Sedimentation at the Jurassic–Triassic boundary, south-west Barents Sea: indication of climate change - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 198

N

A0

A0

Max. Trough
Amplitude

7222/11-1

0

1000

2000

3000

4000

5000

6000

0 10 km

7000

Fig. 7. 3D seismic representation of channelised sandstone bodies in the upper part of the Snadd Formation, SE Loppa
High. A0 corresponds to the cored section (channel) shown in Fig. 5. Seismic image (SG9803) by Inger Laursen (Statoil).

siderite concretions. However, these fine-grained
strata are replaced vertically by an 8 m thick,
sharply based, unit of bioturbated and wave-
rippled sandstones with interbedded muddy
layers, thus giving the lower part of the Fruholmen
Formation a general coarsening upwards grain
size profile.
The bioturbated sandstone is subsequently
overlain by a 25 m thick coarse-grained to fine-
grained sandstone unit (app. 1335 m to 1360 m in
Fig. 8), comprising two, stacked, fining upwards
units, each with very sharp and apparently ero-
sive bases. This major sandstone body is other-
wise characterised by common intra-clast lag
conglomerates (mainly coal pieces and mudrock
fragments), dm-scale cross-stratification and mas-
sive sandstone sections, capped by fine-grained,
current-rippled sandstone.
Intercalated thin sandstone units, laminated
and weakly bioturbated mudrock and thin coal
beds with associated root horizons characterise
the upper 30 m of the Fruholmen Formation in

well 7124/3-1 (app. 1305 m to 1335 m; Fig. 8). A
single, sharp-based and fining upwards, 3 m thick
sandstone unit with some dm-scale cross-stratifi-
cation and current ripple lamination is present in
this interval (app. 1325 m; Fig. 8). Other sandstone
layers are generally thin and inter-bedded with
muddy deposits. A very similar succession is also
seen in Fruholmen Formation in well 7226/11-1
(Fig. 9) on the Norsel High (Fig. 2). Here, the upper-
most part of the formation is cored (app. 1233 m
to 1247 m core depth in Fig. 9) and comprises a
mudrock-dominated succession with associated
thin-bedded sandstones. Rooted horizons are gen-
erally grey with associated carbonaceous rootlets,
however with a notable thin red/grey mottled zone
(app. 1240 m core depth in Fig. 9).
Regionally, in the Barents Sea, deposition in the
Fruholmen Formation was initiated by a major
marine incursion during Early Norian times
(Henriksen et al . 2011). The basal mudrock in the
Fruholmen Formation is related to deposition in a
marine, pro-deltaic environment with the dark