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 519

underlying Not Formation grade upwards into
bioturbated heterolithic tidalites, which are
sharply overlain by the littoral sandstones of the
Garn Formation (Fig. 5). The shallowing-upward
facies succession of the uppermost Not Formation
suggests a normal regression, which was inter-
rupted by a phase of erosion and followed by lit-
toral sandy sedimentation. A similar stratigraphic
relationship has been reported from the adjacent
Smørbukk area, with the formation boundary
attributed to an episode of forced regression
(Corfield et al ., 2001).
The similarity of facies below and above the
formation erosional boundary across the study
area (Fig. 5) suggests that the basal palaeorelief of
the Garn Formation along the line of wells stud-
ied in the Kristin Field (Fig. 4) was probably
negligible.

6506/11- N-3 H

6506/11- 6

6406/2-3 T3

6406/2-R-4 H

Sedimentary facies

6406/2-5 AT 2

The sandstone succession of the Garn Formation
is nearly devoid of mudstone drapes or thicker
interlayers and is considered to be of shallow-
marine origin. Sporadic trace fossils include
Trichichnus , Skolithos , Arenicolites , Ophi-
omorpha , Cylindrichnus , Planolites, Palaeo-
phycus, Chondrites , bivalve burrows and resting
traces (Quin et al ., 2010), which support the
notion of a shallow-marine environment (Bromley,
1996). Six sedimentary facies have been distin-
guished on the basis of sedimentological core
description (Table 1 & Fig. 6):
Facies S PS : sandstones with planar parallel
stratification — attributed to the action of waves
with high near-bottom orbital velocities (Komar &
Miller, 1975) or possibly unidirectional currents
combined with waves (Arnott, 1993) or boosted
to the upper flow regime (Harms et al ., 1975) by
storms and topographic confinement (Amos
et al ., 1995).
Facies S SS : sandstones with swaley cross-
stratification — attributed to an episodic scour-
and-fill action of storm waves combined with
unidirectional currents under a low net rate of
sediment accretion (Arnott & Southard, 1990;
Dumas et al ., 2005; Dumas & Arnott, 2006).
Facies S HS : sandstones with hummocky cross-
stratification — attributed to a similarly episodic
action of storm waves combined with unidirec-
tional currents under a high net rate of sediment
accretion (Arnott & Southard, 1990; Dumas &
Arnott, 2006).

6406/2-5

N

2 km

Fig. 4. The location of main wells in the Kristin Field (see
study area indicated by the blue frame in the left-hand map
in Fig. 1). Cores and wireline logs from the six wells are the
basis of the present study.

(Harms et al ., 1975; Walker, 1984). The term 'facies
association' denotes an assemblage of spatially
and genetically related facies representing a par-
ticular depositional subenvironment.
The statistical notions and methods employed
in this study are from Middleton et al . (1995),
Drummond & Wilkinson (1996) and Davis (2002).
Some crucial geometric-statistical concepts,
derived from Malinverno (1997), are reviewed in
the Appendix.

FACIES ANALYSIS OF THE
GARN FORMATION

The base of the Garn Formation is a regional ero-
sional unconformity (Corfield et al ., 2001). It is
generally sharp, although the facies change across
this boundary is not necessarily profound. In the
Kristin Field, the neritic mudstones of the