Glacial Facies and Fabrics

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Glacial Facies and Fabrics
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General Review of Facies

• Facies
• A body of sediment with a distinctive combination
  of properties that distinguish it from
  neighboring sediments.
• Stratigraphic units distinguished by lithologic,
  structural, and organic characteristics
  detectable in the field.

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3 Methods of Describing Facies

• Genetic facies
• State or imply a specific mode of formation
• Dune-bedded sands
• Lithofacies
• Only describes the physical characteristics of
  the deposit
• Silt laminae
• Cross-bedded sand
• Biofacies
• Defined by the presence of, or lack of,
  biological material

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Ice-marginal Environments
Till Ablation till
G-lac. Drift Dropstones
G-lac. Drift Kame delta
Till Lodgment
Till Moraines
Alluvium Kame terraces
Alluvium Outwash/drift
Alluvium Eskers
Alluvium Outwash
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Sequences Events and Materials

• Active ice
• Lodgment
• Flowtill
• Outwash
• Stagnant ice
• Melt-out

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Till Fabrics

• Orientation of clasts in space
• Reflects accumulated deformation

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Till Fabrics
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Modified Foliation

• Finally, foliation fabric forms fully!

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Glacial Sequences (Boulton)

• Spatial and temporal distribution of erosion AND
  deposition
• Marginal till sequences

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Glacial Sequences (Boulton)

• Spatial and temporal distribution of erosion AND
  deposition
• Marginal till sequences
• Ice sheet synthesis

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Glacial Sequences (Boulton)

• Spatial and temporal distribution of erosion AND
  deposition
• Marginal till sequences
• Ice sheet synthesis

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Till Sequence example Illinois

• Loess/Malden till/red Tiskilwa till/gray Tiskilwa
  till/bedrock
• Unclear boundaries and genesis
• Interpretation of genetic facies

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Till Sequence example Illinois
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Montana plains

• Fullerton et al., 2004, USGS SI-2843

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Till sequence

• Illinoisan
• Wisconsinan
• Late Wisconsinan
• But
• How know age?
• Alternative working hypotheses?

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Till facies

• Glacier tills
• Ice sheet tills
• Modified tills

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Till facies
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Drift of Coastal New England
Interlobate Moraine
Ground Moraine
Terrestrial End Moraines
Marine(?) End Moraines
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End Moraine Facies
Mud/debris flow
Flowtill
Sheetflow
Debris flow
Bar gravel
Debris flow
Sheetflow
HyperX flow
HyperX flow
Sheetflow
Distal flowtill
HyperX flow
Sheetflow
Stream flow
Stream flow
Overbank
Gelifluction
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Facies Distribution

• NOTE
• May be gradation from pure till to type A as well
  as among types!

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Distinction from Outwash
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Grounded Ice andGlaciofluvial locations
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Grounded Ice FaciesUnstratified Diamicts

• Bimodal Partical Size Distribution
• Unsorted pebbles, cobbles, and boulders
• Interstitial matrix of sand, silt, and clay
• Elongate particles show preferred orientation
• Some crude imbrication
• Long axes dipping upstream

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Stratified Diamicts

• Sediments generated by
• Supraglacial, englacial, subglacial processes
• Better sorting
• Lack the bimodal size distribution associated
  with direct deposition
• Pebbles may be rounded by meltwater transport
• Some stratification from reworking
• Seen in the form of kames, kame terraces, eskers