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 LithofaciesDescribes physical characteristics of the depositSilt laminaeCross-bedded sandGenetic faciesState or imply a specific mode of formationFluvial or eolian dune-bedded sandsBiofaciesDefined by the presence / lack of some kind of biological material
5 Glacial Facies and Walther’s Law Travis Corthouts
6 Johannes WaltherI“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.
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 tillitesPoorly sorted sedimentStriated or polished clastsPreferred orientation of long axis (crude imbrication)Diverse clast assemblagesProglacial to Periglagial Facies:Reworked by melt-water, which may produce sedimentary structures.Better sortingFreeze-thaw process in periglacial zones = better stratification.Loess
11 Glacial E.O.Ds and Associated Facies Most diverse grain size sedimentary systemPrimary Glacigenic Deposits(Ice-Contact Zone)Glacifluvial Deposits(Proglacial)Gravity Mass-Movement Deposits(Glacilacustrine/–marine)Suspension Settling and Ice-Rafting(Glacilacustrine/ –marine)Ripples cross-laminated faciesCross-bedded faciesGravel sheetsSilt and mud drapesScree/debris-fall depositsDebris-flow depositsTurbiditesSlide and slump depositsVarvesMud and diamicton dropstonesUndermelt diamictonLodgement tillGlaciotectoniteDeformation tillMelt-out tillOther 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.
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 FaciesDiamictites: 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 contactDeformation/penetration of laminated sediment at bottom contact.
18 Facies model (Anderson, 1989) Especially – effects on vertical & horizontal conductivity18
19 Ice-marginal environments Air / iceIce lakeIce / rock lakeIce / rockAir / ice / rockAir / ice / rock / riverIce riverIce / stream / rockAir / rockTill **Ablation tillG-lac. driftDropstonesG-lac. driftKame deltasTillLodgment tillTillMorainesAlluvium **Kame terracesyellow = stratified drift, blue == unstratified (diamict)** = mass wasting can be involved?AlluviumOutwash/driftAlluviumEskersAlluviumOutwash
40 Grounded Ice Facies: Unstratified Diamicts Bimodal Particle Size Distribution:Unsorted pebbles, cobbles, and bouldersInterstitial matrix of sand, silt, and clayElongate particles show preferred orientationSome crude imbricationLong axes dipping upstream
41 Stratified Diamicts Sediments generated by: Better sorting Supraglacial, englacial, subglacial processesBetter sortingLack the bimodal size distribution associated with direct depositionPebbles may be rounded by meltwater transportSome stratification from reworkingSeen in the form of kames, kame terraces, eskers
43 Glaciofluvial Deposits Can be deposited in:Subglacial and englacial conduitsSupraglacial and proglacial streamsLithofacies reflect local sediment supplyWell stratified and feature sedimentary structures at varying scalesDependent on stream discharge and sediment supply
44 Kames Small mound-shaped accumulations of sand or gravel Form in pockets or crevasses in the iceCommonly feature fining upwards sequencesLarge unsorted clasts overlain by sands & siltsThermal?
45 Eskers Narrow, sinuous ridges of sediment parallel to ice flow Can include gravels, sands, and siltSome facies may be extremely well stratifiedFeature gravels overlain by fine, fluvial sedimentsTopped or interbedded with diamictites
47 Glacier Marine Sediment Facies: Definitions Till – terrestrial, primary glacier deposited diamictonGlacimarine drift – “marine till”Facies – stratigraphic units distinguished by lithologic, structural and organic characteristics detectable in the field (Boggs 2001)
49 Distal Glacier Marine Facies Characteristics Settled sedimentExtreme variation in clast type (lithology and source)Dropstones – with soft sediment deformationStratificationMarine 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 flowsStratificationFine-grained laminae [fine sand/silt – silt/clay]thin from icedark from organicsEyles et al 1991
52 Dropstones Clast lithology – gneiss in mudstone Boulder Subrounded