SED 773 Dispatch: 1.2.06 Journal: SED CE: Hari Journal Name Manuscript No. B Author Received: No. of pages: 18 PE: Revathi

Sedimentology (2006) 1–18 doi: 10.1111/j.1365-3091.2006.00773.x

Sedimentology and stratigraphy of a transgressive, muddy gravel : waterside beach, of Fundy, Canada F SHAHIN E. DASHTGARD*, MURRAY K. GINGRAS* and KARL E. BUTLER *Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB, Canada T6E 2G3 (E-mail: [email protected]) O Department of Geology, University of New Brunswick, PO Box 4400, Fredericton, NB, Canada E3B 5A3

ABSTRACT O Sediments exposed at low tide on the transgressive, hypertidal (>6 m tidal range) Waterside Beach, New Brunswick, Canada permit the scrutinyR of sedimentary structures and textures that develop at water depths equivalent to the upper and lower shoreface. Waterside Beach sediments are grouped into eleven sedimentologically distinct deposits that represent threeP depositional environments: (1) sandy foreshore and shoreface; (2) tidal-creek braid-plain and delta; and, (3) wave-formed gravel and bars, and associated deposits. The sandy foreshore and shoreface depositional environment encompasses the backshore; moderately dipping beachface; and, a shallowlyD seaward-dipping terrace of sandy middle and lower intertidal, and muddy sub-tidal sediments. Intertidal sediments reworked and deposited by tidal creeks comprise the tidal-creek braid plain and delta. Wave-formedE sand and gravel bars and associated deposits include: sediment sourced from low-amplitude, unstable sand bars; gravel deposited from large (up to 5Æ5 m high, 800 m long), landward-migrating gravel bars; and, zones ofT mud deposition developed on the landward side of the gravel bars. The relationship between the gravel bars and mud deposits, and between mud-laden sea water and beach gravels provides mechanisms for the depositionC of mud beds, and muddy clast- and matrix-supported conglomerates in ancient conglomeratic successions. Idealized sections are presentedE as analogues for ancient conglomerates deposited in transgressive systems. Where tidal creeks do not influence sedimentation on the beach, the preserved sequence consists of a gravel lag overlain by increasingly finer-grainedR shoreface sediments. Conversely, where tidal creeks debouch onto the beach, erosion of the underlying results in deposition of a thicker, more complex beach succession. The thickness of this packageR is controlled by tidal range, sedimentation rate, and rate of transgression. The tidal-creek influenced succession comprises repeated sequences of: a thin mud bed overlain by muddy conglomerate, sandy conglomerate,O a coarse lag, and capped by trough cross-bedded sand and gravel. Keywords Beach, conglomerate, macrotidal, mud and gravel, muddy con- glomerate, sedimentology,C stratigraphy, transgressive.

INTRODUCTIONN logical and stratigraphic relationships on modern aids in predicting the extent, thickness, Studies of modern, transgressive gravel beaches and morphology of conglomerates in the sub- provide importantU information regarding facies surface. Waterside Beach is a transgressive, relationships and organization of ancient conglo- muddy gravel beach in the hypertidal Bay of merates. In particular, determining sedimento- Fundy. Because of the area’s extreme tidal range

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists 1 2 S.E. Dashtgard, M.K. Gingras and K.E. Butler

(up to 12 m), foreshore (and shoreface equivalent) foreshore sediments (Clifton, 1981; Massari & sediments are exceptionally well exposed at Parea, 1988). spring low tide. This provides an opportunity to Waterside Beach, New Brunswick, Canada is a assess the sedimentological characteristics of transgressive, muddy gravel beach in the hyper- conglomerates deposited at water depths equival- tidal Bay of Fundy. It is considered that the ent to the upper and lower shoreface (i.e. depos- structures and morphology of the intertidalF ited because of shoaling, breaker, surf, and deposits partly result from depositional processes processes). In this paper: (1) sedimentologically (shoaling, breaker, surf, and swash zone pro- distinct deposits are reported; (2) mechanisms for cesses) and water depths equivalent toO the upper depositing mud beds and muddy conglomerates and lower shoreface. Examination of these mod- on gravel beaches are described; and, (3) inferred ern deposits, therefore, provides insights into the stratigraphic successions of transgressive gravel facies and facies relationshipsO of hydraulically beaches are proposed. reworked shoreface conglomerates. Sedimentological descriptions of modern, wave-dominated gravel foreshores and back- Study area R are common in geological literature. The original model presented by Bluck (1967) recog- Waterside Beach is located on the New Bruns- nized distinct, -parallel zones based on wick coastline of ChignectoP Bay (Fig. 1). Oriented clast-shape selection. This shore-normal zonation northwest–southeast the beach is perpendicular is observed from gravel beaches around the world to the dominant southwest winds (Amos & (Carr, 1969; Carr et al., 1970; Maejima, 1982; Hart Asprey, 1979). During winter cyclones (mainly & Plint, 1989; Postma & Nemec, 1990; Bartholoma¨ November through January) it experiences peak et al., 1998; Bluck, 1999) and may be considered significant waveD heights of 3 m and wave periods typical of high-energy, wave-dominated shore- of 10 sec (Amos et al., 1991). Overall, most lines with a limited fluvial- or marine-sediment significantE waves heights (79%) are below supply. The above model, however, is limited 1Æ25 m with periods of 7 sec or less (Amos et al., to a narrow (average 100–200 m wide) beach- 1991). Waterside Beach experiences a mean tidal normal zone that includes the steeply dipping rangeT of 9 m. Vertical tidal range varies from 6 m beachface (foreshore), berm, and backshore during neap tides to 12 m during spring tides (Bluck, 1967; Carr et al., 1970; Kirk, 1980; Mae- resulting in exposure of up to 1200 m of intertidal jima, 1982; Postma & Nemec, 1990). Modern Czone at low tide. Additionally, up to 650 m of nearshore (shoreface) and more basinal conglo- beach sediments occur sub-tidally (Fig. 2). The merate facies have been described (Hart & Plint, toe of the beach is demarcated by a step that is 1989), but are generally poorly understood.E locally steep (1), but generally weakly defined. Shoreface conglomerate models are therefore, On the landward edge, backshore and beachface mainly derived from outcrop and core (Clifton, deposits abut either salt marsh or bedrock cliffs 1981, 1988; Massari & Parea, 1988; HartR & Plint, (Fig. 1C). 1989, 2003; Caddell & Moslow, 2004; Zonneveld At the northwest end of the beach, sand with & Moslow, 2004). As a result, most modern minor gravel is the dominant sediment; whereas, depositional models for conglomeratesR are a gravel is present near the mouth of Long Marsh composite of modern foreshore deposits, and Creek (Figs 1B and 2). A maintained dike backs ancient shoreface and more basinal deposits the beach in the southeast (Fig. 1B and C). The (Bourgeois & Leithold, 1984). O dike has significantly hindered transgression, yet Shoreface conglomerates are broadly sub- does not appear to interrupt beach sedimentation divided as transgressive and regressive (Wescott patterns in the intertidal and sub-tidal zones & Ethridge, 1982; Bourgeois & Leithold, 1984; (Fig. 2). Postma & Nemec, 1990).C Transgressive conglom- erate successions encountered in the rock record Methods tend to lack backshore and foreshore deposits as a result of erosion duringN transgression (Bourgeois Fieldwork on Waterside Beach was undertaken in & Leithold, 1984). Regressive (progradational) 2003 and 2004. Beach-normal and beach-parallel gravel beaches tend to be characterized by transects were conducted to establish beach repeating sequencesU of coarsening-upward con- zonation and morphology. Line-and-level meas- glomerates with internal erosional surfaces (Bour- urements were used to document changes in geois & Leithold, 1984), and by the preservation of slope and to establish major changes in morphol-

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 3

′ ′ A 65 63 trenches dug mainly perpendicular to deposi- P.E.I. Moncton tional strike. Box cores were collected at most NEW 46′ stations for X-ray imaging. BRUNSWICK High-resolution, single- seismic pro- Study Area Chignecto Bay files were acquired in 2003 and 2004. TheseF Saint John surveys were used to map out the toe of the beach NOVA SCOTIA (Fig. 2), but otherwise are not presented in this

U.S.A. paper. In 2005, a grab-sampling program was BAY OF FUNDY Halifax undertaken to sample sub-tidal beachO and off- shore sediments. Samples collected during this 0 50 100 ATLANTIC OCEAN program are incorporated into the grain-size data ′ 44 44′ N kilometers and are used to map out the horizontal distribu- ′ ′ ′ 67 W 65 63 O tion of sediments in the sub-tidal zone (Fig. 2). B Grain-size distribution on Waterside Beach was determined using one of three techniques: (1) grid Dennis Bea 915 R Long Marsh sampling, (2) bulk-sample dry sieving, and (3) X- Waterside Bea Creek ch ray absorption. (1) Grid sampling (Wolman, 1954; Rice & Church, 1996; Hoey, 2004) was employed ch P for deposits with significant quantities of - Dike CHIGNECTO BAY and boulder-sized clasts. This method involved establishing a 5 m · 5 m or 10 m · 10 m grid in an area considered representative of a deposit, and measuringD the b-axis of clasts (>4 mm) Beach 0 1 23 encountered every 0Æ5 or 1 m across the grid enrage Salt Marsh kilometers (Wolman,E 1954; Church et al., 1987). A matrix sample of sediment <4 mm was then collected C from each grid and sieved to accurately determine theT grain-size distribution of the matrix. (2) Three hundred and fifteen kilograms of sediment (60 samples) was collected for dry sieving. In the Cfield, samples were dried, sieved, and weighed and the coarse fraction (particle diameter >1/) discarded. Representative sub-samples were E extracted from the remaining sample and dry sieved in the laboratory in one phi-size incre- ments to the sand- break (4/). Grain-size R statistics included in this paper are reported for all grab samples, and for intertidal samples where the total sample mass is equal too or greater than 500 m R 100 times the mass of the largest clast observed. This is smaller than sample sizes suggested by Fig. 1. Location map of the study area. (A) Location of Church et al. (1987) and Hoey (2004); but still the Bay of Fundy in Canada, and Waterside Beach in the Bay of Fundy. (B) Diagram ofO Waterside Beach. (C) provides reasonable grain-size information for Airphoto of Waterside Beach in 1996. comparison between deposits (Hoey, 2004). (3) Silt and clay fractions of samples with a signifi- cant fine-grained component (>2% silt and clay) ogy. In total, 5Æ6 km ofC line-and-level measure- were determined by X-ray absorption on a Micro- ments were taken in the shore-normal direction metrics Sedigraph 5100. and 1Æ1 km in the alongshore direction. Stations Mean (/), sorting (r), and skewness were then erected atN intervals in both directions. (Sk) were calculated by graphical analysis (Folk & In areas where sediment distribution was hetero- Ward, 1957) and the method of moments (Krum- geneous, additional stations were established to bein & Pettijohn, 1938; Boggs, 1995). Reported characterize theU sedimentological characteristics mean grain-size values are arithmetic means of each zone. At each station, sedimentary struc- derived by the method of moments using milli- tures were recorded from the surface and from metre values. For ease of comparison these values

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 4 S.E. Dashtgard, M.K. Gingras and K.E. Butler

F O O R P D E T C E R R O C

Fig. 2. Sediment distributionN maps from 2003 and 2004 and profiles of Waterside Beach. Note the significant dif- ferences in the size of the mud zone (D11), bar locations (D8), and tidal-creek braid plain (D6) from 2003 to 2004. All lithologies on the 2003 map correspond to deposits described in Tables 1 and 2 except for the cross-hatch pattern, which demarcatesU a rock platform of Palaeozoic bedrock exposed in the . P1 and P2 indicate the locations of profiles 1 and 2. Points 1 and 2 are referred to in the text. The thick, dashed line on the 2004 map indicates the approximate edge of salt-marsh sediments exposed or buried shallowly on Waterside Beach. Between the two lines the beach is deeply incised into the salt marsh. 2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 5 are converted to the phi scale. Sorting and 1996; McLeod & Johnson, 1999). Blocks eroded skewness values are derived from graphical ana- from the cliffs are friable and disaggregate into lysis of phi-scale, cumulative grain-size curves component grains and clasts. This is manifested allowing for easy comparison of the Waterside as a decrease in outcrop-derived gravel aggregates Beach sediments to standard sorting and skew- away from the cliffs and abrasion platforms ness scales (Folk & Ward, 1957; Boggs, 1995; fringing the beach. It is considered thatF the Hoey, 2004). Reported values are an average of all outcrops provide a significant volume of sand to samples in each deposit (D1 to D11; Tables 1 and the beach, but are only a minor contributor of 2), but do not encompass the full range of mean gravel. A second major source of sandO and the grain sizes, sorting, and skewness measurements. main source of gravel are glacial deposits exposed These values offer a means for easy comparison of sub-tidally. These sediments are considered to be sediment properties between deposits. glacial based on their sedimentologicalO character, In situ sediment samples were collected and mineralogy, and from reconstructed glacial flow imaged using X-ray radiography. Samples were maps presented by Rampton et al. (1984). The collected with a 22Æ5cm· 15 cm · 7Æ5 cm stain- distribution of the depositsR is seismically mapped less-steel box core as described in Bouma (1969). and the composition determined by grab samp- From this, a 22Æ5cm· 14 cm · 2 cm thick slab ling. They are exposed immediately seaward of was extracted and X-rayed to assess sedimentary the beach in the southeast,P but are covered by and biogenic sedimentary structures. By combi- beach sediments in the northwest. ning grain-size data, X-ray images, photos, field descriptions, and GPS measurements, sediment Beach sedimentology distribution maps were generated for the back- shore, intertidal, and sub-tidal zones of Waterside Beach and shorefaceD sediments are subdivided Beach (Fig. 2). into eleven zones (D1 to D11), which represent sedimentologicallyE distinct deposits observed in the sub-tidal, intertidal, and supratidal zones of RESULTS Waterside Beach. Sediment textures and struc- turesT observed in each deposit are summarized in Tables 1 and 2 and Figs 3–5. The deposits are Sediment source broadly divided into three categories: (1) sandy Sediment deposited on Waterside Beach is de- Cforeshore and shoreface (D1 to D5); (2) tidal-creek rived from three main sources. Mud is sourced braid-plain and delta (D6 and D7); and, (3) wave- from the bay; sand from the outcrops surrounding formed gravel and sand bars, and associated Waterside Beach; and, gravel and sand fromE deposits (D8 to D11). The relationship between reworking of glacial deposits exposed sub-tidally. these deposits is complex and their boundaries Sediment sourced from the Bay of Fundy is are commonly gradational. Nevertheless, the primarily fine-grained, comprising silt andR clay deposit interrelationships are tractable, thereby derived from erosion of the seafloor and Palaeo- permitting the development of a characteristic zoic cliffs surrounding Chignecto Bay (Amos & facies model. Asprey, 1979; Amos, 1987; Amos etR al., 1991). In particular, Amos (1987) reports that suspended Deposits 1 through 5 particulate matter in upper Chignecto Bay com- Deposits 1 to 5 encompass sandy foreshore and prises 70–90% silt with approximatelyO 10–20% shoreface sediments (Table 1; Figs 2 and 3). They clay and minor sand. This grain-size distribution form a shore-normal continuum of sediments is similar (but slightly more silt-rich) to those of deposited from the backshore (D1) to the sub- mud deposits (D5 and D11) on Waterside Beach, tidal zone (D5). Below the moderately dipping which yield an averageC grain-size distribution beachface (D2), deposits 3 to 5 occur as a laterally (and range) of 4% (1–7%) sand, 58% (50–66%) extensive, shallowly seaward-dipping terrace silt, and 38% (28–48%) clay. (Fig. 2). The intertidal component of the terrace Erosion of PalaeozoicN and Triassic outcrops is referred to as a low-tide terrace (Masselink & fringing Waterside Beach and Long Marsh Creek Short, 1993) and is the equivalent of the foreshore present a second major source of sediment. These and upper shoreface. The sub-tidal component outcrops predominantlyU comprise siltstone and represents the lower shoreface. Terrace sediments sandstone with recessive shale beds (Amos & exposed at low tide are submerged up to 12 m Asprey, 1979; Plint, 1986; Amos, 1987; St. Peter, during high tide. Consequently, sedimentation

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 6 S.E. Dashtgard, M.K. Gingras and K.E. Butler -by- size: fine- and ST for F O washover fan contact with D1; sharp with D3, 6 equivalent Sharp contact with D2, 6, 8; gradationalInterbedded with with D4, D11 7, 9; equivalent Transitional between D3 & D5 Gradationalwith contact D3, 5, 7, 9 Gradational contact with D4, 7, 9 O Backshore complex and Gradational contact with D2 Depositional environment & Contacts Beachface/foreshore Gradational LTT/upper to middle shoreface LTT/middle to lower shoreface ST/lower shoreface equivalent R P (landward dip) & common disc-shaped cbls near contact with D1 muddy sand gravel lenses, Scattered Trough XB Interbedded WR PB, Discontinuous D E ), T Common disc-shaped cobbles near contact with D2 dipping (3–5 planar-parallel beds of pebbly sand & gravel (landward & seaward dip), WR to CR (landwardseaward & dip) cross-laminated, PB, Gravel lenses, Scattered pebbles, Bubble sand Discontinuous, lunate mud lenses (up to 2 cm thick), C sand lenses Weakly defined bedding, Moderately seaward Sedimentary Structures Major Minor , Trough XB -modified WR, E Scattered pebbles, ; ; r 06 Sk (2)) r Æ 49 3% sand, 02 Sk (1)) Æ Æ ;0 Æ 80 Æ 09 Sk (14)) r

R0 Æ ;0 1 Sk (4)) ,2 ) 0 Æ ;0 / / ; ) 23 / Æ r 5% clay (2)) Very ; ;0 Æ r r 21 01 ;2 Æ Æ 58 Æ 16 / Æ 62 60

R Æ Æ ;2 28 Æ ;0 ;0 / / / 81 Æ 38 Sk (4)) 17 Sk (10)) 2% silt, 45 Æ Æ 22 41 Æ 2 Æ Æ 0 0 ) very coarse skewed c.g. sand (0 ) Very-poorly sorted gravel ( m.g. sand (1 ) 52 (1 (2 O poorly sorted, silty v.f.g. sand (3 Moderately well sorted, Well sorted, coarse skewed C Moderately well sorted, m.g. sand Moderately well sorted f.g. sand Clayey silt (6 N Summary table of sedimentary deposits 1 to 5 at Waterside Beach. seaward-dipping, interbedded pebbly sand & gravel well-sorted sand U WR & CR cross- laminated pebbly sand CR cross-laminated sand sand Deposit Description Sediment Texture D2 Moderately D1 Weakly bedded, rooted Table 1. D3 Trough cross-bedded, D4 Flaser bedded, WR & D5 Clayey silt and silty The values in bracketsnumber after sampling. skewness Abbreviations values are indicate used(f.g.), the in this medium- number table of (m.g.), for samplessub-tidal wave coarse- included terrace. ripples in (c.g.), (WR), the current and ripples reported (CR), very values plane and coarse- beds a (PB), (v.c.g.) star cross-bedding next grained (XB), to and sand. for the grain Under number indicates depositional grid environments, LTT represents low-tide terrace

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 7

F O O D6, 7, 8, 10;Interbedded gradational with with D3, D8 8, 9, 10 Sharp contact with D2,gradational 3; with D4, 7,Interbedded 9, with 10 D8, 10, 11 gradational with D3, 4, 5, 7 (deflation of D8) D5, 6, 7, 8,with 9, D5, 11; 6, Interbedded 7, 8, 9, 11 gradational with D3, 4, 5, 9 gravel bars D3, 4, 5, 6,with 7, D10 9, 11; gradational LTT/mud Sharp contact with LTT/tidal-creek braid plain LTT & ST/wave-generated sandSharp bars contact with D6, 8, 10; Interbedded with D5, 6, 8, 10 Sharp contact with Sharp contact with D8, 10; Interbedded with D6, 8,LTT 10, & 11 ST/wave-generated Sharp contact with Interbedded with D5, 6, 7, 9, 10, 11 Depositional environment & Contacts R P D structures, Runzelmarkken Mud layers in WRGravel troughs, WR mud laminae seaward-dipping gravel & pebbly sand Mud cracks, Flame Trough XB (seaward dip), WR & CR sand & mud LTT & ST/gravel lag Thin, discontinuous Interbedded shallow, E ) ) T C mud, Interbedded WR & PB sand & pebblyScattered sand, pebbles and gravel lenses (landward dip), CR & WR sand seaward-dipping gravel, PB sand between clasts landward dip) gravelly sand, PB sand, WR, CR to shallowly, landward-dipping interbeds of gravel & pebbly sand, Trough XB (landward dip) Wavy-parallel laminated Shallowly (<1 PB, Trough XB Trough XB (dom. UnknownSteeply (up to 29 Unknown ST/tidal-creek sand ‘delta’ Sedimentary Structures Major Minor

; E r ; / 40 97 ; Æ ; Æ r / ;1 29 7% Æ 7% Æ Æ / 32 Sk (4)) 22 Æ Æ 93 R04 Sk (4)) Æ Æ 4% mud (2)) 0 ,4 Æ 5 09 Sk (4)) 14 65 to 0 ) Æ Æ Æ / ) ;0 ; 1 3 r r ;0 ) ) 60 r Æ 69 to 2 05 24 Æ Æ Æ 42 Sk (3))

Æ R 60 48 Sk (2*)) 08 Sk, 7 5% silt, 35 Æ Æ Æ Æ ;2 ;1 / / ;0 ;0 ;0 r r / 26 48 Æ Æ 15 to 0 Æ (generally decreases 3 0 47 57 42 Sk grades offshore15 to 0 Æ Æ Æ Æ ) ) skewed gravel ( 2 sand, 59 clay (6)) 1 distribution ( 0 2 ( skewed v.c.g. sand ( distribution ( / offshore); 0 O) Very-poorly sorted, very fine Poorly sorted sand (1 Heterogenous grain-size Clayey silt (5 Very-pooly sorted gravel Poorly sorted, very coarse HeterogeneousC grain-size N Summary table of sedimentary deposits 6 to 11. dipping, extremely poorly sorted gravel sandy gravel to f.g. sand bedded, wavy-parallel laminated clayey silt & WR muddy sand landward-dipping sand & gravel beds cross-bedded PB sand & gravelly sand U cross-bedded sand & gravel Deposit Description Sediment Texture Abbreviations are the same as in Table 1. D10 Very shallowly seaward D7 Offshore fining, D11 Wavy to lenticular D8 Shallowly to steeply, D9 Interbedded, trough Table 2. D6 Plane- & trough

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A B C F O O R P

5 cm 5 cm 5 cm Fig. 3. X-ray images of D3, D4, and D6. All images are taken from boxD cores oriented beach-normal (seaward direction to the right). (A) Example of landward-dipping trough cross-beds overlain by seaward-dipping current- ripple laminae in D3. Trough cross-bedding is enhanced by air bubbles (dark holes) developed along bedding planes. (B) Deposit 4 dominated by wave- and current-ripple laminae, and plane-beddedE sand. Dark laminae indicate more mud-rich sediments and light laminae more sand-rich. Note the gravel-lined scour near the base of the image (black arrow) and pervasive bioturbation (white arrows). (C) Plane-bedded sandy gravel of D6. The lighter beds are gravel- rich versus the grey, sandier beds. Black spots are pores spaces.T and sediment transport on the terrace (D3 to D5) toesets of D2 and are derived from onshore- is almost completely dominated by shoaling Cdirected currents developed under fair-weather waves. Swash-backwash and surf-zone processes conditions (Table 1; Roy et al., 1994; Reading & dominate deposition on the beachface (D2). Collinson, 1996). Along depositional strike at the Deposit 1 is well-sorted, medium-grained aeo-E top of D3, sand is distributed into low-amplitude lian sand (Table 1) situated in the backshore bars spaced equidistantly (100–200 m). Grain (Profile 1, Fig. 2). The basal contact of D1 (under- size and sorting of bar sediments is ideal for lain by D2) is gradational and marked by layersR of trapping air; hence, these zones tend to be disc-shaped cobbles. Deposit 2 tends to be very dominated by bubble sand (i.e. air trapped in poorly sorted with interbedded, moderately well- sand; Fig. 3A) in the upper 0Æ1to0Æ15 m. Runoff sorted . All beds dip 3 toR 5 seawards. zones dominated by silty sand and silt deposition Deposit 2 is analogous to narrow beachface– occur between the bars. Mud deposited in these foreshore deposits reported from gravel, and zones may be up to 5 cm thick, but is typically mixed sand and gravel beachesO (McLean & Kirk, eroded when the bars shift position. High-energy 1969; Kirk, 1980; Clifton, 1981; Bourgeois & wave conditions are manifested as onshore-direc- Leithold, 1984; Forbes & Taylor, 1987; Massari & ted trough cross-beds in D3 (Fig. 3A), gravel Parea, 1988). Deposit 2 differs from those nar- layers at the base of scours (Fig. 3B), and by rower, more gravel-rich beachesC in that it lacks an gravel-dune foresets. imbricate disc zone or well-defined clast segrega- Deposit 4 encompasses sediment deposited tion. The toesets of D2 are marked by rounded below the mean-tide low-water level and is a cobbles and pebblesN that accumulate at the base transitional zone between D3 and D5 (i.e. equiv- of the foreshore during storms (Bluck, 1967, alent to the middle shoreface). This zone is 1999). These sediments overlie a wave-scoured dominated by wave-ripples with silt infilling surface cutU into salt-marsh deposits that is ripple troughs. The silt deposits are generally excavated during transgression (Dashtgard & thin, lunate, and discontinuous, but may exceed Gingras, 2005). Deposit 3 sands onlap the cobble 6 cm in thickness. Throughout D3 and D4, wave-

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 9

A F COLOUR FIG. D8 D6 D11 O O

B C R D6 P

D11 D E D8

D E T D11 C E

D8 R R D8 5 cm Fig. 4. Photos of D6 to D11. (A) Panoramic view of the relationship between the 5Æ5 m high gravel bar (D8), braided channel of Long Marsh Creek (D6),O and zone of mud deposition (D11). Panoramic taken from the top of the gravel bar looking east, the bay is to the right of the photo and land to the left. (B) Example of interbedded D6 and D11. The mud layer is 0Æ04 m thick and the scale is 0Æ15 m long. (C) Trench excavated normal to the beach on the backside of the gravel bar in photo A (D8). The dashed white lines highlight steeply landward-dipping gravel beds overlain by shallowly seaward-dippingC gravel. Scale is 0Æ15 m long. (D) Photo of a trench excavated normal to the beach in the zone of mud deposition (D11) on photo A. Note the mud-coated gravel within the upper 0Æ15 m of sediment and steeply landward-dipping sand and gravel beds (D8) preserved below mud beds (D11). (E) Image of a beach-normal trench excavated approximatelyN 1 m above the base of the gravel bar in photo A on its stoss face. All gravel clasts 0Æ10 m below the bar surface are coated in mud. Scale is 0Æ15 m long.

and current-ripple laminae are developed under shoaling-waves (Wright et al., 1982; Masselink & fair-weatherU conditions (Fig. 3A and B). When Short, 1993; Masselink, 1993). With continued initially exposed by the falling tide, the terrace is exposure, sheet-like surface drainage reworks covered by wave-ripples, probably resulting from many of the wave ripples into offshore-directed

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 10 S.E. Dashtgard, M.K. Gingras and K.E. Butler

A B F P WR Co Co O 5 cm 5 cm Fig. 5. (A) X-ray image of the wavy-parallel laminated clayey silt (dark layers) and silty sand (light layers) of D9, overlying gravelly sand. U-shaped Corophium volutator burrows (Co) are prevalent throughoutO the mud. (B) X-ray image of D9 showing the variability in the lithology of the deposit. Dark layers are clayey silt, dark grey areas sandy mud, and light layers are gravelly sand. Note the large (P), Corophium volutator burrows (Co) and wave ripples (WR). R current ripples resulting in preservation of ebb- related to sediment grain size and hydraulic current modified wave-ripples (Fig. 3B). energy. High-energyP (active channels) Deposit 5 is the lowest most unit of the terrace are erosive and remove up to pebble-sized clasts and only occurs sub-tidally. It is considered the from the underlying deposit. In moderate-energy equivalent of the lower shoreface (Fig. 2). This channels, sand and gravel is deposited as plane zone is dominated by clayey silt and silty very- beds (Fig. 3C) with intermittent steeply dipping fine grained sand deposition (Table 1) with inter- foresets of -parallelD and stream-normal bedded thin pebbly sand lenses. The offshore channel bars. Grain-size distribution is hetero- pinchout of D5 corresponds to the toe of the geneous;E however, there is an overall decrease in shoreface, and is demarcated by a weakly defined grain size offshore (Table 2). At the seaward end step and a decrease in the slope of the seafloor. of D6, sand and fine gravel winnowed out of upperT and middle terrace deposits is deposited as Deposits 6 and 7 a sand ‘delta’ (D7). The delta extends from the Deposits 6 and 7 comprise plane and trough lower intertidal seaward to the toe of the shore- cross-bedded sand and gravel deposited as a Cface (Fig. 2) where it develops a pronounced (1) result of tidal-creek processes active on the low- step. This sediment is likely the source for the tide terrace at low tide. Water transported up the landward-migrating sand and bars of creeks at high tide (particularly spring high tide)E deposit 9. flood the salt marsh and drain into two tidal lakes, 2 and 10 km landward of the beach. During Deposits 8 through 11 the falling tide, bay waters drain off theR marsh Deposits 8 to 11 are reworked by high-energy and out of the lakes at a relatively constant rate – waves. Deposit 8 encompasses sediment laid down maintaining a relatively steady flow rate within as large (up to 800 m long), landward-migrating the creeks throughout falling- and low-tide.R Tidal- gravel bars (Figs 2 and 4A). In Fig. 4A, the gravel creek waters winnow fine gravel and sand from bar on the right of the photo comprises a 5Æ5 m high upper terrace deposits and transports it to the lee face and 6Æ7 m high stoss face (Profile 2, Fig. 2). lower intertidal and sub-tidalO zones. As a result, Overall, the bars are composed of steeply land- upper and middle terrace sediments exhibit ward-dipping foresets of very-poorly sorted gravel improved sorting and a general shift towards and sand (Table 2; Figs 2, 4C, E and 6). Sediment coarsely skewed sediment. The tidal creeks also migrates up the stoss face of the large bars and redistribute low-tide terraceC sediments into creek- avalanches down the lee slope forming foresets parallel sand and gravel beds. These deposits that dip up to 29 (Figs 2, 4C, E and 6). Interbedded form a braided outwash plain with a very hetero- with these sediments are better sorted, coarsely geneous distributionN of grain size, sorting, and skewed gravels representing hydraulically skewness (D6, Table 2). The hydraulic energy of a winnowed surface sediment. braid channel determines whether gravel, sand or The Waterside gravel bars develop in the mud is activelyU deposited and the thickness of shallow sub-tidal zone (lower shoreface) and that deposit. Moreover, sedimentary structures increase in volume as they migrate onshore. observed in a particular area of the braid plain are Measurements of bar migration indicates that

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 11

pbl pbl pbl cbl mud vf f m c vc gnl cbl mud vf f m c vc gnl cbl mud vf f m c vc gnl

D5 D5 D5 3

3 D7 / D9F 8 D9/ D4 D7 D6 2 O 2 D11 7 D8

O D8 1 D3 D6 1 6 R D10

D8 0 D2 P 0 5 D11 Strip log 2B Strip log 1A D6 D D11 4 D10 pbl mud vf f m c vc gnl pbl cbl mud vf f m c vc gnl cbl ED8 1 2 D5 D11 D5 3 T D4 0 D2 C D6 1 D8 2 Strip log 1B E 0

mud vf f m c vc gnl pbl cbl 1 1 R D8 Strip log 2C

D5 R 0 D2 0

Strip log 1CO Strip log 2A

Wave- and current- Gravel lag CMuddy gravel Wave-scoured contact ripple laminae Weak or possible Trough cross-bedding Gravel Mud (clayey silt & sandy silt) bedding / laminae Planar-parallel bedding Sandy N Salt marsh with roots Visible bedding / laminae (plane beds, steeply and gravel shallowly dipping beds) Fig. 6. Idealized sections that may be expected if Waterside Beach is preserved in the rock record. Strip logs 1A, 1B, and 1C refer toU sections for point 1, and strip logs 2A, 2B, and 2C for point 2 (2003 map, Fig. 2). The logs are discussed extensively in the text. Lithology is not indicated on the strip log unless it differs from the indicated lithology type (i.e. gravel beds in a sand unit). The vertical bars and D’s on the right side of each log refer to the vertical distribution of each deposit type in the section. Scale is in metres.

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 12 S.E. Dashtgard, M.K. Gingras and K.E. Butler annual landward migration along the bar front is mary deposit (D8) removes most fines and con- ) variable, ranging from 0 to over 50 m year 1 centrates large pebbles and cobbles on the beach (Maps 2003 and 2004, Fig. 2). At the landward surface. Secondary infilling of interstitial pores limit of the beach the bars either accrete to the with sand (D9) and mud (D5 and D11) results in beachface (D2) or infill the tidal creeks (Strip logs an increased proportion of fines, hence the fine 2A, 2B, and 2C, Fig. 6). Small bars (<2 m high) skew and very-poor sorting (Table 2). DepositF 10 tend to be washed out by storm waves in the may occur from the top of the low-tide terrace intertidal zone whereas large bars are more (foreshore) to the base of the shoreface (Fig. 2). resilient and migrate landward during storms. The development of large gravel barsO (D8) is Under fair-weather conditions, migration of the both an important mechanism for gravel transport large bars is minimal and is restricted to small, and deposition, and is necessary for the occur- low-amplitude, mixed sand and gravel dunes that rence of extensive mud depositionO landward of migrate up and over the stoss face of the bar. the bars (Fig. 2). The gravel bars dissipate and In sandy systems, bar-forms similar to, but reflect wave-energy resulting in the development smaller than, the Waterside bars are common and of quiescent zones dominatedR by clayey silt have been the subject of numerous studies (King deposition (Figs 2, 4A and 5). Below a threshold & Williams, 1949; McCave & Geiser, 1978; Green- bar-height (1Æ5 m) mud deposition is negligible. wood & Davidson-Arnott, 1979; Kroon & Masse- With increased heightP the mud zone extends link, 2002; Anthony et al., 2004; Yang et al., landward (Fig. 2). This mud is deposited on top 2005). Initially, these intertidal bars were consid- of the existing sediment (Figs 2 and 4A, B) and ered to form as a result of swash processes and pinches or swells in response to the antecedent destroyed by surf processes (King & Williams, topography (Fig. 6). In abandoned channel lows 1949; King, 1972). However, recent work by (D6) or depressionsD in the underlying surface, Kroon & Masselink (2002) shows that onshore mud deposits (D11) are commonly 0Æ15 to 0Æ2m bar-migration results mainly from surf-zone pro- thick. MudE up to 0Æ4 m thick has been observed. cesses and that swash processes play a secondary On topographic highs, mud thickness rarely role. The Waterside bars may then be considered exceeds 0Æ07 m. The clayey silt is wavy parallel intertidal bars that are akin to sub-tidal, inner laminatedT (Fig. 5A) to wave-ripple laminated surf-zone bars (Sunamura & Takeda, 1984; Kroon (Fig. 5B) and is commonly interbedded with sand & Masselink, 2002). and sandy gravel beds deposited during storms or Deposit 9 refers to sediment deposited from Cby ice (Fig. 5B). sandy, low amplitude (<1 m) bars with gently dipping lee and stoss slopes. D9 bars are com- posed of poorly sorted sand and gravel, but tendE DISCUSSION to be predominantly gravelly sand (Table 2; Fig. 6). The increased sand content is partly the Muddy conglomerates and mud beds in result of wave reworking of D7 sand-delta sedi- R conglomerates ments in the lower intertidal and sub-tidal zones (Fig. 2). Sedimentary structures are dominated by Understanding the relationship between the mud trough cross-bedding (dipping in allR directions) deposits (D11), channel deposits (D6), gravel bars and plane beds that form as a result of water (D8), and lag deposits (D10) on Waterside Beach flowing over and off the bar forms. These bars are provides a mechanism for mud deposition in highly unstable and are akinO to the Type 2 bars conglomeratic systems and for the formation of reported by Greenwood & Davidson-Arnott muddy conglomerates. Landward of the gravel (1979). They are also considered to result from bars, mud is deposited as thin layers on top of similar processes (Kroon & Masselink, 2002; braided-channel bars and in abandoned channels Anthony et al., 2004) asC the larger gravel bars of D6 (Figs 4A, B and 5). Initially, the mud is (D8) and may be considered analogous to sub- soupy and easily resuspended by low-energy tidal, inner surf-zone bars as well. hydraulic currents. Subsequent desiccation, Deposit 10 is aN wave-winnowed pebble and dewatering, and/or bacterial (or algal) binding cobble lag (Fig. 2) deposited to seaward of the renders it firm – forming resistant mud beds. landward-migrating gravel bars (D8). The upper An example of this is shown in Fig. 4B where layer of D10U is wave-reworked into weakly a0Æ04 m thick mud bed is interbedded with defined horizontal to gently seaward-dipping braided-channel gravel-bar deposits of D6. Mud- beds (Fig. 6). Hydraulic winnowing of the pri- dy clast- and matrix-supported conglomerates

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 13 develop in front of the landward-migrating gravel mum tide height. This in turn, controls the occur- bars (D8). Gravel transported up the seaward rence of mud deposits on the landward side of the (stoss) side of the bar avalanches down the gravel bars. Short (<1Æ5 m high) bars tend not to landward (lee) face and either accumulates on permit the development of mud beds. Sub-tidal the face or in the mud at the base of the bar. The gravel bars are not restricted by tidal range and may area directly in front of the bar is not affected by occur in microtidal to hypertidal settings. F wave- or tidal-energy; hence, the mud is not Intertidal bars are sub-aerially exposed twice a eroded during bar migration. Gravel avalanching day, resulting in dewatering, desiccation, and down the lee face either rests on top of the mud or algal binding of the mud beds thatO develop sinks into it resulting in mud infilling the spaces landward of the bars. In a sub-tidal environment between gravel clasts. This relationship is repre- dewatering and possibly algal binding may also sented on Strip log 2A (Fig. 6) by muddy gravel in render mud beds firm, but is lessO likely too occur. the basal portion of each D8 deposit. Moreover, bar migration rates are likely to be Muddy conglomerates also develop when mud- higher in a sub-tidal setting as a result of rich sea water seeps through the beach sediments prolonged exposure to surf-zoneR processes. Con- (Fig. 4D and E). Figure 4D is an example of sequently, the occurrence of mud beds in a muddy gravel that occurs below the zone of conglomeratic succession may indicate an inter- mud deposition. Mud-laden sea water percolating tidal environment andP upper mesotidal to hyper- down through the gravel rapidly loses velocity tidal conditions. The occurrence of muddy below the surface resulting in mud deposition in conglomerates however, is less restrictive and the near-surface beach sediment. The mud tends may either indicate sub-tidally formed gravel to coat grains instead of infilling the pore spaces. bars, intertidal bars or mud-laden sea water. If Figure 4E depicts muddy gravels encountered in bedding is apparentD in a muddy conglomerate it a trench approximately 1 m above the low-tide most likely developed from mud-laden sea water terrace on the stoss side of a gravel bar (D8). In seepingE through the gravel; whereas, a lack of this case, mud-laden sea water passing through bedding may be more indicative of bar migration the gravel bar coats sand and gravel clasts with over soupy mud deposits in either a sub-tidal or mud. In both cases muddy gravels are developed, intertidalT setting. although the depth (relative to the beach surface) at which they occur differs. Below the zone of Transgressive muddy gravel beach sequences mud deposition (D11, Fig. 2) muddy gravels C occur in the near-surface sediment (upper Waterside Beach occurs in a hypertidal setting 0Æ15 m) and overly mud-free sand and gravel. where the dominance of wave-processes will Within the gravel bars, muddy gravels occurE result in a facies architecture that corresponds below the upper 0Æ1to0Æ15 m resulting from to that of a transgressive gravel beach. Figure 6 wave winnowing of the near-surface sediment. illustrates six idealized successions that can be The two mechanisms presented for the develop-R predicted if continued transgression resulted in ment of muddy, matrix- and clast-supported con- burial and preservation of Waterside Beach in the glomerates and for the deposition of mud beds in rock record. Strip logs 1A, 1B, and 1C (Fig. 6) conglomerates provide a means to assessR environ- relate to point 1, and strip logs 2A, 2B, and 2C mental conditions of the palaeo-depositional relate to point 2 on Map 2003, Fig. 2. The environment that otherwise may not be discerna- stratigraphic successions presented for points 1 ble. The latter mechanism (requiringO gravel depos- and 2 represent end members of the possible its and mud-laden sea water) suggests that the stratigraphic relationships that exist on Waterside occurrence of muddy conglomerates is a good Beach. Strip logs 1A and 2A are complete trans- indicator that sea water at the time of conglomerate gressive sequences that may either be encoun- deposition was muddy.C The first mechanism tered in systems with high sedimentation rates or necessitates bar formation and migration, which that may develop at or near the maximum trans- is dependent on the location of the bars relative to gressive shoreline. Strip logs 1B and 2B present the beach and on theN local tidal range. Intertidal the expected preserved succession that may be bars exhibit characteristics that are distinct to an encountered in areas with moderate sedimenta- intertidal environment and thus, may be distin- tion, or at the early or late stages of transgression. guished fromU their sub-tidal equivalents. Primar- Strip logs 1C and 2C show sedimentary succes- ily, the height of intertidal bars is restricted by tidal sions that will develop in rapidly transgressing range where bar height cannot exceed the maxi- systems. Continued transgression of present day

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 14 S.E. Dashtgard, M.K. Gingras and K.E. Butler

Waterside Beach should result in preservation of Strip logs 1A, 1B, and 1C depict the facies a succession that resembles either strip logs 1B evolution on top of a wave-scoured contact and2Bor1Cand2C. (wave-ravinement surface) cut into underlying The (extreme) difference in thickness between salt-marsh deposits that develops during trans- sequences constructed for points 1 and 2 is due to gression (Fig. 6). This contact is in turn overlain erosion of the salt marsh at the mouth of by a thin transgressive lag that is sedimento-F Long Marsh Creek (LMC; Fig. 2). This in turn, logically similar to the transgressive lag described is controlled by tidal range, where the cross- by Massari & Parea (1988) and Clifton (1981). The sectional area of a tidal- throat (i.e. where lag comprises toeset sediments of D2O that are LMC debouches onto the beach) is related to the partly wave-reworked resulting in destruction of tidal prism (French, 1993; Pye & French, 1993; bedding (Fig. 6). Above the lag, the rates of Allen, 1997, 2000). On the hypertidal Waterside transgression and sedimentationO controls the Beach the tidal prism is large; hence the cross- thickness of the preserved succession and the sectional area of LMC is also large (8Æ2 m deep, deposit relationships observed. 54 m wide; Dashtgard & Gingras, 2005). Depth Three scenarios are presentedR for the expected measurements taken from the beach and within preserved succession at point 1 (Map 2003, marsh indicate that at the landward end of the Fig. 2). In strip log 1A, the lag (D2) is sharply beach (seaward limit of the marsh), LMC is filled overlain by D3, then D4,P and finally D5 sediments with 4Æ5 m of gravel and sand derived from the that form a continuum of decreasing grain size beach, and is presently filling in a landward upward in the succession. This trend is accom- direction. Seaward of LMC, the erosional profile panied by an increase in mud deposition and of underlying salt-marsh sediments flares later- ripple cross-lamination, and a decrease in trough ally and vertically (as a cone opening seawards) cross-beddingD and gravel content. Strip log 1B from the mouth of the creek to beyond the outer illustrates the case of moderate sedimentation edges of the gravel bars (Map 2004, Fig. 2). rates relativeE to transgression resulting in in- Within this cone the beach and shoreface deposit creased erosion of the low-tide terrace deposits is much thicker; thus, the successions presented (foreshore and upper shoreface) and deposition of in strip logs 2A, 2B, and 2C (i.e. near tidal- middleT and lower shoreface sediments (D4 and channel complex) are nearly three times thicker D5) sediments on top of the gravel lag (Fig. 6). than those in strip logs 1A, 1B, and 1C respect- Finally, strip log 1C presents a succession that is ively (i.e. ambient beach; Fig. 6). Clikely to develop in a rapidly transgressive setting with low sedimentation. In this scenario, the Strip logs 1A, 1B, and 1C entire foreshore and upper shoreface sequence is Assuming Waterside Beach is preserved in theE removed (D2 to D4), with lower shoreface sedi- rock record, strip logs 1A, 1B, and 1C (Fig. 6) are ments (D5) overlying the gravel lag (Fig. 6). idealized sections of the sedimentary succession Because the beach has an abundant source of that may be expected at point 1 (MapR 2003, sand and gravel (i.e. glacial deposits exposed sub- Fig. 2). The three sections are presented to illus- tidally) and experiences relatively rapid trans- trate variations in the preserved succession that gression, it is considered that either strip log 1B can occur under varying rates ofR transgression or 1C (Fig. 6) represents the most likely succes- and/or sedimentation. In general, a complete sion that will be preserved if Waterside Beach sedimentological record will be relatively thin passes into the rock record. and dominated by middle to lowerO terrace depos- its representing mainly shoaling-wave (shoreface) Strip logs 2A, 2B, and 2C processes. In transgressive systems, backshore Strip logs 2A, 2B, and 2C (Fig. 6) depict a much and beachface deposits are normally eroded thicker beach and shoreface sequence that may be (Bourgeois & Leithold,C 1984; Nemec & Steel, expected at point 2 (Map 2003, Fig. 2). As 1984); whereas, shoreface and offshore facies discussed above, erosion of the salt marsh is tend to be preserved (Roy et al., 1994; Reading & much more pronounced near the mouth of Long Collinson, 1996). ThisN is likely to be the case for Marsh Creek and extends seaward as a cone of Waterside Beach with the vertically significant, relatively deeply incised beach sediment (Map but laterally restricted D1 and D2 deposits (Profile 2004, Fig. 2). The complete sequences are a 1, Fig. 2) havingU a limited to nil chance of vertical representation of the complex strati- preservation. The rest of the succession consists graphic relationships between deposits 6 to 11 of a deepening-upward trend. observed on the beach surface (Fig. 2). The depo-

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 15 sitional conditions – rates of transgression and will be preserved when sedimentation rates are sedimentation – for strip logs 2A, 2B, and 2C are much lower than transgression rates. Transgres- the same as those for strip logs 1A, 1B, and 1C sive wave ravinement removes most of the respectively. intertidal (foreshore and upper shoreface) and The base of the successions is demarcated by sub-tidal (middle and upper lower shoreface) a tidally scoured contact cut into salt-marsh deposits. Lower shoreface muds then accumulateF deposits (Strip logs 2A, 2B, and 2C, Fig. 6). In on top of the wave-scoured sediments. The strip log 2A, this surface is directly overlain by resultant package therefore, consists of foreshore a 3 m thick unit of gravel bar (D8) then channel and upper shoreface sediments that infilledO the (D6) deposits representing the initial filling tidal creeks, decapitated by wave ravinement, episode of LMC by gravel-bar sediments. The and capped by lower shoreface muds (Strip log upper part of the bar sediments are hydraulic- 2C, Fig. 6). O ally reworked by tidal-creek waters to form D6. From 3 m to nearly 5 m is a typical sedimentary Application to the rock record package for this succession. Mud deposition R (D11) occurs on top of the channel sediments The sedimentological relationships and theoret- (D6) as a result of gravel-bar formation. Down- ical stratigraphy of Waterside Beach provides ward percolating sea water coats sand and important informationP for facies and facies rela- gravel clasts in the sediment immediately below tionships of transgressive gravel-, muddy gravel-, the mud beds resulting in the development of and mixed sand and gravel-beaches preserved in muddy gravel. Subsequent landward migration the rock record. Firstly, it is observed that archi- of the bar, deposits a thick bedset of steeply tecture, thickness, and extent of transgressive dipping sand and gravel (D8) on top of the gravel-beach depositsD are significantly influenced mud. The basal third of the bar deposit is by the occurrence and size of associated tidal dominated by muddy gravel as a result of mud creeks. TheE size of these creeks is a function of the being forced into the pore spaces between tidal prism (French, 1993; Pye & French, 1993; gravel clasts. The surface sediments of the bar- Allen, 1997, 2000). The successions in strip logs deposited bedset (D8) are hydraulically win- 2A,T 2B, and 2C are very thick reflecting the nowed and reworked by waves into weakly hypertidal nature of Waterside Beach. The thick- developed seaward-dipping plane beds (D10). ness of these units will decrease with a reduction Once the bar reaches the beachface or is washed Cin tidal range; hence, the thick deposits observed out by waves, braided drainage channels of in these strip logs are applicable to upper meso- LMC are re-established on the low-tide terrace tidal to hypertidal settings. Strip logs 1A, 1B, and forming channel-bar deposits (D6). This sedi-E 1C depict much thinner sedimentary successions mentation cycle is repeated vertically (Fig. 6). typical of beach and shoreface sediments depos- After the last bar, channel, and mud unit (at ited outside the zone of tidal-creek influence approximately 7Æ5 m), the D10 beds areR sharply (Fig. 2). The thickness of these deposits is con- overlain by either low-relief sand-bar (D9) or trolled by the rate of sedimentation, transgres- sand-delta (D7) sediments representing the low- sion, and by wave action, and is independent of ermost intertidal and sub-tidal zonesR (Strip log tidal range. Strip logs 1A, 1B, and 1C are there- 2A, Fig. 6). fore, applicable to transgressive gravel, muddy Strip logs 2B and 2C (Fig. 6) depict the same gravel, and mixed sand and gravel successions in sequence as in 2A, but underO varying rates of any tidal setting. transgression and/or sedimentation. Similar to Secondly, sedimentation rate versus trangres- strip log 1A, strip log 2A should be preserved in sion rate controls the thickness and architecture a setting with high sedimentation rates and slow of the preserved succession. In rapidly trans- transgression, such as atC or near the maximum gressing systems and/or those with limited sedi- transgressive shoreline. Strip log 2B will be ment supply, the preserved succession tends to preserved where sedimentation rates are high be thin, either manifested as a gravel lag (Strip log enough to resultN in some aggradation during 1C, Fig. 6) or as a thin (<2 m thick) shore-normal transgression. This results in erosion of the gravel deposit where tidal creeks debouch onto foreshore by transgressive wave ravinement, the beach (Strip log 2C, Fig. 6). In both cases the and partial preservationU of middle and lower successions are capped by lower shoreface silty shoreface sediments (D4 and D5; Strip log 2B, sand and clayey silt deposits. This depositional Fig. 6). Strip log 2C illustrates a sequence that setting is similar to described transgressive beach

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 16 S.E. Dashtgard, M.K. Gingras and K.E. Butler successions and the transgressive components of components of the terrace forming a sand ‘delta’ progradational deposits, which tend to be thin (D7). This sediment is then transported onshore (commonly manifested as a wave-winnowed, by waves as unstable, low-amplitude sandy bars gravel lag) and grade quickly upward into off- of D9. Deposits 8 and 10 represent gravel depos- shore, muddy marine facies (Clifton, 1981; Bour- ited by large, landward-migrating gravel bars (up geois & Leithold, 1984; Massari & Parea, 1988). A to 5Æ5 m high, 800 m long). These bars formF and beach and shoreface succession that results from migrate in response to surf-zone processes (Kroon a rapidly transgressing shoreline with a limited & Masselink, 2002) and are considered sub-tidal sediment supply represents one end member of (shoreface) features exposed as a resultO of the possible successions that may occur. The other extreme tidal range. D11 represents the zones of end member is illustrated in strip logs 1A and 2A mud deposition developed on the landward side (Fig. 6), which are the expected successions of large gravel bars. O when the sedimentation rate is high relative to The occurrence of mud beds in a conglo- the transgression rate. These deposits tend to be meratic succession is most indicative of upper much thicker and occur at or near the maximum mesotidal to hypertidal conditionsR at the time of transgressive shoreline. deposition, and may indicate sub-aerial exposure The stratigraphic successions depicted in strip of mud beds resulting in dewatering, desicca- logs 2A, 2B, and 2C (Fig. 6) develop over an tion, and algal bindingP of the mud. Muddy, erosional surface into salt-marsh deposits scoured clast- and matrix-supported conglomerates may by Long Marsh Creek and enhanced by wave develop from sub-tidally formed gravel bars, action on the beach (Map 2004, Fig. 2). Conse- intertidal bars or mud-laden sea water. If bed- quently, the zone of thick beach deposits devel- ding is apparent in a muddy conglomerate it ops perpendicular to the strike of the beach and more likely developsD from mud-laden sea water may be mistaken for fluvial or estuarine deposits. seeping through the gravel. A lack of bedding This is a significant problem in rapidly trans- may beE more indicative of bar migration over gressing systems where the beach tends to be soupy mud deposits in either a sub-tidal or manifested as a thin gravel lag and the tidal-creek intertidal setting. influenced deposit as a shore-normal gravel unit TheT thickness and preservation of transgressive up to 2 m thick (Strip logs 1C and 2C, Fig. 6). The gravel beaches is dependent on tidal regime, original depositional environment may be ascer- sedimentation rate, and transgression rate. In tained if sedimentary structures, such as steeply Careas where tidal creeks do not influence sedi- landward-dipping gravel beds (D8), horizontal mentation on the beach, a preserved sequence mud beds (D11), and muddy conglomerates (D8) will be thin, consisting of an upward-deepening are observed. E (fining) profile (Strip logs 1A, 1B, and 1C, Fig. 6). Conversely, where tidal creeks do occur landward of the beach, the beach sequence tends to be CONCLUSIONS R much thicker (Strip log 2A, 2B, and 2C, Fig. 6). The thickness of the succession is largely con- Waterside Beach deposit can be subdivided into trolled by the occurrence and size of tidal creeks, eleven sedimentologically distinctR deposits that which is proportional to the tidal prism. At represent three main depositional environments: Waterside Beach, the tidal prism is large, thus (1) sandy foreshore and shoreface; (2) tidal-creek the preserved succession is thick. The thickness braid-plain and delta; and, (3)O wave-deposited of the preserved succession is also strongly gravel and sand bars, and associated deposits. influenced by the rates of sedimentation and Sandy foreshore and shoreface deposits encom- transgression. Where sedimentation is low and pass aeolian-deposited sand of the backshore transgression rapid, the preserved deposits are (D1), moderately seaward-dippingC (3–5) mixed thin – comprising either a thin conglomerate lag sand and gravel of the beachface (D2), and a (Strip log 1C, Fig. 6) or a thin (<2 m thick) gravel shallowly seaward-dipping terrace comprising unit oriented shore-normally (Strip log 2C, intertidal sand (D3)N and silty sand (D4), and Fig. 6). These successions would typically be sub-tidal silty sand and clayey silt deposits (D5). capped by lower shoreface mud. At or near the Deposit 6 includes terrace sediments reworked or maximum transgressive shoreline or in transgres- deposited byU tidal creeks. Sand and fine gravel sive settings with high sedimentation rates the removed from the upper and middle intertidal is preserved gravel deposits are predicted to be deposited in the lower intertidal and sub-tidal much thicker (Strip logs 1A and 2A, Fig. 6).

2006 The Authors. Journal compilation 2006 International Association of Sedimentologists, Sedimentology, 1–18 Sedimentology, stratigraphy of muddy gravel beaches 17

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