References

1
Mesozoic North Sea alkaline volcanism and the
upside-down dripping tap hypothesis Mark C.
Beaumont, J. G. Fitton, J. R. Underhill, J. E.
Dixon School of GeoSciences, University of
Edinburgh, West Mains Road, Edinburgh EH9 3JW
The Zuidwal volcano Location and
Significance Zuidwal is in the Dutch Waddenzee,
buried beneath Cretaceous and younger sediments.
It was initially identified and imaged as a high
on 2D seismic lines, coincident with a magnetic
anomaly. The eroded strongly alkaline volcano is
draped by a gas-producing reservoir sandstone and
disrupts Mesozoic sediments 2km below the sea-bed
in the centre of the NW-SE trending Vlieland
basin. Age dates are conflicting some infer it
to be contemporaneous with the 155Ma Forties
Province but an alternative published Late
Cretaceous age would support migration of
activity with time, southward from the North Sea
triple-junction. Preliminary work suggests that
the basin may be centred on a regional
stratigraphic high, supporting a smaller-scale
repeat of the North Sea Dome.
Zuidwal in its Regional Setting Mesozoic and
earlier magmatism in the Netherlands and the
Dutch North Sea showing the location of the
Zuidwal volcano in the Vlieland basin (after
Sissingh, 2004).
Well-bedded Grey sandstone
(Right) 5m section of core from well Zuidwal
1 Spanning the reservoir sandstone base and the
top of the volcanic agglomerate
Detailed study of Zuidwal is supported by 3D and
2D seismic data, regional stratigraphy, stored
core samples and well logs provided by
TNO (Geological Survey of the Netherlands)
Seismic interpretation was carried out using
Kingdom software, kindly provided by Seismic
Micro-Technology Inc, on workstations housed in
the University of Edinburgh's seismic
interpretation laboratory.
(Above) Seismic Line through Well Zuidwal-1 at
the Volcano Summit. (Below) Oblique View from
the 50 km2 3D Seismic Coverage. The image below
is generated from a grid of interpreted seismic
lines and shows the draping sandstone reservoir
(semi-transparent) overlying the volcano (not
imaged) and disrupted late Jurassic sediments.
Stratigraphic correlation to well logs and core
samples should permit interpretation of the
eruptive and erosional evolution of the volcano
and better constrain its age and uplift history.
(Seismic line is 7km by 1,500m depth 3D image
is 50km2 in area by 0.5s two-way-travel time
500m depth)
The Zuidwal Magnetic Anomaly (TNO)
Alkali-Silica Diagram showing Zuidwal and other
Undersaturated North Sea Volcanics Zuidwal
samples are from clasts in altered agglomerate.
Egersund is a Jurassic nephelinitic occurrence in
the Norwegian Sector (17/9-1). (Egersund other
Dutch centres from Latin (1990) PhD Thesis,
University of Edinburgh. Field names from Le Bas,
M.J., Le Maitre, R.W., et al., 1986. A chemical
classification of volcanic rocks based on the
total alkali - silica diagram. Journal of
Petrology 27, 745750)
(Below) The North Sea Mid-Jurassic Dome a
Potential Stratigraphic Response Template (after
Underhill Partington 1993) Diagrams at 10Ma
intervals showing the stratigraphic response to
thermal doming centred on the North Sea Triple
Junction domal uplift, volcanism at the peak or
just after, subsidence and faulting. The
cross-strike width is 1,000km and the uplift
c.1km (vertically exaggerated). Key question
Does this asthenospheric phenomenon scale down to
one tenth size in the 100km long Vlieland Basin?
Typical draping horizon 1m of turbated
oxidised Red sandstone
(Right) Does Eurasian plate motion since the
Mid-Jurassic point to episodes of transient
asthenospheric upwelling by tracking alkaline
intra-plate volcanism? Bajocian Bathonian
paleogeography,after Ziegler, P. A. (1990).
Geological atlas of western and central Europe.
Maatschappij B.V. , Shell Internationale
Petroleum.
Contact of drape With summit
Volcanic Agglomerate drilled for another 1,000m
Previous work Dixon, Fitton et al. (1981)
documented the alkaline, rift-related magmatism
of Jurassic age in the North Sea and discussed
possible stretching and melt generation
parameters. Latin, Dixon et al. (1990) showed
that although the magmatism occurred where
ß-factors were largest, existing theoretical
models of melt generation related to stretching
(McKenzie and Bickle 1988) could not
satisfactorily account for melt production at the
low ß-factors inferred (c.1.5 to 2 at most) nor
was there an obvious explanation for the
occurrence of magmatism before any discrete
rift-bounding faults had developed. Using
sequence stratigraphic evidence, Underhill and
Partington (1993) showed that the principal
episode of magmatic activity occurred on the
crest of a transient broad dome at the point in
time (Bathonian/Bajocian) when it reached its
highest elevation relative to sea-level, shortly
before it became the location of the Upper
Jurassic rift triple junction and then subsided.
The estimated uplift is of the order of 500
metres, though other workers suggest it may be
more (Perrot, van der Poel et al. 1987). It
occurred on a dome approximately 1,000 km in
diameter defined by the limit of the erosion
surface, marked by correlative conformities.
Further south, Wilson and Patterson (2001) have
attributed a sequence of Tertiary-Quaternary
volcanism, associated with the development of
domal uplift and a rift system, to diapiric
upwelling of small-scale mantle instabilities.
References Dixon, J. E., J. G. Fitton, et al.
(1981). The tectonic significance of
post-Carboniferous igneous activity in the
North-Sea Basin. Petroleum geology of the
continental shelf of North-West Europe
Proceedings of the second conference. L. V.
Illing and G. D. Hobson, Publisher Heyden and
Son, London, United Kingdom 121-137. Latin, D.
M., J. E. Dixon, et al., Eds. (1990). Mesozoic
magmatic activity in the North Sea basin
implications for stretching history, Geological
Society of London, London, United
Kingdom. McKenzie, D. and M. J. Bickle (1988).
"The Volume and Composition of Melt Generated by
Extension of the Lithosphere." Journal of
Petrology 29(3) 625-679. Perrot, J., A. van der
Poel, et al., Eds. (1987). Zuidwal a Neocomian
gas field, Graham Trotman, London, United
Kingdom. Sissingh, W. (2004). "Palaeozoic and
Mesozoic igneous activity in the Netherlands a
tectonomagmatic review." Geologie en Mijnbouw.
Netherlands Journal of Geosciences 83(2)
113-134. Underhill, J. R. and M. A. Partington
(1993). "Jurassic thermal doming and deflation in
the North Sea implications of the sequence
stratigraphic evidence." Geological Society,
London, Petroleum Geology Conference series 4
337-345. Wilson, M. and R. Patterson (2001).
Intraplate magmatism related to short-wavelength
convective instabilities in the upper mantle
Evidence from the tertiary-quaternary volcanic
province of western and central Europe. Mantle
Plumes Their Identification through Time. R. E.
Ernst and K. L. Buchan. Boulder, Geological Soc
Amer Inc 37-58.