Macroform Scale Architectural Elements

TABLE S1: MACROFORM-SCALE ARCHITECTURAL ELEMENTS

CHANNEL ELEMENTS

CH: Channel elements Single or multistory, finger, lens or sheet with concave-up erosional base (Miall 1985, 1996). May include any combination of lithofacies as well as smaller-scale elements (LA, DA, SB, GB etc). Channels with high sinuosity may be subject to chute or neck cut-off, and be filled with FF deposits. Major channels are bound by 5th- order surfaces, and may be 103- 104 m wide (Miall 1985), minor channels by 3rd- and 4th- order surfaces. Can be further divided into ribbon and sheet channels (Friend 1983; Gibling 2006), crevasse channels (Currie et al. 2009), and chute channels (Long 2006).

CHR: ribbon channels. Channels with w/d ratios of < 15:1 (Friend 1983; Eberth and Miall 1991; Miall 1996); Gibling (2006) divides these into narrow (< 5:1) and broad (5- 15:1). Equivalent to solitary ribbon sandstones of Currie et al. (2009).

CHS: sheet-channels. Channels with w/d ratios > 15:1 (Friend 1983; Eberth and Miall 1991; Miall 1996; Gibling 2006). Miall (1985) described channels with w/d ratios > 100:1 as “sheet-like”.

CV: Crevasse channels. Small channels cut through stream banks. Concave up erosional base, bounded by 4th- order surface (Miall 1996). Equivalent to CR of Currie et al. (2009). Eberth and Miall (1991) use CRS for minor crevasse channels (w/d < 10, < 1 m thick) and CRM for deep, stable crevasse channels (1- 10 m thick, 1- 30 m wide).

ChCH: Chute channels. Small bar-top channels: may have evidence of upstream accretion (Long 2006).

IN-CHANNEL AND CHANNEL-PROXIMAL ELEMENTS

GB: Gravel bars and bedforms. Lens- or blanket-shaped units, mesoforms, and macroforms (Gh, Gp and Gt), usually tabular, typically bounded by 3rd- and 4th- order surfaces (Miall 1985, 1996). May occur as multistory sheets, interbedded with SB.

SB: Sandy bedforms. Lens, sheet, blanket, or wedge-shaped sand bodies, formed by migration of ripples, dunes, sand waves, transverse and linguoid bedforms, as well as upper-flow-regime plane beds or washed out humpback dunes (St, Sp, Sh, Sl, Sr, Se, Ss; Miall 1985, 1996). May be present as channel fill, or minor bars, or as a component of simple or compound bars within DA, LA elements. Also present as a component of crevasse channels and crevasse-splay elements. Typically constrained by 1st- or 2nd- order bounding surfaces. SG: Sediment-gravity-flow deposits. Narrow or elongate lobes or multistory sheets (Gmm, Gmg, Gcm), may be interbedded with GB or SB (Miall 1985, 1996). Typically have irregular, non-erosional bases, are 0.5– 3m thick, with width up to 20 m and downstream length of several kilometers.

SE: Sandy sheet elements. Compound sheet-like units of sandy bedforms (SB: St, Sp, Sh, Sl), with w/d ratios > 20:1 (after Cotter 1987).

DA: Downstream accretionary macroforms. Lens of related sandy bedforms (SB: St, Sp, Sh, Sl, Sr, Se, Ss) resting on flat or channeled base, with convex-up 3 rd- order internal erosional surface and upper 4th- order bonding surface (Miall 1999). Typically related to downstream migration of simple or compound macroforms and bars. Equivalent to foreset macroforms (FM) of Miall (1985). Modal orientation of 0th- order foresets is within ± 45° of modal slope of associated 1st- or 2nd- order bounding surfaces.

LA: Lateral accretion macroforms. Wedge, sheet or lobe of SB or GB elements (St, Sp, Sh, Sl, Sr, Se, Ss, Gm, Gt, Gp), characterized by internal lateral accretion surfaces (Miall 1985). Includes heterolithic inclined strata (IHS) and epsilon cross stratification. Typically bounded by 2nd order surfaces. Modal orientation of 0th order foresets is within ± 45° of the strike of the modal slope of associated 1st or 2nd order bounding surfaces.

DLA: Downstream lateral-accretion surfaces. This variant of DA element was introduced by Long (2006) to indicate units, transitional between DA and LA elements, in which modal orientation of 0th- order foresets is between 30 and 60° down slope of the modal strike of associated 1st- or 2nd- order bounding surfaces. Note that Ghazi and Mountney (2009) use DLA to include both downstream accretion and lateral accretion elements within channel fills.

ULA: Upstream lateral-accretion surfaces. This variant of a LA surface was introduced by Long (2006) to indicate LA sets in which the 0th- order foresets of SB indicate that bedforms migrated up the surface of the macroform (30 to 60° up from strike of 1st- or 2nd- order bounding surfaces.

UA: Upstream accretion elements. Opposite of DA, 0th- order structures indicate flow up the back slope of a bar complex (Long 2006).

LS: Laminated sand sheet. Sheet or blanket (Sh, Sl; minor St, Sp, Sr: Miall 1985). May represent deposition from non-channelized flows, as bar-top, bar-flank sands, or as deposits of overbank sheet floods (Ghazi and Mountney 2009). Fielding (2006) suggested that thicker channelized units should be included as upper-flow-regime (URF) elements.

UFR: Upper flow regime elements. Term used by Fielding (2006) to describe channelised sheet, lens and scour fill LS units (Sh, Sl), with convex up geometry. May include humpback and sinusoidal dunes and up-flow and down- flow dipping low-angle cross-beds. Units dominated by backsets terminating up-dip against an upstream-dipping erosion surface, were interpreted as products of deposition in chute and pool environments.

HO: Hollows elements. Scoop-shaped elements, typically with an asymmetric fill (Miall 1996). Typically represented by deep points in channel bases with evidence of convergent flow. Considered to be developed at confluence points where stream channels meet.

CPB: Counter-point-bar deposits. LA sets located at sharp (inner) bends in meandering rivers, down river from point bars. Typically with a lower elevation and higher fines content than associated point-bar deposits (Smith et al. 2009).

FLOODPLAIN FACIES

FF Floodplain fines. Thin to thick blankets of overbank material (Fm, Fl). May include pedogenic horizons (P: Miall 1996). Replaces OF of Miall (1985). Eberth and Miall (1991) use FFP to indicate proximal floodplain facies and FFD to indicate distal floodplain facies. Can occur as fill of abandoned channels (element FF(CH) of Miall 1996).

CS: Crevasse-splay elements. Thin, lobate or lenticular sheets found in channel- proximal settings (Miall 1996). May occur as wings of CHS (Eberth and Miall 1991; Currie et al. 2009; Ghazi and Mountney 2009).

LV: Levee elements. Sheet- or wedge-shaped units (Fl, Sh, Sr), thinning away from channel margins into adjacent floodplains (Miall 1996; Ghazi and Mountney 2009). Possibly equivalent to FFP of Eberth and Miall (1991).

REFERENCES

Currie, B.S., Colombi, C.E., Tabor, N.J., Shipman, T.C., and Montañez, I.P., 2009, Stratigraphy and architecture of the Upper Triassic Ischigualasto Formation, Ischigualasto Provincial Park, San Juan, Argentina: Journal of South American Earth Sciences, v. 27, p. 74-87.

Eberth, D.A., and Miall, A.D., 1991, Stratigraphy, sedimentology and evolution of vertebrate-bearing, braided to anastomosed fluvial systems, Cuttler Formation (Permian to Pennsylvanian), north-central New Mexico: Sedimentary Geology, v. 72, p. 225-252.

Friend, P.F., 1983, Towards the field classification of alluvial architecture or sequence, in Collinson, J.D., and Lewin, J., eds., Modern and Ancient Fluvial Systems: International Association of Sedimentologists, Special Publication 6, p. 345–354. Ghazi, S., and Mountney N.P., 2009, Facies architectural element analysis of a meandering fluvial succession: the Permian Warchha Sandstone, Salt Range, Pakistan: Sedimentary Geology, v. 221, p. 99-126.

Gibling. M.R., 2006, Width and thickness of fluvial channel bodies and valley fills in the geological record: a literature compilation and classification: Journal of Sedimentary Research, v. 76, p. 731-770.

Long, D.G.F., 2006, Architecture of pre-vegetation sandy-braided perennial and ephemeral river deposits in the Paleoproterozoic Athabasca Group, northern Saskatchewan, Canada as indicators of Precambrian fluvial style: Sedimentary Geology, v. 190, p. 71–95.

Miall. A.D., 1985, Architectural-element analysis: a new method of facies analysis applied to fluvial deposits: Earth-Science Reviews, v. 22, p. 261-308.

Miall, A.D., 1996, The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis and Petroleum Geology. Berlin, Springer-Verlag, 582 p.

Smith, D.G., Hubbard, S.M., Leckie, D.A., and Fustic, M. 2009, Counter point bar deposits: lithofacies and reservoir significance in the meandering modern Peace River and ancient McMurray Formation, Alberta, Canada: Sedimentology, v. 56, p. 1655-1669.