Late Glacial and Early Holocene history of Toruń flora in the light of pollen analysis of biogenic sediments from Mokre suburb
Journal Title: Archaeologia Historica Polona - Year 2011, Vol 19, Issue 0
Abstract
The exploration area is situated in the eastern Toruń part, Mokre suburb on VIII Vistula terrace. As a result of geological and geomorphological field mapping old accumulation tanks of biogenic sediments being the remains of palaeochannels of braided river (Niewiarowski, Weckwerth 2006) were recognized under the earthwork and eolic formation layers. Their spatial range (fig. 1) was recreated on the base of drilling analysis and their biostratigraphic attachment was presented relaying on palynological analysis. During archaeological studies carried out in the area of former garden at Żwirko & Wigura st. a layer of peat 32 cm deep was revealed. Two profiles in form of monoliths were obtained of it – one directly from archaeological trench (profile T/Ż-W), the other from geological drilling (profile T/G). Both were subjected to palynological analysis, which became a ground for recognizing vegetation history of that area. The results of pollen analysis were compared in form of percentage diagrams and concentrations (fig. 4–7), divided into local pollen zones (L PAZ), characterizing vegetation belonging to particular periods. The zone of Pinus–Salix (from profile T/G) refers chronologically to Younger Alleröd interstadial phase; at that time pine forest grew around bogs. The zone of Juniperus–Artemisia (T/Ż-W and T/G) was correlated to a cool period of Younger Dryas. Pollen record indicates development of flora typical for park tundra at that period, with pine, birch and juniper scrub. The remained sediment presents holocene accumulation. The zones of Betula–Pinus–Ulmus (profile T/G) and Betula–Pinus (profile T/Ż-W) depict development of birch woods with changeable pine participation, thus concentrations of pollen characteristic for older part of preboreal period. Younger part of that period was characterized by pine woods predomination, where mezocratic species, such as hazel and elm – zones of Pinus–Corylus–Ulmus (T/G) and Pinus (T/Ż-W) were slowly appearing. In Boreal period – zone of Corylus–Ulmus–Alnus (T/G) – pine forest still predominated, but with clear expansion of hazel and increasing role of alder in local tree stand. Palynological analysis of the overlaxing part of the sediment (from the depth of 65 to 80 cm in profile T/Ż-W and from 100 to 120 cm in profile T/G) indicated very weak occurrence of mainly corroded pollen, what confirms instable hydrological conditions at that area. In drier years bogs and organic sediment made of them got parched and degradated. Pollen spectrum of that material is characterized by very destroyed pollen presence and therefore difficult to indicate, sometimes deprived completely of all diagnostic features. That fact made it impossible to interpret those sediment segments correctly. Upper part of both profiles consist of a layer of anthropogenic character (ground leveling earthwork). Summarizing, palynological analysis of biogenic sediment deposited below late mediaeval cultural layer indicated sediment hiatus appearance, which includes the period from the break of preboreal and boreal until modern times. Hence, vegetation reconstruction was possible only from late glacial and early holocene.
Authors and Affiliations
Agnieszka Noryśkiewicz
Keywords
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