Kopalne dęby Quercus robur z pradoliny Odry we Wrocławiu - analiza geologiczna, paleobotaniczna i radiometryczna

The geological profile of Quaternary deposits was excavated at the northern district of the city of Wrocław in an artificial ditch of about 200 m long and 6 m deep. Lower part of the profile, starting from the depth of 3,2 m below the surface down to the base of the ditch consisted of light-yellow sand with partly fragmented intercalations of plant debris (0,2 m thick) at the depth of 4,0 m. The lowermost bed of plant debris marks the same level in which numerous logs of sub-fossil oak (Quercus robur) were found. The excavations along the ditch revealed 22 such logs, the thickness of which is in rang of 0,4-1,4 m. They occurred at the depth of 3,9-5,4 m. Morphology, color and qualities of the sub-fossil wood were very good indicators of the changing conditions of the river transport and sedimentation. Among the dendrochronologically analyzed oak samples, two generations of different ages were recognized and local chronologies were produced. The first one was dendrochronologically dated against the Southern Poland oak standard to the period 1796-1526 BC. This dating is in perfect agreement with the earlier produced result of radiocarbon analysis 3180+/-50 BP. The second chronology (4890+/-60 BP and 5000+/-40 BP) indicate that the oaks of that generation grown at the end of the Atlantic Period. Radiocarbon dating also enabled identification of trunks older than 5000 BP (5580+/-40 BP and 5330+/-40 BP), as well as of an age intermediate between these both chronologies (4370+/-50 BP). The analyses carried out indicate that the analyzed profiles contain mostly oak trunks from the Atlantic and Subboreal periods. They enable dating of the youngest part of the alluvial series to around 1500 BC.