Sedimentology (2002) 49, 1181–1206
Anatomy of shelf deltas at the edge of a prograding
Eocene shelf margin, Spitsbergen
D ONATELLA MELLERE*, PIRET PLINK-BJÖRK LUND and RONALD STEEL
*Department of Geology, University of Padova, Via Giotto 1, 31137 Padova, Italy
(E-mail: dmellere@dmp.unipd.it)
Department of Geology & Geophysics, University of Wyoming, Laramie, 82071 WY, USA
ABSTRACT
Although shelf-edge deltas are well-imaged seismic features of Holocene and
Pleistocene shelf margins, documented outcrop analogues of these important
sand-prone reservoirs are rare. The facies and stratigraphic architecture of an
outcropping shelf-edge delta system in the Eocene Battfjellet Formation,
Spitsbergen, is presented here, as well as the implications of this delta system
for the generation of sand-prone, shelf-margin clinoforms. The shelf-edge
deltas of the Battfjellet Formation on Litledalsfjellet and Høgsnyta produced a
3–5 · 15 km, shelf edge-attached, slope apron (70 m of sandstones proximally,
tapering to zero on the lower slope). The slope apron consists of distributary
channel and mouth-bar deposits in its shelf-edge reaches, passing downslope
to slope channels/chutes that fed turbiditic lobes and spillover sheets. In the
transgressive phase of the slope apron, estuaries developed at the shelf edge,
and these also produced minor lobes on the slope. The short-headed
mountainous rivers that drained the adjacent orogenic belt and fed the
narrow shelf, and the shelf-edge position of the discharging deltas, made an
appropriate setting for the generation of hyperpycnal turbidity currents on the
slope of the shelf margin. The abundance of organic matter and of coal
fragments in the slope turbidites is consistent with this notion. Evidence that
many of the slope turbidites were generated by sustained turbidity currents
that waxed then waned includes the presence of scour surfaces and thick
intervals of plane-parallel laminae within turbidite beds in the slope channels,
and thick spillover lobes with repetitive alternations of massive and flatlaminated intervals. The examined shelf-edge to slope system, now preserved
mainly below the shelf break and dominated by sediment gravity-flow
deposits, has a threefold stratigraphic architecture: a lower, progradational
part, in which the clinoforms have a slight downward-directed trajectory; a
thin aggradational zone; and an upper part in which clinoforms backstep up
onto the shelf edge. A greatly increased density of erosional channels and
chutes marks the regressive-to-transgressive turnaround within the slope
apron, and this zone becomes an angular unconformity up near the shelf edge.
This unconformity, with both subaerial and subaqueous components, is
interpreted as a sequence boundary and developed by vigorous sand delivery
and bypass across the shelf edge during the time interval of falling relative sea
level. The studied shelf-margin clinoforms accreted mostly during falling stage
(sea level below the shelf edge), but the outer shelf later became estuarine as
sea level became re-established above the shelf edge.
Keywords Clinoforms, hyperpycnal flow, shelf-edge deltas, slope lobes,
spillover sheets, turbidite channels and chutes.
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INTRODUCTION
Shelf-edge deltas are now a well-imaged seismic
feature of Holocene and Pleistocene shelf margins
(Suter & Berryhill, 1985; Berryhill et al., 1986;
Matteucci & Hine, 1987; Tesson et al., 1990; Poag
et al., 1990; Morton & Suter, 1996; Kolla et al.,
2000). Although there is an extensive literature on
the seismic character and overall geometry of
shelf-margin deltas (McMaster et al., 1970; Winker & Edwards, 1983; Tesson et al., 1990, 1993;
Field & Trincardi, 1991; Sydow & Roberts, 1994;
Kolla et al., 2000), relatively little is known of
their internal architecture, with only a few
exceptions (e.g. Mayall et al., 1992; DiBona &
von der Borch, 1993).
Shelf-edge deltas are typically developed where
there has been a significant fall in sea level and a
high supply of sediment. In this setting, deltaic
shorelines can move far out across the shelf, often
into a position at or near the break (Coleman
et al., 1983; Suter & Berryhill, 1985; Coleman &
Roberts, 1988). Although most often associated
with relative fall in sea level, shelf-edge deltas
appear nevertheless to be developed in a range of
relative sea-level conditions: (1) during falling sea
level (e.g. Trincardi & Field, 1990; Tesson et al.,
1993; Sydow & Roberts, 1994; Morton & Suter,
1996), in which case the deltas fall into the
category of forced-regressive or falling-stage prograding wedges (Hunt & Tucker, 1992; Plint &
Nummedal, 2000); (2) during minimum and early
rise in sea level (e.g. Posamentier et al., 1988;
Hart & Long, 1996), also known sequence stratigraphically as lowstand wedges; or (3) during
later sea-level rise (e.g. Kolla & Perlmutter, 1993),
forming part of a transgressive systems tract.
The above type of delta is identified in the geological record in two different ways. In Holocene
and Pleistocene strata, the main criterion is the
location of the delta with respect to the site of the
present shoreline and the shelf margin; in these
cases, they are variously termed shelf-perched or
shelf-margin deltas (Suter & Berryhill, 1985) or
shelf-edge deltas (Sydow & Roberts, 1994). In older
successions, shelf-margin deltas are difficult to
identify with certainty, because of the difficulty of
pinpointing the position of the shelf-slope break.
An important condition likely to prevent the
development and preservation of shelf-edge deltas is where sea level falls below the shelf edge for
a prolonged period, and canyons on the upper
slope become coupled directly with incised
fluvial systems on the shelf (Kolla & Perlmutter,
1993). This condition is overcome most easily
when sea level does not fall below the shelf break,
or if the fall below the shelf break is short-lived.
In the present study, the facies and architecture
of well-exposed, Early Eocene shelf-edge deltas
associated with a shelf break and non-canyoned
slope in the Central Basin of Spitsbergen are documented. These deltas were forced slightly beyond
the shelf edge and are now perched on the uppermost slope. Their position indicates a relative
sea-level fall of 50–100 m relative to the former
highstand shoreline. A subsequent rise in sea level
caused the deltas to draw back up onto the shelf.
The fall and rise cycle resulted in the delivery of no
significant volumes of sand beyond the toe of
slope, even though sea level fell below the shelf
edge. However, the basinward-thinning wedge of
sand (more than 70 m at the shelf edge) has significant strike extent (more than 15 km). It is argued
below that this sand wedge resulted from the lack
of significant incision on the upper slope and from
sediment that was dispersed broadly from an apron
of deltas rather than from a point source.
GEOLOGICAL SETTING
The Late Paleocene–Eocene Central Basin of
Spitsbergen was a relatively small foreland basin
that formed in front of the developing West
Spitsbergen fold-and-thrust belt (Harland, 1969,
1995; Lowell, 1972; Kellog, 1975; Spencer et al.,
1984; Steel et al., 1985; Myhre & Eldholm, 1988;
Fig. 1A). Basin infill progressed from west to east,
leaving a spectacular record of large-scale (150–
350 m amplitude) clinoforms that reflect the
overall progradation of the shelf-edge-to-slope
system (Steel et al., 1985; Helland-Hansen, 1990)
(Fig. 2). Sand-prone clinoforms developed by
progradation of deltas across the pre-existing shelf
platform, delivery of sediment beyond the preexisting shelf break and down onto the slope.
Repeated sediment delivery of this type produced
significant shelf-margin growth. Sediment was
supplied mainly from the growing orogenic belt
along western Spitsbergen, some 25–30 km west
of the outcrops in this study. The depositional
systems are well-exposed in three dimensions
along mountainsides dissected by glacial valleys.
The stratigraphic section attains a thickness of
some 1500 m, with clinothems (sensu HellandHansen, 1992) up to 350 m high. Helland-Hansen
(1992) described the clinoform geometry, with
coastal plain topsets and turbidite-rich toesets.
Although the importance of shelf-edge deltas
was not emphasized, Helland-Hansen (1992) did
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Fig. 1. (A) Location and tectonic setting of the studied area. The Central Tertiary Basin is a foreland basin, loaded by
the thrust sheets of the West Spitsbergen Orogenic Belt. The basin is highly asymmetrical and is 90–100 km wide.
(B) Location of the Litledalsfjellet and Høgsnyta outcrops in Reindalen. The shelf-edge delta wedges are up to 70 m
thick, but taper out at the base of slope, some 3–5 km away from the shelf margin.
recognize that the clinoforms were ‘fluvially driven’. More recently, Steel et al. (2000) examined
clinoform trends and growth styles at basin scale.
Most of the clinothems are shale prone (type 4
clinothems of Steel et al., 2000) and can be recognized on the mountainside only by the presence of
heterolithic units of thin-bedded (1–3 cm thick)
sandstones and siltstones that stand out from the
uniform slope shales. Others are sand-prone
across much of the storm- and wave-dominated
shelves, but evidently delivered little sand onto
the slope (type 3). Type 2 clinothems were generated by shelf deltas and are sand-prone along both
shelf and slope segments but with insignificant
sand volumes on the time-equivalent basin floor.
Type 1 clinothems produce basin-floor fans. The
sedimentary wedges of Litledalsfjellet and Høgsnyta are generated by type 2 clinothem complexes.
They form a thick slope wedge that pinches out by
downlap before the base of slope, but attain a
maximum thickness of 70 m just below the shelf
break. In contrast to type 1 clinoforms, no slope
canyons or major slope-collapse features are associated with the type 2 clinoforms (Fig. 3).
METHODS
The sandstone clinothems of Litledalsfjellet
and Høgsnyta are part of the same stratigraphic
interval, referred to hereafter as the Reindalen
clinothem complex (Fig. 4). The clinothems
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Fig. 2. Block diagram with palaeogeographic and stratigraphic overview of the studied succession
during an interval when the lowstand shoreline was at the shelf
edge. The shelf-edge deltas of the
Battfjellet Formation prograded onto
the Gilsonryggen shales and were
fed by the coastal plain system of
the Aspelintoppen Formation.
B
A
Fig. 3. (A) Clinoform types, as recognized by Steel et al. (2000) within the Battfjellet Formation. (B) Block diagram
and profile outlining the shelf-edge terminology used for the studied, sand-prone type 2 clinoforms.
produce a large basinward-dipping, sandstone
wedge that developed on the slope below the
shelf edge. The two mountainsides converge at an
angle of about 20 and are separated by a
5 km wide glacial valley, enabling a partial threedimensional reconstruction of the Reindalen
depositional system (Figs 1 and 4). A total of 24
measured sections, spaced 50–500 m apart, have
been measured on the two mountainsides (Figs 5
and 7). Most of the outcrop allows physical
correlation. On the steepest cliffs (south-westward ends of Litledalsfjellet and Høgsnyta), beds
were correlated by tracing on enlarged photomosaics shot from a helicopter (Fig. 6).
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A
B
C
Fig. 4. (A and C) General overview of the Litledalsfjellet (A) and Høgsnyta (C) clinoform complexes with location of
the measured sections (for details, see Figs 5 and 7). Note the flat-lying youngest clinoforms, chosen as datum for the
construction of the correlation panels. The mountains are 700 m high, and the mountain face is 3–5 km long. The
coastal plain deposits of the Aspelintoppen Formation form the succession in the upper part of the mountains.
(B) Diagram showing the slope angles of the clinoforms in Litledalsfjellet, measured from the most proximal to the
distal reaches. The studied slope wedge (clinoform 1) has a gradient of 3–4.
The choice of datum for the correlation panels
is important. The photomosaics of Litledalsfjellet
and Høgsnyta show that the coastal plain strata in
the upper half of the mountainsides are nearly
horizontal, so that the easterly dip of the underlying clinothems represents the apparent dip of
the slope of the depositional system. The correlation panels in Figs 5 and 7 are therefore hung
from the lowest sandstone unit containing coastal
plain deposits. Minimum water depth at the base
of the Reindalen wedges has been estimated from
the height between the shelf-slope break down to
the clinothem toes (Fig. 4, graph insert). A correction was then made for compaction and for
water depth at the shelf edge.
The average gradient of the slope segment of
the clinoforms is 3–4. The deposits form a shelf
edge-to-slope turbidite apron 3–5 km in downdip
extent and 15 km in strike length. Fine- to
medium-grained sandstones are concentrated in
the most proximal reaches (at the shelf-edge
palaeoshoreline, in the uppermost part of the
outcrops) and extend into water depths estimated
at more than 200 m. The lower slope gradient
eventually declines to 0Æ5 and then flattens onto
the shaley basin floor beyond the sandstone wedge.
THE MORPHOLOGICAL/BATHYMETRIC
PROFILE
Although the shelf-edge and slope deposits
described here derive entirely from shelf-edge
deltas, it is misleading and incorrect to view the
clinoforms as simply deltaic. The deltas built
across a pre-existing platform created during an
earlier phase of shelf-margin accretion at relative
sea-level lowstand. On reaching the shelf edge,
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Fig. 5. Litledalsfjellet cross-sectional panel (see location of the measured section in Fig. 4) with position of the log details and photographs used in the
description of the facies associations.
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Fig. 6. Photomosaic and interpretation of the most proximal reaches of the Litledalsfjellet shelf-edge delta complex.
Anatomy of a prograding Eocene shelf margin, Spitsbergen
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the new generation of deltas prograded down
onto a pre-existing slope. In addition, the delta
front that then draped across the slope did so by
accreting at a steeper angle (downlap) than the
slope itself. Because of this and the now greatly
extended length of the slope apron, ‘slope’ rather
than ‘delta front’ terminology is used here to
describe the setting. This view is consistent with
the extensive channelling/erosion and great volumes of turbidites that occur on the study slope
compared with normal shelf-delta slopes.
The bathymetric profile so constructed consists
of (1) a shelf with width up to 15–20 km and
gradient of less than 0Æ5; and (2) a slope with
length 3–5 km and gradient of 3–4. The gradient
at the base of slope decreases gradually, and the
bottomset (basin floor) of the clinoform becomes
subparallel with the topset. The clinoform set
created by the gradual migration of the shelf edge
reflects a (decompacted) water depth of some
50 m at the shelf break and some 250–300 m down
to the basin floor during highstand of sea level.
FACIES ASSOCIATIONS
Shelf-edge delta deposits
The shelf-edge delta deposits are characterized by
a high sand/shale ratio and consist typically of
coarsening-upward mouth-bar and distributary
channel units. The shelf-edge units accrete at
angles up to 10 onto a slope itself dipping at
some 3–4. This succession merges downdip
directly into sediment gravity flow-dominated
lobes and channels of the slope system.
Proximal mouth-bar deposits (A1)
Description. Association A1 consists of: (1) coarsening-upward sandstone units; (2) sigmoidal
bars; and (3) scour-and-fill features. The association occurs in the most landward and updip
reaches of the Litledalsfjellet and Høgsnyta wedges (profiles 1 and 1–3, respectively, in Figs 5–7).
The coarsening-upward sandstone units consist
of clean, well-sorted sandstones, up to 3 m thick,
forming stacked intervals up to 10 m thick. The
sandstone units are dominated by a variety of
cross-stratified and ripple-laminated bed sets,
0Æ2–2 m thick, separated by up to 0Æ15 cm thick
shale interbeds. The shale interbeds commonly
contain a high amount of coal and plant debris,
usually in patchy lenses or chaotically distributed.
The typical ‘bedform’ of the shelf-edge mouth
bars is a sigmoidal barform similar to the alluvial
‘flood-generated sigmoidal bars’ of Mutti et al.
(1996). In the Reindalen shelf-edge deltas, such
bars consist of repeated alternations of ungraded/
graded to plane-parallel- and ripple-laminated
fine- to coarse-grained sandstone beds (Fig. 8A)
Fig. 7. Høgsnyta cross-sectional panel, modified from Plink-Björklund & Steel (2002) (see location of the measured
section in Fig. 4).
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Fig. 8. Overview and details of shelf-edge delta deposits (location in Fig. 5). (A) Distal mouth-bar association (Facies Association A2). Most of the deposits are
thin sets of ripple- to planar-laminated sandstones. (B and C) River-fed, sigmoidal bars at the shelf-edge delta mouth on Litledalsfjellet (Association A1). Note
the slight landward back-tilt (slight leftward dip of some beds in B) of the head of the bars. (D) Overview of river distributary channel in Høgsnyta. The deposits
are thinly planar laminated, suggesting deposition from flood-dominated hyperconcentrated flows.
Anatomy of a prograding Eocene shelf margin, Spitsbergen
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arranged (in section parallel to palaeoflow) in
high-angle (15–20) accretionary sigmoidal sets
(Fig. 8B and C). Sets are convex upward, 0Æ5–2 m
thick and bounded by erosional surfaces that
truncate the underlying sets. Individual beds and
accretion sets are modified at their tops by waveripple laminations. The barforms are lenticular
(up to 2 m thick, some 6–10 m wide) and are
truncated by flat-lying erosional surfaces or by
small scour-and-fill features in their upcurrent
parts (Fig. 8B). The latter are 0Æ4–1 m deep,
0Æ6–5 m wide, infilled by planar-laminated, occasionally by trough cross-stratified, medium- to
fine-grained sandstones, with abundant rip-up
clasts and coal fragments. In a downcurrent
direction, the sigmoidal lenses broaden, the erosional bounding surfaces tend to become conformable, and the beds progressively flatten and
are dominated by plane-parallel lamination.
Successive sigmoidal barforms stack downstream
and vertically to build up composite mouth-bar
bodies, often cut by capping channels.
Interpretation. The association described above
suggests the presence of an inertia-dominated
river mouth, controlled by periodic, high-velocity, flood-dominated river discharge. Sediment
was dispersed within a turbulent jet onto a
steeply dipping slope, producing elongate,
steep-fronted mouth bars. Rapid dumping of
bedload and coarse suspended material occurred
near the mouth along with slower accumulation
of suspended material further seaward underneath the sediment plume (see also Scruton,
1960). Both suspended load and bedload sediments become progressively finer with increased
distance from the distributary mouths. The bar
complex seems to have been built by amalgamated flood units characterized by an upwardincreasing tabular geometry.
The coarsening-upward sandstone units were
deposited by traction currents, as indicated by the
alternating cross-stratification and ripple-lamination. The thin ungraded, climbing-ripple and
flat-laminated beds in the sigmoidal bars may
indicate deposition by frictional freezing of highdensity turbidity flows (massive to normal-graded
beds; Lowe, 1982), followed by combined tractional and fall-out processes. The occurrence of
capping wave ripples indicates that the depositional depth was above the storm wave base. The
sigmoidal bars possibly originated from hydraulic
jump at the shelf break, with transformation of
the hyperconcentrated flows to rapidly deposited sediment, because of flow expansion and
deceleration. Energy dissipation through intense
turbulence is thought to have been the main
cause of the extensive scouring observed in the
upstream terminations of sigmoidal bars. It is
inferred here that high-gradient distributary channels carried floods directly to the shelf edge.
According to Mutti et al. (1996), the development
of the complete sigmoidal bars, as well as the
thick and extensive individual mouth bars, is
indicative of poorly efficient flows, i.e. flows that
were unable to carry most of their sediment load
further downslope.
Distal mouth-bar deposits (A2)
Description. Distal mouth bars consist of sandprone, heterolithic units of sandstones and shales
organized into coarsening- and thickeningupward motifs, 0Æ5–1Æ5 m thick (Fig. 8). They
develop down the slope for about 1 km from the
proximal mouth-bar complexes and overlie the
more shale-prone heterolithic slope units
(Fig. 8A). Sandstone beds are 0Æ05–0Æ5 m thick.
Their basal contacts are soft-sediment deformed,
slightly erosive and loaded into underlying shale
in places. Sole marks are absent or rare. Most
sandstone beds are current rippled and planeparallel laminated. Normally graded and inversely
graded sandstone beds also occur, capped by
shales. When present, inverse grading usually
characterizes the first few centimetres near the
base of the sandstone beds and often presents
shear lamination.
Sandstone beds show low to moderate lateral
persistence, pinching out downdip or being cut
by slope channels and slump scars. Slump intervals, up to 2 m thick but normally less than 1 m
thick, are usually seen at the base of the coarsening- and thickening-upward units. Shale interbeds are millimetres to a few centimetres thick
and display current-ripple lamination. Sandstone
abundance varies between 60% and 75%. Alternations of slumped, muddy intervals and clean
plane-parallel-laminated sands, such as those
described by Mayall et al. (1992), are also seen
but are not a dominant feature of the shelf edge
described here.
In some places, the boundaries between distal
mouth-bar units are expressed as large-scale
hummocky features, causing a lenticular geometry. The ‘hummocks’ are up to 2 m high, 50–
70 m in wavelength and convex upward. They
have been observed in the proximal part of the
Litledalsfjellet wedge, in the lower half of the
outcrop (Fig. 6) and in Høgsnyta (Fig. 7). Around
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Anatomy of a prograding Eocene shelf margin, Spitsbergen
the edges of such lenticular bodies, scour-and-fill
structures are evident, and some of these were
filled by upslope accretion. Where there are
vertically repeated units of this type, they show
an offset or compensatory stacking pattern.
Interpretation. The sand-prone heterolithic units
represent the distal reaches of the mouth–bar
association, deposited by an array of tractional,
mass-flow and slump processes, such as would be
expected where the mouth bars draped further
down onto the steep upper slope of the shelf
margin. The current-ripple and planar-laminated, fine-grained sandstone beds as well as the
ungraded to normally graded beds overlain by
siltstones indicate deposition by turbidity currents (Bouma, 1962; Middleton, 1967; Walker,
1967; Middleton & Hampton, 1973; Lowe, 1982).
Thinner sandstone beds (less than 0Æ5 m), with
some normal grading, probably resulted from
short-lived surge-type flows. The inverse-graded
to ungraded sandstone beds, with basal shear
laminae and sharply capped by shale, may be a
product of sandy debris flows (Shanmugam &
Moiola, 1995; Shanmugam, 1996). Given the
scarcity of a mud fraction within the sand beds,
the development of viscous flows may have been
inhibited, favouring more frictional and inertiadominated sandy debris flow.
The hummocky features recorded in places
probably reflect lobe switching of the mouth bars,
particularly those accumulated at an early stage of
the wedge when the depositional slopes were
steep.
Channel-fill deposits (A3)
Description. Channels cross-cut the mouth-bar
complexes. Individual channels are characterized
by erosional relief of a few decimetres to a few
metres, and they cut the sigmoidal bars of the
proximal-bar association (Figs 5–7). Most of the
channels visible on Litledalsfjellet are dip oriented. Thickness/width ratio is about 1:20. Channels develop lateral wings up to 15 m long. On
Høgsnyta, channels are 25–100 m wide, with up
to 5 m of vertical relief (Fig. 8D). Channel-fill
deposits typically show a blocky to fining-upward
vertical trend. They consist of erosional-based,
poorly sorted, coarse- to medium-grained, massive or plane-parallel-laminated sandstone beds
5–70 cm thick. The beds infill broad, cross-cutting shallow scours (Fig. 8D), paved by abundant
shale rip-up clasts, coal and wood fragments.
Sandstone beds locally display crude low-angle
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stratification or cut-and-fill-type cross-stratification. The late-stage deposits of channel fills
consist of thinner sandstone beds (3–15 cm
thick), which are massive to planar and ripple
laminated, and separated by shales. Localized
slumps, clay clasts and plant debris are common.
Interpretation. The close association with the
sigmoidal bars, the lack of bioturbation, the
traction structures and the large amount of coal
and wood debris suggest that these channels were
river distributaries. The upward-fining packages
of massive to laminated and cross-stratified channel fills suggest deposition from waning currents
involving traction. Considering the dimensions
and, particularly, the thickness of individual
channel fills, which average a few metres of
vertical relief, it seems likely that a network of
shallow streams operated on the delta system,
sporadically enhanced and deepened by floods.
The presence of repetitive scour-and-fill units
was probably produced during rising flood discharges in the feeder rivers.
Slope deposits
Deposition on the slope, below the shelf edge,
was dominated by the delivery of river-fed mass
flow deposits that formed a broad slope apron,
composed of slope lobes. Slope lobes were fed
and dissected by channels or chutes filled with
coarse-grained sandstones and capped by laterally extensive sandstone sheets produced by longlived, river-fed spillovers. Although the heterolithic lobes are the dominant association of the
slope, smaller lobe systems were also recognized
at the mouth of the chutes and channels or as
overbank deposits from chutes. The four main
facies associations recognized are slope lobes,
channels and chutes, channel and chute-mouth
lobes and spillover lobes. Although slumped
units are moderately common on the slope, in
the present study, they tend to be smaller and less
abundant than those described by Mayall et al.
(1992) from the shelf-edge deltas of the USA Gulf
Coast. However, it is noted that slump deformation is much more common on the slope in cases
of shelf-margin deltas that become deeply incised
by their distributary channels (Steel et al., 2000).
Slope-lobe deposits (B1)
Description. Lobate heterolithic units, some
500 m wide and up to 2 km long, dominate the
slope segments of the clinothems. The lobes are
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directly linked back upslope to a mouth-bar
system and distributary channels (Figs 5–7). The
heterolithic units, up to 15 m thick, are coarsening and thickening upward or fining and thinning
upward and consist of thin-bedded sandstones
and shales. The units are commonly capped by
spillover sandstone sheets and cut by slope
channels and chutes. The heterolithic units show
a variety of thin, laterally extensive beds in
broadly convex-up packages. Sandstone/shale
content varies between 50% and 85%, with the
highest value close to the mouth-bar system.
Individual sandstone beds, of 3–15 cm average
thickness, have diffuse to distinct boundaries and
may pass laterally into thicker amalgamated
sandstone units. Internally, they are plane-parallel to current-ripple laminated (Fig. 9A). Structureless ungraded to normal- and inverse-graded
beds also occur. The latter show sheared laminae
at the bottom (Fig. 9C). Bioturbation is rare except
for some small Chondrites traces.
Interpretation. Thin graded and laminated beds
indicate that waning turbidity currents provided
the normal sedimentation for the heterolithic
units, although inverse grading in some beds
may reflect deposition by sandy debris flows
(Shanmugam & Moiola, 1995; Shanmugam, 1996).
Turbidity flows emanated from nearby distributary-channel mouths as hyperpycnal flows. The
sandier turbidites probably reflect channel flood
stages, as well as transportation of material
locally derived from gravity failure of advancing
mouth bars. Facies organization, the relatively
high sand/shale ratio seen even in the most distal
reaches of the system and the general lack of trace
fossils indicate that sedimentation rates were
very high.
The coarsening-upward (C-U) and finingupward (F-U) motifs are the result of lobe progradation followed by lobe abandonment or lobe
shifting. In the middle part of the Litledalsfjellet
slope, the C-U or F-U motifs are equally common,
Fig. 9. Details of slope-lobe deposits (Facies Association B1, location in Figs 5 and 6). The deposits show a variety of
sedimentary structures from plane-parallel and ripple lamination (A) to normal and inverse grading (B and C),
suggesting deposition from waning turbidity flows and possibly from sandy debris flows. Note in (C) the inverse
grading and shear laminae at the base of the bed.
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Anatomy of a prograding Eocene shelf margin, Spitsbergen
suggesting that the lobe radius remained constant
over time. Where lobes prograded in addition to
gradual shifting, there the C-U motifs dominate
over those that fine upwards.
Channel and chute deposits (B2)
Description. Channelled sandstone bodies are
present on the upper to middle slope reaches of
the Litledalsfjellet and Høgsnyta clinoform complexes (Figs 5 and 7). The bases of such bodies are
sharp and erosive into underlying heterolithic
strata (Fig. 10A), and often paved by shale rip-up
clasts. The erosional channelled features can be up
to 5 m deep, 50–200 m wide when seen in a flowtransverse direction and extend downslope for
more than 3 km. The channels are wider in the
upper slope reaches, where they connect to the
distributary systems, becoming narrower downslope. The channels pass downslope into longitudinally, slightly convex-upward sandstone sheets,
up to 3 m thick, that may extend for up to 1 km to
the base of the slope (Fig. 6). Locally, bowl-shaped
scars were identified at the heads of some channels, cutting the downslope lee-side of mouth bars.
Channel infill consists of poorly sorted, coarseto medium-grained, massive to planar-laminated,
sharp-based sandstone beds infilling scours 0Æ3–
3 m deep (Fig. 10). Shale rip-up clasts and large
amounts of organic debris (coal and plant) are
particularly abundant in the lower part of the
channel fill, paving stacked broad and shallow
troughs (Fig. 10A). The channelled units can be
overlain by fining- and thinning-upward heterolithic strata comprising ungraded to planar-laminated sandstones and siltstones, or by a series of
stacked thinning-upward sandstone beds.
Well-sorted sandstones, massive to pervasively
deformed by water-escape structures, characterize the infill of the bowl-shaped channel heads.
Downslope, the channel infills become finer
grained and thinner and tend to lose both the
upper laminated and the basal ungraded interval.
Although some of the channels can be followed
throughout the longitudinal profile of the slope
(Fig. 6), others show clear evidence of sinuosity
and are found cutting the same spillover sheet
unit at different localities.
Interpretation. The dimensions, geometry and
position of the channels within the slope segment
of the clinoforms, and the direct link to the shelfedge delta system, suggest that most of the channelled units represent the slope continuation of the
shelf-edge delta distributaries. The channels were
1193
supplied directly from the river system, as suggested by the coarseness of the deposits, their thickness and the large volumes of organic debris and
coal fragments.
The thin, normally graded beds with shale
rip-up clasts in upslope reaches indicate deposition from waning turbidity currents. The thick
(0Æ5–3 m) ungraded, plane-parallel or ripple-laminated beds reflect deposition from sustained
turbidity flows (Kneller, 1995; Kneller & Branney,
1995). The thinning- and fining-upward units
with silty tops possibly denote abandonment of
the channels, whereas the thinning upwards
without any significant fining may reflect a more
erosional–depositional phase (Normark, 1970;
Mutti & Normark, 1987; Clark & Pickering, 1996).
Bowl-shaped scars at some of the channel
heads are interpreted as slump scars. Associated
channelled units represent chutes, the deep,
narrow segments of a slump-driven gully system
(Prior et al., 1981; Bouma et al., 1991). Chutes are
common on muddy slopes beyond shelf edges
and are easily recognizable in modern systems
investigated with high-resolution seismic reflection methods (Postma et al., 1988; Bornhold &
Prior, 1990; Prior & Bornhold, 1990; Soh et al.,
1995). On seismic and acoustic profile data,
chutes are straight, can be traced from the shelf
edge onto the upper and middle slope and may
merge into bulges and lobes on the lower slope.
The deposits observed at the downslope end of a
gully system are pervasively convoluted and very
well sorted, suggesting that the gullies originated
by collapse of unstable, well-sorted delta-front
deposits that accumulated rapidly at and beyond
the shelf edge, thus provoking abnormal sedimentary loading on the upper slope.
Channel/chute-mouth lobe deposits (B3)
Description. This association consists of heterolithic units of sandstone and shale forming coarsening- and convex-upward, wedge-shaped
bodies at the mouth of slope channels and chutes
or, in places, diverging from chute channels. The
heterolithic units are commonly up to 3 m thick,
but may stack vertically forming bodies up to
10 m thick, usually overlain by channels/chutes
or spillover lobes. Normally, they are located in
the middle to distal reaches of the slope and can
be followed as progradational packages downslope for hundreds of metres (Fig. 5). Successive
units typically show pinch-out in opposing
directions, probably a compensation feature, with
internal discordances and small-scale basal
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Fig. 10. Details of slope deposits (Facies Association B, location in Fig. 5). (A and B) Slope channels (Association B2) cutting underlying spillover sheets
(Association B4). Note the imbricate shale rip-up clasts concentrated at the base of the channel. The spillover sheet-like beds (C) form long tabular units,
wedging slightly downslope and consisting of thinly laminated sandstones. Transported wood and coal fragments are common and are often concentrated at the
base of the beds.
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2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Anatomy of a prograding Eocene shelf margin, Spitsbergen
erosion surfaces (Fig. 11). The thickness of such
wedges is inversely proportional to their lateral
extent and decreases progressively downslope.
Some coarsening-upward units are followed vertically by thin-bedded sandstones and shales.
Although developed on the mud slope, the
facies shows a relatively high sandstone content
(60–70%). Sandstone beds, 5–75 cm thick, are
fine grained, massive to low-angle planar laminated and draped by shales (Fig. 11). Currentripple lamination is subordinate and present only
in the finest grained heterolithic strata at the base
or top of the coarsening-upward units. Softsediment deformation is common, particularly
in the thickest beds. Thicker beds are erosionally
based and composite. Most split into laterally
1195
wedging thinner beds, with a slight but progressive increase in shale interbeds. Shale interbeds,
up to 20 cm thick, consist of alternations of
laminated mudstone and normally graded to
current-ripple-laminated siltstones.
Interpretation. The pinch-out style of the convex-upward bodies, the association with chutes
and channels and the relatively high sandstone
content despite the relatively distal position on
the slope favour the interpretation of the facies as
chute and channel-mouth lobes. There are three
features consistent with this interpretation: (1)
chutes and channels tend to cut the coarseningupward lobe packages; (2) the downslope
decrease in the height of the convex-upward
Fig. 11. Details of channel/chute-mouth lobes (Facies Association B3) from the middle slope of Litledalsfjellet
(location in Fig. 5). Note the gentle wedging of the deposits in apparently opposite directions and the coarsening- and
thickening-upward motifs.
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
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D. Mellere et al.
units is associated with the downslope decrease
in depth of the channels/chutes and thickness of
the fills as seen in facies B2; (3) the grain size
of the deposits is comparable with the grain size
of the channel/chute fills. The alternation of
massive and low-angle, planar-laminated sandstone beds indicates deposition by turbidity
flows. The normally graded siltstone to laminated
mudstone beds reflect deposition from the tail
ends of waning turbidity currents.
Spillover deposits (B4)
Description. Sandstone sheets that extend
downslope for more than 1Æ5 km have been
recognized in the lower half of the Reindalen
wedges (Fig. 6). They consist of plane-parallellaminated, normally graded to ungraded, fine- to
medium-grained sandstone bed sets up to 2 m
thick. Bed set bases are sharp and slightly erosive,
and some show concentrations of layered and
imbricate shale rip-up clasts (Fig. 10C). Individual beds are up to 8 cm thick (average 3–5 cm
thick), commonly massive to normal graded,
planar laminated, locally current-ripple laminated. The thickest bed sets are amalgamated and
show the highest lateral persistence. Downslope,
some split into distinctive sheet units separated
by shale or concentrations of coal and wood
fragments. The sheets overlie 1Æ5 to 5 m thick
coarsening- and thickening-upward slope-lobe
units (Fig. 10C) and are cut by slope channels
and chutes. Sandstone lobes wedge out both
basinwards and upslope, where they connect to
the distributary channels and mouth-bar systems
(see Fig. 7 between profiles 1 and 2). They
develop at abrupt changes in channel direction
accompanied by sediment failure of the channel
margin and/or scour formation.
Interpretation. The thick beds with alternation
of ungraded and plane-parallel-laminated intervals suggest deposition from sustained turbidity
currents (Kneller, 1995; Kneller & Branney, 1995).
The connection with the mouth-bar systems and
the presence of abundant coal and wood debris
together with the interpreted sustained nature of
the flows indicate a direct link to the shelf-edge
delta distributary system. The sheet-like deposits
emerge from the main distributaries at abrupt
changes in channel direction and are interpreted
to represent spillover lobes (Normark & Piper,
1991). The basal erosional surface is likely to have
been cut during rising flood stage, whereas the
considerable thickness and internal variability of
the unit reflect the sustained nature of the
formative flow. The sandiness, thickness and
lateral persistence of these deposits suggest that
a significant percentage of flows passed through
the spillover points, causing the remaining flow
within the slope channels to decelerate rapidly.
Shelf-edge estuary deposits
The upper part of the Reindalen clinoform
complex is characterized by a succession of slope
lobes (association B1) that lead updip to tidal bars
and tidal channels developed at the mouth of an
estuary. At both localities (Litledalsfjellet and
Høgsnyta), the clinoform sets in this upper part of
the wedge are stacked retrogradationally (Fig. 5).
The slope lobes of the retrogradational clinoform
set are analogous, although thinner bedded and
muddier, to the slope-lobe deposits and the shelfedge delta deposits of the progradational clinoform sets described above. However, the number
and thickness of channels/chutes is much less.
Tide-influenced channel deposits (C1)
Description. A belt of channel and bar complexes marks the uppermost and most landward
reaches of the wedge on Litledalsfjellet (Figs 5
and 6). The channels are bounded by a surface of
erosion that can be followed downslope for
1Æ5 km. Channel margins are step-like and often
draped by sand-prone, up to 1 m thick slump
deposits (Fig. 12A). Lateral wings, a few tens of
metres wide, develop in the uppermost channel
levels. Channel fills are 3–8 m thick, and successive units stack vertically to form complexes up to
15 m thick. Individual channel fills are thinning
and fining upwards and consist of thin-bedded
(3–8 cm thick), structureless to plane-parallel and
ripple-laminated, medium-grained sandstones
(Fig. 12), often draped by siltstone and claystone
drapes. Thicker, trough cross-stratified sandstones are present mostly at the base, but may
also occur through the channel unit. The uppermost parts of the channels typically show couplets of plane-parallel- to wave-ripple-laminated
beds (Fig. 12B), often alternating with shale and
double shale layers. Palaeocurrent directions are
mostly unimodal and oriented landwards.
Bioturbation is present with only small forms of
Planolites at the base of the sandstone beds.
Interpretation. Channel-fill deposits are interpreted in terms of normal to hyperconcentrated
flood currents that were actively reworked by
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Anatomy of a prograding Eocene shelf margin, Spitsbergen
1197
Fig. 12. Tidal-dominated, shelf-edge estuarine deposits from the upper part of Litledalsfjellet (see location in Fig. 5).
flood tides, as suggested by palaeocurrent direction, the presence of shale and double shale
interlayers and the association with tidal bar
deposits. The step-like margins of the channels
suggest multiple phases of erosion and infill.
Tidal bar deposits (C2)
Description. Planar to trough cross-bedded sandstones form bars up to 2 m thick that extend up to
30 m upslope with gentle dip angles (10–15).
The bars overlie and border the flanks of the tidal
channels. Cross-beds are 20–30 cm thick, separated by reactivation surfaces (Fig. 13) and trains
of shale rip-up clasts (Fig. 13C). Internal sets are
sigmoidal, 3–8 cm thick and separated by double
mud drapes.
The bars are composite, with reverse tabular
cross-beds and climbing ripples, particularly
along the bottomsets. Change in dune polarities
and reactivation surfaces are common. Wave
ripples commonly modify the top. Predominant
palaeoflow direction is landward. Trough and
planar cross-beds are, in places, intensely deformed by water-escape structures. Convolute
bedding is abundant, particularly in the most
downslope reaches of the association, with fold
axes oriented downslope. Bioturbation is rare to
abundant, with Planolites, Ophiomorpha and
Thalassinoides traces.
Interpretation. The bipolar palaeocurrent directions, double mud drapes and reactivation surfaces indicate tidal deposition. Bar migration
adjacent to channels suggests deposition in a
mainly subtidal depositional setting (Klein, 1970;
de Raaf & Boersma, 1971; Visser, 1980; Clifton,
1983; Dalrymple et al., 1990). The frequent convolution and water-escape structures were
formed during deposition, as the axial planes of
the folds have a preferential downslope direction. Deformation could have been initiated by
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Fig. 13. Details of the estuarine bars at the top of the Litledalsfjellet wedge (location in Fig. 5). The estuarine bars overlie the headward end of a chute channel
(A). (B) Although palaeocurrent direction is mostly oriented landwards, opposite directions are often seen in successive bars. Note the shale rip-up clasts
separating set boundaries (C).
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2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Anatomy of a prograding Eocene shelf margin, Spitsbergen
sediment creep and wave-induced liquefaction
(Dalrymple, 1979). However, rapid changes in
water level, together with excavation of scarps by
channel migration and downcutting along the
slope, are believed to have been the major local
causes that encouraged liquefaction. The above
features together with evidence for frequent wave
reworking suggest that the channel network and
dune field formed at the mouth of an estuary (e.g.
Dalrymple et al., 1990; Berne et al., 1993).
SHELF-MARGIN ARCHITECTURE
AT LITLEDALSFJELLET
The location of the series of measured profiles on
Litledalsfjellet is shown in Fig. 1. Profiles 1–3
(Figs 5 and 14) are only slightly oblique to the
strike orientation of the palaeoslope, whereas
profiles 4–10 are nearly dip-parallel to the slope.
It should additionally be noted that the landward
end of the Litledalsfjellet outcrop (location 1) lies
some distance basinwards compared with the
landward end of the Høgsnyta, i.e. a more proximal part of the shelf-delta system can be seen on
Høgsnyta.
The present dip configuration of the studied
strata is near the original depositional dip, as can
be deduced from the flat-lying attitude of the
delta plain strata in the upper part of the succession on Litledalsfjellet. Figure 5 shows clearly
that the lower two-thirds of the succession is
overall regressive (slope lobes R1 to R9), whereas
the upper third of the succession is overall
transgressive, with successive slope lobes stepping landwards through time (T1 to T4).
Architecture of the regressive succession
The most conspicuous features of the regressive,
lower half of the succession on Litledalsfjellet are
(1) the relatively coarse-grained channels and
mouth-bar sands at the shelf edge; and (2) the sets
of clinoformal units (slope lobes and subaqueous
channels) that stack on the slope and represent
the main accretion of the shelf margin (Figs 5
and 6).
The prograding slope lobes
The regressive slope succession seen in the crosssection in Fig. 5 consists of nine progradational
clinoform sets of slope lobes (R1 to R9), each with
a thickness up to 12 m. Internally, each lobe
flattens on the lowermost slope, is steepest on the
1199
middle to upper slope and tends to flatten slightly
towards the shelf edge. The clinoform set is
internally progradational (the lobes build gradually down the slope) and consists of: (1) a
downlap surface that has a gradient similar to
the general slope gradient; (2) a muddy but
heterolithic lobe fringe that progrades and laps
down onto the underlying lobe; and (3) a sandy
amalgamation of shallow channels, chutes and
spillover sand sheets that cap the lobe, like
topsets to the prograding heterolithic fringe.
The capping sandy channels and sheets generally lie erosively on the underlying, heterolithic
foresets. This relationship, as well as the common
upward-coarsening and -thickening character of
the latter, strongly suggests that the channels
were feeding the heterolithic lobe fringe, causing
it to prograde. Upward-fining and -thinning
trends within the heterolithic deposits indicate
lateral lobe shifting and abandonment of slope
segments. Because of this and the restricted
lateral dimensions of the lobes, lobe-by-lobe
correlation between Litledalsfjellet and Høgsnyta
is impossible.
In addition to the main elements in the lobes,
there are also minor lobes that were lateral to or
formed beyond the mouths of chutes or channels.
In the latter case, the chutes presumably stopped
short of, or incised beyond, the lobe fringe. Such
minor lobes have dimensions of only tens of
metres and are characterized by spectacular
wedging of beds in addition to upward-coarsening trends (Fig. 11).
Hyperpycnal turbidity currents on the slope
It has been argued above, especially in the
interpretation of turbidites from channels and
spillover lobes, that the channel systems on the
slope were linked directly upslope to the main
distributary channels of the shelf-edge deltas. The
abundance of coal fragments and other organic
debris within the slope turbidites is one of the
most explicit signs that many of the flows were
river fed, rather than derived from slumps on the
slope or from the mouth bar. It is suggested that
many of the flows were quasi-steady, hyperpycnal
turbidity currents (Mulder & Alexander, 2001),
fed from prolonged river flooding and with
sediment concentrations high enough to make
the rivers hyperpycnal (Mulder & Syvitski, 1995,
1996), but probably lower than many surge-type
turbidity flows. The following points summarize
the argument for this type of flow in the Litledalsfjellet slope turbidites:
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Fig. 14. Systems tracts in Litledalsfjellet (A) with outcrop details (B).
SURFACE OF FORCED
REGRESSION
CE
G SURFA
FLOODIN
NDARY
CE BOU
SEQUEN
DISTRIBUTARY CHANNELS
SHELF-EDGE
ESTUARINE DEPOSITS
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2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Anatomy of a prograding Eocene shelf margin, Spitsbergen
1 Drainage and delivery settings. The mountainous drainage area for the rivers feeding out
onto the relatively narrow Battfjellet coastal plain
lay within the West Spitsbergen Orogenic Belt,
only 20–30 km to the west of the study area. It is
known that small mountainous rivers of this type
are capable of bringing a relatively large bedload
to the sea (Milliman & Syvitski, 1992). The
location of these rivers and deltas, at the shelf
edge, would have ensured sand delivery into the
deeper water areas, and the steepness of the
fronting slope would have aided the maintainence of hyperpycnal flow (see Mulder et al.,
1998).
2 Character of the deposits. There is evidence
of sustained flow (for periods longer than, e.g.
slump-generated flows) within the turbidite
deposits, both in the main slope channels and
in the spillover lobes, on the slope. Individual
channelized turbidite bodies contain multiple
erosional scours, without giving any impression
of a series of separate flows. Such thick beds
with internal erosion surfaces suggest accumulative flow (Kneller, 1995) in the channels,
probably reflecting the period of rising flood
stage in the feeder rivers. The waxing flow
tends to scour and cannibalize its own deposits,
as the effect of the rising flood moves steadily
downstream (Mulder et al., 1998; Mulder &
Alexander, 2001). Other important features in
channel deposits include thick (>2 m) units of
plane-parallel-laminated sandstone that contain local, laterally restricted scour surfaces.
Evidence of sustained flow is also seen in
individual spillover lobes. Such lobes occur as
sharp-based sand units up to 2 m thick, but
internally consist of thin (<8 cm), alternating
plane-parallel-laminated and massive intervals,
with increasing amounts of current-ripple
lamination towards the top of the unit. These
units generally give an impression of irregular
aggradation of the bed in depletive flow conditions.
3 Lobe progradation and clinoform growth.
The nature, scale and gradual progradation of the
sandy turbidite lobes, as well as the systematic
growth of clinoforms, also suggest that slope
systems were fed directly from distributary
channels at the shelf edge. This is not to say that
slumping of the mouth bars or collapse of segments of the slope was unimportant in producing
turbidity currents, but the gradual downslope
progradation of the slope lobes is more consistent
with sustained flows.
1201
Architecture of the transgressive succession
Prograding slope lobes also dominate the upper
part of the Litledalsfjellet succession. However,
these lobes, each capped by sheet sandstones
rather than chute channel complexes, step landwards through time (T1–T4), illustrating the
overall transgressive character of this part of the
succession. In the most distal reaches of the
slope, lobes have an aggradational stacking architecture (R8, R9 and T1), before they backstep on
the slope (Figs 5 and 14). At the proximal end of
the transgressive succession, there are wellpreserved distributary channels and some associated mouth bars that fed the slope lobes. The tops
of mouth-bar units show wave-ripple lamination
and broad scours, indicating abandonment and
wave reworking of the delta lobes (e.g. Penland
et al., 1988) (Fig. 12).
Landward migration of the bayline
and estuarine deposits
As sea level continued to rise, the alluvial valley
was drowned by a landward-migrating bayline,
and an estuarine environment formed. The rising
sea level produced a landward-thickening wedge
of stacked estuarine channels and bars, with sheet
sands and shoals further offshore (Figs 5 and 14).
The thickness of the transgressive deposits, up to
20 m on the shelf, was probably enhanced by a high
gradient of ravinement or by a slow landward
translation of the ravinement. The tidal channel
and bar system recognized on Litledalsfjellet was
probably deposited at the mouth of an unbarred
estuarine valley (Rahmani, 1988; Dalrymple et al.,
1992). No traces of intertidal, central mud basin
deposits were recognized in the studied area.
SEQUENCE STRATIGRAPHY
Updip unconformity
The stratal configuration seen in Fig. 5 suggests
that the erosional surfaces at the top of the
youngest clinoform sets in the progradational
lower part of the succession truncate, in a landward direction, progressively older lobes, leaving
erosional terraces or unconformities near the
shelf edge.
This same pattern of updip unconformities is
seen even more clearly on Høgsnyta (Figs 7 and
15; Plink-Björklund & Steel, 2002). This configuration suggests that sea level fell below the shelf
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
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D. Mellere et al.
Fig. 15. Systems tracts in Høgsnyta (A) (modified from Plink-Björklund & Steel, 2002) with outcrop details (B). Note
the sequence boundary in (B). This erosional surface can be followed for 3 km along the outcrop.
edge, leaving the distinctive erosional terraces
and allowing the slope clinoforms to have a
slightly descending geometric trajectory through
time (Fig. 14).
Forced regressive systems tract
The unconformity noted above, the downwarddirected growth trajectory of successive slope
clinoforms (R1–R7) and the ‘below the shelf edge’
location of this package strongly suggest that the
lower part of the succession reflects a falling stage
of relative sea level and should therefore be
referred to as a forced regressive or falling stage
systems tract (Hunt & Tucker, 1992; Plint &
Nummedal, 2000).
The erosive sandy cappings of clinoform sets,
also documented in shelf-edge sand wedges of
the Late Quaternary Rhone Delta (Tesson et al.,
1990) and Late Pleistocene Mississippi–Alabama
Shelf (Sydow & Roberts, 1994), have been argued
to originate by stepped relative sea-level fall,
forcing successively younger delta lobes further
out and further down across the shelf edge.
Fluvial downcutting would have continued on
the shelf as a diachronous process during sealevel lowering. The topsets would then have
been over-ridden and incised by the advancing
and downcutting distributary channels during
the latter part of sea-level fall (Figs 14 and 15).
Top of the forced regressive systems tract:
the sequence boundary
The transition from the regressive (R1–R7) to the
aggradational (R8 and R9) successions in the
Litledalsfjellet wedge is an irregular erosional
surface formed by the multilateral and multistorey stacking of distributary channels and
mouth-bar complexes in the updip areas and
subaqueous channels and sheet sandstones in
downdip areas (Figs 5 and 14). Erosional escarpments are up to 7 m deep (Figs 5 and 6). This
erosional surface can be followed downslope for
up to 3 km. At the shelf break, the surface is well
defined by angular discordances with the underlying heterolithic clinoform sets. Downslope, the
erosional surface produced by the distributary
channel system merges into an erosional surface
produced by gully erosion and then into a more
conformable surface when gully edges merge into
distal lobes. This extensive erosional surface is
interpreted as a sequence boundary. The sea-level
fall caused migration of the youngest delta lobe
out onto and beyond the shelf edge.
Facies analyses indicate that the Litledalsfjellet
delta was a fluvial-dominated system. Wave
reworking and littoral transport processes were
likely to have been overwhelmed by rapid depositional rates on the delta front (see also Coleman,
1978).
One of the interesting aspects of the Reindalen
slope system is the lack of canyons. Most of the
delta-front architecture consists of small distributary channels and mouth-bar complexes, but
apparently none of the channels had enough
capacity to produce significant erosion at the
shelf break, deliver sediment into upper slope
gullies or canyons and develop sandy lower slope
and basin-floor systems. Twichell & Roberts
(1982) noted that canyons occur on the modern
New Jersey slope when the gradient exceeds 3,
with spacing between canyons decreasing as
the gradient increases. However, in the older
Miocene clinoforms of the New Jersey margin
(Fulthorpe & Austin, 1998), canyons are rarely
observed, despite clinoform gradients of more
than 3, a situation resembling that of the
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
Anatomy of a prograding Eocene shelf margin, Spitsbergen
Reindalen wedges. Fulthorpe & Austin (1998)
argued that the lack of evidence for canyons
breaching the clinoform breakpoints can be
interpreted as (1) discharge of major rivers at the
breakpoints occurred outside the studied area; or
(2) fluvial discharge at breakpoints occurred too
briefly to produce large, slope-breaching canyons.
The outcrops at Reindalen allow a three-dimensional examination of the system, as well as of the
shale section beyond the pinch-out of the wedges.
Data suggest that most of the river discharge
occurred at the breakpoints, at places well below
the shelf edge, judging by the basinward extent of
the mouth bars in cycles R7–R9. The gently
curved to linear trends of clinoform breakpoints,
mostly unmarked by canyon erosion, indicate
that sediment was efficiently distributed along
strike as stacked slope lobes, although some
confinement also occurred, given the number of
chutes and channels recognized.
Lowstand and transgressive systems tracts
It is possible that the thin set of strata lying between
R8 and R9, which shows an aggradational stacking
pattern and represents the most pronounced basinward shift of the entire system, can be designated
as a poorly developed lowstand wedge. The overlying backstepping lobe system is a transgressive
systems tract, leading back up to the estuarine
deposits on the outer shelf (Figs 5 and 14).
REINDALEN CLINOFORMS: THEIR ROLE
IN SHELF-MARGIN ACCRETION
The sand-prone clinoforms on Litledalsfjellet and
Høgsnyta resulted from both (1) shelf deltas
extending out to a shelf-edge position, a location
necessary for sand delivery into deep water areas;
and (2) sand delivery (across the shelf break) onto
a non-canyoned slope, so that most of the sand
was retained as a wedge on the slope and not
dispersed beyond the base of slope. This storage
of sand on the slope, up to 70 m thick and
extending up to 15 km along strike, was apparently achieved by the accumulation of sediment
from mostly unconfined, depletive turbidity flows
(sensu Kneller, 1995) and minor sandy debris
flows. The slope channel and chute systems seem
to pinch out on the slope, attesting to the low
efficient nature of the turbidity currents and the
lack of flow initiation on the slope. This type of
sand partitioning in the Reindalen clinothem
complex (type 2 clinoforms of Steel et al., 2000)
1203
(Fig. 3) contrasts with another situation commonly seen elsewhere in Battfjellet Formation
(type 1 of Steel et al., 2000), in which sand
delivered from the shelf edge was focused
through canyons and large channels, i.e. with
significant slope bypass, to accumulate on deepwater fans beyond the base of slope.
Alternation of type 1 and type 2 clinoforms in
the Eocene Central Basin produced alternating
conditions of basin-floor aggradation and slope
accretion. Because type 2 clinoforms, such as in
Reindalen, are much more common than type 1,
shelf-margin growth was the key component in
basin infilling. The Eocene shelf margin prograded more than 60 km, albeit with an irregular and
partly aggradational trajectory.
In addition to sand-prone type 1 and 2 clinoforms, there are abundant shale-prone clinoforms
that were major contributors to basin infilling.
Such shaly intervals commonly represent transgressive and highstand conditions in each relative sea-level cycle, were critically important as
aggradational elements in the stratigraphy and
caused the overall shelf-edge trajectory to have a
component of stratigraphic rise across the basin.
CONCLUSIONS
Documentation of the architecture of Eocene
shelf-edge deltas has allowed insight into the
processes of shelf-margin accretion. This has been
particularly useful for that part of the margin that
is least known in the literature, i.e. the part that
lies below the shelf edge. Litledalsfjellet and
Høgsnyta shelf-edge deltas formed a 70 m thick,
15-km along-strike apron built down onto a 3–4
slope. The system was dominated by the outbuilding of distributary channels and mouth bars
at the shelf edge and by density underflows on the
slope. It is argued that many of the latter were
sustained hyperpycnal turbidity flows because of
the nature of the river drainage, the shelf-edge
location of the deltas, the abundance of coaly and
organic materials in the turbidites, as well as the
character of many of the channel fills and
spillover lobes on the slope.
Channel-fed heterolithic lobes (some 500 m
wide, up to 2 km long and 10–15 m thick),
erosional channels and chutes, channel/chutemouth lobes and spillover sandstone sheets are
the main architectural elements of the slope
association.
Stratal configuration and erosional unconformities suggest that progradation of the shelf-edge
2002 International Association of Sedimentologists, Sedimentology, 49, 1181–1206
1204
D. Mellere et al.
deltas occurred mostly during forced regressive
and lowstand conditions. There was rapid backstepping of the system, with re-establishment of
shelf-edge estuaries when sea level rose again to
above the shelf break during transgression.
The relatively low sediment concentration
(compared with high-density turbidites) in the
hyperpycnal turbidity currents and the lack of
canyons below the Reindalen shelf edge produced
a largely unfocused deltaic discharge onto the
slope. The lack of canyons was critical for preventing sediment bypass on the slope and, thus,
for the absence of deep-water fans beyond the base
of slope. This situation arose despite the demonstrable fall in sea level to below the shelf edge.
ACKNOWLEDGEMENTS
We thank Amoco, Conoco, Exxon, Mobil, Norsk
Hydro, Phillips, Shell, Statoil and UPRC, who
sponsored and enthusiastically supported this
research (Wolf Consortium). We are indebted to
reviewers Ben Kneller and Mike Mayall, and to
Chris Fielding, for their constructive comments,
which helped to improve the manuscript.
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