986 resultados para Peat.


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Non-glaciated Arctic lowlands in north-east Siberia were subjected to extensive landscape and environmental changes during the Late Quaternary. Coastal cliffs along the Arctic shelf seas expose terrestrial archives containing numerous palaeoenvironmental indicators (e.g., pollen, plant macro-fossils and mammal fossils) preserved in the permafrost. The presented sedimentological (grain size, magnetic susceptibility and biogeochemical parameters), cryolithological, geochronological (radiocarbon, accelerator mass spectrometry and infrared-stimulated luminescence), heavy mineral and palaeoecological records from Cape Mamontov Klyk record the environmental dynamics of an Arctic shelf lowland east of the Taymyr Peninsula, and thus, near the eastern edge of the Eurasian ice sheet, over the last 60 Ky. This region is also considered to be the westernmost part of Beringia, the non-glaciated landmass that lay between the Eurasian and the Laurentian ice caps during the Late Pleistocene. Several units and subunits of sand deposits, peat-sand alternations, ice-rich palaeocryosol sequences (Ice Complex) and peaty fillings of thermokarst depressions and valleys were presented. The recorded proxy data sets reflect cold stadial climate conditions between 60 and 50 Kya, moderate inderstadial conditions between 50 and 25 Kya and cold stadial conditions from 25 to 15 Kya. The Late Pleistocene to Holocene transition, including the Allerød warm period, the early to middle Holocene thermal optimum and the late Holocene cooling, are also recorded. Three phases of landscape dynamic (fluvial/alluvial, irregular slope run-off and thermokarst) were presented in a schematic model, and were subsequently correlated with the supraregional environmental history between the Early Weichselian and the Holocene.

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Two new Standard pollen diagrams from the raised bog Ageröds mosse in central Scania are presented and discussed. They have been made giving extensive consideration to the NAP and spores also. The new diagrams comprise in the main only the Post-glacial and can easily be compared with the earlier published Standard diagram from the bog (T. NILSSON 1935). The development of the Post-glacial Vegetation in the surroundings is also discussed and compared with the conditions in the southernmost part of the province (Bjärsjöholmssjön, T. Nilsson 1961). One of the new diagrams has been prepared in connection with the study of a core brought up by means of a special borer in order to bring about C14 datings. The core was almost ömlong and had a diameter of 6 cm. It was divided into pieces of 2-6 cm, which were preserved. After the preparation of the pollen diagram, suitable samples were selected for C14 dating. In all 33 samples, comprising the whole Post-glacial inclusive of the youngest part of the Late-glacial, were C14-dated. With the aid of the C14 dates the growth conditions of the bog are discussed. After very slow Sedimentation of predominantly minerogenous deposits in the last part of the Late-glacial, and still slow Sedimentation of gyttjas in the oldest part of the Post-glacial, the rate of growth (primarily of the gyttja) distinctly increased in the first part of the Late Boreal. A temporary retardation of the growth of the sphagnum peat at the end of the Sub-boreal is probably entirely local. The average rate of growth of the really highly humified parts of the old sphagnum peat amounts to 42 mm per Century, that of the slightly humified young sphagnum peat 81 mm per Century or somewhat more. Based on the C14-determinations, the pollen zone boundaries have been given the following approximate dates: boundary Late-glacial/Post-glacial (DR/PB) 8300 B.C., boundary Pre-boreal/Boreal (PB/BO) 7900 B.C., boundary Early Boreal/Late Boreal (BO 1/2) 6800 B.C., boundary Boreal/Atlantic (BO/AT) 6200 B.C., boundary Early Atlantic/Late Atlantic (AT 1/2) 4600 B.C. (?), boundary Atlantic/Sub-boreal (AT/SB) 3300 B.C., boundary Early Sub-boreal/Late Sub-boreal (SB 1/2) 1700-1800 B.C., boundary Sub-boreal/Sub-atlantic (SB/ SA) 300 B.C., boundary Early Sub-atlantic/Late Sub-atlantic (SA 1/2) 650 A.D.

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Federal Highway Administration, Urban Planning Division, Washington, D.C.

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Federal Highway Administration, Urban Planning Division, Washington, D.C.

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National Highway Safety Bureau, Washington, D.C.

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National Highway Safety Bureau, Washington, D.C.

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National Highway Safety Bureau, Washington, D.C.

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National Highway Safety Bureau, Washington, D.C.