14 C DATES OF PEAT FOR RECONSTRUCTION OF ENVIRONMENTAL CHANGES IN THE PAST DANUTA J. MICHCZYÑSKA 1 , ADAM MICHCZYÑSKI 1 , ANNA PAZDUR 1 and S£AWOMIR ¯UREK 2 1 Department of Radioisotopes, Institute of Physics, Silesian University of Technology, Krzywoustego 2, 44-100 Gliwice, Poland (e-mail: djm@radiocarbon.gliwice.pl) 2 Institute of Geography, Œwiêtokrzyski University, Œwiêtokrzyska 15, 25-406 Kielce, Poland Abstract: Abstract: Abstract: Abstract: Abstract: Cumulative Probability Density Functions (CPDF) for sets of 14 C dates of peat were constructed for different geographic regions of Poland. On the preliminary stage of our study, CPDF for Southern Poland region seemed to be in good correlation with appropriate distribution for Lowlands and Lake Districts region, but rather in anticorrelation with Baltic Coast region. Similarly, CPDF for Baltic Coast region and Lowlands and Lake Districts region seemed to be in anticorrelation. Authors made Monte Carlo experiment to estimate significance of correlation coefficient value. The amount of dates in analysed sets is too low to draw unequivocal conclusions. Key words ey words ey words ey words ey words: RADIOCARBON, STATISTICAL ANALYSIS, PEAT, ENVIRONMENTAL CHANGES, HOLOCENE GEOCHRONOMETRIA Vol. 22, pp 47-54, 2003 – Journal on Methods and Applications of Absolute Chronology 1. INTRODUCTION Since the fifties the radiocarbon dating has become a standard tool for Quaternary geologists and archaeolo- gists, as well as for specialists involved in studies of envi- ronmental processes. Majority of samples dated in Gliwice Radiocarbon Laboratory came from the territory of Po- land. They are regarded as physical data, and elaborated statistically, with a special emphasis on their properties related to the past environmental and climatic changes. Since the seventies an analysis of frequency distribution of 14 C-dated samples in a time scale has been carried out for several selected geographic regions (e.g. Geyh and Streif, 1970; Geyh, 1971; Geyh and Rhode, 1972; Geyh and Jakel, 1974; Geyh 1980; Pazdur and Pazdur, 1986; GoŸdzik and Pazdur, 1987, Michczyñska et. al., 1996). The radiocarbon dating method, which was primarily used sim- ply to determine age of sediment containing dated samples, became an important source of information on the course of some geologic processes in the past. 2. METHODS The result of radiocarbon dating is given as measured radiocarbon age T and its laboratory uncertainty ΔT. A lot of independent factors (such as fluctuations of cos- mic ray flux, atmospheric pressure, humidity etc.) affect the results of measurement. In this situation repetition of measurement gives different results for each case, but these results are subject to specified statistical rules, well described by Gauss probability distribution. The width of Gauss curve depends on uncertainty value – the higher value of uncertainty wider the curve. Result of radiocar- bon measurement: T±ΔT – means that real age of dated sample does not differentiate from result of measurement by more than ΔT with 68% probability. The probability density function of Gauss distribution is described by equation: ú ú û ù ê ê ë é ÷ ø ö ç è æ D - - × D = 2 2 1 exp 2 1 ) ( T T T p J F J , (2.1) where τ is the real radiocarbon age of sample. For a set of radiocarbon dates for specified type of deposits and dates cover considerable range in time and area we calculate the cumulative probability density func- tion CPDF by summing normal distributions connected with particular dates. The cumulative probability density function is shown by equation: , 2 1 exp 1 2 1 ) ( 1 2 å = ú ú û ù ê ê ë é ÷ ÷ ø ö ç ç è æ D - - × D × = N i i i i T T T N f J F J (2.2) where: T i and ΔT i are respectively age and uncertainty of i-sample and N is number of all dates. The graph received in this way has characteristic peaks and gaps. An idea of