transgressive lag deposit in the SW Barents Sea

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transgressive lag deposit in the SW Barents Sea

Formation, composition and application Vilde Bjørnebye

UNIVERSITY OF OSLO 01.06.2019

Department of Geosciences

Master of Science in Geology Geology 60 credits

Thesis submitted for the degree of

Faculty of Mathematics and Natural Sciences

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transgressive lag deposit in the SW Barents Sea

Vilde Bjørnebye

Supervised by Jens Jahren (UiO) and Lina Hedvig Line (UiO)

June, 2019

400µm

Formation, composition and application

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c

Formation, composition and application

http://www.duo.uio.no/

This work is published digitally through DUO - “Digitale Utgivelser ved UiO”.

Characterization of a Jurassic transgressive lag deposit in the SW Barents Sea.

Vilde Bjørnebye 2019

Supervisor(s): Jens Jahren (UiO) and Lina Hedvig Line (UiO)

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It is my privilege to express my gratitude to my supervisors, Professor Jens Jahren and Ph.D Lina Hedvig Line for guiding me through this year accomplishing my Master Degree.

I would like to thank OMV Norge AS and Eirik Stueland for cooperation providing cores and data, but also for giving me the opportunity to work as a summer intern.

I developed my skills and knowledge of the Barents Sea and it has been of great use working with this thesis.

Salahalldin Akhavan, Siri Simonsen, Thanusha Naidoo and Michael Heeremans have been very helpful, providing technical support. Thanks to Kristo↵er Løvstad for assistance and advice.

Furthermore, I am thankful to my co-students for discussions, laughter and mo- tivational talks during lunches. To friends and family for endless encouragement and ”advice”.

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Abstract

Coarse conglomerates mark the transition between the Jurassic sands of the Stø or Tub˚aen formations and the unconformable overlying Fuglen formation, indicating a transgressive event. This event is also visible at the boundary between the Wilhelmøya and Janusfjellet subgroups on Svalbard, implying a regional influence.

A major sea-level rise occurring at the end of the Bajocian has by previous work’s been considered the culminating depositional event.

This project aims to improve the understanding of this transgression, how it a↵ects the distribution of sediments and the processes responsible. Linking the mineral content to the petrophysical response. Assessing the lags possible influence on hydrocarbon distribution and geophysical analyses are other objectives.

Sedimentological descriptions, core samples and well log data from nine wells across the Barents Sea comprise the main database of this study.

The conglomeratic bed consists of reworked and in-situ, early diagenetic products, making it a lag of mixed ages. Nodules of phosphate and siderite along with coarse chert and quartz make up the bulk of the clast assemblage. The transgressive lag has a patchy distribution both in the cored wells and on Svalbard, with variable thickness and content. A thickening northwards trend is discovered in this study.

This might be linked to the paleotopography and net erosion, where thicker lags are associated with paleo-highlands. The matrix of the lag is observed to be well cemented by carbonates or apatites at some location, possibly contributing in hydrocarbon distribution given some lateral extent. However, thin cemented beds as the transgressive lag are likely to deform in a brittle manner when exposed to unloading and stretching, which are crucial parts of the burial history in the Barents Sea.

The clasts and cemented constituents of the lag generates significant peaks in the density and velocity logs at the base of the Fuglen Formation. In geophysical analyses, the strong response from the transgressive lag may obscure the amplitudes generated by the lithology and fluid content of the underlying Stø and Tub˚aen formations.

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Acknowledgements i

Abstract ii

1 Introduction 1

1.1 Study Area . . . 1

1.2 Aims and project description . . . 2

1.3 Methods . . . 4

2 Geological Setting 5 2.1 Introduction . . . 5

2.2 Geological architecture . . . 5

2.3 Paleozoic . . . 7

2.3.1 Silurian to Devonian . . . 7

2.3.2 Carboniferous . . . 7

2.3.3 Permian . . . 9

2.4 Mesozoic . . . 9

2.4.1 Triassic . . . 9

2.4.2 Jurassic . . . 10

2.4.3 Cretaceous . . . 12

2.5 Cenozoic . . . 13

2.5.1 Paleogene, Neogene and Quaternary . . . 13

2.6 The Brentskarshaugen Bed . . . 14

2.6.1 Characteristics of the Brentskardhaugen Bed . . . 15

2.6.2 Depositional Setting . . . 15

3 Theoretical Background 17 3.1 The formation and development of transgressive lags . . . 17

3.2 Importance and use in sequence stratigraphy . . . 19

3.3 Transgressive lags in petroleum systems . . . 20

3.4 Phosphate-enriched Beds . . . 22

3.5 Diageneic processes . . . 24

3.5.1 Early diagenetic reactions and processes . . . 24

3.5.1.1 Meteoric water flushing and mineral dissolution . . 25 iii

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CONTENTS iv

3.5.1.2 Redox reactions . . . 25

3.5.1.3 Biogenic activity . . . 26

3.5.1.4 Carbonate cementation . . . 26

3.5.1.5 Phosphate cementation . . . 27

3.5.2 Mechanical compaction of siliciclastic sediment . . . 28

3.5.3 Chemical compaction of siliciclastic sediment . . . 29

3.5.4 Porosity-preserving mechanisms . . . 32

4 Methods 34 4.1 Database . . . 34

4.2 Sedimentological methods . . . 35

4.2.1 Core logging . . . 35

4.2.2 Facies description . . . 35

4.2.3 Sample database . . . 36

4.3 Petrographical analysis . . . 38

4.3.1 X-ray di↵raction (XRD) . . . 38

4.3.1.1 Preparation of sample . . . 38

4.3.1.2 X-ray di↵raction analysis . . . 38

4.3.1.3 Sources of error . . . 39

4.3.2 Thin sections . . . 40

4.3.3 Scanning Electron Microscope (SEM) . . . 40

4.4 Petrophysical analyses . . . 41

4.4.1 Gamma and spectral gamma logs . . . 42

4.4.2 Sonic log . . . 44

4.4.3 Neutron and Density logs . . . 44

4.4.4 Limitations . . . 46

4.4.5 Uplift estimation . . . 47

4.4.6 Geothermal gradient and maximum burial temperature . . . 48

4.4.7 AVO/AVA analysis . . . 48

5 Results 51 5.1 Sedimentological description . . . 51

5.1.1 The Tub˚aen Formation . . . 53

5.1.1.1 Observations and description . . . 53

5.1.1.2 Interpretation . . . 54

5.1.2 The Stø Formation . . . 54

5.1.3 The transgressive lag . . . 57

5.1.4 The Fuglen Formation . . . 62

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5.2 Petrographic analysis . . . 66

5.2.1 Petrography of the Transgressive lag . . . 66

5.2.1.1 Quartz . . . 68

5.2.1.2 Feldspars . . . 70

5.2.1.3 Phyllosilicates . . . 70

5.2.1.4 Carbonates . . . 72

5.2.1.5 Phosphates . . . 73

5.2.1.6 Sulfides . . . 76

5.2.1.7 Oxides . . . 76

5.2.2 Petrography of the Fuglen Formation . . . 77

5.3 Petrophysical analyses . . . 78

5.3.1 Characteristics of the Transgressive Lag . . . 78

5.3.1.1 Well Correlation . . . 83

5.3.2 Uplift Estimation and Maximum burial temperature . . . . 85

5.3.3 AVA/AVO analysis . . . 90

6 Discussion 93 6.1 Composition and interpretation of the Transgressive Lag . . . 94

6.1.1 Clast assemblage . . . 94

6.1.2 Source and precipitation of phosphate . . . 95

6.1.3 The development of phosphate nodules and siderite concre- tions . . . 100

6.1.4 Matrix and cements . . . 101

6.1.4.1 Red zones . . . 102

6.2 Composition and interpretation of the Fuglen Formation . . . 104

6.3 Distribution and controlling factors of the Transgressive Lag . . . . 105

6.4 Depositional history of the Transgressive Lag . . . 108

6.5 Uplift estimation and implication of late diagenetic processes . . . . 110

6.6 Petrophysical identification of the transgressive lag . . . 111

6.7 Sealing e↵ect of the transgressive lag . . . 112

6.7.1 The influence of early diagenetic cements . . . 113

6.7.2 Impact of burial history . . . 114

6.8 AVA/AVO and synthetic seismic . . . 116

7 Conclusive remarks 118 8 Further Work 120 9 References 122 A Appendix 131 A.1 Appendix A . . . 132

A.2 Appendix B . . . 133

A.3 Appendix C . . . 134

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CONTENTS vi

A.4 Appendix D . . . 144

A.5 Appendix E . . . 145

A.6 Appendix F . . . 147

A.7 Appendix G . . . 149

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Introduction

1.1 Study Area

The Barents Sea is an epicontinental sea bounded by the Atlantic Ocean to the west, the Norwegian and Russian mainland to the south- southeast, the Novaya Zemlya to the east, Svalbard and Franz Josef Land in the north (Figure 1.1). This encompasses an area of about 1.3 million km² making it one of the largest zones of continental shelf worldwide (Dor´e, 1995; NPD, 2018a).

60°0'0"E 50°0'0"E

40°0'0"E 30°0'0"E

78°0'0"N76°0'0"N74°0'0"N72°0'0"N70°0'0"N68°0'0"N

0 75 150 300

Kilometers

Bathymetry Topography

Metre -5 000 -4 000 -3 000 -2 000 -1 500 -1 000 -750 -500 -250 -100 -50 0 25 50 100 250 500 750 1 000 1 500

60°0'0"E 50°0'0"E

40°0'0"E 30°0'0"E

78°0'0"N76°0'0"N74°0'0"N72°0'0"N70°0'0"N68°0'0"N

BARENTS SEA

KARA SEA NO

RWEGIAN SEA S V A L B A R D

N O V A Y A Z E M

L Y A Franz Josef Land

Norway

Russia

Pay Khoy

Kolguyev Bjørnøya

SOUTH-WESTERN BARENTS SEA

Figure 1.1: Map of the Barents sea with topography and bathymetry. The boarder between Russia and Norway is marked with stippled lines. Modified

from Smelror et al. (2009) and Jakobsson et al. (2008), respectively.

1

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Chapter 1 Introduction 2 With discoveries as the Wisting, Johan Castberg, Snøvit and Goliat fields, the Barents Sea has become an area of increased interest since it was opened for petroleum exploration about 40 years ago. The most prolific characteristics has to date been demonstrated in Jurassic deposits, comprising mature sands in the Stø Formation, cap rock characteristics in the Fuglen Formation and an organic rich source rock of the Hekkingen Formation. Other plays are recognized, but still requires further investigation to substantiate the petroleum systems.

Recent estimations made by the Norwegian Petroleum Directorate indicate that over 60% of the undiscovered resources on the Norwegian continental shelf reside within the Barents Sea (NPD, 2018b). However, exploration has not been easy and without disappointments. Examples are the dry Apollo and Atlantis fields north of the Wisting field and the non-commercial Korpfjell field, north-east in the southern Barents Sea. Thus, studying the area‘s complex geology to enhance the knowledge of the shelf has been highlighted by researchers and the petroleum industry. Following, the Barents Sea is regarded a promising area of hydrocarbon discoveries but is still considered an immature petroleum province requiring further research.

1.2 Aims and project description

The aim of this thesis is to evaluate the deposition and distribution of a lag comprising conglomeratic characteristics, interbedded between Jurassic sandstones of the Stø or Tub˚aen formations, and the o↵shore muds of the Fuglen Formation in the southwestern Barents Sea. In previous work, the horizon is interpreted to represent a transgressive lag from its reworked content and stratigraphic position marking an abrupt shift in depositional environment. On Svalbard, the lag is called ”The Lias Conglomerate” or more commonly ”The Brentskardhaugen Bed”

and considered to be of Bathonian age (B¨ackstr¨om & Nagy, 1985). In the southwestern Barents Sea, the transgressive lag is observed in cores, implying a laterally extensive depositional event.

Aiming to interpret the conditions and processes active during deposition, petrographical and sedimentological features will be evaluated. Further, paleotopography will be assessed by looking for local and regional controlling factors on

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sediment distribution. This may contribute in the understanding of the depositional environments and geography at the time of the transgressive event. Sig- nificant depositional hiatuses are typical of the Early to Middle Jurassic epochs from lithostratigraphical reconstructions. As the transgressive lag might hold reworked constituents from these periods, examining the nature and characteristics of such components may provide information of the eroded time span. From this, a geological model of the depositional environments and conditions during the Early to Middle Jurassic may be created. This will contribute to a more complete understanding of the Jurassic Period, which to date is poorly understood.

An other objective is to link the mineralogical content of the lag to its petrophysical characteristics. This to present an approach of how to trace the lag from wireline logs and thus possibly validate the presence of it in new areas. Evaluating the importance and influence the lag has on petroleum systems and geophysical analysis are emphasized and might provide valuable information to further petroleum exploration. The integrated approach of this project is illustrated in Figure 1.2.

Figure 1.2: Illustration of the integrated approach including core logging, petrography and petrophysics. Conseptual figure, not to scale.

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Chapter 1 Introduction 4

1.3 Methods

Sedimentological core logging and sampling of the transgressive lag have been conducted in nine selected wells across the Southwestern Barents Sea (Figure 1.3).

The cores were provided by the Norwegian Petroleum Directorate and OMV Norge AS.

Further, petrographical analyses have been conducted to determine the mineralogy and characteristics of the conglomerate. Petrophysical logs were used to trace the response of the Fuglen-Stø formation transition and to appraise the properties of the transgressive lag in cored and non-cored wells. Figure 1.3 depicts the logged wells in green and wells used for correlation in pink.

Figure 1.3: Map of the location of the studied wells in the southwestern Barents Sea. The core logged wells depicted in green and the wells used for correlation in pink. The position of the wells are obtained from NPD (2018c).

Modified from Smelror et al. (2009).

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Geological Setting

2.1 Introduction

In the following chapter, the geological history of the southwestern Barents Sea will be summarized, explaining the influence from various tectonic events, changing climate and fluctuating sea level throughout time.

2.2 Geological architecture

Geographically, the Barents Sea is divided into a western and an eastern part, separated by a NE-SW oriented structure suggested to originate from the suture zone of the Caledonian orogeny (Henriksen et al., 2011). The eastern Barents Sea comprises major basins with thick Paleozoic and Mesozoic successions, while the western Barents Sea displays structural complexity with highs, platforms and smaller basins. This complex architecture originates from phases of rifting since the collapse of the Caledonian orogeny to the Cenozoic seafloor spreading (Figure 2.1) (Gabrielsen et al., 1990; Smelror, 1994). Preserved successions of Paleogene to Neogene strata and thick Cretaceous deposits are characteristics of the western Barents Sea (Henriksen et al., 2011).

Figure 2.1 displays the major tectonic events from the Carboniferous to Neo- gene. Although multiple tectonic events have been crucial in shaping the mosaic geology of the Barents Sea, three fundamental phases of rifting, set to the Car- boniferous, Jurassic-Cretaceous and Paleogene has been described (Figure 2.1)

5

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Chapter 2 Geological Setting 6

78

76

74

72

70

68

10 15 20 25

MH

Lofoten Basin

Hammerfest Basin Tromsø

Basin

Finnmark Platform Maud

Basin

Bjarmeland Platform Stappen

High

Spitsbergen

Nordaustlandet Kong Karls Land

Fingerdjupet Subbasin

Gardarbanken High

Loppa- High

Carboniferous

Late Jurassic-Early Cretaceous

Late Cretaceous-Paleocene

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0

9 0 1 0 0 110 1 2 0 1 3 0 1 4 0 1 5 0 1 6 0 1 7 0 1 8 0 1 9 0 2 0 0 2 1 0 2 2 0 2 3 0 2 4 0 2 5 0 2 6 0 2 7 0 2 8 0 2 9 0 3 0 0 3 1 0 3 2 0 3 3 0 3 4 0 3 5 0 3 6 0 3 7 0 3 7 5

v v v

v v

W

MesozoicPaleozoic CretaceousJurassicTriassicPermianCarboniferousDevonian Late

Early

Late

Middle

Early

Late

Middle

Lopingian Guadalupian

Late Penns.

Late Miss.

Mid. Miss.

Early Miss.

Mid. Penn.

Early Penn Cisuralian Early

Late Santonian Coniacian Turonian Cenomanian

Albian

Aptian

Barremian Hauterivian Barremian Barriasian Thithonian Kimmerigian Oxfordian

Bathonian Bajoncian Aalenian Toarcian

Plienbachian

Sinemurian Hettangian Rhaetian

Norian

Carnian

Ladinian

Anisian Olenekian Induan Changhsingian Wuchiapingian Capitanian Wordian Roadian Kungurian

Artinskian

Sakmarkian

Asselian Gzhelian Kasimovian Moscovian Bashkirian

Serpukhovian

Visean

Tournaisian

Famennian Calllovian

NeogenePaleogeneCenozoic

Q u a te rn a ry

Miocene PLiocene PLeistocene Holocene

Oligocene

Eocene

Paleocene

Campanian Maastrichtian Danian Thanetian Ypresian Lutetian Bartonian Priabonian^Rupelian Chatian Aquitenian BurdigalianLanghian SerravalianTortonian Messinian Zanclean Piacenzian Gelazian E. Pleist.

M. Pleist.

L. Pleist.

Selandian

Period

Sub-Era Epoch Stage Group FormationsLithostratigraphy Megasequences

Age NordlandSolbakkenNygrunnenAdventdalenKapp ToscanaSassen- dalenTempel fjordenBjarme -landGipsdalenBillefjorden

Torsk

Kvit -ing

Kveite

Kolmule Kolje Knurr Hekkingen

Fuglen Stø Nordmela Fruholmen Snadd Tubåen

Kobbe

Klappmyss Havert

Ørret Røye

Ørn Falk

Isbjørn Polarrev

Ugle Tettegras Soldogg Blærerot

Shelf uplift

Sheared margin

Rifting Rifting Platform uplift

Regional Subsidence

Rifting Ural mountain chain in the east, rifting in the west

8 0

Rift Phases

Continent-Ocean boundary

A B

Figure 2.1: A: Chronostratigraphic event chart of the western Barents Sea.

Modified from Glørstad-Clark et al. (2010). B: Link between the main struc- tures of the area and rift phases. Structural elements are modified from Glørstad-Clark et al. (2010) and the background map is obtained from Faleide

et al. (2015).

(Glørstad-Clark et al., 2010; Henriksen et al., 2011). Each subsequent rift phase was followed by numerous pulses of reactivation (Faleide et al., 2015).

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2.3 Paleozoic

2.3.1 Silurian to Devonian

Sea level fluctuation caused vacillated deposition between carbonates and shallow marine siliciclastics from the Silurian to Late Devonian (Henriksen et al., 2011).

At the initiation of the Devonian, the Barents Sea encompassed shallow marine basins in the east while the Caledonian orogeny developed in the west (Figure 2.2A)(Smelror et al., 2009). The amalgamation of the Laurentian and Baltican plates generated the basement and the fundamental tectonic framework of the Barents Sea with a main arm trending NE-SW. Impending tectonic events are observed to follow the tectonic framework and zones of weakness generated during this time (Ritzmann & Faleide, 2007; Henriksen et al., 2011).

Reactivation of Caledonian fault zones lead to the extension and development of the Nordkapp Basin in Late Devonian to Early Carboniferous. Continental siliciclastics, such as the Old Red Sandstones were deposited in intra-cratonic basins in the western Barents Sea (Smelror et al., 2009).

2.3.2 Carboniferous

At the onset of the Carboniferous, the Barents Sea was located at approximately 20 N with a tropical and humid climate. Throughout the period, alluvial sedimentation dominated in the western Barents Sea, while deltaic to and deep marine conditions characterized the east (Figure 2.2B). The alluvial environment developed from the Devonian molasse environment as the denudation of the Caledonian highs progressed (Henriksen et al., 2011). The deposits were distributed in basins created by subsidence along active fault lineaments (Smelror et al., 2009).

A significant rift phase with connection to the Atlantic, and possibly the Arctic was active from the Late Devonian to Middle Carboniferous (Gudlaugsson et al., 1998; Henriksen et al., 2011). The rift phase, consisting of several tectonic pulses, were distinguished by lineaments trending NE-SW (Figure 2.1B). These events are suggested to have initiated the development of several structural features such as the Tromsø, Fingerdjupet and Maud basins (Gudlaugsson et al., 1998; Smelror et al., 2009; Henriksen et al., 2011).

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Major fold belts Minor deformation front

Emergent areas Coastal to sallow marine

Sallow to deep marine Oceanic domain

volcanic provinces Extension

Compression Sand influx

? Ural Ocean

Pacific Ocean

Baltica Greenland

Caledonides

Sakmarian back-arc basin

Ural FB.

Barents Sea Barents

Sea Chukotka

Chukotka

Laurentia

Laurentia Late Silurian

Carboniferous Pacific Ocean

Chukotka

Arctic shelf Barents

Sea Timan

Pechora Moscow Platform Moscow Platform

Barents Sea

Timan Pechora

Moscow Platform Kazakhstan

Pacific Ocean

Arctic shelf Sverdrup basin

Barents Sea

Timan Pechora

Moscow Platform Siberian Platform

Baltica

Mid.-Late Trias

Kazakhstan Siberian Platform Siberian Platform Kara

Sea Sverdrup basin

Greenland

Baltica Lomonos

ov

E. Cretaceous North America

Siberian Platform

Kara Sea Sverdrup basin

Greenland

Baltica Lomonos

ov

Barents

Sea Timon

Pechora

L. Jurassic

L. Tertiary

Kara Sea Greenland

Baltica Barents

Sea Norwegian- Greenland

Sea

Timan Pechora

Moscow Platform Barentsia

?

A

B

C

D

E

F

Figure 2.2: Evolution of the Barents Sea. A: Late Silurian, amalgamation of Laurentia and Baltica. B: Carboniferous, rifting. C: Mid-Late Triassic, mul- tidirectional sediment influx. D: Late Jurassic, opening of the Atlantic Ocean and uplift of structural highs. E: Late Cretaceous, rifting and shelf exposure.

F: Late Tertiary, glaciation and development of the Norwegian-Greenland Sea.

Modified from Smelror et al. (2009).

A distinct shift in depositional environment emerged in the Upper Carboniferous as the sea level rose and the climate gradually became more arid due to the northwards drift of Pangaea. These environmental conditions facilitated the deposition of carbonate and evaporites (Smelror et al., 2009).

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2.3.3 Permian

At the beginning of the Permian, alternating subsidence-rates associated with the developing Uralian orogeny and glaciation in the southern hemisphere lead to a highly fluctuating sea level (Worsley, 2008). As a consequence, the Barents shelf experienced both flooding and subaerial exposure. Under these conditions, deposition of carbonates and evaporites prevailed (Smelror et al., 2009).

A regional sag basin geodynamically related to the closure of the Uralian Ocean influenced the entire shelf from the Permian to the Early Triassic (Smelror et al., 2009). Rifting occurred with a N-E strike, prominent in the western Barents Sea (Gudlaugsson et al., 1998).

The climate cooled as the continent continued its northwards drift and this, accompanied by the closure of sea-ways, lead to a shift in depositional environment.

Thus, the Early Triassic carbonate platforms were succeeded by the deposition of siliciclastic sediments (Worsley, 2008; Henriksen et al., 2011).

2.4 Mesozoic

2.4.1 Triassic

The magnitude of the Permian subsidence decreased throughout the Triassic and the western Barents Sea became an area of tectonic quiescence (Gabrielsen et al., 1990; Worsley, 2008). Sediments were supplied into the regional sag basin from several provenances. The Baltic shield and Caledonides were significant suppliers, but as the Uralian highland developed, the supply from east increased successively (Smelror et al., 2009; Henriksen et al., 2011). Deposition was primarily controlled by the proximity to the sediment sources but also by transgressive-regressive cycles.

The sediment supply from the Uralian orogeny caused a westward progradation of the coastline and the associated facies (Figure 2.2C). Fluvial to deltaic depositional environments prevailed in the east while marine deposition dominated the areas more distal of the provenances (Glørstad-Clark et al., 2010). Illustrating this, seismic lines show 4-7 km thick Triassic successions in the central basins of the Barents Sea while considerably thinner successions of finer sediments are recorded on Svalbard (Nøttvedt et al., 1993; Ritzmann & Faleide, 2007).

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Chapter 2 Geological Setting 10 Northward extension of the Uralides caused protrusion of the Novaya Zemlya.

This lead to shelf upliftment as the SW Barents Sea represented the foreland bulge to the Novaya Zemlya fold-and-thrust belt. Further, the sea connection was reduced, reinforcing the accumulation of coarse sediments from the Baltic Shield and Caledonides in the south (Henriksen et al., 2011).

2.4.2 Jurassic

The central and northern Barents Sea acted as highlands after the Late Triassic to Early Jurassic uplift (Figure 2.3) (Smelror et al., 2009). Erosion of exposed areas resulted in erosional hiatuses between Triassic and Jurassic deposits (Figure 2.1A).

In the southwestern Barents Sea, sediments were supplied from provenances as the Caledonides and Baltic shield. Furthermore, deposition was to a large extent a↵ected by reworking of previously deposited sediments from the structural highs (Worsley, 2008; Klausen et al., 2018). The Early to Middle Jurassic Stø Formation is a target of petroleum exploration due to its stratigraphic position and textural characteristics. The sandstone encompasses well sorted and mature sand deposited in a marginal marine setting with variable tidal and fluvial influence (Klausen et al., 2018).

During the Middle Jurassic, the Barents Sea was tectonically stabilized. An in- crease in the amount of atmosphericCO2 related to the disruption of Pangea and the northward continental drift resulted in a more humid climate (Dor´e, 1995;

Worsley, 2008).

Cycles of transgressive and regressive events occurred throughout the Jurassic.

However, the magnitude of the fluctuations varied and hence also the influence on the change in depositional environments. A rapid and regional sea-level rise occurred in the Bathonian, creating an abrupt contact between mature sand and marine mudstones. During this event, reworking of the previously deposited sub- strate by the force of the coastal erosion generated a transgressive lag (B¨ackstr¨om

& Nagy, 1985; Worsley, 2008; Smelror et al., 2009).

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50°0'0"E40°0'0"E30°0'0"E

78°0'0"N 76°0'0"N 74°0'0"N 72°0'0"N 70°0'0"N 68°0'0"N

C: Bajocian IIII

IIII

IIII IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIII

II

II 50°0'0"E40°0'0"E30°0'0"E

78°0'0"N 76°0'0"N 74°0'0"N 72°0'0"N 70°0'0"N 68°0'0"N

50°0'0"E40°0'0"E30°0'0"E

78°0'0"N 76°0'0"N 74°0'0"N 72°0'0"N 70°0'0"N 68°0'0"N 78°0'0"N 76°0'0"N 74°0'0"N 72°0'0"N 70°0'0"N 68°0'0"N

D: TithonianB: Toarcian

A: Hettangian 50°0'0"E40°0'0"E30°0'0"E

A

B

C

D150 160 170 180 190 200

Mesozoic

Jurassic

Late Middle Early

Thithonian Kimmerigian Oxfordian Bathonian Bajoncian Aalenian Toarcian Plienbachian Sinemurian HettangianCalllovian

Adventdalen Kapp Toscana

Hekkingen Fuglen Stø Nordmela Tubåen

AgeSub-EraPeriodEpochStageGroupFormation Environments Highland / Denudation area Lacustrine / Fluvial plain Alluvial Coast Shallow-water shelfMarsh / Lacustrine Periodically flooded area Shelf Deep-water shelf

Conglomerate, sandstone Siltstone, claySandstone Sandstone, siltstone, clay

Lithology Clay Black shale (organic-rich)Organic-rich claystone Figure2.3:JurassicdepositionalevolutionoftheBarentsSeafromtheHettangian(A),Toarcian(B),Bajocian(C)andTithonian (D),depictingafluctuatingsea-level,butageneralfloodingthroughouttheperiod.ModifiedafterSmelroretal.(2009).

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Chapter 2 Geological Setting 12 Reaching a maximum of the transgression, the Late Jurassic comprised a time interval of deep marine conditions for most of the Barents Sea. The main cap rock of the Barents Sea, the Fuglen Formation, was deposited at this stage. Bathy- metrically, deep waters of about 200-300m constituted the eastern and northern Barents Sea, whilst shallower conditions existed near the coasts to the south, north on Svalbard and close to the Novaya Zemlya (Figure 2.3D) (B¨ackstr¨om & Nagy, 1985; Smelror et al., 2009). Anoxic bottom conditions prevailed due to submarine barriers and combined with low sedimentation rate and high organic production, source rocks as the Hekkingen formation were deposited (Worsley, 2008).

Late Jurassic rifting related to the opening of the Atlantic Ocean a↵ected the southwestern Barents Sea by elevating structural features such as the Stappen-, Loppa- and Hopen High, and rotating fault blocks (Smelror et al., 2009).

2.4.3 Cretaceous

The rift phase initiated in the Late Jurassic culminated in the Early Cretaceous, comprising the current architecture of highs and basins of the central south-western Barents Sea (Figure 2.1B & Figure 2.2E). In the Bjørnøya, Tromsø and Harstad basins, 5-6 km thick Cretaceous successions are preserved. The magnitude related to the Jurassic-Cretaceous rift-phase and following rapid subsidence (Faleide et al., 1993; Henriksen et al., 2011).

The Early Cretaceous deposits are characterized as fine-grained marine sediments thickening southwards. Structural highs and platforms were areas of carbonate accumulation while the sediment influx to the depocenters was reduced due to the Middle-Late Jurassic transgression. The southwards thickening trend was caused by tilting of the shelf, related to the opening of the Arctic basin (Figure 2.2E).

This northerly uplift lead to regression and development of continental conditions.

A hiatus between the Late Cretaceous and Paleogene deposits was generated due to subaerial shelf exposure (Smelror et al., 2009; Glørstad-Clark et al., 2010).

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2.5 Cenozoic

2.5.1 Paleogene, Neogene and Quaternary

The opening of the North Atlantic Ocean urged magmatic events and the development of new structural elements in the western Barents Sea at the onset of Paleogene (Figure 2.1B & Figure 2.2F). Accompanied by the seafloor spreading, regional uplift and subsequent erosion characterize the Paleogene period (Smelror et al., 2009).

Arising during the Upper Neogene, cycles of glaciation had a large impact on the Barents shelf. Figure 2.4A depicts the extent of the ice cap at about 1 million years ago. Causing subsidence when developing and isostatic rebound when diminishing, the glaciations lead to severe uplift, erosion and re-deposition of the underlying sediments (Faleide et al., 2015). The net uplift has been calculated to be greatest in the north and north-east, emanating in deposition of eroded material in major submarine fans along the western margin (Figure 2.4B) (Henriksen et al., 2011).

The Cenozoic uplift influenced the prospectivity of the Barents Sea by shutting down source rocks and reactivating faults causing leakage and/or redistribution of fluids (Ohm et al., 2008).

Figure 2.4: A: Estimated extent of the ice cap from about 1 Ma ago. Modified from Smelror et al. (2009). B: Net exhumation based on vitrinite and velocity

estimations from Baig et al. (2016).

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2.6 The Brentskarshaugen Bed

The Brentskardhaugen Bed, previously called the Lias conglomerate, was intro- duced by Parker (1967). Subsequently, the horizon has been recorded and described in several publications, such as the work of Pˇcelina (1980), B¨ackstr¨om

& Nagy (1985) and Rismyhr et al. (2018). These articles constitute the basis of the following description of the prevailing conditions on Svalbard during the deposition of the Late Jurassic conglomerate.

The Brentskardhaugen Bed is recognized throughout Svalbard as a phosphorite conglomerate interbedded between the Wilhelmøya and Janusfjellet subgroups (Bäckström & Nagy, 1985; Dypvik et al., 1985). Correlation can be made between the shallow shelf deposits of the Wilhelmøya Subgroup and the marine shales of the Janusfjellet Subgroup to the Stø Formation and Fuglen Formation, respectively in the SW Barents Sea. On Svalbard, the Brentskardhaugen Bed is regarded as the basal part of the Janusfjellet Formation by Birkenmajer & Pu- gaczewska (1975) and Bäckström & Nagy (1985). As such, the conglomeratic bed is assumed to have a time equivalent in the Barents Sea at the base of the Fuglen Formation (Figure 2.5).

Figure 2.5: Correlation between the stratigraphy of the Late Triassic to Middle Jurassic units on Svalbard, Kong Karls Land and the Barents Shelf. Modified

from Mørk et al,. (1999) and Lord et al. (2016).