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claystones record the drowning of the Tilje
Formation deltas and estuaries across the larger
part of the Halten Terrace. The coarsening upward
motifs within the lower part of the Ror Formation
define a forward stepping or normal regressive
stack of basin-margin derived deltaic units. The
basin-marginal forestepping lithosome stack is
capped by two erosively based, sand-rich fluvio-
deltaic sandstone sheets, the upper Tofte and the
basal part of the lower ile members. These two
sandstone sheets are developed only partially over
the southern and central part of the Halten Terrace
(Fig. 9A,B2). They mark abrupt and significant
basinward shift in facies tracts and represent
two detached mixed wave- and tide-influenced
fluviodeltaic lithosomes and form a forced regres-
sive to late lowstand normal regressive lithosome
stack. On the western Trøndelag Platform, i.e. in the
Draugen Field, these forced regressive to lowstand
systems tracts are represented by an erosively based
(?incised) fluvial sandstone sheet.
Along structural highs within the western part
of the Halten Terrace, the Ror-Tofte Formations
are developed as a stack of blocky or coarsening-
upwards to coarsening-to-fining upwards motifs.
These motifs change from aggradational to highly
irregular stacks of sandy, coarse-grained fluvi-
odeltaic lithosomes, with or without basal, inter-
vening and capping marine mudstones. Often
there is a lower progradational unit overlain by a
thicker irregular and thinner retrogradational
unit. These locally developed, coarse-grained
fluviodeltaic lithosomes represent a stack of
braidplain-deltaic and fan-deltaic units (Gjelberg
et al
., 1987; Dalland
et al
., 1988), sometimes with
a tide and current-reworked delta-front and
prodelta area. The locally developed deltaic units
represent the outbuilding and stepwise retreat
towards gradually peneplaned and drowned local
or intrabasinal precursor footwall islands. The
two extensive fluviodeltaic sheets, present within
the central part of the Halten Terrace, represent
outbuilding of basin-marginal, low-gradient,
braidplain and normal river deltas, the former
often with a steep, gravity-flow dominated delta-
front area. However, outbuilding occurred during
fluctuating relative sea-level, with high order falls
and rises, as evidenced by interbedding of shelfal
mudstones.
The aggradational segment (lower (parts) middle
(parts) ile member) comprises an overall aggrada-
tional stack of wave-influenced and tide-influenced
fluviodeltaic lithosomes ranging in thickness from
< 5 m to 15 m. The basal boundary is defined by a
bioturbated inner shelf to shoreface mudstone-
sandstone unit representing a higher-order flooding
surface within the lower ile member (Fig. 9A).
The component higher-order fluviodeltaic
lithosomes show large spatial variability in charac-
teristics and sedimentary architectures. in the
south-eastern half of the Halten Terrace, the lower
part of the segment is comprised of a relatively
sand-rich, laterally extensive fluviodeltaic to estu-
arine sandstone lithosomes, representing the bulk
of the lower ile member. This package is inter-
preted to represent the continued outbuilding of
the braidplain system, but now with a change to
a series of mixed influence deltas bordered laterally
by extensive tidal flats and shorelines (Fig. 9A,B3).
in other areas, the lower ile is composed of stacked,
variably river-influenced, wave-influenced and
tide-influenced fluviodeltaic and marginal marine,
i.e. estuarine and protected shoreline, sandy litho-
somes, which become increasingly tide-dominated
towards the east. On the Trøndelag Platform fur-
ther to the east, (palaeolandward), the segment is
characterised by erosively based, fluvial channel-
fills, interpreted to represented candidate incised
valley-fills.
Thicker, locally developed, braidplain-deltaic,
coarsening-to-fining-upwards sandstone units are
present in the north-western and western Halten
Terrace, as well as along the Nordland Ridge (e.g.
Harris, 1989; Pedersen
et al
., 1989). These repre-
sent a renewed phase of intra-basinal sourced
delta progradation along the downfaulted dip-
slope of basin-bounding highs, such as the Sklinna
and Nordland Ridges, in the western and northern
part of the Halten Terrace (Fig. 9A,B3). The pro-
gradational structure of these localised, basin-
interior sourced fluviodeltaic lithosomes is related
to renewed structuring and uplift of intra-basinal
provenances. Other parts of these intrabasinal
highs, such as the western flank of the Nordland
Ridge, were surrounded by shorelines; again
formed in response to renewed uplift and subae-
rial emergence of these structures.
For both the basin-marginal and intrabasinal
sourced depositional systems, deltaic facies tracts
alternate laterally and vertically with estuarine and
shoreline units. This suggests a lower degree of
incision and amalgamation of fluviodeltaic units
and a larger variability in depositional sub-environ-
ments compared to the underlying regressive seg-
ment. Co-occurrence of deltaic, shoreface and
estuarine facies tracts, suggest along depositional
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