tenerife, Canary Islands, Spain using obsidian hydration dating (OHD). The samples studied include archaeological artifacts and natural rock chips from multiple sites of different elevation and micro-climate settings. We systematically collected samples from the southern dry area around Barranco de las Monjas in the Bandas del Sur. These include a total of 28 isolated artifact scatters (here, a scatter is defined as a minimum spatial unit of artifacts distributed spatially limited range on the surveyed surface), one dwelling, and several pyroclastic deposits containing obsidian clasts. We also collected several artifacts adjacent to a large obsidian flow of Tabonal Negro in the Las Cañadas Caldera. Unsystematic surveys in north of Mt. Teide identified large obsidian outcrops located at Tabonal de los Guanches and Charco del Viento. Size differences among surface-derived obsidian artifacts (i.e., Bandas del Sur, Las Cañadas Caldera, Icod Valley) suggest that pre-Hispanic groups utilized obsidian from multiple outcrops over wide areas. Hydration analysis on 136 obsidian flakes collected from both surface and buried contexts showed only minor obsidian hydration rims (5% of total samples) and varied mean rim thicknesses (0.6–3.5μ). The low percentage of hydration rim formation may be caused by environmental factors such as wind erosion, thermal effects from volcanic or natural ground fires, or due to obsidian geochemistry (low SiO2 and water content of phonolitic obsidian). Surface-collected obsidian flakes from the southern dry area do contain hydration rims along internal fissure. The estimated hydration rates from these samples can provide an approximate age when compared to buried obsidian artifacts with associated radiocarbon dates.

Obsidian Hydration Dating: Summary and Status of a Physics-Based Approach

ABSTRACT Obsidian hydration dating (OHD) is a method of computing archaeological ages based on measuring water absorption by obsidian artifacts, and is widely used in the western United States. This abstract provides a single resource for the OHD user, including advances over the past decade. We describe obsidian mineralogy as it affects OHD; the effects of structural water content on hydration; the mathematical form of the hydration law; methods to control for structural water content and temperature history; methods for computing hydration rates; an analysis of error sources; and a method for conducting an OHD analysis. We address OHD as currently practiced in the western United States, based on optical microscopy, and do not describe newer, experimental methods such as Secondary Ion Mass Spectrometry or infrared (IR) spectroscopy. An associated OHD workbook in MS Excel is available on the website of the International Association for Obsidian Studies.

Beyond Ethnography and Beneath the Bedrock Mortars: The Eastern Transverse Ranges of Southern California as Early Holocene Refugia

ABSTRACT Rock Camp (CA-SBR-342) in the San Bernardino Mountains has been regarded as a seasonal Late Prehistoric Complex acorn processing base camp since it was excavated in the 1960s. Reanalysis of its collections and new investigations at the nearby Willow Creek Crossing sites permit reevaluation of archaeological models for the Transverse Ranges of southern California and the adjacent Mojave Desert. Diagnostic artifacts, site structure, and obsidian hydration dating indicate montane Greven Knoll I (9,400-4,000 BP) occupations in inland southern California several millennia earlier than has been previously posited. Moreover, the presence of stemmed points suggests that the Greven Knoll Pattern of the Encinitas Tradition was introduced into the region directly from the Mojave Desert during the onset of the Altithermal. This analysis also serves as a reminder for archaeologists to use ethnohistoric models with caution and to look beyond the obvious.

A molecular model for obsidian hydration dating

Water diffusion in high silica volcanic melts results in the formation of rhyolite glasses where hydroxyls are linked to the silica tetrahedra. Space between these linkages form pathways for the diffusion of molecular water into the glass surface during secondary hydration. The accumulation of water in the near surface forms a water-rich hydration layer that can be converted to time by the application of experimentally derived diffusion coefficients. In this paper, we summarize mechanisms for water diffusion in obsidian and use a diffusion pathway model as the basis for a more detailed understanding of the parameters that control the magnitude of the water diffusion coefficient, its constancy over time, and how the properties of the glass reflect the thermal history experienced during secondary hydration. We evaluate hypotheses about water diffusion in obsidian with new low temperature (140–200 °C) accelerated hydration experiments and present a calibration for the age determination of obsidian artifacts.

Obsidian Hydration Dating of Proposed Paleoindian Artifacts from Tulare Lake, California

ABSTRACT In this article, we report an obsidian hydration dating (OHD) analysis of 32 obsidian artifacts from the Witt Archaeological Locality in Tulare County, California. The artifacts (Western stemmed points, concave base points, crescents) were recovered from agricultural contexts, where provenience is indeterminate. Effective hydration temperature (EHT) was computed from local meteorological records. Hydration rates were based on geochemical source and adjusted for EHT, and ages computed based on the square–root–of–time model. Of the mean OHD ages, 80% are in the 7,000–9,000 cal BP range. The probability that the actual ages could be Clovis or earlier (>∼13,200 years) was computed based on the mean and standard deviation of the OHD ages.

Temperature-dependent variations in mineralogy, major element chemistry and the stable isotopes of boron, lithium and chlorine resulting from hydration of rhyolite: Constraints from hydrothermal experiments at 150 to 350 °C and 25 MPa

Rhyolite-hosted hydrothermal systems in the continental crust contain valuable energy and mineral resources that make them of special interest across several scientific disciplines. Despite extensive research on these systems, the temperature-dependence of chemical reactions between host rocks and aqueous-rich fluids and the mineralogical transformations resulting from these reactions are not well quantified. To expand our understanding of the controlling processes operating in these systems, we carried out seven laboratory experiments in which rhyolite was reacted with deionized water at 150 °C to 350 °C and 25 MPa. An additional experiment at 200 °C was carried out to examine the effect of dissolved CO 2 on the reactions. The overarching goal of this experimental study was to provide new insights on the temperature-dependence of water-rock interaction in continental hydrothermal systems. We applied a wide range of chemical, isotopic and mineralogical methods to analyze the reacted rhyolite and waters, and the major observations are: (1) the rhyolite progressively hydrates with increasing temperature between 150 °C to a maximum of 8.2 wt% H 2 O at 275 °C; hydration then decreases until 350 °C in conjunction with the destruction of the rhyolite glass and crystallization of secondary mineral phases; (2) the ratio of molecular water (H 2 O m ) to hydroxyl (OH − ) of the water that is dissolved in the reacted rhyolite decreases from ∼7 at 150 °C to ∼4 at 250 °C; (3) the main secondary minerals formed are the zeolite ferrierite (T ≥ 275 °C); biotite, albite and cristobalite mainly form at higher experimental temperatures (T ≥ 300 °C); (4) the reacted waters are nearly saturated with respect to amorphous silica; (5) at temperatures ≥ 275 °C nearly all the chlorine is leached into solution; (6) fluorine leaching from the rhyolite gradually increases between 150 °C and 250 °C, but then gradually decreases at higher temperatures and is incorporated into a secondary mineral phase; (7) dissolved CO 2 in the water enhances alkali metal cation leaching from the rhyolite; and (8) calculated Na-K and silica geothermometer temperatures differ from the experimental temperatures by varying amounts. In addition, apart from some small lithium isotope fractionation at temperatures ≤ 250 °C, the stable isotopes of boron, lithium and chlorine do not fractionate during rhyolite-water reactions, and the stable isotope compositions of these species in the reacted water are similar to those in the reactant rhyolite. These results provide new insights for a broad range of applications, including quantifying processes involving rhyolite glass hydration (obsidian hydration dating, perlite formation and discriminating secondary from magmatic water in rhyolitic matrix-glass of volcanic pyroclasts), for geothermal energy and mineral deposit exploration and for monitoring volcanoes.

Architecturally Modified Caves on Rapa Nui: Post-European Contact Ritual Spaces?

Caves on Rapa Nui that possess well-constructed tunnel entrance features are currently interpreted as places of temporary refuge (ana kionga) used in the late seventeenth century during a period of internal island conflict. The analysis of the cave interior architecture and artifact assemblage from Site 6-357 suggests an alternate interpretation where the caves may have served as prepared ritual spaces where food consumption, sewing and body adornment were conducted. Radiocarbon and obsidian hydration dating indicate that the caves were most likely constructed after European contact and were not present at an earlier time.

Architecturally Modified Caves on Rapa Nui: Post-European Contact Ritual Spaces?

Caves on Rapa Nui that possess well-constructed tunnel entrance features are currently interpreted as places of temporary refuge (ana kionga) used in the late seventeenth century during a period of internal island conflict. The analysis of the cave interior architecture and artifact assemblage from Site 6-357 suggests an alternate interpretation where the caves may have served as prepared ritual spaces where food consumption, sewing and body adornment were conducted. Radiocarbon and obsidian hydration dating indicate that the caves were most likely constructed after European contact and were not present at an earlier time.

In-situ multi-analytical characterization of original and decay materials from unique wall mirrors in the House of Gilded Cupids, Pompeii

The House of Gilded Cupids (Regio VI, Insula 16, 7, 38) was unquestionably one of the most important residences of Ancient Pompeii, where important archaeological artefacts such as mural paintings, mosaics, sculptures and lalariums were rediscovered. This work characterizes two wall mirrors that, together with those recovered from the House of Efebo and the Domus of Euplia, represent the only ones found in the archaeological site of Pompeii. The 2015 and 2016 expeditions of the Analytica Pompeiana Universitatis Vasconicae project performed an in situ multi-analytical study, using only portable non-destructive analytical techniques. Molecular data provided by Raman spectroscopy suggested obsidian was the reflective matrix for both mirrors. Elemental data provided by energy dispersive X-ray fluorescence and laser induced breakdown spectroscopy (LIBS) systems were concordant with Raman spectroscopic results, enabling the detection of Ca, K, Al and Na as the main elements included in the Si matrix characteristic of obsidian igneous rocks. The LIBS data confirmed the presence of obsidian hydration layers. All techniques were used to investigate the degraded white and yellow crusts of the mirrors. Gypsum (CaSO4·2H2O) and nitrocalcite (Ca(NO3)2·4H2O) were identified in the white areas and gypsum and goethite (α-FeOOH) in the yellow crusts. LIBS depth profiling on the white crusts found a layer of nitrocalcite on top of the gypsum layer. Gypsum and goethite were proposed to form after partial dissolution of the mortars patches (with high iron contents) used in modern restorations around the mirrors, followed by a reprecipitation on the surface of the mirrors. Nitrocalcite was proposed to form after the attack of atmospheric NOx on gypsum crusts. These results represent the first analytical work focused on the study of these unique mirrors and provide the knowledge needed for defining more adequate conservation treatments.

A systematic comparison of obsidian hydration measurements: The first application of micro-image with secondary ion mass spectrometry to the prehistoric obsidian

Archaeologists have long used obsidian hydration dating method to give chronometric dates for obsidian artifacts. Models using these equations independently employ different measurement systems, which are based on rim thicknesses determined by optical microscope and hydrogen depths measured by secondary ion mass spectrometry (SIMS), respectively, although the inconsistency of both measurements has been reported. Firstly, this paper describes a systematic comparison that was done on optical rim thicknesses and hydrogen depths by means of an isotope microscope, which provides micro-imaging with SIMS. Depth profiles of hydrogen were precisely obtained from the spots where optical measurements were taken on the archaeological obsidian flakes from two distinctive cultural horizons (older: Upper Paleolithic, younger: Initial Jomon) in the stratified open-air site of Jozuka in southern Kyushu (Japan). Secondarily, using the measurements of hydrogen depths that are the most consistent to the measurements of optical thicknesses, the estimated hydration rate of the Holocene (Initial Jomon) is slower than that of the Late Pleistocene (Upper Paleolithic), implying that the difference in hydration rates was due to the difference of intrinsic water content of obsidian and/or obsidian geochemistry. An application of micro-imaging with SIMS to measure hydrogen depths on obsidian shows promise as a tool for improving the practice of hydration dating and evaluating local climatic condition.

Native acquisition of obsidian in colonial-era central California: Implications from Mission San José

In many regions, the mechanisms by which indigenous people acquired lithic materials during the colonial period are only poorly understood. We take on these issues through the examination of more than 1100 obsidian artifacts recovered from the Native American neighborhood at Mission San José (ca. CE 1797–1840) in central California. We conducted a multifaceted analysis of the assemblage, with an eye toward understanding how indigenous people in this region acquired obsidian after the onset of missionary colonialism. Our study included analysis of technological attributes, geological provenance via X-ray fluorescence spectrometry, and dating through obsidian hydration. Our results demonstrate that native people living at Mission San José acquired obsidian both through long-distance conveyance from source areas and through some recycling of archaeological artifacts. We compare our results to regional precontact patterns of obsidian acquisition and conveyance as well as obsidian assemblages from other colonial-era sites in central California. Taken together, our study indicates persistent yet modified pathways of obsidian acquisition in central California during the colonial period.

Fluted and Basally Thinned Concave-Base Points of Obsidian in the Borden Collection from Inyo County, Alta California: Age and Significance

This article describes, classifies, and provides the calculated ages of 14 basally thinned and fluted points of obsidian in the Borden collection from Rose Valley in southern Inyo County, California. With the exception of one item of Fish Springs obsidian, the specimens are all made of glass from geologic subsources in the Coso Volcanic Field. Typologically, the fragmentary and reworked artifacts appear to represent Clovis, or perhaps Clovis-derived, concave-base lanceolate points. Obsidian hydration measurements permit age calculations that range between approximately 13,793 and 11,308 calendar years ago. The calculated ages of the Borden artifacts are consistent with their discovery on landforms associated with Younger Dryas and very early Holocene wetlands. Our research results also suggest that Clovis technology may have persisted longer in California than it did in the southeastern, central, and southwestern United States.

Bedrock mortars as indicators of territorial behavior in the Sierra Nevada

Bedrock mortars were an integral part of intensive acorn economies in Native California and are a prominent feature of the Late Holocene archaeological record of the Sierra Nevada. Construction of these milling features also indicates a long-term investment in the landscape. Ethnographic evidence suggests the importance of local acorn crops and other resources led to ownership and defense of property and resource rights in many areas. Through a combination of time-sensitive projectile points and obsidian hydration dating, we show that bedrock mortars became widely used in the Sierra Nevada after 1300 cal BP, and that this was coincident with the arrival of the bow and arrow to the region. When and where bedrock milling features occur provides evidence for evolving territorial behavior during the Late Holocene and further insights into how prehistoric Californians leveraged technology and behavioral changes to solve the difficult problem of making a back-loaded resource both palatable and profitable.

AFM and SIMS surface and cation profile investigation of archaeological obsidians: New data

Abstract Obsidian surface roughness and rind structure both play a major influence on the Obsidian Hydration Dating (OHD). AFM (Atomic Force Microscopy) investigation coupled with quadrupole SIMS hydrogen data profiles establish a validation criterion of quantitative evaluation of roughness for OHD dating purposes. More evidence of the importance of the surface morphology at the nanoscale is given for five obsidian tools of different origin. The latter relates to the dynamic ion influx diffusion kinetics between surface and surrounded sediment media, and the obsidian structure, thus, 2D and 3D surface mapping, as well as, cation profiling (H, C, Mg, Al, F, S, Cl, CN, O isotopes) were made by TOF-SIMS and quad-SIMS. It was found that the C and Mg are considered as imposed criteria for accepting suitability of H + profiles for further processing by SIMS-Surface Saturation dating method. The effect of roughness to dating is discussed.

風化変質層の発達速度に関する一考察

Many researchers have studied rates of weathering layer development. Weathering layers broadly include weathering rinds, hydration layers, rock varnish, and weathering crusts, each of which has been discussed within individual research fields. To understand the development of these weathering layers, previous research on the growth rates of weathering layer thickness and formation processes is reviewed. Then, terminology relating to weathering layers is elucidated. Weathering rind development is affected by the porosity and mobility of many elements. Conversely, the obsidian hydration layer is mainly controlled by moisture content and rock varnish is influenced by microbial activities. Environmental differences in the thickness of these thin weathered or alteration layers with weathering time are also examined. Although data are limited, the growth of weathering rind thickness varies by rock types and environmental conditions. The next stage of weathering rind studies will be supported by the progress of analytical methods including isotopic elements, interpretation of rock properties, biomineralization, and introduction of environmental parameters.

Obsidian conveyance and late prehistoric hunter-gatherer mobility as seen from the high Wind River Range, Western Wyoming

Sampling 16 of 52 house features at High Rise Village (HRV; 48FR5891), a large residential locus at 3,273 m (10,720 ft) elevation in Wyoming's Wind River Range produced 25 AMS dates, 23 diagnostic projectile points, 148 obsidian artifacts (mostly retouch debris) as well as abundant chert debitage, small quantities of faunal bone, and groundstone milling equipment. Based on AMS, projectile point, and obsidian hydration data, the site's lodges appear to have been occupied on a sporadic basis mainly between 2,300 and 850 cal BP. Source provenance determination made via X-ray fluorescence spectrometry indicates that most of the obsidian at the site originated in Jackson Hole and secondarily is from Yellowstone Plateau sources, suggesting a Late Prehistoric residentially-mobile, seasonal, and elevationally transhumant settlement system focused on the Jackson Hole area. GIS-based assessments of the costs of procuring the obsidian found at HRV suggests, however, that though economic considerations certainly played a principal role in determining obsidian conveyance decisions, other factors such as social or cultural dynamics may have conditioned the preference for Yellowstone sources over eastern Idaho sources, ultimately suggesting that social boundaries played a role in generating the different toolstone conveyance zones seen in the region during the Late Prehistoric.

Calibrations for the determination of water species in bulk and hydrated obsidian by infrared photoacoustic spectroscopy

The obsidian hydration dating method requires a measurement of the amount of diffused water (%H2OD) within the surface hydration layer and an assessment of the structural water (%OH) contained within the underlying glass matrix. Infrared photoacoustic spectroscopy (IR-PAS) has the ability to sample deeply within the glass and capture both regions simultaneously. The calibrated infrared water band at 3570cm−1 may be used to measure total water (%H2Ot=H2Om+OH) content and the concentration of diffused molecular water (%H2OD) is assessed with the band at 1630cm−1. Subtraction of the band specific concentrations provides an estimate of the obsidian structural hydroxyl (%OH) content. Calibrations of the IR-PAS water bands, to permit inferring water concentrations from IR-PAS measurements, were developed using obsidians of known water content established by standard infrared transmission. Three calibration equations are presented, for H2Ot, H2Om, and OH, along with computed estimates of accuracy.

The significance of obsidian hydration dating in assessing the integrity of Holocene midden, Hokkaido, northern Japan

Since its novel invention in 1960, obsidian hydration dating is now recognized as the chronometric method to give dates of archaeological sites, based on measurements of hydration rim thickness. Contrary to the increased awareness of various factors that affect hydration rates and reliability in measurements, the question whether and the extent to which the validity in the rim thickness measurements corresponds to the interested event has been less discussed. Here, validity of obsidian hydration dates that designate event of human site occupations is discussed in terms of site integrity of the Early Jomon midden in the Holocene site of Ocharasenai (OCH), Hokkaido, northern Japan. Expected integrity of the midden evidently left by prehistoric hunter–gatherers is tested through a comparison of microscopically-measured average rim thicknesses between the primarily extracted specimens and those chosen after assessing the validity. No statistical difference in estimated hydration dates between these two groups supports high integrity of the midden. The estimated date for the Early Jomon occupation at the OCH is 4388–4942 BP, fallen into the end of Middle Holocene. Results of the present examination indicate that obsidian hydration dating will aid to understand site formation processes.