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Tectonic control on sedimentation, erosion and redeposition
of Upper Jurassic sandstones, Central Graben, North Sea
JONATHAN P. WONHAM*, IAN RODWELL , TORE LEIN-MATHISEN*
and MICHEL THOMAS*
* Total E&P Norge, Finnestadveien 44, Dusavik, P.O. Box 168, N-4001 Stavanger, Norway
Total E&P UK, Crawpeel Road, Altens, Aberdeen, Scotland
ABSTRACT
The distribution of Upper Jurassic sandstones in the Central North Sea Basin was
influenced by three structural mechanisms: (1) the contemporaneously evolving
Central Graben rift system that formed the basin and created fault block highs and
basinal grabens; (2) the movement of Zechstein salt (late Permian age) which can be
locally very thick and (3) bathymetric features controlled by the Jurassic deformation
of Triassic pods (salt minibasins). Rift development involved movement on deep
seated, normal faults with offset seen at Rotliegend level (Permian). Zechstein salt
decouples this fault displacement from the deformation of younger strata. As a result
of the individual or combined effects of footwall uplift, salt movement or grounding of
pods on the underlying Rotliegend, areas of former Triassic or Upper Jurassic deposi-
tion were subsequently reworked erosively and redistributed. It has been found that
spiculitic sandstone layers within Upper Jurassic Fulmar Formation sandstones serve
as useful horizons for correlation and help highlight intra-Jurassic erosive truncation
of shoreface sandstones. Erosion of structurally controlled highs can result in rework-
ing of earlier deposited shoreface sandstones, the products of this erosion being some-
times re-deposited as turbidites that are transported short distances before being
ponded in depositional lows such as the hangingwall of major faults. The development
of significant erosion surfaces within Upper Jurassic shallow marine sandstones is
linked to tectonic mechanisms. It is probable that these surfaces are not basin wide
sequence boundaries; rather they are local surfaces reflecting the dynamic and geo-
graphically varied evolution of the basin. Previous proposals that many phases of
incised valley development occurred during the Late Jurassic generating 3rd order
sequence boundaries do not appear to be backed by sedimentary evidence. While tur-
bidite sandstones are evidently developed at various times in the basin history, their
relationship to proximal fluvial systems and incised valleys is unproven. A preferred
interpretation is that local tectonic uplift and shoreface erosion are the main mecha-
nisms for redistributing Jurassic and older sediments.
Keywords: North Sea Central Graben, Upper Jurassic, tectonics, turbidite, shoreface,
sequence stratigraphy.
INTRODUCTION
and Fulmar (Johnson et al ., 1986; Spaak et al .,
1999; Kuhn et al ., 2003) in the UK sector. These
fields contain, or have produced, economically
important hydrocarbon reserves. Elgin-Franklin,
for example, is the world's largest high pressure,
high temperature, development and has supplied
up to 7% of the UK's natural gas requirement.
Several of these fields sit within the high pres-
sure and high temperature (HPHT) play of the
In the UK Central North Sea and the adjacent
Norwegian Southern North Sea sectors, Upper
Jurassic sandstones form prolific, good quality, res-
ervoir rocks in large fields such as Gyda and Ula
(Stewart, 1993) in the Norwegian Sector and Elgin-
Franklin (Lasocki et al ., 1997; 1999), Shearwater
(Jeremiah & Nicholson, 1999, Gilham et al ., 2005)
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