| Summary: | Syngenetic permafrost forms when alluvial, aeolian and/or colluvial sediment accumulates under cold‐climate conditions. Observations from within the CRREL permafrost tunnel near Fairbanks, Alaska, indicate that layered, lenticular‐layered and micro‐lenticular cryogenic structures are characteristic of this type of permafrost. In contrast, reticulate cryogenic structures indicate local thaw modification. During the growth of syngenetic permafrost, episodes of thermokarst erosion may operate preferentially along ice wedges leading to the development of gullies and tunnels in the near‐surface sediments. The local thaw unconformities that result are inferred by the recognition of thermokarst‐cave ice (‘pool’ ice), and various soil and ice pseudomorphs. These may be regarded as further characteristics of syngenetic permafrost growth. Copyright © 2004 John Wiley & Sons, Ltd.
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