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Glacial Facies

Glacial Facies. chapter 10. Glacial Facies and Fabrics. General Review of Facies. Facies A body of sediment with a distinctive combination of properties that distinguish it from neighboring sediments.

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Glacial Facies

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  1. Glacial Facies chapter 10

  2. Glacial Facies and Fabrics

  3. 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.

  4. 3 Methods of Describing Facies • Lithofacies • Describes physical characteristics of the deposit • Silt laminae • Cross-bedded sand • Genetic facies • State or imply a specific mode of formation • Fluvial or eolian dune-bedded sands • Biofacies • Defined by the presence / lack of some kind of biological material

  5. Glacial Facies and Walther’s Law TravisCorthouts

  6. Johannes Walther I“It is a basic statement of far-reaching significance that only those facies and facies-areas can be superimposed primarily which can be observed beside each other at the present time.”

  7. Walther’s Law "Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally" • As adjacent depositional environments migrate laterally, sediments from one environment will come to lie on top of another. • This overlapping will produce a vertical progression of facies which mirrors the original lateral distribution of depositional environments.

  8. Puget lobe glacial facies –lateral movement  vertical sequence

  9. Walther’s Law Exceptions • The law is invalid where the contact between different lithologies is non-conformable (due to lack of deposition), or during cases of rapid environmental change when non-adjacent environments may replace one another.

  10. Facies Characteristics Ice Contact Facies: • Unstratified diamictites and tillites • Poorly sorted sediment • Striated or polished clasts • Preferred orientation of long axis (crude imbrication) • Diverse clast assemblages • Proglacial to Periglagial Facies: • Reworked by melt-water, which may produce sedimentary structures. • Better sorting • Freeze-thaw process in periglacial zones = better stratification. • Loess

  11. Glacial E.O.Ds and Associated Facies Most diverse grain size sedimentary system Primary Glacigenic Deposits (Ice-Contact Zone) Glacifluvial Deposits (Proglacial) Gravity Mass-Movement Deposits (Glacilacustrine/–marine) Suspension Settling and Ice-Rafting (Glacilacustrine/ –marine) • Ripples cross-laminated facies • Cross-bedded facies • Gravel sheets • Silt and mud drapes • Scree/debris-fall deposits • Debris-flow deposits • Turbidites • Slide and slump deposits • Varves • Mud and diamicton dropstones • Undermelt diamicton • Lodgement till • Glaciotectonite • Deformation till • Melt-out till • Other tills… E.O.D = Environment of Deposition

  12. Ice-contact zone = very poorly sorted sediment = glaciotectonite... TILLS! Pro/periglacial zone with a braded melt-water stream. Facies will be more sorted and stratified, as well as more fine grained. Possible cross-bedded facies.

  13. Stratigraphic Column Killer Ice!!!

  14. A B C

  15. Glacial sedimentation is dominated by retreat deposits. • Advancing glaciers are more likely to destroy older glacial facies sequences than retreating glaciers. • Therefore, Walther’s Law is most applicable to facies sequences and associations for receding glaciers.

  16. Indicator Facies • Diamictites: Commonly deposited at ablation zones along glacial margins as melt-out tills or any poorly sorted gravelly deposit. • Loess: Often accumulates in periglacial region as wind-blown deposits. • Varves: Usually originate from annual deposits in proglacial and periglacial lakes but may also originate from other cyclic deposits caused by seasonal waxing/waning of glaciers. • Dropstones: Good indicator of glacial lacustrine/-marine environments where ice rafted debris was deposited as dropstones.

  17. How we know it’s a dropstone: “On-lap” of sediment at top contact Deformation/penetration of laminated sediment at bottom contact.

  18. Facies model (Anderson, 1989)

  19. Ice-marginal environments Till ** Ablation till G-lac. drift Dropstones G-lac. drift Kame deltas Till Lodgment till Till Moraines Alluvium ** Kame terraces Alluvium Outwash/drift Alluvium Eskers Alluvium Outwash

  20. THE END

  21. from here on – not presented in class slides from MSU class

  22. Sequences: Events and Materials • Active ice • Lodgment • Flowtill • Outwash • Stagnant ice • Melt-out

  23. Till Fabrics • Orientation of clasts in space • Reflects accumulated deformation

  24. Till Fabrics

  25. Modified Foliation • Finally, foliation fabric forms fully!

  26. Glacial Sequences (Boulton) • Spatial and temporal distribution of erosion AND deposition • Marginal till sequences

  27. Glacial Sequences (Boulton) • Spatial and temporal distribution of erosion AND deposition • Marginal till sequences • Ice sheet synthesis

  28. Glacial Sequences (Boulton) • Spatial and temporal distribution of erosion AND deposition • Marginal till sequences • Ice sheet synthesis

  29. Till Sequence example: Illinois • Loess / Malden till / red Tiskilwa till / gray Tiskilwa till / bedrock • Unclear boundaries and genesis • Interpretation of genetic facies

  30. Till Sequence example: Illinois

  31. Montana plains • Fullerton et al., 2004, USGS SI-2843

  32. Till sequence • “Illinoisan” • Wisconsinan • Late Wisconsinan • But… • How know age? • Alternative working hypotheses?

  33. Till facies • Glacier tills • Ice sheet tills • Modified tills

  34. Till facies

  35. Drift of Coastal New England Outwash Outwash Interlobate Moraine “Ground Moraine” Terrestrial End Moraines Marine(?) End Moraines

  36. End Moraine Facies Flowtill Mud/debris flow Sheetflow Debris flow Bar gravel Debris flow Sheetflow HyperX flow Distal flowtill HyperX flow Sheetflow HyperX flow Sheetflow Stream flow Stream flow Overbank Gelifluction

  37. Facies Distribution • NOTE: • May be gradation from pure till to type A as well as among types!

  38. Distinction from Outwash

  39. Grounded Ice andGlaciofluvial Locations

  40. Grounded Ice Facies:Unstratified Diamicts • Bimodal Particle 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

  41. 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

  42. Glaciofluvial Deposits

  43. Glaciofluvial Deposits • Can be deposited in: • Subglacial and englacial conduits • Supraglacial and proglacial streams • Lithofacies reflect local sediment supply • Well stratified and feature sedimentary structures at varying scales • Dependent on stream discharge and sediment supply

  44. Kames • Small mound-shaped accumulations of sand or gravel • Form in pockets or crevasses in the ice • Commonly feature fining upwards sequences • Large unsorted clasts overlain by sands & silts • Thermal?

  45. Eskers • Narrow, sinuous ridges of sediment parallel to ice flow • Can include gravels, sands, and silt • Some facies may be extremely well stratified • Feature gravels overlain by fine, fluvial sediments • Topped or interbedded with diamictites

  46. Glacier Marine Sediment Facies By: Scott Patterson Geol 445 Glacier Geology 4/5/03

  47. Glacier Marine Sediment Facies: Definitions Till – terrestrial, primary glacier deposited diamicton Glacimarine drift – “marine till” Facies – stratigraphic units distinguished by lithologic, structural and organic characteristics detectable in the field (Boggs 2001)

  48. Proximal vs. Distal Eyles et al 1991 & Boggs 2001

  49. Distal Glacier Marine Facies Characteristics • Settled sediment • Extreme variation in clast type (lithology and source) • Dropstones – with soft sediment deformation • Stratification • Marine fossils (forams and diatoms)

  50. Sediment plumes off a glacier (Cofaigh, 2001) Soon to be Settled Sediment; Norway

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