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response of up to 140 API units is characteristic.
The lack of bioturbation suggests a hemipelagic
origin under anoxic conditions. This is the char-
acteristic Kimmeridge Shale facies.
Facies T2: Silt laminated mudrocks - consisting
of dark, laminated mudrocks with regular thin
(mm-scale to cm-scale) silt laminae (Fig. 7E) that
correspond well to the T
1
to T
4
fine grained turbid-
ite divisions of Stow & Shanmugam (1980).
Laminae are sometimes disrupted by bioturba-
tion. This facies is interpreted as a distal or lobe
fringing turbidite deposit.
Facies T3: Heterolithic sand-mud couplets -
consisting of fine to medium-grained sandstones
with a wide-range of bed thickness (cm to dm
thickness). The sandstones are often heterolithi-
cally interbedded with T2 facies and can form fin-
ing upwards packages up to 2 m thick. A hierarchy
of structures resembling Bouma's B-C-D-E divisions
(Bouma, 1962) is commonly developed; however,
laminae are sometimes disrupted by bioturbation.
Sandstone beds, often with scattered siltstone
clasts, show a sharp loaded basal contact with
underlying mudstones. Sandstones are massive
and structureless or with dish and pillar or flame
structures suggesting dewatering. Indistinct hori-
zontal lamination is present and thin beds (<3 cm
thick) display low amplitude ripples with mud
drape development (Fig. 7C). This facies is inter-
preted as the deposit of mixed-load turbidity
currents. Gowland (1996) postulates an origin
either by storm events or moderate density
turbidity currents for this facies type.
Facies T4: Massive amalgamated sandstone -
consisting of largely massive, medium-grained
sandstone forming units typically 1 m to
10 m thick. Graded bedding is mainly absent.
Carbonaceous material is scattered throughout
and becomes concentrated into horizontal lami-
nae towards the top of sandstone beds (Fig. 7B).
Climbing ripples are sometimes observed
(Fig. 7D). The top of sandstone units can be bio-
turbated by
Chondrites
. The sandstones are later-
ally continuous and mapping shows a lateral
extension of up to 6 km
2
. This facies is interpreted
as the deposit of high-density turbidity currents.
A similar interpretation for this type of facies is
postulated by Gowland (1996). Mapping suggests
that sandstone units of this type were deposited as
lobes or sand sheets in depositional lows.
Facies T5: Bioturbated silty sandstone (called
'Clyde Member') - consisting of massive, fine to
medium-grained, poorly sorted and extensively
bioturbated grey-green sandstones. Thin graded
sandstone beds occur occasionally and clay-lined
Zoophycus
burrows are present throughout. This
facies is interpreted as a shallow shelf deposit with
occasional storm influence. Biostratigraphic dating
suggests that this facies is laterally equivalent to
Facies T4 over a distance of approx. 400 m.
Gowland (1996) describes one further facies type
which might be attributed to mass flow processes.
This is a matrix or clast-supported pebble sand-
stones with intraclasts of reworked Triassic, Middle
Jurassic or phosphatic material. This deposit is
attributed to either: (a) storm-generated flows and
wave current winnowing associated with lowstand
shoreline development and transgressive surfaces,
or (b) high density turbidity currents or debris
flows compatible with a deeper marine setting.
The major control on the morphology of the
Ribble Sandstone is structural causing the thick-
ness to range from 60 m to 2.5 m over less than
1 km distance (Robinson, 1990). This is a common
feature of turbidite deposition throughout the
Central Graben as confirmed by mapping of local
and regional tectonic elements. Within the Ribble
Sandstone Member and elsewhere in the Fulmar
Formation of Fulmar Field, soft sediment defor-
mation structures are widespread. Robinson
(1990) considers it probable that the observed
dewatering, fracturing and mudslides (within the
Avon Shale) are the result of external shocks
rather than sediment overloading. In addition to
remobilising the turbidites, faulting, salt move-
ment and periodic earthquakes are considered a
possible trigger mechanism for turbidite flows to
be initiated. In other areas, sand remobilisation
features such as injectite beds and dykes can be
observed. These sand injectites erode and trans-
port claystone clasts that have been prised and
ripped from the shales in which they are encased
(e.g. Kimmeridgian Farsund Formation core of
well NO-2/4-18R; Fig. 7F; well situated 1 km to
the NE of well 2/4-14 shown on Fig. 1).
Other authors have considered these, or similar
facies, in different ways. Jeremiah & Nicholson
(1999), for example, identified sandstones of tur-
bidite origin in several Central Graben wells
(22/30b-11, 23/26b-15, 30/13-4, from the Erskine,
Shearwater and Elgin-Franklin area (located at the
four corners area of Quad 22, 23, 29 and 30). The
sandstones were interpreted as being deposited by
high density turbidites to form stacked amalga-
mated sandstone beds with planar lamination,
occasional current ripples or symmetrical wave
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