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Glacial Facies chapter 10. Glacial Facies and Fabrics.

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Presentation on theme: "Glacial Facies chapter 10. Glacial Facies and Fabrics."— Presentation transcript:

1 Glacial Facies chapter 10

2 Glacial Facies and Fabrics

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

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

5 Glacial Facies and Walther’s Law Travis Corthouts

6 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  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. "Facies adjacent to one another in a continuous vertical sequence also accumulated adjacent to one another laterally"

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. 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 Unstratified diamictites and tillites Poorly sorted sediment Poorly sorted sediment Striated or polished clasts Striated or polished clasts Preferred orientation of long axis (crude imbrication) Preferred orientation of long axis (crude imbrication) Diverse clast assemblages 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 Primary Glacigenic Deposits (Ice-Contact Zone) Lodgement till Glaciotectonite Deformation till Melt-out till Other tills… Glacifluvial Deposits (Proglacial) Ripples cross- laminated facies Cross-bedded facies Gravel sheets Silt and mud drapes Gravity Mass- Movement Deposits (Glacilacustrine/–marine) Scree/debris-fall deposits Debris-flow deposits Turbidites Slide and slump deposits Suspension Settling and Ice-Rafting (Glacilacustrine/ –marine) Varves Mud and diamicton dropstones Undermelt diamicton E.O.D = Environment of Deposition Most diverse grain size sedimentary system

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 Killer Ice!!! Stratigraphic Column

14 C B A

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 : Deformation/penetration of laminated sediment at bottom contact. “On-lap” of sediment at top contact

18 Facies model (Anderson, 1989)

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 Till Lodgment till Alluvium Outwash/drift G-lac. drift Dropstones Till Moraines Alluvium Eskers G-lac. drift Kame deltas Alluvium ** Kame terraces Alluvium Outwash

20 THE END

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

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

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

24 Till Fabrics

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

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

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

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

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

30 Till Sequence example: Illinois

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

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

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

34 Till facies

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

36 End Moraine Facies 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 Massive gravel Bedded diamict Distal Fine diamict Sandy diamict Sand sheets Sandy diamict Bedded sand X-stratified sand Laminated silts Massive silts Mud/debris flowFlowtillSheetflow Debris flow Bar gravel SheetflowHyperX flow SheetflowStream flow Gelifluction Overbank SheetflowDistal flowtill

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

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 segmenteduniform Sed/water source Supraglacial stream Subglacial stream DischargeUnsteady More uniform Hydraulics  downstream Uniform

39 Grounded Ice and Glaciofluvial Locations

40 Grounded Ice Facies: Unstratified Diamicts Bimodal Particle Size Distribution: Bimodal Particle Size Distribution: Unsorted pebbles, cobbles, and boulders Unsorted pebbles, cobbles, and boulders Interstitial matrix of sand, silt, and clay Interstitial matrix of sand, silt, and clay Elongate particles show preferred orientation Elongate particles show preferred orientation Some crude imbrication Some crude imbrication Long axes dipping upstream Long axes dipping upstream

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

42 Glaciofluvial Deposits

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

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

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

46 Glacier Marine Sediment Facies 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 Settled sediment Extreme variation in clast type (lithology and source) Extreme variation in clast type (lithology and source) Dropstones – with soft sediment deformation Dropstones – with soft sediment deformation Stratification Stratification Marine fossils (forams and diatoms) Marine fossils (forams and diatoms)

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

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

52 Dropstones Clast lithology – gneiss in mudstone Clast lithology – gneiss in mudstone Boulder Boulder Subrounded Subrounded


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