This study presents a sequence stratigraphic framework for the Late Cretaceous interval in the offshore Mid-Norway area based on an extensive biostratigraphic review of wells. Key microfossil events are used to correlate sequence boundaries, transgressive surfaces, and surfaces of maximum marine transgression for integration with wireline logs and seismic data. Several periods of deep-water sandstone development within sequences are identified as potential reservoirs. Biostratigraphy played an important role in recognizing and correlating Late Cretaceous sequences in the region due to the predominantly claystone lithology masking stratigraphic breaks in wireline logs.

1. STRATIGRAPHIC CALIBRATION OF LATE CRETACEOUS SEQUENCES,
OFFSHORE MID NORWAY AREA.
M. A. CHARNOCK 1
and S. CRITTENDEN 2
(1) Norsk Hydro Research Centre, N-5020 Bergen, Norway
(2) SC Independent Geological Consultant, Chagford Devon, United Kingdom
E-mail: Mike.Charnock@hydro.com
ABSTRACT
The deeper water areas of the Vøring Basin, offshore Mid- Norway area, represent one of the
last major frontier areas for hydrocarbon exploration in the Norwegian Sector. To date, single
wells have been drilled on some of the larger structures e.g. Helland-Hansen Arch, Gjallar
Ridge and Vema Dome targetting thick sequences of Upper Cretaceous, deep marine clastics.
With the exceptions of the giant Ormen Lange gas field on the Møre margin and the Nyk High
(gas discovery), hydrocarbon sucess rate has been low and disappointing but this is considered
to be mainly related to understanding the hydrocarbon source and migration historyrather than
the lack of significant reservoirs. The challenge has been to integrate the biostratigraphy, well-
logs and seismic information to produce a regionally applicable, sequence stratigraphic
framework to link these structures and improve our understanding of the geological evolution
of the area.
This study presents the sequence stratigraphy and biostratigraphic characterisation of the
Upper Cretaceous interval and the interpretation is based on an extensive biostratigraphic
review of wells from Quadrants 6305 to 6707. The surfaces have been defined, in practical
terms, by a series of 'key' microfossil events based on a combination of palynology (marine
microplankton) and micropalaeontology (planktonic and benthonic foraminifera, radiolaria
and diatoms) to correlate surfaces designated as representing either sequence boundaries (SB),
transgressive surfaces (TS) or surfaces of maximum marine transgression (MTS) for integra-
tion with wireline logs and seismic stratigraphy. A series of type sections are designated using
or relating these, wherever possible to the wells designated by Dalland et al. (1988) in their
development of a lithostratigraphic scheme for the better understood Halten Terrace area of
the eastern basin margin and the biostratigraphic zonation is calibrated to the standard
chronostratigraphic framework established for European Basins by Hardenbol et al. (1998). It
is possible to relate most of the microfossils events to stratigraphies established elsewhere,
particularly the Shetland facies developed in the Viking Graben of the North Sea basin,
suggesting a provincial similarity that is useful for large scale correlation.
The main periods of deep - water sandstone development are within sequences K50 (early
- late Turonian): 'Upper Lange Sandstones', K60 (late Turonian - Santonian): Lysing Forma-
tion ('latest Turonian'- Coniacian) and 'Kvitnos Sandstones' (Santonian); K70 ('latest' Santo-
nian - middle Campanian): 'Nise Sandstones' and K90 (late Campanian - late Maastrichtian):
'Springar Sandstones'. Long distance stratigraphic correlations, depositional environments
and sediment sourcing are presented and discussed.
Intra - Late Cretaceous stratigraphic breaks are relatively rare, and difficult to identify from
the wireline log responses of the predominantly claystone intervals in this deeper water area
with the exception of the Cretaceous/Tertiary rifting event which shows variable but
sometimes significant truncation of the underlying Shetland Group.
Biostratigraphy has therefore had an important role in the recognition, interpretation and
correct regional correlation of Late Cretaceous sequences in the offshore Mid - Norway area.