Fróðskaparrit - 01.01.1991, Side 66

Fróðskaparrit - 01.01.1991, Side 66
70 A NOTE ON THE OCCURENCE OF LAND PLANARIANS Fig. 1. Sites of pre-settlement Plantago lanceolata men- tioned in the text. on the northern shore of Bitrufjordur, a 3m deep stream section cut into marine silts of at least 8m thickness is truncated at its land- ward and upper surface by an erosional scarp which is itself draped by a sand and gravel deposit (Fig 2). This deposit contains a lOcm thick layer of peat which slopes sea- wards from 8.5m asl to about 6.5m asl. Statigraphically above the peat layer is a dis- tinct beach ridge composed of course marine sands and gravels. Contained within this ridge is a lOcm thick layer of peat whose up- per surface gives way to gravel and cobbles capped by soil. Incremental samples were taken through the entire section for sedi- ment, pollen and microfaunal analysis. Sam- ples 3-10 were taken from the main section whereas samples 1-2 came from the beach ridge which lies stratigraphically above, but seaward of, the main section (Fig 2). The pollen diagram from these samples suggests a sedge-grass tundra, with some dwarf wil- low and birch, juniper, heaths and heathers (Fig 3). The diagram can be divided into two: a basal assemblage with grasses around 20% of total pollen and sedges thereby reduced, and an upper assemblage heavily dominated by sedges and a considerable inci- dence of spores. Of significance here is the early occurrence of P. lanceolata (2% of to- tal pollen) at 3.5m depth at the base of the diagram. It also occurs at two points above this at values of 1% and less than 1% total pollen. Examination of the samples for microplankton revealed a rich, decidedly boreal, fauna of which the basal section, corresponding to the marine silts, yielded a predominantly marine taxa deriveđ almost exclusively from a shallow lagoonal or estua- rine environment (Hansom and Briggs, 1991). The pollen and microplankton suggest a boreal aspect throughout with a shallow lagoonal marine environment up to 8m asl. Radiocarbon dating of both the upper and lower peats indicates that freshwater condi- tions at 8830 BP (Grn-15844) were temporar- ily halted at about 6910BP (Grn-15843) by a high energy marine event which deposited a beach ridge replete with marine taxa on top and in front of the eroded surface of the silts. It follows that the P. lanceolata pollen in the lower part of the curve pre-dates 8830 BP and therefore that the species was present in this part of Iceland considerably before the arrival of humans. Exactly how long the species has been
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