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Palaeoenvironmental record of a Late Quaternary permafrost tunnel in the Vault Creek, Fairbanks region, Alaska

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Meyer, H. , Yoshikawa, K. , Schirrmeister, L. , Andreev, A. , Wagner, D. and Hubberten, H. W. (2005): Palaeoenvironmental record of a Late Quaternary permafrost tunnel in the Vault Creek, Fairbanks region, Alaska , 1st CLIC International Science Conference, 11-15 April 2005, Beijing, China. .
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Abstract:

The Fairbanks area in Interior Alaska is characterised by discontinuous permafrost and a continental climate with mean annual air temperatures of about -3 ºC and annual precipitation of 263mm measured at Fairbanks Airport (1971-2000). The permafrost consists of sediment and ground ice, and preserves the signals for the reconstruction of late Quaternary environment and climate.The Vault Creek gold mining tunnel is located 40km north of Fairbanks, Alaska, and was established since 1990 by a local private gold miner. It is the deepest (> 40m) and longest permafrost tunnel (>200 m) ever being subject for research, comparable to the famous Fox research tunnel near Fairbanks constructed in 1963 by the US Army Corps of Engineers (CRREL). The study site has about 120m thick permafrost. Average permafrost temperatures at 2m below ground surface are relatively warm with 0.78°C. In this region, permafrost is considered to have developed after Sangamon (or Eemian) interglacial period.The sedimentary sequence consists of 40 m of late Quaternary deposits above schistose bedrock. These are: (1) alluvial sediments mainly consisting of fluvial gravels with sand and several peat lenses in the lower part and (2) ice-rich silty sediments, most likely loess with high amounts of organic material including fossil bones as well as ice wedges in the upper part. In between, (3) a transition horizon of fluvial gravels interbedding with loess and ice wedges was held out. First AMS dates point out that loess accumulation took place in the area around 42 ka BP, whereas the fluvial sediments show infinite 14C ages. In general, ice wedges are periglacial features containing information about winter temperatures, which were derived by stable isotopes (d18O and d2H). Both, ice wedges and sediments were deformed presumably by post-depositional slope processes. In this paper, a picture of the regional environmental history is drawn using sedimentology, palynology, radiocarbon dating, greenhouse gases, hydrochemistry and stable isotope geochemistry.

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