Highstand Shelf-margin Delta System

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    A highstand shelf-margin delta system from the Eocene

    of West Spitsbergen, Norway

    Carlos A. Uroza , Ronald J. Steel

    Department of Geological Sciences, The University of Texas at Austin, 1 University Station, C-1100, Austin, TX 78712, USA

    Received 26 March 2007; received in revised form 19 November 2007; accepted 7 December 2007

    Abstract

    Demonstration of shelf-margin accretion by shelf-edge deltas during rising and highstand of relative sea level has important consequences for

    deepwater sand depositional models. Although highstand shelf-edge deltas are conceptually feasible and have been recently argued from

    subsurface data, we describe here the first outcrop example, thus providing facies and architectural data on this important category of delta. Deltas

    are able to reach the shelf-edge during rising sea level, if one or more of the key conditions of sediment supply, shelf width/gradient, or basinal

    processes are such as to allow complete cross-shelf progradation before the onset of delta auto-retreat. Such highstand deltas promote the retention

    of high volumes of sand on the aggrading shelf and coastal plain, and thus potentially have a reduced sand budget available for delivery to the

    deeper water areas. Clinoform 17, one of a series of eastward-prograding, shelf-margin clinoforms from the Eocene Battfjellet Formation on West

    Spitsbergen, contains a sand-rich delta complex sited near the clinoform shelf-slope rollover, and is argued to be a highstand (rising relative sea

    level) shelf-margin delta based on: (1) its highly aggradational architecture shown by an unusual (compared to other clinoforms) regressive unit

    thickness and its marked stacking of parasequences, (2) coeval accumulation of delta-plain and lagoonal deposits that are well-preserved in the

    landward reaches of the same clinoform, and (3) its context within a mappable, longer-term rising shelf-edge trajectory (through 5 clinoforms). It

    is likely that the delta reached its shelf-edge location because the shelf was narrow (less than 20 km), and not because of high sediment supply or

    relative sea-level fall. The delta system was markedly wave-dominated as might be predicted at a shelf-edge site.The sand-rich, shelf-edge portion of Clinoform 17 consists of (1) a 3035 m thick regressive deltaic unit with offshore mudstones and thin

    tempestite layers, wave-dominated delta-front sandstones, and tidalfluvial-distributary channels on the delta topsets, (2) an overlying 1523 m

    thick, aggrading-to-transgressive shoreface/barrier unit with associated tidal-inlet/estuarine channel-fill deposits, and (3) an uppermost, b20 m

    thick regressive deltaic unit similar to (1). The slope successions of the units described in (1) and (3), beyond and below the shelf-edge, contain

    thin upper-slope tempestite sheet sandstones, within an otherwise shale-dominated environment. Neither sandy slope channels nor basin-floor fans

    are observed within the otherwise shale-prone deepwater segments of the clinoform.

    2008 Elsevier B.V. All rights reserved.

    Keywords: Highstand shelf-margin delta; Rising shelf-edge trajectory; Auto-retreat; Rising relative sea level

    1. Introduction

    Shelf-edge deltas developed during conditions of relative

    sea-level fall are well-known from the Pleistocene shelf-margin

    in the Gulf of Mexico (Suter and Berryhill, 1985; Sydow and

    Roberts, 1994; Morton and Suter, 1996; Roberts et al., 2000),

    the Eocene of West Spitsbergen (Mellere et al., 2002; Plink-

    Bjrklund and Steel, 2005), the Porcupine Basin offshore

    Ireland (Johannessen and Steel, 2005), and the PlioPleistocene

    Orinoco delta in Trinidad (Sydow et al., 2003) among others.

    Shelf-edge deltas are conventionally associated with low sea

    level because falling sea level is known to be an efficient driver

    for bringing shorelines entirely across the shelf (Muto and Steel,

    2002). However, deltas that crossed the shelf to the shelf-edge

    area during rising relative sea level (highstand conditions) have

    not been architecturally documented though these have been

    conceptually postulated by Burgess and Hovius (1998), imaged

    Available online at www.sciencedirect.com

    Sedimentary Geology 203 (2008) 229245www.elsevier.com/locate/sedgeo

    Corresponding author.

    E-mail address: [email protected] (C.A. Uroza).

    0037-0738/$ - see front matter 2008 Elsevier B.V. All rights reserved.doi:10.1016/j.sedgeo.2007.12.003

    mailto:[email protected]://dx.doi.org/10.1016/j.sedgeo.2007.12.003http://dx.doi.org/10.1016/j.sedgeo.2007.12.003mailto:[email protected]
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    on seismic data by Bullimore et al. (2005), and described from

    subsurface data by Carvajal and Steel (2006).

    The two conditions that would most likely promote highstand

    deltas at or near the shelf-edge are: (1) high and continuous

    sediment flux from supply-dominated deltas (e.g., Einsele, 1996;

    Burgess and Hovius, 1998), and (2) narrow shelves (Fleming,

    1981; Ito and Masuda, 1988). A narrow shelf causes shelf-transittime to be brief and would allow the delta to reach the shelf-edge

    before auto-retreat is enacted (Muto and Steel, 1997, 2002).

    Narrow shelf settings would clearly sustain shelf-edge deltas

    irrespective of whether sea level was falling or rising. Deltas that

    are supply-dominated, and driven to the shelf-edge by high

    sedimentflux (rather than by negative accommodation)are ableto

    transit even moderately wide shelves under conditions of rising

    relative sea level. Such supply-dominated deltas not only accrete

    at the shelf-margin, but also have the potential to deliver large

    volumes of sand to the deepwater slope and basin-floor areas as

    occurs in the Maastrichtian Fox HillsLewis system, SE

    Wyoming (Carvajal and Steel, 2006). It should also be noted

    that this high-supply condition is likely to have an additional

    effect. Even where the shelf-margin prism is wide (and therefore

    potential transit distance for deltas is great) the transgressivetransit may take the retreating deltas only a short distance back

    across the shelf, i.e., the deltas remain on the outer-shelf platform

    site throughout a series of cycles (Burgess and Hovius, 1998;

    Burgess andSteel, in press). This situation is in contrast to settings

    where sea level plays a larger role, i.e., where accommodation-

    drive forces deltas to transgress back across much of the shelf

    platform during each half-cycle. We illustrate here a case where

    deltas reach a shelf-edge position during rising and highstand sea-

    Fig. 1. (A) The Central Tertiary Basin and the West Spitsbergen Orogenic Belt (modified from Blythe and Kleinspehn, 1998). (B) The Van Mijenfjorden Group,

    showing the Lower Eocene Battfjellet Formation (modified from Steel et al., 1985). (C) Location of the study area in Van Keulenfjorden, showing the location of themountains Storvola and Hyrnestabben, and the 17 measured profiles from both mountains. See also the approximate shelf-break location for Clinoform 17.

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    level conditions, not because of high supply (calculation of shelf-

    margin accretion/aggradation rates show that the supply was

    relatively low), but because shelf width was less than 20 km.

    However, despite the deltas being perched at the shelf-edge there

    was little sand delivered down into the deepwater areas beyond, to

    judge from the absence of slope channels or basin-floor fans. The

    deltas simply aggraded at the shelf-margin.

    The Eocene Battfjellet Formation in West Spitsbergen,

    Norway (Fig. 1) provides good examples of deltas that prograded

    to the shelf-edge during both falling and rising sea-level

    conditions. The Battfjellet Formation succession is composed ofabout 20 sand-prone, eastwards prograding, shelf-margin clino-

    forms (Steel and Olsen, 2002) each deposited during a time

    interval of a few 100 ky (4th-order sequences) (Steel and Olsen,

    2002; Petter and Steel, 2006). In this study we selected Clinoform

    17, which is located towards the top of the Battfjellet Formation.

    This clinoform is markedly aggradational along its topset (Fig. 2),

    shows landward-interfingering with delta-plain and lagoonal

    deposits and lacks deep channelized erosion, characteristics

    typical of shoreline successions that accumulate during relative

    rise of base level, i.e., with normal regression (Helland-Hansen

    and Martinsen, 1996). This aggradational growth style contrasts

    greatly with what is observed in some other clinoforms of the

    Battfjellet succession (Fig. 3), where there are much thinner andmore amalgamated progradational units into which there are

    multiple fluvial incisions, suggesting much flatter shoreline

    Fig. 2. General view of the 3 component units 17A, 17B and 17C within Clinoform 17 at Profile 13 location. The clinoform topset succession here is about 80 m thick.Note the two upward-coarsening parasequences in 17A, and the significant thickness (shoreface and barrier/tidal-inlet succession) of unit 17B.

    Fig. 3. Schematic shelf-edge trajectories for 4th-order Clinoforms 1417 (Battfjellet Formation). Figure is not to scale andis vertically exaggerated(slope angle: 34).

    Note the initial flat trajectories for Clinoforms 14 and 15 (implying stable to falling relative sea level) prior to rise and transgression. For Clinoforms 16 and 17, the

    trajectoryis generallycontinuously rising, implying a lack of sea-level fall. Sketch shows partitioning ontothe shelf, slope and basinfloor. Shelf-edge deltas develop on

    theshelfsegment of theclinoforms;slopechannels and basin-floorfansare developed in theearlystage of Clinoforms 14 and possibly 15. Clinoform # 14is an exampleof type 1; # 15 could be either type 1 or 2; and # 16 and 17 are examples of type 3. A type 4 clinoform is not present in this succession.

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    trajectories or even falling relative sea level (e.g., Mellere et al.,

    2003). The aggradational style of clinoform 17 implies that much

    of the sediment budget is likely to have been trapped within the

    coeval coastal plain and shelf segments of the clinoform, with

    correspondingly less potential to deliver sand to the deepwater

    slope and basin floor (Fig. 3).

    The purpose of this paper is to characterize Clinoform 17 interms of its facies associations, external geometry, internal

    architecture and sequence stratigraphy. We will evaluate the role

    of waves, tides, and river currents in molding the component

    sand-bodies and will argue that the entire clinoform developed

    under rising relative sea level.

    2. Geological setting

    2.1. Structure and stratigraphy

    Spitsbergen is the largest island of the Svalbard archipelago,

    located to the north of mainland Norway (Fig. 1) and in thenorthwest corner of the Barents shelf (Kellogg, 1975). Early

    Eocene transpression, as N Greenland slid northwards past the

    Barents shelf, during the opening of the NorwegianGreenland

    Sea, formed the West Spitsbergen Orogenic Belt (Harland, 1969;

    Steel and Worsley, 1984) with areas of basement uplift, folding

    and thrusting along a NNWSSE trending fold- and thrust belt

    (Fig. 1A). Regional flexural subsidence produced by loading of

    thrust sheets along the orogenic belt formed the Central Tertiary

    Basin (Steel et al., 1985; Braathen et al., 1999). During initial

    periods of activethrusting, the subsiding area was a foreland basin,

    but through continued thrusting it may have taken on the character

    of a piggy-back basin in the study area (Blythe and Kleinspehn,

    1998). Infilling of this basin occurred with moderate subsidencerates (Schellpeper, 2000), with sediments supplied mainly

    transversely from the growing orogenic belt to the west

    (Helland-Hansen, 1990). The basin filled by the development

    and growth of large-scale clinoforms (200400 m high)

    representing a linked coastal plain/shelf/slope/deepwater basin-

    floor system that systematically migrated eastwards in the Early

    Eocene (Helland-Hansen, 1992; Steel and Olsen, 2002). The

    sedimentary succession, latest Paleocene through Early Eocene in

    age (Manum and Throndsen, 1986), is about 1.5 km in thickness

    and has a lithostratigraphy consisting of the Frysjaodden (deep-

    water slope and basin floor), Battfjellet (shoreline and shelf) and

    Aspelintoppen (coastal plain and estuarine) Formations (Fig. 1B).

    2.2. Battfjellet formation clinoforms

    The basin transect transverse to the fold-and-thrust belt along

    Van Keulenfjorden (Fig. 1) contains some 20 shelf-margin

    clinoforms, which have previously been classified into four

    types depending on: (1)the progradational trajectory at the shelf-

    break, (2) the degree of fluvial channel incision at the shelf-edge,

    and (3) the presence or absence of thick sand at this outermost

    part of the shelf (see Steel et al., 2000). Type 1 clinoforms show a

    flat-to-downward shelf-break trajectory with marked fluvial

    erosion and often collapse features, resulting in sand by-pass and

    partitioning into the slope and basin floor (e.g. Crabaugh and

    Steel, 2004; Petter and Steel, 2006). Type 2 clinoforms have a

    flat or low-angle rising trajectory but lack large channels or deep

    erosion at the shelf-edge and deposit shelf-attached turbidite

    aprons on the slope, without the development of basin-floor fans

    (e.g. Plink-Bjrklund et al., 2001; Mellere et al., 2002).

    Clinoform 17, presented here, is an example of Type 3 cli-

    noforms where there was significant cross-shelf sand transport,but a generally rising shelf-edge trajectory and consequent

    aggradational style of the clinoform topsets resulted in only

    modest to negligible volumes of sand being delivered onto the

    slope or basin floor (see also Deibert et al., 2003). On the outer

    shelf, the deltas were substantially reworked by waves, and

    much sand was carried alongshore, because of exposure to open

    ocean swell and storm waves. Type 4 clinoforms are entirely

    muddy on the outer shelf and deepwater reaches because the

    deltas did not reach even the outer-shelf areas of the system.

    Clinoform Types 1 and 2 are relatively thin (2050 m) along

    their topset reaches, and generally show evidence of stable to

    falling relative sea level during development. Type 3 clinoforms,described herein, have thicker (N80 m un-decompacted) and

    more aggradational (significant marine mudstone interfingering)

    topsets, show a more marked parasequence stacking, lack deep

    fluvial incisions, and so are interpreted to have developed with

    continuously rising relative sea level (Fig. 3).

    Clinoform 17 has an intermittently exposed length of about

    15 km from Brogniartfjellet to its distal reaches on Hyrnes-

    tabben, and a thickness of about 80 to 100 m (un-decompacted)

    in the Storvola and Hyrnestabben areas, respectively. Internally,

    Clinoform 17 has three distinctive units (Fig. 2), two of them

    (17A and 17C) showing regression with aggradation, whereas

    the middle one (17B) is initially progradational but becomes

    highly aggradational to slightly backstepping.

    3. Methodology

    The study transect of Clinoform 17 (Fig. 1) is oriented within

    20 of a true depositional-dip section. Fieldwork consisted of:

    (1) measuring 18 vertical sedimentary profiles (see Fig. 1C for

    location of profiles 117) at progressively downdip locations

    along 3 mountainsides (Brogniartfjellet, Storvola and Hyrnes-

    tabben), located in the Van Keulenfjorden area of West

    Spitsbergen, (2) outcrop photographing from both the ground

    and helicopter to delineate the general sand-body geometry, and

    to aid in the characterization of the deltas and other relatedfacies, and (3) gamma-ray profiles through part of the

    succession in three locations in order to compare the gamma-

    ray response with most of the facies associations. The external

    geometry and internal architecture of Clinoform 17 were

    documented using helicopter photomosaics and a constructed

    correlation panel of measured profiles. This panel was hung

    from a transgressive mudstone level lying above and parallel to

    the shelf platform of Clinoform 17.

    4. Early Eocene shelf-margin accretion in Van Keulenfjorden

    The Spitsbergen shelf-margin (along the exposed transect)

    shows a relatively low accretion rate into the basin. The shelf-

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    break prograded at a rate of about 5 km/my and aggraded at a rate

    of 192 m/my, together suggesting relatively low sediment-supply

    conditions compared to other margins of similar clinoform

    amplitude (Carvajal and Steel, 2006; Steel et al., in press). This

    low apparent rate of sediment supply strongly suggests that the

    Spitsbergen deltaic delivery systems would have required the aid

    of negative accommodation (sea-level fall) in order to partitionsignificant sand volumes out beyond the shelf-edge into the

    deepwater slope and basin floor. However, for Clinoform 17,

    there appear to be no coeval deepwater sands, and rather than sea-

    level fall, there is evidence of continuous sea-level rise. It is most

    likely that it was mainly the narrowness of the shelf that allowed

    the deltas to reach the shelf-edge. For both Clinoform 17 and the

    underlying Clinoform 16, the deepwater slope was markedly

    mud-prone, with only very thin tempestite beds seen on the distal

    mountainside of Hyrnestabben.

    5. Facies associations

    The three units of Clinoform 17 show some common

    features in terms of facies associations. The lower and upper

    units (17A and 17C) pass upwards from offshore mudstones at

    the base, to a wave-dominated delta front, which is then

    truncated by tidally-and-fluvially-influenced distributary chan-

    nels towards the top of the succession. However, unit 17B

    consists of muddy lagoonal facies in its basal and landward

    reaches, followed by a thin transgressive mudstone and

    overlying shoreface facies that are truncated by tidal-inlet

    deposits with an offshore mudstone capping. These deposits are

    fronted by a vertically-aggrading barrier island succession.

    Facies associations are organized here in two groups: units 17A

    and C, and unit 17B. Each group is in some manner described

    from shallower to deeper paleowater depth.

    5.1. Facies associations for units 17A and C

    5.1.1. Tidally-influenced fluvial-distributary channels

    This association overlies (typically erosionally) the upward-coarsening deposits of units 17A and 17C (described below in

    Section 5.1.2), and shows a general fining-upwards of grain size

    (Figs. 4 and 5). The association in unit 17A consists mainly of

    fine- to medium-grained cross-stratified sandstones that have

    planar and trough cross-strata with westward orientation,

    though south to southeastward-oriented cross-strata are also

    found (see Fig. 4). Towards West Storvola, the sandstones are

    medium- to fine-grained with mainly eastward-oriented planar

    and trough cross-strata (but also some south to southeast-

    oriented cross-stratification), lack marine indicators, and show

    erosional surfaces with coal debris and mud pebbles within the

    cross-stratified beds (Fig. 5). In unit 17C, there is an abundanceof eastward-oriented cross-stratification, structureless beds,

    convolute bedding, multiple internal erosional surfaces with

    coal debris and mud pebbles, and current-ripple laminae atop

    the individual sets of cross-strata.

    The erosional bases and general fining-upward tendency of the

    individual sandstonebodies high in units17A andC, with abundant

    cross-strata, and association with underlying delta-front facies

    (see Section 5.1.2 below), suggest distributary channels (Bhatta-

    charyaand Walker, 1991; Coleman et al., 1964). At some locations,

    especially towards the east of Storvola, an abundance of westward-

    oriented paleocurrents in the distributarychannels, and the presence

    of subordinate southeastward-oriented cross-strata, suggest that

    Fig. 4. Tidally-influenced distributary channel deposits from unit 17A, Profile 16 ( Fig. 1), East Storvola. (A) Cross-stratified sandstone at the base of a tidally-

    influenced channel fill (35 cm stick as scale). (B) Tidally-influenced channel eroding the flat to swaley cross-stratified delta-front deposits. (C) Medium-grained

    sandstone with landward-oriented cross-strata sets (flood-tide generated dunes) and smaller-subordinated ebb-oriented cross-strata on top (section in C is 90 cm thick.(D) Cross-stratification (bidirectional) located few meters laterally of photo C (section in D is 80 cm thick).

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    there was some tidal influence in the channels (Dalrymple and

    Choi, 2007). Towards the westward (landward) end of the system,

    the distributary channels contain abundant eastward-oriented

    trough and planar cross-strata, created by the downdip migration

    of3D and 2D dunes (Miall, 1978). Here, we also use the consistent

    seawards orientation of paleocurrent data (see Fig. 5) as a signal ofthe fluvial influence (see also Selley, 1968; Long, 1978). The

    gamma-ray curves in Figs. 4 and 5 show a blocky character for

    both channel types, which is typical of such deposits.

    5.1.2. Wave-dominated delta-front deposits

    This association, identified in units 17A and 17C, is

    characterized by upward-coarsening and thickening successions

    (up to 57 m thick) containing a high sand/mud ratio, which are

    capped by thick-sand channelized units (see earlier Section

    5.1.1). The association overlies transitionally the deposits of the

    muddy association described below in Section 5.1.3. The

    sandstones are mostly well-sorted and fine-grained, but rangefrom very-fine to lower medium-grained. They show a

    predominance of flat lamination, swaley cross-stratification

    (2080 cm sets that can be followed 10 s of m laterally), and

    wave-ripple lamination (Figs. 6 and 7), though hummocky

    cross-strata, current-ripple lamination, scattered Ophiomorpha

    burrows and soft-sediment deformation structures (load casts,

    pillows and water escapes structures) (Figs. 6 and 7) are also

    common. Locally, mud pebbles are found within the hummocky

    and swaley cross-stratified facies (Fig. 6). Sets of planar and

    trough cross-stratification, associated with sets of wave-ripple

    laminae, are also found especially towards the top of the

    individual coarsening-upward sand packages. It is also common

    to find abundant plant and other organic material within the

    finer-grained beds. Gamma-ray response (Fig. 6) shows a

    decreasing-up pattern for this association.

    The upward-coarsening successions of 17A and C are

    interpreted as delta-front deposits, with the corresponding

    prodelta deposits immediately below, because of their channe-

    lized capping (see Fig. 6 and Section 5.1.1 above), the verticalgrain size trend, the vertical thickness of the whole section (up

    to 25 m thick) including the prodelta below (see Section 5.1.3),

    and the presence of abundant plant and other organic matter in

    the finer-grained beds. The occurrence of hummocky and

    swaley cross-stratification indicates the strong influence of

    storm waves on the delta front (Dott and Bourgeois, 1982;

    Leckie and Walker, 1982; Walker et al., 1983; Swift et al., 1983;

    Walker and Plint, 1992). The presence of load-cast, pillows and

    water escapes structures associated with the swaley and

    hummocky cross-stratified beds may possibly result from the

    cyclic effect of storm waves on unconsolidated sediments (see

    Molina et al., 1998; Alfaro et al., 2002). Also, the occurrence ofmud pebbles within the hummocky and swaley-stratified facies

    may correspond to lag deposits (Kreisa, 1981) created by

    storms. Intervals of wave-ripple laminae are a common feature

    in the upper part of the individual storm-beds, and may indicate

    fair-weather wave reworking. The intervals up to medium-

    grained sandstone with sets of planar and trough cross-strata

    (also capped by wave-ripple lamination) may indicate more

    proximal mouth-bar facies on the delta front.

    5.1.3. Prodelta to offshore mudstones with occasional thin-

    bedded sandstones

    These are abundant at the bottom of unit 17A and also

    present at the base of unit 17C (Hyrnestabben location). This

    Fig. 5. Fluvial-distributary channel facies without obvious tidal influence, unit 17A, Profile 1, West Storvola. (A) Mudstone pebbles and coal debris at the base of

    trough cross-stratified sets (20 cm stick as scale). (B) Erosional contact (highlighted by yellow line) between fluvial-distributary channel and delta-front facies (50 cm

    stick as scale).

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    association is up to 18 m thick and composed mainly of gray

    mudstones, but also contains some thin beds of very-fine to fine

    sandstone, in beds and bedsets up to 1 m thick. These thin beds

    (usually b40 cm) are ripple-laminated or flat-laminated, or

    show alternating rippled (mostly current-ripples, but also wave

    ripples in some parts) and flat-laminated intervals. Bioturbation

    is mostly represented by Phycosiphon and some Planolites

    traces.

    Because of its stratigraphic position, fine grain size and

    marine-like bioturbation, the association is interpreted as off-

    shore/prodelta to shelf deposits, with thin turbidite-like beds (flat-

    to-ripple-laminated beds) that are probably tempestites because

    Fig. 7. Common sedimentary structures in the delta front: (A) soft-sediment deformation (load casts and water escape structures) at base of the sandy delta-front

    succession of unit 17A, Profile 15, Storvola (meter stick as scale). (B), (C) and (D) Symmetrical wave ripples from Profiles 6, 10, and 17 respectively. 20 cm stick asscale in D.

    Fig. 6. Upward-coarsening, wave-dominated delta-front facies (including base of distributary channel on top of delta front); Profile 1, West Storvola ( Fig. 1) (vertical

    scale in meters). (A) Stacked swaley cross-stratified sandstone sets. (B) An 80 cm thick section of swales alternating with wave-ripple lamination. (C) Soft-sediment

    deformation at the bottom of the delta front (50 cm meter stick as scale).

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    of their wave-rippled capping (see also Myrow and Southard,

    1991, 1996) and their updip association with wave-dominated

    shoreline deposits. Reineck and Singh (1972) described similar

    laminated sand beds within shelf mudstones from the modern

    North Sea and interpreted them as storm deposits.

    5.1.4. Upper-slope turbidite-like beds (tempestites)These are found on the mountainside of Hyrnestabben

    mostly at the bottom of unit 17A, and they occupy an upper-

    slope setting on the clinoform, just basinwards of the shelf-slope

    break. Updip, they are also associated with the delta front

    described in Section 5.1.2. These beds are composed of sharp-

    based, thin sets of flat- to ripple-laminated, fine to very-fine

    sandstone, interbedded with mudstones. It is common to find

    Phycosiphon trace fossils within the muddy beds (A. Uchmann,

    2004, personal communication).

    Because of their slope setting and association with an updip

    delta front that is storm-wave dominated, these beds are likely to

    be storm-wave generated from the shelf-edge area and drivenout onto the upper slope as tempestites during storms (see also

    Myrow and Southard, 1991, 1996).

    5.2. Facies associations for unit 17B

    5.2.1. Fluvial crevasse channels and splays (within coastal

    plain deposits)

    This association is preserved on west Storvola (see panel in

    Fig. 12) and on Brogniartfjellet (west of Storvola). It comprises

    relatively thin (11.5 m thick), channelized successions of fine-

    grained sandstone with sets of trough cross-strata and current-

    ripple lamination towards their top (Fig. 8). Structureless

    sandstone is common and soft-sediment deformation is also

    present. These channelized units are frequently capped by coal

    layers. Within this association, there are also thin sheet-like

    packages of fine to very-fine sandstone with current-ripples and

    wavy bedding.

    The abundant coal layers capping the channels, suggestsdeposition within the coastal plain and rapid abandonment to

    areas of vegetation (see Guion, 1984; Fielding, 1985). This, in

    turn, strongly suggests that these thin channelized successions

    do not reflect distributary channels but are ephemeral crevasse

    channels, with their associated crevasse splays (sheet-like sand-

    bodies), that occasionally broke out from the distributaries

    during floods (Elliott, 1974; Fielding, 1984). The sandstone

    bodies of this association are similar in character to those

    described by Plink-Bjrklund (2005) for the coastal plain of the

    Aspelintoppen Formation on Brogniartfjellet and Storvola.

    5.2.2. Lagoonal deposits (brackish-water mudstones)This association is composed of mudstone deposits, which

    are rich in carbonaceous matter (thin coal layers, plant and coal

    fragments), and is mainly located westwards of the tidal-inlet-

    channel deposits of unit 17B (see panel in Fig. 12). Towards the

    west of Storvola, they are also interbedded with the fluvial

    crevasse channel and crevasse-splay deposits, described above

    in Section 5.2.1.

    We interpret these deposits as brackish-water lagoonal

    mudstones because of their abundant organic content (Reading

    and Collinson, 1996) and the absence of marine fauna (D. Van

    Nieuwenhuise, 2007, personal communication). They also

    Fig. 8. Fluvial channel and crevasse-splay deposits from unit 17B, Profile 2, West Storvola. (A) Trough cross-stratified sandstone at base of channel (85 cm stick asscale). (B) Rippled sandstone probably associated with crevasse-splay deposits. 17 cm stick as scale (lower right of photo).

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    occupy a position behind the tidal-inlet-barrier complex of unit

    17B (see Fig. 12).

    5.2.3. Tidal-inlet deposits

    This association is erosionally based, dominates unit 17B in

    places and is up to 15 m thick. It is composed of clean, well-to-

    moderate sorted, fine to coarse-grained sandstone, with cross-sets that have characteristic and persistent northwestward-

    directed paleocurrents (Fig. 9). Individual cross-sets are up to

    1.5 m. thick, and some are capped by wave-ripple lamination.

    This association is generally in erosional contact with the

    underlying shoreface and barrier bar deposits (Figs. 9 and 12).

    The gamma-ray response of this association is blocky in

    character, with a slight increasing-upward trend towards the top

    of the succession (see Fig. 9).

    These deposits are interpreted as inlet-channel infill (Hoyt

    and Henry, 1967; Kumar and Sanders, 1974; Moslow and Tye,

    1985) because of their location between lagoonal and barrier

    deposits, their marked and deep channelized erosion andpersistent flood-tidal paleocurrents (northwestward-oriented),

    great thickness, and their incision into the wave-generated

    shoreface and barrier deposits.

    5.2.4. Shoreface

    This association, particularly found at the bottom of unit

    17B, is up to 9 m thick, and contains some coarsening-upward

    packages (up to 35 m thick). Plane parallel-laminated fine-

    grained sandstones with wave-ripple capping, and hummocky/

    swaley cross-stratified sandstone sets, also capped by wave-

    ripple lamination, dominate the association (Fig. 10). Bioturba-

    tion is common, with mainly Ophiomorpha burrows (Fig. 10B)

    and soft-sediment deformation (mainly load casts) is also

    prominent. Some planar and trough cross-strata, wavy lamina-tion, and current-ripple lamination, also occur. Gamma-ray

    response, for this association, shows a decreasing upward

    pattern (Fig. 10).

    We interpret this facies association as shoreface deposits,

    based on the following: (1) it is a coarsening-upward facies

    succession (above marine mudstones) that was deposited during

    coastal progradation (sensu Walker and Plint, 1992), (2)

    occasionally there are sharp-based sandstone beds with hum-

    mocky cross-strata and wave-ripple lamination, which corre-

    spond to storm-beds (see also Dott and Bourgeois, 1982; Walker

    et al., 1983), (3) there is an absence of a fluvial feeder landwards

    of the association (see Fig. 12), (4) this wave-dominatedsuccession did not prograde as far as the earlier deltaic system.

    5.2.5. Sandy barrier complex

    This association occurs within unit 17B and it is represented

    by an upward-coarsening succession (up to 13 m thick) (Fig. 11)

    with similar facies to those described above in Section 5.2.4.

    Sandstone is mostly fine-grained, well-sorted, with mainly

    Fig. 9. Tidal-inlet-channel facies from unit 17B, Profile 9, Mid Storvola. (A) Channel eroding into the shoreface facies (40 cm stick at lower portion of photo). (B) and(C) Tabular cross-bedding oriented landwards (45 cm stick as scale in B, and 30 cm in C).

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    swaley cross-stratified and plane parallel-laminated sets, though

    hummocky cross-strata sets are also common. Individual

    bedsets are 1040 cm thick and commonly capped by wave-

    ripple lamination (Fig. 11). Sets of swaley cross-strata within

    this association reach a few m in wavelength. Ophiomorpha

    burrows are common, and minor low-angle cross-bedded

    sandstones are also found within the succession.

    All the features described above are indicative of a wave-

    dominated shoreface setting (Walker and Plint, 1992). However,

    the position of this association near the shelf-slope break (see

    Fig. 11. Barrier-bar facies from the seaward end of unit 17B, Profile 16, East Storvola. (A) Swaley cross-stratification (50 cm stick as scale). (B) Plane-parallel and

    wave-ripple lamination in alternation within sandstones. (C) Close-up of middle portion of A showing SCS (30 cm stick as scale). (D) Swaley cross-stratifiedsandstone capped by wave-ripple laminated sandstone. Walking stick scale in B and D: 70 cm.

    Fig. 10. Shoreface facies from unit 17B (regressive component), Profile 9, Storvola. (A) Shoreface facies truncated by tidal-inlet channel (see truncation T

    highlighted by red line). Outcrop section in A is about 2.2 m. (B) Flat-laminated sandstone with Ophiomorpha burrows (see black pen as scale).

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    Fig. 12. Correlation Panel and helicopter photomosaics for Clinoform 17, Battfjellet Formation, West Spitsbergen. The whole clinoform is interpreted to have developed du

    located towards the eastern and western ends of Storvola respectively.

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    Fig. 12) and its thickened aggradational character (Fig. 11)

    suggest that this association is a barrier complex (McCubbin,

    1981; Reinson, 1992; Friis et al., 1998) related to the initiation

    of transgression in the system. This barrier complex is mostly

    developed on eastern Storvola and pinches out into mudstones

    between Storvola and Hyrnestabben (see correlation panel in

    Fig. 12).

    6. Clinoform 17: geometry, architecture, and formative

    processes

    6.1. Geometry and architecture

    The geometric configuration of Clinoform 17 as a whole, as

    well as of the component sand-bodies of this deltaic and barrier

    lagoon succession, is illustrated in Fig. 12. The clinoform is

    mainly seen in a 2-D, near-downdip section. Similarly to the

    stratigraphic configuration of the underlying clinoforms (num-

    bers 12

    16) on Storvola, a shelf-slope break is preserved inClinoform 17. This slope break must occur between the two

    mountains, because Storvola contains the shelf-edge deltas,

    whereas on Hyrnestabben the same clinoform mostly shows

    muddy slope deposits with thin tempestite sands (Fig. 12).

    Fig. 12 clearly illustrates the general rising character of the

    shoreline trajectory within the progradational trend of the

    Clinoform 17 shoreline system (yellow and light red colors),

    and the coeval, parallel rising belts of coastal plain/lagoonal

    (green colors) and offshore (blue) deposits. In addition tothese topset components of the clinoform, the shale-prone,

    upper-slope component of the shelf-margin can also be seen at

    the right-hand end of the correlation panel on the mountain

    Hyrnestabben. Complicating this overall stratigraphy in

    Fig. 12, the three main phases of shoreline development are

    evident, namely an early regressive phase (17A), a middle

    aggradational to slightly transgressive phase (17B), and a late

    regressive phase (17C). Phases 17A and C are thick wave-

    dominated delta successions with well-preserved feeder

    distributary channels emphasizing the normal character of

    shoreline progradation. Phase 17B represents an intervening

    interval of initial coastline progradation with aggradation andthen slight transgression, during which an inlet-channel and

    barrier/lagoon coast developed. This temporary aggradation/

    Fig. 13. Schematic summary of the depositional history of Clinoform 17, including the depositional setting for the three component units. The whole deltaic system isinterpreted to have been deposited under highstand conditions. Figure is vertically exaggerated. Slope angle: 3 4.

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    transgression in 17B further emphasizes the overall aggrada-

    tional character of Clinoform 17.

    Clinoform 17 resembles the geometry of other documented

    clinoform successions that developed associated with a rising

    shelf-edge trajectory. For example, Bullimore et al. (2005)

    documented seismic-scale clinoforms with high-angle positive

    shelf-edge trajectory in the Norwegian Sea Molo Formation.Here, they attributed this condition to normal regression in

    which coastal plain units were deposited and preserved in the

    topset segment of the clinoforms (see Bullimore et al., 2005,

    Figs. 6 and 8).

    6.2. Variability of depositional processes on the clinoform

    Clinoform 17 shows evidence of an interplay of fluvial,

    wave, tidal, and storm ebb-surge processes, though the wave

    domination on the open coast is clear throughout the record of

    the overall regressive-aggradational shelf transit of the deltaic

    system. Wave-domination is evidenced both on the delta-frontdeposits of units 17A (Figs. 6 and 7) and 17C, and the shoreface

    (Fig. 10) and barrier facies (Fig. 11) of unit 17B. Storm ebb-

    surge processes (Mount, 1982; Dott and Bourgeois, 1982;

    Cheel, 1991) acted at different times during the regressive

    transit of the delta system, and they were responsible for the

    deposition of the thin tempestite sand beds within the mud-

    prone prodelta to offshore and upper-slope environments, and

    probably the hummocky cross-stratified beds. Strong tidal

    influence, on the other hand, is seen especially well in the

    aggradational to transgressive deposits of unit 17B (Fig. 9), and

    in the distributary channels of units 17A (Fig. 4) and 17C.

    Fluvial influence is implicit at all times during the coastal

    regression and is especially implied by the system reaching the

    shelf-break area despite the overall aggradational tendency. The

    fluvially-influenced portion of the distributary channels is well-

    preserved in 17A (Fig. 5) and 17C.

    7. Discussion

    7.1. Clinoform 17: a highstand shelf-edge delta system

    The characteristics of Clinoform 17 described above show

    clearly that:

    It is a sand-rich delta system.

    The delta system was sited on the shelf-margin, near the

    shelf-slope break of the clinoform (Figs. 12, 13 and 14).

    The markedly aggradational character of the delta complexduring progradation strongly suggests that relative sea level was

    rising during its development (see also Helland-Hansen and

    Gjelberg, 1994; Bullimore et al., 2005). There is no evidence of

    forced regression (sensu Posamentier et al., 1992) or relative sea-

    level fall. The partly aggradational/transgressive middle interval

    (unit 17B) in Clinoform 17 further reinforces its overall

    aggradational character (Figs. 12 and 13).

    Despite its shelf-slope break site, the deltas were apparently

    able to deliver only modest volumes of sand out onto the

    Fig. 14. The conventional lowstand model (A) vs. the highstand model (B) proposed here for clinoform growth, Battfjellet Formation, West Spitsbergen.

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    adjacent deepwater slope, and there was no visible development

    of turbidite slope channels, or basin-floor fans (see also Deibert

    et al., 2003) despite relatively good exposure on adjacent

    mountains.

    These features together strongly suggest that Clinoform 17

    represents a highstand (rising relative sea level) shelf-edge deltasystem that crossed a relatively narrow shelf (Fig. 13). The

    occurrence of highstand shelf-edge deltas is somewhat unusual

    in the literature because falling relative sea level is commonly

    invoked to account for deltas at the shelf-edge, giving rise to

    lowstand shelf-edge deltas (Muto and Steel, 2002; Porbski and

    Steel, 2003) (Fig. 14). Clinoform 17 can therefore be used to

    test some literature concepts concerning highstand deltas at the

    shelf-edge.

    7.2. Clinoform 17: an outcrop test of highstand shelf-edge

    deltas

    7.2.1. Occurrence of shelf-edge deltas during highstand

    Although no previous highstand shelf-edge deltas have

    been described from outcrops, there have been a number of

    suggestions as to the conceptual feasibility of highstand deltas

    reaching the shelf-edge. Initial suggestions were made by

    Burgess and Hovius (1998), especially for short shelf-transit

    distances. Such occurrences were disputed by Muto and Steel

    (2001), who emphasized the auto-retreat tendencies of deltas

    during rising sea level, especially during long shelf transits.

    However, later subsurface descriptions of highstand shelf-

    edge deltas (50100 km wide shelves), made by Carvajal and

    Steel (2006), concluded that this was possible because of a

    supply domination during shelf transit. Also, Hiscott (2003)documented highstand delta lobes (though muddy), sited on

    the outer continental shelf to upper slope, from the Late

    Quaternary Baram delta of northwestern Borneo. This history,

    plus the outcrop evidence from Clinoform 17 herein, suggests

    that:

    Most deltas can attain a shelf-edge position at lowstand of

    sea level, irrespective of shelf width, and generate sands into

    deepwater areas. This scenario is the conventional one, is

    accommodation driven, and does not require a high fluvial

    drive (see also Porbski and Steel, 2006; Yoshida et al., 2007)

    (Fig. 14A).Deltas can attain a shelf-edge position at highstand of sea

    level if sediment supply is very high, irrespective of shelf width,

    and can also generate deepwater sands. This is the supply-

    driven scenario (see Carvajal and Steel, 2006).

    Even low-supply delta systems, such as has been argued for

    Clinoform 17, can reach the shelf-edge as highstand deltas if

    shelf width is narrow. Nevertheless slopes are likely to be

    muddy, and delivery of deepwater sand is likely to be minimal,

    unless the shelf width is reduced severely.

    The delivery and accumulation of large volumes of deep-

    water sands is most favored by (a) high sediment supply, (b)

    deltas drawn to the shelf-edge by falling relative sea level, and

    (c) significantly narrow shelves.

    7.2.2. Wave influence at the shelf-edge

    Other characteristics of highstand deltas have been proposed.

    For example, Porbski and Steel (2006) and Yoshida et al.

    (2007) have suggested that shelf-edge deltas should normally be

    wave-dominated, because waves arriving at the shelf-edge from

    the open ocean are large, but tend to become smaller as they

    cross the shelf. This was also observed by Sydow et al. (2003) intheir study of reservoirs near the Pliocene Orinoco shelf-edge in

    offshore Trinidad. However, Suter and Berryhill (1985); Morton

    and Suter (1996); and Roberts et al. (2000) showed their studied

    Pleistocene shelf-margin deltas as fluvial-dominated with some

    wave-modification. On the other hand, Cummings et al. (2006)

    recorded strong tidal signals on the front of Cretaceous deltas

    near the Nova Scotia shelf-edge, but showed that this was

    probably due to the deltas being sited within a shelf-edge

    embayment. Shelf-edges are probably more likely to be

    embayed at sea-level lowstand, whereas shorelines on highstand

    shelf-edges are more likely to be straight and open, and

    therefore wave-dominated. This was also suggested anddocumented by Ainsworth et al. (in press) from subsurface

    reservoir data. The outcrop data presented here on Clinoform 17

    are consistent with a relationship between rising sea level

    (irrespective of the cause of rise) at the shelf-edge and the

    occurrence of wave-dominated shorelines.

    7.2.3. Enhanced thickness and parasequence development in

    highstand shelf-edge delta units

    The greater thickness of regressive deltaic units at the shelf-

    edge compared to the inner shelf is obvious because of the

    greater water depth normally encountered towards the outer

    shelf. This increased shelf-edge thickness was suggested to be

    further enhanced by rising relative sea level, and the propositionmade that this thickness increase would be accompanied by an

    increased number of parasequences in the unit (Porbski and

    Steel, 2006). In the study of the Orinoco Pliocene shelf-margin

    reservoirs (Sydow et al., 2003), rising relative sea level created

    by high subsidence rates caused the wave-dominated sequences

    to be unusually thick, and with multiple parasequences (N150 m

    in places). This thickness aspect is consistent with the character

    of the Clinoform 17 data. Contrary to this, Morton and Suter

    (1996) reported a significant thickness reduction in several late

    Quaternary deltaic sequences (Gulf of Mexico) that were

    formed under a rapid lowering in sea level.

    8. Conclusions

    Shelf-margin deltas preserved in Clinoform 17 of the Eocene

    Battfjellet Formation on Spitsbergen are argued to have

    developed during conditions of rising relative sea level

    (highstand), because of their thick aggradational and parase-

    quence-prone character. The wave-dominated character of the

    delta-front and barrier deposits, suggesting an open, straight

    coast, is consistent with this. The strong fluvial drive and high

    flux of sediment normally associated with highstand shelf-edge

    deltas cannot be argued here because the shelf-margin

    progradation rate is estimated to have been low. So, the reason

    the Clinoform 17 deltas reached the shelf-break was the

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    narrowness of the shelf itself. If the shelf had been wider, these

    low-supply deltas would have retreated before reaching the

    outer shelf, in accordance with auto-retreat principles.

    The well-exposed outcrops of Clinoform 17 add to our

    knowledge of highstand shelf-edge deltas, and suggest the

    following characteristic features:

    Deltaic units are unusually thick because they occurred in

    deeper water at the shelf-edge and because rising relative sea

    level caused aggradation of the body and a rising shelf-edge

    trajectory.

    The aggradation of the sediment body was achieved by a

    vertical stacking of parasequences. This also caused the shelf-

    edge delta to contain short-lived shale-prone transgressive

    incursions.

    The deltas are wave-dominated, as would be expected

    because shelf-edge areas are almost always exposed to open

    ocean waves. Where coastline morphology is less straight,

    signals of tidal influence would be better preserved.Highstand deltas in general deposit and store a large

    proportion of their sediment budget on the shelf and coastal

    plain, whereas falling-stage deltas deliver more of their

    sediment into deepwater areas. Where the shelf-edge deltas

    are of high supply type, deepwater sands might still be

    expected beyond the shelf-edge. Where supply is low, as in the

    studied succession, the deltas reached the shelf-margin because

    the shelf was narrow, and the deepwater slope and basin floor

    tended to be mud-prone.

    Because highstand shelf-edge deltas are aggradational, they

    contain no major widespread erosional surface or sequence

    boundary, in contrast to falling-stage deltas.

    Acknowledgements

    We thank the WOLF Consortium (BP, Norsk Hydro, Statoil,

    Shell, BHP Billiton, ConocoPhillips, and Pdvsa) for their

    financial support to cover the field work and for lively discussion.

    Thanks to the Jackson School of Geosciences at the University of

    Texas at Austin for their administrative support. Also, the authors

    recognize the valuable contribution of Atle Folkestad, Andrew

    Petter, Piret Plink-Bjrklund, Alfred Uchmann, and Cristian

    Carvajal, through assistance in the field or contribution to this

    research. Dr. Marc Edwards is thanked for a constructive review

    of an early draft of this paper. We especially acknowledge Drs.Chris Fielding, M. Royhan Gani, and Jesus Soria, for their

    constructive criticism in reviewing the manuscript.

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