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New stratigraphic insights in the 'Late Jurassic' of the Southern Central Sea Graben and Terschelling Basin (Dutch offshore) and related exploration potential

Author: Abbink, O.A. · Mijnlieff, H.F. · Munsterman, D.K. · Verreussel, R.M.C.H.
Type:article
Date:2006
Institution: TNO Bouw en Ondergrond
Source:Geologie en Mijnbouw/Netherlands Journal of Geosciences, 3, 85, 221-238
Identifier: 239454
Keywords: Geosciences · Dutch offshore · Exploration · Hydrocarbons · Late Jurassic · Paralic and shallow marine deposits · Spiculite · Stratigraphic trap · Stratigraphy · hydrocarbon exploration · Jurassic-Cretaceous boundary · lithostratigraphy · sedimentary sequence · sequence stratigraphy · Atlantic Ocean · Benelux · Central Graben · Eurasia · Europe · Friesland · Frisian Islands · Netherlands · North Sea · Terschelling · West Frisian Islands · Western Europe · Portlandia

Abstract

Middle Jurassic - Early Cretaceous strata are a target for oil and gas exploration in the Dutch offshore. During the initial stages of the 'Late Jurassic' offshore exploration, various oil fields and a few gas fields were discovered of which only one, the F3-FB field, proved to be economically viable. In the Northern Offshore of the Netherlands, latest Middle Jurassic (Callovian) - earliest Cretaceous (Ryazanian) strata are mostly limited to the Dutch Central Graben and Terschelling basins. Outside the Dutch Central Graben and the Terschelling Basin only thin veneers of these strata occur on the fringing highs such as the Schill Grund High and the Step Graben. The geology of this non-marine to shallow marine succession is complex. The combination of lateral facies changes, repetitive log and facies characteristics in time, sea-level and climate changes, salt tectonics and structural compartmentalisation hamper straightforward seismic interpretation and log correlation. The large number of lithostratigraphic units defined in the Stratigraphic Nomenclature of the Netherlands illustrates the complexity of this time-interval. In recent years, new biostratigraphic techniques and newly acquired stratigraphic data led to the identification of a series of events which can be related to the tectonic, climatic, environmental and stratigraphic development of the 'Late Jurassic' in the Dutch Central Graben and Terschelling basins. Based on these data, three stratigraphic sequences can be recognized. Sequence 1 (Callovian - earliest Kimmeridgian) records the initiation of the Dutch Central Graben, Sequence 2 (early Kimmeridgian - early Portlandian) that of the initiation of the Terschelling Basin. During sequence 3 (late Portlandian - Ryazanian) the Dutch offshore was draped by a regional transgression. These insights have directly impact on the exploration potential, which is discussed in two play concepts. The first is a strat-trap play in the fluvial/paralic sediments of Sequence 1 in the lows between the graben boundary and salt domes. The second example is the Spiculite play, which comprises a bioclastic sandstone reservoir at the top of a dome with a 4-way dip closure. These two examples highlight the necessity of understanding the paleoenvironment and geography for assessing the future exploration potential.