1.3 Methods

Our field investigations were carried out in the summer of 2001 and 2002. They included a detailed archaeological survey with the use of GPS equipment. The coordinates and altitude of all archaeological sites and major landforms were measured and recorded. Subsequently, the data were processed with the use of ArcView package and presented in the form of digitised electronic maps and 3-D projections.

Two archaeological teams carried out the stratigraphic excavations of two key sites, Serteya 13 and Serteya 2 with the aid of a high density levelling grid. In the latter case, archaeological deposits were recorded and retrieved from below the lake level with the use of underwater equipment.

Archaeological artefacts, bone remains and botanical macrofossils were hand collected from waterlogged sediments and three-dimensionally recorded in accordance with the archaeological and lithological stratigraphy. Bone remains from these and previous excavations were identified at the Institute of Zoology, Russian Academy of Sciences, St Petersburg. Botanical macrofossils were identified at the Laboratory of Geochronology and Ecology, University of St Petersburg. Wood samples were studied botanically, and their tree rings were measured at the laboratory of the Hermitage Museum. Wood and charcoal samples from archaeological sites were radiocarbon dated at the Radiocarbon Laboratory of the Institute for History of Material Culture, St Petersburg.

Statistical analysis of the radiocarbon dates was carried out at the School of Mathematics and Statistics, University of Newcastle upon Tyne. This analysis is based on the X2 test, and requires knowledge of the total errors of the date measurements, rather than just the instrumental ones that only characterise the accuracy of the radiocarbon age measurement in the laboratory (Dolukhanov and Shukurov in press). The lower limit of the total uncertainty was assessed based on statistically significant datasets belonging to archaeologically and culturally homogeneous sites. In several cases, discussed later, it has been possible to isolate a date subset coeval in the statistical sense, and therefore considered as the most probable age of the archaeological object.

A sediment coring was undertaken in an area adjacent to the excavation site Serteya 2 with the use of the 'Russian hand piston-corer'. The pollen, diatom analyses and the radiocarbon dating were performed at the Laboratory of Geochronology and Ecology, University of St Petersburg. Samples for the pollen and diatom analysis were taken at every 50mm; samples for radiocarbon analysis, every 100mm.

Another coring (#63) was made 1.5km further to the north. With the use of the same equipment, 8.5m of sediments were sampled for pollen, diatom and geochemical analyses. The chronological control was provided by the radiocarbon dating. As in the previous case, the samples for the pollen and diatom analysis were taken at every 50mm; samples for radiocarbon analysis, every 100mm. Sixteen samples were taken for the geochemical analyses. Altogether 59 radiocarbon dates were obtained using the conventional dating methods described elsewhere (Arslanov et al. 1999).

Pre-treatment of samples for pollen analysis was carried out with the use of the laboratory technique described by Berglund and Ralska-Jasiewiczowa (1986, 456). For each sample, 600-400 pollen grains were counted, and the pollen counts were expressed in percentages from the total amount of pollen grains of terrestrial plant species using the traditional procedure (Berglund and Ralska-Jasiewiczowa 1986, 462).

Diatom analysis was performed for the total sequence. The samples were treated with 30% H2O2 and enriched by a heavy liquid with specific gravity of 2.6. The coverslip was mounted with the use of an aniline resin, with a refraction index of 1.6. For the identification of the diatoms a light microscope with magnification of ×1000 was used. The following standard reference sources were used: Diatomovyi analiz 1951; Diatomovye vodorosli SSSR 1974; 1991; Cleve-Euler 1953; 1955; and Krammer and Lange-Bertallot 1991.

Geochemical analyses were performed for the samples from core #63. The components were measured with the use of X-ray fluorescence spectrometry (XRF). Organic matter was measured using the loss-on-ignition (LOI) method. The data thus obtained were processed with the use of correlation and factor analyses.


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