Sedimentary Geology 279 (2012) 23–41

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Sedimentary Geology

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Recognition of wave-dominated, tide-influenced shoreline systems in the rockrecord: Variations from a microtidal shoreline model

Boyan K. Vakarelov a,⁎, R. Bruce Ainsworth b, James A. MacEachern c

a WAVE Consortium, The University of Adelaide, Adelaide, SA, 5005, Australiab Australian School of Petroleum, The University of Adelaide, Adelaide, SA, 5005, Australiac Earth Sciences, Simon Fraser University, Burnaby, British Columbia, Canada V5A 1S6

⁎ Corresponding author.E-mail addresses: bvakarelov@asp.adelaide.edu.au, b

(B.K. Vakarelov).

0037-0738/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.sedgeo.2011.03.004

a b s t r a c t

a r t i c l e i n f o

Article history:Received 3 May 2010Received in revised form 6 March 2011Accepted 21 March 2011Available online 26 March 2011

Keywords:TideShorefaceWave-dominatedTide-influencedTidal beachFacies model

Existing wave-dominated facies models are based on microtidal coastlines and do not adequately addresswave-dominated environments influenced by significant tidal ranges. Observations from modern environ-ments show that such systems are abundant along tide-influenced shorelines facing wide shelves and largeembayments, such as much of the northern Australia coast; yet equivalent deposits have been rarelyrecognized from the ancient record. Geomorphological literature shows that tidal influence on wave-dominated shorelines has the effect of shifting the shoaling, breaking, and swashwave zones up and down thebeach profile; when the tidal range is appreciable, sedimentation is affected significantly. Many macrotidal,wave-dominated systems (tidal range N4 m), for example, are non-barred and are characterized by poordevelopment of dune-scale bedforms in the subtidal zone and along the beach profile. Other systems dodevelop cross stratification, but this occurs in the intertidal zone rather than the subtidal zone as is implied inexisting wave-dominated facies models. The association of many wave-dominated, tide-influencedenvironments with shallow shelves also suggests that major storms may be capable of reworking sedimentsignificant distances from the shoreline.We present an ancient example of a wave-dominated, tide-influenced, fluvial-affected system (Wtf) from theCampanian Bearpaw to Horseshoe Canyon Formation transition near Drumheller, Alberta, Canada, which hasbeen described in closely spaced outcrop exposures and core. Wave domination in the coarsening-upwardinterval is unambiguous and is represented by abundance of micro-hummocky cross stratification and otherstorm beds in the mudstone-dominated portions, a well-defined swaley cross stratified sandstone interval,and an up to four meter thick, horizontal planar stratified interval interpreted to have been formed by swashwaves. Tide influence is suggested by common double carbonaceous and mud drapes and well-developedtidal rhythmites. The anomalously thick horizontal planar interval described above is interpreted also to berelated to tides that shift the zones of wave reworking up and down the beach profile. Fluvial influence issuggested by the presence of fluid mud beds in the lower portion of the succession and the abundance ofcarbonaceous debris through the entire interval. The boundary between the mudstone-dominated andsandstone-dominated portions of the succession is sharp and scoured, and is interpreted as the boundarybetween a subaqueous delta front or mudstone belt below and a wave-dominated, tide-influenced shorelineabove. Observations in this study and a survey of geomorphologic literature lead to a new proposed model offacies distributions for a wave-dominated, tide-influenced system. Additional ancient case studies are neededin order to generate robust facies models capable of dealing with the full variability of such systems.

vakarelov@sedbase.com

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Tidal influence in otherwise wave-dominated systems is rarelydescribed from the ancient record, even though many modern wave-dominated shorelines are significantly affected by tides (e.g., Short,1991; Masselink and Hegge, 1995; Masselink and Turner, 1999; Levoy

et al., 2000; Dashtgard et al., 2009). The existing facies models forwave-dominated, shallow marine systems essentially imply ‘micro-tidal’ conditions, and consider solely the effects of wave energy, stormclimate (storm energy vs. storm frequency) and sediment caliber onthe resulting facies successions (e.g., Walker and Plint, 1992; Clifton,2006). An integral part of such models is the distinction between an‘upper shoreface’ and a ‘lower shoreface’ interval. Upper shorefacesare largely associated with fair-weather wave processes and thedevelopment of wave-forced currents, leading to the dominance ofcross stratification (Walker and Plint, 1992; Hampson and Storms,

24 B.K. Vakarelov et al. / Sedimentary Geology 279 (2012) 23–41

2003; Clifton, 2006). Bioturbation in such regimes is sporadicallydistributed and generally of lower intensity, with the exception ofintrastratal concentrations of Macaronichnus segregatis (MacEachernand Pemberton, 1992; Saunders et al., 1994). Lower shorefaces aredominated mainly by some combination of fair-weather bioturbationand storm-generated event beds, with fair-weather waves largelyconfined to the role of sediment sorting and winnowing of clay andsilt (Howard and Frey, 1984; MacEachern and Pemberton, 1992;MacEachern and Bann, 2008). These models are well-supported byobservations from modern microtidal wave-dominated shorelines,which have been intensively studied and are relatively wellunderstood (Curray et al., 1969; Short, 1984; Wright and Short,1984; Clifton, 2006). Observations from modern wave-dominated,meso-, macro-, and mega-tidal systems (tidal beaches/tide-modulat-ed shorefaces) (Hayes, 1979; Short, 1991;Masselink and Hegge, 1995;Yang et al., 2008; Dashtgard et al., 2009), on the other hand, suggestthat some of the assumptions upon which “shoreface models” arebased may fail with increasing tidal ranges.

Themorphology and sediment dynamics of beaches and shorefacescan be greatly affected by increases in tidal range, illustrated by agrowing body of literature on modern mesotidal, macrotidal, andmegatidal beach systems (e.g., Heward, 1981; Wright et al., 1982;Short, 1991; Masselink and Short, 1993; Masselink and Hegge, 1995;Masselink and Turner, 1999; Levoy et al., 2000; Anthony and Orford,

Fig. 1. Stratigraphic nomenclature for the Cretaceous units of the Alberta Basin. The Late Camcentral Alberta Plains, and passes upwards out of the Bearpaw Formation. The unit is equivalnortheastern plains. Modified from MacEachern and Gingras (2007).

2002; Bernabeu et al., 2003; Masselink et al., 2006; Yang et al., 2008;Dashtgard et al., 2009). Such studies demonstrate that wave-dominated shorelines can form easily in settings affected by hightidal ranges, especially along unprotected shorelines exposed to oceanswells (e.g., Wright et al., 1982; Levoy et al., 2000; Yang et al., 2008).Themost important impact of a large tidal range on beach dynamics isthe shift of position ofwave agitation throughout the tidal cycle,whichaffects both the duration and the nature of wave processes influencinga given part of the beach-shoreface profile, with tide-generatedcurrents being subordinate (Masselink and Hegge, 1995; Masselinket al., 2006; Dashtgard et al., 2009). This shift occurs in microtidalregimes aswell; however the scale of shift isminimal anddoes not leadto profound changes in the wave regime at any one location. In morestrongly tidally influenced systems, these shifts are pronounced and aconsequence of this is that markedly different wave processes (e.g.,shoaling, breaking, swash waves) may dominate the subtidal, lowerintertidal and higher intertidal zones (e.g., Dashtgard et al., 2009).Large tidal ranges tend to increase beach width and decrease overallbeach gradients, resulting in the toning down of sediment transportprocesses andmorphodynamic changes (Levoy et al., 2000; Masselinket al., 2006). Small to intermediate tidal ranges allow the formation ofwell-developed ‘slip-face intertidal bars’ (Masselink et al., 2006),whereas further increases in tidal ranges commonly result in loweramplitude morphological features such as ‘low-amplitude ridges’ and

panian Horseshoe Canyon Formation comprises the part of the Edmonton Group in theent to the Puskwaskau of the northwestern Alberta Plains and has been eroded from the

Fig. 2. Map of the study area, showing the position of outcrop measured section (RDV-8) and location of the cored well ARC CH 20–79. Gray dots represent positions ofprevious measured sections from Ainsworth (1994). The map uses UTM coordinates.The solid black lines on the margins of the map represent Township/Range boundaries.

25B.K. Vakarelov et al. / Sedimentary Geology 279 (2012) 23–41

‘sandwaves’, or formation of relative flat and featureless intertidalareas (Wright et al., 1982; Masselink et al., 2006; Yang et al., 2008).

High tidal ranges also have important impacts on subtidal areas,seaward of an intertidal beach. The wave-generated subtidal bars insuch settings tend tobemore poorly developed and, inmanymacrotidaland megatidal wave-dominated systems, can be lacking entirely(Wright et al., 1982; Short, 2006; Dashtgard et al., 2009). In macrotidalsettings, the subtidal areas can also be affected by significant longshoretidal currents that are capable of moving sediment along shore and canreverse direction (Wright, 1981; Liu et al., 2002). The association ofmany macrotidal beaches with wide and shallow continental shelves(Clarke and Battisti, 1981; Klein, 1982; Anthony and Orford, 2002)suggest that the lower shoreface to offshore portions of suchdepositional systems are particularly prone to reworking during majorstorms events. Many of the Australian tidal beaches, for example, arefrequently affected by cyclones (Short, 2006).

Observations from modern wave-dominated, tidally influencedsystems clearly suggest that the impact of tides is significant and thatrecognizable suites of facies for such deposits should exist (e.g.,Dashtgard et al., 2009). This is further reflected by the significantvariability observable in modern tidal beaches, which have beensuccessfully subdivided into distinct beach types based on processesand morphology (Wright et al., 1982; Masselink and Hegge, 1995;Short, 2006). Nonetheless, tidally influenced shoreface deposits arerarely discussed in the sedimentological literature. Ancient examplesof tidal deposits, and the suite of diagnostic sedimentary structureswith which they are associated, are based largely on observationsfrom ‘funnel-shaped’ bodies of water, such as estuaries, tidal channels,and narrow tectonic valleys, all of which are dominated by stronglybi-directional, rectilinear tidal currents (Dalrymple et al., 1990; Boydet al., 2006; Dalrymple and Choi, 2007). Tidal currents on openshelves, on the other hand, have more complex expressions and arebetter modelled as tidal ellipses that usually portray predictablevariations in the tidal current vector during a tidal cycle (e.g., Wright,1981; Valle-Levinson et al., 2000). Such currents can share similaritieswith the confined bi-directional currents discussed above. They canreverse at times of peak flow (e.g., Liu et al., 2002), and becharacterized by alternating velocities that result in cyclic pulses ofsediment transport and deposition affected by daily tide cycles, aswell as spring-neap tidal cycles (e.g., Hemer et al., 2004). Wespeculate that such a style of deposition can potentially result in theformation of features that are otherwise considered as inshore tidalindicators, such as tidal rhythmites and double mud drapes. As rotarytides may be characterized by ‘velocity lows’ rather than truly ‘slackwater’ conditions, at which times tidal current direction may be at ahigh angle (often perpendicular) to the directions of peak current, theresponse of bedforms on the sea bedmay bemore complex than in thecase of purely rectilinear tides. Additional factors such as wavesuspension of sediment, which is then transported by peak tidalcurrents (e.g., Vincent et al., 1998) may make tidal influence in mixedwave/tide-influenced systems more difficult to discern.

We present a case study of a wave-dominated, tide-influenceddeposit from the Campanian Bearpaw Formation, which crops outnear Drumheller, Alberta, Canada. Excellent outcrop exposure and thepresence of nearby cored intervals from the same unit make detailedfacies observations possible, facilitate the evaluation of the relativeimportance of wave and tidal processes in this mixed-influencesystem, and should permit recognition of similar deposits elsewhere.We suggest that wave-dominated, tide-influenced deposits (alsoreferred to as tidal beaches, tide-dominated beaches, and tide-modulated shorefaces) may be a common feature in the ancientrecord, which have thus far remained largely unrecognized owing to alack of suitable recognition criteria and facies models. The dominantand subordinate processes in this case are determined by estimatingthe percentage of preserved sedimentary structures in the system(Ainsworth et al., 2011, see further discussion).

2. Study area and geological overview

The Upper Cretaceous (Campanian to Maastrichtian) intervalrepresents the transition between the Bearpaw and HorseshoeCanyon formations (Fig. 1). The sedimentary succession crops outalong the Red Deer River valley approximately 15 km south ofDrumheller, Alberta, Canada (Fig. 2). At the time of deposition, thearea lay on the western margin of the Western Interior Basin (WIB).The Bearpaw–Horseshoe Canyon transition forms the base of a thickclastic wedge, the Edmonton Group (Irish, 1970), which built out intothe foreland basin in response to the accretion of terranes in theCordillera to the west (Stockmal et al., 1994; Miall et al., 2008). TheHorseshoe Canyon Formation has been interpreted as marginalmarine at this location by all previous workers (e.g., Shepheard andHills, 1970; Rahmani, 1988; Saunders, 1989; Ainsworth, 1991, 1992,1994; Ainsworth and Walker, 1994; Lavigne, 1999). The dominantdepositional environments that have been proposed include wave-dominated shorefaces, wave- and storm-dominated deltaic lobes,tide-dominated estuarine complexes, back-barrier lagoons, andcoastal swamps. Tide-generated sedimentary structures were origi-nally identified from the estuarine deposits by Rahmani (1988). Tidalinfluence was also described in the wave-dominated shorefacedeposits (Ainsworth, 1991, 1994).

This study builds upon the stratigraphic framework established inprevious investigations by Shepheard and Hills (1970), Rahmani(1988), and Ainsworth (1991, 1992, 1994). Ainsworth (1991, 1992,1994) divided the succession into eight Allomembers (A to G). Thefocus of this study is Allomember A, the wave-dominated, tide-influenced, and fluvial-affected succession that forms the basaloutcrop unit in the study area (Figs. 3 and 4A).

3. Methods

Allomember A (herein referred to as Unit A) was examined inoutcrop as well as subsurface core. The outcrop component of the

Fig. 3. Core description of ARC-CH 20–79 and vertical outcropmeasured section RDV-8 through Unit A. The profiles show the overall coarsening-upward trend of the units frommud-dominated lower successions to sand-dominated upper successions, overlain by a rooted horizon and a coal-bearing interval in Unit B.

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study focused on an area where Unit A is preserved in its entirety(section RDV-8 in Ainsworth, 1991, 1992, 1994). The core componentinvolved examination of slabbed continuous intervals of Unit A from

100–133.8 m in ARC CH 20–79 (EEiD 46904), located at 15-33-27-18W4M (Canadian Coordinate Convention), approximately two kmnortheast of the outcrop belt (Fig. 2). Elsewhere in the study area, the

Fig. 4. Selected lithofacies shots from outcrop and core, showing evidence for wave influence in Unit A. A) Coarsening-upward succession at RDV-8 in outcrop, displaying thetransition from the mud-dominated interval at the base (FA1 and FA2) to the sand-dominated interval on top (FA3 and FA4), overlain by a rooted horizon. B) Sharp base of the sand-dominated succession and swaley cross-stratification. C) Scoured base of a swaley cross-stratified sand-dominated interval, reflecting local erosion and sediment bypass. The scoursurface marks the transition between FA2 and FA3. D) Horizontal planar stratified uppermost interval of sand-dominated succession (FA4), containing carbonaceous-rich intervalsthat display features characteristic of tidal rhythmites (n— neap tide; s— spring tide). E) The same horizontal planar stratified sandstone facies of FA4 as observed in core of ARC CH20–79 (depth 100.5 m). The unit contains subtle expressions ofMacaronichnus segregatis (Ma). Scale on bottom is 3 cm. F) Sand-dominated expression of FA2 from the ARC CH 20–79 core, showing carbonaceous detritus demarcated low-angle parallel stratification (cd) of SCS. This unit shows BI 1 with isolated Cylindrichnus (Cy). Scale is 3 cm (depth 114.1 m).G) Muddy interbed within the sand-dominated component of FA2 in ARC CH 20–79, showing thick, graded silty mudstone drapes over combined flow ripples (cfr). The unit isunburrowed (3 cm scale; depth 114.3 m). H) Sand-dominated heterolithic interval of FA2 from the ARC CH 20–79 core, showing oscillation ripples (osc) and wavy parallel laminatemarked with carbonaceous detritus (cd), locally draped by mud. Isolated navichnia (na), reflecting sediment swimming behaviors, attest to probable fluid mud conditions (3 cmscale; depth 112.2 m).

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upper part of Unit A is erosionally truncated by an incised valleycomplex (Unit B) (Ainsworth, 1994). Analysis of core (122.2–143.6 m) from nearby well ARC CH 19–79 (EEiD 055194), located at04-19-28-18W4 some 6.5 km northwest of ARC CH 20–79 and

approximately 1.8 km northeast of the outcrop belt, was includeddespite the incomplete record of Unit A, because the core quality ofbasinal facies are superior. Detailed sedimentological and ichnologicalobservations were integrated to develop facies for constraining

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probable depositional environments. Surficial weathering of theoutcrop hinders detailed examination of the thinly interbeddedsandstone and shale components of the outcrop. This facies, however,is well expressed in the slabbed cores. Examination of the samestratigraphic interval in closely spaced core and outcrop sectionsallowed detailed facies observations in sandstone- and mudstone-dominated portions of the succession, as well as observations ofstratigraphic features on different spatial scales. The core and outcropsedimentological logs were correlated using similarities in faciestrends, the presence of regionally extensive coal beds, and a rootedhorizon. Coal beds in the study area are continuous across distances ofkilometers, and provide excellent correlation markers (Ainsworth,1991, 1992, 1994).

4. Sedimentology

Sedimentary logs from Unit A are shown in Fig. 3; selectedoutcrop and facies shots are shown in Figs. 4 to 8. Faciesobservations from Unit A in outcrop and core indicate that the

Fig. 5. Outcrop photo and interpreted bedding diagram of a swaley cross-stratified interval,carbonaceous-rich intervals. The carbonaceous concentrations are interpreted to representcarbonaceous lens can be seen in Fig. 6G.

interval generally coarsens upward from a largely homogenizedsandy mudstone with thin, parallel laminated sandstone layers(Facies Association 1) in the basal portion, through heterolithic,mudstone- and siltstone-dominated lower portions (Facies Associ-ation 2) to a sandstone-dominated upper portion (Facies Associa-tions 3 and 4) (Fig. 4A). The entire coarsening-upward succession iscapped by a rooted horizon with dense, unburrowed sandy and siltyroot-bearing mudstones passing into a regionally mappable coalbed [‘Coal O’ of Shepheard and Hills (1970)] two to three metersabove the contact. The base of the mudstone-dominated lowerinterval is not exposed in outcrop. In core of ARC 20–79, asandstone-dominated heterolithic interval of rippled sandstoneand dense, siderite-cemented mudstone drapes is overlain abruptlyby bioturbated sandstones that pass into bioturbated silty mud-stones of Facies Association 1. In the ARC 19–79 well, the burrowedsandstone grades through a 1 m thick zone of thinly bedded,sporadically burrowed sandstones and mudstones before passinginto the burrowed silty mudstones of Facies Association 1. Thetransition between the mudstone- and sandstone-dominated

showing the upward transition of swale bedsets lacking carbonaceous debris into moretidal influence after storms. Details of a tidal rhythmite present in a partially preserved

Fig. 6. Lithofacies examples of Unit A from core and outcrop showing evidence of tides. A)Mudstone-dominated heterolithic interval of FA2, showing current ripple (locally sigmoidal;yellow arrow) lamination, interlaminatedwithmudstone (white arrow) anddrapedwithmudstone. Soft-sediment deformation (ss) is locally present, as are syneresis cracks (sy). Theunit is largely unburrowed (BI 1), with isolated fugichnia (fu) (3 cm scale; depth 111.0 m). B) Mudstone-dominated heterolithic unit of FA2, immediately underlying that of photo A,showing current ripples with mudstone couplet on foresets (white arrows). Note the intercalation of sandstone and mudstone in the toesets of the ripples (yellow arrow). Somecarbonaceous mudstone layers truncate underlying sandy lamina-sets, demonstrating bedload transport of the flocculatedmud (red arrow). Syneresis cracks (sy) are present locally.The unit is unburrowed (3 cm scale; depth 111.1 m). C) Mudstone-dominated heterolithic unit of FA2, showing mudstone couples along current ripple foresets (white arrows) andmudstone drapes over sandy bedforms. Minor soft-sediment deformation (ss) is present, Noncohesive mud layers with high interstitial water contents favor sediment-swimmingstructures (navichnia; na). Unit shows BI 2, with isolated Planolites (P) and Cylindrichnus (Cy). (3 cm scale; depth 116.6 m). D) Double carbonaceous mudstone drapes (cd) from asandstone of FA4 in ARC CH 20–79 (3 cm scale; depth 102.5 m). E) Example of a tidal rhythmite (n — neap tide; s — spring tide) in FA2 dominated by a planar stratified doublecarbonaceous drape-bearing interval at its base, passing into a current ripple cross-laminated double carbonaceous drape-bearing interval on top. White arrows show locations ofobserved double drapes. The sandstone bed shows an escape structure (fugichnia; fu), Trichichnus (Tr), and isolatedmudstone rip-up clasts (rc). Mudstone layers show low numbersof Planolites (P), and Chondrites (Ch). Facies displays BI 2. Scale is 3 cm (118.3 m). F) Sets of double carbonaceous drapes from a swaley cross-stratified interval in outcrop (whitearrows). G) Detail of carbonaceous lens from Fig. 5, showing the cyclic variation between carbonaceous bedsets and heterolithic sandstone/carbonaceous bedsets, interpreted as tidalrhythmites (n — neap tide; s — spring tide).

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portions (Facies Association 2–Facies Association 3) of the coars-ening-upward successions in outcrop generally appears sharp(Fig. 4B). At outcrop section RDV-8, the transition is marked by a

locally scoured surface abruptly separating heterolithic mudstonesand sandstones below from an amalgamated swaley cross-stratifiedsandstone-dominated interval above (Figs. 4C and 5). In the ARC

Fig. 7. Examples of facies from FA1 and FA2 in the ARC CH 20–79 core. A) Sandy mudstone of FA1, showing remnant bedding of sand recording biogenically reworked tempestites(yellow arrows). Unit shows BI 4, with common Phycosiphon (Ph), Chondrites (Ch), and Cosmorhaphe (Cs), and rare Scalarituba (Sa), Asterosoma (As) and Zoophycos (Z). Scale is 3 cm(depth 123.5 m). B) Sandy mudstone of FA1, with remnant tempestite (yellow arrow) preserving low-angle parallel laminae. The unit shows BI 3–4, with robust Phycosiphon (Ph),Scalarituba (Sa), Cosmorhaphe (Cs), Planolites (P), Chondrites (Ch), Zoophycos (Z), Thalassinoides (Th) and rare Palaeophycus (Pa). Scale is 3 cm (depth 123.1 m). C) Thickertempestites (yellow arrows) in FA1 sandy mudstones. Mudstones show BI 4, with robust Phycosiphon (Ph) and Cosmorhaphe (Cs), diminutive Asterosoma (As), and uncommonScalarituba (Sa). Scale is 3 cm (depth 122.4 m). D) Mudstone-dominated heterolithic unit of FA2, where it grades out of FA1. Note the introduction of dense, fissile and largelyunburrowed mudstone drapes (red arrows), locally with navichnia (na). Tempestites (yellow arrows) are intercalated. Oscillation ripples (osc) with muddy interlaminae are alsopresent. The facies shows sporadic bioturbation with an average BI value of 3, although at the bed scale, BI ranges from 0–4. Ichnogenera include Phycosiphon (Ph), Chondrites, (Ch),and Asterosoma (As). Scale is 3 cm (depth 118.8 m). E) Mudstone-dominated heterolithic unit of FA2, characterized by largely unburrowed fissile mudstone interbeds (red arrows),locally showing scoured basal contacts (e.g., the lowest red arrow). Navichnia (na) is locally associated with these mudstone layers. Oscillation ripples (osc) and a parallel laminatedtempestite (yellow arrow) are present. Carbonaceous detritus (cd) marks laminae locally. The unit shows BI2, with Phycosiphon (Ph), Chondrites (Ch) and Planolites (P). Scale is 3 cm(depth 118.0 m). F) Somewhat sandier heterolithic interval of FA2, showing thin, erosionally based parallel laminated tempestites (yellow arrows) and oscillation ripples (osc)intercalated with carbonaceous detritus-rich mudstone interbeds (cd) and burrowed sandy mudstone. The unit shows BI 3 overall, with Phycosiphon (Ph), Chondrites (Ch),Cylindrichnus (Cy), Planolites (P), and fugichnia (fu). Scale is 3 cm (depth 117.8 m). G) Sand-dominated heterolithic unit of FA2, showing tempestite-generated low-angle parallellamination interpreted as HCS. The sandstone contains mudstone rip-up clasts (rc), and carbonaceous detritus (cd), locally in couplets. Carbonaceous drapes show a change fromwidely spaced to closely spaced concentrations, attributed to spring tide and neap tide, respectively. Phycosiphon (Ph) is present near the top of the bed. The laminae is subtlydisrupted, giving it a fuzzy appearance, and is attributed to cryptic bioturbation. Scale is 3 cm (depth 112.9 m). H) Sand-dominated heterolithic unit of FA2 showing carbonaceousdetritus-rich drapes (cd) marking low-angle parallel lamination. Minor oscillation ripple lamination is present near the middle to the photo. Dark, carbonaceous mudstone drapesmantle the sandstone beds (red arrows). Traces are uncommon, with the unit showing BI 1–2. Traces include Rosselia (Ro) and Palaeophycus (Pa). Scale is 3 cm (depth 111.7 m).

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19–79 core, the transition is likewise sharp; however, in ARC 20–79,the transition occurs across several subtle coarsening-upwardcycles 1–3 m thick (Fig. 3) before abruptly passing into thick,amalgamated SCS sandstone. The entire coarsening-upward suc-

cession contains abundant carbonaceous debris, which locally formsdistinct carbonaceous laminae, and rare beds. The coarsening-upward succession has been subdivided into four facies associations(Facies Associations 1–4), which are discussed below.

Fig. 8. Examples of facies from FA3 and FA4 in the RDV-8 outcrop section and the ARC CH 20–79 core. A) Close-up photo of SCS from the outcrop shown in Fig. 4, showing erosionalamalgamation (yellow arrows) of low-angle parallel laminated and minor cross-stratified sandstone beds of FA3. Scale is 50 cm. B) Thick tempestite of FA3 in core, showing lowangle planar parallel lamination. Unit is unburrowed, although cryptic bioturbation may be present. Scale is 3 cm (depth 107.5 m). C) Sandstone of FA3 in core, showing low angleplanar parallel lamination. Unit is unburrowed, with the exception of possible cryptic bioturbation. Scale is 3 cm (depth 106.0 m). D) Outcrop exposure of siderite-cementedmudstone ball of Rosselia (Ro) from SCS sandstones of FA3. Scale is 5 cm. E) Close-up of siderite-cemented fragment of Ophiomorpha borneensis (O) in sandstones of FA3. Scale is2 cm. F) Highly bioturbated interval containing Macaronichnus segregatis (Ma) within horizontal planar-stratified sandstones of FA4 at the top of Unit A. Scale is 5 cm. G) Beddingplane of sandstone bed in FA4, showing slightly more resistively weathering fills of Macaronichnus segregatis (Ma). Scale is 5 cm. H) Sandstone at the top of FA4, with cross-cuttingrhizoliths (rt) subtending from the rooted zone capping Cycle A. Scale is 5 cm. I) General outcrop view of the top of Cycle A, showing FA3 passing into FA4, and capped by thecemented rooted zone (red arrow) of the overlying coastal plain. Scale is 1 m.

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4.1. Facies Association 1 (FA1): lower offshore or “inner shelf”

4.1.1. DescriptionThe base of Unit A is a mudstone-dominated interval, which shows

a gradual upward increase in grain size, sandstone/mudstone ratio,and sandstone layer thickness into Facies Association 2. It is poorlyexpressed in outcrop sections, and progressively better exposed assandstone interbeds become thicker and more abundant. Coreexpressions, however, are excellent (Fig. 7A–C). FA1 is weaklyheterolithic and dominated by bioturbated silty and sandy mudstone,with lesser bands of fissile, silt-poor, unburrowed mudstone, and thin(mm- to cm-scale) parallel laminated to oscillation ripple laminatedvery fine- to fine-grained sandstone layers (Fig. 7A–C), particularly asthe succession grades into FA2 (Fig. 7D). Sandstone layers and theirbed thicknesses increase upwards. Some cross-laminated sandstonesare draped with dense, largely unburrowed mudstone layers. Thickersand layers are sharp-based and possess wavy parallel laminaeinterpreted as micro-hummocky cross stratification (HCS) (Fig. 7B).Less common are horizontal planar parallel laminated intervalssuggesting sheet flow conditions. Carbonaceous detritus is commonthroughout the interval and locally concentrated along beddingplanes. Locally, this detritus marks cross laminae. Thinner sandstoneshave been pervasively burrowed, and display biogenically mottledupper and lower contacts (Fig. 7A). Mollusc shell fragments are rare,

but are concentrated at the bases of some sandstone beds. Sideritecement is locally associated with some mudstones and locally formincipient nodules. Thin, indistinct bentonite layers occur from 137–138 m in the ARC CH 19–79 core.

Bioturbation, measured in terms of Bioturbation Index (BI) (Taylorand Goldring, 1993), is highly variable at the bed scale, but generally ishigh overall. Individual layers range from BI 0 (thicker sandstones) toBI 5 (thinner sandstone layers). Rare, laminated mudstone drapestend to show BI 0–1, with most burrows corresponding to deep tierpenetrations from overlying silty mudstone intervals. Trace fossils areuniformly distributed throughout most of the succession (Fig. 7A–C).Suites are dominated by robust Helminthopsis, Phycosiphon, mud-filled Chondrites, Cosmorhaphe, Scalarituba, possible Gordia, mud-filledand compacted Thalassinoides, and Planolites. Small numbers ofSchaubcylindrichnus freyi, Zoophycos, and Asterosoma occur in somemudstone layers. Diplocraterion, Teichichnus, and fugichnia are locallypresent in some sandstone layers.

4.1.2. InterpretationFacies Association 1 is interpreted to record progradation and

shoaling in a lower offshore position, approximately equivalent indepositional conditions to an open inner shelf environment. Theichnological suites are characteristic of the Zoophycos Ichnofacies.Most burrows in the silty mudstones reflect surface grazing, deposit-

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feeding and possible microbial farming behaviors on soft, cohesivesubstrates, typical of quiet-water, fully marine conditions lying wellbelow fair-weather wave base. High bioturbation indices reflectprolonged fair-weather conditions typified by slow, continuousaccumulation via suspended sediment settling. Storm influence inthe setting is indicated by the introduction of thin layers of micro-HCSand wave ripples. The sporadic distribution, variable intensity ofburrowing, and presence of fugichnia associated with these tempes-tites are consistent with short-lived episodic pulses of sedimentaccumulation. The upward increase in abundances and thicknesses ofthese tempestites support shoaling associated with progradation.Carbonaceous debris marking on some laminae hints at rhythmicallyfluctuating energies, possibly of tidal origin. The laminated and largelyunburrowed mudstone drapes indicate rapid emplacement of clayinto a setting otherwise characterized by slow, continuous suspensionsediment settling. Rapid mud accumulation is interpreted to berelated to the distal (bottomset) portions of a prograding subaqueousdelta or mudstone belt, supplied by sediment from a fluvial pointsource in the area. Some of this sediment may have been affected bytidal current remobilization.

4.2. Facies Association 2 (FA2): upper offshore to distal lower shoreface

4.2.1. DescriptionFacies Association 2 comprises mudstone-dominated heterolithics

(Fig. 7D–F) that grade upwards into sandstone-dominated hetero-lithics (Fig. 7G and H). With this upward increase in sandstone/mudstone ratio is also an upward increase in sediment caliber (veryfine- to fine-grained sand), and sandstone layer thickness. Themudstone-dominated portion of the facies association is moderatelyexposed in outcrop, improving markedly as sandstone/mudstoneratios and sand bed thicknesses increase. Subsurface expressions ofFA2 are excellent.

Mudstone layers range from mm- to cm-scale thicknesses.Mudstones are characterized by bed-scale variations frommoderatelyto thoroughly bioturbated silty mudstones, to dense, fissile and locallysiderite-cemented, largely unburrowed mudstones. Unburrowed toweakly burrowed mudstones are gray in color, locally silt-poor andapparently structureless, normally graded, and/or containing thinparallel interlaminae of silt and sand (Figs. 4G, and H; 6A–C; and 7E).These mudstones commonly drape sandstone layers. In some in-tervals, graded and laminated mudstones directly overlie scouredsurfaces truncating underlying sand laminae (Figs. 6A, B; and 7E). Thepredominantly unburrowed mudstones gradually replace pervasivelybioturbated silty mudstone layers, and comprise the dominant fine-grained component of sand-dominated heterolithic intervals (e.g.,Fig. 7D and E). Rare current ripples with mud interlaminae alongforesets are locally intercalated within some mudstone layers (Fig. 6Aand B). Syneresis cracks are present, although uncommon (Fig. 6A andB). Organic debris occurs throughout the interval, locally occurring assingle and double carbonaceous drapes marking stratification(Figs. 6C, and 7G). Bed-scale stratification is more common in theupper portion of the interval.

Coarse siltstone and sandstone layers range from cm- to dm-scalethicknesses. Sandstones are very fine to fine grained, and arecommonly sharp based, with sharp, gradational, or locally cross-laminated tops. Gradationally based sandstone layers are also present,but less common. Sandstone layers contain planar parallel lamination,and abundant, well-developed oscillation ripples (Figs. 4F and H, 6A–C, and 7D–F). Some sharp-based beds contain low-angle planarparallel stratification resembling small-scale (“micro”) hummockycross-stratification (micro-HSC) and long-wavelength oscillationripples. Horizontal planar parallel-laminated amalgamated bedsetsseveral tens of centimeters in thickness are more abundant upward.Starved current ripples (Fig. 6A–C) and rare combined flow ripples(Fig. 4G) are intercalated locally. Scour surfaces, which are locally

mud filled and rhythmically laminated, are also present (Figs. 6A and7E). Soft-sediment deformation (loading and convolute bedding)occurs upwards through the succession, but is not abundant (Fig. 6A).Large-scale soft-sediment deformation was observed in an adjacentsection to RDV-8 in outcrop (RDV-1; Ainsworth, 1994). Carbonaceousdetritus is locally concentrated along bedding planes, and commonlydemarcates internal laminae within the sandstone layers. Single anddouble carbonaceous drapes appear throughout the interval in bothplanar- and cross-laminated beds (Fig. 6A–C). Such drapes arecommonly associated with lamina sets that show rhythmic changesin the thickness of successive laminae (Figs. 6B and 7G). This Facies isalso observed in outcrop in the Willow Creek area (Fig. 3; Ainsworth,1991, 1992, 1994); Cone-in-cone structures are locally present,associated with sideritic nodules.

The facies association shows markedly variable distributions ofburrowing and generally reduced bioturbation intensities. Laminationand bedding in the interval are, therefore, well preserved. TheBioturbation Index in the interval varies between BI0 and BI4, but ismore typically in the BI 0–3 range. Rare beds, typically siltymudstones, show BI 5 alternating with laminated or structurelessmudstone layers showing BI 0–2, particularly near the base of thesuccessionwhere FA2 grades upwards from FA1 (Fig. 7D). Bioturbatedmudstones decrease in abundance as sand bed proportions andthicknesses increase, so that the facies association shows a generalreduction in BI values upwards. Sandstone layers tend to show BI 0–2,with most layers unburrowed and draped with mud, or weaklyburrowed along their upper margins (e.g., Fig. 7E and H). Theichnological suite comprises Phycosiphon, silt- and mud-filled Chon-drites, Cylindrichnus, mud-filled Planolites, Helminthopsis, Schaubcylin-drichnus freyi, and possible Gordia. Cryptobioturbation (cf. Pembertonet al., 2008) occurs in some parallel laminated sandstones (e.g.,Fig. 7G). Upwards, sandstone layers contain isolated Rosselia (locallyallochthonous mud balls), fugichnia, Diplocraterion, Teichichnus,Rhizocorallium, Ophiomorpha, Skolithos, Palaeophycus, and Trichichnus.Burrows are sporadically distributed. Navichnia or sediment-swim-ming structures (Gingras et al., 2007), corresponding to the “mantle-and-swirl” structures of Lobza and Schieber (1999), disrupt somebedding contacts, consistent with fine-grained sediment containingabundant interstitial pore waters.

4.2.2. InterpretationFacies association 2 records generally upward increasing deposi-

tional energies, depositional rates, and periodicity of sedimentation,reflected by the upward-coarsening grain size trend coupled withincreasing sandstone bed thickness and degree of erosional amal-gamation. Mudstone-dominated heterolithics grade out of FA1, andshow higher proportions of grazing structures and deposit-feedingstructures in bioturbated fair-weather silty and sandy mudstones ofthe upper offshore, alternating with higher energy and rapidlydeposited sandy tempestites compared to overlying units (cf.Fig. 7D and E). The greater abundance of unburrowed to weaklyburrowed, graded to laminated mudstone drapes and carbonaceousdetritus reflects encroachment of a nearshore subaqueous delta ormud belt mobilized by tides and waves. The paucity of burrowingwithin these mudstone layers attests to periods of very rapid mudaccumulation; rates that far exceeded the ability of grazing fauna torecolonise or otherwise disrupt the sediment. The presence ofinterlaminae of silt and sand, as well as current ripples with mud-draped foresets are consistent with tidal transport of fluid mud or asbedload transport of flocculatedmud. Rare syneresis cracks may pointto short-lived periods of salinity reduction, but this constitutes aminor aspect of the environment; the widespread presence ofPhycosiphon, Cosmorhaphe, and Chondrites attests to the largelymarine character of the setting.

Sharp-based, horizontal planar to low-angle laminated sandstoneevent beds throughout the interval suggests deposition during

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episodic waxing and waning currents, interpreted to be related tostorm-induced geostrophic flow (Clifton, 2006). Direct wave influ-ence is indicated by abundant oscillation ripples. In addition to stormand wave control, the interval shows strong evidence for tidalinfluence, reflected by abundant double mud/carbonaceous drapes,interpreted to have been deposited from suspension during flowattenuation during tidal cycles. Current ripple cross-lamination,though uncommon, likewise supports the presence of tides. Thegreater abundance of unburrowed, laminated to graded mudstonedrapes and interbeds in the sand-dominated heterolithic intervalsindicates that this mud did not accumulate by slow suspendedsediment settling. The mud layers appear to have accumulated ingenerally high-energy conditions in the presence of wave agitation,tidal currents and periodically high-energy storms. These mudstonelayers are interpreted to reflect deposition in a mudstone belt orsubaqueous delta environment located offshore from the mainshoreline, where sediment transport occurred as fluid mud duringdiscrete events. Low levels of bioturbation throughout the sand-dominated succession suggest an ichnologically stressed environmentduring deposition, probably mainly related to heightened sedimen-tation rates and/or the mantling of the event beds with fluid muds (cf.MacEachern et al., 2005). Monospecific suites in some beds corre-spond to post-event opportunistic colonization, typical of bothtempestites and sediment-gravity deposits. Cryptobioturbation sup-ports the rapid emplacement of sandy substrates with oxygenatedinterstitial water, and is a common feature of tempestites and otherevent beds in shallow marine settings (e.g., Pemberton et al., 2008).Subordinate stresses may have included periodically lowered salin-ities, suggested by local syneresis cracks.

As such, the mud-dominated portions of the FA2 successionindicate accumulation at and below fair-weather wave base, typical ofupper offshore to distal lower shoreface conditions in the presence ofa moderate to high storm regime. Sand-dominated portions of theheterolithic succession record accumulation well above fair-weatherwave base, consistent with the proximal lower shoreface, despite theubiquitous presence of mudstone layers. This is because themudstonelayers do not represent suspended-sediment settling in quiet-waterregimes below fair-weatherwave base, but rather, “high-energy”mudaccumulation via clay flocculation and fluid mud transport. Thedecrease in bioturbation intensity into the sandstone-dominatedheterolithic intervals attests to the combination of storm energy,influx of rapidly deposited mud, and the tidally driven, high-frequency shifts in wave regime across the depositional profile (cf.Dashtgard et al., 2009).

4.3. Facies Association 3 (FA3): storm-dominated lower shoreface(subtidal zone)

4.3.1. DescriptionErosionally overlying the heterolithic successions of FA2 is a

sandstone-dominated interval (Fig. 3), designated Facies Association3. The boundary between the two is sharp and, in places, undulatoryowing to small-scale scour (Fig. 4B and C). The scour in outcrop occurson a decimeter scale in width and centimeter scale in depth. In core,the contact is sharp, and truncates underlying laminae, though itsexpression is difficult to discern from other sharp-based sandstonelayers. Overlying the scoured surface is a sandstone-dominatedinterval consisting of decimeter-scale, erosionally amalgamated,moderately well- to well-sorted, fine-grained sandstone. Sandstonesare dominated by truncation-bounded, low-angle, planar to undula-tory parallel laminated beds occupying scours resembling swales, andare interpreted as swaley cross-stratification (SCS) (Figs. 4B, 5, and8A–C). Hummocks (convex upward laminae) are poorly developed inall outcrop sections visited andwere not identified in core. The swaleycross-stratified interval is almost entirely lacking mudstone laminaeand beds, with non-sandstone components dominated by carbona-

ceousmaterial. Bedsets infilling the swale scours tend to bemore sandrich toward their bases, and more heterolithic and organic richtowards their tops (Fig. 5). The sandstone-to-organic debris ratio insuch successions can vary rhythmically upward. Heterolithic organic-rich intervals can also show internal double carbonaceous drapes(Fig. 6G). Organic-rich intervals tend to be scoured by overlyingswales. Carbonaceous detritus is locally concentrated along beddingplanes, and commonly demarcates laminae and lamina-sets withinthe beds, which locally manifest as couplets (Fig. 6G). Woodfragments are locally present. Very rarely individual, dune-scalecross beds can be identified in the upper portion of FA3 in outcrop.Soft-sediment deformation is also present locally. Bioturbationthroughout the interval ranges from BI 0–2, mainly BI 0–1. Someoutcrop beds contain Ophiomorpha and Rosselia (Fig. 8D and E),whereas subsurface occurrences contain these and isolated fugichnia,Palaeophycus andMacaronichnus. Cryptobioturbation occurs through-out many of the SCS sandstones.

4.3.2. InterpretationThis facies association preserves a record of high-energy and

probably high frequency episodic deposition, which is reflected by thepresence of SCS. This suggests deposition dominated by combinedoscillatory and unidirectional flow conditions on the shelf duringstorms (Swift et al., 1983). Facies models often show SCS to overlayintervals dominated by HCS (Clifton, 2006), which, in this case, is notobserved. Preferential formation of swales rather than hummocks hasbeen attributed to the lower aggradation rates due to low deposition–to–transport ratios that typically occur in shallower water duringstorms (Dumas and Arnott, 2006). The upward increase of carbona-ceous laminae and bedswithin swale bedsets suggests waning currentvelocities and increased depositional rates for material with lowersettling velocities. Organic-rich intervals showing rhythmic beddinglikely represent immediately post-storm (waning energy) sedimen-tation that was not completely eroded by subsequent storm-relatedscour (Figs. 5 and 6G). Fairweather beds, if accumulated, had a lowpreservation potential and were only rarely preserved. The rhythmicbedding and couplets of carbonaceous laminae in such intervalssuggest regularly fluctuating flow velocities, which may be attribut-able to tidal influence in the subtidal zone. Other processes such asvariation in storm intensities cannot be unequivocally excluded fromgenerating such style bedding, but we consider this far less likely thantidal currents. Presence of very rare cross-bedded intervals suggestsoccasional conditions of dune formation and preservation, althoughtheir general scarcity implies that such conditions were unusual.

Bioturbation consists of low numbers of ichnogenera typical ofearly opportunistic colonization of marine sandy substrates. Thesestructures are also more deeply penetrating or were generatedsubstratally, favoring their preservation over shallow-tier structures.The paucity of burrowing records the limited preservation potential ofnon-storm beds and/or the reduced colonization window betweensuccessive storm events. High-latitude settings, which are prone topronounced seasonality in storms, are characterized by successive,high frequency storms during winter periods, and fair-weatherconditions (with slower sedimentation rates) persisting through thesummer months (e.g., Duke, 1985; Erikson and Slingerland, 1990).These conditions can lead to thick intervals of weakly and sporadicallyburrowed tempestites dominated by low-diversity opportunistictrace fossil suites (e.g., Frey, 1990; Saunders et al., 1994; Pembertonand MacEachern, 1997; Bann et al., 2008). Cryptobioturbation recordsthe activity of meiofauna living within the pore spaces between sandgrains and the corresponding subtle disruptions of grain positionsthrough their pursuit of food resources (cf. Pemberton et al., 2008 for areview). Meiofauna can extend well below the sediment-waterinterface, provided the sand layers possess oxygenated waters. Suchconditions are met in relatively shallow water with strong waveenergies. As such, the facies association records the preferential

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preservation of tempestites in proximal shoreline positions (e.g.,proximal lower shoreface regimes).

The abrupt scoured transition between FA2 and FA3 supportserosion and sediment bypass at this interface. This suggestssedimentation in water depths wherein the seabed was affected bycurrents sufficiently strong to winnow and remove fine-grainedsediment, but where bedload material was allowed to be depositedpermanently. FA3 likely represents storm deposition in limited waterdepths, that prograded on top of and likely downlapped the topsetportion of a subaqueous delta/mudstone belt represented by FA1-F2succession.

4.4. Facies Association 4 (FA4): upper shoreface to foreshore (intertidalbeach deposit)

4.4.1. DescriptionThe swaley cross-stratified sandstones of FA3 pass upward into a

low-angle to horizontal planar stratified sandstone interval, desig-nated as Facies Association 4 (Figs. 4D and 8I), which is capped, inturn, by a rooted horizon (Fig. 8H and I) and a regionally mappablecoal (Coal 0). Some beds contain indistinct or cryptic laminae.

The planar stratified interval is approximately 4 meters thick inboth the outcrop section of RDV-8 and core of ARC CH 20–79 (Fig. 3).The dominant sediment caliber of the succession is typically upperfine- to medium-grained sand. Sandstones are well to moderately-well sorted. Rare siderite-cemented mudstone interbeds are locallyintercalated. Bedding planes are sub-parallel and non-undulating, andare sporadically lined with laterally extensive carbonaceous layers(Fig. 4D). Internally, sand beds are horizontally laminated tostructureless. The carbonaceous layers can be internally laminatedto bedded and show rhythmic variations in laminae and bedthicknesses (Fig. 3E). Unidirectional ripple-scale cross-laminationhas been observed in some carbonaceous beds in outcrop, with well-defined carbonaceous drapes along their foresets. The occurrence ofripple forms and ripple cross-lamination in the entire interval is,nonetheless, low. Carbonaceous intervals commonly contain coarse-grained sand and small granules of terrigenous origin.

This facies is generally unburrowed (BI 0), although some layerstoward the top of the succession display BI 1–3 with isolatedPalaeophycus and Macaronichnus segregatis (Fig. 8F and G). Plantroots cross-cut the stratification near the top of the association(Fig. 8H and I) and, in outcrop, can be traced for hundreds of meters.The presence of this surface in core and outcrop suggests that thismarker may be distributed sub-regionally.

4.4.2. InterpretationFacies Association 4 records sheet flow conditions along low-angle

dipping to sub-horizontal depositional surfaces, consistent withswash zone deposition on beach environment. The horizontal planarstratified, carbonaceous layer-bearing interval is coarser grained thanthe underlying swaley cross-stratified interval and conformablyoverlies it. The paucity of burrowing is typical of these depositionalconditions (e.g., MacEachern and Pemberton, 1992; Saunders et al.,1994; Bann et al., 2008). The presence of Palaeophycus andMacaronichnus segregatis reflects dwelling structures and substrataldeposit-feeding structures, respectively, which locally occur inforeshore regimes. The reworking of the substrate by the high-energywaves that are typical of such regimes largely preclude burrowing,with the exception of substratal feeding.

The interval is capped by a rooted horizon traceable for hundredsof meters in outcrop as a relatively planar surface lacking evidence ofscour, suggesting that subaerial exposure was not associated withchannelized incision. The above observations suggest that the planarstratified interval is genetically related to the underlying strata, and ispart of an overall progradational, coarsening-upward and shallowing-upwardmarginal marine succession. The rooted horizon is overlain by

a 2 to 3 m thick tidal flat deposit (Ainsworth, 1991, 1992, 1994;Ainsworth and Walker, 1994) that is interpreted to be geneticallyrelated to the overlying Unit B incised valley, and not the Unit Ashoreface. The tidal flat deposit is capped by the 0.5 to 1 m thick “Coal0” (Fig. 3).

The horizontal planar stratified interval needs to be reconciledwith the widespread evidence for storm domination and tidalinfluence in the underlying swaley cross-stratified sandstones ofFA3 and heterolithic intervals of FA2. FA4 directly overlies FA3without an intermittent, planar tabular or trough cross-stratifiedinterval typical of the upper shoreface (Clifton, 2006), suggesting thatthe systemwas not barred and that conditions during depositionwerenot suitable for significant dune formation in the subtidal or intertidalzones. Observations from large numbers of modern beach systemssuggest that swash bars tend to form poorly on twomain beach types:(1) microtidal beaches affected by high wave energy when availablegrain sizes are relatively fine (bmedium sand) (Clifton, 2006; Short,2006); and (2) beaches that are affected by a significant tidal range(Short, 2006). We argue that the succession was formed as part of awave-dominated beach deposit that was significantly affected bytides. We consider the dominant currents in the system to be wave-generated, with the main influence of tides limited to the movementof the wave swash zone up and down the beach profile, as observedon modern tidal beaches (Wright et al., 1982). Shoreline systems inwhich tides dominate over waves are better referred to as tidal flatsrather than beaches, even when they are sand dominated. Wespeculate that the thickness of FA4 (~4 m in both core and outcrop)may be a rough approximation of the tidal range during deposition,marking the system high mesotidal to low macrotidal. This interpre-tation is supported by both the data presented (medium grain size ofsediment, association with tidal influenced FA1, 2 and 3) andobservations frommodern systems. Even though in core, FA4 containstwo internal coarsening-upward packages, we consider this to be alocal phenomena as a similar grain size trend, or any evidence formajor shoreline re-organization, has not been observed in theequivalent succession in outcrop. We therefore consider the entireforeshore interval to be one genetically related unit rather than acomposite succession. We consider FA4 to have been deposited insimilar environment to modern tidal beaches that are not prone todevelopment of large-scale bedforms capable of generating crossstratification (e.g., Wright et al., 1982; Masselink and Hegge, 1995;Short, 2006), and as such the system was likely different from themodern tidal beach described in Dashtgard et al. (2009) where crossstratification was observed in the intertidal zone.

5. Discussion

The coarsening-upward succession observed collectively in FA1,FA2, FA3 and FA4 shows evidence of: (1) wave and storm reworking(presence of storm beds, swaley cross stratification, and swash zonesedimentation); (2) tide influence (presence of double carbonaceousand mud drapes, tidal rhythmites, and non-barred character ofsuccession); and (3) a nearby fluvial source of sediment input(presence of fluid mud beds and abundance of carbonaceous debristhroughout the entire succession). Even though the migration of fluidmud beds can be affected by both wave and tide-generated currents(e.g., Cattaneo et al., 2003; Walsh et al., 2004), we consider them asfluvial in origin as these are usually ultimately associated with afluvial point source. We use the process classification systemdescribed in Ainsworth et al. (2011), which separates marginalmarine systems into fifteen process categories (W,Wt,Wf,Wtf,Wft, T,Tw, Tf, Twf, Tfw, F, Fw, Ft, Fwt, Ftw), where ‘w’, ‘t’, and ‘f’ stand for‘wave’, ‘tide’ and ‘fluvial’, respectively. The capital letter signifies thedominant process, while the second and third lower case lettersrepresent the secondary and tertiary processes that affect a system. Aclassification category is assigned based on estimating the relative

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proportion of sedimentary structures that can be attributed to eachprocess. Applying the classification to this study, we estimate thecombined thickness of storm beds in FA1 and FA2, in addition to thecombined thickness of the swales and horizontal planar beds in FA3and FA4 dominate the succession, the combined thickness of bedsbearing tidal structures, such as double mud drapes and tidalrhythmites is second, and the combined thickness of fluvialdominated beds such as fluid mud and carbonaceous beds is third inproportion. We therefore categorize the entire interval as wavedominated, tide influenced and fluvial affected (Wtf).

Even though wave-dominated, tide-influenced systems haverarely been described from the ancient record, tidal beaches arevery common on modern coastlines, and can, in fact, be the dominantbeach type in certain settings. In a continent-wide study of 10,685beach systems in Australia, Short (2006) found that 31.6% of the sandycoastlines of the continent fell under a ‘tide-dominated beach’category (high tide range and relatively low wave energy). Innorthern Australia where tidal ranges are generally high, it wasfound that 83% of beaches were of this type. Assuming that manyancient basins were affected by similar coastal depositional condi-tions, such systems must be relatively common in the geologicalrecord.

Wave-dominated, tide-influenced beach/shoreface deposits, how-ever, remain poorly recognized in the rock record, likely due to theirsubdued tidal signatures compared to other tide-dominated environ-ments. Many such systems may be interpreted as wholly wavedominated with the tidal influence not recognized (Dashtgard et al.,2009). Ancient tide-dominated deposits are most commonly de-scribed from funnel-shaped shorelines, such as estuaries or narrowvalleys where the tidal prism is significant, and tidal currents tend todominate over other processes responsible for sediment transport.The shapes of such basins amplify tides and effectively constrain tidalcurrent transport into rectilinear landward and seaward directions(Dalrymple and Choi, 2007). Such basin shapes also tend to sheltertheir coasts from direct wave approach. As a result, the mostcommonly recognized ancient tidal successions are from environ-ments with strong reversing tidal currents, well-defined slack-waterconditions at high and low tide, and minimal wave influence. Underthese conditions, various tidal indicators such as double mud drapes,mud drapes on foresets and/or toesets of ripples, dunes and bars,flaser–wavy–lenticular bedding, tidal rhythmites, opposing directionsof ripple/dune foresets, and sigmoidal bedding, are well developed(e.g., Visser, 1980; Boersma and Terwindt, 1981) and facies modelsare well established (Boyd et al., 2006; Dalrymple and Choi, 2007).

Tide influence at shorelines that border large embayments oroccur along coasts facing wide shelves, tends to be affected by morecomplex current patterns that are driven by both tides and waves; inthese regimes, conventional ‘tidal indicators’ may be less welldeveloped (e.g., Yoshida et al., 2007; Yang et al., 2008; Dashtgard etal., 2009). Existing facies models have not historically dealt effectivelywith such environments (Yoshida et al., 2007). Tidal signatures can beexpected to be discrete because: (1) tidal currents are not necessarilyrectilinear, and may be better described as ellipsoidal; (2) peak tidalcurrent velocities can occur in a shore-parallel direction rather than ina seaward or landward direction (e.g., Wright et al., 1982); (3) manytidal indicators have comparatively poor preservation potential due toreworking by more persistently shoaling waves, or may not bedeveloped at all; and 4) those tidal features that are preserved tend tobe subtly expressed. The coarsening-upward succession of Unit Adescribed in this study was probably deposited under similarconditions.

The proportion of tidal indicators in Unit A varies between the fourfacies associations. Features indicative of tidal processes are absent orhave been biogenically obliterated in the bioturbated mudstones ofFA1 (Fig. 7A–C). Tidal indicators, on the other hand, are wellexpressed in the mudstone-dominated heterolithic portion of the

coarsening-upward succession of FA2 (Fig. 6A–C and E; Fig. 7E and F)and less well developed in the sand-dominated portion of FA3 andFA4 (e.g., Fig. 6D). Tidal structures are more discernible in thesubtidally generated, swaley cross-stratified sandstones of FA3 than inthe intertidal, horizontal planar-stratified sandstones of FA4. Such adistribution is related to the increased effectiveness of wavereworking in shallower water and the intertidal zone.

The direct tidal indicators that appear most prevalent in this studyare double carbonaceous/mud drapes and tidal rhythmites, withdouble drapes being most common. Both tidal indicators have beenobserved in FA2 and FA3 and are poorly developed in FA1 and FA4.The paucity of double drapes in FA4 is in agreement with observationsfrom modern storm-influenced open coast tidal flats, where doubledrapes are poorly developed (Yang et al., 2008). Double drapes andtidal rhythmites have been observed to coexist in the same strataset(Fig. 6E), wherein a set of double carbonaceous drapes occurs withinthe lower horizontal planar-laminated sand bed as well as the uppercross-laminated portion of a bed interpreted as a tidal rhythmite. Inthe latter, drapes occur as part of the cross-laminae sets, suggestingincremental ripple migration due to current velocity fluctuationsdriven by daily tidal cycles. A similar facies of double carbonaceousdrapes and tidal rhythmites from a wave-dominated, tide-influencedshoreface system has been recognized in the Jurassic Plover Formationof the northwestern Australian shelf (Ainsworth, 2003; Ainsworthet al., 2008) (Fig. 9).

The presence of double drapes in a wave-dominated shallowmarine interval is of interest, since such tidal indicators are typicallyassociated with funnel-shaped shorelines, such as tidal channels andestuaries, where slack-water conditions can occur at times of tidalcurrent reversals (Dalrymple and Choi, 2007). Modern seabed currentmeasurements from open shelf environments (Fig. 10) suggest thatvariations in current velocities may be one mechanism to explain theformation of such features (Sternberg et al., 1996; Liu et al., 2002;Hemer et al., 2004). It is shown that the absolute values of tidalcurrent velocities in such environments fluctuate over both daily andneap-spring tidal cycles. Seabed current velocities may fluctuatebetween values close to zero and velocities capable of transportingbedload material, which can result in sediment organization andtheoretically lead to the generation of carbonaceous drapes and muddrapes (e.g., Liu et al., 2002; Hemer et al., 2004). If the rotary tidalcurrent measurements at the seabed are ellipsoidal in shape with twohigh and two low velocity peaks during a tidal cycle, conditions maybe conducive to the formation of double drapes. It would, nonetheless,be expected that double drape formation under such settings will beless well pronounced compared to shoreline shapes causing rectilin-ear tides. Double drapes associated with a number of tempestitesobserved in this study suggest that superimposition and interferencebetween tides and storm-related geostrophic flow may also result invariations of current velocities that would permit the deposition ofsuch features (Fig. 6C).

The expression of tidal indicators in the SCS sandstones (FA3) ofUnit A is subtle, reflecting the predominance of wave reworking inshallower water. The swaley cross-stratified interval (FA3) clearlyshows the dominance of storm reworking over tidal current transportin the preserved record. The limited preservation of non-storm bedsand/or a reduced colonization window between successive stormevents, leads to thick intervals of weakly and sporadically burrowedstorm beds dominated by low-diversity opportunistic trace fossilsuites. Such conditions aremet in relatively shallowwater with strongwave energies, typical of strongly storm-influenced proximal shore-line environments.

In such deposits, direct tidal evidence is mainly limited to theupper parts of the swaley bedsets formed during the waning stages ofstorms, and it is much better expressed in rarely preserved fair-weather intervals. This is especially well illustrated by the tidalrhythmites preserved as carbonaceous debris-rich bedsets in Fig. 5

Fig. 9. Tidal influence in a wave-dominated interval from the Jurassic Plover Formation, Australian northwest shelf. A) Paired carbonaceous drapes formed within possible neap (n)to spring (s) tidal cycles. Unit shows BI 1–2, with isolated Ophiomorpha (O), Teichichnus (Te), and fugichnia (fu) (Sunset-1, 2166 m). B) Possible spring (s) and neap (n) cycles(Sunrise-2, 2125 m). Both sections of core are taken from an otherwise wave-dominated sandstone interval. White dotted lines represent scours likely related to storm-generatedcurrents.

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and 6G, which are partially eroded by an overlying storm scoursurface. We speculate that a similar sedimentological character mayoccur in many storm-dominated, tide-influenced open shelf environ-ments, where stratasets formed during major storms possess a higherpreservation potential than do the tide-dominated fair-weatherintervals.

The interpreted intertidal beach succession (FA4), made up oflargely unburrowed, thick, horizontal planar-stratified sandstones, isrelatively deficient in direct tidal indicators, even though tides areinterpreted to constitute the first-order control on its generation.Tides, in this case, directly control the mode and timing of wavereworking in the intertidal zone, by shifting the position of breakingwaves and swash zones between the low- and high-tide levels. Tidesin such environments are, nevertheless, subordinate to waves in theircapacity to directly generate currents and move sediment (Wright,1981; Masselink and Hegge, 1995). The only exception to this is thepossible domination of tidal-current processes in the subtidal andlower intertidal zones occurring during high-tide periods inmegatidal

Fig. 10. Examples of tidal influence on measured seabed current velocities in open shelfenvironments from Torres Strait — Gulf of Papua (modified from Hemer et al., 2004)and the Amazon Shelf (modified from Kineke et al., 1991). Current velocities in suchenvironments vary with both daily and neap/spring tidal cycles, and would havedifferent abilities to move sediment as bedload, which may result in cyclicsedimentation. A velocity of 20 cm/s is drawn as a rough boundary between nobedload and bedload transport (Boggs, 2006).

beach systems (Wright et al., 1982; Masselink and Hegge, 1995;Hequette et al., 2008). The dominance of daily wave reworking isillustrated by the planar stratified, sand-dominated facies, andrelatively homogeneous character of the sediment. It is this uniformcharacter and the lack of well-developed wave, combined flow, andunidirectional current ripples with mudstone partings, that differen-tiates this deposit from a tidal flat (cf. Flemming, 2003), which wouldbe an example of a tide-dominated facies that may or may not bewave influenced. Tidal flats typically show more complex lithofaciesassociations, owing to the greater importance of tidal currents oversedimentation (Flemming, 2003; Yang et al., 2008). Facies Association4 does not show hummocky-cross stratification, as has recently beenreported from the open-coastal tidal flats of Korea that are affected bywinter storms (Yang et al., 2005, 2008). This suggests that eitherstorms were not capable of generating significant scour in theintertidal zone, that fair-weather wave reworking may ultimatelyrework the storm deposits, and/or that water depths (even at hightide) are insufficient to permit formation of HCS in mesotidal andlower macrotidal conditions. Similar horizontal planar-stratifiedintervals capped by rooted horizons have been observed in otherallostratigraphic intervals of the Horseshoe Canyon Formation in thestudy area by the authors, suggesting that wave-dominated, tide-influenced, intertidal sedimentation was a recurring scenario in thearea.

5.1. Towards building a wave-dominated, tide-influenced system model

Several generalizations can be made about the effect of tides onwave-dominated systems, and therefore, of the differences insedimentation between such systems and wave-dominated systemsnot significantly affected by tides. Wave-dominated, tide-influencedsystems (Wt) have been differentiated in modern settings from non-tidal wave-dominated systems (W) in terms of facies and ichnology(cf. Dashtgard et al., 2012). Probably the biggest effect of tides on awave-dominated shoreline is the shifting of the area affected byshoaling, breaking, and swash wave zones during the tidal cycle. Inmacrotidal and megatidal settings, such effects can be especiallysignificant (Wright et al., 1982; Masselink and Hegge, 1995; Short,2006; Dashtgard et al., 2009). Some of the major outcomes of this are:1) decreased time available for wave reworking in the subtidal zone(limited to low tide); and 2) increased effectiveness of breaking andswashing waves in the intertidal zone, which may dissipate some oftheir energy reworking intertidal bars (if such are present) (Masselinket al., 2006). Intertidal bars mostly form on mesotidal beaches by

37B.K. Vakarelov et al. / Sedimentary Geology 279 (2012) 23–41

breaking waves during the rising tide, which are then partiallyreworked by swash waves during the falling tide, until they are fullyemergent at low tide (Masselink et al., 2006). In wave-dominatedsystems affected by significant tidal ranges (macrotidal andmegatidal

Fig. 11. An idealized conceptual model illustrating some of the key differences between mwave-dominated systems are more prone to forming along narrower and deeper shelves, whare more prone to occur on wide, shallow shelves and embayments, where the shoreface-toand swash zones along the beach profile in strongly tide-influenced systems, causes differemore important. Low accommodation, wave-dominated, tide-influenced systems may alsoshallower water depths, causing erosion and bypass of fine-grained sediment. Such sedimenbelt. Bottom: Comparison between idealized facies successions of a wave-dominated micro

coastlines: tidal ranges N4 m), more pronounced shifts in the waveregime during the tidal cycle commonly lead to poor development ofsubtidal and intertidal bars and dune-scale bedforms, although suchfeatures may be present (Short, 2006; Dashtgard et al., 2009).

icrotidal, mesotidal, and macrotidal wave-dominated environments. Top: Microtidal,ere shoreface-to-shelf gradients are higher. Macrotidal, wave-dominated environments-shelf gradients are lower. This effect, combined with the shifting of shoaling, breakingnces in deposited facies zones, where intertidal sedimentation becomes proportionallybe affected by storm-wave erosion significant distances from the shoreline, due to thet may migrate farther offshore and accumulate as part of a subaqueous delta or a mudtidal shoreface system and a wave-dominated macrotidal shoreface system.

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Geomorphological definition of several tide-modified and tide-dominated beach types (Short, 2006), which include barred andnon-barred categories, points to the natural variability of suchsystems, which would also be represented in the ancient record.

We present, herein, a model for the facies characteristics observedin the wave-dominated, tide-influenced system described in thisstudy, coupled with observations from some modern macrotidalcoastlines and tidal shelves, and compare it to a non-tide influencedsystem (Fig. 11). The tide-influenced shoreface model aims to aid inthe identification of similar deposits in the stratigraphic record. Themodel is based on the following assumptions. 1) Wave-dominatedshorelines with significant tidal influence are assumed to beassociated with either open shorelines facing wide shelves orshorelines adjacent to moderate-to-large embayments and seaways.2) Amplification of tides will most likely occur on wide and shallowshelves with open access to an ocean. As a result, these settings haverelatively low accommodation. Extreme storms can rework sedimentat significant distances from the shoreline (Fig. 9), with bypass of fine-grained material to deeper water and significant reworking and scourat the seabed. 3) Wave-dominated, non-tide influenced systems aremore likely to be associated with deeper, higher gradient shelves,which are less effective at amplifying tides and experience lessfrictional dampening of waves (Fig. 11). The higher shelf gradients, inthis case, will result in more efficient across-shelf transport of sand todeeper water, and to potentially thicker, sand-dominated successions.

The wave-dominated, tide-influenced model shows the followingdifferences from a purely wave-dominated model: (1) Wave-dominated, significantly tidally influenced systems are prone torapid progradation into shallower water, resulting in thinner,coarsening-upward successions, with the potential for significantsediment bypass, scour by storms and tides, and formation of sharp-based, sand-dominated intervals and subaqueous deltas/mudstone

Fig. 12. An idealized depositional model for the entire Unit A succession represented as a durelative position of the four facies associations is shown along the depositional profile. FA1 ansubaqueous delta/mud belt; FA3 and FA4 are interpreted to be deposited in the subtidal andinterval and the sandstone-dominated FA3-FA4 interval is interpreted to be related to minoCourse-grained sediment is entrapped in these areas while fine grained sediment is bypassedto indicate that the main sites of sandstone and mudstone deposition in this system may h

belts. This without implying forced regression. (2) Wave-dominated,tide-influenced systems are prone to generating horizontal planar-stratified intervals generated by wave activities in the intertidal zonethat typically lack or display poorly developed cross-stratified uppershoreface intervals that typify microtidal systems (Fig. 11). (3) Tidalindicators are less well-developed compared to tide-dominatedenvironments, and are best represented by double mud/carbonaceousdrapes and tidal rhythmites. Sandstone-dominated portions tend tobe more homogeneous and less heterolithic than most tidal sand flats.(4) The thickness of planar-stratified intertidal deposits (if thesuccession is complete) may serve as a proxy for estimating thetidal range operating in the system at the time of deposition, and istypically thicker than 2 m. Exceptions to this model are also observedin modern systems. Dashtgard et al. (2009), for example, shows theformation of well-developed cross-stratification in the middle tolower intertidal zone on a megatidal beach-shoreface system in theBay of Fundy, Canada. Cross-stratification has also been described inthe intertidal zones of other tidal beaches (e.g.,, Normandy, Levoy etal., 2000). On the other hand, they are absent from other systems (i.e.,Cable Beach in West Australia, Wright et al., 1982; see also Short,2006). This variability is to be expected due to the different waveenergies, beach gradients, and sediment calibers between individualsystems. Dashtgard et al. (2009) demonstrated that ‘tide-modulatedshorefaces’ can be differentiated based on facies and ichnology.Additional work however is needed to build a robust facies model.

5.2. Sharp-based shorefaces, forced regressions and mudstone belts

Sharp-based shorefaces are often used as indicators for relative sealevel falls or forced regressions (e.g., Plint, 1988, 1991; Hunt andTucker, 1992, 1995; Posamentier et al., 1992). Indeed, the sharp-basedcontact of FA3 at the Drumheller outcrop location has been previously

al clinoform system (with a shoreface and a subaqueous delta/mud belt portions). Thed FA2 are interpreted to have been deposited on the bottomset and foreset portions of aintertidal portion of a shoreface. The abrupt transition between the heterolithic FA1-FA2r erosion/sediment bypass along the topset portion of the subaqueous delta/mud belt.and deposited farther offshore. The horizontal scale in the figure is relative but its aim isave been offset by distances of tens of kilometers.

39B.K. Vakarelov et al. / Sedimentary Geology 279 (2012) 23–41

interpreted as being due to a relative sea level fall (Ainsworth, 1991,1992, 1994). However, the propensity for wave-dominated, tide-influenced systems to prograde into shallow receiving basins wherestorm waves can effectively rework sediment long distances from theshoreline permits the formation of sharp-based shorefaces without adrop of relative sea level. This is due to storm- and tide-generatedcurrents having the capacity to transport fine-grained sediment intodeeper water across distances of tens of kilometers, while only locallyreworking coarser-grained sediments—the migrated fine-grainedsediment typically accumulates in distinct sediment bodies referredto as subaqueous deltas or mud belts, which may be significantlyremoved from the main shoreline (e.g., Alexander et al., 1991,Cattaneo et al., 2003; Walsh et al., 2004; Draut et al., 2005). Currentscour during storms in shallow receiving basins would be furtherenhanced by changes in water depth induced by daily tidal cycles atthe same location. Reworking of offshore sediment during stormswould be more efficient at low tide than at high tide, which mayaccount for the vertical changes in organic content in many of theobserved swale bedsets. The wave-related shear stresses at the seabedwould be changing with the tidal cycle which may result in differentcapacities of wave-generated currents to suspend sediment of varyingsize and density (organic fragments vs. sand).

Mud accumulation in subaqueous deltas and mud belts, and theirpotential ancient equivalents, is of great contemporary researchinterest. A significant number of such systems have been described onHolocene shelves: Columbia River (Nittrouer and Sternberg, 1981);Yangtze River (Butenko et al., 1985); Huanghe River (Nittrouer et al.,1986; Alexander et al., 1991; Liu et al., 2004); Fly River (Harris et al.,1993;Walsh et al., 2004); Po River (Cattaneo et al., 2003); AtchafalayaRiver (Draut et al., 2005; Neill and Allison, 2005); Monterey Bay(Eittreim et al., 2002); Iberian Shelf (Dias and Nittrouer, 1984);Louisiana Shelf (Frazier, 1974); the Amazon shelf (Kuehl et al., 1982);Ganges-Brahmaputra (Goodbred et al., 2003); Ebro Shelf (Maldonadoet al., 1983; Diaz et al., 1996); and the northern California continentalshelf (Borgeld, 1985; Wheatcroft et al., 1996), among others. Ancientequivalents, however, have been only rarely described and have beentypically interpreted based on aerially mapped clinothem geometriesrather than facies criteria (e.g., Asquith, 1970; Vakarelov, 2006;Hampson, 2010). Even though we cannot constrain the shape andclinothem geometry of the packages bounding FA1 and FA2 in thisstudy, we speculate from a facies perspective that these deposits wereaccumulated as part of an ancient subaqueous delta or mud belt(Fig. 12). This interpretation is based on the character of the FA1-F2interval and the sharp contact with the overlying FA3-FA4 interval.FA1, in this case, is interpreted as background shelfal deposits or aspart of a bottomset clinothem of a subaqueous delta/mudstone belt,whereas FA2 is interpreted to have been deposited as part of anactively prograding subaqueous delta/mudstone belt foreset clin-othem (Fig. 12) (see Walsh et al., 2004 for an overview of thesefeatures). Sedimentological observations that support such aninterpretation are: (1) the abundance of interpreted fluid mud bedsin FA2 and to amuch lesser extent FA1; (2) ichnological evidence suchas navichnia, opportunistic colonization and fugichnia, indicatingrapid emplacement of such beds; and (3) ichnological (low diversitysuites) and sedimentological evidence (syneresis cracks) of onlyminor salinity stresses during deposition of FA2, suggesting deposi-tion in an open shelf setting that was well removed from direct rivermouth discharge. Similar fluid mud-rich facies have been observed ina number of modern subaqueous deltas, such as the Fly River (Walshet al., 2004) and the Atchafalaya (Neill and Allison, 2005). Theinterpretation of the FA1-FA2 succession as a subaqueous delta/mudstone belt package is further supported by the sharp contact withFA3. The contact bears decimeter-scale scours which separatesmudstone from sandstone-dominated facies above. Scouring andsediment bypass is well documented along the topset components ofmodern subaqueous delta andmud belt clinothems, which can extend

for tens of kilometers seaward from the shoreface portion of the mainshoreline (e.g., Walsh et al., 2004; Draut et al., 2005).

6. Conclusions

1) Wave-dominated, tide-influenced (Wt) systems (tidal beaches)are abundant on modern coastlines, but remain poorly recognizedin the ancient record. Studies of modern, wave-dominated systemsshow that increases in tidal range lead to major differences inbedform development and facies distribution. For example, wave-dominated, tide-influenced systems are commonly associatedwith wide, shallow continental shelves and large embayments,where major storms are able to rework sediment significantdistances from the shoreline. The relatively featureless, swash-wave-dominated style of sedimentation in the intertidal zone inmany macrotidal and megatidal systems results in significantdeviations from the classical, microtidal, wave-dominated shore-line facies model.

2) We describe an ancient example of a wave-dominated, tide-influenced, fluvial-affected (Wtf) shoreface succession from theCampanian Bearpaw to Horseshoe Canyon Formation transition,which crops out near Drumheller, Alberta, Canada. The coarsen-ing-upward succession is described in both outcrop and core, andhas been split into: (i) an offshore mudstone-dominated faciesassociation (FA1); (ii) an upper offshore to distal lower shorefaceheterolithic facies association (FA2); (iii) a proximal lowershoreface swaley cross-stratified facies association (FA3); and(iv) an intertidal-zone, horizontal planar-stratified facies associa-tion (FA4). The entire coarsening-upward succession is capped bya sub-regionally mappable root-bearing horizon lacking evidenceof significant erosion.

3) Tidal influence within the coarsening-upward succession issuggested by abundant double carbonaceous/mud drapes andtidal rhythmites, as well as large-scale facies trends. Tidalindicators are effectively absent from the pervasively bioturbatedoffshore mudstone units of FA1. In this portion of the succession,tidal features are probably biogenically obliterated, consistentwith slow rates of deposition in fully marine conditions. Tidalindicators are most abundant in the lower mudstone-dominatedheterolithic portion of the succession (FA2), attributed to minimalfairweather wave reworking at deeper water depths coupled withreduced bioturbation intensities. In these mudstone-dominatedheterolithic sections, double carbonaceous/mud drapes and tidalrhythmites are common and are locally superimposed in the samestrata-sets. Elevated deposition rates and higher frequency event-style deposition leads to heightened preservation of physicalstructures and reduced bioturbation intensities. Additionally, fluidmud drapes over sandy bedsets tends to inhibit endobenthiccolonization. In shallower water depths, waves and stormsminimize the preservation of fair-weather deposits, which tendsto overprint the tidal signal. As such, evidence of tides areprogressively subtler through the upper part of FA2, through FA3and into FA4. In the swaley cross-stratified sandstones of FA3, forexample, direct evidence for tidal influence is limited to the upperportions of swale bedsets, and is best represented in theuncommonly preserved fair-weather deposits that have beenobserved in outcrop. In the intertidal planar-stratified intervals ofFA4, direct tidal indicators are the least well preserved, owing tothe overwhelming domination of swash-wave-generated currentsover the weaker tidal currents. The presence of tides can,nonetheless, be inferred from the anomalous thickness of theplanar stratified interval (~4 m), and from facies observations incarbonaceous-rich layers. The thickness of a horizontal planar-stratified succession in such an interval has been used as a roughproxy for the tidal range in ancient systems.

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4) The observed facies associations show significant differences fromthe widely utilized facies models for wave-dominated shorelinesystems. We introduce a modified facies model for wave-dominated, tide-influenced systems, based on observations de-rived from this study and from modern systems. This modelattempts to account for several encountered differences. a) Theboundary between the mudstone-dominated and sandstone-dominated portions of a coarsening-upward succession can besharp and scoured, but it is of autogenic origin. In this case, theabrupt transition is not attributed to forced regression but todeposition in a low accommodation setting (common for tidallyinfluenced systems), where major storms and tides were able torework sediment great distances from the shoreline and accumu-late an offshore subaqueous delta/mudstone belt. b) Successionsmay show a predominance of swaley cross-stratification ratherthan hummocky cross-stratification, particularly in storm-influ-enced shallow basins. c) Upper shoreface cross-stratification maybe poorly developed or absent, owing to poor development of barsand large-scale bedforms. d) Successions may be capped withanomalously thick, horizontally planar-stratified sandstones,corresponding in thickness to the intertidal zone, reflecting thelarger tidal range. Unlike a sandy tidal flat, these units tend toshow little evidence of tidal influence, owing to the dominance ofwave swash over tidal currents in this setting.

Acknowledgments

We wish to extend our gratitude to the sponsors of the WAVEConsortium (Bapetco, BHPBP, Chevron, ConocoPhillips, Nexen, OMV,Shell, Statoil, Todd Energy, and Woodside Energy) for partial fundingof this work. This project was also partly funded via a Natural Sciencesand Engineering Research Council (NSERC) Discovery Grant awardedto JAM. Andrew Beaton, Curtis Evans and David Bechtel at the EnergyResources Conservation Board (ERCB), and Tyler Hauk at the AlbertaResearch Council (ARC) were instrumental in locating and providingaccess to the original geophysical well logs for the boreholes, as wellas earlier stratigraphic studies of the area, and are warmly thanked.Shahin Dashtgard kindly determined the DLS locations for the coredwells in the Drumheller area. We are very thankful for very thoroughand thoughtful reviews by D.A. Eberth and Stacy Lynn Reeder.

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