The Garn Formation (Bajocian-Bathonian) in the Kristin Field, Halten Terrace: its origin, facies architecture and primary heterogeneity model - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 525

Table 2. The thickness percentages of the individual facies and their assemblages in the studied cores. These thickness
data may serve as one-dimensional irst-order estimates of the corresponding volumes.

WELLS

Facies and
associations 6406/2-5 6406/2-5 AT2 6406-2-R-4H 6406/2-3 T3 6506/11-6 6506/11-N-3H

Facies S PS 26.7% 60.5% 35.0% 42.9% 12.6% 34.0%

Facies S SS 0.6% 0.4% 0.0% 0.3% 0.8% 2.0%

Facies S HS 0.7% 0.0% 0.2% 1.3% 2.3% 0.5%

Facies S RL 44.3% 10.2% 6.2% 23.3% 24.1% 23.3%

Facies S CS 27.7% 28.9% 58.5% 32.1% 60.2% 33.6%

Facies S M 0.0% 0.0% 0.1% 0.1% 0.0% 6.6%

FA A 32.0% 30.0% 60.0% 33.0% 68.0% 45.0%

FA B 64.0% 65.0% 14.0% 63.0% 12.0% 43.0%

FA C 4.0% 5.0% 26.0% 4.0% 20.0% 12.0%

1988), or may possibly be subject to erosional sand
bypass (Le Bot et al ., 2005).
Facies association C consists of facies S PS (54 vol.%
to 95 vol.%) and facies S RL (3 vol.% to 32 vol.%,
mainly wave-ripple cross-laminated), which alter-
nate with each other and are interspersed with the
isolated beds of facies S HS (≤11 vol.%) or S SS
(≤6 vol.%) and solitary small cross-sets of facies S CS
(≤8 vol.%). This facies assemblage constitutes
4 vol.% to 26 vol.% of the Garn Formation, occurs
repeatedly as a depositional cover of the previous
two facies associations (Fig. 10) and virtually pre-
dominates in the uppermost part of the formation in
two wells (Fig. 8). Facies association C is interpreted
to represent episodes of wave-dominated and tid-
ally-influenced sedimentation, similar to that char-
acterising shorefaces and other littoral shoals on
many shelves (Grant & Madfen, 1979; Swift et al .,
1979; Bourgeois, 1980; Clifton & Dingler, 1984; Swift
& Thorne, 1991; Cacchione et al ., 1994). These
deposits in the present case are thought to signify
shallower-water conditions than those of facies
associations A and B, because of the evidence of a
perennial wave action (facies S PS and S RL ) punctu-
ated by storm events (facies S HS and S SS ) and the
scarcity or poor preservation of tidal dunes (wave-
truncated facies S CS ).

et al . 2001; Johannessen & Nøttvedt, 2008). The
platform was a part of the seaway, but was broad
and receiving little sand from the Scandinavian
shoreline. It received sand from the west, spread
out by storms and tidal currents whenever the
accommodation for sand storage on the adjoining
Halten Terrace reached its minimum. The deeper
axial part of the seaway would have amplified
tidal currents (Montenat et al ., 1987; Sztanó & De
Boer, 1995; Corfield et al ., 2001), which might
have been circulatory and inherently asymmetri-
cal or whose southward flow could have been
enhanced by Boreal storms (see McBride, 2003).
Southward palaeocurrents and tidal sandstone
bodies were also recognised in the adjacent East
Greenland seaway (Surlyk, 1991, 2003).
The Halten seaway probably comprised a series
of incipient shallow grabens and half-grabens
formed by extensional faults or fault-propagation
flexures (Blystad et al ., 1995; Corfield & Sharp,
2000; Corfield et al ., 2001; Marsh et al ., 2010). The
Garn Formation in the Kristin Field consists of shal-
low-marine sandstones and has a considerable
thickness. The thickness increases towards the east
and abruptly decreases across the Trestakk-
Smørbukk Fault (Fig. 2B), which suggests deposition
in an actively subsiding shallow graben (Fig. 11).
The occurrence of conglomeratic facies at the west-
ern extremity of the field (well 6506/11-3) may cor-
respond to the western margin of the hypothetical
graben and supports the notion of westerly sedi-
ment supply (Fig. 11). The Grip High horst at the
time was probably an elongate island or a belt of
islands (Doré 1992; Quin et al ., 2010) and would
have had small water catchments, unlikely to form
large river deltas. Its palaeoshoreline is not preserved
but was probably wave-dominated and might have
included small gravelly river deltas or fan deltas

Depositional model

Regional palaeogeographical reconstructions sug-
gest that the Early to Middle Jurassic sedimenta-
tion in the Halten Terrace area occurred within
the northern reaches of a narrow seaway extend-
ing southwards from the open Boreal Sea, bounded
by the sand-supplying Grip High to the west and
passing into a mud-prone Trøndelag Platform to
the east (Gjelberg et al . 1987; Doré 1992; Brekke