Paleobathymetry_wave_graded_shelves_Dunbar_&_Barret_(2005).pdf

Estimating palaeobathymetry of wave-graded continentalshelves from sediment texture

G. B. DUNBAR* and P. J. BARRETTAntarctic Research Centre, Victoria University of Wellington, PO Box 600, Wellington, New Zealand(E-mail: [email protected])

ABSTRACT

The concept of the wave-graded continental shelf, with sea floor sediment

coarsening from offshore mud to shoreface sand, has been well known from the

time of Johnson (1919). Although most of the modern shelf shows textures

unrelated towater depth on account of relict features or sediment starvation, the

geological record ismore likely to preserve sites where sediment is being fed to a

subsiding inner-shelf. These consistently show the landward-coarsening

pattern of the wave-graded shelf, recording past water depth history in

accumulated sea floor sediment. The landward-coarsening pattern is driven

primarily by wave-induced bed shear stress, which increases shoreward

exponentially, although it also varies from place to place with wave climate,

and can be influenced by sediment concentration and currents. In this study, the

relationship between bed shear stress, sediment texture and water depth has

been investigated by comparing per centmud andwave climate data from shore-

normal transects of three modern wave-graded coastal settings: Wellington

Harbour (low energy) and the Manawatu coast (moderate energy) in New

Zealand, andMonterey Bay in California (moderate–high energy). Samples from

all three locations show a progressive change frompoorly sortedmud offshore to

well-sorted fine sand nearshore, with the sand–mud transition ranging from 3 m

(low energy) to 50 m (moderate–high energy), reflecting differences in average

bed shear. Repeat measurements of per cent mud on seasonal, annual and

decadal time scales along a Manawatu coastal transect showed no measurable

change, demonstrating equilibrium between sediment supply, wave energy,

water depth and sediment texture. A simple model based on the relationship

between wave climate, shear stress and per cent mud, and using data and

conditions from the modern Manawatu coast, is applied to two mid-Pliocene

cyclothems exposed 50 km inland, giving results comparable with estimates

from foraminifera and the deep-sea isotope record. Per cent mud offers more

detail for palaeobathymetric trends in shallowwater shelf strata thanother proxy

depth recorders, although it is limited to depths abovewave base and requires an

independent estimate of wave climate if depths are to be quantified.

Keywords Continental shelves, palaeobathymetry, sediment texture, wavegrading.

INTRODUCTION

Estimating depositional water depth for sedimen-tary sequences in continental shelf settings is

important in several fields of earth science,notably in palaeoclimatology as a recorder of icevolume changes, in seismic sequence analysis ofcontinental shelf sediments, where cyclic chan-ges in sea-level are considered to have been themain influence on depositional style, and indetermining the subsidence history of shelf

*Present address: G. B. Dunbar, Research School ofEarth Sciences, Australian National University, Can-berra, ACT 0200, Australia.

Sedimentology (2005) 52, 253–269 doi: 10.1111/j.1365-3091.2004.00695.x

� 2005 International Association of Sedimentologists 253

basins. Past estimates of water depth orpalaeobathymetry of shelf sediments have beenbased largely on depth-sensitive fossil assem-blages preserved in the enclosing sediment,especially foraminifers and molluscs. Howeverthese have limited value where diagnostic speciesabundance is low, stratigraphic intervals are non-fossiliferous, or there is a lack of reliable modernecological analogues.Stratigraphers have long recognized that varia-

tions in particle size can be a useful guide topalaeowater depth in facies analysis of wave-dominated shelf sediments (e.g. Clifton, 1986,1988; Kitamura et al., 1994; Naish & Kamp,1997a; McIntyre & Kamp, 1998), although to datethere have been few attempts to place this on aquantitative footing. There are, however, twooutstanding advantages to using sediment textureas a proxy for water depth: (i) it is readilymeasurable in all clastic sedimentary sequences;(ii) the physical principles on which the size–water depth relationship is founded are invariantover time.This approach to palaeobathymetric analysis

requires two assumptions: (i) the depositionalsetting is known to be that of a wave-graded shelf;and (ii) the strength of the wave climate can beestimated.In this paper the relationship between particle

size distribution (texture), wave climate andwater depth is examined by comparing per centmud and wave climate data from shore-normaltransects of three examples of modern wave-graded coastal settings; Manawatu coast, NewZealand (moderate wave energy), WellingtonHarbour, New Zealand (low wave energy); andMonterey Bay, California (moderate–high waveenergy). It is suggested that the observed relation-ships provide a basis for palaeobathymetrictrends to be estimated for sedimentary stratadeposited in a nearshore environment, and thatnumerical values for water depth can be obtainedif wave climate (height and period) can beestimated. This approach to palaeobathymetry isthen applied to two Pliocene shallow marinecyclothems from the Wanganui Basin, New Zea-land, inland from the present-day Manawatucoast, assuming that the present-day wave climateprevailed.

BACKGROUND

Leeder (1999, p. 461) succinctly summarizesthe conceptual basis for this paper with the

following words ‘Overall, weather-dominatedshelves tend to show a general offshore decreasein grain size and Holocene sediment thicknessin response to attenuating wave power.’.Although much of the present continental shelfcontains relict or palimpsest sediments, thoseparts of the inner-shelf where sediment isaccumulating today should be recording thisseaward-fining profile, reflecting the balancebetween grain size, water depth and waveenergy. Furthermore, it is self-evident that areasof sediment accumulation on the shelf will bepreferentially preserved (compared with ero-sional or non-depositional intervals) in thestratigraphic record. This leads to the likelihoodthat sedimentation patterns in sedimentarystrata deposited on the continental shelf duringperiods of earth history characterized by cyclicchanges in sea-level will reflect changes inwater depth.The idea of seaward-fining sediment texture is

widely used in the stratigraphic literature as thebasis for interpreting vertical facies changes insedimentary sequences. The hydraulic basis forthis has been well established in sedimentologi-cal and coastal engineering literature dating fromthe 1940s, and a brief outline of this follows.Development of a seaward-fining textural profileon a prograding coast requires a decrease in bedshear stress proportional to water depth. Thiscondition is generally fulfilled on wave-domin-ated coasts where the ‘skin friction’ shear stress(i.e. that component of the total shear stressresponsible for entraining sediment) for any givenwave can be expressed as:

sw ¼ 0�5qfwU2m ð1Þ

where q is fluid density, fw a skin friction factorand Um is the maximum near-bed velocity.Um can be calculated from linear wave theory:

Um ¼ pHsig

Tp sinhð2ph=LÞ ð2Þ

where h, Hsig, Tp and L are water depth, signifi-cant wave height (average of the highest one-thirdof all waves), peak (spectral) wave period andwavelength respectively (Pickrill & Currie, 1983).This theory does not accurately predict velocitiesunder breaking or drawing waves, but adequatelydescribes deeper water wave velocities that are ofinterest here.The friction factor, fw, can be calculated using

the following equation (Li & Amos, 2001):

254 G. B. Dunbar and P. J. Barrett

� 2005 International Association of Sedimentologists, Sedimentology, 52, 253–269

fw ¼ exp 5�213 kb=Abð Þ0�194�5�977� �

; Ab=kb > 1�7ð3Þ

where kb is bed roughness factor (initially equal to2Æ5 · mean grain diameter, and solved iterativelyusing bedform geometry predicted using theroutine of Li & Amos, 2001), and Ab is the orbitalexcursion amplitude of water particles near thebed as a wave passes overhead. Ab is given by theexpression:

Ab ¼ Um=ð2p=TÞ ð4Þ

Combining these parameters allows computationof bed shear stress at a given depth on the sea bed.This relationship is presumed to hold for time-

averaged bed shear stress, and is reflected in theproportion of mud that persists in sea-floorsediment at a given depth. The relationship canbe viewed in terms of a simple hydrodynamicmodel. Because sediment is typically consideredto remain in suspension when the critical shearvelocity (shear velocity, U*, in m sec)1, is relatedto shear stress by s ¼ U2

�q, where q is fluiddensity in kg m)3) for entrainment of a particle(U*) exceeds its settling velocity (W), each com-bination of wave climate and water depth will

have a threshold grain size below which allsediment remains in suspension. According totheory this threshold should be around 130 lm(Fig. 1A), with finer sediment having lower set-tling velocities so that once in suspension thesegrains will increasingly tend to remain there (e.g.Inman, 1949). Coarser grains, with their highersettling velocities, will be preferentially transpor-ted as bed load (although at very high shearvelocities such material may also be carried insuspension). This different response of differ-ently sized particles to shear stress leads to aneffective separation of material carried as bedload or near the bed in intermittent suspension,and suspended load, as long as sediment move-

τ

Fig. 1. Diagrams showing the boundary between sus-pended load and bed load in theory and practice.(A) Relationship between grain size and critical shearvelocity (stress) for movement of spherical quartzdensity particles in water at 20 �C, showing the theor-etical coarse limit for particle suspension (see text fordiscussion). The diagram shows that material finer than�130 lm (2Æ94/) should be preferentially transportedin suspension, whilst coarser material should betransported as bed load. Movement threshold is basedon the Yalin parameter of Miller et al. (1977, their fig.4), a Shield’s type function derived under unidirec-tional flow, but also applicable to oscillatory flow(Madsen & Grant, 1975). Settling velocities for glassspheres in seawater from Gibbs et al. (1971, their table6). (B) Log-probability cumulative size frequencycurves for selected water depths from a shore-normaltransect off the Manawatu coast (Fig. 2, line of Transect1, data from Perrett, 1990, appendix 1B). The ‘break’ orchange in slope (see text) shows that the size boundarybetween two subpopulations lies mostly between 72and 58 lm (3Æ8 and 4Æ1/) rather than > 130 lm as mightbe expected from Fig. 1A. The coarser population isthought to represent sediment transported along thebed or in intermittent suspension and the finer popu-lation is derived from material slowly settling fromsuspension. The boundary between the two popula-tions is approximated in this paper by the sand–mudboundary (62Æ5 lm or 4/).

Palaeobathymetry of wave-graded continental shelves 255


ment is dominated by non-cohesive behaviour.This is known to be the case for sand–mudmixtures recently deposited on the sea floor,which are initially non-cohesive because biotur-bation and wave disturbance act so as to preventdewatering and consolidation (Drake & Cac-chione, 1986).The log-probability plots of size data from

Transect 1 off the Manawatu coast show twocurve segments interpreted as grain subpopula-tions, the coarser population representing mate-rial transported primarily along, or close to, thebed in intermittent suspension, and the finerrepresenting material deposited from suspensionthroughout the water column. Although thebreak between these lies mostly between 3Æ8and 4Æ1/ (Fig. 1B), 4/ (62Æ5 lm), the sand–mudboundary has been chosen as a practical limit forseparating the two subpopulations, and per centmud as the parameter for estimating the propor-tion of suspended load accumulating in coastalwaters.

STUDY AREAS

Three coastal settings, two in New Zealand andone in California, are described below, along withthe Wanganui Basin inland from the Manawatucoast. The Wanganui Basin strata were sampledfor late Pliocene inner-shelf sediments to showhow the results of this study can be applied toancient sequences.

The Manawatu coast

The Manawatu coast (Fig. 2) lies on the westernside of the North Island of New Zealand, and isexposed to westerly winds and swells fromacross the Tasman Sea (Kibblewhite, 1982;Harris, 1990). The influence of the long period(> 7 sec) swell decreases to the south as thecoast becomes progressively more sheltered byFarewell Spit (Fig. 2A). Wave-rider buoys (Fig. 2)have provided data that show a decrease inaverage significant wave height from 2Æ4 m atthe Maui Oil Production Platform (Kibblewhite,1982) to 1Æ3 m at Wanganui (Macky et al., 1988).Further south, visual observations of the waveclimate at Peka Peka (summarized in Perrett,1990) suggest a further decrease in significantwave height to � 0Æ5 m, the value accepted herefor this transect location, the most southerly offive sampled. Mean wave period is 7 sec (Perrett,1990).

Along-shelf currents are known to move atvelocities up to 0Æ4 m sec)1, but the extent of theirinfluence is plainly subordinate to wave-inducedshear stress (Perrett, 1990). Diving observationsshow the sea floor to be covered, during fair-weather periods at least, by fields of shore-parallelripple marks to depths of around 35 m, indicatingthe predominant influence of wave-induced shearstress over long-shore currents at these depths.Figure 3 shows a schematic shore-normal pro-

file near the southern limit of the southernManawatu near-shore sediment prism (Perrett,1990), described in terms of the model of Elliott(1986). Coastal sediment charts and approxi-mately 200 line-km of 3Æ5 kHz seismic data(NIWA Ltd, Wellington, New Zealand) show thatsediment supplied to the coast by the six majorrivers forms a prograding prism that downlapsonto a post-last glacial maximum (LGM) sub-bottom reflector. This post-LGM sediment prismthins to the west, and pinches out between 7 and12 km from the coast. Examination of seismiclines 8 and 9, seaward of the Whanganui andWhangaehu Rivers (Fig. 2), shows no recogniz-able accumulation of Holocene sediment in thatregion. Instead, the sea floor truncates steeplydipping sub-bottom reflectors in places and ischaracterized by ridge-like features with only athin, discontinuous sediment cover. Coastal sedi-ment charts for areas north of the Rangitikei Riverand south of Kapiti Island also show the shelf isstarved of modern sediment (with the exceptionof a small delta at the Whanganui river mouth),resulting in widespread relic and palimpsestfacies (Carter, 1975; Lewis, 1979; Lewis & Mitch-ell, 1980; Gillespie & Nelson, 1996).

Wellington Harbour

Wellington Harbour, a roughly circular basin witha single entrance leading south to Cook Strait(Fig. 4), provides a low-energy environment forstudy. Sediment is supplied by the Hutt River,which enters the harbour from the north at theeastern end of Petone Beach. Swell waves enterthe harbour from Cook Strait, whilst local windwaves are generated within the harbour duringsoutherlies accounting for approximately 30% ofthe total wind record. There is little quantitativewave data for Wellington Harbour. Croad (1986)recorded 83 days worth of data from Seaview inthe winter of 1985 and found that the averagesignificant wave height during the period studiedwas � 0Æ2 m with zero crossing times from 2Æ5 to4 sec.



Monterey Bay

Monterey Bay is a coastal embayment that isexposed to the west along the central Californiacoast (Fig. 5). Chin (1984) and Chin et al. (1988)undertook a comprehensive sedimentological

study with uniboom seismic profiles showingprograding clinoforms within a lobate bulge ofHolocene sediments extending from the SalinasRiver mouth into the Bay. These sedimentsoverlie a regional unconformity thought to rep-resent the Pleistocene surface. Sea-floor samples

Fig. 2. Map of the Manawatu coast, New Zealand, with inset showing its location with respect to the North Island ofNew Zealand. The seaward extent of prograding Holocene sediment along the Manawatu coast is denoted by adashed line and its clinoform geometry illustrated by four representative seismically defined cross-sections (left sideof figure) (based on seismic data provided by NIWA Ltd). Beyond this zone and northward along the Wanganui coast,sea-floor sediment is relict or palimpsest in nature. The map also shows grab sample and wave-rider locations, andthe principal rivers supplying sediment to the coast. Their annual suspended sediment load is shown in brackets(from Griffiths & Glasby, 1985).



show per cent mud contours lie parallel to theshoreline, except for the extreme south of thestudy area, in the lee of Monterey Peninsula,where they shoal markedly. The 50% mudcontour typically occurs at water depths be-tween 40 and 50 m. Waves have been recordedat Marina (Fig. 5) by the US Army Corps ofEngineers and 5Æ5 years of these data are repor-

ted by Xu (1999). Average significant waveheight is 1Æ2 m, and mean peak wave period is11 sec.

Fig. 3. A schematic diagram of thedevelopment of a wave-graded shelfand the normal textural pattern ofsea-floor sediment off the Manawatucoast for transect 1 (see Fig. 2 forlocation). Adapted from Elliott(1986) with field and wave climateobservations from Perrett (1990).

Fig. 4. Map of Wellington Harbour, showing the loca-tion of Petone Beach and the grain size transects.Bathymetric contours are in 10 m increments.

Fig. 5. Map of Monterey Bay, California, a high-energywave-dominated coast, showing the location of thethree shore-normal transects of Chin (1984), and theirexposure to the swell from the Pacific Ocean. The filledtriangle indicates the location of the wave recorder (Xu,1999). Bathymetric contours are in 10 m increments.Contours for depths > 100 m are not shown.



METHODS

The Manawatu coast was sampled along fivenormal transects (Fig. 2) on the 24th and 26th ofJuly 2001 aboard the Victoria University of Wel-lington (VUW) research vessel Raukawa Challen-ger (see Supplementary material, Table S1). Atotal of 53 samples were collected at 5 m waterdepth intervals between 5 and 50 m water depth,as determined by the vessel’s echo sounder. Thetop 3–4 cm of material in the grab was scooped offusing a plastic mug and placed in a 500 ml plasticscrew top jar. As the samples were collected soonafter (1–2 days) a significant rainfall event inManawatu, some stratification was observed insamples recovered between 20 and 40 m belowsea-level (bsl). A thin (2–3 mm) layer of mud wasdraped over thicker (�5 mm) sandy layer in thisregion. In spite of the short amount of timefollowing the rain event, benthic organisms (inparticular tubeworms) were already beginning tobioturbate this material. In order to provide anestimate of the long-term average size distributionthis process is completed by vigorously homo-genizing the whole sample prior to analysis. Thebeach samples were collected separately whereTransects 1–4 intersected the coast from �40 mseaward of the high tide mark (i.e. from the lowershore face) on 10 August 2002.The Petone Beach transect was sampled by

divers in August and November of 1994 (Dunbaret al., 1997). A total of 51 samples was collectedand mixed, subsampled and processed in thesame way as the Manawatu samples.The Monterey Bay samples were collected from

three shore-normal transects with a Smith–McIn-tyre grab and analyses presented by Chin (1984).The Wanganui Basin samples were collected

from outcrops on the banks of the RangatikeiRiver using a hammer and plastic bag, fromsections measured with a Jacob’s staff throughcycle R6 (Naish & Kamp, 1997a). Samples from R3were provided by T. Naish.All VUW grain-size analyses were carried out

using sieves and a SediGraph (MicromeriticsInstrument Corp., Norcross, GA, USA). Consolid-ated (i.e. outcrop) samples were gently disaggre-gated by crushing between wooden blocks intoaggregates fine enough (typically < 2 mm) to befurther broken down by ultrasound. Between18 and 30 g (dry weight) of sample was thentreated with 27% H2O2 to remove organic matter.Abnormally large carbonate fragments were alsoremoved prior to analysis. The sample was thenwet-sieved at 63 lm into coarse and fine fractions,

and both fractions dried and weighed. The coarsefraction was then dry-sieved at 1/2/ intervals anda 1–2 g sub-sample of the fine fraction analysedby SediGraph 5100. As wet sieving invariablyretains some coarse silt, dry sieving was extendedto catch 4Æ5 and 5Æ0/ fractions. The weightsretained were then merged with the SediGraphresults.

RESULTS

Analytical results for 108 modern beach andsea-floor samples from the Manawatu coast andPetone foreshore are included in Sedimentology’selectronic archive (see Supplementary material,Table S2). Data are reported as frequency per centin 0Æ5/ intervals for the range )1 to 10/ (2000–1 lm) and the per cent finer than 10/. Folkgraphic statistics are used in describing thesediments in the following sections.

Manawatu Coast

Transects 1–4, off the Manawatu Coast, all showsimilar textural trends with increasing waterdepth (Fig. 6A). The beach face itself is charac-terized by very well-sorted fine sand [mean2Æ5–2Æ7/, standard deviation (s.d.) 0Æ27–0Æ39/]and < 0Æ3% mud, whereas between 5 and 20 mbsl sediment is well-sorted, unimodal, fine–veryfine sand (mean 3Æ0–3Æ4/, s.d. mostly 0Æ3–0Æ7/and mud content mostly from 3 to 10%). Modalsize shows little variation alongshore but a con-sistent decline offshore from the beach face.However, between 25 and 40 m bsl a rapid changein texture occurs. Although modal size remainsrelatively constant (2Æ5–3Æ5/) mean size decreasesfrom �3Æ3 to 5Æ5/, sorting becomes poorer (bybetween 1 and 2/) and per cent mud increasessignificantly to between 50 and 70%, resulting inpositively skewed frequency distributions. Fordepths below �40 m the sediment is a sandy mudwith an indistinct mode between 3Æ0 and 3Æ5/, amean size of between 5Æ2 and 7Æ6/, very poorsorting (2Æ4–4Æ5/) and a mud content between 60and 85%. Although the overall pattern of increas-ing mud with increasing water depth is the samefor each transect, the amount of mud is slightlylower for equivalent water depths in the moreexposed northerly transects 3 and 4.The northernmost transect (5), however, shows

textural changes for depths > 20 m that are verydifferent from the lines to the south (Fig. 6A).Here, the sea floor comprises moderately poorly



sorted sand with abundant shell fragments,notably disarticulated valves of the scallopPecten novozealandiae, which occur between20 and 34 m bsl. Examination under binocularmicroscope also shows that these samplescontain significant amounts of black, titano-magnetite sand. This sand records the southernextension of shore-parallel black sand ribbonsderived from the erosion of Mt Taranaki andesite,interpreted as relict features formed duringtransgression ca 9–12 ka, although the surfacesediment may still move a little during storms(Lewis, 1979).Size–frequency distributions of sea-floor sedi-

ments along Transect 1 have previously beendetermined by Perrett (1990), who collected sam-ples in the winter of 1988 and the late summerand winter of 1989, and found no measurableseasonal change in texture. Compared with thedata presented in this study differences are small,everywhere along this transect being < 12%, andtypically < 5% (Fig. 6A).

Wellington Harbour

Three sample collections (one in August andtwo in November, 1994) taken along the sametransect off Petone Beach, Wellington Harbour,show grain-size trends similar to those observedoff the Manawatu Coast, except that the shiftfrom sand to mud takes place at much shal-lower water depths – around 4 m bsl. In thislow-energy wave climate, the change from well-sorted fine sand in the lower beach face (mean2–2Æ5/; s.d. 0Æ2–0Æ4/) to a poorly sorted mud(mean 6–8/; s.d. 2Æ5–3Æ5/) occurs over a waterdepth of < 6 m. Data from these three samplesets show that this pattern has also remainedstable on a seasonal timescale (Fig. 6B).

Monterey Bay

For Monterey Bay, the higher-energy coast,samples from three transects were analysedby settling tube for the sand fraction and

Fig. 6. Per cent mud for shore-normal transects off three wave-dominated coasts of differing energy levels. (A) Fivetransects off the Manawatu coast, New Zealand (Fig. 2). Transects 1–4 were taken across an accreting near-shoresedimentary wedge and show increasing per cent mud with water depth. In contrast, transect 5 was taken from theedge of a region of net erosion with relic and palimpsest residual sediment, and the sediment remains coarse alongthe transect length. One sample (circled) does not fit the trend. (B) Transects off three coastlines with low-, moderate-and high-energy wave climates: (i) Wellington Harbour (Petone Beach). The original transect by Petone Wharf (Fig. 4)sampled in August 1993, was replicated in November 1994; (ii) Manawatu coast. The original transect off Peka Pekaand sampled in June, 1988, was replicated in March 1989, July 1989 (Perrett, 19990) and July 2001 (this paper);(iii) Monterey Bay. Data from three adjacent transects reported by Chin (1984), and located in Fig. 5. The profilesshow that the same textural pattern persists on time scales greater than 12 months (Wellington Harbour and Man-awatu coast) and spatial scales of tens of kilometres alongshore (Manawatu coast and Monterey Bay). Two samples(circled) do not fit the trend.



spectrophotometer for the mud fraction (Chin,1984). However the mud per cent values weredetermined directly by sieving, and hence aredirectly comparable with those analysed at VUWfrom the Manawatu coast. The same seaward-fining trend is evident, with a gradation fromwell-sorted fine sand nearshore to moderatelysorted very fine sandy mud at between 50 and50 m bsl and with mud exceeding 80% beyond70–80 m bsl (Fig. 6B).

Comparison between the three modern coastalsettings

Figure 7 provides a visual comparison ofthree sets of histograms representing transectsfrom moderate–high-, moderate- and low-energycoasts. The pattern of change in each set ofhistograms, from well-sorted beach sand toslightly sandy very poorly sorted offshore mud,along with an offshore decline in modal sandsize, is similar, and can be illustrated for all threeprofiles with the same lithological log (Fig. 7D).Figure 8 compares the bed shear stress based onaverage wave parameters for each of the threecoastal settings, showing how larger waves keepmud in suspension to greater water depths in apredictable fashion.

A simple sedimentation model for offshorefining of sediment texture

Results presented here and those of Perrett (1990)show that the textural profile off Peka Peka isstable between seasons, and on decadal timescales (Fig. 6A). The persistence of these trendsover time demonstrates a long-term equilibriumbetween sediment supply, bioturbation, waveenergy and water depth. Furthermore, observa-tions of the sea floor off the Manawatu coast, aswell as the grain-size results, allow it to bedivided into three broad zones:

1 a shallow-water high-energy zone where bedshear consistently exceeds the threshold oferosion for mud;

2 an intermediate moderate-energy zone wherethe mud erosion threshold is periodicallyexceeded; and

3 a deep-water low-energy zone, below the muderosion threshold, and dominated by muddeposition.

Grain-size analyses of shallow-water sedimentson each transect are well-sorted fine sand typicalof transportation along the bed and in intermit-tent suspension, whereas those in deep water aremud typical of deposition from suspension, with

Fig. 7. Histograms of transects from Monterey Bay (Trackline 13, A), Manawatu coast (Transect 1, B) and WellingtonHarbour (Transect 7a, C), showing the similarity in textural pattern, leading to the same conceptual lithologic log,despite their differences in the depth of the sand–mud transition. Depositional water depths in bold type. Note thatthe size frequency data from Monterey Bay were determined using a settling tube for sand and spectrophotometer formud (Chin, 1984), the latter underestimating clay percentage.



mixtures of these two size populations at inter-mediate depths (Fig. 9). Both mud and sand aredelivered to the coast by rivers, primarily at floodstage where the mud moves offshore in two ways:(i) it remains in suspension in the fresh (and thuslow density) river flood water that floats out overthe denser sea water; and (ii) it is maintained insuspension near the shore by wave action. Incontrast, sand settles out quickly nearshore, andis dispersed alongshore in the littoral zone, wherewave-induced bed shear is sufficiently high tosort and transport it. The resulting gradationalshore-normal textural profile from well-sortedsand to poorly sorted mud develops from mixing(by bioturbation) of these two populations. Thesize–frequency curves for individual samples aretherefore a reflection of the relative abundance ofeach population (e.g. Jago & Barusseau, 1981;Sheridan et al., 1987), which depends on thefrequency at which the critical shear stress for the

erosion of mud-sized material is exceeded and therate of biological mixing. This process providesan explanation for the continuous variation in theper cent mud (itself an approximation of accu-mulation from ‘suspended load’), from the beachface to offshore deep water, and a direct relation-ship between the per cent mud and water depthfor a particular wave climate. This relationship isquantified in the next section.

Quantifying the relationship between waveclimate and sediment texture

The textural data for transects 1–4 off the Mana-watu coast are translated to a per cent mud versusdepth curve by fitting a fourth-order polynomialcurve through a cross-plot (Fig. 10). As notedearlier, inspection of the data reveals slightly lowerper cent mud at similar water depths for Transects3 and 4 (see Supplementary material, Table S2),perhaps reflecting the slightly higher wave energyexpected for this section of the coast, but in theabsence of ameans of verifying differences inwaveenergy the data from all four transects have beenused. The following empirical equation relateswater depth to per cent mud:

D ¼� 0�00000303m4 þ 0�00073m3 � 0�0576m2

þ 2�173mþ 0�8265 ð5Þ

The 95% prediction band gives an uncertaintyof ±�10 m for this data set, consistent over thesampled depth range (Fig. 10). However fordepths beyond �60 m (�80% mud), where shearstresses are consistently low (and mud consis-tently high), all that can be estimated is theminimum water depth. Uncertainties related tovariations in wave climate and sediment supplyover time may potentially be estimated by com-puter modelling but this is not attempted here.

APPLICATION TO AN ANCIENTEXAMPLE: PLIOCENE CYCLES OF THEWANGANUI BASIN

The Wanganui Basin (Fig. 2) contains a 4 kmthick sequence of Plio-Pleistocene shallow mar-ine strata that is exposed to the north and east ofthe Manawatu coast. They were deposited in asetting and a climatic regime not too differentfrom today’s inner-shelf sediments, and provide atest for the concept and the model developed inprevious sections. The strata also record numer-ous eustatic sea-level changes in the form of

Fig. 8. Calculated values of bed shear stress derivedfrom average wave statistics of significant wave height(Hsig) and peak period (Tp) under a range of wave cli-mates (Petone data from Croad, 1986; Peka Peka datafrom Perrett, 1990; Monterey Bay data from Xu, 1999and Chin, 1984) according to the method of Li & Amos(2001). Values are calculated for discrete points andjoined by linear interpolation. The re-suspensionthreshold of sediment finer than 4/ (63 lm), theapproximate boundary between grain-size subpopula-tions, occurs at a bed shear stress of �0Æ08 N m)2.



lithologically and faunally defined shallow mar-ine sedimentary cycles of 41 and 100 kyr duration(Abbott & Carter, 1994; Abbott, 1997; Naish &Kamp, 1997a,b; Saul et al., 1999). The Rangitikei

River section within the Wanganui Basin con-tains �1100 m of Late Pliocene to Pleistocene(2Æ6–1Æ7 Ma) strata divided into 20 sedimentarycyclothems. These cycles correlate with marineisotope stages 58–99 (Naish & Kamp, 1997a),where fluctuations in d18O indicate sea-levelchanges within each cycle of approximately70 m. Published semi-quantitative estimates ofpalaeobathymetry for these strata are based on astatistical comparison between the depth associ-ations of extant foraminifera and their distribu-tion across the modern New Zealand continentalshelf (Naish, 1997; Naish & Kamp, 1997a,b). Thistreatment has yielded 13 water depth-relatedforaminiferal associations defining palaeo-shore-face, innermost shelf, inner-shelf, mid-shelf andouter-shelf environments.

Methods and results

The 49 outcrop samples collected from twosediment cycles within the Rangitikei Basin showsimilar patterns in stratigraphic section (Fig. 11)to those identifiable in the modern WanganuiBight (Fig. 7D). The base of each section is a thinlimestone bed that rests on the transgressivesurface of erosion, having been winnowed duringthe deposition of the transgressive systems tract

Fig. 9. Model to explain the relative abundance of sediment modes attributed to transport as (1) bed load/inter-mittently suspended load and (2) suspended load for shallow-, mid-depth- and deep-water samples. Grain-size datafrom Manawatu coast transect 1. Modal distributions and statistics were determined using the ‘SFT’ software fromhttp://www.ees1.lanl.gov/Wohletz/SFT.htm (procedure explained in Sheridan et al., 1987; Wohletz et al., 1989).

Fig. 10. Interpolated fourth-order polynomial curverelating per cent mud to water depth for samples fromtransects 1 to 4 off the Manawatu coast. The 95% pre-diction band (i.e. 95% of any additional data would beexpected to lie within this band) is also shown.



(TST) as sea-level rose from its lowstand position.Above this and forming the bulk of the cycle liesthe highstand systems tract (HST), which com-prises poorly sorted slightly sandy mud (morethan 90% mud, mean 5Æ5–8/; s.d. 2Æ1–4Æ0/). Thepattern for each cycle is not identical though. R6has a sandy interval from 24 to 36 m above thebase, with as little as 30% mud at 30 m. Such amid-highstand sandy interval is not evident inthe equivalent position in R3. The HST sandymud grades up over a few metres into well-sortedfine sand (mean 2Æ3–3Æ5/; s.d. 0Æ4–1Æ1/), whichforms the uppermost sediment of each cycle.

Interpretation

To interpret sediment texture in terms of waterdepth an assumption must be made about theprevailing wave climate at the time the sedimentswere deposited. For the cycles described here apalaeogeographical reconstruction of the regionby Lewis et al. (1994) shows the geographicalsetting to have been a broad south-west-facingembayment like that of today. Wave climate isalso assumed to be similar to that of today(Hsig ¼ 0Æ5 m, Tp ¼ 7 sec), based on similar pal-aeogeographical setting and the knowledge thatmost of the cycle was deposited in a highstand

(interglacial climate) setting. During glacial peri-ods, when global wind strengths are thought to behigher, this approach will probably underesti-mate depositional water depth. However itshould also be noted that Hesse & McTainsh(1999), on the basis of particle size analysis ofwind blown dust in the Tasman Sea, found noevidence that LGM westerly winds were anystronger than winds (and by implication, waveclimate) during the present interglacial period.Palaeobathymetry based on sediment texture,

and using modern Manawatu wave climate para-meters, has been calculated for cycles R3 and R6(marine isotope stages 96–94 at �2Æ43 Ma and 90–88 at �2Æ30 Ma respectively) in the RangitikeiRiver section of the Wanganui Basin (Naish &Kamp, 1997a; Fig. 12). The cycles include sedi-ments deposited in a continental shelf environ-ment throughout transgressive, highstand andregressive phases of eustatic sea-level. The trans-gressive phase of sea-level in both cycles istypically characterized by thin fossiliferousdeposits that have been interpreted as zones ofstratigraphic condensation (a situation compar-able with the modern northern Wanganui shelf,as seen in transect 5; Figs 2 and 6A). These reflectvery low terrigenous accumulation or erosion,and correspondingly higher carbonate productiv-

Fig. 11. Lithologic logs and histograms of Pliocene cycles from the Wanganui Basin, showing the similarity inpattern to modern shore-normal transects.



Fig. 12. Lithology and inferred palaeobathymetry of two Pliocene sediment cycles from the Rangitikei River,Wanganui Basin, New Zealand (Naish & Kamp, 1997a). The textural estimates of palaeobathymetry were madeassuming sediments were deposited in a wave climate like that experienced off the present-day Manawatu Coast.Palaeobathymetry based on foraminifera are shown for comparison.



ity (Naish & Kamp, 1997a), and because of thistheir sediment texture may not be in equilibriumwith wave climate.Sediments above this are characterized by

massive, sparsely fossiliferous, siltstones andmudstones deposited in the highstand phase.These have inferred water depths of more than50 m, apart from a significant shallowing between24 and 36 m in R6. These are followed byregressive sediments, typically moderate to well-sorted sands, inferred to have been deposited indepths of < 10 m. Interestingly, regressive sandsand highstand muds are separated by a prominentregressive surface of erosion (RSE), an intra-sequence surface formed by wave erosion ofunderlying sediments in response to a rapidlowering of sea-level implying a sharp dislocationof facies from silty inner-shelf depths to a shore-face environment (Hunt & Tucker, 1992; Num-medal et al., 1993; Naish & Kamp, 1997a; Fig. 9).Comparison of the foraminiferal palaeodepth

estimates (Naish, 1997; Naish & Kamp, 1997a;Figs 12 and 13) and grain-size estimates show theyproduce similar results, with an overall pattern ofdecreasing water depth up cycle, including anabrupt shallowing associated with the RSE. Themost notable difference between the two is the�50 m shallowing centred on a point 30 m abovethe base of cycle R6, which is not clearly recog-nized from the foraminiferal data, and an inabilityto resolve depths where the percentage of mudexceeds �80% (i.e. outer-shelf depths).

Independent estimates of glacioeustatic sea-level change can be made by comparing theglacial and interglacial vales of d18O from for-aminifera collected from equatorial or deep oceanregions where the effects of temperature changeson isotopic fractionation are minimized (Chap-pell & Shackleton, 1986; Shackleton, 1987). Whileseveral additional factors (vital and salinityeffects) can influence the relationship betweend18O and sea-level, an accepted approximation is�0Æ1& per 10 m of sea-level change (Chappellet al., 1996). On this basis, the eustatic sea-levelrange for cycles R3 and R6 would be 50 and 70 m(0Æ5 and 0Æ7& respectively), similar to the esti-mates made from grain size and foraminifera.Within cycle 3, a muddy interval 35–36Æ5 m

above the base lying between inferred shallowwater sediments, could be interpreted as repre-senting a 20–30 m increase in relative sea-level,but the context indicates fine-grained sedimenta-tion in a sheltered tidal mud flat environment. Noforaminifer data were available for this interval.This feature illustrates the importance of recog-nizing that the model can only be valid wherewave climate can be reliably estimated, or at leastpresumed to be constant (for gauging relative sea-level change).

DISCUSSION

The formulations that underpin the model pre-sented here form the basis of many ‘shelf-scale’sediment transport algorithms (e.g. Harris & Cole-man, 1998; Orpin et al., 1999; Li & Amos, 2001)and represent a simple way of relating modernfacies to those observed in the rock record. Whilstrecognizing that they do not represent the fullcurrent state of knowledge on sediment transportdynamics, especially in the nearshore and shore-face zones, the model proposed here appearsmore realistic than, for example, the widely citedSwift and Thorne model (Swift et al., 1972; Swift& Thorne, 1991). Swift and Thorne invoke a‘progressive sorting’ mechanism (a Markov chainprocess), whereby a single population of grains isprogressively worked and reworked across thecontinental shelf, leading to a decrease in meansize and to better sorting with distance fromshore. However in the coastal settings reportedhere, mean size decreases and sorting becomespoorer as the proportion of mud increases, apredictable outcome of the mixing of two sub-populations, but inconsistent with the Swift andThorne model.

Fig. 13. Scatter plot of palaeowater depth estimatedusing foraminiferal biofacies ranges and per cent mud.The data are from cycles R3 and R6 (Fig. 12) wheregrain size and foraminiferal assemblages were meas-ured at the same, or similar (with two vertical metres),stratigraphic depth.



Deviations from the landward-coarsening tex-tural pattern described here may occur wheresediment supply is extremely low and sea-floorsediment contains relict material or has becomepalimpsest, reflecting sedimentation during pre-vious lower stands of sea-level. Much of themodern continental shelf around New Zealandfalls into this category (Carter, 1975) and suchsediments can be recognized in the rock record as‘condensed sections’, typically containing relat-ively high proportions of biogenic carbonate andoutsized clasts. At the other extreme, in areas ofextremely high sediment input, wave power maybe insufficient to completely rework sedimentinto an equilibrium textural profile (e.g. McCave,1971; Nittrouer & Sternberg, 1981; Drake &Cacchione, 1985). Further complications mayarise where non-oscillatory currents (rip currents,tidally forced longshore currents) are a significantsource of bed shear stress, and these are not takeninto account in the model presented here. How-ever, the key question for the geological commu-nity is what is the preservation potential for thesesituations compared with those described, forexample, by Pickrill (1983) in his review of wave-built shelves on low-energy coasts where heconcludes ‘The profile form, shelf sedimentsand nearshore dissipation of wave energy suggestthat the shelf evolves as an equilibrium form inresponse to contemporary wave processes’.The geological record does include many thick

sequences of continental shelf strata, and for overtwo decades sequence stratigraphic analysis hasmade use of both glacioeustatic and tectonicallyinduced variations in past sea-level to explainlithologic changes within these records. Indeed,the case for a strong relationship between litho-logy and eustatic sea-level has been confirmed ata sequence level for Plio-Pleistocene stratathrough correlation with the marine oxygen iso-tope curve (Abbott & Carter, 1994; Kitamura et al.,1994; Naish & Kamp, 1997a). The model proposedhere allows sea-level variations recorded by thesestrata to be estimated through individual se-quences in relative terms, and in numerical termsalso, where wave climate can be estimated frompresent-day patterns or from wind fields takenfrom regional palaeoclimate models.

ACKNOWLEDGEMENTS

This research was funded through a New ZealandFoundation for Research, Science and Technology(FRST) post-doctoral fellowship to G. B. Dunbar.

Initial research on this topic was undertaken in1989/90 by T. Perrett with financial support fromthe Victoria University of Wellington InternalResearch Committee, and technical assistancefrom Alex Pyne. PJB also thanks the GEOL 202/221 class for keeping the topic alive each year sincePerrett’s work through discussions of a classexercise on this topic.We thankRobertWilliamsonfor his assistance in collecting samples from theManawatu coast, Scott Nodder and Geoffroy Lam-arche at the National Institute of Water and Atmo-sphericResearchLtd (NIWA)providedaccess to anextensive collection of unpublished seismic data.We also thankMikeMillar formaking available theresults of his BSc Hons project on Rangitikei RiverCycle 6, and for his technical assistance in carryingout the grain-size analyses for the modern Wanga-nui Bight sediments. Tim Naish provided samplematerial from Rangitikei River Cycle 3. Thismanuscript has benefited from numerous discus-sions with colleagues, especially Alan Orpin(NIWA), Tim Naish (GNS) and reviews by PaulKomar and an anonymous reviewer.

SUPPLEMENTARY MATERIAL

The following material is available from http://www.blackwellpublishing.com/products/journals/suppmat/SED/SED695/SED695sm.htm.Table S1. Sample locations off the Manawatucoast.Table S2. Grain-size frequency data and statistics(Manawatu transects T1–T5 and Petone transects7–9).

REFERENCES

Abbott, S.T. (1997) Foraminiferal paleobathymetry and mid-

cycle architecture of mid-Pleistocene depositional

sequences, Wanganui Basin, New Zealand. Palaios, 12,267–281.

Abbott, S.T. and Carter, R.M. (1994) The sequence architec-

ture of mid-Pleistocene (0.35–0.95 Ma) cyclothems from

New Zealand: facies development during a period of orbital

control on sea-level cyclicity. In: Orbital Forcing and Cyclic

sequences (Eds P.L. de Boer and D.G. Smith). Int. Assoc.

Sedimentol. Spec. Publ., 19, 367–394.Carter, L. (1975) Sedimentation on the continental terrace

around New Zealand: a review. Mar. Geol., 19, 209–237.Chappell, J. and Shackleton, N.J. (1986) Oxygen isotopes and

sea level. Nature, 324, 137–140.Chappell, J., Pandolfi, J., Ota, Y., Pillans, B., Omura, A., Esat,

T. and McCulloch, M. (1996) Reconciliation of late Qua-

ternary sea levels derived from coral terraces at Huon Pen-

insula with deep sea oxygen isotope records. Earth Planet.

Sci. Lett., 141, 227–236.



Chin, J.L. (1984) Late Quaternary Coastal Sedimentation

and Depositional History, South Central Monterey Bay,

California. Unpubl. MSc thesis, San Jose State University

Library, 164 pp.

Chin, J.L., Clifton, H.E. and Mullins, H.T. (1988) Seismic

stratigraphy and late Quaternary shelf history, south-central

Monterey Bay, California. Mar. Geol., 81, 137–157.Clifton, H.E. (1986) Interpreting paleoenergy levels

from sediment deposited on ancient wave dominated

shelves. In: Shelf Sands and Sandstones (Eds R.J. Knight

and J.R. McLean). Can. Soc. Petrol. Geol. Mem., II, 181–

190.

Clifton, H.E. (1988) Sedimentologic approaches to paleobath-

ymetry, with applications to the Merced formation of cen-

tral California. Palaios, 3, 507–522.Croad, R.N. (1986) Lowry Bay Marina, Port Nicholson. Part 1.

Wave Measurements. Ministry of Works and Development

Report M3.86/5.

Drake, D.E. and Cacchione, D.A. (1985) Seasonal variation in

sediment transport on the Russian River shelf. Cont. Shelf

Res., 4, 495–514.Drake, D.E. and Cacchione, D.A. (1986) Field observations of

bed shear stress and sediment resuspension on continental

shelves, Alaska and California. Cont. Shelf Res., 6, 415–

429.

Dunbar, G.B., Barrett, P.J., Goff, J.R., Harper, M.A and Irwin,S.L. (1997) Estimating vertical tectonic movement using

sediment texture. Holocene, 7, 213–221.Elliott, T. (1986) Siliciclastic shorelines. In: Sedimentary

Environments and Facies, 2nd edn (Ed. H.G. Reading),

pp. 155–188. Blackwell Scientific, Oxford.

Gibbs, R.J., Matthews, M.D. and Link, D.A. (1971) The rela-

tionship between sphere size and settling velocity. J. Sedim.Petrol., 41, 7–18.

Gillespie, J.L. and Nelson, C.S. (1996) Distribution and control

of mixed terrigenous-carbonate surficial sediment facies,

Wanganui Shelf, New Zealand. NZ J. Geol. Geophys., 39,533–549.

Griffiths, G.A. and Glasby, G.P. (1985) Input of river-derivedsediment to the New Zealand Continental shelf: I. Mass.

Estuar. Coast. Shelf Sci., 21, 773–787.Harris, T.F.W. (1990) Greater Cook Strait: Form and Flow.

D.S.I.R. Marine and Freshwater (N.Z.), Wellington, 212 pp.

Harris, P.T. and Coleman, R. (1998) Estimating global shelf

sediment mobility due to swell waves.Mar. Geol., 150, 171–177.

Hesse, P.P. and McTainsh, G.H. (1999) Last glacial maximum

to early Holocene wind strength in the mid-latitudes of the

Southern Hemisphere from aeolian Dust in the Tasman Sea.

Quatern. Res., 52, 343–349.Hunt, D. and Tucker, M.E. (1992) Stranded parasequences and

the forced regressive wedge systems tract: deposition during

base level fall. Sedim. Geol., 81, 1–9.Inman, D.L. (1949) Sorting of sediments in the light of fluid

mechanics. J. Sedim. Petrol., 19, 51–70.Jago, C.F. and Barusseau, J.P. (1981) Sediment entrainment on

a wave-graded shelf, Roussillon, France. Mar. Geol., 42,279–299.

Johnson, D.W. (1919) Shore Processes and Shoreline Devel-opment. Wiley, New York, NY, pp. 405–493.

Kibblewhite, A.C. (1982) Ocean wave properties. In: Maui

Development Environmental Study. Report on Phase Two

1977–1982 (Eds A.C. Kibblewhite, P.R. Bergquist, B.A.

Foster, M.R. Gregory and M.C. Miller), pp. 25–48. BP Shell

Todd Oil Services Ltd, Woolmore.

Kitamura, A., Kondo, Y., Sakai, H. and Horii, M. (1994) Cyclicchanges in lithofacies and molluscan content in the early

Pleistocene Omma Formation, central Japan related to the

41 000-yr orbital obliquity. Palaeogeogr. Palaeoclimatol.Palaeoecol., 112, 345–361.

Leeder, M. (1999) Sedimentology and Sedimentary Basins:

From Turbulence to Tectonics. Blackwell Science Ltd,

Oxford, 592 pp.

Lewis, K.B. (1979) A storm-dominated inner shelf, Western

Cook Strait, New Zealand. Mar. Geol., 31, 31–43.Lewis, K.B. and Mitchell, J.S. (1980) Cook Strait Sediments.

N.Z. Oceanogr. Inst. Chart, Coastal Series, 1:200000.

Lewis, K.B., Carter, L. and Davey, F.J. (1994) The opening of

Cook Strait: interglacial tidal scour and aligning basins at a

subduction to transform plate edge. Mar. Geol., 116, 293–312.

Li, M.Z. and Amos, C.L. (2001) SEDTRANS96: the upgraded

and better calibrated sediment-transport model for contin-

ental-shelves. Comp. Geosci., 27, 619–645.Macky, G.H., Cumming, R.J. and Valentine, E.M. (1988)

Measurements of Ocean Wave Climate at Wanganui and

Himatangi Beach. D.S.I.R. Hydrology Centre, Christchurch,

Report No. CR 88.26.

Madsen, O.S. and Grant, W.D. (1975) The threshold of sedi-

ment movement under oscillatory waves: a discussion.

J. Sedim. Petrol., 45, 360–361.McCave, I.N. (1971) Wave effectiveness at the sea bed. J. Se-

dim. Petrol., 41, 89–96.McIntyre, A.P. and Kamp, P.J.J. (1998) Late Pliocene (2.8–

2.4 Ma) cyclothemic shelf deposits, Parikino, Wanganui

Basin, New Zealand: lithostratigraphy and correlation of

cycles. NZ J. Geol. Geophys., 41, 69–84.Miller, M.C., McCave, I.N. and Komar, P.D. (1977) Threshold

of sediment motion under unidirectional currents. Sedi-

mentology, 24, 507–527.Naish, T. (1997) Constraints on the amplitude of late Pliocene

eustatic sea-level fluctuations: new evidence from the New

Zealand shallow-marine sediment record. Geology, 25,1139–1142.

Naish, T. and Kamp, P.J.J. (1997a) Sequence stratigraphy of

sixth-order (41 k.y.) Pliocene-Pleistocene cyclotherms,

Wanganui basin, New Zealand: a case for the regressive

systems tract. Geol. Soc. Am. Bull., 109, 978–999.Naish, T. and Kamp, P.J.J. (1997b) Foraminiferal depth

palaeoecology of late Pliocene shelf sequences and systems

tracts, Wanganui Basin, New Zealand. Sedim. Geol., 110,237–255.

Nittrouer, C.A. and Sternberg, R.W. (1981) The formation

of sedimentary strata in an allochthnous shelf environ-

ment: the Washington continental shelf. Mar. Geol., 42,201–232.

Nummedal, D., Riley, G.W. and Templet, P.L. (1993) High-

resolution sequence architecture: a chronostratigraphic

model based on equilibrium profile studies. In: Sequence

Stratigraphy and Facies Associations (Eds H. Posamentier,

C.P. Summerhayes, B.U. Haq and C.P. Allen). Int. Assoc.Sedimentol. Spec. Publ., 18, 55–68.

Orpin, A.R., Ridd, P.V. and Stewart, L.K. (1999) Assessment

of the relative importance of major sediment transport

mechanisms in the central Great Barrier Reef lagoon. Aust. J.

Earth Sci., 46, 883–896.Perrett, T.L. (1990) Variations in Sediment Texture and Biota

Off a Wave-dominated Coast, Peka Peka, New Zealand.Unpubl. MSc thesis, Victoria University of Wellington, 135

pp.



Pickrill, R.A. (1983) Wave-built shelves on some low-energy

coasts. Mar. Geol., 51, 193–216.Pickrill, R.A. and Currie, R.G. (1983) Computer programs to

estimate wave generated orbital velocities and threshold

erosion velocities. Curr. Res. A Geol. Survey Can., 83-1A,253–261.

Saul, G., Naish, T.R., Abbott, S.T. and Carter, R.M. (1999)

Sedimentary cyclicity in the marine Pliocene-Pleistocene of

the Wanganui basin (New Zealand): sequence stratigraphic

motifs characteristic of the past 2.5 M.y. Geol. Soc. Amer.

Bull., 111, 524–537.Shackleton, N.J. (1987) Oxygen isotopes, ice volume and sea

level. Quatern. Sci. Rev., 6, 183–190.Sheridan, M.F., Wohletz, K.H. and Dehn, J. (1987) Discrim-

ination of grain-size subpopulations in pyroclastic flows.

Geology, 15, 367–370.Swift, D.J.P. and Thorne, J.A. (1991) Sedimentation on con-

tinental margins, I: a general model for shelf sedimentation.

In: Shelf Sand and Sandstone Bodies: Geometry, Facies,

and Sequence Stratigraphy (Eds D.J.P. Swift, G.F. Oertel,

R.W. Tillman and J.A. Thorne). Int. Assoc. Sedimentol.

Spec. Publ., 14, 3–31.Swift, D.J.P., Ludwick, J.C. and Boehmer, W.R. (1972) Shelf

sediment transport, a probability model. In: Shelf Sediment

Transport: Process and Pattern (Eds D.J.P. Swift, D.P. Duane

and O.H. Pilkey), pp. 195–223. Dowden Hutchinson and

Ross, Strousburg, PA.

Wohletz, K.H., Sheridan, M.F. and Brown, W.K. (1989) Par-ticle size distributions and the sequential fragmentation/

transport theory applied to volcanic ash. J. Geophys. Res.,94, B11, 15, 703–715, 721.

Xu, J.P. (1999) Local wave climate and long-term bed shear

stress characteristics in Monterey Bay, CA. Mar. Geol., 159,341–353.

Manuscript received 10 March 2004;revision accepted 8 November 2004



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