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GEOLOGICA ULTRAIECTINA Mededelingen van de Faculteit Geowetenschappen Universiteit Utrecht No. 270 Stratigraphical and structural setting of the Palaeogene siliciclastic sediments in the Dutch part of the North Sea Basin Iwan de Lugt 1 Cover illustration: a well log from the North Sea Basin This research was carried out at the Stratigraphy-Paleontology Group, Faculty of Geosciences, Utrecht University and was financed by the Netherlands Institute of Applied Geoscience, TNO-NITG. Address: Budapestlaan 4 3584 CD Utrecht The Netherlands Internet site: www.geo.uu.nl ISBN-10: 90-5744-135-7 ISBN-13: 978-90-5744-135-6 2 Stratigraphical and structural setting of the Palaeogene siliciclastic sediments in the Dutch part of the North Sea Basin Stratigrafie en tektoniek van de Palaeogene siliciklastische sedimenten in het Nederlandse gedeelte van het Noordzeebekken (met een samenvatting in het Nederlands) PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van de rector magnificus, prof. dr. W.H. Gispen ingevolge het besluit van het college voor promoties in het openbaar te verdedigen op maandag 15 januari 2007 des middags te 12.45 uur. door Iwan Rommert de Lugt geboren op 31 maart 1975 te Leiderdorp, Nederland 3 Promotores: Prof. Dr. Th.E. Wong Prof. Dr. J.E. Meulenkamp 4 ... a good idea stated within an insufficient theoretical frame loses its explanatory power and is forgotten. Hans Reichenbach (1957) They are grubby little creatures of the sea floor 530 million years old, but we greet them with awe because they are the Old Ones, and they are trying to tell us something. Stephen Jay Gould – Wonderful life Hora est pedel Universiteit Utrecht Voor Madelon, natuurlijk. 5 Table of contents Chapter 1 - Introduction 1.1 General introduction 9 1.2 Geological setting 12 1.3 Aim and outline of this thesis 17 1.4 Revised Palaeogene nomenclature 18 Chapter 2 - The tectonic evolution of the southern Dutch North Sea during the Palaeogene: basin inversion in distinct pulses. Abstract 21 1. Introduction 21 2. Data and methods 22 2.1 Data 22 2.2 Seismic stratigraphy 22 2.3 Construction of depth and thickness maps 24 2.4 Quantitative subsidence analysis 26 3. Geological development of the Broad Fourteens Basin 30 3.1 Mesozoic setting 30 3.2 Palaeocene 31 3.3 Eocene 33 3.4 Pyrenean inversion 35 3.5 Oligocene 36 3.6 Neogene 37 4. Discussion 37 4.1 Subsidence patterns 37 4.2 Basin inversion 38 5. Conclusions 40 Acknowledgements 41 Chapter 3 – Reconstruction of the Late Palaeogene tectonic activity of the southern Dutch North Sea, based on a sequence stratigraphic interpretation of log correlations. Abstract 43 1. Introduction 43 1.1 Lithostratigraphic framework 43 1.2 Geological setting and previous studies 45 2. Data and methods 47 2.1 Data 47 2.2 Wireline log correlations and sedimentary sequence interpretation 51 2.3 Age dating of the sequences 51 3. Sequence stratigraphic development 54 6 3.1 Large scale geometry 54 3.2 Detailed sequence correlation 55 3.2.1 Landen Formation (Thanetian) and Basal Dongen members (Early Ypresian) 55 3.2.2 Ieper Member (Ypresian) 55 3.2.3 Brussels members (Lutetian) 57 3.2.4 Asse Member (Bartonian) 60 3.3 Late Eocene tectonic uplift 61 4. Discussion 61 5. Conclusions 62 Chapter 4 – On the occurrence of a Early Eocene (Late Ypresian) tectonic pulse in the southern Dutch North Sea Basin. Abstract 63 1. Introduction 63 2. Data and methods 63 3. Observations 69 3.1 Seismic geometry observations 69 3.2 Sedimentological observations 69 3.3 Subsidence analysis 71 4. Discussion 73 5. Conclusions 76 Chapter 5 –The Cenozoic evolution of the Broad Fourteens Basin and Roer Valley Graben in the context of the development of the West European Rift System. Abstract 77 1. Introduction 77 2. Geological development 79 2.1 West European Rift System 79 2.2 Broad Fourteens Basin and Roer Valley Graben 82 3. Discussion 83 3.1. Stress propagation 85 3.2. Tectonic activity 85 4. Conclusions 89 Chapter 6 – Synthesis 91 References 93 Appendices 98 Samenvatting 107 Dankwoord 109 Curriculum Vitae 111 7 8 Chapter 1 Chapter 1 Introduction 1.1 General introduction The Cenozoic North Sea Basin (Fig. 1.1a) is an intracratonic, saucer-shaped depression, straddling the Mesozoic North Sea Rift System (P.A. Ziegler, 1990). The basin was formed by isostatic adjust- ment due to post-rift thermal subsidence of the lithosphere, which was accentuated by sediment loading (P.A. Ziegler, 1990; Huuse, 2000). The present-day configuration of the North Sea Basin became apparent during the Mid- to Late Palaeocene. Roughly funnel-shaped, the present North Sea spans from –3°W to 7°E and from 50°N to 60°N. The basin is bordered by the European mainland in the East, Fennoscandia in the northeast and the British Islands in the West. North of the British Isles, and via the British Channel, the North Sea is connected to the North Atlantic Ocean (Fig. 1.1a). Fig. 1.1 a) The North Sea and the outline of the landmasses surrounding it. The outline of the North Sea Rift System is indicated. b) Outline of the study area (shaded) within the Dutch North Sea sector. The outline of the Mesozoic Broad Fourteens Basin (BFB) is indicated with a dotted line. 9 Introduction From the Late Palaeocene to the end of the Oligocene, the southern part of the North Sea was a ramp-type margin (Jacobs and De Batist, 1996) on which siliciclastic sediments were deposited. This depositional setting is characterized by a less than one-degree gradient of the basin floor and the lack of a clear shelf break (Fig. 1.2). Seismic clinoforms are difficult to resolve and coastal on- laps are often not present. On a ramp-type margin, sedimentary units are deposited semi-parallel in continuous horizontal layers. Units can be recognised over a very large area (e.g. Vandenberghe et al., 2001). The North Sea Basin experienced open marine conditions during most of the Palaeogene, interrupted by periods of uplift during which large parts of the area were sub-aerially exposed. The sediments that were deposited in the southern Dutch North Sea are mainly alternations of clays and sandy silts. The Cenozoic lithostratigraphic subdivision of the Netherlands (Van Adrichem Boogaert and Kouwe, 1997) is based on these alternations, and the occurrence of regional uncon- formities.Towards the basin centre, the contrast between the lithological units is minimized as the siliciclastic grain size decreases with increased distance from continental source areas. sea level coarse sand fine sand silt Fig. 1.2 Schematic cross-section of a ramp-type continental shelf. Note the lack of a clear shelf break and the semi-parallel deposition of the sedimentary units. The North Sea area has been extensively studied since the discovery of significant hydrocarbon re- serves during the 1960’s. The basin has been densely covered by seismic surveys, exploration and production wells, and a wealth of cores and samples was collected. This information was supple- mented with onshore outcrop data. Lithostratigraphic frameworks (NAM and RGD, 1980; Isaksen and Tonstad, 1989; Knox and Cordey, 1992; Marechal, 1993; Van Adrichem Boogaert and Kouwe, 1993-1997), geological maps and regional syntheses (e.g. Heybroek, 1974; 1975; P.A. Ziegler, 1975; 1978; 1990; 1994; W.H. Ziegler, 1975) have been published. Several studies focussed on the tectono-stratigraphic evolution of the North Sea Rift System (e.g. Van Wijhe, 1987a; Badley et al., 1989; Dronkers and Mrozek, 1991; Williams, 1993; Huyghe and Mugnier, 1994; 1995). Nu- merical and analogue modelling yielded additional information about the structural and thermal evolution of the North Sea Rift System (Kooi and Cloetingh, 1989; Kooi et al., 1989; Brun and Nalpas, 1996; Van Wees and Cloetingh, 1996; Van Balen et al., 2000; Nielsen and Hansen, 2000) and provided information about the mechanisms involved in rifting and inversion (e.g. Koopman et al., 1987; McClay, 1989; Huyghe and Mugnier, 1994; Eisenstadt and Withjack, 1995; Nalpas et al., 1995). During recent years, sequence stratigraphic studies of seismic and well data have increased the temporal resolution of interpretations (e.g. De Batist and Henriet 1995; Laursen et 10 Chapter 1 al., 1995; Jacobs and De Batist, 1996; Neal, 1996; Hardenbol et al., 1998; Michelsen et al., 1998; Vandenberghe et al., 1998). Many investigations in the North Sea Basin were based on industrial data sets. These data focus on commercially interesting stratigraphic intervals and areas. As a result, information is limited for several stratigraphic intervals. For instance, research devoted to the evolution of the Dutch part of the North Sea often scarcely mentions the siliciclastic succession of the Palaeogene. This is regrettable; two of the main inversion phases affecting the North Sea Rift System occurred during the Palaeogene, but no detailed temporal and spatial tectono-stratigraphic reconstructions of the Palaeogene evolution of the Dutch part of the North Sea Basin have been published. Only general occurrence maps and lithostratigraphic descriptions are available (e.g. Keizer and Letsch, 1963; Van Staalduinen et al., 1979; Letsch and Sissingh, 1983; Zagwijn, 1989; Van Adrichem Boogaert and Kouwe, 1997; Vinken, 1998). SW NE 0 2 4 Depth (km) 6 Cenozoic 0 50 km Mesozoic Palaeozoic and Basement Fig. 1.3 Regional transect across the Dutch North Sea (redrawn after Dronkers and Mrozek, 1991), illustrating the generalized view of the Cenozoic interval obtained at such a scale. The geometry of the Late Palaeocene-Oligocene sediments in the Dutch part of the North Sea Basin seems to be straightforward on the large scale at which regional geological transects usually are shown (Fig.