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 521

Table 1. A summary of the descriptive characteristics and genetic interpretation of the sedimentary facies distinguished in
the studied cores of the Garn Fm. in Kristin Field.

Facies co de Facies name and description Genetic interpretation

S PS Sandstones with planar parallel stratification :

These arenitic sandstones are very fine-grained
to very coarse-grained, occasionally bearing
granules. The units of this facies are solitary
sets or cosets of planar parallel strata and range
in thickness from < 1 cm to 640.5 cm, averaging
26 cm. Strata sets are up to 25 cm thick,
separated by slightly inclined (≤5°) planar
truncation surfaces in cosets.

This facies represents tractional depo-
sition of sand by waves with high
near-bottom orbital velocities (Komar
& Miller, 1975) or by the action of
marine currents, either combined
with waves (Arnott, 1993) or boosted
to the upper flow regime (Harms
et al ., 1975) by storms and topo-
graphic confinement (Amos et al .,
1995). The flat truncation surfaces,
commonly with very coarse sand
and/or granules, may represent ero-
sive storm events (Clifton & Dingler,
1984; Arnott, 1993).

S SS Sandstones with swaley stratification : These

arenitic sandstones range from very fine/fine-
grained to medium/coarse-grained and form
units 7 cm to 39.5 cm thick, averaging 14.5 cm.
The units have erosional bases and are isolated
sets or sporadically cosets of concave-upward
and flattening-upward parallel strata recog-
nised as swaley stratification.

This facies represents tractional
deposition of sand by an episodic
scour-and-fill action of storm waves
combined with unidirectional current
under a low net rate of sediment
accretion (Arnott & Southard, 1990;
Dumas et al ., 2005; Dumas & Arnott,
2006).

S HS Sandstones with hummocky stratification : These

arenitic sandstones range from fine-grained to
medium/coarse-grained and form units 7 cm to
29 cm thick, averaging 12 cm. The units have ero-
sional bases and are sets of nearly flat or slightly
concave-upward to convex-upward parallel strata
recognised as hummocky stratification.

This facies represents tractional depo-
sition of sand by an episodic action
of storm waves combined with
unidirectional current under a high net
rate of sediment accretion (Arnott &
Southard, 1990; Dumas & Arnott, 2006).

S RL Sandstones with ripple cross-lamination :

These sandstones are very fine-grained to
coarse-grained and form units 0.5 cm to
186 cm thick, averaging 16 cm and ranging
from solitary sets to cosets of ripple-scale cross-
laminae. They vary from arenitic to slightly
wackey, with occasional intra-set mud flasers
0.1 cm to 0.3 cm thick and inter-set mud drapes
0.1 cm to 0.7 cm thick, sporadically up to
7.5 cm. Cross-lamination patterns indicate rip-
ples ranging from symmetrical to asymmetrical,
including mud-draped bidirectional bedforms.

This facies represents tractional depo-
sition of sand by the action of waves
with low near-bottom orbital veloc-
ities (Komar & Miller, 1975) or by
sea currents in the lower range of
lower flow regime (Harms et al .,
1975). Bidirectional ripples indicate
a reversing flow and the occurrence
of mud drapes/flaser indicates flow
slackening episodes, as is gener-
ally characteristic of tidal currents
(Reineck & Singh, 1980).

S CS Sandstones with planar cross-stratification :

These arenitic sandstones are fine-grained to
very coarse-grained, forming planar cross-strata
sets with mainly tangential basal parts. The
cross-sets are 7 cm to 250 cm thick, averaging
31 cm, and range from solitary to multiple,
stacked upon one another as cosets up to 12 m
in thickness. Many thin cross-sets are erosional
relics (bottomsets) of thicker ones. Some cross-
sets show interstratal mud drapes, intrasets of
backflow ripple cross-lamination and/or reac-
tivation surfaces. Dipmeter data indicate that
the cross-strata are dipping mainly towards the
SSW, less commonly towards the NNE.

This facies represents tractional deposi-
tion of sand by marine currents in the
higher range of lower flow regime,
forming straight-crested or sinuous-
crested subaqueous 2D dunes (Harms
et al ., 1982). The evidence of flow
reversals (opposedly dipping cross-
strata sets, backflow ripples, reac-
tivation surfaces) and brief pauses
in sand transport (interstratal mud
drapes) indicate tidal currents
(Reineck & Singh, 1980).