3d structure and formation of hydrothermal vent … · 2017-04-11 · 26 the mid-norwegian margin...

3D STRUCTURE AND FORMATION OF HYDROTHERMAL VENT

COMPLEXES AT THE PALEOCENE-EOCENE TRANSITION, THE

MØRE BASIN, MID-NORWEGIAN MARGIN

Journal: Interpretation

Manuscript ID INT-2016-0159.R1

Manuscript Type: 2015-12 Subsurface expression of igneous systems and their impacts on petroleum systems

Date Submitted by the Author: 25-Jan-2017

Complete List of Authors: Kjoberg, Sigurd; (CEED) The Centre of Earth Evolution and Dynamics, University of Oslo, Department of Geosciences Schmiedel, Tobias; (PGP) GEO Physics of Geological Processes, University of Oslo, Department of Geosciences Planke, Sverre; Volcanic Basin Petroleum Research AS; (CEED) The Centre of Earth Evolution and Dynamics, University of Oslo, Department of Geosciences Svensen, Henrik; (CEED) The Centre of Earth Evolution and Dynamics, University of Oslo, Department of Geosciences Millett, John; Volcanic Basin Petroleum Research AS; University of Aberdeen, Department of Geology and Petroleum Geology Jerram, Dougal; DougalEarth; (CEED) The Centre of Earth Evolution and Dynamics, University of Oslo, Department of Geosciences Galland, Olivier; (PGP) GEO Physics of Geological Processes, University of Oslo, Department of Geosciences Lecomte, Isabelle; NORSAR; Universitetet i Bergen, Department of Earth Science Schofield, Nick; University of Aberdeen, Department of Geology and Petroleum Geology Haug, Øystein; (PGP) GEO Physics of Geological Processes, University of Oslo, Department of Geosciences Helsem, Andreas; Statoil ASA

Keywords: 3D, interpretation, volcanics, Europe

Subject Areas: Case studies

https://mc.manuscriptcentral.com/interpretation

Interpretation

This paper presented here as accepted for publication in Interpretation prior to copyediting and composition. © 2017 Society of Exploration Geophysicists and American Association of Petroleum Geologists.

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1

3D STRUCTURE AND FORMATION OF HYDROTHERMAL VENT COMPLEXES AT 1

THE PALEOCENE-EOCENE TRANSITION, THE MØRE BASIN, MID-NORWEGIAN 2

MARGIN 3

Sigurd Kjoberg(1), Tobias Schmiedel(4), Sverre Planke(1, 2), Henrik H. Svensen (1), 4

John M. Millett(2), Dougal A. Jerram(1,3), Olivier Galland(4), Isabelle Lecomte(5,6), Nick 5

Schofield(7), Øystein T. Haug (4) and Andreas Helsem(9) 6

7

(1) The Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Norway 8

(2) Volcanic Basin Petroleum Research (VBPR), Oslo, Norway 9

(3) DougalEarth, Solihull, UK 10

(4) Physics of Geological Processes (PGP), University of Oslo, Norway 11

(5) NORSAR, Kjeller, Norway 12

(6) university of Bergen, Norway 13

(7) University of Aberdeen, UK 14

(8) Statoil, Norway 15

16

Email: [email protected] - [email protected] - [email protected] - 17

[email protected] - [email protected] - [email protected] - 18

[email protected] - [email protected] - [email protected] - 19

[email protected] - [email protected] 20

Original paper date of submission: 28.09.2016 21 22

Revised paper date of submission: 25.01.2017 23

24

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ABSTRACT 25

The mid-Norwegian Margin is regarded as a type-example of a volcanic rifted margin, 26

formed prior to, and during, Paleogene break-up of the NE Atlantic. The area is characterized by 27

the presence of voluminous basaltic complexes such as extrusive lava and lava delta sequences, 28

intrusive sills and dikes, and hydrothermal vent complexes. We present a detailed 3D seismic 29

analysis of fluid and gas induced hydrothermal vent complexes in a 310 km2 area in the Møre 30

Basin, offshore Norway. We find that formation of hydrothermal vent complexes is 31

accommodated by deformation of the host rock when sills are emplaced. Fluids are generated by 32

metamorphic reactions and pore fluid expansion around sills and are focused around sill tips due 33

to buoyancy. Hydrothermal vent complexes are associated with doming of the overlying strata, 34

leading to the formation of draping mounds above the vent contemporary surface. Both the 35

morphological characteristics of the upper part and the underlying feeder structure (conduit zone) 36

are imaged and studied in 3D seismic data. Well data show that the complexes formed during the 37

early Eocene, linking their formation to the time of the Paleocene-Eocene thermal maximum 38

(PETM) at c. 56 Ma. The well data further suggest that the hydrothermal vent complexes were 39

active for a considerable time period, corresponding to a c. 100 m thick transition zone unit with 40

both primary A. Augustum and re-deposited very mature Cretaceous and Jurassic palynomorphs. 41

The newly derived understanding of age, structure, and formation of hydrothermal vent 42

complexes in the Møre Basin contributes to the general understanding of the igneous plumbing 43

system in volcanic basins and their implications for the paleoclimate and petroleum systems. 44

45

46

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INTRODUCTION 47

At the mid-Norwegian Margin, the Paleocene-Eocene interval represents the time period 48

of the early NE Atlantic rifting and continental break-up (Gibb and Kanaris-Sotiriou, 1988; Bell 49

and Butcher, 2002). Evidence for volcanic activity in sedimentary basins is found along the 50

entire European NE Atlantic margin (e.g. Doré et al., 1999). Volcanic processes and deposits 51

may have significant impact on the structural and geodynamic development of the rifted margin 52

and associated sedimentary basins, i.e the Karoo Basin, the Rockall Basin, the Faroe-Shetland 53

Basin, and the Neuquén Basin (Svensen et al., 2012; Magee et al., 2014; Smallwood and Maresh, 54

2002; Schofield et al., 2017). The Møre Basin study area is located beneath the outer shelf and 55

slope region offshore mid Norway, and shows classical examples of how volcanic activity and 56

igneous intrusions within sedimentary strata may impact the basin structure (Skogseid et al., 57

1992; Brekke, 2000). Short and long term impacts includes deformation, differential compaction, 58

uplift, heating of host rock and pore fluids, metamorphism, and the formation of hydrothermal 59

vent complexes. 60

The distribution and nature of volcanic intrusions and associated hydrothermal vent 61

complexes represent key elements in basin evolution, and it is therefore important to better 62

constrain the age of the main volcanic episode and the coherent venting processes. In addition, 63

the venting process has been related to greenhouse gas expulsion to the atmosphere, thereby 64

providing a link to the transient climatic shift during the Paleocene-Eocene Thermal Maximum 65

(e.g., Svensen et al., 2004). The climatic records during this period are well documented from a 66

number of sections worldwide (Zachos et al., 2001; Zachos et al., 2008), and recent results show 67

that the only drilled HVC in the Vøring Basin (borehole 6607/12-1) formed during the PETM 68

plateau, thereby demonstrating a relationship between the long duration of the PETM and the gas 69

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venting (Frieling et al., 2016). Similar Kilometer-scale hydrothermal vent structures have been 70

described elsewhere in seismic data (e.g., Planke et al., 2005; Hansen et al., 2005; Grove 2013) 71

and in outcrops (e.g., Svensen et al., 2006) in several basins. These vent structures all share 72

structural similarities, including complete brecciation, fluidization and inward dipping reflections. 73

However, the upper parts of these vents imaged on seismic data often exhibit distinct structural 74

features (eye, crater and dome shapes). The mechanisms leading to different structures are 75

currently unknown. In addition, the structural features observed on seismic data differ from those 76

described in field and outcrop studies. It is not clear whether the differences between seismic 77

features and geological observations are real structural differences or the result of artifacts in the 78

seismic images. 79

The aim of this study is to increase our understanding of the formation and age of 80

hydrothermal venting in volcanic basins. This study is based on structural imaging and detailed 81

mapping of morphological features in a 3D seismic survey acquired in the Møre Basin, together 82

with well-log data and analyses. We further apply a new workflow to better constrain the 83

complex structures of hydrothermal vent complexes on seismic images, using a combination of 84

qualitative laboratory models and advanced seismic modeling. These results may help to identify 85

potential artifacts related to fluid and sediment remobilization in seismic images. 86

87

GEOLOGICAL SETTING MØRE BASIN 88

The mid-Norwegian margin developed through a series of post-Caledonian rift phases 89

that culminated with the onset of seafloor spreading at ca. 56 Ma in the Norwegian-Greenland 90

Sea (Mosar et al., 2002). The Møre and Vøring margin segments, each between 400-500 km long, 91

are separated by the Jan Mayen Fracture Zone (Figure 1; Faleide et al., 2008). The deep Møre 92

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and Vøring basins formed during Late Jurassic–Early Cretaceous rifting episodes (Figure 1). The 93

basins are characterized by thick Cretaceous sedimentary accumulations, and can in places reach 94

up to 13 km, of which 8-9 km comprises the Cretaceous succession (Gernigon et al., 2003). 95

Continental breakup was accompanied by large-scale igneous activity, forming kilometer-thick 96

basaltic complexes on both sides of the continent-ocean boundary (Brekke, 2000). At the same 97

time, extensive igneous sheet-intrusions were emplaced in the Møre Basin, and hundreds of 98

hydrothermal vent complexes were formed by pressure increase and devolatilization in the 99

contact aureoles around the sills (Planke et al., 2005; 2015; Svensen et al., 2004, 2010; Frieling 100

et al., 2015). The Møre Basin subsequently subsided, leading to deposits of marine mud and ooze, 101

and finally thick sequences of glacially-derived sediments and slide material (Faleide et al., 102

2008). 103

104

Stratigraphy 105

The seismic well-tie in the Paleogene and Neogene (Cenozoic) successions are confident 106

(Figure 2). However, the sequences below 4.4 s TWT of late Cretaceous age are difficult to tie 107

because of imaging problems and lack of well data. The stratigraphy includes five formations 108

and is described from the oldest to youngest unit. In the study area, the lowermost interpreted 109

formation is the Springar Formation. It consists of predominantly greyish-green claystones 110

interbedded with stringers of carbonates and sandstone (Dalland et al., 1988). Limestone beds 111

exceeding over ten meters in thickness interbedded with shale are encountered at an interval 112

from 4076 – 4140 meters (MD). The Springar Formation is overlain by the Paleogene Tang 113

Formation which is characterized by dark grey to brown claystone with minor sandstone and 114

limestone (Dalland et al., 1988). The lithology of the lowermost part and transitional zone into 115

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the Springar Formation is interpreted as the Danian sandstone reservoir of the Tulipan discovery. 116

These sandstone layers are typically 1-7 meters thick and interbedded with siltstone and 117

claystone in the depth range between 3901-4000 m (MD). 118

The Tare Formation is defined by dark grey, green or brown claystones with some thin 119

sandstone stringers and a variable content of tuffaceous material. The tuff content is highest 120

towards the basal section of the formation, with increasing volume in the lowermost Eocene 121

sediments. The Tare Formation is overlain by the late Eocene to middle Miocene Brygge 122

Formation, which is part of the Hordaland Group (Deagan and Scull, 1977; Dalland et al., 1988). 123

The Brygge Formation consists mainly of claystone, interbeds of sandstone and bio-siliceous 124

ooze (Hjelstuen et al., 1997). The two uppermost formations in the study area are the Lower 125

Miocene to recent Nordland Group which is sub divided into the Kai Formation and the upper 126

Pliocene Naust Formation (Dalland et al., 1988). The Kai Formation consists of alternating 127

claystone, siltstone and sandstone with interbedded limestone, and the Naust Formation mainly 128

comprises claystone and siltstone. 129

130

Formation and source of hydrothermal vent complexes (HTVC) 131

The formation of HTVC’s requires that fluid pressure within contact aureoles overcomes 132

the rock strength and the lithostatic pressure. Instantaneous overpressure-release occurs if the 133

pressure build-up is faster than the pressure release and seepage in the host-rock. Jamtveit et al. 134

(2004) and Nermoen et al. (2010) proposed a model where the venting mechanism is based on 135

boiling and expansion of pore water as the cause for pressure build-up. If the fluids generated are 136

greater than allowable through Darcy flow, a critical state is reached and venting can occur 137

(Jamtveit et al., 2004; Nermoen et al., 2010). Lithological information from the Møre Basin 138

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show that the host rock consists of primarily mudstone, claystone and sandstone at the HTVC 139

interval. Mudstone heating can result in clay mineral dehydration and organic matter breakdown 140

to CO2 and CH4, contributing to overpressure generation (cf. Svensen et al., 2004, 2007; Aarnes 141

et al., 2010). The fluid generation is critically dependent on the heat transfer from the sill and is a 142

function of host rock properties, sill thickness and temperature, and the geothermal gradient 143

(Aarnes et al., 2010; Grapes, 2010). 144

Fluids generated in contact aureoles have low densities and a greater buoyancy compared 145

to the pore fluids in the sedimentary rocks. The presence of lighter components, such as methane, 146

may dissolve in the fluids or migrate as a gas phase during the formation of HTVCs (Svensen 147

and Jamtveit, 2010; Wang and Manga, 2015). The volume of these carbon-bearing gases depends 148

on the total amount of organic carbon in the host rock (Whitaker, 1986). 149

150

DATA AND METHODS 151

Seismic and well data 152

The seismic data used in this paper consists of a subsection (310 km2) of the ST0105 153

(Tulipan) 3D survey (2100 km), collected and processed in connection with the PL251 license in 154

2005. The survey is situated in the western part of the Møre Basin, offshore mid-Norway (Figure 155

1). The data are 3D time migrated, and the overall quality is regarded as very good. The main 156

frequency spectrum of the data is about 20-40 Hz (3.7-4.5s TWT). This implies a dominant 157

wavelength of 30-50 m, corresponding to a vertical seismic resolution of about ~10 m (δh=λ/4: 158

one quarter of the dominant wavelet). The data are regarded as zero-phase, and displayed so that 159

white/blue (depending on color scheme) denotes increase in acoustic impedance. 160

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Borehole check-shot and conventional wireline log data from the Tulipan well (6302/6-1; 161

Figure 2) show that velocities vary from about 2000 m/s at the seafloor to more than 3000 m/s at 162

the base of the interpretation interval. Finally, 6302/6-1 borehole stratigraphy, petrography, and 163

biostratigraphy reports were made available from Statoil. Results from these reports are 164

summarized in Figure 2. 165

166

Seismic interpretation 167

In total, 14 seismic horizons were interpreted regionally in the study area based on the 168

seismic well-tie to 6302/6-1 (Figure 2). The interpretation focused on the Paleocene and Eocene 169

sequences, in particular the Intra Brygge 2, Top Tare, Intra Tare, HV1 and HV3 horizons. These 170

horizons are well-defined, continuous events in the study area (Figure 2) and were used to define 171

the upper part of the hydrothermal vent complexes. In addition, sills and lava flows where 172

interpreted using the approach of Planke et al. (2015). 173

The upper part of each vent complex is defined as a domed region with down lapping 174

internal reflections on HV1. In 3D, the dome structures display an ellipsoidal geometry. Thus the 175

lengths of both minor and major axes could be determined. The conduit height is defined as the 176

depth between the termination of the interpreted underlying feeder sill and the HV1 surface. The 177

depth to the sill is not always clearly defined because a vent complex may have originated from 178

deeper, poorly imaged sills. 179

180

Sandbox and seismic modeling 181

One of the main challenges regarding interpretation of seismic images and complex 182

geological structures is to avoid potential pitfalls and miss interpretations due to e.g., seismic 183

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artifacts, illumination and resolution issues. To overcome this challenge, new seismic modeling 184

appears as a valuable tool to separate the real structure from a seismic artifact (Lecomte et al., 185

2015). 186

The principle of seismic modelling is to use geometric and attribute input parameters to 187

produce a synthetic seismic image. The comparison between the input geometry and the resulting 188

image is a key aspect of deciphering between the real structures and the artifacts on seismic data. 189

As geometric input parameter for hydrothermal vent complexes, a laboratory experiment of fluid 190

overpressure structures in granular and unconsolidated media has been undertaken. These 191

experiments proved very useful to unravel the dynamics of venting, with applications to 192

pockmarks, mud volcanoes, hydrothermal vent complexes and kimberlite pipes (Nermoen et al., 193

2010; Haug et al., 2013; Galland et al., 2014). Importantly, the structures simulated in the 194

laboratory are comparable in geometry to the structures observed in the field, although the 195

laboratory models have to be upscaled. 196

The sandbox experiment setup consisted of a vertically orientated, air-filled Hele‐Shaw 197

cell measuring 60x60 cm (Haug et al., 2013; Nermoen et al., 2010). The cell is sealed at the 198

bottom and the vertical sides, while the top part of the cell remains open. Each experiment was 199

prepared by slowly pouring alternating olivine sand and quartz sand through a funnel, from the 200

top of the cell to a desired filling height. Over-pressurized air from a constant supply was 201

injected into the sand through an inlet placed within the bed. The flow velocities in the 202

experiment were regarded as constant, since the air supply was induced at a uniform pressure 203

throughout the experiments. Digital images during the experiment were captured at 7 frames per 204

second using a high resolution camera. 205

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The most representative picture obtained during the sandbox experiment served as a 206

target model for the synthetic seismic modeling. The target model was implemented into the 207

modelling software (SeisRox) as a 2D layer model. The sand makes up the basic geometry of the 208

model, and is defined by the different layers related to the sedimentary sequences and the 209

coherent change in elastic values (Vp- and Vs- velocities). The following assumptions were 210

further implemented: 211

• The horizontal and vertical sizes of the background picture are defined as 1800 m and 212

850 m, respectively, based on dimension analysis done during seismic interpretation. 213

214

• Velocity data available from sonic logs at the HTVC ranges from Vp ~ 2000-2500 m/s 215

and Vs ~ 1100-1800 m/s, increasing with depth. 216

217

• Two sets of velocities properties (Vp and Vs) were implemented to create the 218

impedance/reflectivity model. These values range between: Vp ~ 2000-2300 m/s and Vs 219

~ 1200-1300 m/s. 220

221

• Density in the model varies from 2.0-2.2 g/cm3. 222

223

• The seismic properties within each zone are homogeneous and identical throughout the 224

sequence, with no internal reflections. 225

226

• Seismic modeling 20 Hz, corresponding to the HTVC interval. 227

228

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229 RESULTS 230

Distribution of sills and vent complexes 231

All HTVC’s mapped in this study are related to underlying sills. The majority of the vent 232

complexes are associated with the saucer shaped Tulipan sill located in the central part of the 233

study area (Schmiedel et al., in press). Due to the distinctive sill geometry, it is regarded as an 234

important element in explaining the behavior, position and structural development of the 235

HTVC’s. The extensive sill complex in the Tulipan 3D cube is interpreted based upon the same 236

method as the horizon interpretation (e.g. Planke et al., 2015). The sills are identified as high 237

amplitude reflections within the sedimentary strata, and display local transgressive segments. 238

Three sills have been mapped and picked as separate horizons. The lowermost sill is difficult to 239

map with confidence, due to the acoustic masking of the overlying intrusions. The Tulipan sill is 240

a saucer-shaped intrusion, and is easily recognized in the seismic section. Figure 2 shows that the 241

Tulipan sill is forcing a dome-shaped morphology of the overlying Base Carbonate, Top 242

Springar and Top Danian horizons (Schmiedel et al., this volume, in press). The Base Carbonate 243

and Top Springar horizons are intersected and pierced by the transgressive segments of the sill, 244

resulting in the most prominent HTVC’s in the study area. 245

Figure 4 shows the relationship between the underlying sills and the position of the 246

different HTVC’s. HV1 is the horizon of which the dome reflections are down-lapping. The 247

spectral decomposition horizon in Figure 4 shows a clear relationship between the geometry of 248

the underlying sills and the location of the vent complexes. Most of the vent complexes are seen 249

along the outer margins of the Tulipan sill. The differences in rim elevation at the sill margin 250

cause the conduit zones to shallow and deepen, depending on the sill position and elevation. 251

Deeper situated vents are observed where the sills are less inclined. 252

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253

Seismic characteristics of the HTVC 254

The recognition of the hydrothermal vent complexes is based primarily on interpretation 255

of two horizons in the Paleogene sequence, HV1 and Top Tare (Figures 2 and 4). The reference 256

horizon HV1 is defined by the seismic characteristics and well-defined geometry of the upper 257

part of the vent complexes. In this study, 13 individual vent complexes have been identified and 258

analyzed (Figures 4 and 5). 259

The upper part of the HTVC is seen in the seismic cross-section as a dome down lapping 260

onto the HV1 paleosurface (Figures 5 and 6). The geometry and structural context display 261

similarities to vent complexes described elsewhere on the Norwegian Margin and in the Faroe 262

Shetland Basin (Planke et al., 2005; Schofield et al., 2015). However, only vent complexes with 263

dome-shaped upper parts are present in the study area. Slight depressions are observed at the 264

base of some structures, but the overall structure consists of a down lapping dome, and no eye- 265

or crater-shaped features are found as in the study of Planke et al. (2005). All of the vent 266

complexes mapped in this study display a dome feature above HV1. Not all the domes are down 267

lapping onto HV1, but the majority do (11 of 13), suggesting that this is a dominant behavior of 268

the HTVC’s in this part of the Møre Basin. Figure 6 illustrates domes on the HV1 horizon where 269

the height of the structure is about 0.1 s (TWT), corresponding to 80-100 m. The domes are used 270

to give a qualitative measurement of the geometries of the upper part of the vent complexes 271

(Table 1; Figure 7). 272

The HTVC depth is essentially a measurement of the dome structural relief, made by 273

defining a datum linked to the underlying HV1 horizon (Figure 3). Table 1 present the sizes of 274

the 13 individual HTVC’s, showing sizes in the 70-120 m range. The horizons above HV1 are 275

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characterized by a series of convex structures, which are described as draped mounded structures. 276

The term ‘mounded structure’ is used as a descriptive term in this paper to define the topographic 277

relief of the dome above HV1 (Figure 5). To determinate the extent of these structures the 278

horizons was picked as a well-defined, high amplitude and continuous stratigraphic boundary, 279

defined by the presence of the uppermost part of the convex mounded reflections. 280

HTVC's are observed below mounding structures on the Top Tare horizon. They 281

typically display sizes ranging from 600-2000 m in diameter and 70-120 m in height, with an 282

elevated time ratio of 0.1 s (TWT). These mounded structures are exclusively observed in the 283

Paleocene-Eocene transition zone and the lower part of the intra Eocene interval. This interval is 284

defined by a relatively abrupt decline in gamma and sonic response in well 6302/6-1 (Figure 2). 285

In the stratigraphic completion log the interval is described as claystone with thin sandstone 286

stringers with variable content of tuffaceous material. The sonic values in this interval could 287

suggest a transition to more under-compacted and homogeneous clay-sandstone compositions 288

beneath the tuff deposits. 289

290

Vent conduit zone 291

The vent conduit is interpreted as the disrupted, altered or brecciated zone where fluids 292

and mobilized sediments migrated towards the paleosurface. The conduits are seen as disrupted 293

reflections, resulting in a chaotic character of the originally stratified host sedimentary rocks. 294

The 3D data show the conduits as vertical zones in the seismic data, where the amplitudes and 295

reflections are distorted (Figures 3 and 5), consistent with earlier work in the basin and elsewhere 296

(e.g. Heggland, 1998). 297

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The conduit zones show variable morphologies. Some are conical and become thinner 298

downwards towards the sill tip, while others display cylindrical morphologies. Not all the 299

conduit zones display a traceable path from the dome down to their origin. In cases where the 300

flow pattern is diverted by displaced fault blocks or magmatic bodies, the prediction of the sill 301

and aureole origin is difficult. However, the conduits do not appear to follow fault planes in 302

general, and systematic fault cutting is not observed. 303

In the cases where the conduit zones and the links to sills are uncertain, it might be a 304

result of seismic imaging and detection problems. The overburden might also play a role in the 305

interpretation. High amplitude reflections may mask underlying strata, or create seismic artefacts 306

by obscuring the underlying reflections (Schroot and Schüttenhelm, 2003). Reflections in the 307

surrounding host strata are often seen to dip towards the conduit zone and upper part of the 308

HTVC. This feature is best observed in the seismic section crossing large HTVC’s. 309

310

Sandbox modelling results 311

Each of the experiments started with similar litostatic stress conditions for the granular 312

bedding in the Hele‐Shaw cell (Figure 8). Compressed air from a pressurized tank was gradually 313

imposed trough the inlet by manually increasing the air flux using a valve. The pressure was 314

increased slowly until the predefined supply pressure was reached and the fluid-induced 315

deformation of the matrix was obtained. 316

In experiments were the simulated overburdens exceeded 9 cm, a static bubble formed on 317

top of the inlet (Figure 8). The bubble did not change size (width or height) trough time, at a 318

given (constant) pressure. The presence of the static bubble also induced lateral compaction of 319

the matrix, together with a moderate uplift resulting in two steeply dipping reverse shear bands 320

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on each side of the inlet (Figure 8, t3 and t4). The dip angle, and diameter of the conical reverse 321

shear bands are influenced by the filling height, with increasing values for additional material 322

filling. When further increasing the pressure to values beyond the equilibrium threshold, the 323

bubble rapidly moved towards the surface initiating the fluidization. 324

Fluidization is characterized by rapid upward transport of the grains together with the 325

ascending bubble. This transport enables convective movement aligned with the inlet and at the 326

center of the structure. This convective flow generated inward dipping beds at both sides of the 327

fluidization zone. The concentration of fluidized deformation was centralized within the reverse 328

shear bands. At the surface above the fluidization zone, crater deposits formed as grains were 329

erupted (Figure 9). 330

We have compared the results from the Hele-Shaw cell with those from the seismic 331

interpretation. Although HTVC’s are symmetrical 3D structures and the sandbox experiment 332

resulted in two dimensional confined structures, correlation between basic parameters such as 333

height, width and length is still valid. Figure 10 shows similarities between at the upper part of 334

the HTVC’s compared to the upper part of the sandbox structures. The plots indicate how 335

crater/dome structures scale approximately linearly with the conduit/filling height ratio. This is a 336

trend also obtained from the seismic data, where taller conduit zones are associated with larger 337

surface structures (Table 1). Although a linear correlation may not represent the best fit in terms 338

of the actual HTVC’s, the height/width dependency is significant. Therefore, the sandbox models 339

capture first-order features of the natural HTVC. 340

341

Seismic modelling 342

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By estimating a simple overburden model and taking into account the combination of 343

survey/migration aperture, we can retrieve and highlight the illuminated reflections at a given 344

depth interval and reference point (Lecomte et al., 2015). The illumination of the target is in 345

practice depending on the survey geometry and the wave propagation in the overburden, and will 346

also vary according to the location of the target (lateral and depth). Our seismic modelling 347

allowed for direct control of what would be the maximum dip illuminated at the target, i.e., all 348

reflection dips between horizontal and the maximum dip imaged (Lecomte et al., 2016).Three 349

maximum illuminated dips were therefore tested during the seismic modelling procedure (25°, 350

45°, and 90°), corresponding to limited, reasonable, and perfect (ideal) survey/migration 351

apertures, respectively (Figure 11). 352

The synthetic model was able to capture complex features of the piercement structure and 353

produce realistic geometries and deformation fields. Although the differences between 25° and 354

perfect (90° max dip) illumination may be subtle, there are differences due to resolution and 355

geometric effects. From the 25° max dip, features exceeding the 25° incline angle will disappear 356

in the seismogram (black arrows in Figure 11). Additionally, the disrupted conduit zone appears 357

as blurry and transparent in the seismogram compared to the 45° and perfect illumination. This 358

observation supports that a narrow survey aperture prohibits steeper reflections to be illuminated 359

compared to a wide aperture. The 45° corresponds to symmetrical illumination of the modelling. 360

Angles exceeding 45° max dip is not illuminated in the seismogram. Note that the steeper 361

dipping reflections in the conduit zone seem to have a more lateral and continuous extension. 362

When comparing the conduit interior between the 45° and the perfect illumination, the latter it is 363

slightly improved with respect to reflection strength. 364

365

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DISCUSSION 366

The hydrothermal vent complexes provide evidence for focused fluid and gas migration 367

in the Møre Basin close to the Paleocene-Eocene transition. A number of questions arise from 368

our mapping, including aspects of the detailed interpretation of the seismic data and the age of 369

the HTVC’s. The key to these questions can be constrained by examination of the seismic and 370

stratigraphic data, and the experimental and synthetic modelling. The discussion below focuses 371

on the HTVC’s as one complete system, including morphology, formation mechanisms and age 372

correlations. 373

374

Dome shape and differential compaction model 375

A characteristic feature associated with explosive volcanism of hydrothermal venting is 376

the formation of craters (Nermoen et al., 2010; Haug et al., 2013, Galland et al., 2014). The 377

opposite is found regarding the HTVC’s interpreted in the 3D cube, i.e., domes and not craters. 378

The formation of HTVC’s at the HV1 horizon shows a characteristic down-lapping dome 379

structure on the paleosurface defining the upper part (Figure 6). Differential compaction is a 380

mechanism that may explain the doming above the HTVCs. 381

All materials will compact due to gravitational stresses when loaded. Differential 382

compaction develops for instance in inhomogeneous sedimentary deposits, where the material 383

properties vary (e.g., Miles and Cartwright, 2010; Jackson, 2012; Zhao et al., 2014). Variation in 384

how the different materials behave during this process is dependent on their composition and 385

porosity. The result can be seen as local areas compacting more than others, and that geological 386

structures may be affected geometrically during compaction stresses (Figure 12). This process 387

has previously been described in terms of the upper vent geometry by Skogseid et al. (1992) and 388

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Planke et al. (2005), where it was considered as a possibility for the vent-fill to compact less than 389

the surrounding strata, thus causing the characteristic dome morphology. 390

The presence of long-lived seepage through vents from underlying strata (e.g. Svensen et 391

al., 2003; Iyer et al., 2013) could also have contributed to reduced compaction of the vent 392

structure. If these fluids migrated and were trapped in the upper vent structure by the deposition 393

of overlying sealing sediments, overpressure could have developed which in turn may have 394

inhibited further compaction. 395

396

HTVC formation and the sandbox experiment 397

It is clear that the HTVC’s result from focused fluid flow to generate the structural 398

features seen in the seismic data. We have identified similarities when comparing seismic cross-399

sections of HTVC’s with the sandbox experiments (Figures 3 and 9). When fluid pressure was 400

increased beyond the equilibrium threshold, fracturing and brecciating developed above the 401

source. The fluidized zone in the sandbox experiment acted as the conduit zone in the natural 402

setting, a pathway for fluids to reach the surface. The fluidization in the sandbox experiment 403

developed two regions where the first consisted of a narrow conduit zone and the second an 404

upper crater zone (Figure 9). These two morphological features can be correlated to the upper 405

and lower part of the HTVC’s (cf., Jamtveit et al., 2004; Planke et al., 2005). 406

Field data shows that the HTVC’s contain brecciated sedimentary rocks with lithological 407

differences compared to the surrounding strata (Jamtveit et al., 2004; Svensen et al., 2006). 408

Similar findings are evident from the conduit zone in the sandbox experiment. Moreover, both 409

field observations, seismic and experimental data show well-developed inward dipping strata 410

towards the conduit zone (e.g., Planke et al., 2003; Svensen et al., 2006). The experiment time-411

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lapse photographs of Figure 8 shows convective flow during material transport, resulting in 412

volume reduction followed by collapse and the generation of inward dipping beds. 413

The main difference between the sandbox models and the seismic data is the shallow 414

structures: the sandbox exhibit well developed crater morphology above the in-filled fluidized 415

conduit zone, whereas HTVC’s interpreted in the 3D cube exhibit domes. As mentioned earlier, 416

we interpret these domes as a result of differential compaction, a process that cannot be modeled 417

in the sandbox. 418

419

420

Synthetic seismic 421

The synthetic modelling emphasizes the importance of internal structures in generating 422

seismic amplitude anomalies. Figure 11 shows a comparison between the different modelling 423

runs. Even though the resulting seismic images produced are generically similar, there are clear 424

structural differences. One of the most prominent characteristics when comparing the 25° to 45° 425

max dip is how the reflections in the images are displayed (Figure 13). By widening the survey 426

distance and migration aperture in the model, steeper reflection dips at a given reference point 427

are obtained. Perfect illumination has the widest survey/migration aperture, and the 25° the 428

narrowest. Comparing the seismic and the synthetic section, the near horizontal reflections are 429

displayed properly, but this is not the case for the dipping reflections. The combination of survey 430

aperture and layer dip makes for two different structural interpretations of the seismograms. 431

When comparing these results to the actual seismic section of the HTVC’s, we find that the 432

dipping reflections in the conduit zone usually do not exceed c. 45°-50°. From the seismic 433

modelling we found out that 45° max illumination dip was reasonable for the considered 434

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overburden model and a standard migration aperture value. This may imply that the processed 435

data is unable to properly visualize reflections above this angle. A reasonable maximum 436

illuminated dip is taken to be about 45°, and seems to fit between our modelling estimation and 437

what is observed on the actual images. 438

A direct implication of this is that strongly dipping structural features within the HTVC’s 439

can be overlooked or misinterpreted (Figure 13). The synthetic modelling thereby provides a 440

method for more confident interpretations of geological features, plus the ability to validate 441

seismic attributes and artefacts to avoid pit-falls and misinterpretations. 442

443

Age and evolution of the Møre Basin vent complexes 444

Age determination of the HTVC’s in this study is based on the seismic interpretation, 445

well-tie correlations and published palynological data focusing on the sediments at the upper 446

HTVC interval. The interval between the HV1 and HV3 horizons represents the development 447

and emplacement of the HTVC’s. These observations include the intrusive nature of the conduit 448

zone below this transition zone, down-lapping domes, radial faults and tuffaceous claystone at 449

the paleosurface of HV1. From the well data and check-shots, the measured depth of this interval 450

is correlated to be between 3350 and 3450 m (Figures 14 and 15). 451

The biostratigraphic evidence from this transition zone comprises a somewhat enigmatic 452

assemblage with mixed age biostratigraphic indicators between the clear signatures from the 453

underlying Tang and overlying Tare formations. Clear and clean occurrences of the dinocyst 454

Apectodinium augustum are identified at 3350 and 3390 m (last natural occurrence, LO in the 455

well) which suggests that the interval most likely comprises the TP5A zone of the Earliest 456

Eocene (Figure 14). This species is widely used as a marker species for the Paleocene-Eocene 457

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transition (Ali and Jolley, 1996; Passey and Jolley, 2009; Schmitz et al., 2004; Sluijs et al., 2006). 458

Classification of the interval is complicated by the occurrence of older Paleocene palynomorphs 459

(e.g. Tang markers such as Alisocysta margarita, Palaeoperidinium pyrophorum, Areoligera 460

gippingensis, Spiniferites 'membranispina'; note that these did not occur in the expected order) 461

along with the frequent occurrence of Cretaceous fossils like Sidridinium borealis, 'ancient' 462

bisaccates, and Upper Triassic Ricciisporites tuberculatus. The interval may therefore represent 463

the upper parts of the Tang Formation with abundant caving from zone TP5A, or alternatively in 464

situ TP5A with reworking from Tang and older formations. The mixed nature of the assemblage 465

supports significant reworking within the interval and therefore the clear occurrences of 466

Apectodinium augustum are used to support an Earliest Eocene (54.9-55.8 Ma) age for the 467

transition zone and therefore the HTVC development within the Møre Basin study area (Figure 468

14). 469

A wide range in thermal maturity of the retrieved fossils is documented from the 470

transition zone suggesting a source near the sill. For instance, some of the Cretaceous and older 471

re-worked fossils are almost black in the 3410-3440 m. Tuffaceous material was also identified 472

within the interval. Along with the high temperature signatures, older sediments and volcanic 473

detritus indicate that both local and basin-wide eruptions, causing plumes of mixed age 474

sedimentary rocks along with their bio-markers (e.g. Schofield et al., 2015), could have 475

contributed to the mixed assemblages of the transition zone at this time. 476

477

Paleocene-Eocene thermal maximum (PETM) 478

The HTVC formation coincides with one of the most extreme transient shifts in climate 479

during the Cenozoic. The Paleocene-Eocene Thermal Maximum (PETM) occurred at ~56 Ma 480

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and lasted between 100-200 kyr (e.g., Norris and Röhl, 1999; Westerhold et al., 2009). This 481

event is associated with a significant temperature rise of the oceans and the atmosphere, together 482

with changes in ocean chemistry and extinction of benthic foraminiferal species traceable in the 483

biostratigraphical record (e.g., Kennett and Stott, 1991; Röhl et al., 2000; Röhl et al., 2007). 484

The PETM is coeval with the initial opening of the NE Atlantic Ocean (Storey et al., 485

2007), which has been linked to magma emplaced in the Møre Basin (e.g., Svensen et al., 2004; 486

Frieling et al., 2016). Although no direct evidence for contact aureoles have been identified 487

during the seismic interpretation, contact metamorphism around sills is well understood and lead 488

to the generation of CH4, CO2 and H2O from heating of organic-bearing sedimentary rocks (e.g., 489

Aarnes et al., 2015). Vent complex statistics from both the Møre and Vøring basins by Planke et 490

al. (2005) indicate that potentially thousands of individual HTVC’s formed within the PETM and 491

may have acted as one of the main sources for carbon (Svensen et al., 2004). Sedimentary basins 492

influenced by LIP’s may thus represent settings characterized by rapid release of carbon-bearing 493

gas. 494

495

CONCLUSIONS 496

Seismic mapping in the Møre Basin offshore mid Norway has documented an extensive 497

hydrothermal vent complex of Paleocene-Eocene age. Thirteen individual vent complexes have 498

been mapped within the 310 km2 large study area. All the observed venting structures are located 499

above sill intrusions, and are therefore assumed to have develop as a direct consequence of sill 500

emplacement and contact metamorphism. The complex architecture of the HTVC’s may be 501

explained by mobilization of sedimentary rocks from above the sills, caused by local fluid over-502

pressure and fluid migration. The HTVC’s were formed primarily during explosive eruption of 503

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gases, liquids and sedimentary rocks, resulting in depressions and craters at the seafloor. The 504

upper parts of the HTVC’s are dominated by domes and mounded features measuring up to 2.5 505

km in diameter and 120 meters in height. The upper parts of the vent complexes terminate 506

consistently at the Paleocene-Eocene transition above the Tang Formation. This study has used 507

state-of-the-art methods to produce unique 3D images of seismic reflection-data together with 508

simulated modelling to map out the HTVC’s within the Møre Basin. The methods utilized, 509

demonstrate how the final analyses can provide new images of sediment deformation and 510

fluid/gas migration patterns using 3D seismic and modelling procedures. Combining these makes 511

it possible to recognize geometries with considerable confidence, along with mapping important 512

relationships between fluid-flow pathways and structural behavior with high precision. 513

By implementing well-tie correlations and biostratigraphical analysis, the age of these 514

structures are within the 54.9-55.8 Ma range. This period is characterized by intrusive events 515

during the initial volcanism phase at the mid-Norwegian Margin, corresponding to the NE 516

Atlantic break-up. The hydrothermal vent complexes were likely active for a substantial time 517

period in the earliest Eocene. The vent formation likely corresponds to a c. 100 m thick 518

Tang/Tare transition zone with A. Agustum and re-worked Cretaceous and older fossils 519

displaying high maturities possibly caused by contact metamorphism. Timing of the HTVC’s 520

coincides with one of the most extreme climatic shifts in the Cenozoic, the PETM, and our data 521

and conclusions stress the link between the generation and release of carbon gases from the Møre 522

Basin and the global environmental change. 523

524

ACKNOWLEDGEMENTS 525

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We thank Statoil for providing us with the PL251 (Tulipan) geophysical and geological 526

reports for well 6302/6-1. Thanks to NORSAR for the free academic use of the SeisRox software 527

during the modelling procedures, and to Schlumberger for the free academic use of Petrel 2015. 528

Spectral Decomposition was carried out using FFA Geoteric software at University of Aberdeen. 529

FFA are thanked for donation of the software license to the University of Aberdeen”. We further 530

acknowledge the support from the Research Council of Norway through its Center of Excellence 531

funding scheme, project 223272 (CEED), and from the MIMES project (Grant number: 244155). 532

We also gratefully acknowledge the support by the Faculty of Mathematics and Natural Sciences 533

of the University of Oslo to TS. Clayton Grove and Craig Magee are thanked for their many 534

insightful comments and suggestions that helped improve the paper substantially. 535

536

537

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REFERENCES 538

Aarnes, I., S. Planke, M. Trulsvik, and H. Svensen, 2015, Contact metamorphism and 539

thermogenic gas generation in the Vøring and Møre basins, offshore Norway, during the 540

Paleocene–Eocene thermal maximum: Journal of the Geological Society: 172, no. 5, 588-598, 541

doi: 10.1144/jgs2014-098. 542

543

Aarnes, I., S, Planke., M, Trulsvik., and H, Svensen., 2015, Contact metamorphism and 544

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Norwegian Sea. Geo-Marine Letters, 23, no. 3-4, 351-358. 746

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mounds in the Pearl River Mouth Basin, northern South China Sea: Marine Geology, 355, 162-766

172. 767

768

769

770

771

772

LIST OF FIGURES 773

774

Figure 1. Location map showing the study area in the Møre Basin on the mid Norwegian 775

margin. The 3D survey is approximately 2100 km2, and the interpreted study area is 776

approximately 310 km2. 777

778

Figure 2. Summary diagram showing the key interpreted horizons and synthesis of well 779

6302/6-1 lithostratigraphic data. See Figure 1 for profile location. 780

781

Figure 3. Schematic drawing together with seismic section showing the measurement 782

criteria for the dome and conduit zone height and width of a hydrothermal vent complex. 783

784

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Figure 4. Dome geometry and morphology. A) Time-structure map of the Top Tare (~ 785

Intra Eocene) horizon. White circles indicate the position of the dome structure of the HTVC, 786

labelled v.1 to v.13. B) Spectral decomposition of the HV1 paleosurface (red: 22 Hz, green: 787

27Hz, blue: 31 Hz). The figure is illustrating the relationship between the underlying Tulipan sill 788

complex and the HTVC’s seen on the HV1 surface. 789

790

Figure 5. Perspective view of the intra (lower) Eocene horizon Top Tare and a seismic 791

crossline-section of the representative mounded structures of the HTVC’s. The seismic section 792

below displays the HTVC v.4. Note that the structure is restricted to between the intervals of the 793

Paleocene-Eocene (between the sill tip at the Base Carbonate layer and the dome at Top Tare). 794

795

Figure 6. A) 3D seismic interpretation of the v.6 dome structure, down lapping onto the 796

HV1 horizon. B) Corresponding 2D projection of the v.6 dome structure. C) "Variance cube”-797

slice from the HV1 horizon seen from above. Figure illustrates the 3D mapped and time-slice 798

variance representation of domes v. 4 and v. 6. The variance cube highlights lateral 799

discontinuities such as faults. The fault pattern away from both vents, suggest development 800

simultaneous to the vents formation. 801

802

Figure 7. Bar diagram showing the dome sizes for the measured HTVC’s in Table 1. 803

804

Figure 8. Time-lapse sequence of sandbox experiment. (t1): initial configuration of the 805

static bedding. (t2): Static bubble forming at the centered inlet, fluid induced deformation of the 806

matrix. (t3): Gas bubble grows to the surface, triggering the onset of fluidization and eruption of 807

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material at the structure rim and crater. (t4): Re-sedimentation of piercement structure, material 808

funnel fed after experiment. 809

810

Figure 9. Morphological zones defined in the experiment which enables a correlation to 811

the natural occurring HTVC’s. 812

813

Figure 10. Comparison-plot between HTVC’s and piercement structures in the sandbox 814

experiment: A) Minor width plotted against the conduit height. B) Major width plotted against 815

the conduit height. C) Crater width plotted against filling height (in sandbox experiment). 816

817

Figure 11. Synthetic seismic modelling of a model derived from the sandbox experiment. 818

Elastic properties based on well 6302/6-1 at the HTVC interval. Arrows in uppermost figure 819

highlights how different reflection dips are affected by seismic imaging. 820

821

Figure 12. Schematic model displaying key development stages during vent formation. A) 822

Emplacement of intrusion promotes fluid generation and overpressure causing overburden failure 823

and explosive hydrothermal venting which blankets the surrounding area with vent material and 824

older sediments. Large volumes of carbon outgassed into the water column and atmosphere. B) 825

After the initial high energy venting, activity gradually wanes with long-lived gas seepage 826

occurring over many thousands of years and periodically promoting small-scale sediment 827

eruptions, which fill the crater and build up a shallow angle dome. C) Post venting sedimentation 828

blankets the dome and builds up a potentially sealing cover over thousands to millions of years. 829

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Compaction of surrounding strata may exceed that of the hardened or potentially over-pressured 830

vent material resulting in differential compaction and the accentuation of the dome feature. 831

832

Figure 13. A) HTVC (v.6) seismic section, illustrating how the dipping reflections are 833

displayed in the image, and the uncertainty that follows with steeper dipping reflections. B) 25° 834

max dip illumination in the seismogram. Restricted illuminated reflections above 25°, black 835

arrows indicate structural differences between the two angel dependent models. C) 45° max dip 836

illumination in the seismogram. The dominant frequency of the seismic is 20 Hz. 837

838

839

Figure 14. Summary of biostratigraphic age constraints of venting interval. A) Table 840

showing the key taxa distributions correlated with relative age and horizons interpreted at the 841

HTVC interval. Palyno-zones correspond to taxa distribution at given time stages. B) Seismic 842

section and taxa resolution of the HTVC interval. Depth of seismic horizons calibrated with 843

check-shot data from well 6302/6-1. 844

845

Figure 15. Figure summarizing different data implemented to resolve the key questions 846

regarding the HTVC’s in the Møre Basin. The investigation focus on (1) the vent complex 847

geometries, (2) the induced surface deformation patterns, (3) the intrusions (heat source) relation, 848

as well as (4) the emplacement depth and age of the hydrothermal vent complexes. 849

850

LIST OF TABLES 851

852

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Table 1. List summarizing the measured parameters for the 13 HTVC’s mapped in this 853

study. See Figure 4 for location of the individual complexes. Where the specific part of the 854

HTVC’s could not be measured with confidence, N/A (Not Available) is entered in the table. 855

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Figure 1. Location map showing the study area in the Møre Basin on the mid Norwegian margin. The 3D

survey is approximately 2100 km2, and the interpreted study area is approximately 310 km2.

Figure 1

45x26mm (300 x 300 DPI)

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Figure 2. Summary diagram showing the key interpreted horizons and synthesis of well 6302/6-1 lithostratigraphic data. See Figure 1 for profile location.

Figure 2

142x114mm (300 x 300 DPI)

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Figure 3. Schematic drawing together with seismic section showing the measurement criteria for the dome and conduit zone height and width of a hydrothermal vent complex.

Figure 3 45x24mm (300 x 300 DPI)

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Figure 4. Dome geometry and morphology. A) Time-structure map of the Top Tare (~ Intra Eocene) horizon. White circles indicate the position of the dome structure of the HTVC, labeled v.1 to v.13. B) Spectral

decomposition of the HV1 paleosurface (red: 22 Hz, green: 27Hz, blue: 31 Hz). The figure is illustrating the

relationship between the underlying Tulipan sill complex and the HTVC’s seen on the HV1 surface. Figure 4

130x201mm (300 x 300 DPI)

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Figure 5. Perspective view of the intra (lower) Eocene horizon Top Tare and a seismic crossline-section of the representative mounded structures of the HTVC’s. The seismic section below displays the HTVC v.4.

Note that the structure is restricted to between the intervals of the Paleocene-Eocene (between the sill tip at the Base Carbonate layer and the dome at Top Tare).

Figure 5 147x122mm (300 x 300 DPI)

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Figure 6. A) 3D seismic interpretation of the v.6 dome structure, down lapping onto the HV1 horizon. B) Corresponding 2D projection of the v.6 dome structure. C) "Variance cube”-slice from the HV1 horizon seen from above. Figure illustrates the 3D mapped and time-slice variance representation of domes v. 4 and v. 6. The variance cube highlights lateral discontinuities such as faults. The fault pattern away from both vents,

suggest development simultaneous to the vents formation. Figure 6

91x98mm (300 x 300 DPI)

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Figure 7. Bar diagram showing the dome sizes for the measured HTVC’s in Table 1. Figure 7

240x353mm (300 x 300 DPI)

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Figure 8. Time-lapse sequence of sandbox experiment. (t1): initial configuration of the static bedding. (t2): Static bubble forming at the centered inlet, fluid induced deformation of the matrix. (t3): Gas bubble grows to the surface, triggering the onset of fluidization and eruption of material at the structure rim and crater.

(t4): Re-sedimentation of piercement structure. Figure 8

63x47mm (300 x 300 DPI)

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Figure 9. Morphological zones defined in the experiment which enables a correlation to the natural occurring HTVC’s. Figure 9

81x45mm (300 x 300 DPI)

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Figure 10. Comparison-plot between HTVC’s and piercement structures in the sandbox experiment: A) Minor width plotted against the conduit height. B) Major width plotted against the conduit height. C) Crater width

plotted against filling height (in sandbox experiment).

Figure 10 190x395mm (300 x 300 DPI)

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Figure 11. Synthetic seismic modelling of a model derived from the sandbox experiment. Elastic properties based on well 6302/6-1 at the HTVC interval. Arrows in uppermost figure highlights how different reflector

dips are affected by seismic imaging.

Figure 11 143x244mm (300 x 300 DPI)

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Figure 12. Schematic model displaying key development stages during vent formation. A) Emplacement of intrusion promotes fluid generation and overpressure causing overburden failure and explosive hydrothermal venting which blankets the surrounding area with vent material and older sediments. Large volumes of carbon outgassed into the water column and atmosphere. B) After the initial high energy venting, activity gradually wanes with long-lived gas seepage occurring over many thousands of years and periodically

promoting small-scale sediment eruptions, which fill the crater and build up a shallow angle dome. C) Post venting sedimentation blankets the dome and builds up a potentially sealing cover over thousands to

millions of years. Compaction of surrounding strata may exceed that of the hardened or potentially over-

pressured vent material resulting in differential compaction and the accentuation of the dome feature. Figure 12

108x67mm (300 x 300 DPI)

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Figure 13. A) HTVC (v.6) seismic section, illustrating how the dipping reflectors are displayed in the image, and the uncertainty that follows with steeper dipping reflectors. B) 25° max dip illumination in the seismogram. Restricted illuminated reflectors above 25°, black arrows indicate structural differences

between the two angel dependent models. C) 45° max dip illumination in the seismogram. Figure 13

75x52mm (300 x 300 DPI)

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Figure 14. Summary of biostratigraphic age constraints of venting interval. A) Table showing the key taxa distributions correlated with relative age and horizons interpreted at the HTVC interval. Palyno-zones

correspond to taxa distribution at given time stages. B) Seismic section and taxa resolution of the HTVC interval. Depth of seismic horizons calibrated with check-shot data from well 6302/6-1.

Figure 14 190x203mm (300 x 300 DPI)

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Figure 15. Figure summarizing different data implemented to resolve the key questions regarding the HTVC’s in the Møre Basin. The investigation focus on (1) the vent complex geometries, (2) the induced surface deformation patterns, (3) the intrusions (heat source) relation, as well as (4) the emplacement

depth and age of the hydrothermal vent complexes. Figure 15

86x41mm (300 x 300 DPI)

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Table 1. List summarizing the measured parameters for the 13 HTVC’s mapped in this study. See Figure 4 for location of the individual complexes. Where the specific part of the HTVC’s could not be measured with

confidence, N/A (Not Available) is entered in the table. Table 1

70x58mm (300 x 300 DPI)

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This article has been cited by:

1. http://orcid.org/0000-0001-9368-7494Tobias Schmiedel1Sigurd Kjoberg2Sverre Planke3Craig Magee4Olivier Galland1NickSchofield5Christopher A.-L. Jackson4Dougal A. Jerram61University of Oslo, Physics of Geological Processes (PGP),Department of Geosciences, Oslo, Norway. E-mail: [email protected]; [email protected] Oslo, Centre for Earth Evolution and Dynamics (CEED), Department of Geosciences, Oslo, Norway. E-mail:[email protected] of Oslo, Centre for Earth Evolution and Dynamics (CEED), Department of Geosciences,Oslo, Norway and Volcanic Basin Petroleum Research AS (VBPR), Oslo, Norway. E-mail: [email protected] CollegeLondon, Basins Research Group, Department of Earth Science and Engineering, London, UK. E-mail: [email protected];[email protected] of Aberdeen, Department of Geology and Petroleum Geology, School of Geosciences,Aberdeen, UK. E-mail: [email protected] of Oslo, Centre for Earth Evolution and Dynamics (CEED),Department of Geosciences, Oslo, Norway and DougalEARTH Ltd., Solihull, UK. E-mail: [email protected].. 2017.Mechanisms of overburden deformation associated with the emplacement of the Tulipan sill, mid-Norwegian margin.Interpretation 5:3, SK23-SK38. [Abstract] [Full Text] [PDF] [PDF w/Links] [Supplemental Material]

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http://dx.doi.org/10.1190/INT-2016-0155.1

http://library.seg.org/doi/full/10.1190/INT-2016-0155.1

http://library.seg.org/doi/pdf/10.1190/INT-2016-0155.1

http://library.seg.org/doi/pdfplus/10.1190/INT-2016-0155.1

http://library.seg.org/doi/suppl/10.1190/INT-2016-0155.1

3d structure and formation of hydrothermal vent … · 2017-04-11 · 26 the mid-norwegian margin...

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