Adam Michczynski

Is it Possible to Find a Good Point Estimate of a Calibrated Radiocarbon Date

The result from probabilistic calibration of a radiocarbon date is given in the form of a probability density function. Consequently, reporting a 68% or 95% confidence interval has became a commonly accepted practice. However, many users of 14C dates still try to present the results of calibration as a single point. This manner of presentation is often applied during the construction of age-depth models due to its convenience and simplicity. In this paper, the author tests whether it is possible to find a good point estimate of a calibrated 14C date. The idea of the tests is to compare, using computer simulation, the true value of the calendar age with the age calculated based on the probabilistic calibration of the 14C date and the method of finding the point estimate. The test is carried out for the following point estimates: mode, median, average, the central point of the confidence intervals, and the local mode inside the confidence intervals. The results show that none of these may be considered as a good estimate.

Frequency Distribution of Radiocarbon Dates as a Tool for Reconstructing Environmental Changes

Large sets of radiocarbon dates of 1019 peat, 155 speleothem, and 100 tufa samples, as well as dates of 330 flu- vial samples, were investigated in order to estimate environmental variability during the last 16,000 calendar years in Poland. All 14C dating was carried out in the Gliwice Radiocarbon Laboratory, and results are stored in the RoS database. Probability density functions (PDFs) were created by summing up (on the calendar timescale) individual age probability distributions of all dates for different types of material and for different regions of Poland. We used an updated version of the Gliwice Radio- carbon Laboratory calibration program GdCALIB. The 14C dates were calibrated using the IntCal04 calibration curve (Reimer et al. 2004), and results were compared with other paleoenvironmental records. The authors conclude that analyzing PDFs of different types of sediments can be helpful in the qualitative reconstruction of the past environment. The PDF for peat samples primarily reflects paleohydrological conditions; the PDFs for speleothem and tufa samples reflect changes in tem- perature and humidity, while analysis of the PDF created for fluvial data is in a general agreement with the PDFs constructed for peat samples.

Record of the meso- and neoholocene palaeoenvironmental changes in the Jesionowa landslide peat bog (Beskid Sądecki MTS. Polish Outer Carpathians)

The paper presents an analysis of depositional sequences of landslide peat bog situated in the depressions developed within the landslide landforms Jesionowa in the Beskid Sądecki Mts. (Outer Carpathians). The peat bog, with depositional sequence 2.80 m long, started to form at the beginning of the Atlantic Phase ca. 6390–5910 cal BC. Palynological and lithological analyses as well as several (14) radiocarbon age determinations of different horizons in the sediments enabled the reconstruction of palaeoenvironmental changes during the Meso-and Neoholocene. The increase in climate humidity at the beginning of the Subboreal and Subatlantic Phases was observed as delivery of minerogenic material to the peat bog basin and formation of a mineral horizon and an illuvial level within the peat. The particularly intensive delivery of allochthonous material to the peat bog took place at the beginning of the Subboreal Phase and was the result of both significant humid climate and increased human impact (colonization of the Funnel Beaker Culture) in the landslide area. Similar influence of younger colonisations of landslide area (Przeworsk Culture and, later, Valachian colonisation) was also recorded within the deposits of peat bog (illuvial and mineral horizons) in the early Subatlantic Phase. Rejuvenation of the landslide zone and formation of the younger landslide were connected with the increase in climate humidity at the beginning of the Subboreal Phase. The peat bog deposits situated within this younger landslide, which are ca. 1.8 m thick, are significantly contaminated with mineral material.

Age-Depth Model of Lake Soppensee (Switzerland) Based on the High-Resolution 14C Chronology Compared with Varve Chronology

An age-depth model for laminated sediments of Lake Soppensee is constructed using radiocarbon ages of macrofossils and a depositional model of the OxCal v 4.1 program with the updated IntCal09 data set. The resulting calendar chronology is compared with the varve chronology that was built for this record in a previous study (Hajdas 1993); there is a very good agreement between the 2 approaches. This illustrates the potential of high-resolution 14C dating for construction of reliable, high-resolution calendar timescales for sedimentary records. Based on the age-depth model of this study, the Vasset/Killian tephra found in sediment of Soppensee dates to a calendar age of 9291?9412 cal BP (2-σ range) while the Lachersee tephra dates to 12,735-12,871 cal BP (2-? range). Precise dating of the Late Glacial boundaries is possible with this chronology but requires more precise correlation between proxies and records than typically practiced.

Dating Bones near the Limit of the Radiocarbon Dating Method: Study Case Mammoth from Niederweningen, ZH Switzerland

Preparation of bone material for radiocarbon dating is still a subject of investigation. In the past, the most problematic ages appeared to be the very old bones, i.e. those with ages close to the limit of the dating method. Development of preparative methods requires sufficient amounts of bone material as well as the possibility of verification of the ages. In the peat section at Niederweningen, ZH Switzerland, numerous bones of mammoth and other animals were found in the late 19th century. The first accelerator mass spectrometry (AMS) radiocarbon ages of those bones from 1890/1891 excavations placed the age between 33,000 and 35,000 BP. The excavations in 2003/2004 provided additional material for 14C dating. An age of 45,870 ± 1080 BP was obtained on base (NaOH step) cleaned gelatin from mammoth bone, which was very close to the age of 45,430 ± 1020 BP obtained for the peat layer that buried the mammoths. The 14C age of gelatin cleaned using the ultrafiltration method obtained in this study, 45,720 ± 710 BP, is in a very good agreement with the previously obtained results. Moreover, the study shows that 3 pretreatment methods (base+Longin, Longin+ultrafiltration, and base+Longin+ultrafiltration) give ages consistent with each other and with the age of the peat section.

RECORDS OF THE MIDDLE - AND LATE HOLOCENE PALAEOENVIRONMENTAL CHANGES IN THE PCIM-SUCHA LANDSLIDE PEAT BOGS (BESKID MAKOWSKI MTS., POLISH OUTER CARPATHIANS)

Records of the Middle - And Late Holocene Palaeoenvironmental Changes in the Pcim-Sucha Landslide Peat Bogs (Beskid Makowski Mts., Polish Outer Carpathians) The paper presents analysis of depositional sequences of two peat bogs situated in the depressions developed within the landslide landforms Pcim Sucha in the Beskid Makowski Mts. (Outer Carpathians). The older peat bog, with depositional sequence 3.75 m long, started to form at the decline of the Boreal Phase ca 7570-7330 cal BC. Palynological and lithological analyses as well as numerous (18) radiocarbon datings of different horizons in the sediment enabled reconstruction of palaeoenvironmental changes of the Middle and Late Holocene. Increase in climate humidity at the beginning of the Atlantic, Subboreal and Subatlantic Phases were observed as deliveries of minerogenic material to the peat bog basin and formation of illuvial and mineral layers within peat. The particularly intensive delivery of allochtonous material to the peat bog took place at the beginning of the Subatlantic Phase and was the result of both significant humid climate and increased human impact (colonization of the Przeworsk Culture) in the landslide area. Rejuvenation of the landslide zone and formation of the second landslide were connected with this period and processes. Deposits of peat bog situated within this younger landslide, which are ca 1.3 m thick, are significantly contaminated with mineral material.

14C absolute chronology of pyramid III and the dynastic model at Pachacamac, Peru

Pachacamac, covering an area of about 600 hectares (ha) near the Pacific shore, is one of the largest and most important archaeological sites in Peru. Most of the monumental adobe-made buildings of the later pre-Inca period (or Late Intermediate Period, about 10th-15th century AD) are so-called pyramids with ramps (the role of the ramps has been interpreted in different ways). Precise dating of the pyramids appears as a crucial step in defining the functions of Pachacamac in pre-Inca times. In this paper, we present the results obtained from 3 field campaigns at Pyramid III, one of the biggest buildings of the site. A total of 24 radiocarbon datasets from 4 different laboratories will help us to place the various steps of development of Pyramid III on a timescale, defined on the basis of the excavations. More absolute dates are available from another pyramid with ramps, which allow us to make comparisons and propose a new model of interpretation for the Pachacamac site during the Late Intermediate Period (LIP).

14C Chronology of Mesolithic Sites from Poland and the Background of Environmental Changes

Mesolithic sites in modern Poland are mainly located in the southern part of the country. Radiocarbon dating of organic material, such as charcoals, wood, and peat, provide a time frame of human settlements in those regions, and dating of speleothems and peat formations provide information on climatic conditions and the timing of climatic change in the region. Here, we present the results of calibrated (super 14) C ages from 3 main Mesolithic sites: Glanow, Chwalim, and Calowanie. Summary probability density distributions of the calendar ages were obtained, and time ranges were ascribed to the cultures in conjunction with archaeological information. These distributions also reveal the changes in human settlement.

The Application of ICELS Systems for Radiocarbon Dating

Liquid scintillation counting (LSC) for radiocarbon dating is a less expensive method than accelerator mass spectrometry (AMS), provides a high degree of accuracy, and is less prone to contamination due to the larger sample sizes. However, to obtain high precision, a long counting time is needed. The Gliwice Radiocarbon Laboratory is seeking to obtain an increased counting capacity with 2-3 mL benzene samples than we presently can achieve with our 2 Quantulus systems. We are therefore investigating the possibility of using a simple, single-phototube LS system (ICELS) for dating samples younger than 5000 yr. We present the first results of this investigation, including the measurement of 3 VIRI and 3 FIRI intercomparison samples.

RADIOCARBON DATING OF THE TEMPLE OF THE MONKEY—THE NEXT STEP TOWARDS A COMPREHENSIVE ABSOLUTE CHRONOLOGY OF PACHACAMAC, PERU

The ongoing Ychsma Project aims to shed light on the chronology and function of the late Prehispanic period at the well-known archaeological site of Pachacamac, Peru, through extensive archaeological research. The Temple of the Monkey is a special building that has been cleared, mapped, and excavated within the general framework of the study of pyramids with ramps, the most common form of monumental architecture at the site. Through the application of radiocarbon measurements, it can be shown that the temple has been used for around 150 yr and therefore is quite different from other pyramids with ramps previously studied (see Michczynski et al. 2003). Details of the temple, 14C sample selection, and methodology, as well as results, are discussed in this paper. The research has allowed us to make significant advances in the current understanding of pyramids with ramps and the function of the site of Pachacamac as a whole.