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with more matrix-supported pebbles at the base
than at the top. The beds of facies PFC are interca-
lated with subordinate beds of deformed chalk
facies DC (Figs  12E, 12 F, 12I, 13G, 13I and 13 J),
e.g. in well 2/8-15 at 3421.9 m to 3386 m), forming
PFC-DC couplets.
Chalk clasts become increasingly rare upwards
as facies PFC passes gradationally into the homo-
geneous chalk of facies HC (Table  2). HC facies
also occurs at the base of the upper channel-fill
unit in well 2/8-15 (e.g. depth interval 3433.3 m to
3422.5 m in well 2/8-15) where it is interbedded
with coarse PFC facies (Fig. 12C). Overall, the HC
facies make up around 10% of the upper channel-
fill unit in both wells 2/4-12 and 2/8-15. The HC
facies commonly shows no sedimentary or bioge-
neic features, but occasionally burrows have been
observed (Figs 12D, 12H and 13H).
Porosity profiles derived from wireline-log data
show a repeated pattern of stacked high-to-low
porosity intervals composed of high-porosity/
low-density base overlain by low-porosity/high
density top (Figs  8 and 9). In both wells 2/4-12
and 2/8-15, these high-to-low porosity alternations
occur arbitrarily within stacked PFC intervals
interbedded with thinner DC intervals and are not
associated with a specific facies type or facies
associations (Figs 8 and 9).
Interpretation: The upper channel-fill unit is
interpreted as a series of stacked pebbly debris
flow deposits (facies PFC, Table  2) which are
interbedded with, or pass gradationally upwards
into, low density turbidity current (facies HC) and
slump deposits (facies DC). The coarse-tail grading
recognisable in some debris-flow beds can be
attributed to a large-scale turbulent churning in
the viscous mass flow. The rare bioturbations
indicate intermittent establishment of a benthic
fauna on debrites on the sea floor between succes-
sive mass flow events.
The chalk substrate at this early time was poorly
consolidated and consists of a highly porous (70%
to 80%; Scholle 1977) thixotropic calcareous ooze
making it intrinsically unstable on sloping areas.
Debris flows may have been generated from different
areas, all of which are quite probably possible
sources for these gravity flows. Firstly, they may
have been produced by slope failures in areas from
outside the channel such as the surrounding
structural highs (e.g. Lindesnes Ridge). Secondly,
they may also have been generated by slope failure
of the channel margins. A third possible mecha-
nism for generating small scale debris flows might
have been by the collapse of sub-seismic scale
ridges (slopes of 5º to 15º) generated by currents
within the channel trough. This type of chalk debris
flow associated to ridges has been described from
outcrops at Etretat (Quine & Bosence, 1991). The
debris flows originating outside the channel on
surrounding structural highs may have been cap-
tured by the channel topography and deflected
down the channel axis.
Facies associations in the areas marginal
to the channel
Description: The chalk deposits in the areas
marginal to the channel consist of a lower por-
tion (35% to 40% of the interval) composed of
chalk with primary laminations of facies LC
(Table 2) intercalated with bioturbated homoge-
neous chalk of facies BHC. The BHC facies con-
tains flint nodules and has decimetre-thick beds
of the packstone-grainstone chalk of facies PGC
(e.g. well 2/4-A6; Fig.11). These facies pass
abruptly upwards into pebble floatstone chalk
facies PFC (Table 2) that forms metre-thick beds
with high clast concentration. Facies PFC has a
matrix supported texture with well-rounded
clasts ranging from coarse sand to pebble grade.
The deposits occasionally show minor soft-
sediment deformation. Facies PFC makes up
~ 30% of the succession in the areas marginal to
the channel and is intercalated with metre-thick
beds of deformed chalk of facies DC (e.g. well
2/4-A8, Fig.  10), homogeneous chalk of facies
HC (Table  2) and thinner beds of bioturbated
homogeneous chalk (facies BHC) or laminated
chalk (facies LC). These facies constitute a fur-
ther 30% to 35% of the succession in the areas
marginal to the channel. It is noted that the 2/4-
A8 well situated closer to the channel shows
development of deformed chalk facies, whereas
the 2/4-A6 and 2/7-14 wells situated further
from the channel do not.
Interpretation: In terms of facies types and
facies association, the succession in the areas
marginal to the channel is similar to that
observed in the channel-fill, but thinner. The
basal deposits are interpreted to consist of
autochthonous pelagic chalk (facies BHC,
Table 2) with occasional beds generated by distal
low density turbidity currents and mud clouds
(facies LC). The flint nodules may represent epi-
sodic periods characterised by low rate of sedi-
mentation (cf. Clayton, 1986).
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