Cation-ratio Dating Research Articles

Age estimation of tectonically exposed surfaces using cation-ratio dating of rock varnish

Cation-ratio dating (RCD) is a non-destructive and rapid means of dating rock varnish. This study explored that use of rock varnish RCD as a means of aging tectonically exposed surfaces in a semi-arid region of northwestern Greece with varying degrees of tectonic activity. Tectonic structures in the study region were identified and aged using conventional dating techniques, and faults were classified as active, potentially active, or inactive. A stringent field sampling methodology was adopted which successfully determined the concentrations of calcium, potassium, and titanium cations in rock varnish on the exposed surfaces of these faults. Results showed that RCD was a valuable tool for dating tectonic structures, and could be used to determine their activation age. The rapidly obtained results of this study could be used to expedite the identification of active and potentially active faults. Furthermore, these findings would contribute to neotectonic mapping efforts and other studies that relate to the tectonics of a specific area. The RCD method was less destructive and more accurate compared to alternative numerical dating methods and was a rapid means of identifying tectonically active faults. It has the potential to be employed in managing future disasters and mitigating serious economic repercussions from tectonic activity.

A review of the history of dating rock varnishes

The history of rock varnish dating spans almost 20 years from the initial suggestion to use uranium series isotopes through the use of a geochemical ratio (cation-ratio dating) to the current application of accelerator mass spectrometry radiocarbon dating (AMS 14 C ). Uranium isotopes were ignored while other dating methods were tested exhaustively on several continents. Evidence of the unreliable dating of the formation of varnishes using cation-ratios was demonstrated by examples of environmental and textural observations reflecting localised leaching, and by chemical analyses that contradicted the fundamental assumptions of the method. The radiocarbon dating of substances embedded in varnishes is also problematic where carbon compounds and sources are not identified. The incompatible coexistence of different carbonaceous components, a recent controversial issue, is explained with reference to different environments of formation. The future of AMS 14 C dating of rock varnishes centres around overcoming the practical limitations of sampling and analysing extremely small quantities of carbon-bearing substances. Future directions for dating varnished rock surfaces may include innovative refinements to the U-series, cosmogenic isotope and luminescence methods.

Cation-Ratio Dating and Archaeological Research Design: Response to Harry

Harry's recent paper in this journal critiques the use of cation-ratio dating to assess the age of surface-collected artifacts as part of a rejection of this dating technique in general. However, Harry's negative conclusions are difficult to reconcile both with the seemingly successful application of cation-ratio dating as part of the Intermountain Power Project (IPP) in California, the only other project in which surface artifacts have been cation-ratio dated, as well as with Harry's own data. The present comment details substantial differences in (1) the rigor and sophistication of the research designs applied by Harry and the IPP research and (2) the integrity of the sites on which these two projects worked, and points out important components of Harry's data that are inconsistent with her conclusions. Cation-ratio dating is certainly not yet perfected as a dating technique, but the available data indicate clearly that Harry's critique is seriously flawed.

Reply to Bamforth

Bamforth contends that research conducted into cation-ratio dating at CA-KER-140 was flawed because of (1) a poorly conceived research design, (2) a lack of site integrity, and (3) misinterpretation of the chemical data. He further argues that processes affecting artifact stability at KER-140 were absent from the IPP sites. As a result, he suggests that the conclusions presented in my earlier article are unsound and irrelevant to the interpretation of previously derived cation-ratio dates. In this article I respond to these assertions. Specifically, I demonstrate that Bamforth has failed to establish grounds for dismissing either the KER-140 research design or the chemical results obtained from that study. In addition, I review descriptions of the IPP sites presented elsewhere by Bamforth and conclude that these descriptions support the interpretation of artifact instability at the IPP sites.

Cation-Ratio Dating of Varnished Artifacts: Testing the Assumptions

Dorn (1983) has proposed that changes in rock varnish chemistry can be used to date varnished artifacts. Specifically, he suggests that the varnish cation ratio, (K + Ca)/Ti, decreases as the age of the varnished surface increases. Although the method is generating significant archaeological interest, many of its underlying assumptions remain undemonstrated. This paper examines one premise of the method, that the varnishing process is regular. Data obtained from varnish distributional studies challenge this assumption and, when compared with the chemical data obtained from the same archaeological site, suggest that the cation-ratio dating technique may not be able to provide accurate dates for most varnished artifacts.

Evidence Suggesting That Methods of Rock-Varnish Cation-Ratio Dating Are neither Comparable nor Consistently Reliable

Using samples from a prehistoric quarry site in the Mojave Desert, we tested and compared the two principal methods of rock-varnish cation-ratio dating, analysis of rock-varnish scrapings (R. I. Dorn, 1983, Quaternary Research 20, 49-73 and 1989, Physical Geography 13, 559-596) and analysis of rock varnish in situ (C. D. Harrington and J. W. Whitney, 1987, Geology 15, 967-970). Because we found no consistent relationship between the varnish cation ratio (K + Ca)/Ti, and the relative age of the varnish, neither method could be used to "cation-ratio date" the underlying chert artifacts. Moreover, in situ analyses yielded systematically higher cation ratios and lower Ti abundances than bulk analyses of scraped varnish or microprobe analyses of varnish in cross section. Our results, when considered along with other recently published evidence, indicate that these two methods of varnish chemical analysis and cation-ratio dating may not be comparable, nor consistently reliable, chronometers.

NEW PERSPECTIVES ON COLLUVIAL BOULDER DEPOSITS IN THE SOUTHWESTERN GREAT BASIN, USA

Colluvial boulder fields are ubiquitous on desert hillslopes in the Basin and Range Province. Five chronometric methods indicate that colluvial boulder fields in this region have been active in the late Pleistocene and Holocene: visual appearance, radiocarbon dating of wood, macrofossil analysis, varnish radiocarbon dating, and varnish cation ratio dating. A new method is presented to constrain the ages of colluvial boulder fields, using the presence of stable rock varnish and 36Cl; this method indicates that colluvial deposits at Buckhorn Mesa, southern Nevada, must be ≤ 310 ka. Rather than interpreting colluvial deposits from the traditional desert geomorphology framework of “relict” or “active,” we suggest that these features be studied from the perspective of ongoing processes using an independently established chronometic sequence.

AMS Radiocarbon and Cation-Ratio Dating of Rock Art in the Bighorn Basin of Wyoming and Montana

Samples of organic matter and rock varnish from seven rock-art sites in the Bighorn Basin of Wyoming and Montana were collected for dating purposes. Petroglyphs sampled include Dinwoody-style figures, shield-bearing warriors, and other well-known Plains rock-art motifs. Accelerator mass spectrometry (AMS) dating of 10 petroglyphs yielded dates from the Early Archaic to the Protohistoric periods. A strong numerical relation between varnish leaching and time was found for petroglyphs older than 1,000 years, permitting the derivation of a cation-leaching curve (CLC) and calibrated cation-ratio (CR) ages for 15 different petroglyphs. No clear numerical relation between varnish leaching and time was found for petroglyphs less than 1,000 years old, possibly due to historical damage or past environmental conditions. As a result, calibrated CR ages could not be derived for six petroglyphs, and they are considered to be only younger than 1,000 years. Although further research is needed to establish whether one CLC can be used for all petroglyphs in the region, these studies constitute the first numerical chronology for rock art in the Bighorn area. Results indicate the occurrence of spatially discrete, but temporally concurrent styles in the Bighorn Basin during the last 800-900 years.

DISTRIBUTION AND CHEMICAL COMPOSITION OF MICROCOLONIAL FUNGI AND ROCK COATINGS FROM ARID AUSTRALIA

Microcolonial fungi are found on rock coatings at various sites throughout the arid regions of Australia. Fungi tend to concentrate in depressions, although it is uncertain whether they contribute to enlargement of microhollows. As determined by SEM-EDAX, the chemical characteristics of microcolonial fungi are variable but do not reflect those of the surfaces on which they are found. Most fungi contain calcium, sulfur, chlorine and sometimes phosphorus, but not manganese, in quantities greater than those of adjacent rock coatings. Major sources for accumulated elements may be rainfall or dust. Some elements, especially calcium, are apparently concentrated temporarily in microcolonial fungi, with amounts present in dead organisms being relatively low. The incorporation of some dead microcolonial fungi into developing rock coatings is therefore unlikely to lead to anomalously high calcium levels for cation ratio dating. As rock coatings contain trace or undetectable amounts of some other elements concentrat...

Cation-ratio dating of rock-engravings: a critical appraisal

For a century, pictures painted and carved on to rock surfaces have been a vital and alluring strand of prehistoric evidence. Yet their dating remains a fundamental problem. The last few years have seen an interest in direct dating of rock-art, both painted and engraved, using the small-sample capabilities of the accelerator radiocarbon technique. Here. issue is taken with the security of one of the new methods, the cation-ratio technique for dating engraved figures in arid regions where a ‘desert varnish’ forms - a method whose results have already been published in Antiquity in 1988 and again in the present issue (pages 246–55 above).

Accuracy of rock-varnish chemical analyses: Implications for cation-ratio dating

To compare methods of rock-varnish chemical analysis and cation-ratio determination,we prepared three glass standards, synthetic analogues of rock varnish. Analysis of these standards demonstrates that material of varnishlike composition can be accurately and precisely analyzed by means of quantitative, energy-dispersive electron microscopy (SEM-EDS).However, a blind interlaboratory comparison and reexamination of published data show that most published cation ratios of varnish are probably inaccurate because the technique used most frequently to determine rock-varnish composition, proton-induced X-ray emission (PIXE), did not accurately measure the concentration of Ti in the presence of Ba, a ubiquitous component of rock varnish. This inaccuracy suggests that the premise of cation-ratio dating and dates generated by this method should be reevaluated.

Cation-ratio dating of rock varnish: Why does it work?

Cation-ratio dating of rock varnish is an empirical surface-exposure dating method based on decreases in the cation ratio (Ca+K):Ti over time. Although these changes were attributed to the preferential leaching of Ca and K from varnish, the existence of such leaching has not been demonstrated. In varnish collected from the Cima volcanic field, California, distributions of the minor elements used in cation-ratio (CR) dating reflect varnish stratigraphy as defined by the major elements Mn, Fe, and Si. In general, K is associated with Si, Ca with Mn, and Ti with Fe. Because of these associations, variations in CRs both within samples and between samples typically reflect variations in major element composition associated with varnish stratigraphy. No systematic changes with depth or age are present in the ratios K:Si or Ca:Mn as would be expected if K and Ca have been preferentially leached from varnish. Available data suggest that, instead of a leaching process, thickness-dependent changes in the amount of substrate being incorporated into varnish analyses contribute to the empirical trend of decreasing CR with increasing surface age, although further research is required to verify this hypothesis.

Precision of rock-varnish chemical analyses and cation-ratio ages

New data and statistical analyses indicate that the precision of the mean rock-varnish cation ratio determined for a geomorphic surface and the uncertainty of the age calculated from that ratio are controlled by the area of varnish included in each chemical analysis, the precision with which each cation ratio is determined, and the number of independent chemical analyses. This study has implications for the interpretation of published cation-ratio ages and the future use of cation-ratio dating.

DATING ROCK VARNISHES BY THE CATION RATIO METHOD WITH PIXE, ICP, AND THE ELECTRON MICROPROBE

The measurement of rock varnish cation-ratios [(K+Ca)/Ti] and barium is evaluated by analyzing the same varnish scrapings with PIXE, inductively coupled plasma, neutron activation and wavelength dispersive electron microprobe. Results among these different methods are generally similar for ratios, but absolute concentrations differ in part due to uncertainties associated with weighing small samples. Barium concentrations are typically less than 1 % by weight; higher concentrations can be found in varnishes with depressions eroded into the varnish by fungi and lichens, and later infilled with aeolian detritus often including barium sulfate. Since these infilled hollows are known to produce anomalous varnish cation ratios, high barium values can, therefore, be used as an indicator that a sample is inappropriate for cation-ratio dating. The glacial chronology at Pine Creek, California, is revised in light of new data and a better understanding of variables influencing varnish chemistry.

Settlement, raw material, and lithic procurement in the central Mojave Desert

This paper explores the prehistoric use of two quarries in the central Mojave Desert. Technological analysis and cation-ratio dating of refitted core/flake sequences indicate that patterns of raw material selection, reduction strategies, and the range of objects produced at and removed from the sites remained essentially constant over time despite major changes in human mobility and settlement organization. Changes are evident in the rates at which the sites were exploited, the degree of reduction carried out at one site over time, and the kinds of products emphasized at one of the sites during one period. These results indicate that human use of these sites was conditioned by a range of factors, in addition to mobility strategies, including regional patterns of raw material quality and abundance and quarry location.

Cation-ratio dating of rock varnish: a geographic assessment

Cation-ratio dating of rock varnish: a geographic assessment

Cation-ratio dating of petroglyphs using PIXE

A central problem in archaeological research has been the Chronometrie dating of petroglyphs (rock engravings). Recent improvements in the understanding of the chemistry of rock varnish (or patina) that develops on rock surfaces in arid regions has resulted in the development of a calibrated dating technique, cation-ratio (CR) dating. This is based on calibrating chemical changes in minor and major trace elements in the varnish over time. PIXE is used to determine the bulk chemical constituents of small samples of varnish mechanically removed from within petroglyphs. Recent applications in western North America have yielded petroglyph dates of great importance in understanding the origins of art and the antiquity of human settlement in the western hemisphere. In particular the CR dates on petroglyphs suggest that humans moved into the New World about 10 K yrs earlier than previously believed, and that the making of petroglyphs was one of the most ancient and long-lived cultural traditions in aboriginal North America.

Cation-ratio dating of rock-engravings from the Olary Province of arid South Australia

Desert varnish, the distinctive coating on exposed rock surfaces in arid regions, can be dated by cation ratios, providing a rare means directly to date petroglyphs. A first application of the method, much used in north America, is here reported from Australia, where it indicates minimum ages up to 30,000 years old. And it also shows that the style of figures, so often taken as a measure of chronology, is in this instance largely independent of age.

Cation-Ratio and Accelerator Radiocarbon Dating of Rock Varnish on Mojave Artifacts and Landforms

The first accelerator radiocarbon dates of rock varnishes are reported along with potassium/argon ages of lava flows and conventional radiocarbon dates of pluvial lake shorelines, in an empirical calibration of rock varnish K(+) + Ca(2+)/Ti(4+) ratios with age in the Mojave Desert, eastern California. This calibration was used to determine the cation-ratio dates of 167 artifacts. Although cation-ratio dating is an experimental method, some dates suggest human occupation of the Mojave Desert in the late Pleistocene.

Chronometric and Relative Age Determination of Petroglyphs in the Western United States

Abstract This paper presents chronometric age determinations of petroglyphs from the Coso Range and Cima volcanic field and relative dating from other locations in the western United States using the new rock varnish technique of cation-ratio dating. Our results verify the proposed Great Basin relative stylistic chronology, which indicates that curvilinear abstract was followed by rectilinear abstract and representational. However, these styles have greater antiquity than previously proposed, suggesting new interpretations for the significance of the Coso Range rock art.