The Rapitan Group

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					The Rapitan Group

 Katherine Myles and
   Erin Challenger
   Setting the Scene
   Relevance of the Rapitan
   Sedimentary Logs and traditional interpretation
       Deposition environment
       Climatic conditions
   Banded Iron Formation
   Summary
                 Setting the Scene

   What is the Rapitan Formation?
       Location - Mackenzie Mountains, Yukon and
        Northwest Territories decompressor
                            QuickTime™ and a
                   TIFF (Uncompressed)
                      are needed to see this picture.
       400 km arc
       Age - Upper Proterozoic
       Mainly sedimentary formation including
        deposits of palaeo-glacial origin

Map of Rapitan Group Location

    Young, G. M. 1976, Precambrian Research, v.3 p137-158
        Relevance of the Rapitan?
 Banded Iron Formation - economic
 Palaeo-glacial significance

     Facilitates climate reconstruction
     Provides interesting conundrum re.
      Processes of formation
               Stratigraphic Section
   Research in ‘60s and
   Grant Young 1976

   Upitis 1960
       Upper Rapitan is post-
       Middle Rapitan -
        glacial deposits
       Lower Rapitan - glacial
        deposits and iron
                                  Young, G. M. 1976, Precambrian Research, v.3 p137-158
              Stratigraphic Section
   Lower Rapitan
      Well bedded laminated
       mudstones - deep/quiet
      Striae on hard dropstones
       (e.g. chert) - glacial
      Iron formation -
       controversial origin

                                   Young, G. M. 1976, Precambrian Research, v.3 p137-158
• Glaciomarine environment
• Different thermal regimes result in different processes and
hence different deposits.
• Carey and Ahmad 1960

            Young, G. M. 1976, Precambrian Research, v.3 p137-158
                     Deposit-regime link
                                                           Dry Based
                                                              Marine sediments

                                                              Fewer glacial sediments

                                                              Many dropped erratics

                                                           Wet based
                                                              Much glacial sediment

                                                              Thick diamict

                                                              Rarer erratics

Young, G. M. 1976, Precambrian Research, v.3 p137-158
         Banded Iron Formation
 Why BIF? Uncertainty: Continental Rifting Theory
     Grant Young 1984
                        QuickTime™ and a
 3 main characteristics- Process of formation conundrum
               TIFF (Uncompressed) decompressor
                  are needed to see this picture.
   1. Hematite and jasper deposition
   2. Presence of evaporite minerals
   3. Presence of dropstones and mixtites
   2 possible processes of formation
       1. HOT CLIMATE
          Iron concentration increased due to
          Desert environment evaporation accounts for
           evaporite minerals
          No account for dropstones

       2. COLD CLIMATE
          Increase in iron due to freezing of sea water
           onto dry-based glacier
          Massive withdrawal of water during
           widespread glaciation concentrates evaporite
          Material dropped from iceberg zone and
           floating shelf of dry-based glacier
   Rapitan Upper Proterozoic formation
   Variation in unit characteristics led to
    inferences being made about glacial
    thermal regime and associated climate
   BIF and IF showed characteristics that
    implied cool climate (high latitude) at time
    of deposition
   Rapitan log would benefit from re-
    analysis, applying current knowledge and
   Carey, S.W. and Ahmad, N. 1960. Glacial marine sedimentation.
    In Raash, G.O. (Editor) Geology of the Arctic. University of Toronto
    Press, Toronto, Ontario. 2: 865-894
   Eisbacher, G.H. 1985. Late Proterozoic rifting, glacial
    sedimentation and sedimentary cycles in the light of Windermere
    deposition, Western Canada. Paleogeography, Paleoclimatology,
    Paleoecology. 51:231-254.
   Young, G.M. 1976. Iron formation and glaciogenic rocks of the
    Rapitan Group, Northwest Territories Canada. Precambrian
    Research. 3:137-158
   Young, G.M. 1984. Proterozoic plate tectonics in Canada with
    emphasis on evidence for a Late Proterozoic rifting event.
    Precambrian Research. 25:1-3

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