Stacked ﬂuvial and tide-dominated estuarine deposits in ... · Fig. 1. Spitsbergen archipelago is situated in Norwegian Arctic (A). Location of Eocene Central Basin of Spitsbergen,

Stacked fluvial and tide-dominated estuarine deposits in high-frequency (fourth-order) sequences of the Eocene Central Basin,Spitsbergen

PIRET PLINK-BJORKLUNDGoteborg Dynamic Stratigraphy Group, Department of Earth Sciences: Geology, Goteborg University, Box460, SE-405 30 Gothenburg, Sweden (E-mail: [email protected])

ABSTRACT

Eighteen coastal-plain depositional sequences that can be correlated to

shallow- to deep-water clinoforms in the Eocene Central Basin of

Spitsbergen were studied in 1 · 15 km scale mountainside exposures. The

overall mud-prone (>300 m thick) coastal-plain succession is divided by

prominent fluvial erosion surfaces into vertically stacked depositional

sequences, 7–44 m thick. The erosion surfaces are overlain by fluvial

conglomerates and coarse-grained sandstones. The fluvial deposits show

tidal influence at their seaward ends. The fluvial deposits pass upwards into

macrotidal tide-dominated estuarine deposits, with coarse-grained river-

dominated facies followed further seawards by high- and low-sinuosity tidal

channels, upper-flow-regime tidal flats, and tidal sand bar facies associations.

Laterally, marginal sandy to muddy tidal flat and marsh deposits occur. The

fluvial/estuarine sequences are interpreted as having accumulated as a series

of incised valley fills because: (i) the basal fluvial erosion surfaces, with at least

16 m of local erosional relief, are regional incisions; (ii) the basal fluvial

deposits exhibit a significant basinward facies shift; (iii) the regional erosion

surfaces can be correlated with rooted horizons in the interfluve areas; and (iv)

the estuarine deposits onlap the valley walls in a landward direction. The

coastal-plain deposits represent the topset to clinoforms that formed during

progradational infilling of the Eocene Central Basin. Despite large-scale

progradation, the sequences are volumetrically dominated by lowstand

fluvial deposits and especially by transgressive estuarine deposits. The

transgressive deposits are overlain by highstand units in only about 30% of

the sequences. The depositional system remained an estuary even during

highstand conditions, as evidenced by the continued bedload convergence in

the inner-estuarine tidal channels.

Keywords Coastal plain, estuarine, fluvial, incised valleys, sediment parti-tioning, tide-dominated.

INTRODUCTION

The Aspelintoppen Formation in the EoceneCentral Basin of Spitsbergen consists of alternat-ing fluvial and estuarine deposits that can be‘walked out’ downdip into coeval shallow- todeep-marine sequences (Fig. 1) of the BattfjelletFormation. The coastal-plain succession is con-tinuously exposed in 500 · 5000 m scale mount-ainside exposures (Fig. 2) that are oriented

approximately parallel to the depositional dip.The exposures thus provide excellent constraintson downdip facies transitions as well as thevertical stacking of the fluvial/estuarine deposi-tional sequences. There are relatively few placeswhere the relationships between marine andalluvial/coastal plain depositional systems canbe examined in continuous exposures likethis (Shanley & McCabe, 1991, 1993, 1994, 1995;Shanley et al., 1992; Hettinger et al., 1993;

Sedimentology (2005) 52, 391–428 doi: 10.1111/j.1365-3091.2005.00703.x

� 2005 International Association of Sedimentologists 391

Legaretta et al., 1993; Wright & Marriott, 1993;Gibling & Bird, 1994; Gibling & Wightman, 1994;Aitken & Flint, 1995 and Olsen et al., 1995; Plintet al., 2001).

Unlike most of the existing sequence strati-graphic models for coastal-plain successions (e.g.Shanley & McCabe, 1991, 1993; Olsen et al.,1995), the Aspelintoppen Formation of the Eo-cene Central Basin preserves mainly stackedlowstand fluvial and transgressive estuarinedeposits. In contrast to current estuarine orvalley-fill models of Zaitlin et al. (1994), or mostof the coastal-plain models (Shanley & McCabe,1993; Olsen et al., 1995), little or no sedimentaccumulated on the coastal plain during high-stands of sea-level (see also Plint et al., 2001)despite the overall progradational character of the

succession. Estuaries have been generally consid-ered to typify transgressive coastlines (e.g. Boydet al., 1992), and estuaries that occupy drownedvalleys are extremely common along moderntransgressive coasts (Dalrymple et al., 1992).However, the Spitsbergen database discussedbelow shows that estuaries can persist evenduring the (early) highstand (see also Allen &Posamentier, 1993).

Estuaries are defined in this paper according toDalrymple et al. (1992) as ‘a seaward portion of adrowned valley system which receives sedimentfrom both fluvial and marine sources and whichcontains facies influenced by tide, wave andfluvial processes’. The estuaries documented inthe Eocene Central Basin are interpreted as tide-dominated macrotidal estuaries. Despite the

Fig. 1. Spitsbergen archipelago is situated in Norwegian Arctic (A). Location of Eocene Central Basin of Spitsbergen,east of West Spitsbergen Orogenic Belt (B). The basin was infilled with south-eastward-migrating clinothems (C andD). The broken lines represent the shelf-edge position of individual clinothems and the arrows show the generalsediment supply direction and clinoform migration path (C). Coastal-plain sequences on Brogniartfjellet are coevalwith shallow- to deep-marine clinothems on Storvola, and coastal-plain sequences on Storvola with shallow- todeep-marine clinothems on Hyrnestabben (D and E).

392 P. Plink-Bjorklund

� 2005 International Association of Sedimentologists, Sedimentology, 52, 391–428

abundance of modern macrotidal estuaries andthe high preservation potential of estuarinedeposits (Demarest & Kraft, 1987; Dalrympleet al., 1992), ancient examples are still rare (e.g.Clifton, 1982; Galloway & Hobday, 1983). Studiesof modern macrotidal estuaries (Amos & Long,1980; Lambiase, 1980a,b; Bartsch-Winkler &Ovenshine, 1984; Amos & Zaitlin, 1985; Harris& Collins, 1985; Allen & Rae, 1988; Bartsch-Winkler, 1988; Woodroffe et al., 1989, 1993;Dalrymple et al., 1990) show them to be highlyefficient sediment traps, with landward transportof large volumes of sediment. The presence of netlandward movement of sediment from outside ofthe estuary mouth (averaged over a period ofseveral years) is one of the primary features thatdistinguish estuaries from delta distributarieswhere the net transport is seaward.

The main aims of this paper are: (i) to describethe facies and stratal architecture of the coastal-

plain fluvial and tidal estuarine deposits in theEocene Central Basin of Spitsbergen; (ii) to dem-onstrate that the fluvial/estuarine sequences weredeposited in incised valleys, and the coastal-plain succession was formed by a series ofvertically stacked incised valley fills; and (iii) toshow that lowstand, and especially transgressivedeposits volumetrically dominate the fourthorder (ca 100 000–300 000 years) coastal-plainsequences in this basin.

GEOLOGICAL SETTING

During the Tertiary, Spitsbergen was situatedalong a transform fault margin (the HornsundFault Zone) separating the North American andEurasian plates as the Lomonosov Ridge and theNorwegian-Greenland Sea rift began to open(Steel et al., 1981; Steel & Worsley, 1984; Steel

Fig. 2. Seismic-scale coastal plain, shelf and slope clinoforms on (A) Storvola and (B) Brogniartfjellet. Themountainside exposure on Storvola is ca 5 km long, and on Brogniartfjellt ca 6 km long. Both exposures are north-west–south-east oriented.

Stacked fluvial and tide-dominated estuarine deposits in high-frequency sequences 393


et al., 1985; Teyssier et al., 1995; Braathen et al.,1999). Transpression in the Palaeocene to Eoceneformed the West Spitsbergen Orogenic Belt withareas of basement uplift, and folding and thrust-ing along a NNW–SSE trending zone (Fig. 1).Regional flexural subsidence produced by loadingfrom the orogenic belt formed the Central TertiaryBasin (Braathen et al., 1999). This basin was aforeland basin during the initial period of activethrusting, but became a piggy-back basin (Blythe& Kleinspehn, 1998) on account of forelandpropagation of thrusting. The Lomfjorden andBillefjorden fault zones east of the Central Basinprobably represent late stage reactivation of deep-seated reverse faults (Braathen et al., 1999).

The Eocene Central Basin was asymmetricallyinfilled by rivers draining a rising and eastward-migrating Western Spitsbergen fold-and-thrustbelt (Harland, 1969; Eldholm et al., 1984). Theeastward and south-eastward migration of thebasin depocentre, driven by tectonic loading,created an asymmetric sedimentary succession(Helland-Hansen, 1990) that is more than 1Æ5 kmthick in the west, thinning to <600 m in the east.The basin is one of the few basins in the worldthat preserves shallow to deepwater clinoforms ata seismic scale in large mountainside exposures(Kellogg, 1975; Helland-Hansen, 1992). The clino-forms, and their equivalent ‘rock units’ referred toas clinothems (Rich, 1951) reflect the outgrowthof the basin margin driven by sediment supplyfrom the fold-and-thrust belt to the west (Fig. 1).Each clinoform surface is a time line and repre-sents the morphologic profile extending from thecoastal plain to the marine shelf and down intothe deeper water slope and basin-floor environ-ments. The term ‘clinoform’ is used here in abroader sense than first defined by Rich (1951),i.e. for the entire length of the time line. Thetopset of the clinoforms (coastal-plain facies belt)belongs to the Aspelintoppen Formation, and theforeset and bottomset (shelf, slope and basin-floorfacies belts) to the Battfjellet Formation (Fig. 3).The Battfjellet clinoforms sharply overlie theGilsonryggen Member shales (Fig. 3). The char-acteristics of some of these clinoforms have beendiscussed by Steel et al. (2000), a classification ofclinoform types was outlined by Mellere et al.(2002), and characteristics of some shelf-margindelta types documented by Plink-Bjorklund &Steel (2005). The slope reaches of the clinoformshave been discussed in Plink-Bjorklund et al.(2001) and Plink-Bjorklund & Steel (2002), andinitiation of turbidites by river effluent in Plink-Bjorklund & Steel (2004).

The Aspelintoppen Formation thus constitutesthe continental counterpart of a thick overallregressive shelf, slope and basin-floor succession(Kellogg, 1975; Steel et al., 1981; Steel & Worsley,1984; Steel et al., 1985). It is >500 m thick inplaces, has an abrupt and/or interfingering rela-tionship with the shelf, slope and basin-floorparts of the clinoforms belonging to the BattfjelletFormation. The Aspelintoppen Formation is gen-erally aggradational and mud-prone, with a sand/mud ratio of ca 0Æ25. It comprises fresh/brackish-water shales, alternating with non-marine andmarine brackish-water sandstones, coals and silt-stones (Steel et al., 1981).

FACIES ASSOCIATIONS

The sedimentology of the Aspelintoppen For-mation coastal-plain deposits was documentedon two mountainsides, Brogniartfjellet andStorvola, along northern shores of Van Keulenf-jorden (Fig. 1). The mountainsides have anorthwest to southeast orientation, and providea roughly dip-orientated section. Each of the

Fig. 3. Palaeocene and Eocene stratigraphy in TertiaryCentral Basin of Spitsbergen (Steel et al., 1985).



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Fig. 5. A representative measured section through fluvial deposits of FA 1, and palaeocurrent measurements derivedfrom cross-strata. Numbers by the measured section refer to facies (see Table 1). (A) Channel fills commonly havemultiple erosion surfaces (dashed lines). (B and E) Coarse-grained, cross-stratified sandstones erosionally overlievery-fine-grained muddy tidal sandstones. Fluvial channels are typically filled with (C) cross-stratified coarse- tomedium-grained sandstones and conglomerates rich in lithic fragments (D). Coal fragments are common (F). Low-angle-cross-stratification occurs in places (G) and soft-sediment deformation is common (H). Coal horizons (I) andplant roots (J) are common at the top of channel-fill units.



Fig. 6. Measured sections and palaeocurrent measurements from a fluvial channel fill, ‘walked out’ in a dip-parallelsection on Brogniartfjellet. Dashed lines identify erosion surfaces.

Fig. 7. Fluvial channel fills can be ‘walked out’ into coeval tidally influenced deposits further seawards (southeast).Example from Storvola.



mountainsides exposes coastal-plain deposits inupper parts of the mountains (Fig. 2). Thecoastal-plain deposits on Brogniartfjellet are

time-equivalent to shelf and slope deposits onStorvola, and coastal-plain deposits on Storvolahave their contemporary shelf succession on the

Fig. 8. A representative measured section through tidally influenced fluvial deposits of FA 2. Numbers by themeasured section refer to facies (see Table 1). Tidal influence is marked by subordinate landward-oriented palaeo-current directions. The medium- to fine-grained sandstones contain bimodal cross-strata (A), a variety of high- andlow-angle compound cross-strata (B and E). Tidally influenced fluvial deposits occur as channel-fill units and havemultiple erosion surfaces (dashed lines in C). Sigmoidal cross-strata or mud drapes are rare (D). Coal horizons (F) arerather common at the top of channel-fill unit.



next mountain to the southeast, Hyrnestabben(Fig. 1D and E).

Viewed from a distance, the coastal-plain faciesbelt on Brogniartfjellet and Storvola is aggrada-tional and mud-prone, although the whole basininfill progrades to the south-east/east (Fig. 1). Theonly obvious stratigraphic markers are thin sand-prone, erosionally based levels that can be‘walked out’ in a downdip direction across thecoastal-plain facies belt (Fig. 4).

Sedimentary facies were studied by usingmeasured vertical sections, ‘walking out’ strati-graphic levels downdip, and interpretation ofphotomosaics taken from a helicopter. The docu-mented sedimentary facies are grouped into sevenfacies associations based on textures, sedimentarystructures, geometry, palaeocurrent indicators,lateral facies transitions and position of the facieson the dip-orientated transect. The individualsedimentary facies are summarized in Table 1,and Figs 5–19.

Facies Association 1: fluvial deposits

Facies Association (FA) 1 consists of lenticularsandbodies that are 2–16 m thick and that can betraced for up to 6–7 km across the NW–SE-oriented mountainside outcrops (Fig. 4). Thesandbodies are dominated by granule conglomer-ates and coarse-grained sandstones (Fig. 5C, D).These lenticular sandbodies typically have mul-tiple basal and internal erosion surfaces, and theamount of downcutting is in most cases equal tothe thickness of the sandbody itself, i.e. 2–16 m(Figs 5A,B and 6). The sandbodies are volumet-rically dominated by trough-cross-stratified,coarse-grained, lithic sandstones (Facies 3), andin most places based by crudely bedded (Facies 2)and trough-cross-stratified (Facies 1) lithic con-glomerates, coal fragments (up to 5 cm in diam-eter), and occasional clay chips (Figs 5 and 6,Table 1). The conglomerates and coal fragmentstypically occur above the internal erosion surfa-ces. The cross-set thickness varies from 0Æ1 to0Æ9 m, but is most commonly 0Æ20 to 0Æ35 m.

The trough-cross-stratified sandstones (Facies3) are interbedded with planar cross-stratifiedsandstones (Facies 4), low-angle cross-stratifiedsandstones (Facies 5), and plane parallel-lamin-ated sandstones with parting lineations (Facies6). Most of the channel fills do not fine upwardssignificantly, but are capped by 0Æ01–0Æ5 m thickvery fine- to fine-grained rippled sandstones(Facies 13), and plane parallel-laminated sand-stones and mudstones (Facies 17). In some places,

fine-grained rippled sandstones (Facies 13), andplane parallel-laminated sandstones and mud-stones (Facies 16) occur adjacent to the lenticularsandbodies.

Palaeocurrent directions derived from cross-strata and ripples vary within individual sand-stone bodies by up to 90�, but generally only 40–50�. The mean palaeocurrent direction variesbetween 100�SE and 170�SE, and most of thecurrents are in the range 90�E to 180�S (Figs 5 and6).

Water-escape structures, soft-sediment defor-mations and overturned cross-beds are commonin thicker units (Fig. 5H). Leaves, wood and otherplant fragments, rooted horizons or coal layersoccur occasionally at the top of, and adjacent tothe channel-shaped units (Fig. 5I and J).

InterpretationThe lithic conglomerates and coarse-grained sand-stones, the extensive unidirectional (towards theSE) cross-stratification, together with the channel-shape, significant basal erosion, wood and plantfragments, coal and root horizons, and lack ofmarine trace fossils suggest deposition in fluvialchannels. The trough-cross-stratified conglomer-ates and sandstones (Facies 1 and 3) were depos-ited in 3D dunes and in bars. The associatedcrudely bedded conglomerates represent lagdeposits related to the migration of the channelthalweg and dunes (Kleinhans et al., 2002). Theplanar cross-stratified sandstones (Facies 4), low-angle cross-stratified sandstones (Facies 5), andplane parallel-laminated sandstones with partinglineations (Facies 6) were formed as 2D dunes,scour fills, and upper flow-regime plane bedsrespectively. The ripple-laminated sandstones(Facies 13), and plane-parallel-laminated sand-stones and mudstones (Facies 17) were depositedon adjacent floodplains or mark abandonment ofchannels.

The multiple erosion surfaces indicate repeatedepisodes of channel incision and infill. The lackof lateral accretion beds, the coarse grain size ofthe channel fills, the low abundance of overbankdeposits and relatively low palaeocurrent variab-ility suggest that the channels had relatively lowsinuosity (Bridge et al., 2000). The abundantwater escape structures and associated soft-sedi-ment deformation indicate high rates of depos-ition, consequent water escape and bed collapse,or frequent slumping of channel banks (Owen,1996). The overturned cross-strata mark high bed-shear stresses, suggesting high river-current shearstrengths (Owen, 1996).



Facies Association 2: tidally influenced fluvialdeposits

Facies Association 1 can be walked-out into FA2, by following the channel-shaped units to-wards the south-east along the mountainsides(Fig. 7). FA 2 consists of lenticular coarse- tofine-grained sandbodies, 1Æ5–15Æ0 m thick, withmultiple internal erosion surfaces. The amountof erosion is similar to the thickness of thesandbodies. The sandbodies contain upwards-fining successions of bipolar cross-stratifiedsandstones (Facies 7), compound cross-stratifiedsandstones (Facies 9), low-angle bipolar cross-stratified sandstones (Facies 8), plane-parallel-laminated sandstones with parting lineations(Facies 6), and rare sigmoidal cross-stratification(Facies 10; Fig. 8 and Table 1). Cross-set thick-nesses in simple cross-strata vary between 0Æ2

and 0Æ4 m, whereas in compound cross-stratabetween 0Æ3 and 1Æ0 m. Bipolar ripple-laminatedvery-fine-grained sandstones (Facies 14) cap thelenticular sandbodies.

There is a wide range of compound (orinclined) cross-stratification in sandstones of FA2 (Fig. 8B and E). In places the cross-strata aresteeply dipping (25–30�) with reactivation surfa-ces, occasional mud drapes, or ripples climbingup the inclined surfaces. In other places, com-pound cross-strata are characterized by low-angle(5–15�) dipping surfaces with decimetre-scalecross-strata climbing up or down these surfaces.Occasionally, the decimetre-scale cross-sets maybe overlain by asymmetric ripples or mud drapes.The high-angle compound cross-stratification ismore common than the low-angle compoundcross-stratification in FA 2. Mud drapes ororganic debris drapes are rare. The sigmoidal

Fig. 9. Depositional sequences 12–15 on the western side of Brogniartfjellet. See Fig. 3 for location. Arrows on theright side indicate landward stepping facies shifts. The photo is a helicopter-taken photomosaic.



cross-stratification is rare, and recognized bydowncurrent transitions in foreset angle fromgently dipping to more steeply dipping and backto gently dipping, accompanied by increasing todecreasing cross-strata thickness within the sets,bounded by reactivation surfaces (Fig. 8D).

Palaeocurrent directions derived from cross-strata and ripples group into two sectors, north-west and southeast directions. The south-easterly

palaeocurrents vary within individual sandstonebodies by up to 90�, but generally only 40–50�(Figs 7 and 8). The mean south-easterly palaeo-current direction varies between 124� and152�SE, and most of the currents are in the range110� to 170�SE. The north-westerly palaeocur-rents vary within individual sandstone bodies byup to 100�, but generally only 30–40� (Figs 7 and8). Mean north-westerly palaeocurrent direction

Fig. 10. Depositional sequences 13–19 on eastern side of Brogniartfjellet. See Fig. 3 for location. Arrows on the rightside mark landward- and seaward-stepping facies shifts. See Fig. 9 for key.



varies between 260� and 330�WNW, and most ofthe currents are in the range 260� to 350�WNW.The palaeocurrent directions derived from planeparallel-laminated intervals vary between 120�and 170�SE.

Water-escape structures, soft-sediment defor-mations and overturned cross-beds are common

in thicker units. In places leaves and woodfragments, rooted horizons or coal seams occurat the top of the lenticular units (Fig. 8F).

InterpretationThe channel shape, extensive trough-cross-stratification, coarse grain size, bipolar, but

Fig. 11. Depositional sequences 20–29 on Storvola. See Fig. 3 for location. Arrows on the right side mark landward-and seaward-stepping facies shifts.



dominantly south-eastwards palaeocurrents,compound cross-strata, occasional mud drapes,together with the walked-out transition fromfluvial channels, presence of plant roots and lackof marine fossils suggest deposition in tidallyinfluenced fluvial channels (e.g. Allen, 1991),where the fluvial channel changes into a tidal–fluvial channel below the upstream tidal limit(Dalrymple et al., 1992).

The bipolar cross-strata (Facies 7 and Facies 8)indicate reversing currents of approximatelyequal strength, whereas the compound cross-strata (Facies 9) reflect a dominant south-east-ward current and a subordinate north-westwardcurrent. The reactivation surfaces on steeplydipping cross-strata indicate that a bedform lee-side is changed into the stoss-side by reversals inflow direction (e.g. Boersma, 1969; Boersma &Terwindt, 1981a,b; Allen & Homewood, 1984;Shanley et al., 1992), or migration of super-imposed bedforms (McCabe & Jones, 1977;Dalrymple, 1984; Shanley et al., 1992).

The compound cross-stratification with asym-metric ripples climbing up the lee faces ofhigh-angle cross-strata indicate a much strongerdominant current (e.g. Allen, 1980). Thedecimetre-scale cross-strata separated by low-angle inclined set boundaries show that the

dominant and subordinate currents did not differthat greatly in strength (see Allen, 1980). The lowabundance of the low-angle compound cross-strata indicates that the subordinate (i.e. north-westerly) current rarely achieved high velocity,and the depositional environment was dominatedby the south-easterly river current. The occa-sional mud drapes were deposited during slack-water periods. Individual cross-sets in thesefacies are interpreted as tidal bundles, depositedand modified in response to neap–spring–neaptide fluctuations (e.g. Allen, 1980; Boersma &Terwindt, 1981a,b; Dalrymple, 1984).

The sigmoidal beds with increasing to decreas-ing foreset angle and cross-strata thickness areinterpreted as representing as acceleration chan-ging to full vortex flow conditions, followed bydeceleration within a single ebb tide (sigmoidalbeds in Shanley et al., 1992; see also Boersma &Terwindt, 1981b; Allen & Homewood, 1984;Kreisa & Moiola, 1986; Uhlir et al., 1988). Thereactivation surfaces bounding the sigmoidalbeds have also here been interpreted as resultingfrom reversals of flow directions (Boersma, 1969;Boersma & Terwindt, 1981a,b; Allen & Home-wood, 1984; Shanley et al., 1992). The reactiva-tion surfaces within the individual sigmoidalbeds have been attributed to the migration of

Fig. 12. Lateral relationship between tidally influenced fluvial deposits and high-sinuosity tidal channel deposits onmountainside outcrop. Palaeocurrent measurements derived from cross-strata are shown in black, whereas the dip-direction of master surfaces (lateral accretion surfaces) is shown in grey.



superimposed bedforms (McCabe & Jones, 1977;Dalrymple, 1984; Shanley et al., 1992).

The plane parallel-laminated sandstones (Fa-cies 6) were deposited during upper-flow-regimeconditions when south-easterly directed rivercurrents dominated. The bipolar ripple-lamin-ated sandstones (Facies 10) represent abandon-ment of channels or were deposited ininterchannel areas.

Fluvial deposits: lateral and verticaltransitions

Fluvial deposits of FA 1 comprise laterally con-tinuous units of relatively thin fluvial conglo-merates and coarse sandstones above regionalerosion surfaces (Figs 9–11). Most of the fluvialchannel fills are 4–5 m thick, whereas some reach16 m locally (sequence 14 in Fig. 9; sequences 14

Fig. 13. A representative measured section through high-sinuosity tidal channel deposits of FA 3. Numbers by themeasured section refer to facies (see Table 1). Palaeocurrent measurements derived from cross-strata are shown inblack, whereas the dip-direction of master surfaces (lateral accretion surfaces) is shown in grey. Low-angle com-pound cross-strata (A and F) and lateral accretion sets (B and C) dominate the facies association. Bimodal cross-strata(D) occur in places. Organic debris drapes and mud drapes (E, H and I) are ubiquitous. Individual beds in accretionsets are rippled, plane-parallel laminated or structureless (G). Small-scale soft sediment deformation is common (J).Both, plant roots (H and L) and marine/brackish trace fossils (escape burrows on the photo K) occur in FA 3.



and 19 in Fig. 10; sequence 29 in Fig. 11). Indi-vidual fluvial channels can be ‘walked out’ acrossthe whole coastal-plain length, i.e. for 6–7 km

along the individual mountainsides (Fig. 3), andthey occur with vertical spacing of 7–44 m(Figs 9–11).

Fig. 14. Lateral relationship between high-sinuosity tidal channel deposits and coeval low-sinuosity tidal channeldeposits further to the southeast (seawards). The latter can be ‘walked out’ into upper-flow-regime tidal flats and tidalsand bars even further to the south-east. Palaeocurrent measurements derived from cross-strata are shown in black,and the dip direction of inclined master surfaces and lateral accretion surfaces in grey.

Fig. 15. A representative measured section through low-sinuosity tidal channel deposits of FA 4. Numbers by themeasured section refer to facies (see Table 1). Low-angle compound cross-stratification (A, E and F) dominates, buthigh-angle compound cross-stratification (B), low-angle cross-stratification (C), and bipolar cross-strata (D) also occurin these erosionally based (H), very-fine grained sandstones. Both plant fragments and marine/brackish trace fossilsoccur (G and I). Pl – Planolites, Sk – Skolithos, Te – Teichichnus.





Tidally influenced fluvial deposits of FA 2occur at the south-eastward (seaward) ends of thefluvial channels (sequences 19, 20 in Fig. 11), orwhere the tops of the fluvial channel fills gradeinto tidally influenced fluvial deposits (sequences14 and 15 in Fig. 9; sequence 14 in Fig. 10;sequences 23, and 29 in Fig. 11). The verticalchange into tidally influenced deposits marks thelandward migration of the bayline, and occurredwhen fluvial channels were submerged below themean tidal limit.

Besides the described fluvial intervals, the FA 1and 2 also occur, at the landward end of the tidal-dominated intervals that are discussed in moredetail below (sequence 16 in Fig. 10; sequences20, 21, 23, 27 in Fig. 11).

Facies Association 3: high-sinuosity tidalchannels

Facies Association 2 can be walked out into FA 3,by following the channel-shaped units towardsthe south-east along the mountainsides (Fig. 12).FA 3 consists of lenticular sand-prone bodies,0Æ6–4 m thick and 8–25 m wide. The associationtypically has a basal erosion surface, but theamount of erosion is only 0Æ6–1Æ0 m (in rare cases

up to 1Æ5 m). The lenticular bodies consist ofcompound cross-stratified fine-grained sand-stones with bipolar dip directions in adjacentsets (Facies 9), inclined heterolithic strata (Facies12), and bipolar cross-stratified fine-grained sand-stones (Facies 7; Table 1; Fig. 13). Grain size inFA 3 does not exceed fine sand. Mud drapes areubiquitous through the FA 3.

A wide range of compound (or inclined) cross-stratification (Facies 9) occurs in FA 3, similar toFA 2. However, in FA 3 the compound-cross-strata are dominated by broad, low-angle (5–15�)dipping surfaces with smaller sets of cross-strati-fication or ripple cross-lamination dipping up ordown the bedding surfaces (Fig. 13A and F). Thesmaller sets of cross-strata are in many placesoverlain by asymmetric ripples and/or muddrapes. Cross-stratification with reactivation sur-faces is also common, and the reactivation surfa-ces are typically covered with single or doublemud drapes or coal drapes (Fig. 13E, H, and I).

The inclined heterolithic strata (Facies 12) in0Æ4–1Æ0 m thick sets, consist of low-angle (5–10�)inclined or sinusoidal beds, 1–5 cm thick. Theindividual sinusoidal beds consist of sandstone-mudstone couplets. The sandstone intervals arestructureless, plane parallel- or ripple-laminated.

Fig. 16. A representative measured section through upper-flow-regime tidal flat deposits of FA 5. Numbers by themeasured section refer to facies (see Table 1). Plane-parallel lamination with current lineations (D) dominates, butoccasional trough-cross-stratification (A, B and C), and occasional sigmoidal stratification (A) also occur. Erosionsurfaces with several tens of centimetres of erosion are rather common (E).

Fig. 17. Tidal sand bars are large elongate bedforms that can be ‘walked out’ for several kilometres along dip-direction mountainside exposures. Palaeocurrent measurements derived from cross-strata are shown in black,whereas dip-direction of master surfaces (where measured) is shown in grey.



Fig. 18. A representative measured section through tidal sand bar deposits of FA 6. Numbers by the measuredsection refer to facies (see Table 1). Palaeocurrent measurements derived from cross-strata are shown in black, anddip direction of inclined master surfaces in grey. Trough-cross-stratified sandstone sets with bimodal palaeocurrentdirections in adjacent depositional units (A, E and F) dominate. Occasional sigmoids (A and B), and high-anglecompound cross-strata (C) occur. In seaward reaches of the outcrop belts the tidal sand bar deposits erosionally coverwave-reworked intensively bioturbated sandstones (A and D).



The sandstone intervals are in places erosionallybased (2–10 cm of erosion). The mudstone inter-vals drape the sandstone intervals (Fig. 13B andG). The sandstone–mudstone couplets can betraced from the upper parts of the inclined stratato the basal portions. The dip of the inclinedheterolithic strata is oriented in a directionnormal to the palaeocurrent indicators derivedfrom cross-stratification (see below). Bipolarcross-stratified sandstones (Facies 7) are fine-grained and their foresets and bottomsets arecommonly draped with single or double mud-stone or coal drapes (Fig. 13D). The cross-sets areonly 0Æ1–0Æ2 m thick, and in places climbing atthe top of the inclined heterolithic sets.

Palaeocurrent directions derived from cross-strata and ripples group into two modes, northwestand southeast. The south-easterly palaeocurrentsvary within individual sandstone bodies byup to 110�, but generally up to 80� (Figs 12–14).Mean south-easterly palaeocurrent directionsvary between 100� and 170�SE, and most of thecurrents are in the range 90�E to 180�S. The north-westerly palaeocurrents vary within individualsandstone bodies by up to 130�, but generally up

to 80� (Fig. 13). Mean north-westerly palaeocur-rent directions vary between 280� and 345�NW,and most of the currents are in the range 270� to350�NW. Most of the inclined heterolithic setsdip towards 10�–90�NE and 180�–270�SW.

Water-escape structures, and decimetre-scalesoft-sediment deformation are common (Fig. 13J).In places plant and wood fragments, rootedhorizons or coal layers occur at the top of thelenticular units (Fig. 13H and L). In other placesSkolithos, Planolites, rare Teichichnus burrows,or escape burrows are found (Fig. 13K).

InterpretationThe channel-shape, extensive bipolar compound-cross-stratification, ubiquitous single and doublemud drapes, and marine/brackish trace fossilssuggest deposition in tidal channels. The inclinedheterolithic strata are interpreted as lateral accre-tion deposits on tidal point bar surfaces, andindicate that FA 3 was deposited in high-sinuos-ity tidal channels. Rooted horizons and coallayers mark abandonment of the channels.

The bipolar cross-strata (Facies 7) indicatereversing currents of approximately equal

Fig. 18. Continued.



strength, whereas the compound cross-strata (Fa-cies 9) reflect the existence of a dominant and asubordinate current. Compared to the high-anglecompound-cross-strata in FA 2, the low-anglecompound-cross-strata indicate that the domin-ant and subordinate currents did not differ thatgreatly in strength (see Allen, 1980). The low-angle ‘master’ bedding surfaces are formed bymore intense reworking of the dominant-currentbedforms by the subordinate current. The rework-ing is directly proportional to the strength of the

subordinate current (Dalrymple et al., 1990). Thetransition from low-angle compound cross-stratainto smaller sets of cross-strata, into currentripples and mud drapes reflects deceleratingcurrent velocity (e.g. Shanley et al., 1992), andis interpreted as reflecting a tidal cycle.

The persistent mud drapes that can be tracedfrom the upper surface of the lateral accretion setsinto the deepest parts of the channel, combinedwith inclined sandstone beds that are ripple-laminated or plane-parallel-laminated through-

Fig. 19. A representative measured section through marginal tidal mixed- to mud-flat and marsh deposits of FA 7.Numbers by the measured section refer to facies (see Table 1). Flaser, wavy and lenticular bedding (A, B, C, E and G)dominate the locally bioturbated (F) marginal tidal flat deposits that represent an inter-tidal succession of decreasingcurrent energy. Coaly mudstones and coals (B) rich in plant fragments, roots, stems in growth position, in placesreworked by pedogenic processes (C, H, I and J) are interpreted as the uppermost, supratidal parts of tidal mud flatsand marshes. Pl – Planolites, Sk – Skolithos, Te – Teichichnus.



Table

1.

Sed

imen

tary

facie

s.

Facie

sT

extu

res

Str

uctu

res

Pala

eocu

rren

td

irecti

on

sT

race

foss

ils

an

dbio

taO

ccu

rren

ce

Inte

rpre

tati

on

1:

Tro

ugh

cro

ss-s

trati

fied

con

glo

mera

te

Gra

nu

les

an

doccasi

on

al

pebble

,coal

cla

sts

(<5

cm

),cla

ych

ips

Tro

ugh

-cro

ss-s

trati

fied

,in

pla

ces

soft

-sed

imen

td

efo

rmed

Un

imod

al:

80�–

180�

Wood

0Æ2

–0Æ4

mth

ick

cro

ss-

sets

clo

seto

the

base

of

ero

sion

all

ybase

dle

nti

cu

lar

un

its,

an

dabove

inte

rnal

ero

sion

surf

aces

Mig

rati

on

of

3D

du

nes

inch

an

nels

,u

nid

irecti

on

al

cu

rren

t

2:

Cru

dely

bed

ded

con

glo

mera

te

Gra

nu

les

an

doccasi

on

al

pebble

s,coal

cla

sts

(<5

cm

),cla

ych

ips

Cru

dely

norm

all

ygra

ded

,st

ructu

rele

ss,

or

imbri

cate

dW

ood

0Æ0

5–0Æ2

mth

ick,

at

the

base

of

ero

sion

all

ybase

dle

nti

cu

lar

un

its,

lin

ein

tern

al

ero

sion

surf

aces

Lag

dep

osi

ts,

lon

git

ud

inal

bars

,u

nid

irecti

on

al

cu

rren

t

3:

Tro

ugh

cro

ss-s

trati

fied

san

dst

on

e

Fin

e-

tocoars

e-g

rain

ed

san

dst

on

es,

coal

cla

sts

(<4

cm

),occasi

on

al

cla

ych

ips

Tro

ugh

-cro

ss-s

trati

fied

,in

pla

ces

overt

urn

ed

cro

ss-s

trata

an

dso

ftse

dim

en

td

efo

rmati

on

.M

ult

iple

ero

sion

surf

aces

lin

ed

wit

hcoal

cla

sts

or

cla

ych

ips

Un

imod

al:

80�–

180�

Wood

,le

aves,

roote

dh

ori

zon

s(u

pto

1m

lon

gro

ots

).O

ccasi

on

al

coal

layers

at

the

top

0Æ1

–0Æ9

mth

ick,

most

com

mon

ly0Æ2

0–0Æ3

5m

thic

kcro

ss-s

ets

inero

sion

all

ybase

dle

nti

cu

lar

un

its

0Æ6

–15Æ5

mth

ick

Dow

nst

ream

mig

rati

on

of

3D

du

nes,

obli

qu

em

igra

tion

of

lon

git

ud

inal

bars

inch

an

nels

,u

nid

irecti

on

al

cu

rren

t

4:

Pla

nar

cro

ss-s

trati

fied

san

dst

on

e

Fin

e-

tocoars

e-g

rain

ed

san

dst

on

es,

coal

cla

sts

(<4

cm

),occasi

on

al

cla

ych

ips

Pla

nar-

cro

ss-s

trati

fied

,in

pla

ces

soft

-sed

imen

td

efo

rmed

Un

imod

al:

80�–

180�

Wood

,le

aves,

roote

dh

ori

zon

s(u

pto

1m

lon

gro

ots

).O

ccasi

on

al

coal

layers

at

the

top

0Æ2

–0Æ9

mth

ick

cro

ss-s

ets

inero

sion

all

ybase

dle

nti

cu

lar

un

its

0Æ6

–15Æ5

mth

ick

Dow

nst

ream

mig

rati

on

of

2D

du

nes,

obli

qu

em

igra

tion

of

bars

inch

an

nels

,u

nid

irecti

on

al

cu

rren

t5:

Low

-an

gle

cro

ss-s

trati

fied

san

dst

on

e

Fin

e-

tom

ed

ium

-gra

ined

san

dst

on

es,

coal

cla

sts

an

dcla

ych

ips

Low

-an

gle

(<10�)

cro

ss-s

trati

ficati

on

,in

pla

ces

soft

-sed

imen

td

efo

rmed

0Æ2

–0Æ3

mth

ick

cro

ss-s

ets

inte

rbed

ded

wit

hh

igh

-an

gle

cro

ss-

stra

ta,

inero

sion

all

ybase

d,

len

ticu

lar

un

its

inF

A1

Scou

rfi

lls,

or

wash

ed

-ou

td

un

es,

un

idir

ecti

on

al

cu

rren

t

6:

Pla

ne-p

ara

llel

lam

inate

dsa

nd

ston

e

Fin

e-g

rain

ed

san

dst

on

es,

coal

cla

sts

an

dcla

ych

ips

Pla

ne-p

ara

llel

lam

inati

on

,p

art

ing

lin

eati

on

sIn

pla

ces

wood

an

dp

lan

tfr

agm

en

ts.

Occasi

on

al

roots

an

dcoal

layers

at

the

top

0Æ2

–0Æ3

mth

ick

bed

sin

terb

ed

ded

wit

hh

igh

-an

gle

cro

ss-

stra

ta,

inero

sion

all

ybase

d,

len

ticu

lar

un

its

or

in0Æ5

–1Æ5

mth

ick

tabu

lar

un

its

Up

per-

flow

-regim

ep

lan

ebed

s

7:

Bip

ola

rcro

ss-s

trati

fied

san

dst

on

e

Fin

e-

tocoars

e-g

rain

ed

san

dst

on

es,

occasi

on

al

mu

dd

rap

es,

coal

cla

sts

an

doccasi

on

al

cla

ych

ips

Tro

ugh

-or

pla

nar-

cro

ss-s

trati

fied

,in

pla

ces

overt

urn

ed

cro

ss-s

trata

an

dso

ftse

dim

en

td

efo

rmati

on

.M

ult

iple

ero

sion

surf

aces

lin

ed

wit

hcoal

cla

sts

or

cla

ych

ips

Bim

od

al:

80�–

180�

an

d250�–

350�

Inp

laces

wood

an

dp

lan

tfr

agm

en

ts,

occasi

on

al

roots

an

dcoal

layers

at

the

top

.In

oth

er

pla

ces

Skoli

thos,

Pla

noli

tes,

rare

Teic

hic

hn

us,

or

esc

ap

ebu

rrow

s

0Æ1

–0Æ4

mth

ick

cro

ss-

sets

inero

sion

all

ybase

d0Æ3

–5Æ0

mth

ick

len

ticu

lar

un

its

Mig

rati

on

of

3D

du

nes

inch

an

nels

,bid

irecti

on

al

cu

rren

tsof

equ

al

stre

ngth



Table

1.

Sed

imen

tary

facie

s.

Facie

sT

extu

res

Str

uctu

res

Pala

eocu

rren

td

irecti

on

sT

race

foss

ils

an

dbio

taO

ccu

rren

ce

Inte

rpre

tati

on

8:

Low

-an

gle

bip

ola

rcro

ss-

stra

tifi

ed

san

dst

on

e

Fin

e-

tom

ed

ium

-gra

ined

san

dst

on

es,

occasi

on

al

mu

dd

rap

es,

coal

cla

sts

an

dcla

ych

ips

Low

-an

gle

(<10�)

cro

ss-s

trati

ficati

on

,in

pla

ces

soft

-sed

imen

td

efo

rmed

,in

pla

ces

ubiq

uit

ou

sre

acti

vati

on

surf

aces

Bim

od

al

Inp

laces

wood

an

dp

lan

tfr

agm

en

ts,

or

occasi

on

al

roots

an

dcoal

layers

at

the

top

0Æ1

–0Æ3

mth

ick

cro

ss-

sets

,in

ero

sion

all

ybase

dle

nti

cu

lar

un

its

Scou

rfi

lls,

or

wash

ed

-ou

td

un

es,

rew

ork

ing

by

subord

inate

cu

rren

t,bid

irecti

on

al

cu

rren

t9:

Com

pou

nd

cro

ss-s

trati

fied

san

dst

on

e

Very

-fin

e-

tocoars

e-g

rain

ed

san

dst

on

es,

inp

laces

mu

dd

rap

es

or

org

an

icd

ebri

sd

rap

es

(1)

hig

h-a

ngle

(25–30�)

cro

ss-s

trata

wit

hre

acti

vati

on

surf

aces

an

dm

ud

dra

pes,

(2)

hig

h-a

ngle

(25–30�)

cro

ss-s

trata

wit

hsm

all

er

sets

of

cro

ss-s

trata

or

rip

ple

scli

mbin

gu

por

dow

nth

esu

rfaces

(3)

low

-an

gle

(5–15�)

cro

ss-s

trata

wit

hsm

all

er

sets

of

cro

ss-s

trata

or

rip

ple

scli

mbin

gu

por

dow

nth

esu

rfaces

Bim

od

al

80�–

180�

an

d250�–

350�

Inp

laces

wood

an

dp

lan

tfr

agm

en

ts,

or

occasi

on

al

roots

an

dcoal

layers

at

the

top

.In

oth

er

pla

ces

Skoli

thos,

Pla

noli

tes,

rare

Teic

hic

hn

us,

or

esc

ap

ebu

rrow

s

0Æ3

–1Æ0

mth

ick

cro

ss-

sets

inero

sion

all

ybase

d0Æ6

–5Æ0

mth

ick

len

ticu

lar

un

its

Dow

ncu

rren

tm

igra

tion

of

3D

du

nes

an

dobli

qu

em

igra

tion

of

bars

inch

an

nels

,bid

irecti

on

al

cu

rren

t,m

ud

dra

pes

from

slack-w

ate

rp

eri

od

s

10:

Sig

moid

al

cro

ss-s

trati

fied

san

dst

on

e

Fin

e-

tom

ed

ium

-gra

ined

san

dst

on

es

Dow

ncu

rren

ttr

an

siti

on

info

rese

tan

gle

from

gen

tly

dip

pin

gto

more

steep

lyd

ipp

ing

an

dback

togen

tly

dip

pin

g,

accom

pan

ied

by

incre

asi

ng

tod

ecre

asi

ng

cro

ss-s

trata

thic

kn

ess

wit

hin

the

sets

,bou

nd

ed

by

reacti

vati

on

surf

aces.

Bim

od

al

110�–

170�

an

d240�–

350�

Inp

laces

wood

an

dp

lan

tfr

agm

en

ts,

or

occasi

on

al

roots

an

dcoal

layers

at

the

top

0Æ2

–0Æ4

mth

ick

sets

inero

sion

all

ybase

d1Æ5

–5Æ0

mth

ick

len

ticu

lar

un

its

Accele

rati

on

ch

an

gin

gto

full

vort

ex

flow

con

dit

ion

s,fo

llow

ed

by

decele

rati

on

wit

hin

asi

ngle

tid

e

11:

Tro

ugh

-cro

ss-

stra

taon

incli

ned

mast

er

surf

aces

Med

ium

-to

coars

e-

gra

ined

san

dst

on

es

Incli

ned

mast

er

surf

aces

wit

hsu

peri

mp

ose

dcro

ss-s

trata

Bim

od

al,

cro

ss-s

trata

280�–

360�

150�–

180�,

mast

er

surf

aces

70�–

140�

220�–

280�

Cro

ss-s

ets

:0Æ0

5–0Æ5

m,

dep

osi

tion

al

un

its:

5–15

m

Mig

rati

on

of

3D

du

nes

on

late

rall

yaccre

tin

gbar

surf

aces

12:

Incli

ned

hete

roli

thic

stra

ta

Fin

e-

an

dvery

-fin

e-g

rain

ed

san

dst

on

es

bou

nd

ed

by

mu

dst

on

ela

min

ae

Incli

ned

(at

an

gle

sbetw

een

10–15�)

,in

tern

all

yst

ructu

rele

ss,

pla

ne-p

ara

llel

lam

inate

dor

rip

ple

-lam

inate

dsa

nd

ston

est

rata

,se

para

ted

by

mu

dd

rap

es

Skoli

thos,

Pla

noli

tes,

rare

Teic

hic

hn

us,

or

esc

ap

ebu

rrow

s

San

dst

on

es:

0Æ0

1–0Æ1

m;

mu

dst

on

es:

to0Æ0

05

min

0Æ3

–3Æ0

thic

ku

nit

s

Tid

al

bu

nd

les

inla

tera

laccre

tion

sets

(poin

tbars

)

13:

Rip

ple

-la

min

ate

dsa

nd

ston

e

Very

fin

e-

tofi

ne-g

rain

ed

san

dst

on

e,

an

dsi

ltst

on

es

Asy

mm

etr

ical

rip

ple

sU

nim

od

al:

80�–

180�

Wood

,le

aves,

roote

dh

ori

zon

s(u

pto

1m

lon

gro

ots

).O

ccasi

on

al

coal

layers

0Æ0

01–0Æ0

5m

thic

kri

pp

lese

ts,

infl

at-

base

dta

bu

lar

un

its

that

cap

len

ticu

lar

un

its

Un

imod

al

cu

rren

tri

pp

les

dep

osi

ted

du

rin

gaban

don

men

tof

ch

an

nels

,or

inoverb

an

ken

vir

on

men

t14:

Bim

od

al

rip

ple

-la

min

ate

dsa

nd

ston

e

Very

fin

e-

tofi

ne-g

rain

ed

san

dst

on

e,

an

dsi

ltst

on

es,

occasi

on

al

mu

dd

rap

es

Asy

mm

etr

ical

rip

ple

sB

imod

al

80�–

180�

an

d250�–

350�

Inp

laces

wood

an

dp

lan

tfr

agm

en

ts.

Occasi

on

al

roots

an

dcoal

layers

at

the

top

0Æ0

01–0Æ0

5m

thic

kri

pp

lese

ts,

infl

at-

base

dta

bu

lar

un

its

that

cap

len

ticu

lar

un

its

Bim

od

al

cu

rren

tri

pp

les

dep

osi

ted

du

rin

gaban

don

men

tof

ch

an

nels

,or

inoverb

an

ken

vir

on

men

t15:

Bim

od

al

rip

ple

dsa

nd

ston

ebed

sw

ith

mu

dd

rap

es

Very

fin

e-

tofi

ne-g

rain

ed

san

dst

on

es

sep

ara

ted

by

mu

dd

rap

es

Bip

ola

rd

ipd

irecti

on

sin

ad

jacen

tri

pp

lese

ts,

sep

ara

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out, suggest a relatively even shear velocitydistribution within the channel (Shanley et al.,1992). Such a velocity distribution is markedlydifferent from that normally encountered in flu-vial systems (see also Thomas et al., 1987; Rah-mani, 1988; Smith, 1988; Nio & Yang, 1991). Thefine interlamination of sandstones and mud-stones in tidal point bars is interpreted asreflecting deposition during single tidal cycles(Bridges & Leeder, 1976).

The ubiquitous occurrence of mud drapesreflects deposition within the turbidity maximumzone (McCave, 1979; Jouanneau & Latouche,1981; Dalrymple et al., 1990; Allen, 1991; Dal-rymple, 1992). Deposition of fine-grained sedi-ment occurs due to abrupt changes in shearvelocity and is promoted by flocculation of clayparticles due to salinity mixing of fluvial freshwater and marine waters (Nichols & Biggs, 1985).

Facies Association 4: low-sinuosity tidalchannels

Facies Association 3 can be walked out into FA 4by following the lenticular bodies towards thesouth-east along the mountainsides (Fig. 14). FA 4consists of lenticular sand-prone bodies, 0Æ6–4 mthick and 10–15 m wide. The association istypically erosionally based, but the amount oferosion is only 0Æ6–1Æ0 m (in rare cases up to 1Æ8 m,Fig. 15H). The lenticular bodies consist of com-pound cross-stratified fine-grained sandstoneswith bipolar dip directions in adjacent sets (Facies9), bi-directional cross-stratified sandstones(Facies 7), and low-angle cross-stratified sand-stones (Facies 8; Table 1; Fig. 15). Mud drapes areubiquitous, but somewhat less abundant than inthe FA 3. Grain size does not exceed fine sand.

The compound cross-stratified sandstones (Fa-cies 9) are in most places fine grained. In placesthe cross-strata are steeply dipping (25–30�) withreactivation surfaces and mud drapes, or smallercross-strata or ripples climbing up the inclinedsurfaces. In most places, the compound cross-strata are characterized by low-angle (5–15�)dipping surfaces with smaller sets of cross-strati-fication or ripple cross-lamination climbing up ordown the bedding surfaces (Fig. 15A–C, E and F).The bipolar cross-stratified sandstones (Facies 7)are fine grained (Fig. 15D). Cross-sets are typic-ally 0Æ1–0Æ2 m thick. The low-angle (<10�) cross-strata (Facies 8) display reactivation surfaces anda slightly sigmoidal shape, but lack mud drapes.

Palaeocurrent directions derived from cross-strata and ripples group into two modes, north-1

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west and south-east directions. The variationof palaeocurrent directions within individuallenticular bodies is less compared with FA 3.The south-easterly palaeocurrents vary withinindividual sandstone bodies by up to 70�, butgenerally only 40–50�. Mean south-easterly pal-aeocurrent directions vary between 105� and150�SE, and most of the currents are in the range100� to 160�SE. The north-westerly palaeocur-rents vary within individual sandstone bodies byup to 80�, but generally only 40–50�. Mean north-westerly palaeocurrent directions vary between270� and 310�NW, and most of the currents are inthe range 280� to 310�NW (Figs 14 and 15).

Water-escape structures, and decimetre-scalesoft-sediment deformation are common. In placesplant and wood fragments, rooted horizons orcoal layers occur at the top of the lenticular units(Figs 14 and 15). In other places, Skolithos,Planolites, rare Teichichnus burrows, or escapeburrows are found (Fig. 15).

Facies Association 4 has many similarities withFA 3, as both associations are characterized by adominance of very fine- to fine-grained sand-stones with bipolar palaeocurrent indicators,ubiquitous mud drapes, occurrence of roots aswell as marine trace fossils. The difference is thatFA 4 lacks inclined heterolithic strata, has anarrower distribution of palaeocurrents, and muddrapes are somewhat less common.

InterpretationThe channel-shape, extensive bipolar compound-cross-stratification, ubiquitous single and doublemud drapes, and marine/brackish trace fossilssuggest deposition in tidal channels. Rootedhorizons and coal layers mark abandonment ofthe channels. The lack of lateral accretion beds,together with lower variability of palaeocurrentdirections suggests lower sinuosity of tidal chan-nels in FA 4 compared to otherwise very similarFA 3. The bipolar cross-strata (Facies 7) andcompound cross-strata (Facies 9) are interpretedsimilarly to FA 3. The low-angle cross-strata (8)are interpreted as reflecting intense reworking bythe subordinate current similar to low-anglecompound-cross-strata. The intense reworkingmay have removed the mud drapes.

Facies Association 5: upper-flow-regime tidalflats

Facies Association 4 can be walked out into FA 5by following the lenticular bodies to the south-east along the mountainside (Fig. 14). FA 5

consists of plane parallel-laminated sandstones(Facies 6), and occasional trough cross-stratifiedsandstones (Facies 7) and sigmoidal cross-strati-fied sandstones (Facies 10; Fig. 16, Table 1).

The plane parallel-laminated sandstones (Fa-cies 6) show parting lineations, and consist offine-grained sandstones. Individual beds, 0Æ2–0Æ4 m thick, are sandy throughout, and in placeserosionally based (Fig. 16A, B, C and D). In otherplaces, the beds are composed of a lower set ortwo of trough cross-stratified sandstones, or arecapped by a set of sigmoidal beds (Fig. 16E). Thebeds are grouped into 0Æ5–1Æ2 m thick deposition-al units that can be followed for more than akilometre along the mountainside exposures(Fig. 17).

The 0Æ1–0Æ2 m thick sets of trough cross-stratifiedsandstones (Facies 7) are fine to medium grained,and have occasional coal fragments in foresets. Thesigmoidal cross-strata (Facies 10) display reactiva-tion surfaces, but lack mud drapes. Individual setsare up to 0Æ3 m thick, and consist of fine- tomedium-grained sandstones.

Palaeocurrent indicators derived from partinglineations, sigmoidal beds and cross-strata aretowards the north-west. The palaeocurrent direc-tions vary within individual sandstone bodies byonly up to 20�, and the mean palaeocurrentdirection varies between 260�SW and 350�NW,and most of the directions are in the range240�SW to 350�NW. The south-easterly palaeo-currents from cross-strata are in the range of110�SE to 190�SW. Palaeocurrent directions showreversals in adjacent units (1–3 m thick), ratherthan in adjacent sets.

InterpretationPlane parallel-laminated fine-grained sandstoneswith parting lineations and strongly dominantnorth-westerly palaeocurrent directions, togetherwith sand-prone cross-strata, indicate upper flowregime traction deposition by flood currents. Theplane parallel-laminated intervals formed inmaximum tidal flow velocities, whereas thecross-strata at the base or top developed duringaccelerating or waning flow conditions (e.g. Kre-isa & Moiola, 1986).

Upper flow regime (UFR) tidal sand flats havebeen considered diagnostic for macrotidal estuar-ine environments, as they have only beenreported from the axial portions of modern tide-dominated macrotidal estuaries (Hamilton, 1979;Lambiase, 1980a,b; Dalrymple et al., 1990; Dal-rymple, 1992). Current speeds that exceed2 m s)1, and water depths <2–3 m have been



measured in modern environments, where upperflow regime plane beds form in fine sand (Dal-rymple et al., 1990).

Most of the cross-stratified sandstones weredeposited by slower ebb currents, whereas thesigmoidal beds show landwards palaeocurrentdirections. The reversal of palaeocurrent direc-tions in adjacent depositional units (severalmetres thick) rather than in adjacent cross-setssuggests that flood and ebb currents used slightlydifferent paths for several tidal cycles.

Facies Association 6: tidal sand bars

Facies Association 5 can be walked out into FA 6by following the plane-parallel laminated sand-bodies to the southeast along the mountainsides(Figs 14 and 17). FA 6 consists of quartz-rich,well-sorted, medium- to coarse-grained sand-stones. FA 6 is dominated by about 5–15 m thickinclined master surfaces with superimposed dec-imetre-scale cross-strata (Facies 11). In places,sigmoidal beds (Facies 10) and compound-cross-strata (Facies 9) occur (Figs 17 and 18, Table 1).

The dip of the inclined master surfaces isoriented in a direction at 40� to 60� to thepalaeocurrent indicators derived from superim-posed cross-stratification. These large inclinedbeds are erosionally based. The amount of erosionvaries from a few decimetres to several metres,and in rare cases up to 10 m. The erosionallybased inclined beds are organized into deposi-tional units that thin updip and downdip, andthey can be walked out on mountainside expo-sures for 1–2 km (Fig. 17).

The superimposed cross-sets are 0Æ05–0Æ5 mthick and display bipolar palaeocurrent direc-tions in adjacent depositional units, a few deci-metres to a few metres thick (Fig. 18). This is incontrast to FA 2, 3 and 4 where the palaeocurrentdirections are bipolar in adjacent sets. Grain-sizetends to vary together with the palaeocurrentreversals in the depositional units. Sigmoidalbeds (Facies 10) are more common in FA 6 than inother facies associations. Compound-cross-strata(Facies 9) are less common, and represented byhigh-angle cross-strata with reactivation surfaces,or high-angle cross-strata with smaller sets ofcross-strata or asymmetric ripples dipping up theinclined surfaces.

Palaeocurrent directions derived from cross-strata group into two sectors, north-west andsouth-east. The north-westerly currents domin-ate over the south-easterly currents. The north-westerly palaeocurrents vary within individual

sandstone bodies by up to 50�, but generallyonly 30� (Figs 17 and 18). Mean north-westerlypalaeocurrent directions vary between 280� and350�NW, and most of the currents are in therange 280�NW to 360�N. The south-easterlypalaeocurrents vary within individual sandstonebodies by up to 30� (Figs 16 and 18). Meansouth-easterly palaeocurrent directions vary be-tween 150� and 170�SE, and most of thecurrents are in the range 150�SE to 180�S.Palaeocurrent directions from the inclined mas-ter surfaces dip towards 70�NE–140�SE and220�SW–280�NW (Figs 17 and 18).

When walked out further southeast, FA 6 cutsinto wave-reworked and heavily bioturbateddeposits (Fig. 18). The wave-reworked depositsare characterized by wave ripples, low-angle (<5�)cross-strata, swaley cross-strata, and very inten-sive bioturbation (including Ophiomorpha, Tere-bellina). When walked out towards the northwest,upper-flow-regime tidal flats (FA 5) overlie FA 6(Fig. 17). In other places, FA 6 is covered by coallayers, coaly mudstones or by FA 7.

Facies Association 6 has been documented onlyin some of the sequences (sequences 13, 15, 16and 18 on Brogniartfjellet, and sequences 20, 21and 24 on Storvola, Figs 10 and 11), as they occurin the most south-eastward (seaward) end of thecoastal-plain exposures.

InterpretationThe erosional base, extensive trough-cross-strati-fication, lateral accretion, coarse grain-size, bipo-lar palaeocurrent directions in adjacentdepositional units, together with the significantheight and length of the sandbodies suggestsdeposition as tidal sand bars in a subtidal envi-ronment. Such large tidal bars are characteristicof the seaward portions of most macrotidal envi-ronments (Hayes, 1975; Harris, 1988; Dalrymple &Zaitlin, 1989; Dalrymple et al., 1990). Tidal sandbars have been described from estuaries, tide-dominated delta fronts and tide-dominated shal-low-marine settings (sand ridges; Swift, 1975;Dalrymple et al., 1990). A lack of bioturbationand mud drapes in the tidal bars is most probablydue to the rapid migration of these large bedforms(Amos et al., 1980; Yeo & Risk, 1981).

The reversals of palaeocurrents in adjacent setsindicate that flood and ebb currents used slightlydifferent paths (see also Dalrymple et al., 1990;Dalrymple, 1992). The more quartz-rich andbetter-sorted character of the sandstones indicatesan active marine sediment supply by floodcurrents.



Facies Association 7: mixed to muddy tidalflats and marshes

Facies Association 7 occurs lateral to the des-cribed FA 2–6. FA 7 is volumetrically dominatedby heterolithic beds of ripple-cross-laminatedfine- to very fine-grained sandstones, separatedby mud drapes (Facies 15). In some places theasymmetrical ripples have opposite dip direc-tions in adjacent sets (Table 1, Fig. 19A, B, C, Eand G). In other places the ripples are unidirec-tional. The mud drapes vary in thickness from amillimetre to 0Æ5 cm. In places the rippled hetero-lithic beds are dominated by sandstone, or thesandstone-mudstone content is equal, and inother places the mudstone dominates the hetero-lithic beds. Sandstone-prone beds with aggrada-tional asymmetric ripples (Facies 16) are alsocommon. These beds vary from climbing ripplesto vertically aggrading ripples, separated by thinmud drapes (Fig. 19H).

Small-scale deformation is common in bothtypes of rippled beds (Fig. 19D). In places therippled beds are bioturbated (Skolithos, Plano-lites, Fig. 19F), in other places they are inten-sively rooted or reworked by pedogenicprocesses. Locally, whole tree leaves (Fig. 19J)occur and fragments of plant stems are found inthe growth position (Fig. 19H and I).

Facies 15 and Facies 16 grade laterally andvertically into 0Æ3–9 m thick organic-rich mud-stones (Facies 18). The mudstones commonlycontain root traces, and are rich in tree leaves,plant stems in growth position and up to 20 cmthick coal layers (Fig. 19B). Characteristically, therippled beds of Facies 15 and Facies 16 becomefiner-grained upwards and grade into organic-richmudstones, or they become coarser-grained up-wards and are cut by tidal channels or bars. Inplaces lenticular sandstone-prone bodies (Facies9), 0Æ5–1 m thick occur. These lenticular bodiesare typically based by a lag of mud clasts andconsist of compound-cross-stratified fine-grainedsandstones.

Palaeocurrent directions derived from ripple-cross-lamination are very widely spread.Although there are two dominant groups (towards280�NW and towards 110�SE), the directions varyby almost 360� (Fig. 19).

InterpretationThe succession of bipolar rippled heterolithicbeds with mud drapes (Facies 15) is interpretedas flaser, wavy and lenticular bedding, accordingto the sandstone/mudstone ratio (see Reineck &

Wunderlich, 1968). Flaser, wavy and lenticularbedding with marine/brackish trace fossils typi-cally indicates deposition from reversing tidalcurrents (Reineck & Wunderlich, 1968; Reineck &Singh, 1980) and represents an inter-tidal succes-sion of decreasing current energy (Dalrymple,1992). Rippled sands are deposited during max-imum tidal flow, whereas mud drapes formduring ensuing slack-water periods.

Low-angle sinusoidal lamination (Facies 16)has been documented as formed by ripples thatclimb at angles exceeding the stoss slope angles ofripples (Allen, 1968; Yokokawa et al., 1995). Thistype of lamination has also been called ‘sinusoi-dal ripple-lamination’ (Jopling & Walker, 1968) or‘draped lamination’ (Ashley et al., 1982). Increas-ing angles of climb in this type of ripple lamin-ation indicate that the ratio of the vertical bedaggradation rate to the downstream ripple migra-tion rate increases (Ashley et al., 1982), i.e. theratio of deposition between suspended bed mater-ial and traction bed load increases (Jopling &Walker, 1968), compared to flaser and wavylamination beds.

Organic-rich mudstone and coals (Facies 18),rich in plant fragments and roots and in placesreworked by pedogenic processes are interpretedas the uppermost, supratidal parts of tidal mudflats and marshes. The small-scale channelledunits of compound cross-stratified sandstones(Facies 9) indicate deposition in tidal gullies thatcrossed the tidal flats (Dalrymple et al., 1991).The great variability of palaeocurrents suggeststhat the tidal currents tend to become shoreline-perpendicular in FA 7. FA 7 is interpreted asintertidal to supratidal mixed to mud flats andmarshes that rim the margins of the higher energytidal environments described in FA 2–6.

Tidal deposits: lateral and vertical transitions

Tidal deposits (FA 4–7) stratigraphically overliethe basal fluvial channels, and form the bulkvolume of the coastal-plain depositional se-quences in the Eocene Central Basin. The fluvialand tidally influenced fluvial deposits (FA 1 and 2)are restricted to the most north-westward (land-ward) portions of the tidally dominated intervals(Fig. 20). They pass to the south-east into high- (FA3) and low-sinuosity (FA 4) tidal channel deposits,and then into upper flow-regime tidal flat deposits(FA 5) and at the seaward end of the profile intotidal sand bars (FA 6). The low-energy tidal mixedto mud flats (FA 7) occur lateral (marginal) to thedescribed axial succession (Fig. 20).



Fig. 20. Seaward facies transitions, grain-size trends and palaeocurrent directions indicate deposition in a tide-dominated estuary. The estuary model is redrawn after Dalrymple et al. (1992). Palaeocurrent measurements derivedfrom cross-strata are shown in black, and dip direction of inclined master surfaces in grey.



Grain-size decreases along the described axialprofile towards the south-east, from conglomer-ates and coarse-grained fluvial sandstones (FA 1)to medium- and fine-grained tidally influencedfluvial sandstones (FA 2), and into fine- to veryfine-grained sandstones with ubiquitous muddrapes in high-sinuosity tidal channels (FA 3;Fig. 20). Grain size also decreases towards thenorthwest from the seaward end of the profile,from coarse- to medium-grained tidal sand bars(FA 6), to medium- and fine-grained UFR tidalflats (FA 5), and into fine- to very fine-grained andmud-drape-rich low- and high-sinuosity tidalchannels (FA 4 and 3). These grain-size trendsindicate bedload convergence in the high-sinuos-ity tidal channel setting (Fig. 20). Along with thiscentral bedload-transport convergence, largequantities of suspended load fines also accumu-lated in the form of ubiquitous mud drapes.Alternative depocentres for the suspended loadare the inter- to supra-tidal marginal tidal flatsand marshes (FA 7; Fig. 20), where significantvolumes of mud also accumulated (Figs 9–11).

Palaeocurrent indicators show a dominantsouth-eastward (seaward) directed current in thetidally influenced fluvial channels (FA 2), cur-rents of equal strength in the high- and low-sinuosity tidal channel (FA 3 and 4), and adominantly north-westward (landward) directedcurrent on the UFR tidal flats (FA 5) and in tidalsand bars (FA 6; Fig. 20).

The described facies transitions, together withgrain-size and palaeocurrent trends indicatedeposition in tide-dominated estuaries (Dalry-mple et al., 1992). Modern examples of tide-dominated estuaries include Cobequid Bay andthe Salmon River (Dalrymple & Zaitlin, 1989;Dalrymple et al., 1990, 1991), the Severn River,England (Hamilton, 1979; Harris & Collins, 1985),and the South Alligator River, northern Australia(Woodroffe et al., 1989, 1993). Most modern tide-dominated estuaries are macrotidal, althoughtidal-dominance can occur at much smaller tidalranges if wave action is limited or the tidal prismis large (Hayes, 1979; Davis & Hayes, 1984). Thepresence of UFR tidal flats (FA 5), howeverstrongly suggests macrotidal (i.e. tidal range ishigher than 4 m, Davies 1964) conditions (Dal-rymple et al., 1992) in the Spitsbergen estuaries.Tide-dominated estuaries are characteristicallycomprised of: (1) river-dominated headwardchannels (FA 1 and 2 in this paper), (2) a mixedenergy middle portion within a tidal channel (FA3 and 4 in this paper), (3) a tide-dominated outerportion with UFR tidal flats and tidal sand bars

(FA 5 and 6 in this paper), and (4) marginal tidalflats and marshes (FA 7 in this paper).

The tidally influenced fluvial deposits (FA 2)indicate that rivers became tidally influencedbelow the mean high tide, but the net sedimenttransport was still seawards due to the long-termdominance of river flow over tidal currents. Thisportion is in a setting analogous to the ‘innerstraight’ portions of tidal channels in Dalrympleet al. (1992); Fig. 20). The sediment is furthertransported into the meandering portion of thetidal channel (FA 3), where the highest frequencyof mud drapes together with high sinuosityindicate that in this location the total energyminimum occurs, and tidal and fluvial energy isapproximately equal (Ashley & Renwick, 1983;Dalrymple & Zaitlin, 1989; Woodroffe et al., 1989,1993; Dalrymple et al., 1992). This setting issimilar to the ‘meandering’ portion of a tidalchannel of Dalrymple et al. (1992), where depos-ition of fine-grained populations of both fluvial-and marine-derived sediment occurs. Basinwardsfrom the meandering tidal channel, in the low-sinuosity tidal channel (FA 4) the tidal energy isslightly higher, as witnessed by the lower fre-quency of mud drapes. This setting is similar tothe ‘outer straight’ portion of the tidal channel inDalrymple et al. (1992). Further seawards, thetidal channel broadens into a funnel, and marine-derived sediments are deposited in UFR tidal flats(FA 5) and in tidal sand bars (FA 6). The UFRtidal flats (FA 5) indicate that the flood-tidalenergy maximum lies landward from the tidalsand bars (FA 6) (Harris, 1988; Dalrymple &Zaitlin, 1989; Dalrymple et al., 1990, 1992). Thetidal maximum occurs in this headward portionof the estuarine funnel, because the incoming tideis progressively funnelled into a smaller cross-sectional area (Myrick & Leopold, 1963; Wrightet al., 1975; ‘hypersynchronous’ behaviour ofNichols & Biggs, 1985). The mixed- to muddy-tidal flats and marshes (FA 7) reflect graduallydecreasing tidal energy and gradually shallowingdepositional environment away from the axis ofthe estuary (Fig. 20).

COASTAL PLAIN RESPONSE TOSEA-LEVEL CHANGES

The Eocene Central Basin infill is overall progra-dational and consists of clinoforms that migratedto the south-east (Fig. 1). The coastal-plain faciesbelt, however, is very aggradational and mud-prone (Fig. 2), except for the fluvial channels



associated with regional erosion surfaces. Theseerosion surfaces that cut across the whole coastalplain (Fig. 4) are used to divide the coastal-plainsuccession into a series of depositional sequencesthat are 7–44 m thick. Eighteen depositionalsequences were studied along the Van Keulenf-jorden transect on two different mountainsidesover a distance of some 15–20 km. The coastal-plain succession on Brogniartfjellet (sequences12–19; Figs 9 and 10) is broadly time-equivalentwith shelf to slope clinothems on Storvola andbasin-floor clinothems on Hyrnestabben. Thecoastal-plain succession on Storvola (sequences20–29; Fig. 11) is broadly time equivalent withshelf to slope clinothems on Hyrnestabben(Fig. 1).

Each of the stratigraphic sequences consists of(1) lowstand deposits (FA 1 and 2) just above themajor erosion surface, (2) transgressive depositswith landward-stepping, estuarine deposits (FA1–7), and (3) highstand deposits with aggrada-tional to seaward-stepping, estuarine deposits(FA 1–4, 7). The third segment has been docu-mented in only about 30% of the sequences(Figs 9–11).

Sequence boundaries

The basal erosion surface of each sequence erodesinto older estuarine deposits with local erosionalrelief of up to 16 m (Fig. 21A). In places, wherethe erosion surfaces are exposed in a moreoblique view, abundant rooted horizons andhorizons intensively reworked by pedogenic pro-cesses (e.g. ferruginous features, very intensivebioturbation by roots and loss of all sedimentary

structures, Fig. 19B) occur lateral to the deepestincisions (sequence 22 in Fig. 11; Fig. 21B). Thefull lateral extent of the erosion surfaces isunknown.

InterpretationThe prominent and widespread erosion surfacesthat are overlain by coarse-grained fluvial channeldeposits, are interpreted as sequence boundaries,because (1) these erosion surfaces are traceable ina dip-direction across the whole coastal-plainfacies belt, (2) the depth of incision is significant(local erosional relief up to 16 m), and (3) theseerosion surfaces are overlain by fluvial depositsthat mark a significant seaward facies shift(Fig. 21C and D). Sequence boundaries formedduring the fall of relative sea-level to its lowestposition. Extensive rooting and pedogenesisoccurred in time-equivalent interfluve segmentsadjacent to the deeper incisions.

Lowstand deposits

The most prominent, more-or-less continuoussandstone levels that stand out on the photomo-saics (Fig. 21A) are the levels where fluvial (FA 1)and tidally influenced fluvial (FA 2) channelsoccur across the entire coastal plain (Figs 9–11).The fluvial channels (FA 1) grade seawards andupwards into tidally influenced fluvial deposits(FA 2, Figs 7 and 9–11). The fluvial units are insome sequences up to 16 m thick, but in mostsequences 3–5 m thick.

Fine-grained overbank deposits adjacent to thefluvial channels are documented only in a fewplaces (sequence 12 in Fig. 9, sequence 17 in

Fig. 21. Basal erosion surfaces (dashed lines), overlain by fluvial deposits, cut more than 16 m (A) into tidal depositsof previous sequences. Lateral to fluvial incisions, palaeosols occur (B). Fluvial deposits that overlie outer estuarinetidal sand bar deposits (C), or tidal flat deposits (D) mark a significant seaward shift of depositional facies.



Fig. 10, sequences 20, 27 and 28 in Fig. 11), andare characterized by thin-bedded, ripple-lamin-ated very-fine- to fine-grained sandstones, andplane-parallel-laminated sandstones and mud-stones.

Rooted horizons and coals commonly occur atthe tops of fluvial channel fills. In strike-orientedoutcrops, multiple soils and root horizons occurlateral to the channel margins (Fig. 21B). Most ofthe documented rooted horizons in the coastal-plain succession are limited to the lowstanddeposits, especially where the fluvial channelsgrade upwards into tidally influenced fluvialchannels.

At the base of some sequences, there is a singlefluvial or tidally influenced fluvial channel(sequences 12, 13, 14 and 15 in Fig. 9; sequences13, 14, 15 and 18 in Fig. 10; and sequences 21, 25,26, 27 and 28 in Fig. 11). In other sequences,multiple vertically stacked fluvial or tidallyinfluenced fluvial channels occur, separated byan aggradational muddy interval or floodingsurface (sequence 16 in Fig. 10; and sequences20, 22, 23, 24 and 28 in Fig. 11).

InterpretationThe fluvial and tidally influenced fluvial chan-nels reflect deposition in rivers that becametidally influenced at their the river mouths, belowthe mean high tide (Fig. 22A). The successions ofcoarse-grained fluvial and tidally influenced flu-vial deposits that shift abruptly seawards acrossolder inner- and outer-estuarine deposits of pre-vious sequences are interpreted as lowstanddeposits. The upwards transition from fluvial totidally influenced fluvial deposits indicatesdeposition during the initial relative sea-levelrise. Associated rooted horizons and pedogeni-cally reworked levels suggest that areas betweenthe active channel belts, underwent prolongedsubaerial exposure. (Figs 9–11).

In those sequences that show vertically stackedfluvial or tidally influenced fluvial channels,separated by mud-prone flooding intervals, thebasal channel fill is represented as early lowstandfill, whereas the upper channel deposits belong tolate lowstand. This kind of intra-lowstand flood-ing surface has been described also from contem-poraneous shallow- to deep-marine portions ofthe Eocene clinoforms. Such intra-lowstandflooding is hitherto not widely recognized, but ithas been suggested that it marks the sea-level riseback above the shelf-edge (Plink-Bjorklund &

Fig. 22. During lowstand fluvial deposits accumulatedon the coastal plain (A), in incised valleys erodedduring sea-level falls. River channels were tidallyinfluenced in their seaward ends. Rising relative sea-level drowned the valleys and landward-steppingestuarine deposits accumulated (B and C). The trans-gressive estuarine deposits young landwards as theyonlap. During HST the inner parts of the valleys startedfilling ‘in situ’ (D), and marshes developed over largerareas, as rate of sea-level rise decreased. Gradually theinner estuarine deposits shifted seawards, and theyoungest HST deposits covered the oldest transgressivedeposits.



Steel, 2005). The rising sea-level would havedrowned incised river mouths or distributarychannels (at the shelf edge), and caused tempor-ary sand storage in the fluvial system, until thefluvial systems aggraded, and deltaic systemsprograded back to the shelf edge again to formthe late lowstand deltas (Plink-Bjorklund & Steel,2005). Similar drowning of river mouths, thatcauses temporary sand storage within the fluvialsystem, has been described from modern rivers.

Transgressive surface

At the top of the fluvial channel deposits there isa marked transgressive surface that signifiesvalley drowning and the landward migration ofthe bayline, separating the fluvial lowstanddeposits from the estuarine transgressive depos-its. The transgressive surface separates fluvialaggradation from landward-stepping estuarinedeposition in seaward portions of the coastalplain. On the more landward reaches of thecoastal plain, fluvial aggradation may continueacross the transgressive surface. In these cases the

transgressive surface separates amalgamated,lowstand fluvial deposits from more aggrada-tional fluvial deposits, interbedded with flood-plain, marsh or tidal flat deposits (sequences 13,14 in Fig. 9; sequences 25, 27, 28 in Fig. 11).

Transgressive deposits

The fluvial channels are generally overlain bytide-dominated estuarine deposits (Figs 9–11).These tidally dominated estuarine deposits havea landward-stepping character as they can be seento onlap the basal fluvial deposits in a landwarddirection (Fig. 23A; sequence 16 in Fig. 10). Atthe landward ends of the exposed estuaries (i.e.inner estuarine segments), the landward-steppingis implied by a landward shift of the tidallyinfluenced fluvial channels, and high- andlow-sinuosity tidal channels, i.e. the tidallyinfluenced fluvial channels are replaced by thehigh-sinuosity tidal channels, and the high-sinu-osity tidal channels are replaced by the low-sinuosity tidal channels at gradually higherstratigraphic levels (Figs 9–11). At the seaward

Fig. 23. Estuarine deposits of the landward-stepping facies onlap (white arrow) the basal fluvial deposits in alandwards direction (A). In some sequences the landward-stepping deposits have a basal by tidal ravinement surfacethat cuts through the underlying estuarine deposits (B and C). In places the tidal ravinement surface merges with thesequence boundary. In other sequences, and dominantly in more landward reaches of the sequences, the tidalravinement surface occurs higher up in the sequence, and inner-estuarine or marginal facies occur above the fluvialdeposits and below the outer-estuarine deposits (D).



end of the exposed estuaries (outer estuarinesegment), the landward stepping is implied bythe landward shift of UFR tidal flats and tidalsand bars.

The tidal sand-bar deposits rest on highlyerosional basal tidal ravinement surfaces that insome cases cut through the whole underlyingestuarine and fluvial deposits, and merge with thesequence-bounding erosion surface (sequence 13in Fig. 10, and sequence 21 in Figs 11, 23B andC). In most sequences the tidal ravinement surfa-ces occur within the landward-stepping estuarinedeposits, some distance above the basal fluvialsegment (Fig. 23D). In some sequences the tidalravinement occurs on several stratigraphic levels(sequence 20 in Fig. 11). In most cases, the tops ofthe tidal sand bars mark the landward- to sea-ward-stepping turnaround, i.e. the most land-ward position of outer-estuarine deposits.

The transgressive deposits volumetrically dom-inate the depositional sequences. In contrast tothe lower, fluvial segments, the middle transgres-sive segments are mud-prone, and the only thickand prominent sands are those that occur as tidalsand bars (Fig. 17). The high- and low-sinuositytidal channels are also sandy, but the sands arerather thin (0Æ6–1Æ5 m thick) and discontinuous.

The majority of the mudstones were depositedon marginal tidal flats and marshes. The fluvialoverbank deposits grade seawards and upwardsinto tidal sand to mud flats. This gradual verticaltransition from unipolar rippled and plane paral-lel-laminated beds into more rhythmically bed-ded ripple-laminated beds with mud drapes, andfinally into bipolar lenticular, wavy or flaserbedded units is especially well seen in sequence28 on Storvola (Fig. 11). Depositional units of themarginal sand to mud flats and marshes have acoarsening-up character in the transgressive seg-ment, as gradually higher energy parts of themarginal tidal flats cover the lower-energy areas.Tidal-flat deposits in seaward portions of theestuaries (outer estuarine segment) tend to bemore bioturbated that those in more landwardportions (inner estuarine segment). The latter aremore rich in coal layers, rooted horizons, andplant debris. Coal layers are more abundant in thelowest parts of the landward-stepping segments.

InterpretationThe landward-stepping estuarine succession thataccumulated above the lowstand deposits isinterpreted as transgressive estuarine deposits.A relative sea-level rise is indicated by a land-ward shift of all depositional environments, a

landward onlap, and the development of tidalravinement surfaces (Fig. 22B and C).

Maximum flooding surface

The maximum flooding surface is recognized bythe turnaround from landward-stepping to sea-ward-stepping successions in the seaward rea-ches of the coastal plain. In sequences where theouter estuarine tidal sand bars are present, themaximum flooding surface coincides with the topof the tidal bar deposits (sequences 13, 14, 15, 16and 18 in Fig. 10; sequences 20, 21 and 24 inFig. 11). In the landward reaches of the coastalplain, the highstand deposits are missing or themaximum flooding surfaces have not been recog-nized.

Highstand deposits

The highstand deposits, where present (se-quences 13, 14, 15, 16 and 18 in Fig. 10,sequences 20, 21 and 24 in Fig. 11), comprisesedimentary facies similar to those in the under-lying transgressive deposits. The highstand seg-ment differs from the transgressive segment by (1)a seaward-shift of inner-estuarine facies, (2) moreextensive root horizons and coal layers, and (3) ahigher proportion of marsh deposits.

The seaward shift is mainly indicated byreplacement of outer-estuarine facies with inner-estuarine facies (sequences 15 and 18 in Fig. 10,sequences 20 and 21 in Fig. 11), or low-sinuositytidal channels by high-sinuosity tidal channels(sequences 16 and 18 in Fig. 10, sequence 20 inFig. 11) in successive vertically stacked deposits.The coaly mudstones and coal layers of marshesare volumetrically more significant in the sea-ward-stepping segments compared to the land-ward-stepping segments. Coal layers becomemore abundant towards the top of the seaward-stepping segments.

The presence of high-sinuosity tidal channels,where fluvial-derived and marine-derived depos-its converge, indicates continued bedload con-vergence into the inner estuary, and stronglyindicates that deposition still occurred in anestuarine environment, rather than on a tide-dominated delta plain. Dalrymple et al. (1992)argued that the presence of net landward move-ment of sediment derived from outside the estu-ary mouth (averaged over a period of severalyears) is one of the primary features that distin-guish estuaries from delta distributaries, wherethe net sediment transport is seawards. Similar



seaward-stepping of facies in tide-dominatedestuaries, with the relative distribution of faciesremaining essentially constant has been docu-mented from the South Alligator River estuary(Woodroffe et al., 1989, 1993; see also Harris,1988) and the Gironde Estuary (Allen & Posa-mentier, 1993) since the end of the Holocenetransgression. In a tidally influenced delta, sandsfine seawards unidirectionally, in contrast to theestuaries where sands are coarsest at the head andmouth (see Harris, 1988; Dalrymple et al., 1991).

InterpretationThe seaward-stepping estuarine successions indi-cate decreasing rates of sea-level rise, and areassigned to the highstand systems tract(Fig. 22D). The higher abundance of coals andcoaly mudstones together with the seaward-shiftof inner-estuarine facies strongly suggest thataccommodation in the inner portions of theestuaries was infilled, and marshes developedover larger areas. Similar regressive phases ofestuary development in the Gironde Estuary(Allen & Posamentier, 1993), and the SouthAlligator River estuary (Woodroffe et al., 1989,1993; see also Harris, 1988) occurred duringhighstand of sea-level. Highstand estuaries werealso predicted from conceptual models (Dalrym-ple et al., 1992).

INCISED VALLEYS?

The estimation of the total depth of erosion, i.e.eventual incised valley depth, is not completelyclear, because the outcrops are dominantly dip-parallel. The database, however, strongly suggests

that the estuarine deposits backfilled incisedvalleys, eroded during the preceding sea-levelfalls. The criteria for recognizing incised valleysoutlined by Zaitlin et al. (1994) can be recognizedhere: (i) the basal erosion surfaces are regionalincisions; (ii) the basal fluvial deposits exhibit asignificant basinward facies shift; (iii) the base ofthe incised valleys can be correlated with rootedhorizons in the interfluve areas; and (iv) theestuarine infills onlap landwards the valley walls.Moreover, tide-dominated estuaries require con-finement in a narrow, funnel-shaped geometry(see Dalrymple et al., 1992; Zaitlin et al., 1994),suggesting that the whole thickness of the indi-vidual depositional sequences may have beenconfined within the valleys. This gives anapproximate estimate for the minimal valleydepth for individual sequences, assuming thatthe valley fills were simple, i.e. each valley wasfilled completely during one lowstand-transgres-sive-highstand sequence (see Rahmani, 1988;Wood & Hopkins, 1989; Zaitlin et al., 1994).

The thickness of the depositional sequencesvaries from 7 to 44 m. The database also showsthat the thickest sequences tend to be associatedwith sequence boundaries with the most localerosional relief (Fig. 24). Correlation with shal-low- and deep-marine portions of the sameclinoforms shows that such thick coastal-plainsequences with high local erosional relief pro-duced coeval slope or basin-floor sandstone bod-ies (e.g. sequence 14). Thin sequences with littlebasal erosional relief, on the other hand, generallydid not produce sands beyond the shelf edge.

This implies that the incised valleys of theEocene Central Basin coastal-plain were at least 7to 44 m deep, as it is not known if the valleys

Fig. 24. The thickest sequencestend to be associated with the se-quence boundaries that have mostlocal erosional relief. Such coastal-plain sequences (e.g. sequence 14)were more likely to produce duringfalling stage and lowstand coevalslope or basin-floor sandstone bod-ies.



were filled completely by each of the depositionalsequences. The sequences that have highstandsystems tracts, were obviously filled at least intheir landward reaches, whereas the sequencesthat lack highstand deposits may not have beenfilled during a single sea-level fall-to-rise cycle,unless their highstand portions were erodedduring following sea-level fall, or the highstanddeposits are located further seawards (see below).

SEDIMENT PARTITIONING ON THECOASTAL PLAIN

Falling-stage deposits have not been clearlyidentified in the coastal-plain deposits of theAspelintoppen Formation; although they couldbe locally present but difficult to differentiatefrom lowstand deposits. The fluvial deposits areassigned to the lowstand, rather than to the fallingstage, because they become characteristicallytidally influenced upwards, indicating a base-level rise and bayline migration up the valley.Assigning the amalgamated fluvial channel-filldeposits to the lowstand systems tract is consis-tent with existing stratigraphic practice (e.g.Shanley & McCabe, 1993; Zaitlin et al., 1994;Olsen et al., 1995), although the recognition ofthe intra-lowstand flooding in some of thesequences is unusual. The lowstand was themain phase of fluvial deposition in the EoceneCentral Basin. As the bayline moved significantlyup the valley during the early transgressive time,the clearly identifiable transgressive surfaceformed that separates fluvial deposits from over-lying estuarine deposits (Fig. 22A). However, inlandward reaches of the coastal plain, the trans-gressive surface occurs within the fluvial succes-sion, separating amalgamated channels belowfrom more aggradational channels above (see alsoShanley & McCabe, 1993; Olsen et al., 1995; Plintet al., 2001), as seen in sequence 14 (Figs 9 and10), where early transgressive tidally influencedfluvial deposits in Fig. 9 correlate into estuarinedeposits in Fig. 10. By the time of the latetransgressive systems tract, the estuaries hadmigrated further up-valley, leaving behind alandwards onlapping and landwards youngingtransgressive succession (Fig. 22C). This impliesthat the oldest transgressive estuarine depositsare found close to the incised valley mouth,whereas in the landward reaches of an incisedvalley the estuarine deposits belong to the latetransgressive systems tract. The transgressivesystems tract was the main phase of coastal-plain

aggradation in the Eocene Central Basin of Spits-bergen. During early stages of highstand time,when sea-level rise rate decreased, the estuariesstopped migrating landward, and started fillingin situ (see Dalrymple et al., 1992). The earliesthighstand deposits are found in the inner parts ofthe incised valleys, and the highstand depositsgradually prograded seawards (Fig. 22D). High-stand deposits, where present, are documentedonly in the outer-estuarine reaches of thesequences, as inner estuarine reaches of se-quences 13 and 14 in Fig. 9 consist of lowstandand transgressive tracts, whereas outer-estuarinereaches of the same sequences in Fig. 10 alsocontain highstand deposits. This probably reflectsa lack of accommodation in the inner-estuarinereaches (see Plint et al., 2001). The maximumflooding surface is easy to identify in outerestuarine reaches, where it separates early trans-gressive deposits from highstand deposits andthus the seaward facies shift is clear, as opposedto the inner estuarine reaches, where the maxi-mum flooding surface separates the latest trans-gressive deposits from the earliest highstanddeposits.

CORRELATION TO MARINE SEQUENCES

The detailed correlation of coastal-plain sequencesto their shallow- and deep-marine counterparts isnot the objective of this paper. However, it shouldbe mentioned that the depocentre shifted along thecoastal-plain to deepwater clinoforms duringthe relative sea-level cycles. As explained above,the falling-stage deposits are insignificant on thecoastal plain, whereas on the contemporary shelfand slope falling stage deltas accumulated, as thesediment was fed through the incising valleys.Lowstand deposits were also mainly partitionedbeyond the shelf edge in lowstand deltas, althoughaggradation of fluvial deposits within incisedvalleys also occurred. The intra-lowstand floodingsurface is traceable across the shelf edge and ontothe slope, where it separates the falling-stage andearly lowstand deposits from the prograding latelowstand wedge (Plink-Bjorklund & Steel, 2005).During the transgression, however, the depocentrewas on the coastal plain and inner shelf, assediments were fed into the estuaries both fromthe fluvial and marine sources. Earliest highstanddeposits were partitioned on the coastal plain, butthe depocentre moved out onto the shelf, ashighstand deltas occur within the shelf segmentsof some of the clinoforms. These shelf deltas are



slightly younger than the highstand deposits in thedescribed estuaries.

CONCLUSIONS

Eighteen, fourth-order coastal-plain depositionalsequences, 7–44 m thick, were documented in theEocene Central Basin of Spitsbergen. The deposi-tional sequences consist of basal fluvial deposits,covered by tide-dominated estuarine deposits.Coastal-plain aggradation occurred due to estua-rine infilling of incised valleys, cut during relat-ive sea-level falls.

The incised valleys were filled with: (1) low-stand fluvial deposits, (2) transgressive estuarinedeposits, and (3) highstand estuarine deposits. Thetransgressive deposits volumetrically dominatethe coastal-plain succession, as transgressive timeswere the main phase of coastal plain aggradation.The transgressive estuarine deposits are oldest inseaward reaches of the incised valleys, and youngand onlap landwards. The highstand deposits,preserved on the coastal plain, are interpreted asestuarine rather than deltaic, because of continuedbedload convergence in the inner-estuarine envi-ronment. Highstand deltas developed further sea-wards, and were slightly younger compared to thecoastal-plain estuaries.

ACKNOWLEDGEMENTS

Conoco, Mobil, Norsk Hydro, PDVSA, Phillips,Shell, Statoil and UPRC have financed this workas a part of the Wyoming Consortium on Linkageof Facies Tracts (WOLF). The Swedish Founda-tion for International Cooperation in Researchand Higher Education (STINT) provided a post-doctoral research stipend for Piret Plink-Bjorkl-und. Brian Zaitlin and Robert Brenner reviewedan earlier version of the manuscript and aregratefully acknowledged.

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Manuscript received 26 March 2001; revision accepted11 January 2005



Documents

Stacked ﬂuvial and tide-dominated estuarine deposits in ... · Fig. 1. Spitsbergen archipelago is situated in Norwegian Arctic (A). Location of Eocene Central Basin of Spitsbergen,