I4C and U-Series Dating of Plitvice Travertines. . Holocene Travertines of the Plitvice National Park* 14C and U-Series Dating. AD years there have been many attempts in U-series dating of bones using a variety of application of U-series dating to bone (see also Rae et al., a,b). Their dating model was thickness of μm. The smaller spot. The U-series laboratory focuses on development and application of U-series dating techniques to provide a robust chronological framework for.
There is a simple relationship between tau and the half-life. The half-life is equal to the natural logarithm of 2 which is 0. So, although radioactive decay is generally specified in terms of half-lives, calculations are always done in terms of tau.
C14 Cave Art The age of cave paintings has traditionally been determined by measuring carbon 14 levels. One obvious problem with this is that one has to scrape part of the painting off the wall in order to analyze the carbon content, destroying part of the painting.
The other problem is that the paintings are presumed to be tens of thousands of years old, which is on the very flat part of the carbon 14 exponential curve, where contamination could be a problem.
It would be very difficult to tell a contaminated 30, year-old painting from an uncontaminated 3, year-old painting.
Uranium–thorium dating - Wikipedia
Paleolithic cave art is an exceptional archive of early human symbolic behavior, but because obtaining reliable dates has been difficult, its chronology is still poorly understood after more than a century of study.
Discrepancies between multiple 14C determinations on a single painted motif have been common, as are discrepancies between the dates of different chemical e. Our U-series ages ranged from 0. All we care about is that the measurements ranged from years to 40, years, which hardly inspires confidence in the method. We should also explain the difference between calendar years and radiocarbon years.
So, correction coefficients have been developed for historic times to convert radiocarbon years accurately to calendar years. Those correction coefficients have been extrapolated to prehistoric times based on presumed prehistoric CO2 levels. They use a tricky method we will explain in a moment. The tricky method they use tells more about the age of the Earth than it does about the age of the paintings. Back to their method of dating the paintings: Anyone who has been to a cave knows stalactites, stalagmites, columns, and draperies form gradually in caves.
These cave formations are simply differently shaped deposits of minerals such as calcite on the floor, walls, and ceiling of caves. Ancient cave art is painted on one layer of these deposits, and covered by another layer. If one can tell how old the layer under the painting is, and how old the layer over the painting is, then one can set upper and lower bounds on the age of the painting. This means one can date the painting by taking samples from the wall near the painting without damaging the painting itself.
The method is described in the supplementary material on the Science website, but not published in the journal itself.
Over time, there is ingrowth of Th from the radioactive decay of U until radioactive equilibrium is reached where all isotopes in the series are decaying at the same rate. An additional problem is the incorporation of detritus in the precipitating calcite.
This can be from wind-blown or waterborne sediments. Detrital sediments will bring U and Th and usually will result in the apparent age of a contaminated sample to be an overestimate of the true age. However, the presence of the common thorium isotope, Th, indicates the presence of contamination, and there are several methods to correct the U-series date for it. Note the conservative error on this assumption.
While the date obtained using measured detritus values agrees within error in both cases with the date using an average crustal silicate, we must be cautious in using dates corrected using the insoluble detritus.
To be cautious therefore, we base our interpretation of the dates for samples O and O on dates corrected with our assumed rather than measured detrital value. Therefore, when the water evaporates in the cave, leaving the minerals behind on the cave wall, there is some uranium but no thorium when the flowstone first formed. Later, they presume, some of the uranium decays to produce all the thorium in the flowstone. Is that assumption reasonable? Can one really assume that no thorium was present in the water that evaporated to form the flowstone?
How much thorium would it take to produce a false old age for a modern formation? Not much, as we will see, later. Second, the method depends upon equilibrium or lack thereof. The assumption is that the newly formed flowstone contains uranium but no thorium. As time goes by, the uranium will decay resulting in less uranium and more thorium.
The absence of information on the uranium levels makes impossible any discussion of the possible uranium mobility by leaching that might have led to an upward distortion of U-Th dates.
For the latter, the values presented are either lower than one — which is rarely observed — or clearly higher, which indicates the complex geochemical history both of the karst and the water percolating into the cave to produce these calcareous veils. We could, for example, evaluate the impact of leaching of part of the uranium originally contained in the sample.
These corrections lead to only minor modifications in the ages calculated if the level of contamination is low. Let us return to the article by Pike et al. Given the importance of the archaeological interpretations that have been drawn from the dates, these two points should be discussed by the authors.
Testing the hypothesis of the closure of the geochemical system and appreciating the relevance of the corrections applied to U-Th ages thus remain an essential stage in confirming the reliability of results. It was possible to carry out this type of verification in the case of a calcite veil with a total thickness of 2. The upper layer on which those paintings were created has an age of years terminus post quemwhich is in agreement with data resulting from Austronesian archaeology.
In addition, a fine layer of red pigment located within the calcite veil, 1 mm from the surface, could be circumscribed in time by the dating of layers of a thickness of 0. This was deposited between 29, years terminus post quem and 24, years ago terminus ante quem.
The range is still wide, but the information is much more accurate than if the layer had been analyzed as a whole. The precautions to be taken in interpreting the data are thus more important for this type of study.
S1 of the additional documentation in Pike et al. Finally, we should emphasize the non-negligible risk of removing a variable quantity of the substrate of geological age when sampling these fine veils, as demonstrated by Fontugne et al. Application of 14C dating to calcareous deposits and relevance of U-Th cross dating with other methods Even though 14C dating of calcite is not exempt from problems, particularly in connection with the presence of dead carbon, the comparison of the results of U-Th and 14C methods applied to calcareous deposits from cave art walls is a necessity in testing their respective reliability and consistency.
The problem of the incorporation of dead carbon lacking or poor in 14Cderiving from the surrounding limestone or from ancient carbon in the soil, has been the subject of numerous studies see for example Vogel and Kronfeld, ; Genty et al. This cross dating is also facilitated by the fact that the analytical techniques accelerator mass spectrometry for 14C and multi collector inductively coupled plasma mass spectrometry for U-Th requires only very small samples; around 20 milligrams to a few hundred milligrams for 14C and U-Th respectively, which limits the sample size and the resulting destruction of the paintings.
Three samples removed from different points of this drapery were dated by the two methods. The ages obtained — around 9, years — agreed well in only one case out of three, suggesting that the paintings, aged in excess of 10, years, were produced before the arrival of the Austronesian population. For the third sample, however, the U-Th age was three times greater circa 27, years than that of the 14C circa yearssuggesting that the U-Th dating was affected by a significant systematic error linked to the degradation of the drapery by the runoff waters and to the resulting dispersal of the uranium.
A similar approach associating the comparison of U-Th and 14C ages was employed in the decorated shelters of the Serra da Capivara National Park in Piaui Brazil on the calcareous deposits formed above the paintings Fontugne et al.
For some of these samples, the comparison of the results demonstrated the impact of the limestone contaminations of the wall on the U-Th ages, which were found to be considerably older than the 14C results. In still other cases such as those of the U-Th and 14C cross dating of a speleothem from the Altamira cave in Spain, see Labonne et al. These three articles Plagnes et al. It is regrettable that a similar approach was not employed by Pike et al.
These examples also demonstrate the importance of carrying out multiple datings when the thickness of the sample allows it in order to test the stratigraphic order of the results. Finally, we should mention other dating methods, as yet unused in the case of decorated caves, which are based on disequilibria in the uranium family and employ measurements of radium Ra or protactinium Pa, Cheng et al. These have already proved to be of interest in establishing cross-chronologies and validating or disproving U-Th dates of calcareous deposits.
But a reverse scenario may also take place, with the dispersal of the uranium leading to the overestimation of the age of the sample Fruijtier et al. Even though they are difficult to implement for small samples of calcite removed from decorated walls, such cross-dating methods are essential in proposing a reliable chronology for these calcitic deposits whose geochemical development is always complex. Archaeological interpretations The preceding paragraphs describe the numerous difficulties inherent in the application of the U-Th method to dating cave art works, and the extreme caution that must be taken when interpreting the results in the case of a single analysis carried out on a calcite deposit covering such representations.
There are two reasons for stating these reservations. First of all, there are the intrinsic factors linked to the hydrogeological phenomena involved and then there are the factors linked to the hypotheses imposed by the method. In terms of the dating of stalagmitic formations, the application of the U-Th method to the dating of thin layers of calcite covering prehistoric art works presents a much more difficult problem, as we are unaware of which humid period the calcite formed in, or the duration of the phenomenon.
If we analyze the entire thickness of the deposit, which is often the case, we obtain an average age that may be unrelated to the actual age of the prehistoric work. For the age determined to be similar to that of the age sought, the calcite must have been deposited immediately after the creation of the painting, deposition must have taken place over only a very brief period, and no further deposition must have occurred during the following millennia.
Such a concatenation of circumstances must be exceptional. What is more likely is that calcite deposition will have occurred during periods in which the climatic conditions were favorable humidbetween the creation of the work and the present day, and that it will have taken place over a long period. If this is the case, the age that we will obtain will represent only a small fraction of the time that has actually elapsed.
On the archaeological interest of a terminus ante quem Geochronologists are aware that this method provides only a terminus ante quem and that this can be far removed from the creative act that we wish to date.
This is clearly the prevailing situation in the majority of cases involving dating calcite veils. The growth of the calcite veils is controlled principally by environmental factors external temperature and precipitation and, like the 8. Many of the calcite deposits covering cave art works may therefore be Tardiglacial or Holocene the last 12, years or may date from a period of relative warming during a glacial period, which moves us closer to the creation date of the works.
The ages determined for the calcite veils may also represent an average of several phases of growth. However, this information provides useful elements for reflection once the validity of the ages has been verified on a methodological level. In this way, the oldest age obtained for a panel is an element that contributes to a geochronological discussion. This is the approach employed in the study of the cave of Creswell Crags in the United Kingdom Pike et al. Six of the results fell between and years, two around years, and among the three dates before 10, years, there were two in the interval 13, — 14, years.
The authors considered that these latter dates provided relevant information on the period in which the engravings were created, particularly as they fell into the calibrated interval 13, — 15, cal. BP deduced from the 14C dating of anthropomorphically modified bone splinters present in the archaeological level. Even if this coincidence does not provide irrefutable proof, it contributes to the accumulated geochronological data that enable human activity in the cave to be located in time.
While it is true that these dates do not contradict the attribution of the art works to the Upper Paleolithic, on the basis of the terminus ante quem principle, they do not provide any new information. In a great number of cases, the terminus ante quem obtained by U-Th is significantly later i. For example, around two-thirds of the dates obtained by Pike et al. To resolve the question posed by the spread over time of the calcite formation, it is necessary to carry out a very fine analysis of the microstratigraphy of the deposits in order to separately date very thin layers.
This was carried out successfully in the cave in East Timor mentioned above Aubert et al. Substantially different results have sometimes been reported for samples taken only a few centimeters apart. For example, in the cave of La Garma, a braid of calcite crossing the back of an ibex drawn on the wall fig.
Breuil attributed this set of red symbols to the earliest phase of Cantabrian rock art — Aurignacian tracing by H. The mismatch between these values obtained by two different techniques within a radius of barely 50 cm demonstrates that either the calcareous deposits were subject to phenomena relating to open geochemical systems as described above, or that the calcite deposits post-dating the representations are not contemporary.
In this way, the uncertainties linked to the duration of the formation of the deposit and to local variations mean that we obtain only average values which act as a terminus ante quem that may in fact be relatively far removed from reality.
The question deserves discussion in relation to the oldest ages appearing in the article by Pike et al. Given their archaeological impact, it is essential to confirm the validity of these results by means of more detailed geochemical analysis and by other independent datings. Chronological models for Cantabrian Palaeolithic art The chronological models for cave art, in particular those applying to the Cantabrian region, have been subject to major fluctuations over time.
Leroi-Gourhan, in his revision of the Breuil system, is in turn in favor of a much shorter chronology from which the Aurignacian is practically absent.
Regarding the Cantabrian region, he attributes the majority of the pre-Magdalenian works to his style III, i. Over recent decades, Spanish researchers have carried out an in-depth re-examination of the Cantabrian stylistic chronology, which has led them to propose older Fig. In the cave of Pondra, for example, a calcareous crust was dated to 27, years by TL, thereby providing an ante quem age for an underlying red deer protome fig. We have mentioned above the case of the red figures from La Garma dated by TL and U-Th to between 26, and 37, years.
Finally, we should examine the 14C datings carried out on small pieces of charcoal collected from drawings and paintings in the decorated caves of Altamira, El Castillo, Covaciella and La Garma, all of which corresponded to the Magdalenian period Valladas et al. Modern Humans or Neanderthals? Particular interest has been paid by Pike et al. These authors take advantage of the fact that this date is located within the confines of the transition between Neanderthals and the first Modern Humans to introduce the hypothesis that Neanderthals may have been the authors of these red marks.
Journalists have perfectly understood the Fig. In theory, this is of course possible, but to re-launch such a hypothesis on such flimsy fragile evidence is not scientifically serious. We must remain cautious and refrain from any excessive exploitation of these results until independent chronological and chronometric data are available to confirm them.
An extremely interesting graphic presented in the article in Science Pike et al. This is confirmed by numerous calibrated radiocarbon dates Reimer et al. Without supporting the assertion that this Aurignacian industry was produced by the Neanderthals, which no prehistorian today claims, we must admit that Anatomically Modern Humans were already present in western Europe well before 40, years ago.
The radiocarbon dates that we currently have available situate the earliest symbolic wall representations at between 38, and 34, cal. BP average of available AMS dates.