INTERPRETING SEDIMENTS WORKSHOP: GLACIAL SEDIMENTS

Grahame J. Larson

Traverse City, Michigan July 28 – August 1 , 2014

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Extent of the last ice sheet

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The 20,000 14C year old Gardena bryophyte bed, north-central Illinois. [Image: L. Follmer]

The 10,000 14C year old Lake Gribben buried forest, northern Michigan. [Image: K. Pregitzer]

Sample of the 11,800 14C year old Cheboygan bryophyte bed, southern Michigan. [Image: G. Larson]

Sangamon Geosol (beneath shovel) at the Felts Section, northern Illinois. [Image: B. Curry]

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Extent of drift sheets in the mid-continent of North America. [Compiled from Ehlers and Gibbard 2004]

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Comparison of time-distance diagrams for Illinois and the Lake Michigan basin (modified from Johnson et al. 1997) and the eastern and northern Great Lakes (Karrow et al. 2000).

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Glacial Sedimentation in the Great Lakes Region • Sediments deposited directly from ice • Sediments deposited by meltwater • Sediments deposited in glacial lakes

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Sediments deposited directly from ice Till (definition from Bennett and Glasser, 2009) sediment deposited by glacier ice has not been disaggregate may have been subjected to some deformation, either

subglacially or supraglacially normally consists of pebbles, cobbles or boulders

within a fine-grained matrix

Duck Lake Till, Peterson Park, Lower Michigan. [Image: K. Kincare] 7

Diamictons and tills Diamicton – is non-sorted or poorly sorted unconsolidated sediment of no assumed genisis and that contains a wide range of particle sizes

Examples: Debris-flow deposits – deposited by mass movement on land Turbidites – deposited by turbidity currents in water Tills - deposited by glacier ice

All tills are diamictons but not all dimictons are tills

Death Valley debris-flow deposit. [Image: Tim Cope] Northern Maine till. [Image: G. Larson] 8

Michigan puddingstone. Precambrian in age. Origin is Lorrain Quartzite located 30-40 miles southeast of Sault Sainte Marie, Ontario.

Gowgonda tillite. Precambrian in age. Origin is southern Ontario. [Image: J. Dexter]

TilliteS - assumed to be the lithified equivalents of glacial till

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Till depositional domains Subglacial tills Deposited by direct lodgement Deposited by subglacial melting Deposited by cavity deposition Formed from subglacial deformation Supraglacial tills

Deposited by supraglacial melting

Schematic showing till depositional domains of a glacier

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Subglacial till - deposition by direct lodgement Melting by geothermal heat and heat from sliding brings

englacial debris particles in contact with the glacier substrate.

Friction results in reduced particle velocity and ice flow around particles.

Particles will lodge into the substrate when their forward velocity is reduced to zero.

Deposition may be assisted by plowing into a soft substrate, jamming against lodged particles, and lodgement of a debris-rich ice mass.

Path taken by a particle when melting is occurring at the bed of a flowing glacier. [Image: modified from Sudgen and John (1976)]

Schematic showing a clast flowing (ploughing) into a soft substrate. [Image: G. Larson]

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Deposition by direct lodgement Melting by geothermal heat and heat from sliding brings

englacial debris particles in contact with the glacier substrate.

Friction results in reduced particle velocity and ice flow around particles.

Particles will lodge into the substrate when their forward velocity is reduced to zero.

Deposition may be assisted by plowing into a soft substrate, jamming against lodged particles, and lodgement of a debris-rich ice mass.

Example of jamming against lodge particles. [Image: G. Larson]

Example of lodgement of a debris-rich ice mass. [Image: modified from Boulton (1982)].

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Characteristics of till deposited by lodgment Particle packing – dense, well

consolidated Particle lithology – dominated by local

rock types Particle size – either bimodal or

multimodal Particle shape – rounded edges,

striated and faceted, some bullet shaped

Particle fabric – elongated particles have strong fabric aligned to ice flow

Structure – massive and generally matrix supported; structureless; well developed shear planes, boulder clusters or pavement; may include some channel deposits

Schematic showing shear structures in lodgement till. [Image: modified from Boulton (1970)]

Lodgement till, Sólheimajökull forefield, Iceland. [Image: Ó. Ingólfsson]

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Subglacial till - deposition by subglacial melting Ice containing debris moves slowly or becomes

stagnant. Melting at glacier bed by geothermal heat brings

debris particles in contact with the glacier substrate. Particles are released by melting and accumulate on

the glacier substrate.

Schematic showing path taken by a particle when melting is occurring at the bed of stagnant ice. [image: G. Larson]

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Characteristics of till deposited by subglacial meltout Particle packing – dense, consolidated, but

less so than by the lodgement process because of no basal shear stress and generally thinner ice

Particle lithology – dominated by local rock types but may show inverse superposition

Particle size – either bimodal or multimodal, some fines may be removed by winnowing

Particle shape – rounded edges, striated and faceted

Particle fabric – elongated particles have strong fabric aligned to ice flow, but generally with a greater range of orientation and less inclination than that typical of lodgement process

Structure – usually massive and matrix supported; crude-to-well developed relic stratification may be present; no evidence of primary shearing , boulder clusters or pavements may be present; may include some channel deposits; subsequent modification due to flowage

Schematic showing subglacial deposition by meltout.

Basal meltout till (?) from Minnesota. [Image: M. Johnson]

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Subglacial till - deposition in a subglacial cavity (rare in lower Michigan) Cavities can form where glacier ice flows over bedrock

obstructions, especially where the ice is thin and fast moving .

Debris at the glacier bed can enter into a cavity as debris-rich ice “curles”, fine slurry from the ice-rock interface, melting from the glacier sole and clast expulsion.

Cavity till deposition, Casement Glacier, Alaska. [Image: G. McKenzie] 16

Characteristics of till in a subglacial cavity Particle packing – dense to loosely packed Particle lithology – dominated by local rock types Particle size – either bimodal or multimodal Particle shape – rounded edges, striated and faceted Particle fabric - elongated particles have poor to strong fabric Structure – usually massive and matrix supported

Till “curles”, Casement Glacier, Alaska. [Image: G. McKenzie]

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Subglacial till - “deposition” from subglacial deformation High water pressure develops in pores of unfrozen

sediments beneath the glacier sole reducing the resistance between individual grains.

The sediment develops characteristics of a slurry-like mass that flows in response to shear stress imposed by the overriding glacier.

Sediment deformation beneath Breidamerkurjokull, Iceland. [Image: modified from Boulton and Hindmarsh (1987)]

Schematic showing deformation of till beneath ice stream B, West Antarctica. [Image modified from Alley et al. (1986)]

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Subglacial till - “Deposition” from subglacial deformation Deformation can occur by

pervasive (ductile deformation) or discrete shear (brittle deformation).

Rate of deformation will vary spatially and temporally (sticky spots).

Accumulation of sediment will occur if more sediment is advected into an area than out (compressive flow).

Downcutting and assimilation of new sediment will occur if more sediment is advected out of an area than in (extentional flow).

Glaciotectonized Kara Diamicton. Yamal, Russia1997 (reversed); http://www3.hi.is/~oi/siberia_photos.htm

Deforming bed, Bering Glacier, Alaska. [Image: G. Larson] 19

Different levels of subglacial deformation. [Modified from Hart and Boulton (1991)]

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Charcteristics of a deforming bed Particle packing – dense, consolidated Particle lithology – diverse range of

lithologies reflecting that of original sediments

Particle size – diverse range of sizes reflecting that found in original sediment; may contain rafts of original sediment

Particle shape – dominated by original sediment that is being deformed

Particle fabric – Poor elongated clast fabric if pervasively sheared, strong if discretely sheared

Structure – usually massive and matrix supported; structureless if pervasively sheared, folded, thrusted if discretely sheared

A deformation till (?), Netherlands. [Image: G. Larson]

Schematic showing formation of a deformation till. [Image: G. Larson]

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A reassessment of subglacial till types It is now generally recognized that

subglacial tills owe their origin to a combination of sedimentary processes, of which deformation dominates.

Many of the micro and macromorphological characteristics of subglacial tills are similar to those of a fault gauge.

It is therefore best to interpret the origin of subglacial tills in a tectonic framework.

Fault gauge in the Gharif formation of Northern Oman. [Image: Wouter van der Zee]

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Till Domains Subglacial tills Deposited by direct lodgement Deposited by subglacial melting Deposited by cavity deposition Formed from subglacial deformation Supraglacial tills

Deposited by supraglacial melting

Till depositional domains of a glacier

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Supraglacial till – Deposited by supraglacial melting Melting at the glacier surface

releases debris within the ice, either at a high level or near the bed of a glacier.

Left undisturbed the debris accumulates at the glacier surface forming a debris mantle.

Schematic showing formation of supraglacial meltout debris

Supraglacial meltout debris, Casement Glacier, Alaska. [Image: G. McKenzie]

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Characteristics of till deposited by supraglacial melting Particle packing – poorly

consolidated Particle lithology – variable, may

include far-travelled rock types Particle size – either bimodal or

multimodal, some fines may be removed by winnowing

Particle shape – angular, unstriated when debris derived from a high level; rounded edges, striated and faceted when debris derived from near ice base

Particle fabric - elongated particles have poor to strong fabric

Structure – crude to well developed bedding

Supraglacial meltout till, Matanuska Glacier, Alaska. [Image: G. Larson]

Schematic showing formation of supraglacial meltout till. [Image: G. Larson]

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Supraglacial debris-flow deposits Rarely is supraglacial till preserved

in the geologic record. Variations in thickness of

accumulating debris causes variations in insulation of the ice and leads to an uneven ice-surface topography.

Debris over ice topographic highs slumps or flows and is redistributed to topographic lows.

Resedimentation by slump and debris flow occurs multiple times as the ice surface melts eventually leaving an irregular chaotic landscape.

Progressive development of supraglacial debris-flow deposits with down-wasting of buried ice. [Modified from Eyles (1979)]

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Landscape dominated by debris-flow deposits, Matanuska Glacier, Alaska. [Image: G. Larson]

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NNW/SSE-trending drumlins 5 miles south of Charlevoix, MI. [Image: L. Maher]

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BREAK TIME

Characteristics of drumlins Smooth, oval-shaped or elliptical hills of glacial origin Between 5 and 50 m high and 10-3000 m long Length to width ratio of <50 Proximal slope usually steeper than distal slope Tend to occur in multiples or “swarms” Composed of till, bedrock, deformed mixtures of till,

sand and gravel and undeformed beds of sand and gravel

Large drumlin fields in the Great Lakes region. [Image: R. Schaetzl} 29

Theories for the Origin of Drumlins Subglacial deformation (Boulton, 1987) – Two zones of

enhanced sediment flow either side of a slowly deforming obstacle and a zone of slower flow in its lee produces a sheath of “soft” sediment around the obstacle.

Subglacial meltwater (Shaw, 1994) – Inverted erosional marks at the ice bed formed during a subglacial outburst flood are infilled with deposits of sand and gravel that are subsequently capped by a deforming bed.

Drumlin field. Manitoba, Canada. [Image: nsidc.org] 30

Sediments deposited from meltwater Subglacial

Kame deposits Esker (channel fill) deposits

Ice-marginal Kame terrace deposits Outwash deposits (fluvial)

Development of kame, kame terrace and esker deposits. [Image: Flint (1971))

Development of an outwash deposit. [Image: modified from L. Benítez]

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Characteristics of kame deposits Formed within an ice-walled

channel or depression in stagnant ice

Composed of poorly to well sorted stratified sand and gravel; may include lacustrine sediments, debris-flow deposits and boulders

Rapid lateral variations in grain size Margins cut by normal

(extensional) faults; bedding often deformed by subsidence of buried ice

Can vary in shape from “mound-like” to “flat-topped”

Can occur singularly or in groups

Typical sedimentary structures found in kames. [Image: modified from Boulton (1972)]

Kame in lower Michigan. [Image: G. Larson]

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Characteristics of esker deposits Formed subglacially or englacially

within an ice-walled tunnel or supraglacially within an ice channel

Can be <1 to hundreds of kilometers long

Composed of well rounded cross-bedded sand and gravel; may include lacustrine sediments, ‘till balls’ and boulders

Flanks cut by normal (extensional) faults; bedding sometimes deformed by subsidence of buried ice

Can be single-ridged, braided, or beaded

Englacial esker melting out of ice, Burroughs Glacier, Alaska. [Image: G. Larson]

Blue Ridge esker, Michigan. [Image: G. Larson]

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Characteristics of kame terrace deposits Formed between the ice margin

and a topographic restraint Composed of poorly to well sorted

stratified sand and gravel; may include lacustrine sediments, debris-flow deposits and boulders

Proximal margins cut by normal (extensional) faults; bedding often deformed by subsidence of buried ice

Can include kettle holes, particularly near proximal margin

Can form multilevel surfaces

Formation and diversity of kame terraces

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Kame terraces, Breidarmerkuljökull, Iceland. [Image: G. Larson]

Development of an outwash plain Outwash fans build up in front of

relatively stationary ice margins with the apex of each fan located near where meltwater emerges from the ice.

Coarse material is deposited close to the meltwater source and finer material is deposited further downstream.

Outwash fans along an ice margin may merge away from the glacier to form a large outwash plain drained by a braided river system.

Discharge in the braided river system will greatly vary both daily and seasonally and result in erosional and depositional cycles.

The final surface morphology of an outwash plain will depend on the amount of buried ice and supply of sediment.

Schematic showing the formation and development of a simple outwash fan. [Image: modified from Bennett and Glasser (2009)]

Outwash plain (sandur), Skeidararjökull,

Iceland. [Inage: G. Larson] 35

Characteristics of an outwash deposit Proximal – mainly multistorey, massive or crudely

bedded gravel with imbrication; associated with longitudinal bars and lag deposits in gravel-dominated steams

Medial – mainly horizontally bedded massive gravel to pebbly sand; associated with linguoid or lobate bars in gravel-sand dominated streams

Distal – mainly horizontally bedded sand to silt; associated with poorly differentiated channels and bars in sand-silt dominated streams

Facies of an outwash deposit. [Image: Zielinski and van Loon (2003)]

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Proximal Medial Distal

Proximal outwash, Kalamazoo, Michigan. [Image: G. Larson]

Medial outwash, Warham, Massachusetts. [Image: G. Larson]

Distal outwash, Warham, Massachusetts. [Image: G. Larson]

Facies of an Outwash Depsit

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Ice-marginal lake, southeast Alaska. [Image: G. Larson]

Sediments deposited in glacial lakes Grounded glacier – deposition by a combination of meltout,

lodgement and deformation Floating ice margin – deposited within a water body

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Middle to distal subaqueous grounding-line fan deposit, Champlain Valley, NY. [Image: L. Gillett]

Schematic representation of a grounding line fan. [Image: R. Powell (1990)]

Sedimentary processes associated with a grounded glacier Direct deposition by meltwater

currents Settling from suspension Resedimentation from gravity

flows ‘Rain-out ‘ by icebergs Current reworking

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Schematic representation of kame delta. [Image: Bennett and Glasser (2009)]

Kame delta, Mohawk Valley, New York [Image: G. Larson]

Development of a kame delta Forests- formed from

sediment avalanches down the delta front

Bottomsets – formed by fine-grained sediment flows in the prodelta environment

Topsets – formed from fluvial deposition on delta surface

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Gilbert style delta

Glaciolacustrine sediments, Glacier Bay, Alaska. [Image: G. Larson]

Sedimentary processes in a water body ‘Rain out’ from icebergs Settling from suspension Subaqueous resedimentation by

gravity flows Current reworking Sediments can be very varied

Model of glaciolacustrinesedimentary processes. Image: modified from Eyles (1984)]

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Glacial geomorphic map of Grand Traverse Bay region. [Image: modified from Lundstrom et al. (2003)]

Stop 1 Stop 2

Stop 3

Stop4

Traverse City

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Glacial geomorphic map of Grand Traverse Bay region. [Image: Lundstrom et al. (2003)] 43

Field trip stops for interpreting sediments workshop, August 16, 2010

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Hotel

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Selected References: Alley, R.B., Blankenship, D.D.,Bently, C.R. & Ronney, S.T. (1986). Deformation of till beneath ice stream B, West Antactica. Nature, 322, 57-9. Boulton, G.S. (1970). On the deposition of subglacial and melt-out tills at the margin of certain Svalbard glaciers. Journal of Glaciology, 9, 231-245. Boulton, G.S. (1972). Modern Arctic glaciers as depositional models for former ice sheets. Journal of the Geological Society of London, 128, 361-393. Boulton, G.S. (1982). Subglacial processes and the development of glacial bedforms. In Davidson-Arnott, R., Nicking, W. & Fahey, B.D. (eds), Research in Glacio-fluvial and Glaciolacustrine Systems, Geo Books, Norwich, 1-31. Boulton, G.S. (1987). A theory of drumlin formation by subglacial sediment deformation. In Menzies, J. & Rose, J. (eds), Drumlin Symposium, Balkema, Rotterdam, 25-80. Boulton, G.S. & Hindmarsh, R.C.A. (1987). Sediment deformation beneath glaciers: rheology and geological consequences. Journal of Geophysical Research, 92, 9059-82. Bennett, M.R. & Glasser, N.F. (2009). Glacial Geology: Ice Sheets and Landforms. Wiley-Blackwell, 385 p. Eyles, N. (1979). Facies of supraglacial sedimentation on Icelandic and Alpine temperate glaciers. Canadian Journal of Earth Sciences, 16, 1341-1361. Ehlers, J. & Gibbard, P.L. (2004). Quaternary Glaciations – Extent and Chronology, Part II. Elsevier, 488 p. Flint, J.F. (1971). Glacial and Quaternary Geology. John Wiley & Sons, 892 p. Hart, J.K. & Boulton, G.S. (1991). The inter-relation of glaciotectonic and glaciodepositional processes within the glacial environment. Quaternary Science Reviews, 10, 335-350. Lundstrom, S., Kincare K.A., Grannemann, N.G., Yancho, S., Passino-Reader, D.R., Van Sistine, D.P., & Havens, J.C. (2003). Quaternary geologic framework of the Grand Traverse Bay region, Michigan: relationships to water, land, and ecological resources. Geological Society of America Abstracts with Programs, 35, 67 Shaw, J., (1994). A qualitative view of sub-ice-sheet landscape evolution. Progress in Physical Geography, 18, 159-84. Sudgen, D.E. & John, B.S. (1976). Glaciers and Landscape. John Wiley and Sons, New York, 376 p.