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fully marine Dunlin Shale. Final drowning of the
system is considered to have been rapid over a
large area causing a relatively sudden facies
transition at the base of the Amundsen Fm (base
Dunlin Group) to fully offshore marine deposits.
Continental Statfjord Group deposits are linked to
age equivalent marine sediments in the southern
North Sea implying that the palaeo-coastline for
most of 'Statfjord times' was located south of the
Utsira High; i.e. approximately 300 km to 350 km
south of the Statfjord Field area (Ryseth, 2001;
Fig.  8). The top of the Statfjord Group on the
Statfjord Field is essentially flat and a backstep-
ping of the uppermost Statfjord facies with time-
equivalent Dunlin deposits interfingering can
only be seen to the north and west of the Statfjord
Field area.
For this study, facies observations from 2990 m
of core and associated wireline information from
20 wells from the Statfjord, Snorre, Gullfaks Sør
and Gullfaks Fields was used. A lithofacies
description scheme was established which was
used to define nine facies associations. Sub-
sequently, the Statfjord Group reservoir correla-
tion and zonation work discussed here was limited
to 11 cored wells in the Statfjord Field.
to the correlation of surfaces with stratigraphic
significance as well as establishing the relative
importance of these surfaces in a hierarchical
framework.
Seismic data for the Statfjord Group on Statfjord
Field are of generally poor quality and of limited
use for correlation. Furthermore, after many years
of injection and production, the Eiriksson Fm is
more or less homogenised pressure-wise, while the
more isolated Raude sandstone bodies show more
variable pressure regimes. There are limited areas
of pressure communication across the Raude to
Eiriksson boundary but, in general, a pressure jump
exists at this stratigraphic location which was used
to support the Raude to Eiriksson boundary identi-
fication based on core and log data.
Stratigraphic analysis
Identification of A/S change in the Statfjord Group
relies on core observations (Figs  9 and 10).
Following the lines of reasoning presented above,
for a given interval, minimum A/S periods are
identified by either a combination of most vertisol-
like features and highest maturity in the palaeosols
(for example, most intense red colouration, layered
calcretes, intense rooting) or, where present, the
base of the multi-storey channel sandstone unit
with the coarsest and/or most mineralogically
immature lag deposits (Figs  6 and 9 to 11). The
development and preservation of a palaeosol hori-
zon implies that the net sediment accumulation
rate in the location where the soil developed
became neutral or weakly aggradational for a long
time causing burial of the soil without significant
erosion. Consequently, the site of pedogenic altera-
tion on the floodplain was either distal and/or
topographically raised above the fluvial channel
(Leeder, 1975). Mature palaeosols, especially those
featuring mature calcretes, require considerable
periods of stability for growth (Todd, 1996) in the
order of 10 5 yr for the most mature soils. During this
time, the nearest channel belt has to remain at a
distance sufficiently large to allow the develop-
ment of a stable interfluve environment and to not
affect palaeosol formation processes. A situation
like this is considered a local A/S relative minimum
(Fig. 12, Well 1). Observing these sedimentary fea-
tures at the same stratigraphic level in multiple
neighbouring wells suggests that the occurrence of
these mature palaeosols is a semi-regional, strati-
graphic phenomenon (Fig.  11A) controlled by
external forcing factors, rather than local, autogenic
Correlation and zonation challenges
Analysis of depositional environments suggests
strongly that no marked proximal-distal trends can
be identified on Statfjord Field-scale ( approximately
5 x 24 km; Fig. 2). Stratigraphic trends in sandstone
body connectivity are currently difficult to detect
and only apparent at low resolution, large-scale
correlations. In addition, reliable field-wide corre-
lation zones, formed by fine-grained floodplain
sediment, are nearly absent.
The succession also suffers from a severe lack of
biostratigraphic data. Miospores occur abundantly
in some fine-grained intervals but abundance
events are local due to variations in source, disper-
sal and deposition. In addition, very few, good,
age-diagnostic marker species for correlation occur.
Megaspores are the only microfossil group with
potential for Upper Triassic-Jurassic stratigraphic
analysis of continental strata (Morris et al ., 2009).
Additionally, chemostratigraphy and magneto-
stratigraphy do not have the required resolution in
the Statfjord Group. The inability to recognise time
lines though the fluvial succession, in addition to
the difficulty to physically trace key stratigraphic
surfaces, imposes a significant uncertainty related
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