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nodules. PA2, like PA1 contains scattered small
calcrete nodules, whereas nodular carbonate hori-
zons, vertically stacked carbonate nodules, rhizo-
cretions, root structures and burrows are common,
although not abundant. Compound pedocomplexes
are slightly dominating, whereas composite and
cumulative pedocomplexes are nearly equally
represented (Fig. 11).
facies of L04 to L01 are characterised by relatively
high clay/sand ratios and percentages of very fine-
grained material and are dominated by cumulative
pedocomplexes (Fig. 11).
Palaeosol assemblage 4 (PA4)
Palaeosol assemblage PA4 is characteristic of
floodplain successions in the allostratigraphic
units S5 to S4 in the lower Statfjord Group (LSG).
The mudrocks generally change from dominantly
reddish-brown in S5 to increasingly mottled and
greenish to grey upwards in S4. PA4 mudstones
are mottled with low-chroma vertisols (MF4),
replacing the red-coloured entisols/inceptisols
or high chroma vertisols of PA3 in the under-
lying ULF.
Individual palaeosol horizons are up to 5m to
7 m thick. Laminated mudrocks (MF1) and reworked
mudrocks (MF5) are very rare. The mottling pattern
is mainly related to gleying and oxidation along
cracks and ped margins. Carbonate nodules and
rhizocretions become generally absent in unit S4.
Slickensided horizons and soil peds are common,
though not abundant, whereas desiccation cracks
and root structures are rare. Coalified plant debris
is common in mudrocks and channel sandstones.
The palaeosols of LSG are typified by a high con-
tent (up to 9%) of goethite in some mudrock units
(see below).
PA4 has a highly bimodal grain-size distribu-
tion, dominated by medium to coarse-grained
sand and fine clays (<2 µm). The assemblage
is characterised by some intensively slicken-
sided horizons and complex mottling patterns
and a dominance of cumulative pedocomplexes
(Fig. 11).
Palaeosol assemblage 3 (PA3)
Palaeosol assemblage PA3 characterises the thick
floodplain successions in ULF (L04 to L01). The
mudstones are mostly red and reddish-brown and
dominated by mudrock facies MF3 with high
chroma vertisols (Table 6, Figs 8, 10 and 13).
Entisols/Inceptisols (MF2) and reworked mudrocks
(MF5) are also common. Individual Vertisol profiles
can be up to 6 m to 7 m thick and are commonly
truncated and overlain by laminated mudrocks,
reworked mudrocks or sheet-flood sandstones
(Fig. 13). In PA3 some horizons (0.4 m to 0.7 m thick)
with nearly coalesced carbonate nodules (c.50% to
60% of total mudrock volume) occur, often with
complex overprinting of crystallaria (Müller
et al
.
2004). Some of the vertisols contain intensively
slickensided horizons. Vertically stacked calcrete
nodules, carbonate box-work structures, rhizocre-
tions, root structures, burrows, soils peds (Müller
et al
., 2004) and deep and wide sand-filled desicca-
tion cracks, are all abundant features of PA3.
The vertical arrangement of mudrocks above
channel sandstones is, in general, laminated
mudrocks (MF1) overlain by entisols/inceptisols
(MF2) and vertisols (MF3) (Fig. 12). Up to 2 m to
3 m thick zones of reworked mud aggregates are
associated with vertisols, particularly in the tran-
sition zone from ULF to LSG. In well 34/4-9S in the
Snorre Field, a bone of the plant-eating dinosaur
Plateosarus
has been found in deep-red floodplain
mudstone in the allostratigraphic unit L03 (Hurum
et al
., 2006).
Mudrocks with complex mottling patterns (MF4)
also occur in the uppermost part of the Lunde
Formation and in the lower part of the Statfjord
Group (LSG). The mottling is mainly related to
the presence of pseudo-gleying (reduction) along
desiccation cracks and peds. A few thin (<0.2 m),
olive-green, restricted gleyed horizons are identi-
fied (Table 6). These olive-green horizons have a
generally higher goethite content than the adjacent
mudrocks and are also present in the upper part of
the Statfjord Group (USG) (see below). The mudrock
Palaeosol assemblage 5 (PA5)
PA5 refers to the allostratigraphic units S3 to S1 in
the upper part of the Statfjord Group (USG). The
palaeosols in these mudrocks are dominantly grey
and greenish-grey; a reddish-brown colour is very
rare and observed only within S3. Slickensided
surfaces are present, though not abundant and
some angular soil peds have been recorded. As
described above from FSA1, coalified root and
rootlet structures occur, but are not abundant,
whereas coalified plant debris (wood) is rather
common at the base of fluvial channels. Dark grey
organic-rich thin mudstone beds are present.
Primary sedimentary lamination can be preserved
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