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Formation to group and the previous members to
formations. In our paper we apply the lithostrati-
graphic definitions and terminology of Lervik
(2006) for the Hegre and Statfjord groups (Fig. 2).
The chronostratigraphy of the Hegre Group and
the continental part of the Statfjord Group is based
on terrestrial palynomorphs; in addition, ostra-
cods and foraminifera have been employed for
the upper marine part of the Statfjord Group and
the overlying Amundsen Formation of the Dunlin
Group (Eide, 1989; Lervik
et al
., 1989; Charnock
et al
., 2001; Goldsmith
et al
., 2003) (Fig. 2). Due to
poor preservation conditions in the continental
redbed facies, the biostratigraphic data of the
Hegre and Statfjord groups are generally scarce
and widely dispersed, both stratigraphically and
geographically. The chronostratigraphic subdi-
vision and regional correlation is consequently
uncertain (Eide, 1989; Lervik
et al
., 1989; Goldsmith
et al
. 2003).
Eide (1989) showed that in the Snorre Field
(Fig. 1) the Alke Formation and the Lunde
Formation (previous upper Lunde member) reveal
various palynomorph assemblages, with Assemblage
I comprising approximately the present Lunde
Formation and Assemblage II the present Alke
Formation. The palynomorph assemblages are char-
acterised by lacustrine/brackish water green algae,
with
Plaesiodictyon mosellanum
always being
present in Assemblage II and
Botryococcus
sp.
sporadically in Assemblage I. Eide (1989) sug-
gested that the difference in microfloral compo-
sition between Assemblage II and Assemblage I
might be the result of different depositional
environments (discussed below) and assigned a
Norian to Early Rhaetian age to Assemblage II
(Alke Formation) and an Early Rhaetian age to
Assemblage I (Lunde Formation).
The palynological data of the Triassic in the
North Sea were evaluated by Goldsmith
et al
.
(2003). Their chronostratigraphic reinterpretation
is adopted in this paper with slight modifications
made by Lervik (2006). According to Goldsmith
et al
. (2003) a mid Norian to late Norian age for the
Lunde Formation (the previous upper Lunde
member) is indicated by a palynomorph assem-
blage that includes
Kraeuselisporites reissingerii
,
Enzonalasporites vigens
and
Riccisporites tuber-
culata
. In addition to this Norian age, the Lunde
Formation probably also includes the lower Rhaetian
(Eide, 1989; Lervik
et al
. 1989) (Fig. 2).
The location of the Triassic-Jurassic boundary
in the Tampen Spur area is very uncertain due to
lack of diagnostic fossil assemblages within the
actual interval (Deegan & Scull, 1977; Vollset &
Doré, 1984; Nystuen & Fält, 1995). The Rhaetian-
Hettangian boundary is generally considered to
be located in the upper part of the Raude For-
mation (Goldsmith
et al
., 2003) (Fig. 2). The basal
Jurassic palynomorph assemblages lack the typi-
cal Triassic suite of species and are dominated by
Chasmatosporites
sp. and
Cerebropollenites thier-
gartii
(Goldsmith
et al
., 2003). The Hettangian to
Sinemurian and Sinemurian to Pliensbachian
boundaries are not well constrained by palyno-
logical data; the fluvial Eiriksson Formation is
likely to be dominantly Hettangian and the
marine Nansen Formation Sinemurian to Early
Pliensbachian (Charnock
et al
. 2001). Large num-
bers of the palynomorph
Deltoidospora spp
. are
recorded in the Statfjord Formation in the Snorre
Field well 34/7-7 and also in wells 31/4-4A and
34/10-30 in the Tampen Spur area (Müller, 2003).
Recent outlines of Triassic to Early Jurassic
palynology in north-western Europe and its sig-
nificance for palaeoclimate are given by Hubbard
& Boulter (2000), Kürschner & Herngreen (2010)
and Bonis & Kürschner (2012).
The Hegre Group consists of interchanging
mudstone and sandstone. The Induan to Carnian
Teist Formation consists of interbedded sand-
stone, claystone, mudstone and marl. The deposi-
tional environment is interpreted as ephemeral
fluvial channels migrating into distal mud basins
(Nystuen
et al
., 1989; Lervik, 2006). The Ladinian
Lomvi Formation is a massive sandstone unit
inferred to be aeolian and partly fluvial (Nystuen
et al
., 1989). The Alke Formation is dominated by
reddish-brown, grey and grey-green mudstones
and marls with thin, fine-grained, sheet-like sand-
stone beds. The depositional environment of the
Alke Formation in the northern North Sea area is
considered to have been typified by lacustrine
and terminal mud basins with proximal alluvial
fans (Nystuen
et al
., 1989, 2008; Lervik
et al
. 1989;
Lervik, 2006; McKie & Williams, 2009), possibly
with some intermittent marine incursions (Eide,
1989; Goldsmith
et al
., 2003) (see below).
The lower boundary of the Lunde Formation in
the Tampen Spur area is marked by fluvial chan-
nel-sandstone bodies resting on lacustrine and
terminal mud-basin deposits of the Alke
Formation. Pebbly conglomerate beds at the base
of the Lunde Formation contain extrabasinal
granitic and quartzitic clasts. The boundary, corre-
lated through several wells in the Tampen Spur
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