Tectonic control on sedimentation, erosion and redeposition of Upper Jurassic sandstones, Central Graben, North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 476

often become an important controlling factor on
Upper Jurassic deposition (Vendeville & Jackson,
1992a/b; Vendeville & Guerin, 1998; Guerin et al .,
1998), notably over salt highs or in areas of inter-
pod salt wall collapse (Fig. 2). Zechstein salt,
where present, had two main influences: (1) it
controlled the deposition of the Triassic with the
formation of Triassic salt minibasin or 'pod' struc-
tures (Smith et al ., 1993; Stewart et al ., 1999;
Stewart & Clark, 1999; Stewart, 2007; Jackson
et al ., 2010); and (2) it decoupled the movement of
basement Rotliegend faults from that of overlying
faults. Thus, the controls on Upper Jurassic depo-
sition are a hybrid between normal extensional
tectonism as seen in the Northern North Sea and
halokinesis.

are developed following the drowning of fault
block footwalls and are said to have caused a
switching off of deposition of coarse clastics (i.e.
shoreface sandstone deposits) in both the basin
centre and marginal areas due to major reorgani-
sation of both basinal and shelfal palaeogeogra-
phies (Partington et al ., 1993a). Regional synthesis
work on sequence definition such as that carried
out by Fraser et al . (2002) rely on earlier biostrati-
graphic studies (e.g. Partington et al ., 1993a;
Duxbury et al ., 1999) to define genetic, tecton-
ostratigraphic sequences bounded by MFSs that
are used as a basis for Upper Jurassic palaeogeo-
graphic mapping.
The aim of biostratigraphic dating is to identify
regionally developed sedimentary packages of
coeval deposits which can be grouped into geneti-
cally related depositional sequences (Partington
et al ., 1993a, b; Jeremiah & Nicholson, 1999). The
conceptual framework of sequence stratigraphy
(Van Wagoner et al ., 1988; Van Wagoner et al .,
1990) aims to explain the development of these
depositional sequences in terms of relative sea-
level changes. If such sea-level fluctuations were
entirely of eustatic origin, high-stand and low-
stand events would be very precise time markers.
However, rifting and salt movement were both
very active in the Central Graben and this has led
to both regional and local tectonic overprints, the
effects of which cannot be separated from eustatic
variations.
More recently, the concept of synchronous
sequence stratigraphic surface development around
the basin has been a contentious issue. The rela-
tively comforting statement of Fraser et al . (2002)
that: “Whatever their main controls, observed
sequence boundaries and maximum flooding
surfaces (MFSs) are still probably isochronous
within the relatively small area represented by
the North Sea Basin” are challenged by the work
of biostratigraphers who consider that “rifting-
induced tectonic events, produced coeval flood-
ing and uplift” (Jeremiah & Nicholson, 1999). A
number of studies have placed sequence strati-
graphic development within a context of varying
accommodation space creation due to extension
of normal faults and deal with some of the
challenges of applying sequence stratigraphy in a
tectonically active setting (Howell & Flint, 1996;
Ravnås & Steel, 1998; Ravnås et al ., 2000).
Biostratigraphic dating of the more deeply
buried Upper Jurassic sandstones has a poor reso-
lution. The sandstones of the Elgin and Franklin

STRATIGRAPHIC FRAMEWORK

The lithostratigraphic nomenclature of the Upper
Jurassic is quite complex and has not been used in
a consistent manner across the basin. There are
several reasons for this: (1) the transgressive and
diachronous character of the Oxfordian-Volgian
sandstones; (2) the relative scarcity/unreliability
of the biostratigraphic dating, commonly made
more difficult by HPHT conditions which degrade
the microfossils; (3) the naming of sandstones
according to the field in which they were drilled,
rather than to a regional reference and (4) the geo-
graphical location of the Central Graben basin
straddling the UK/Norway/Danish borders, lead-
ing to three sets of nomenclature for the same
formations.
In this study, we prefer to make use of the
genetic stratigraphy for the Jurassic introduced by
Partington et al . (1993a, b) which is well known
and has been used in the description of several
major fields such as Fulmar (Kuhn et al ., 2003),
Erskine (Coward, 2003), Gyda (Partington et al .,
1993a) and Elgin-Franklin (Lasocki et al ., 1999).
The lithostratigraphic naming is placed within
the context of the biostratigraphic division (Fig. 3)
in the same manner as Partington et al . (1993b).
Fig. 3 provides a summary of the presence of
shoreface and turbidite sandstones in various
fields throughout the basin and biostratigraphi-
cally dated maximum flooding surfaces (MFS)
within the shales above and below these sand-
stones. Certain MFSs are described as 'Tectonically
Enhanced' (TEMFS), for example the Eudoxus J63
TEMFS and the Fittoni J71 TEMFS. These TEMFSs