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Well 6406/2-5
Well 6406/2-5 At2
Well 6406/2-R-4H
Well 6406/2-3-T3
Well 6506/11-6
4
no core
no core
no core
no core
no core
3
no core
no core
no core
no core
no core
2
no core
no core
no core
no core
1
no core
no core
no core
vf fm
c
silt
sand
Facies
vf fm
c
0
Facies associations:
A
silt
sand
vf fm
c
Facies
silt
vf fm
c
Facies
silt
sand
sand
B
vf fm
c
Facies
silt
sand
Facies
Tidal ridge
deposits
Inter-ridge
deposits
Planar cross-stratification
Massive
Ripple cross-lamination
Cross-lamination
with mud flasers
Planar parallel stratification
Bioturbation
Fig. 5.
The basal contact of the Garn Fm. with the underlying Not Fm. (Fig. 3) in cores from the Kristin Field (for the location
of wells see Fig. 4). The sharp unconformable base of the formation, considered to be a wave-cut erosional surface, is used
as a datum.
Facies S
RL
: sandstones with ripple cross-
lamination — attributed to the action of waves with
low near-bottom orbital velocities (Komar & Miller,
1975) or to weak unidirectional currents in the
lower range of lower flow regime (Harms
et al
.,
1975).
Facies S
CS
: sandstones with planar cross-
stratification — attributed to the action of unidi-
rectional currents in a higher range of lower flow
regime, forming long-crested subaqueous 2D dunes
(Harms
et al
., 1982).
Facies S
M
: massive sandstones — attributed to
sporadic dune collapses or local sea floor lique-
faction due to earthquakes (Seed, 1979; Field
et al
.,
1982) or cyclic loading by storm waves (Seed &
Rahman, 1978; Okusa & Uchida, 1980).
The descriptive characteristics of the individual
facies are summarised in Table 1 and their relative
thickness percentages in the studied cores are
given in Table 2. The most abundant are facies S
CS
(28% to 60%) and S
PS
(13% to 60%). Facies S
M
is
rare (≤ 0.1%) and its only significant occurrence
(6.6%) in well 6506/11-N-3H suggests local lique-
faction, perhaps due to proximity to a seismically
active fault (cf. Fig. 4).
The spectrum of facies indicates a current-
dominated and wave-dominated depositional
setting with sporadic storm events, characterised
by a sufficiently high hydraulic energy to trans-
port sediment of up to granule size and keep mud
perennially in suspension. Such conditions typify
many inner shelves, particularly the shoreface
zone and other littoral shoals (Johnson & Baldwin,
1996; Molgat & Arnott, 2001), as well as sand-prone,
narrow epicontinental seaways with enhanced
tidal currents (Keene & Harris, 1995; Mellere &
Steel, 1996; Slingerland
et al
., 1996; Carr
et al
.,
2003; Longhitano & Nemec, 2005).
Facies associations
On the basis of the stratigraphic grouping of sedi-
mentary facies in the well logs and their tentative
lateral correlation, the Garn Formation in the study
area is recognised to consist of three main facies
associations (Figs 7 & 8). They are described briefly
and interpreted below. Volumetric estimates are
one-dimensional, based on the thicknesses of
facies and their assemblages in the individual
wells (Table 2).
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