Yorgos Facorellis

Study of the parameters affecting the correlation of background versus cosmic radiation in CO2 counters : Reliability of dating results

Systematic treatment of the data recorded by our guard counters and corrections introduced for meteorological factors has allowed observations on solar events clearly manifested in the readings. Examples are the solar flares of March 1989 and especially of June 1991, which caused a ca. 10% decrease in the cosmic radiation flux reaching the counters. A sinusoidal variation in the cosmic-ray flux with a period of one year is also clearly manifested in the data. The observation that the background in the (super 14) C measurements depends on the intensity of the cosmic radiation has led to the use of monthly correlations for the determination of the best background value to be used in the age calculations. This reduces the error significantly. However, various factors such as random statistical fluctuations of the background measurements may affect the slope of the correlations and consequently the calculated age of the samples. Long-term observations of the relation between background values and coincidence counts have led to constraints in the slope of the correlation. A simple extension of the fitting procedure is explored, which maintains the physically meaningful range of the slopes, but is flexible to adjust for the seasonally varying contributions to the variations of the cosmic-ray flux.

Locating archaeological horizons with 14C sediment dating : The case of the lost city of Helike

In 373 BC a catastrophic earthquake and seismic sea wave destroyed Helike, a Greek city near Aigion on the southern shore of the Gulf of Corinth. The ruins were buried by sediments of unknown depth, leaving no trace of the city. We here discuss the radiocarbon dating of organic sediment samples recovered from seven boreholes drilled on the coastal plain in the area where ancient sources located Helike. Most of the samples apparently acquired a substantial addition of older carbon from natural sources, and hence their apparent ages are older than the true ages of sedimentation. However, if we assume that the addition is systematic, we can use the apparent ages to show that the sedimentation rate was initially rapid (about 1 cm yr (super 1) ) for the strata between 40 and 10 m below the surface, and then decreased by an order of magnitude about 6500 yr ago. A related change in the sediment deposition at about the same time has been found in many other marine deltas throughout the world, probably due to the deceleration of the global sea-level rise. We conclude that in the boreholes sampled by the present data, the horizon corresponding to ancient Helike is less than 8 m deep.

The Cave of Pan, Marathon, Greece—AMS Dating of the Neolithic Phase and Calculation of the Regional Marine Reservoir Effect

The Cave of Pan is located on the N/NE slope of the hill of Oinoe (38°09′31.60′′N, 23°55′48.60′′E), west of modern Marathon. In rescue excavation campaigns during the last three years, among other finds, charcoal and seashell samples were also collected. The purpose of this study is the accelerator mass spectrometry (AMS) dating of the cave’s anthropogenic deposits and the calculation of the regional marine reservoir effect during the Neolithic period. For that purpose, 7 charcoal pieces and 1 seashell were dated. Our results show that the cave was used from the second quarter of the 6th millennium (Middle Neolithic period) until the beginning of the 5th millennium BC. Additionally, one sample collected from a depth of 2 cm from the present surface of the cave yielded an age falling within the 6th century AD, giving thus the absolute time span of the cave use. Moreover, the radiocarbon ( 14 C) ages of one pair of charcoal-seashell samples showed that the marine reservoir age R(t) in the estuarine Marathon Bay region during the 5th millennium BC is 775±57 yr and the local sea surface reservoir deviation ΔR is found to be 402±63 14 C yr (within 1σ).