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Glacial Facies chapter 10 26 May 2009.

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1 Glacial Facies chapter 10 26 May 2009

2 Glacial Facies and Fabrics

3 General Review of 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
Travis Corthouts

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 Diagram is backward? 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)
Especially – effects on vertical & horizontal conductivity 18

19 Ice-marginal environments
Air / ice Ice  lake Ice / rock  lake Ice / rock Air / ice / rock Air / ice / rock / river Ice  river Ice / stream / rock Air / rock Till ** Ablation till G-lac. drift Dropstones G-lac. drift Kame deltas Till Lodgment till Till Moraines Alluvium ** Kame terraces yellow = stratified drift, blue == unstratified (diamict) ** = mass wasting can be involved? Alluvium Outwash/drift Alluvium Eskers Alluvium Outwash


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
Interlobate Moraine “Ground Moraine” Outwash Terrestrial End Moraines Marine(?) End Moraines

36 End Moraine Facies Proximal Fine diamict Massive gravel Coarse diamict
A (mass flow deposits - dominated ice-marginal fan) B (mass flow and waterlaid ice-marginal fan) C (waterlaid deposits - dominated ice-marginal fan) Proximal Fine diamict Massive gravel Coarse diamict Imbricate gravel Bedded diamict Distal Sandy diamict Sand sheets Bedded sand X-stratified sand Laminated silts Massive silts Flowtill Mud/debris flow Sheetflow Debris flow Bar gravel Debris flow Sheetflow HyperX flow HyperX = hyperconcentrated 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
Features End moraine fan Braidplain Location ice contact zone Extraglacial Extent small (km) large (X0-X00 km) Planform fan asymmetric ridge or rampart irregular plain, valley fill Slope steep (2-20°) usually low Long. profile segmented uniform Sed/water source Supraglacial stream Subglacial stream Discharge Unsteady More uniform Hydraulics  downstream Uniform

39 Grounded Ice and Glaciofluvial 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: Better sorting
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 & 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

51 Settled Sediment - Varves
Sources: outer/inter flows Stratification Fine-grained laminae [fine sand/silt – silt/clay] thin from ice dark from organics Eyles et al 1991

52 Dropstones Clast lithology – gneiss in mudstone Boulder Subrounded

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