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Dakota Aquifer Program--Geologic Framework--Stochastic Modeling

Appendix D

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Architectural elements and lithofacies classification

Lithofacies classification, from Miall (1978)

Lithofacies Sedimentary structures Interpretation
Gmsmassive, matrix supported gravelgrading debris flow deposits
Gmmassive or crudely bedded gravel horizontal bedding, imbrication longitudinal bars, lag deposits, sieve deposits
Gtgravel, stratifiedtrough crossbeds minor channel fills
Gpgravel, stratifiedplanar crossbeds linguoid bars or deltaic growths from older bar remains
Stsand, medium to v. coarse, may be pebbly solitary (theta) or grouped (pi) trough crossbeds dunes (lower flow regime)
Spsand, medium to v. coarse may be pebbly solitary (alpha) or grouped (omikron) planar crossbeds linguoid, transverse bars, sand waves (lower flow regime)
Srsand, very fine to coarse ripple marks of all types ripples (lower flow regime)
Shsand, very fine to very coarse, may be pebbly horizontal lamination, parting or streaming lineation planar bed flow (l. and u. flow regime)
Slsand, finelow angle (< 10 degrees) crossbeds scour fills, crevasse splays, antidunes
Seerosional scours with intraclasts crude cross-beddingscour fills
Sssand, fine to coarse, may be pebbly broad, shallow scours including eta crossbedding scour fills
Flsand, silt, mudfine lamination, very small ripples overbank or waning flood deposits
Fscsilt, mudlaminated to massive backswamp deposits
Fcfmudmassive, with freshwater molluscs backswamp pond deposits
Fmmud, siltmassive, dessication cracks overbank or drape deposits
Frsilt, mudrootletsseatearth
Ccoal, carbonaceous mudplants, mud films swamp deposits
Pcarbonatepedogenic featuressoil

Model 6--the classic sandy, mixed-load meandering river.

drawing of meandering stream

Architectural elements in fluvial deposits

Element Symbol Principal lithofacies
Geometry and relationships
ChannelsCHany combination finger, lens or sheet; concave up erosional base; scale and shape highly variable; internal concave-up secondary erosion surfaces common
Gravel bars
and bedforms
GBGm, Gp, Gt lens, blanket; usually tabular bodies; commonly interbedded with SB
Sandy bedformsSBSt, Sp, Sh, Sl,
Sr, Se, Ss
lens, sheet, blanket, wedge; occurs as channel fills, crevasses, splays, minor bars
FMSt, Sp, Sh, Sl,
Sr, Se, Ss
lens resting on flat or channelled base, with convex-up second-order internal erosion surfaces and upper bounding surface
Lateral accretion
LASt, Sp, Sh, Sl,
Se, Ss; less commonly
Gm, Gt, Gp
wedge, sheet, lobe; characterized by internal lateral accretion surfaces
gravity flows
SGGm, Gms lobe, sheet; typically interbedded with GB
sand sheets
LSSh, Sl; minor St,
Sp, Sr
sheet, blanket
Overbank finesOFFm, Flthin to thick blankets; commonly interbedded with SB; may fill abandoned channels

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Kansas Geological Survey, Dakota Aquifer Program
Updated Jan. 8, 1997.
Scientific comments to P. Allen Macfarlane
Web comments to webadmin@kgs.ku.edu
The URL for this page is HTTP://www.kgs.ku.edu/Dakota/vol1/geo/stoAppE.htm