Aretz et al_2011.pdf - ORBi - Université de Liège

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Kölner Forum Geol. Paläont., 19 (2011)
M. ARETZ, S. DELCULÉE, J. DENAYER & E. POTY (Eds.)
Abstracts, 11th Symposium on Fossil Cnidaria and Sponges, Liège, August 19-29, 2011
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Devono-Carbonifeous carbonate platform systems of the Netherlands
Fokko F.N. VAN HULTEN
Energie Beheer Nederland B.V., P.O. Box 19063, 3501 DB - Utrecht, The Netherlands;
fokko.hulten-van@ebn.nl
Paleozoic carbonate build-ups, globally important for hydrocarbon exploitation, are generally not
associated with the Netherlands or with the larger Southern North Sea area. In the last ten years
information of new wells and seismic have changed this perception. Recent seismic interpretations have
indicated massive Mississippian carbonate bioherms far below conventional petroleum exploration targets
in the Netherlands (ABBINK et al. 2009; VAN HULTEN & POTY 2008; KOMBRINK 2008). Recent UK exploration
on the Mid North Sea High also provides new insights. The amount of data on these reefs is very limited.
The following summary is intended to provide an overview.
The recently released Dutch well information dates the platforms as Mississippian, with a Devonian
core. Some of the reefs are very sizeable. In particular, the platforms in the Friesland and Groningen area
are comparable with the well-known Caspian carbonate buildups (WEBER et al. 2003). These Mississippian
platform carbonates are also underlain by Devonian reefs. For years the same paleogeographic map could
be used for North Western Europe because of lack of new data. A revised paleogeography of the West
European Devonian and Mississippian is now required to fit the new data.
Because of the great present day depth, it is not clear if the reefs are a new frontier or are situated below
the economic basement of hydrocarbon exploration. New insights may provide new opportunities for the
petroleum industry but the presence of big reefal reservoirs can also be of importance for thermal
exploitation in the densely populated Netherlands.
Paleogeographic reconstructions cannot be made without a good understanding of the structural
framework of North West Europe. For the Devono-Carboniferous sedimentation systems, the Caledonian
structuration is important. During the Devonian after the Caledonian events during the Silurian, deposition
in the general North Sea area commenced. Most well information is available from two major highs, the
Mid North Sea High in the North and the London-Brabant Massif in the South. They delineate a large intracratonic
basin in the Netherlands. Perhaps more important than the highs, is the nature of this basin area in
between. Based on crustal properties, a deep ocean area can be postulated over part of this basin area. This
can be confirmed by subcrop maps of the Upper Carboniferous at the base Permian Unconformity. With
such a map, general outlines of highs, coinciding with Mississippian carbonate platforms, can be deduced.
The same highs, or at least parts thereof, are assumed existent during the Devonian. The resulting shape of
the paleo-ocean combined with paleowind considerations, with trade winds from the south east in the
Devonian and north east during the Mississippian, make it likely that some highs were created by fringed
carbonate platforms.
The direction of the structuration in the Netherlands, as can be seen in the general fault patterns,
parallels the Sorgenfrei and Teisseyre-Tornquist Zones in southern Scandinavia. Batholiths in the
Netherlands are known of the Mid North Sea High and most likely of the Groningen area.
The Devonian is generally perceived to have little hydrocarbon potential and is hardly drilled into.
There are no Devonian outcrops in the Netherlands. The nearest Devonian rock in outcrop is found in
Southern Belgium, Germany, and the UK. Dutch Devonian well control is also sparse because of the depth
of Devonian age sediments, generally exceeding 4,000 m. This means that the sedimentological setting is
generally deduced from information of surrounding countries. The few wells that reach the Devonian are
located close to the major highs and are of limited value for a representative paleogeography. The
characteristic UK Old Red Continent fluvial facies may be present in parts of the Netherlands. However,
part of the Netherlands is almost certainly deep oceanic. It is plausible that during the Givetian and
Frasnian, carbonate platform growth starts at the fringes of this ocean area, comparable to the sequence in
the southern part of Belgium. In the Middle Devonian, carbonate development is described, not just from
the classical platforms in Southern Belgium, but also in the UK and Germany. Of importance are cored
limestones in the UK well 38/3-1 close to the Mid North Sea High. The fossiliferous lime mudstones,