The Iceland Palaeomagnetism Database (ICEPMAG V1.0)

Home , Eastern Region (Iceland), Fagradalsfjall, Western Region (Iceland)

The Iceland Palaeomagnetism Database (ICEPMAG v1.0)

Justin A. D. Tonti-Filippini

FacultyFaculty of of Earth Earth Sciences Sciences UniversityUniversity of of Iceland Iceland 20182018

THE ICELAND PALAEOMAGNETISM DATABASE (ICEPMAG V1.0)

Justin A. D. Tonti-Filippini

60 ECTS thesis submitted in partial fulﬁlment of a Magister Scientiarum degree in Geophysics

Supervisor Maxwell Christopher Brown

Faculty Coordinator Páll Einarsson

Faculty of Earth Sciences School of Engineering and Natural Sciences University of Iceland Reykjavík, October 2018 The Iceland Palaeomagnetism Database (ICEPMAG v1.0) 60 ECTS thesis submitted in partial fulﬁlment of a M.Sc. degree in Geophysics

Faculty of Earth Sciences School of Engineering and Natural Sciences University of Iceland Sturlugata 7 101, Reykjavík, Reykjavík Iceland

Telephone: 525 4000

Bibliographic information: Justin A. D. Tonti-Filippini, 2018, The Iceland Palaeomagnetism Database (ICEPMAG v1.0), M.Sc. thesis, Faculty of Earth Sciences, University of Iceland.

Printing: Háskólaprent, Fálkagata 2, 107 Reykjavík Reykjavík, Iceland, October 2018 For Mary and Nicholas

Abstract

Iceland’s lavas preserve a unique record of Earth’s magnetic ﬁeld for the past sixteen million years, and were used by early pioneers of palaeomagnetism to test several concepts which became crucial to modern geoscience. Iceland represents one of very few high latitude (>60◦) locations where long sequences of lavas suitable for palaeomagnetic research are accessible. Since the early 1950s, research in Iceland has produced a large collection of palaeomagnetic data which has not previously been collected into a comprehensive database. ICEPMAG (http://icepmag.org/) compiles palaeomagnetic data published in journal articles, academic theses and other databases from over 9,200 sampling sites in Iceland - one of the world’s largest collections of palaeomagnetic data from a single location. ICEPMAG was constructed utilising the principles and structure of GEOMAGIA50, and maintains the vocabulary of MagIC to allow easy transfer to the global palaeomagnetic database. The ICEPMAG database can be searched through a publicly available website which provides a range of customisable constraints, including rock and sample/specimen types, age constraints, dating methods, palaeointensity methods, geographic constraints (by region, location and between speciﬁed coordinates), authors and years of publication, as well as statistical constraints such as directional polarity, α95 and precision parameter κ. Query results are presented in a results table, with options to produce interactive maps of site locations, VGP plots and downloadable spreadsheets. All the entries in ICEPMAG contain palaeointensity or palaeodirectional data: 8649 contain direction only, 218 intensity only, and 337 both direction and intensity. ICEPMAG will contribute an additional 50 studies and 6,570 sites to the global MagIC database.

Contents

List of Figures ix

List of Tables xi

Abbreviations xiii

Acknowledgements xv

1. Introduction1

2. Background5 2.1. Overview of palaeomagnetism ...... 5 2.1.1. Early history (pre 18th century) ...... 5 2.1.2. The birth of palaeomagnetism (18th to 20th century) . . . . .6 2.2. Palaeomagnetism in Iceland ...... 8 2.2.1. Early developments (1920s to 1960s) ...... 8 2.2.2. Palaeodirectional work (1964 to 2018) ...... 12 2.2.3. Palaeointensity studies ...... 16 2.3. Existing palaeomagnetic databases ...... 17 2.3.1. Magnetic Information Consortium (MagIC) ...... 18 2.3.2. GEOMAGIA50 Paleomagnetic Database ...... 18 2.3.3. IAGA Global Paleomagnetic Database (GPMDB) ...... 18 2.3.4. Absolute Palaeointensity (PINT) Database ...... 19 2.3.5. PALEOMAGIA (Paleomagnetic Information Archive) . . . . . 19

3. Methodology and framework 21 3.1. Construction of the database ...... 21 3.1.1. Building the source library ...... 21 3.1.2. Designing the database structure ...... 23 3.1.3. Adding data to ICEPMAG ...... 24 3.1.4. Programming the server and website ...... 26 3.2. Practical experience ...... 28

4. Data types and experimental methods 29 4.1. Study/contribution details ...... 29 4.2. Geographic information ...... 29

vii Contents

4.3. Geological information ...... 31 4.4. Dating methods ...... 32 4.5. Sampling information ...... 33 4.6. Laboratory measurements ...... 34 4.7. Magnetisation and susceptibility ...... 35 4.8. Direction calculations ...... 36 4.9. VGP calculations ...... 39 4.10. Palaeointensity methods ...... 40 4.10.1. ‘Thellier’ type methods ...... 41 4.10.2. ‘Shaw’ methods ...... 42 4.10.3. Microwave methods ...... 42 4.10.4. Other methods ...... 42 4.11. Dipole moments (VDM and VADM) ...... 43

5. Online implementation and functionality 45 5.1. ICEPMAG website ...... 45 5.1.1. Home page ...... 46 5.1.2. Study page ...... 46 5.1.3. Query form ...... 46 5.1.4. Results page ...... 51 5.1.5. Location map ...... 54 5.1.6. VGP plot ...... 55 5.1.7. Data download ...... 56

6. Overview of ICEPMAG data 57 6.1. Geographic distributions ...... 57 6.2. Temporal distributions ...... 60 6.3. Palaeointensity results ...... 61 6.4. Other distributions ...... 63

7. Conclusion 67 7.1. Summary ...... 67 7.2. Path forward ...... 69 7.2.1. MagIC uploads ...... 69 7.2.2. Updates and error checking ...... 69

References 71

A. Appendix 83

viii List of Figures

1.1. A well-exposed sequence of lavas in Lundarháls, western Iceland. . . . .2 1.2. Geological map of Iceland - bedrock classified by age, with regions and major towns and roads ...... 3 3.1. Overview for methodology for the construction of the ICEPMAG database 22 3.2. Workflow for population of master and relational tables from source library 25 3.3. SQL relational table for regions of Iceland with corresponding integer IDs 26 3.4. Workflow from compilation of the ICEPMAG database to output of website ...... 27 3.5. Example of PHP scripting to generate SQL statement for region/s selected on query page ...... 28 4.1. Regions of Iceland ...... 31 4.2. Example of palaeomagnetic sampling with a portable drill in Lundarháls, western Iceland, photo taken by J. Tonti-Filippini, 22nd June 2018. . . . 33 4.3. Oriented palaeomagnetic sample drilled from an Icelandic lava, photo taken by J. Tonti-Filippini, 6th July 2018...... 35 4.4. Orientation of a palaeomagnetic core in Lundarháls, western Iceland, photo taken by J. Tonti-Filippini, 20th June 2018...... 37 5.1. Home page of the ICEPMAG website (screenshot) ...... 45 5.2. Example of study page containing details of the papers included in ICEP- MAG (searched authors for ‘Brown’) ...... 46 5.3. Query form - outputs (screenshot) ...... 47 5.4. Query form - include result options (screenshot) ...... 47 5.5. Query form - geographic constraints (screenshot) ...... 48 5.6. Query form - age constraints (screenshot) ...... 48 5.7. Query form - publication constraints (screenshot) ...... 49 5.8. Query form - rock, sample and specimen types (screenshot) ...... 49 5.9. Query form - palaeointensity and dating methods (screenshot) ...... 50 5.10. Query form - site statistics and polarity (screenshot) ...... 50 5.11. Results page - an example of query parameters (screenshot) ...... 51 5.12. Results page - an example of basic search query results (screenshot) . . . 52 5.13. Results page - an example of additional results columns from a detailed search (screenshot) ...... 52 5.14. Results page - an example table of references returned by a query (screenshot) ...... 52

ix List of Figures

5.15. Results page - an example of the region and location tables returned by a query (screenshot) ...... 53 5.16. Results page - an example of palaeointensity and dating method tables (screenshot) ...... 53 5.17. Results page - an example of the additional relational tables returned from a detailed query (screenshot) ...... 54 5.18. Results page - an example of a location map produced from a query (screenshot) ...... 55 5.19. Results page - an example of a VGP plot produced from a query (all VGP calculations from the Westfjords region) ...... 56 5.20. Results page - an example of the link to a downloadable spreadsheet (screenshot) ...... 56 6.1. Map of ICEPMAG site locations (all results) ...... 58 6.2. Histogram of all ICEPMAG sites by latitude and longitude ...... 58 6.3. Histogram of sites by geographic region ...... 59 6.4. Histogram of sites by reference ID (see Table A.2) ...... 59 6.5. Histogram - sites by age (all results) ...... 60 6.6. Histogram - sites by age (Holocene only) ...... 61 6.7. Histogram - sites by palaeointensity method ...... 61 6.8. Geographic distribution of all palaeointensity results ...... 62 6.9. Histogram - all palaeointensity results by latitude and longitude . . . . . 63 6.10. Histogram - palaeointensity sites by age (all results) ...... 63 6.11. Histogram - number of studies by reference year (5 year intervals) . . . . 64 6.12. Histogram - number of sites published by reference year ...... 64 6.13. Histogram - number of samples collected per site (all results <12) . . . . 65 6.14. Histogram - sites by α95 value ...... 65 6.15. Histogram - sites by precision parameter κ (<4000) ...... 66 6.16. Histogram - sites by estimated bedding dip ...... 66 7.1. Error checking and update process for ICEPMAG ...... 70

x List of Tables

3.1. Relational table - Region IDs ...... 24 4.1. Master table - study details ...... 29 4.2. Master table - geographic information ...... 30 4.3. Master table - geological descriptions and data ...... 32 4.4. Master table - dating methods and data ...... 33 4.5. Master table - sampling information ...... 34 4.6. Master table - laboratory measurements ...... 34 4.7. Master table - magnetisation and susceptibility ...... 36 4.8. Master table - direction calculations ...... 38 4.9. Master table - VGP calculations ...... 40 4.10. Master table - palaeointensity ...... 43 4.11. Master table - dipole moments ...... 44 A.1. Master data ﬁelds/column names and relational tables ...... 84 A.2. Relational table - Reference IDs ...... 88 A.3. Relational table - Region IDs ...... 94 A.4. Relational table - location IDs ...... 94 A.5. Relational table - geologic class IDs ...... 101 A.6. Relational table - geologic type IDs ...... 101 A.7. Relational table - dating method IDs ...... 101 A.8. Relational table - sample type IDs ...... 101 A.9. Relational table - specimen type IDs ...... 101 A.10. Relational table - demagnetisation type IDs ...... 102 A.11. Relational table - specimen direction calculation IDs ...... 102 A.12. Relational table - sample direction average method IDs ...... 102 A.13. Relational table - site direction average method IDs ...... 102 A.14. Relational table - directional polarity IDs ...... 103 A.15. Relational table - palaeointensity method IDs ...... 103 A.16. Relational table - alteration check IDs ...... 103

Abbreviations

α 95% confidence interval after Fisher (1953) or approximation 95 (see Butler, 1998) a.s.d. angular standard deviation ARM anhysteretic remanent magnetisation avg. average calc. calculation DOI Digital Object Identifier GAD geocentric axial dipole GPMDB Global Paleomagnetic Database GPTS Geomagnetic Polarity Time Scale IAGA International Association for Geomagnetism and Aeronomy II in-field/in-field IZ in-field/zero-field ka thousand years old KTT Koenigsberger-Thellier-Thellier Ma million years old MD multi-domain MagIC Magnetics Information Consortium magn. magnetisation MSP-DB multispecimen parallel differential pTRM Myr million years NRM natural remanent magnetisation pTRM partial thermoremanent magnetisation PI palaeointensity SD single-domain σ standard deviation (or stdev.) θ63 angular standard deviation (a.s.d.), see Butler (1998) TRM thermoremanent magnetisation VADM virtual axial dipole moment VDM virtual dipole moment VGP virtual geomagnetic pole VRM viscous remanent magnetisation ZI zero-field/in-field

xiii

Acknowledgements

This work was made possible by a number of outstanding people to whom I am greatly indebted. I’d like to take this opportunity to thank: • Maxwell Brown, for his patience and encouragement, and for supervising me through this process; • Páll Einarsson, for his wisdom and guidance; • Ann Hirt, for teaching me the ways of thermal demagnetisation; • Leó Kristjánsson, for providing much of the data as a digital compilation, and whose immense body of research made this project remarkably easier; • those who started the ‘MAGIA’ database concept and lay the foundations for this work: Lauri Pesonen, Fabio Donadini, Kimmo Korhonen and Peter Riisager; • the generous contributors to the Stack Exchange forums, who led me out of the darkness on multiple occasions; • all the staff and faculty members of the University of Iceland, ETH Zürich, and the University Centre of Svalbard, especially those involved with the Nordplus exchange and Swiss-European Mobility programs, who enabled me to pursue my studies; and • finally, all the people who have opened their doors to me over the past two years, including Jo and Dave, Mariella, Giuseppe, Tomas, Valla, the Hom- burgers, the Springers, the Boujus and the Hillers, and especially Alma and Kolbeinn, who accepted my chocolate bribe and took me in out of the rain when I first moved to Reykjavík.

1. Introduction

It is generally accepted that Earth’s magnetic field is generated by convecting metal- lic fluid in its outer core (Jackson et al., 1997). The direction and strength of this field changes over time, and direct and detailed observations of these changes have been recorded since at least the 16th century, as early sailors relied on precise compass measurements for marine navigation (Jonkers et al., 2003). To obtain information about the geomagnetic field prior to historical observations, we must rely on measuring the magnetisation of rocks, sediments and archaeological artefacts. Some materials can acquire a permanent magnetisation parallel to Earth’s magnetic field at the time of their formation, and the study of this effect forms the basis of palaeomagnetism (Butler, 1998).

Lavas provide some of the best material for palaeomagnetic study. At elevated temperatures, after lavas are extruded onto Earth’s surface, the magnetic moments of ferromagnetic iron oxides contained within them statistically align with the direction of the local magnetic field, with a magnitude proportional to the field’s strength. When cooled to ambient temperatures this magnetisation, called a natural remanent magnetisation (NRM) or in this case a thermal remanent magnetisation (TRM), can be preserved up to billions of years (Butler, 1998). In a laboratory, measurements of the direction and strength of this magnetisation can be made and, with prior orientation of the lava sample in situ, used to infer the characteristics of the palaeomagnetic field.

Sequences of such lavas (e.g., Fig. 1.1) are particularly abundant in Iceland - a landmass built up by quasi-continuous eruptive activity over the past sixteen million years (Wilson et al., 1972). Iceland is unique in its proximity to a volcanic hotspot and an actively spreading tectonic plate boundary, and represents the only well- exposed section of the mid-Atlantic ridge (Watkins and Walker, 1977). Iceland’s landmass is composed of extensive piles of ﬂood basalts which generally tilt towards the central spreading ridge. The oldest lavas exist in the northwest and eastern regions of the country, away from active volcanic centres along the length of the ridge, as shown in Fig. 1.2. The basaltic lava piles are often exposed in deep vertical sequences as a result of glacial and hydraulic erosion and subsequent uplift (Watkins and Walker, 1977). Due to its remarkable formation, as well as a sparse population, low vegetation cover and minimal exposure to geological inﬂuences, such as mineral alteration and tectonic upheaval, Iceland presents an ideal location for

1 1. Introduction studying long-term palaeomagnetic ﬁeld variations.

Figure 1.1: A well-exposed sequence of lavas in Lundarháls, western Iceland, photo taken by J. Tonti- Filippini, 19th June 2018.

The scientific potential of the palaeomagnetic archive preserved in Icelandic lavas began to be realised in the 1950s, as the field of palaeomagnetism found its feet. Since that time, palaeomagnetic research in Iceland has produced results from over 9,200 lavas, one of the world’s largest collections of palaeomagnetic data from a single location. These data have proved to be vital for understanding the behaviour of the palaeomagnetic field, as Iceland is one of only a few high latitude (>60◦) locations where lavas suitable for palaeomagnetic research are exposed. Data from Iceland have contributed to the development of several concepts fundamental to modern geoscience. However, palaeomagnetic data from Iceland have not previously been compiled into a comprehensive and easily accessible database, and, at the time of writing, only 2,634 sites from Iceland have been incorporated into the global palaeomagnetic database, MagIC (see Section 2.3.1).

In this thesis, I describe the design and application of ICEPMAG, the Iceland Palaeo- magnetism Database, which is intended to promote the use of Icelandic paleomagnetic data in global analyses of paleomagnetic ﬁeld behaviour. Statistical analyses of data from Icelandic lavas, discussed in later sections, have shown that relatively few samples are required to determine accurate palaeomagnetic ﬁeld directions due to strong magnetisation and minimal tectonic disturbance. However, when compiling global palaeomagnetic datasets, Icelandic data can be overlooked as blanket

2 Figure 1.2: Geological map of Iceland - bedrock classified by age, with regions and major towns and roads, Haukur Jóhannesson and Kristján Sæmundsson, 2009, courtesy of Opendata: http://www. ni.is/rannsoknir/landupplysingar/skilmalar Licence, according to article 31 of Act on Information no. 140/2012 Náttúrufræðistofnun Íslands – Icelandic Institute of Natural History, as adapted by Conor Graham, Centre for GIS and Geomatics, Queen’s University Belfast, 27th January 2018. criteria are often applied to filter the quality of data (e.g., Cromwell et al., 2018). Recommended thresholds for these reliability criteria, usually based on studies of lavas from other parts of the world, can be set higher than necessary for Icelandic lavas, potentially excluding some significant data.

Iceland’s lavas have also been somewhat underutilised in the study of palaeointensity variations, i.e. long-term variations in palaeomagnetic field intensity and field behaviour during excursions, transitions and reversals. An extensive and well-stratified lava pile presents rare opportunities to study long sequences of palaeointensity variations, however, to date relatively few palaeointensity studies have been carried out in Iceland. This is likely due in part to the low success rate for palaeointensity measurements in Iceland - also discussed in later sections. There are 555 sites in the ICEPMAG database which report palaeointensity measurements, and only 337 of these report both intensity and direction (i.e. 218 sites report palaeointensity but not direction).

The project detailed in this document was proposed to compile all available palaeomagnetic data from Icelandic lavas into a single location and make this information publicly available. This was achieved by combing published journal articles, aca-

3 1. Introduction demic theses and other palaeomagnetic databases, and organising collected data into a consistent format. ICEPMAG is accessible through an interactive website which allows users to query and plot data using customisable ﬁlters. Data collected are also to be uploaded into MagIC; contributing an additional 50 studies (and 6,570 sites) to the global database.

4 2. Background

2.1. Overview of palaeomagnetism

2.1.1. Early history (pre 18th century)

Known descriptions of natural magnetism date back to the Ancient Greeks in the sixth century B.C., with speculation about the mysterious properties of magnetic lodestones - Courtillot and Le Mouël (2007) provides an excellent report of the history of geomagnetism and palaeomagnetism prior to the 20th century, which is briefly summarised in this section. The Chinese developed some of the earliest compasses between the first and sixth century A.D., but the technology was not developed in Europe until the mid-twelfth century. Research of the time culminated in Petrus Peregrinus’s ‘Epistola de Magnete’ in 1269, still considered to be one of the most significant advances in scientific magnetism. Using a sphere carved from a lodestone, Peregrinus demonstrated the concept of magnetic poles, i.e. that lines drawn in alignment with the stone’s magnetic field will meet at two exactly opposed points (the north and south poles), just like the meridian lines of Earth. However, Peregrinus did not suggest that Earth itself could contain a giant magnetic dipole, proposing rather that magnetic materials align with the north celestial pole “of the sky” (Courtillot and Le Mouël, 2007).

While debated even before the time of Peregrinus, the idea that the source of the magnetism observed on Earth’s surface could be internal and not “heavenly” did not take hold until late in the 16th century. Most notably, William Gilbert sought to cement this idea in his treatise ‘De Magnete’ in 1600, observing the behaviour of magnetised needles suspended around a terrella (Courtillot and Le Mouël, 2007). This period also witnessed increased acknowledgement of the concepts of magnetic variation or ‘declination’, i.e. that there is a diﬀerence in horizontal angle between the direction of magnetic north (indicated by the orientation of a compass needle) and geographic north (Earth’s rotational pole), and ‘inclination’, i.e. that the magnetic ﬁeld’s angle of dip varies with distance from the pole (as realised by the behaviour of the needles suspended around Gilbert’s terella, and Peregrinus’s lodestone). Jonkers et al. (2003) details the development of the concepts of declination

5 2. Background and inclination, motivated by the needs of marine navigators who began to observe changes in the declination of their compasses across locations as early as the 15th century.

Gilbert, among many others, believed that the locations of the rotational (geographic) and magnetic poles had to agree and did not change over time, attributing observed inconsistencies in declination to crustal anomalies, such as mountains and ocean basins, as he believed that Earth’s magnetisation derived from its crust. In contrast, one of Gilbert’s students, Mark Ridley, suggested that apparent dependence of measured inclination on latitude indicated a source towards the centre of the planet and not in the crust. Guillaume le Nautonier, one of Gilbert’s contempo- raries, believed that the anomalies in declination were global in scale and estimated that Earth’s magnetic dipole was actually oﬀset, or tilted away, from its rotational axis. le Nautonier’s model, although crude, eventually proved to be superior to Gilbert’s as a ﬁrst-order approximation (Courtillot and Le Mouël, 2007).

Continuation of detailed observations in the following decades showed that Earth’s magnetic field is much more complicated than what can be explained by a simple dipolar model, titled or otherwise. Systematic measurements also indicated that the declination and inclination of Earth’s magnetic field did not just vary in space, but also in time. The discovery of this ‘secular variation’ of the magnetic field, and the establishment of the first dedicated magnetic observatories, fuelled much speculation and theorising about possible source mechanisms throughout the seventeenth century. Perhaps the most promising theory developed in this century was proposed in 1692 by Edmond Halley, who suggested that Earth may consist of two concentric magnetic shells, separated by a fluid and rotating at different speeds, one being an outer shell fixed to the crust and the other being some solid nucleus or core deep in Earth’s centre (Courtillot and Le Mouël, 2007).

2.1.2. The birth of palaeomagnetism (18th to 20th century)

The eighteenth century saw more significant progress in geomagnetism: global magnetic surveys produced the first charts for global declination and inclination; shorter-term variations and patterns (diurnal and seasonal) in the magnetic field were recognised and linked to external sources (e.g., polar aurora); and Charles- Augustin Coulumb developed the quantitative law of magnetic attraction in 1785 (Courtillot and Le Mouël, 2007). The roots of palaeomagnetism began to take hold as scientists wondered about the past behaviour of the geomagnetic field, and speculated that information about this behaviour may be acquired from the magnetisation of rocks. Perhaps most notably, during a survey in 1797, Alexander von Humboldt discovered rocks on a mountaintop in the Palatinate of south-west Ger- many that were magnetised in “widely scattered” directions (Frankel, 1987). von

6 2.1. Overview of palaeomagnetism

Humboldt was already interested in terrestrial magnetism, having previously found a rock magnetised with a direction opposite to the present day field, and was using a compass to map magnetic anomalies near a mountain summit (Courtillot and Le Mouël, 2007). von Humboldt continued his work on geomagnetism into the nineteenth century, famously documenting a consistent decrease in the total magnetic field strength (or intensity) from the poles to the equator during a voyage to South America (Cour- tillot and Le Mouël, 2007). The concept of measuring relative intensity was still a novelty at the time, despite the effect (of stronger magnetisation at magnetic poles) being known at least since the days of Peregrinus and his lodestone. von Humboldt would later advocate for establishing a worldwide network of magnetic observatories, which stimulated his subsequent collaboration with Carl Friedrich Gauss (Courtillot and Le Mouël, 2007). Gauss would become a giant in the history of geomagnetism, devising the mathematical infrastructure needed to describe geomagnetic field measurements, which had developed to contain the full vector (declination, inclination and intensity).

While the field of geomagnetism was well advanced by the 1850s, palaeomagnetism was still in its infancy. Some prominent advances had been made by Joseph Fournet and Achille Joseph Deless; in 1848, Fournet published an essay detailing experiments carried out on various magnetic ores and rocks, with detailed descriptions for the properties of each mineral, and distinguished a difference between ‘induced’ magnetisation, i.e. temporary magnetisation of a material which aligns with an applied field, and ‘remanent’ magnetisation, i.e. magnetisation which persists after the applied field has been removed (Courtillot and Le Mouël, 2007). Another important contribution was made by Macedonio Melloni in 1853, who had experimented on lavas from Mount Vesuvius. Melloni found that the lavas would lose their magnetisation upon heating and then, upon cooling, acquire a permanent magnetisation in alignment with the present day field. From this he deduced that lava flows should preserve the state of Earth’s magnetic field at the time of their eruption (Courtillot and Le Mouël, 2007).

Early in the twentieth century, Bernard Brunhes, a French geophysicist and one of the earliest pioneers of palaeomagnetism, made a discovery which initiated more than half a century of scientific controversy. With knowledge of the work of Melloni, as well as Giuseppe Folgheraiter (who in 1894 had extended Melloni’s findings to other magnetic rocks), Brunhes realised he could determine past field directions by measuring the magnetisation of rocks (Courtillot and Le Mouël, 2007). In his subsequent research, published in 1906, Brunhes made a crucial observation that some rocks could be magnetised in a direction opposite to the present-day magnetic field (see Brown, 2010). From this, he reasoned that Earth’s magnetic field must have been reversed when the rocks were formed, i.e. what is currently the magnetic north pole must have been the magnetic south pole at some time in the past. Disagreement

7 2. Background over Brunhes’s finding and its implications would continue until after World War II, when palaeomagnetism realised its global significance in Earth Science, a chapter in which the magnetised lavas of Iceland played a significant role (Frankel, 1987).

2.2. Palaeomagnetism in Iceland

Early explorers of Iceland had made observations of anomalous compass behaviour during their travels, an effect similarly observed by von Humboldt in the Palati- nate. In 1753, during the first known ascent of the Snæfellsjökull volcano in western Iceland, Eggert Ólafsson and Bjarni Pálsson noted the erratic behaviour of their compass needle (Kristjánsson, 1982). The high concentration of magnetic iron oxides (i.e. magnetite or titanomagnetite) in Icelandic lavas and intrusions means that these bodies are strongly magnetic, enough to cause rotation of a compass needle when placed nearby (Einarsson and Sigurgeirsson, 1955). This may have resulted in the erratic behaviour of Ólafsson’s and Pálsson’s compass needle. Paul de Løvenørn, a Danish naval officer and cartographer, suggested such an explanation for the unstable directions of his compass when visiting Icelandic ports during a voyage in 1786 (Kristjánsson, 1982). Although not a useful effect for sailors, the variability of a compass needle when placed next to a lava was utilised by scientists over 150 years later in mapping out lavas of similar age across Iceland - this is revisited later in the chapter.

Frankel (1987), Merrill and McElhinny (1983) and Kristjánsson (1982, 1993), summarised below and supplemented with other citations as appropriate, detail the rise of palaeomagnetism in Iceland and the contributions of Jan Hospers, among others, to its early development after his arrival in 1949. A young postgraduate student at the time, Hospers was the ﬁrst to publish an extensive palaeomagnetic study of Icelandic lavas. Since then the lavas of Iceland have yielded a signiﬁcant amount of palaeomagnetic data and contributed to several discoveries in the advancement of continental drift and plate tectonic theory, some of the foundations of contemporary geoscience.

2.2.1. Early developments (1920s to 1960s)

Although Jan Hospers is often attributed with the discovery of some key concepts in palaeomagnetism, including the first detailed demonstration of geomagnetic field reversals, he wasn’t the first to test these theories, even in Iceland (Frankel, 1987). Following the work of Brunhes and others, Paul Louis Mercanton speculated that if Earth’s magnetic field had reversed, then rocks with a reverse magnetisation should

8 2.2. Palaeomagnetism in Iceland be found all over the world. Mercanton (1926) obtained samples from Iceland, the Faroe Islands, East Greenland, Spitsbergen, Mull (Scotland), Jan Mayen Land and Australia, and observed that the directions of magnetisation did not correspond to the present geomagnetic field conditions - some aligned with the present field and others were roughly reversed from it (Merrill and McElhinny, 1983). Around the same time, Motonori Matuyama observed a similar effect in lavas from various parts of Northeast Asia, noticing that younger rocks tended to be normally magnetised while older rocks could be reversely magnetised. From this he inferred that polarity may depend on age, and agreed with Mercanton’s findings that at several times in the past Earth’s magnetic field “was probably in a greatly different or nearly opposite state” (Matuyama, 1929). Raymond Chevallier had also visited Iceland in the 1920s but sampling was limited and the potential of Iceland’s basalts for palaeomagnetic studies was not fully appreciated for another twenty years (Kristjánsson, 1993).

The timing and objectives of Hospers’s visit to Iceland were quite fortuitous. While enrolled to obtain his PhD at Cambridge University, Hospers found himself accom- panying M. G. Rutten and R. W. van Bemmelem, whom he had studied under at the University of Utrecht (Netherlands), on a trip to study the volcanology and tectonics of Iceland. van Bemmelem, whose father had worked on establishing base- line measurements for ‘secular variation’ of the magnetic field in 1893 by analysing marine navigation records from 1540-1680, suggested that Hospers may be able to correlate the notoriously difficult Icelandic lavas by measuring differences in their palaeomagnetic intensities, as determined by the strength of their natural remanent magnetisation or ‘NRM’ (Frankel, 1987).

During a mapping campaign from Akureyri to Mývatn (central northern Iceland) in 1950, Hospers collected 25 lava samples for palaeomagnetic measurements, typically with only one sample per flow (Kristjánsson, 1982). (Coincidentally, Alfred Wegener, in preparation for his crossing of Greenland, had led an expedition across similar territory from Akureyri to Vatnajökull in 1912, the same year he had first presented his ideas about continental drift, but did not publish any observations about Iceland’s geology (Kristjánsson, 2001).) Specimens from the first campaign were measured at the Imperial College in London, with calculations of both “direction and intensity of magnetisation” (Hospers, 1953). In 1951, Hospers collected another 633 hand samples which he took back to Cambridge to measure on a small astatic magnetometer. As a precaution, in the event his specimens disintegrated during transport, Hospers also analysed specimens in the field, where possible, using a portable vertical force balance to measure the direction of their vertical component (Hospers, 1953).

Assuming each specimen preserved some past orientation of the geomagnetic dipole, Hospers wanted to convert the measured direction of each specimen (declination and inclination) into a corresponding virtual geomagnetic pole (VGP) on Earth’s surface, and plot the migration of poles over time (this concept is revisited in Section

9 2. Background

4.9). To help describe his results, Hospers was referred to Sir Ronald Fisher who had previously worked on (but not published) a method of spherical statistics in the 1920s (Merrill and McElhinny, 1983). Fisher provided the necessary calculations after hearing about the problem from his Cambridge colleague and friend (and Hos- pers’s unoﬃcial supervisor), Keith Runcorn (Frankel, 1987). Fisher used Hospers’s measurements of remanent magnetisation from Icelandic lava ﬂows as an example when he later published his method in a landmark paper (Fisher, 1953) - a method which still widely utilised today.

Hospers, with Fisher’s help, became the ﬁrst to calculate pole positions from palaeomagnetic directions. Hospers also introduced the geocentric axial dipole (GAD) hypothesis: “that the mean position of the magnetic poles (taken over a period of several thousand years) coincides with the geographic poles” (Hospers, 1955). The concepts of polar wander, i.e. migration of the magnetic poles over geological time, and continental drift, i.e. movement of continents with respect to ﬁxed magnetic poles, had received much attention since being popularised by Wegener in 1912. Hospers concluded that the amount of polar wandering suggested by Wegener and others “cannot be reconciled with the new data” (Hospers, 1955). (However, the apparent validity of the GAD hypothesis, as tested on Icelandic lavas, would later become crucial for testing the ideas of continental drift - this is revisited later in the section.)

Hospers’s samples also contained key evidence for reverse magnetisation which, along with others of the time from France (Roche, 1951, 1953, 1956, 1958) and western Turkmenistan (Khramov, 1958), were used to confirm Brunhes’s initial observations and convinced many scientists of the reality of geomagnetic field reversals (Frankel, 1987). A self-reversal mechanism in some ferromagnetic minerals had been popularised following the discovery of a particular rock type in Japan - this turned out to be a rare phenomenon but fuelled arguments against magnetic field reversals for some time (Brown, 2010). Hospers concluded “that only the assumption of a repeatedly reversing magnetic field can satisfactorily account for the observations” (Hospers, 1953).

During his second visit, in 1951, Hospers worked with Icelandic scientists, Trausti Einarsson and Þorbjörn Sigurgeirsson, who continued to build on palaeomagnetic research in Iceland. Sigurgeirsson realised that an ordinary compass could be used to measure the polarity of Icelandic lavas and, beginning with Einarsson in 1953, subsequently mapped thousands of lava flows (Kristjánsson, 1982). Einarsson and Sigurgeirsson published their first paper on palaeomagnetism in 1955 (Einarsson and Sigurgeirsson, 1955; Einarsson, 1957), confirming and extending many of Hos- pers’s results, and anticipating several outcomes of later rock magnetic research on Icelandic basalts (Kristjánsson, 1993).

The two Icelandic scientists continued their palaeomagnetic research after 1955.

10 2.2. Palaeomagnetism in Iceland

Einarssion began mapping polarity zones for various parts of Iceland, intending to use them as a geological mapping aid, assigning N (normal) or R (reverse) to each zone and numbering them backwards in time (Kristjánsson, 1993). This novel geochronological technique was the same concept behind later development of the global Geomagnetic Polarity Time Scale (GPTS), i.e. the idea that long sequences of alternating magnetic polarity across layers of rocks and sediments could be used as a kind of unique stratigraphic ‘barcode’ to assist in geological age determination (see Tauxe, 2010, chap. 14).

During the polarity mapping campaign it was realised that a lava’s primary remanence may be affected by a secondary component, as the directional measurements became more difficult to make as the age of the lavas (and amount of alteration) increased (Kristjánsson, 1982). A secondary magnetic component can be acquired over time and mask the true direction of the primary component captured in a rock during emplacement. In order to obtain more accurate remanence measurements, Sigurgeirsson worked with an Icelandic physics student, Ari Brynjolfsson, to design a 5-Hz spinner magnetometer to measure the direction and intensity of magnetisation in basaltic lava samples (Brynjólfsson, 1957). Prior to measurement the samples were subjected to ‘alternating field’ (AF) demagnetisation in a one-axis demagnetisation apparatus; Brynjólfsson (1957) showed that a secondary component of ‘viscous remanent magnetisation’ (VRM) could be removed by partial demagnetisation, iso- lating the primary component. VRM can be acquired by some minerals subjected to a external field (e.g., Earth’s magnetic field) for a long period of time (e.g., millions of years). Despite earlier work on demagnetisation of rocks in other parts of the world, “this seems to have been the first successful demonstration that a stable primary remanence direction was being isolated by the AF technique” (Kristjánsson, 1993).

This pioneering work enabled Sigurgeirsson to study intermediate or transitional directions (i.e. low-latitude VGPs) found at the boundaries of polarity zones. Such detailed study allowed for the calculation of ‘pole paths’, “indicating a definite path followed by the magnetic pole during the reversal of the magnetic field” (Sigurgeirs- son, 1957), with the assumption that the geomagnetic field maintains its dipolar nature during reversals. Sigurgeirsson’s illustration of the “R3-N3” reversal, measured in the mountains of the Hvalfjörður area, was probably the first of its kind anywhere in the world, and also suggested that the field was weaker during a polarity transition (Kristjánsson, 1993). The measurements from Hvalfjörður proved to be important evidence for the long-term behaviour of the geomagnetic field, and “was one of the very few known sites in the world for a decade or more to yield details on geomagnetic transitions” (Kristjánsson, 1982).

The work of Hospers, Einarsson, Sigurgeirsson and Brynjólfsson provided a basis for many key palaeomagnetic methods and concepts, and particularly strong evidence for reversals of Earth’s magnetic ﬁeld, which contributed to a major paradigm shift

11 2. Background in Earth science. The field of palaeomagnetism perhaps realised its greatest significance in the 1950s and 60s, as geophysicists sought to reconcile Wegener’s fossil evidence for seafloor spreading and continental drift with the new palaeomagnetic techniques now available to them. Apparent validation of the GAD hypothesis, as demonstrated by Hospers, allowed geophysicists to approximate past locations and movements of continents with respect to fixed magnetic poles. This, as well as detailed topographic and magnetic polarity mapping of the bottom of the ocean, provided some of the key evidence for seafloor spreading; identification of symmetri- cal normal and reversed polarity zones around the mid-ocean ridge, which could be correlated into a global GPTS (e.g., Cande and Kent, 1992; Ogg, 2012), eventually led to widespread acceptance of Wegener’s ideas and advancement of plate tectonic theory.

The idea that palaeomagnetism could be used to test the concepts of polar wandering and continental drift had been raised by Mercanton in the 1920s and repeated by others, but no-one had mentioned any speciﬁc ideas about how this could be done (Frankel, 1987). The pioneering studies and novel palaeomagnetic observations carried out in Iceland proved to be somewhat pivotal for acceptance of Wegener’s theory. Iceland’s geographic stability and lack of continental drift enabled this, as the long-term nature of Earth’s magnetic dipole, and its apparent relationship to the rotational pole, could be accurately analysed. Somewhat ironically, Hospers dismissed the concept of continental drift during his research in Iceland and concluded that his measurements contradicted the theory of polar wandering, although he recognised “...that Iceland plays no signiﬁcant role in Wegener’s theory and is not suitable as a testing ground” (Hospers, 1953).

2.2.2. Palaeodirectional work (1964 to 2018)

Numerous palaeomagnetic studies have been carried out in Iceland since the pioneering work of the 1950s. Kristjánsson (2013) divides the major collections of palaeomagnetic samples into three time periods, based generally on the number of samples collected per flow: • 1964-65 (∼ 2 samples per flow) • 1972-79 (≥ 3 samples per flow) • 1980-2012 (≥ 4 samples per flow) While some palaeomagnetic research was continued by Sigurgeirsson, Rutten, Wensink and others in the late 1950s and early 60s (e.g., Rutten and Wensink, 1959; Rutten, 1960; Wensink, 1964), the 1964-65 campaign produced the first major collection of samples for palaeomagnetic purposes in Iceland. Led by Rod Wilson (University of Liverpool), at the suggestion of George Walker (Imperial College),

12 2.2. Palaeomagnetism in Iceland mapping and drill-core sampling (at two samples per flow) were carried out for 300 lava flows in Southwest Iceland and 1100 flows in East Iceland over two years. (The field teams also included S. E. Haggerty, P. J. Smith, P. Dagley, N. D. Watkins, J. Edwards and L. Kristjánsson (Kristjánsson, 1993).) For many years, the East Ice- land collection represented one of the largest collected for palaeomagnetic purposes anywhere in the world and “the most comprehensive source of data from a single region on long-term (0.1 - 10 Myr) variations of the geomagnetic field” (Kristjánsson, 1985b). Measurements from the campaign, performed mostly at Imperial College and Liverpool University (with some remanence measurements in Reykjavík), along with supplementary sampling in 1967 and 1973, generated numerous papers and theses (Kristjánsson, 1993).

Initial results from the 1964-65 East Iceland collection were published by Dagley et al. (1967), with details later published by Watkins and Walker (1977). The results from Southwest Iceland were never published in detail (Kristjánsson and Jónsson, 2007). Accomplishments of the campaign include: confirmation of reversals between 2 - 13 Ma; application of reversals in stratigraphy across 10 km or more; and demonstration of long-term dependence of virtual dipole moment (VDM) upon VGP latitude (Kristjánsson, 2008) - the VDM concept is discussed in Section 4.11. However, Kristjánsson (2002) considers that the low number of samples collected per flow limits the statistical significance of these results, and that the directional results “may also contain some systematic errors, as a movement of the mean pole indicated by them has not been confirmed in subsequent studies”.

Watkins returned for more field work between 1972 - 79, focussing on the lava piles of north-western Iceland, intending to expand the GPTS (Watkins, 1972). Samples taken from about 2,400 flows (generally 3 cores per flow) were analysed at the Univer- sity of Rhode Island and, in collaboration with Ian McDougall from the Australian National University, the results included many K-Ar age determinations (Kristjáns- son, 1993). Studies published from the results (e.g., McDougall et al., 1977, 1984), extended the GPTS to over 6 Ma, with improvements in the age boundaries and the addition of several reversal events.

A number of valuable statistical studies were also carried out on the measurements (e.g., Harrison, 1980; Kristjánsson and McDougall, 1982; Kristjánsson, 1985b; Kristjánsson and Jóhannesson, 1989). These studies yielded some conclusions that were at odds with conventional notions of the time regarding the long-term nature of the geomagnetic ﬁeld, e.g., the average rate of reversals observed in Icelandic data was at least 8/Myr but other estimates, based on oceanic anomaly inversions (like those in the global GPTS), indicated only ∼5/Myr during the past 15 Myr (Kristjánsson, 1985b). This suggested that the oceanic record may not be observing the full range of variations exhibited by the ﬁeld.

Field work from 1980 to 2012 included several large stratigraphic projects involv-

13 2. Background ing hundreds of lavas each (over 3,000 in total), as well as many smaller projects (Kristjánsson, 2013). After being generally adopted for the 1979-1980 Reyðarfjörður collection in East Iceland (Helgason, 1982), at least 4 samples for each flow were collected. This is considered adequate for unaltered Icelandic lavas as the values of 95% confidence radii (α95) are generally <5° for this number of samples (Kristjánsson, 2013) - this is discussed further in Section 6.4. Recent campaigns have generally targeted areas away from the main volcanic centres in order to avoid hydrothermal and tectonic disturbances. Samples have also been demagnetised to confirm the stable remanence direction, with replacement samples collected for any that are magnetically unstable or severely incongruous (Kristjánsson and Jónsson, 2007).

Results from palaeomagnetic studies carried out in Iceland after 1980 have confirmed many of the earlier findings (Kristjánsson and Jónsson, 2007). Since 1980 the major objectives of studies in Iceland have been to: • improve controls for local stratigraphic mapping and/or extend the length of the GPTS (e.g., Kristjánsson et al., 1980; McDougall et al., 1984; Helgason and Duncan, 2001; Kristjánsson and Jóhannesson, 1996; Kristjánsson et al., 2004); or • further characterise reversals, excursions and other variations of the palaeomagnetic field (e.g., Levi et al., 1990; Tanaka et al., 1995; Kristjánsson, 1999; Udagawa et al., 1999; Jicha et al., 2011). Kristjánsson (2013) analysed a collection of 5,200 stable lava flows of 1 - 16 Ma age, sampled in Iceland between 1973 and 2012, suitable for statistical studies. The database contains “optimally AF-cleaned remanence directions, arithmetic average remanence intensities (after 10 mT treatment) and estimated ages”. These data are supplemented by a further 200 - 600 lavas which are not used in all analyses, either for their lack of intensity information or 95% confidence radii in excess of 12 - 15°.

Estimated ages of the sampled lavas in the Icelandic dataset compiled by Kristjáns- son (2013) have a reasonably even distribution: 29% are 1 - 6 Ma old, 40% are 6.5 - 12 Ma, and 31% are 12.5 - 16 Ma. The mean remanence direction of accepted lavas has a declination D = 3° and an inclination I = 75.1°, and the frequency distribution of VGP latitudes is “smoothly continuous” (Kristjánsson, 2013).

As concluded previously by Kristjánsson and McDougall (1982), there do not ap- pear to be any preferred pole paths during polarity transitions during the past 16 Myr, as the distribution of longitudes in mid to low latitude VGPs is fairly evenly spread in the Icelandic dataset (Kristjánsson, 2013). The concept of preferred pole paths is controversial; several studies in the early 1990s (e.g., Laj et al., 1992; Con- stable, 1992), identified a bias in the distribution of transitional VGPs towards two antipodal longitude bands. The potential existence of these preferred pole paths has significant implications for understanding of the nature of the geomagnetic field and

14 2.2. Palaeomagnetism in Iceland the processes which generate it (e.g., the motion of conductive fluid in the core of the ‘geodynamo’ and conditions at the core-mantle boundary). If realistic, this bias would suggest that the “mantle exerts a significant control over the reversal process” (McFadden et al., 1993) and requires a physical explanation. Laj et al. (1991) suggested a link between the preferred pole paths and regions of “fast seismic-wave propagation (and therefore low temperature) in the lower mantle”. Exactly how and why reversals occur, and the potential influence of mantle processes, is a topic that is still subject to considerable debate (e.g., Valet and Fournier, 2016; Brown et al., 2018; Hounslow et al., 2018).

It is shown that primary remanence intensities calculated from Icelandic lavas can be averaged to estimate local variation in mean field intensity as a function of VGP latitude (Kristjánsson, 2013): the mean field intensity from the Icelandic dataset is shown to decrease by a factor of about 4 when the virtual geomagnetic pole (VGP) moves from polar to equatorial regions. This is quite remarkable and suggests a strong relationship between field intensity (NRM intensity after 10 mT cleaning) and directional stability. However, a comparable assessment of “mean palaeo-field intensities” (or absolute palaeointensity) versus VGP latitude is more problematic (Kristjánsson, 2013).

Also considered by Kristjánsson (2013) is the subject of long-term variations in the rate of polarity reversals and the magnitude of the dipole moment. This is another topic over which consensus has not yet been reached (e.g., Valet et al., 2005; Consta- ble and Korte, 2006; Buﬀett and Davis, 2018). This also has signiﬁcant implications for our understanding of deep Earth processes and estimating the likelihood of a reversal in the near the future. A trend in the angular standard deviation (a.s.d.) values for remanence directions and VGP positions was previously observed in Ice- landic data over the past 16 Myr (Kristjánsson and Jóhannesson, 1989), suggesting a long-term decrease in the angular amplitude of secular variation. Despite further studies of Icelandic data (e.g., Kristjánsson, 1995; Kristjánsson et al., 2003), little evidence for this has been observed elsewhere, which may be due to the “general inadequacy of available worldwide volcanic palaeomagnetic data to address some fundamental issues of this nature” (Kristjánsson, 2013).

Since 2013, work has continued on the magneto-stratigraphy and geochronology of Iceland (e.g., Helgason and Duncan, 2013, 2014), as well as the production of regional magnetic polarity maps (e.g., Helgason et al., 2015; Helgason, 2016). Kristjánsson (2014, 2015, 2016) conducted several palaeomagnetic studies in north-west Iceland, targeting major excursions and polarity transitions, which will aid future geological mapping of the peninsula, where relatively little geological research has been carried out. Døssing et al. (2016) targeted a transitional event in north-east Iceland to obtain “high-standard paleodirectional and paleointensity data” from a high-northern latitude. Pinton et al. (2018) reported on paleomagnetic dating of Holocene lava ﬂows from south-west Iceland.

15 2. Background

2.2.3. Palaeointensity studies

Absolute palaeointensity, as distinct from the NRM intensity or ‘strength’ of a rock’s magnetisation discussed in Section 2.2.1, refers to the intensity of the geomagnetic field at some point in the geological past. Assuming that the remanent magnetisation of a volcanic rock is linearly proportional to the ambient field in which it cooled (and that this proportionality remains constant), it should be possible, in principle, to determine the intensity of an ancient magnetic field (see Tauxe and Yamazaki, 2007). This proportionality will vary naturally from rock to rock, but by heating a rock in a known laboratory field and then measuring the rock’s artificially acquired remanence (or laboratory remanent magnetisation) once cooled, one can obtain the proportionality constant for that rock. With these assumptions and knowledge of both the proportionality constant and the laboratory field, it is possible to infer the strength of the ancient field in which the rock cooled. Of course, in reality, this is not so easy; Valet (2003) provides an excellent review of palaeointensity methods.

Only a comparatively small number of studies have investigated absolute palaeointensity in Iceland (e.g., Schweitzer and Soffel, 1980; Marshall et al., 1988; Gogu- itchaichvili et al., 1999c; Brown et al., 2006; Ferk and Leonhardt, 2009; Camps et al., 2011; Stanton et al., 2011; Tanaka et al., 2012). These palaeointensity studies built on the earlier work of Smith (1967b), who found good material for studying palaeomagnetic field intensities during the 1964 - 65 campaign and published the first palaeointensity determinations on Icelandic lavas (Kristjánsson, 2013). Recent studies on palaeointensity determinations, which since the 1970s have focused mainly on the strength of the transitional field, have seen a shift towards palaeointensity variations of the stable field (e.g., Cromwell et al., 2015; Døssing et al., 2016; Tanaka and Yamamoto, 2016). Relevant palaeointensity studies are discussed further in Section 4.10.

Absolute palaeointensity determinations are important for constraining models of the geodynamo and the evolution of geodynamic processes over geological timescales, as the strength of the ﬁeld is intrinsically linked to deep Earth processes. Absolute palaeointensity measurements from volcanic records are also particularly important for calibrating and correlating long continuous records of relative palaeointensity, such as those taken from sediment cores from the ocean ﬂoor, with which absolute determinations are not possible (Valet et al., 2005).

However, absolute palaeointensity determinations are technically challenging and time-consuming, with a typical success rate in the order of 10 to 20% (Valet, 2003). Palaeointensity in Iceland has been particularly diﬃcult; with respect to lava piles in other parts of the world, Iceland’s basaltic lavas have a relatively low oxidation state and alter “all too readily during the necessary laboratory heating” (Roberts and Shaw, 1984).

16 2.3. Existing palaeomagnetic databases

Many of the palaeointensity studies in Iceland have been carried out on samples from areas close to the central volcanic zones or glaciated areas (see Section 6.3). Older rocks, such as those in the Westfjords region, may be more suitable for palaeointensity, however, to date nobody has trialled palaeointensity on rocks from north-west Iceland. Choosing materials with rock magnetic properties suitable for palaeointensity is another approach that may be fruitful in Iceland, e.g., volcanic glass (Cromwell et al., 2015).

The global dataset for absolute palaeointensity determinations remains sparse both temporally and spatially. Kristjánsson (2013) states that significant between-site and within-site scatter is observed in Icelandic (and global) palaeointensity datasets, and suggests that more dedicated research and the adoption of a more stringent set of quality criteria is needed. High failure rates and large uncertainties plague palaeointensity measurements, which are heavily affected by: chemical alteration (both in situ and during laboratory heating); discrepancies between laboratory and natural cooling rates; and ‘multi-domain’ (MD) behaviour of grains, as opposed to ‘single-domain’ (SD) behaviour (Michalk et al., 2008). Various methods have been devised to eliminate or minimise these effects; a more detailed discussion of absolute palaeointensity methods is provided in Section 4.10, in regards to the metadata accommodating the ICEPMAG database.

2.3. Existing palaeomagnetic databases

In the early 1960s, as the ﬁeld of palaeomagnetism realised its importance in the development of Earth science, the need for global databases emerged in order to couple palaeomagnetic and radiometric dating information. Early ‘pole catalogues’ combined with age information (e.g., Khramov, 1971, 1979; Irving et al., 1976; McEl- hinny and Cowley, 1977), allowed for testing of key concepts such as the geocentric axial dipole (GAD) hypothesis, continental drift, polarity reversals, excursions and other long-term variations of the geomagnetic ﬁeld (Veikkolainen et al., 2014). The need to link palaeomagnetic data with data from other Earth sciences led to the generation of modern relational databases from the late 1980s onwards (e.g., Peso- nen and Torsvik, 1989; Barton, 1991; McElhinny and Lock, 1991; Tanaka and Kono, 1994). Summaries of the main global palaeomagnetic databases currently active are provided below.

17 2. Background

2.3.1. Magnetic Information Consortium (MagIC)

In 2003, a prototype for an online palaeomagnetism database was developed by the Magnetics Information Consortium (MagIC), taking advantage of faster computers with larger storage capabilities (Tauxe et al., 2016). MagIC (https://www2.earthref. org/MagIC/) is an online relational database for palaeomagnetism, the goal of which is store all measurements and their derived properties for studies of palaeomagnetic directions (inclination, declination) and their intensities, as well as information on rock magnetism. The service relies on user contributions, as well as uploads from an internal project team. MagIC is built around a hierarchical system of (in de- scending order): contributions, locations, sites, samples, specimens, experiments and measurements. The database is capable of retaining data down to the lab measurement level (the direct output of laboratory equipment), and holds over four million of these individual measurements. The overriding concept is to organise data by publication.

ICEPMAG, in contrast, only contains down to the third hierarchical level (or ‘site’ level), with some limited sample and specimen level information. At the time of writing, MagIC contains over 4,100 contributions worldwide, with data from over 153,000 individual sites. It currently holds 27 contributions from Iceland, with information from 2,634 sites. The structure of MagIC and how it relates to this project is discussed in Section 3.1.2.

2.3.2. GEOMAGIA50 Paleomagnetic Database

GEOMAGIA50 (http://geomagia.gfz-potsdam.de/), originally released in 2006, aims to provide a comprehensive online database for published archeomagnetic, volcano and sediment palaeomagnetic and chronological data from the past 50 ka. The database (now version 3) is continually updated. It currently contains more than 15,000 declination, inclination and palaeointensity data from over 460 studies published since 1959 (Brown et al., 2015).

ICEPMAG is built upon the structure and principles of GEOMAGIA50, but incor- porates the vocabulary of MagIC. This is described further in Section 3.1.2.

2.3.3. IAGA Global Paleomagnetic Database (GPMDB)

The International Association for Geomagnetism and Aeronomy (IAGA) encouraged the development of multiple databases for a variety of individual palaeomagnetic

18 2.3. Existing palaeomagnetic databases data compilations, such as pole positions, archaeomagnetic directions and palaeointensity measurements. The compilations were initially provided as Microsoft Access ﬁles that supported several search features (McElhinny and Lock, 1996). At the time, no formal archive existed for magnetic measurements and results outside of internal laboratory databases (Tauxe et al., 2016).

These compilations led to the creation of the IAGA Global Paleomagnetic Database (GPMDB), which was funded through contributions from nine countries and developed using the ORACLE Relational Database Management System (Lock and McElhinny, 1991). The database, which contains published palaeomagnetic poles and directions from 7513 rock units, was last updated in February 2005 (version 4.6) and is currently hosted by the National Oceanic and Atmospheric Administration (https://www.ngdc.noaa.gov/geomag/paleo.shtml/).

2.3.4. Absolute Palaeointensity (PINT) Database

The Absolute Palaeointensity Database, PINT (http://earth.liv.ac.uk/pint/), also sponsored by IAGA, aims to catalogue every published absolute palaeointensity measurement older than 50 ka, along with relevant metadata (Biggin et al., 2010). First compiled in 1994, and last updated in May 2015 (version 2015.05), the database currently contains over 4000 records from over 330 studies published since 1938.

2.3.5. PALEOMAGIA (Paleomagnetic Information Archive)

PALEOMAGIA (http://h175.it.helsinki.ﬁ/database/), which dates back to 1986, aims to allow easy access to Precambrian palaeomagnetic data. It includes data from the GPMDB, new information from peer-reviewed journals and some archival data omitted from the GPMDB (Veikkolainen et al., 2014). The database, last updated in March 2017 (version 2.03) contains more than 3,400 data.

3. Methodology and framework

3.1. Construction of the database

The aim of ICEPMAG (The Icelandic Palaeomagnetism Database) was to develop an online database of palaeomagnetic directions and intensities obtained from Ice- landic lavas, which would be accessible to all Earth scientists and able to retrieve data quickly. ICEPMAG is designed following the structure of GEOMAGIA50 and utilises the vocabulary of MagIC. The ICEPMAG database includes relevant geochronological information (e.g., K-Ar and 40Ar/39Ar ages) as well as other metadata, such as descriptions of the palaeomagnetic methods used to determine directions and intensities, statistical analyses, sampling methods, location information, and rock type/composition.

The workﬂow and key stages of the construction of ICEPMAG are summarised in Fig. 3.1 and expanded upon in the following sections. The lower left-hand side of Fig. 3.1 (adapting the dataset for uploading into MagIC) is considered outside the scope of this project but is shown for illustrative purposes; this is discussed further in Section 7.2.

3.1.1. Building the source library

The ﬁrst stage in the construction of the database was to conduct a search for relevant literature and other sources. This would build a library from which all data would be taken. The primary resources for this search included: • An online archive compiled by Leó Kristjánsson (https://notendur.hi.is/leo/) as well as a digital compilation/spreadsheet containing 5,825 entries supplemented with some metadata (see Kristjánsson, 2013) • ISI Web of Science (http://webofknowledge.com/) • Google Scholar (https://scholar.google.com/) • Magnetics Information Consortium (https://www2.earthref.org/MagIC/)

21 3. Methodology and framework

Journal articles

Academic Other Source library theses databases

Design database structure

MagIC GEOMAGIA50 Add data to tables vocabulary structure

Compile Adapt dataset MySQL server database

Upload to MagIC ICEPMAG website

Figure 3.1: Overview of methodology for the construction of the ICEPMAG database: trapeziums = inputs, rectangles = processes, diamonds = decision points, rounded rectangles = start/stop points; solid arrows = direct workﬂow, dashed arrows = indirect workﬂow; red dotted box = population of master and relational tables (see Sections 3.1.3), blue dotted box = interpretive scripting operations (see Section 3.1.4)

The initial search resulted in 246 papers directly or indirectly related to the geomagnetism and/or palaeomagnetism of Iceland. These papers were checked for original palaeomagnetic data (i.e. with palaeodirections and/or palaeointensity data at the site level) from investigations of Icelandic lavas. Papers containing other types of data (e.g., from aerial geomagnetic surveys, rock magnetic studies, marine sediments etc.) were excluded. After analysing each of these papers, only 77 studies contained (site level) data suitable for the ICEPMAG database. At the time of writing, only 27 of these studies have been uploaded into MagIC.

The majority of the suitable studies (54 of 77) were published in these journals: • Earth and Planetary Science Letters (https://www.journals.elsevier.com/earth-and-planetary-science-letters/)

22 3.1. Construction of the database

• Geophysical Journal International (https://academic.oup.com/gji/) • Geophysical Journal of the Royal Astronomical Society (now Geophysical Journal International/) • Jökull Research Journal (https://jokulljournal.is/) • Journal of Geophysical Research (https://agupubs.onlinelibrary.wiley.com/journal/21562202/) • Physics of the Earth and Planetary Interiors (https://www.journals.elsevier. com/physics-of-the-earth-and-planetary-interiors/) Studies not found in published journals, such as academic theses, were sourced from libraries either internal (e.g., Institute of Earth Sciences, University of Iceland) or external (e.g., Orkustofnun, Reykjavík).

3.1.2. Designing the database structure

ICEPMAG follows the site-sample-specimen hierarchy, as described by Butler (1998): a site represents an individual unit or bed of an igneous complex (e.g., a lava ﬂow or dike); a sample is a separately oriented piece of rock taken from a site (e.g., a drill core); and a specimen is a piece of a sample used to make a measurement in a laboratory. Each entry (or row) of ICEPMAG’s master table corresponds to a particular site where samples were taken for palaeomagnetic measurements.

The columns of the master table represent the possible data fields for each site. The types of data typically published in palaeomagnetic studies were compiled while building up the source library. This information was used to determine appropriate fields for the ICEPMAG database. Relevant fields were also drawn from the GE- OMAGIA50 archeomagnetic and volcanic database (Brown et al., 2015), on which ICEPMAG is structured.

Also considered were the data model (v3.0), method codes and vocabulary lists for the MagIC database, with future uploads and interaction with this database in mind. MagIC’s data model supports a large number of fields, a number of which are compulsory for uploading to MagIC; some of MagIC’s data fields rely on controlled vocabulary lists and predefined abbreviations. Respect for these fields and vocabulary lists was an important consideration in choosing appropriate fields for the ICEPMAG database.

This process resulted in the selection of 104 data ﬁelds (see Tables 4.1 - 4.11 and appendix Table A.1) which each correspond to a column in the master table. Selected data types are detailed and discussed in Section 4. Several of the data ﬁelds in the

23 3. Methodology and framework master table are linked to relational tables; instead of storing complicated text in the master table, some of the data are entered in the master table as integer IDs which correspond to entries in a separate table. E.g., Table 3.1 shows the integer IDs which are stored in the ‘region_id’ column (of the master table) and the regions to which they correspond (in the relational table) - the regions of Iceland are discussed further in Section 4.2.

Table 3.1: Relational table - Region IDs ID Region (English) Region (Icelandic) 1 Capital Region Höfuðborgarsvæði 2 Southern Peninsula Suðurnes 3 Western Region Vesturland 4 Westfjords Vestﬁrðir 5 Northwestern Region Norðurland vestra 6 Northeastern Region Norðurland eystra 7 Eastern Region Austurland 8 Southern Region Suðurland

3.1.3. Adding data to ICEPMAG

Once the data fields and structure of the database had been decided upon, the database tables could be populated. This was achieved by progressing through the source library study by study and adding data to the master table and updating corresponding entries in the relational tables (see Fig. 3.2) - the master table is maintained as a *.csv spreadsheet (to be later converted - see Section 3.1.4) while the relational tables were created directly as *.sql files. Primary data fields were supplemented by various metadata, such as sampling and laboratory techniques, statistical methods, geographic information, geological descriptions, and age estimations. If a secondary version of a data field was present (e.g., directional data corrected and uncorrected for regional tilt), this was also copied into ICEPMAG as an alternative field (also discussed further in Section 4).

Data were transferred by one of several methods: downloading data directly from MagIC (if already uploaded); copying data directly from a published spreadsheet (if attached as an appendix); translating tables from a published PDF document using a PDF reader; or typing out data manually (a last resort, if the PDF could not be read digitally). If copied from spreadsheets or existing databases, data copied into ICEPMAG was cross-checked against the original source material or published study. Several errors, usually typographical, were found in some of the MagIC contributions and the database maintained by Kristjánsson (2013). A separate notes ﬁle was made for each study added to ICEPMAG, including a summary of where the data was copied from, detected mistakes/errors, a description of the data format and any additional comments, as well as comments made by Leó Kristjánsson (either in the

24 3.1. Construction of the database

ICEPMAG relational tables (*.sql): Reference ID (A.2) Region ID (A.3) Location ID (A.4) Geologic class ID (A.5) Geologic type ID (A.6) Dating method ID (A.7) Sample type ID (A.8) Source library Specimen type ID (A.9) Demagnetisation type ID (A.10) Specimen direction calc. ID (A.11) Sample direction avg. ID (A.12) Fields in master table Site direction avg. ID (A.13) (*.csv) - see Table A.1 Polarity ID (A.14) Palaeointensity method ID (A.15) Alteration check type ID (A.16)

Figure 3.2: Workflow for population of master and relational tables from source library (relates to red box in Fig. 3.1). Several relational tables which are not currently used in ICEPMAG but relate to MagIC have been omitted (see full list in appendix Table A.1). unpublished notes file mentioned above, or in personal communication). These notes files are available through the ICEPMAG website.

This process was aided by an existing compilation of 5,825 sites from Iceland, as described by Kristjánsson (2013). This compilation was provided in the form of a spreadsheet which contains 10 data fields per site: site name, numbers of samples used, declination, inclination, VGP latitude, VGP longitude, α95 (95% confidence interval), J100 (NRM intensity after 10mT AF demagnetisation), directional polarity (i.e. normal, transitional, reverse), and age estimate (Ma). The database’s spreadsheet is accompanied by an unpublished notes file with a summary of the data fields and short descriptions of each study in the collection. The notes also includes descriptions of studies not included in the collection and justification for their exclusion.

There are a number of studies which produced directional data from Icelandic lavas but were not published in detail and are not currently included in the database (e.g., Wilson et al., 1972; Peirce and Clark, 1978; Kristjánsson and Gudmundsson, 1980; Herrero-Bervera et al., 1996, 1999. Kristjánsson and Jónsson (2007) estimate that these studies contain unpublished data from more than a thousand lava ﬂows. The possibility of incorporating unpublished data into ICEPMAG is considered part of the future work.

25 3. Methodology and framework

3.1.4. Programming the server and website

After the database had been compiled, it was transferred to a local MySQL server so the data could be queried by external scripting. MySQL is an open-source relational database management system (https://www.mysql.com/). The structure of the MySQL server was copied and adapted from GEOMAGIA50, and utilised a number of scripts based on the Python programming language (https://www.python.org/). The relational tables were created as SQL files (e.g., Fig. 3.3) so they could be pushed directly to the MySQL server. The master table was converted from a CSV file into an SQL file with the use of a Python script (see Fig. 3.4). The repository of the new MySQL server was backed up and uploaded to GitLab, an online Git-repository manager (https://gitlab.com/).

Figure 3.3: SQL relational table for regions of Iceland with corresponding integer IDs (see Fig. 4.1) - special Icelandic characters (e.g., ‘æ’, ‘ö’, ‘ð’) have been replaced with their HTML equivalents (e.g., ‘æ’, ‘ö’, ‘ð’)

Once the MySQL host server was functional, the ICEPMAG website was created so the data could be easily accessed. The ICEPMAG website is also based on the design and structure of GEOMAGIA50, from which it was adapted, and involves a combination of PHP and HTML scripting (standard web programming languages). The website is able to call the MySQL server, a number of Python scripts, and a Google Maps JavaScript API (Application Programming Interface - see https: //cloud.google.com/maps-platform/); the functionality of these features is discussed in a Section 5.1.

The workﬂow from compilation of the ICEPMAG database tables to the outputs of the ICEPMAG website (relating to the blue box in Fig. 3.1) is shown in Fig. 3.4:

• The master table (after being adapted by a Python script) and the relational tables are uploaded to the MySQL server, which is backed up to an online Gitlab repository.

26 3.1. Construction of the database

Master Relational ICEPMAG query table (CSV) tables (SQL) page (PHP)

Python script Interpretive MySQL server (CSV to SQL) PHP scripting

Gitlab backup

ICEPMAG results page (PHP)

Create location Create VGP plot Create CSV results map (Google API) (Python script) ﬁle (Python script)

Figure 3.4: Workﬂow from compilation of the ICEPMAG database to output of website (relates to blue box in Fig. 3.1) - shows how compiled data is uploaded to the MySQL server and the interaction between the ICEPMAG website and the MySQL server

• Some of the relational tables are called by the ICEPMAG query page (through the MySQL server) and displayed as ﬁlters/search options (see Section 5.1.3). • The query page allows the user to query the database with various search options (e.g., sites from a particular region of Iceland). Queries are parsed through PHP scripts which interpret requests and send them to the MySQL server in the form of an SQL ‘statement’ (e.g., Fig. 3.5). • The MySQL server returns the results of the statement request which are then parsed to the results page. • The results page prints the results to a number of HTML tables and calls additional Google API or Python scripts (if these options are selected by the user - see Section 5.1) which are also printed to the results page. E.g., the script in Fig. 3.5 would return an SQL statement like this (if ‘Westfjords’ was selected on the query page):

“select * from ICEPMAG inner join REGIONS on ICEPMAG.REGION_- ID = REGIONS.ID where (REGIONS.NAME = ’Westfjords’)”

When parsed through the MySQL server, this statement would return all results contained in ICEPMAG which have an entry in the ‘region_ID’ column matching the ID for the ‘Westfjords’ region (Table 3.1).

27 3. Methodology and framework

Figure 3.5: Example of PHP scripting to generate SQL statement for region/s selected on query page

3.2. Practical experience

As part of this research project, to gain insight into palaeomagnetic reserach, the author participated in a variety of laboratory and field work. This included some thermal and alternating field demagnetisation of samples from Iran, at the laboratory of the Earth and Planetary Magnetism Group in ETH Zürich (over four months). The author also accompanied researchers on a field trip to retrieve samples from the Lundarháls valley in western Iceland (in June 2018) and participated in subsequent laboratory work (sample preparation, demagnetisation and susceptibility measurements) at the University of Iceland’s Palaeomagnetism Laboratory.

28 4. Data types and experimental methods

The following sections outline the data fields contained in the ICEPMAG database. Some of the fields contain integer IDs, which correspond to separate relational tables (see appendix Table A.1 for full list). Data fields not currently utilised by the ICEPMAG website (e.g., only used for transferring to MagIC) have been omitted from this section.

4.1. Study/contribution details

The integer ID in Table 4.1 links to information about the study or paper in which the site was published (i.e. at MagIC’s ‘contribution’ level). The information was stored in this way so long/complicated text (e.g., title of study, list of author names) was not stored in the master table but in a dedicated relational table. The relational table can also store hyperlinks to the DOI (Digital Object Identiﬁer - a permanent link to the study) and the reference in MagIC if it is stored there.

Table 4.1: Master table - study details Data ﬁeld Description Format (units) Integer ID corresponding to study listed in REFS table - Reference ID contains information about authors, title, year, integer (ID) (Table A.2) publication details, and DOI and MagIC links.

4.2. Geographic information

The master table ﬁelds listed in Table 4.2 contain information about the location of the site. This includes precise coordinates as well as the location, area and region name.

29 4. Data types and experimental methods

Table 4.2: Master table - geographic information Data field Description Format (units) Region ID Integer corresponding to name of region in REGIONS integer (ID) (Table A.3) table. Location ID Integer corresponding to name of location in integer (ID) (Table A.4) LOCATIONS table. Required MagIC field. Latitude of site in degrees (-90 to 90). Required MagIC Site latitude number (◦) field. Site Longitude of site in degrees east of meridian (0 to 360). number (◦) longitude Required MagIC field.

The ‘regions’ correspond to Iceland’s subdivisions, as specified in ISO-3166-2:IS (https://www.iso.org/obp/ui/#iso:code:3166:IS) and shown in Fig. 4.1. These regions are commonly used to divide Iceland for certain purposes, e.g., for statistical purposes and the postal code system. This system was used as these regions are clearly defined and also present in Google Maps. This was favoured over any sort of geological boundary system as boundaries are not clearly defined and there is no agreed convention for geological areas or zones in Iceland, e.g., EVZ, NVZ, SISZ etc. in Cromwell et al. (2015). This is a layer of metadata added for more efficient searching of data: region names generally not given in the papers so the have generally been inferred from published maps or coordinates. Similarly, if coordinates (latitude and longitude) were not given in the paper, approximate coordinates were inferred from published maps or from the location name.

While compiling the data, a distinction between ‘location name’ and ‘area name’ was necessary as studies often list: a precise location name (e.g., stream, gorge, crater, volcano, mountain, hill, lava ﬂow, heath, waterfall, cliﬀ, lagoon, bay/cove, rock, farm, minor road, sub-fjord, promontory, beach, gully, island); and/or a wider area name (e.g., fjord, valley, township, river, ridge system, mountain range, major road/highway, canyon, lake, peninsula, coast, county). ‘Location name’ and ‘area name’ were eventually combined into one relational table (Location ID) to make searching easier (see appendix Table A.4).

30 4.3. Geological information

Figure 4.1: Regions of Iceland (1 = Capital Region, 2 = Southern Peninsula, 3 = Western Region, 4 = Westfjords, 5 = Northwestern Region, 6 = Northeastern Region, 7 = Eastern Region, 8 = Southern Region, red dots = administrative centres, red lines = major urban subdivisions, white areas = major glaciers), adapted from Bjarki S., courtesy of Wikimedia Commons, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=228645 (accessed 15th Aug 2018)

4.3. Geological information

Palaeomagnetic studies are usually linked to prior or new geological mapping of the location being investigated. Often these are included in the published paper as a stratigraphic proﬁle or geological log. The ﬁelds listed in Table 4.3 contain IDs which link to descriptors for a site’s geological class (e.g., igneous) and type (e.g., lava, dike) in relational tables, which are required for uploading to MagIC and controlled by the MagIC vocabulary.

The geological data ﬁelds also contain information about the orientation of the bedding at the site. Bedding information is usually, but not always, used for tilt correction in direction calculations - this is speciﬁed in Section 4.8. Sometimes the bedding dip angle is given as a range; in this case the average is taken (e.g., “3-6” is entered as “4.5”). If the bedding orientation is only approximated (e.g., “southwest” or “northeast”) then an approximate number in degrees was assigned (e.g., “225” or “45”).

31 4. Data types and experimental methods

The vast majority of the sites in ICEPMAG contain data from lavas (∼9,000), however there are some exceptions. Eiriksson et al. (1990) and Kristjánsson (2004) investigated palaeomagnetic directions in sediments (22 sites and 30 sites, respectively) from the Tjörnes peninsula in northern Iceland. Eiriksson et al. (1990) also contains six results from tuﬀs. Smith (1967b) contains thirteen results from baked laterites in western and eastern Iceland. 152 sites contain data from Icelandic dikes (e.g., Piper et al., 1977; Kristjánsson et al., 1980; Kristjánsson, 1985a; Linder and Leonhardt, 2009; Eriksson et al., 2014).

Table 4.3: Master table - geological descriptions and data Data field Description Format (units) Geologic Integer ID corresponding to entry in GEOLOGIC CLASS class ID integer (ID) table. Required MagIC field. (Table A.5) Geologic type Integer ID corresponding to entry in GEOLOGIC TYPE ID (Table integer (ID) table. Required MagIC field. A.6) Bed dip angle Estimated dip angle of bedding in degrees (0-90). number (◦) Bed dip Estimated orientation of bedding dip direction in degrees number (◦) direction (0 to 360 from geographic north).

4.4. Dating methods

Dating of samples in Iceland has relied mostly on geological estimates or relative geochronology. The primary radiometric dating methods are potassium-argon (K- Ar) and argon-argon (40Ar/39Ar). According to Cromwell et al. (2015), Icelandic basalts have a low potassium content so eﬀorts to obtain absolute ages using radiometric dating methods have been limited. Both of these radiometric methods rely on the radioactive decay of 40K which has a long half-life (or small decay constant); therefore small amounts of 40Ar only accumulate after hundreds of thousands of years (Levi et al., 1990). Radiocarbon (14C) dating has also been limited as it is hard to ﬁnd carbonised material and “the absolute range of this method is limited to ∼50ka” (Cromwell et al., 2015). Jicha et al. (2011) tested some uranium-thorium (238U-230Th) dating in southwest Iceland.

The fields listed in Table 4.4 relate to the dating method and age estimate for a site. Most of the age estimates for palaeomagnetic studies in Iceland are very approximate, typically in the order of ± 1-2 million years, and given only with an upper and lower bound. It is often possible to infer an age from identification or correlation with a reversal boundary or transition, but precise dating is difficult. With more geochronological investigations and improved dating methods, there is a significant opportunity to constrain the age estimates in ICEPMAG.

32 4.5. Sampling information

Table 4.4: Master table - dating methods and data Data ﬁeld Description Format (units) Dating method ID Integer ID corresponding to entry in DATE ID table. integer (ID) (Table A.7) Age Estimate of site age. number (Ma) σ (age) Standard deviation of age estimate, if given. number (Ma) Min. age Lower bound for age estimate number (Ma) Max. age Upper bound for age estimate number (Ma)

4.5. Sampling information

Most of the palaeomagnetic sampling in Iceland is carried out by portable drill (e.g., Fig. 4.2), with diameter of about one inch (∼2.5 cm). Other sampling methods include block or hand sampling. Sampling campaigns typically begin in the oldest lavas at the bottom of an exposed lava pile (e.g., Fig. 1.1) and proceeds uphill towards younger lavas.

Figure 4.2: Example of palaeomagnetic sampling with a portable drill in Lundarháls, western Iceland, photo taken by J. Tonti-Filippini, 22nd June 2018.

The ﬁelds in the master table, listed in Table 4.5, relate to the sampling carried out at the site including: site name, position, and the number and type of samples collected. Studies generally contain information about elevation (above sea level),

33 4. Data types and experimental methods height (above an arbitrary point), cumulative thickness, or depth (down drillhole). This can be detailed at the site level or provided as a stratigraphic proﬁle (as in Section 4.3).

Table 4.5: Master table - sampling information Data field Description Format (units) Name designated to site (i.e. lava or flow unit) in paper. Site name Usually 1 or 2 letters followed by a number (e.g. AB01). text Required by MagIC. Estimated height of sampling location (or cumulative Height thickness of flow) above arbitrary point (i.e. not above number (metres) sea level), or depth down drillhole (negative). Elevation (or Estimated height above (positive) or below (negative) sea number (metres) altitude) level. # collected Number of samples (e.g. cores) taken from a site. integer samples Sample Text list of sample names collected at site (if listed). text list names Sampling Integer corresponding to entry in SAMPLE TYPES table. type ID Relates to method of field sampling/type of samples integer (ID) (Table A.8) collected.

4.6. Laboratory measurements

After a sample or core is retrieved from the ﬁeld (e.g., Fig. 4.3), it is cut into several specimens of ∼2 cm length. Various measurements are carried out on these specimens depending on the nature of the study. For palaeodirectional studies in Iceland, typically only one specimen per sample has been measured.

The master table ﬁelds listed in Table 4.6 contain general information about the types of experiments and laboratory protocols performed on collected samples, as well as information about the quantity and types of specimens collected. Further details and results of susceptibility, demagnetisation, palaeointensity and anisotropy experiments are outlined in the following sections.

Table 4.6: Master table - laboratory measurements Data ﬁeld Description Format (units) # measured Number of specimens measured per sample. integer specimens Specimen Text list of specimen names (if given). text list names Continued on next page

34 4.7. Magnetisation and susceptibility

Table 4.6 – continued from previous page Data ﬁeld Description Format (units) Specimen Integer ID corresponding to entry in SPECIMEN_TYPES type ID integer (ID) table. (Table A.9) Demag type Integer ID corresponding to entry in DEMAG_TYPE_ID ID (Table integer (ID) table. A.10) Peak demag Maximum AF demagnetisation samples subjected to (e.g. number (mT) step 10 mT = 100 Oe).

Figure 4.3: Oriented palaeomagnetic sample drilled from an Icelandic lava, photo taken by J. Tonti- Filippini, 6th July 2018.

4.7. Magnetisation and susceptibility

The master table ﬁelds listed in Table 4.7 relate to the procedures carried out to determine the magnetisation and susceptibility of the specimens. Most commonly, only a volume normalised magnetisation is reported in papers, as well as in the compilation described by Kristjánsson (2013). The magnetisation is usually reported as J100 (demagnetised to 100 Oe or 10 mT) or JNRM .

35 4. Data types and experimental methods

Table 4.7: Master table - magnetisation and susceptibility Data field Description Format (units) Measured intensity of magnetisation, volume normalised. Magn. (vol) Often reported as J100 (demagnetised to 100 Oe or 10 number (A/m) mT) or JNRM . σ magn. Standard deviation of magnetisation (volume normalised). number (A/m) (vol) Magn. number Measured intensity of magnetisation, mass normalised. (mass) (Am2/kg) σ magn. number Standard deviation of magnetisation (mass normalised). (mass) (Am2/kg) AF step (or “cleaning peak”) at which magnetisation is Demag level number (mT) reported (e.g., J100 is demagnetised to 100 Oe or 10mT). number Susc. (vol) Average magnetic susceptibility (volume normalized). (dimensionless) number σ (susc.) Standard deviation of mean susceptibility. (dimensionless) Magnetising Present day field intensity at the sample location. number (A/m) field Koenigs- Ratio of remanent magnetization to induced number berger magnetization (product of susceptibility and Earth’s (dimensionless) ratio magnetic field strength).

4.8. Direction calculations

After a palaeomagnetic sample has been drilled in the field, it is oriented in situ before being separated from the rock. Orientation is performed with a geological compass which sits on top of an inclinometer (e.g., Fig. 4.4). This allows for the dip angle (or ‘plunge’) and direction (or ‘azimuth’) of the core to be recorded. In Iceland, as the magnetic bearing of a compass can be affected by the presence of magnetised basalts, the orientation of the core is usually taken with reference to the sun or the sighting of a distant object with a fixed location (e.g., a building or mountain peak).

Specimens cut from the samples are then demagnetised (see Section 4.7) to determine the magnetisation and direction of the primary NRM. The declination and inclination of the palaeomagnetic ﬁeld can then be calculated with reference to the orientation information. The direction for a site is usually obtained by averaging the directions obtained across multiple samples (typically >4) taken from the site. The master table ﬁelds listed in Table 4.8 relate to the direction calculations carried out during demagnetisation of the specimens.

In Iceland, the NRM directions of specimens have generally been calculated, after AF cleaning to 10 mT, through analysis of orthogonal vector plots, but these are usually

36 4.8. Direction calculations

Figure 4.4: Orientation of a palaeomagnetic core in Lundarháls, western Iceland, photo taken by J. Tonti-Filippini, 20th June 2018. not published in papers. Principal component analysis or ‘PCA’ (Kirschvink, 1980) has been used to an extent recently (e.g., Beske-Diehl and Li, 1993; Goguitchaichvili et al., 1999b; Camps et al., 2011; Jicha et al., 2011; Stanton et al., 2011; Oliva-Urcia and Kontny, 2012; Vérard et al., 2012; Eriksson et al., 2014; Cromwell et al., 2015; Døssing et al., 2016; Tanaka and Yamamoto, 2016), but wasn’t considered necessary in many studies. Changes in NRM direction after the ﬁrst 10 mT step on Icelandic lavas “were usually small and random”, and multicomponent analysis (e.g., PCA) was deemed to be inappropriate for rocks containing only a single stable component (Leó Kristjánsson, personal communication, 16th August 2017).

Generally, only one specimen is measured from each sample, so averaging of specimen directions for each sample is not required. If multiple specimens are measured then usually the average declination and inclination is used for the sample (e.g., Tanaka et al., 1995). In published papers the two terms (samples and specimens) are often confused or used interchangeably.

To obtain a direction (declination and inclination) for each site, it is standard prac- tice to employ ‘Fisherian statistics’ (Fisher, 1953) when calculating the mean direction across multiple specimens (or samples). This is often described in papers as a ‘Fisher mean’. This method calculates the precision parameter κ (Eq. 4.1), which describes the distribution scatter, and a circle of conﬁdence α95 (Eq. 4.2), which is the probability that the true mean direction lies within this circle. Where N is the number of directions (i.e. samples or specimens), and R is the length of the mean

37 4. Data types and experimental methods vector:

N − 1 κ = (4.1) N − R

" #! −1 N − R 1 α = cos 1 − 20 N−1 − 1 (4.2) 95 R

Leó Kristjánsson (personal communication, 16th August 2017) makes a further distinction (maintained in ICEPMAG - see Table A.13) between a ‘κ-maximising’ method and a preferred method of minimising α95. Many of the Icelandic studies through to 1984 (and a few afterwards) used the ‘κ-maximising’ method where “a computer program selects those direction vectors (from the data available after 10, 15, 20 and possibly 25mT treatment) which yield the longest vector sum” (Kristjánsson, 2004). However, it is considered that this method could erroneously select an apparently good set of sample directions that are only clustered by chance, so after 1984 a preferred method was employed where the mean with the lowest α95 was chosen after all the specimens had been demagnetised at the same ﬁeld (Leó Kristjánsson, personal communication, 16th August 2017).

Table 4.8: Master table - direction calculations Data ﬁeld Description Format (units) Specimen Integer ID corresponding to entry in direction calc integer (ID) SPECIMEN_DIR_CALC_ID (Table A.11) ID Sample Integer corresponding to sample direction average method direction avg integer (ID) from SAMPLE_DIR_AVE_METHOD_ID (Table A.12) ID Site direction Integer ID corresponding to entry in integer (ID) avg ID SITE_DIR_AVE_METHOD_ID (Table A.13) Tilt Applied correction for tectonic tilt in degrees. number (◦) correction Dec Declination at site in degrees from true north (0 to 360). number (◦) Inclination at site in degrees from the horizontal (-90 to Inc number (◦) 90). For any alternative declination measurements (e.g. Dec (alt) number (◦) uncorrected for tilt). For any alternative inclination measurements (e.g. Inc (alt) number (◦) uncorrected for tilt). ◦ α95 95% conﬁdence limit for direction in degrees. number ( ) ◦ θ63 Angular standard deviation (a.s.d) for direction in degrees. number ( ) number R Resultant Fisher vector. (dimensionless) number K Fisher’s dispersion parameter (κ). (dimensionless) Continued on next page

38 4.9. VGP calculations

Table 4.8 – continued from previous page Data ﬁeld Description Format (units) Comparison of Fisher dispersion K after and before tilt number K ratio correction. (dimensionless) # direction Number of samples used in site direction calculation. integer samples # direction Number of specimens used in sample direction integer specimens calculation.

4.9. VGP calculations

The master table fields listed in Table 4.9 relate to the statistics of VGP calculations. If accurate palaeodirections can be obtained, then a VGP can be defined for each site, as long as the site’s latitude (λs) and longitude (φs) are known. Using the inclination (I) determined for the site, the ‘magnetic co-latitude’ (θm, Eq. 4.3) can be defined. This is the angular difference between the longitude and latitude of the site and the location of the VGP, i.e. the radius of the circle, centred on the site location, which defines all possible VGP positions (see Tauxe, 2010):

tanI ! θ = cot−1 (4.3) m 2

With the co-latitude, the VGP latitude (λp, Eq. 4.4) can be found (where D = declination, λs = site latitude):

sinλp = sinλs.cosθm + cosλs.sinθm.cosD (4.4)

This is determined by using the law of cosines to derive θp (Eq. 4.5), because θp = (π/2 − λp) and θs = (π/2 − λs):

cosθp = cosθs.cosθm + sinθs.sinθm.cosD (4.5)

To determine the VGP longitude (φp), the angular diﬀerence between the pole and site longitude (∆φ, Eq. 4.6) must be calculated:

sinD.sinθ sin∆φ = m (4.6) cosλp

39 4. Data types and experimental methods

Therefore, the VGP longitude (φp) is:

φp = φs + ∆φ (for cosθm > sinλs.sinλp)

φp = φs + 180 − ∆φ (for cosθm < sinλs.sinλp)

Table 4.9: Master table - VGP calculations Data field Description Format (units) # VGP Number of samples used for VGP calculation. integer samples VGP latitude Latitude for VGP between -90 and 90. number (◦) VGP Longitude for VGP between 0 and 360. number (◦) longitude VGP latitude Alternative VGP latitude as calculated from alternative number (◦) (alt) dec/inc (e.g. uncorrected for tilt). VGP Alternative VGP longitude calculated from alternative longitude number (◦) dec/inc (e.g. uncorrected for tilt) (alt) Integer ID corresponding to entry in DIR_POLARITY Polarity ID integer (ID) (Table A.14) VGP DP Parallel latitude uncertainty (95% confidence) of VGP. number (◦) VGP DM Meridian uncertainty (95% confidence) of VGP. number (◦) ◦ VGP A95 Fisher circle (95% confidence) of VGP number ( )

4.10. Palaeointensity methods

Lavas acquire their NRM primarily through ‘thermoremanent magnetisation’ (TRM). Above a certain temperature, called the ‘Curie temperature’ or ‘blocking temperature’, a lava has no remanent magnetisation (it is paramagnetic). Crystals will start to form in a lava above the Curie temperature, but will not be magnetic (initially). As a lava cools down below the Curie temperature, the magnetic moments of certain minerals (e.g., titanomagnetite, magnetite, hematite) become magnetic and their magnetisation aligns (on average) with Earth’s magnetic ﬁeld. This statistical alignment becomes ﬁxed in the rock and can preserve a TRM over geological time (Tauxe and Yamazaki, 2007).

Absolute palaeointensity determinations, as discussed in Section 2.2.3, generally rely on replacing the NRM with a TRM in a known ﬁeld and comparing the acquired magnetisation with the rock’s natural magnetisation. Absolute palaeointensity techniques used in Iceland are discussed below.

40 4.10. Palaeointensity methods

4.10.1. ‘Thellier’ type methods

In Iceland, the majority of palaeointensity studies have been carried out using stepwise heating methods (and various derivatives), as first established by Koenigs- berger (1938) and Thellier and Thellier (1959), also referred to as ‘Thellier’ or ‘Koenigsberger-Thellier-Thellier’ (KTT) methods. The basic idea behind the Thel- lier method is to show that the laboratory acquired TRM is linearly related to the NRM later replaced. This is done by progressively replacing the NRM with a partial (laboratory) TRM or ‘pTRM’ by heating up specimens in stages (temperature steps) and then letting them cool in a known field (see Tauxe, 2010, chap. 10). An advantage of this method is that it is generally clear when linearity has broken down, through alteration or non-ideal grain effects.

The original Thellier method in its classical form (Thellier and Thellier, 1959), also called the infield-infield or ‘II’ method, contains an assumption (the ‘Law of Reciprocity’): “that a magnetization acquired by cooling from a given temperature is entirely replaced by re-heating to the same temperature” (Tauxe, 2010). This method has been applied in Iceland by Schweitzer and Soffel (1980), Goguitchaichvili et al. (1999a,c,b), Camps et al. (2011), Stanton et al. (2011), and Tanaka and Yamamoto (2016).

A popular variation on the classic method is attributed to Coe (1967), in which the specimen is cooled in a zero-field prior to heating and cooling in a known field, also called the ‘zero-field/in-field’ (ZI) method; this allows for the remaining NRM to be directly measured at each step (Tauxe, 2010, chap. 10). At each temperature step a ZI pair is made until the specimen is fully demagnetised/remagnetised. Coe’s variation has been utilised in Iceland by Senanayake et al. (1982), Marshall et al. (1988), Levi et al. (1990), Tanaka et al. (1995, 2012), and Vérard et al. (2012). The ZI and II methods allow for ‘pTRM checks’, i.e. differences between the first and second TRM at a given temperature step suggest the ability to acquire a TRM has changed and the results may be suspect.

A recent modification of Coe’s variation, called ‘IZZI’ (Tauxe and Staudigel, 2004), alternates between zero-field/in-field (ZI) and in-field/zero-field (IZ) steps. This allows for detection of a ‘pTRM tail’, which is the difference between the IZ and ZI steps. A pTRM tail can be present when specimens are effected by multidomain (MD) grains, resulting in a zig-zag pattern on a NRM-TRM plot. This technique has been used on Icelandic lavas by Michalk et al. (2008) and Cromwell et al. (2015). Other studies in Iceland, e.g., Linder and Leonhardt (2009) and Ferk and Leonhardt (2009), have included alteration and additivity checks (in addition to pTRM tail checks), as specified by the ‘MT4’ method (Leonhardt et al., 2004).

41 4. Data types and experimental methods

4.10.2. ‘Shaw’ methods

An alternative approach to palaeointensity, intended to be faster than the Thellier method, was popularised by Shaw (1974). In the Shaw method, prior to heating, the specimen’s NRM is measured and then subjected to progressive levels of alternating ﬁeld (AF) demagnetisation; this establishes the ‘coercivity spectrum’ of the specimen (see Tauxe, 2010, chap. 10). A total TRM (heating above Curie temperature) is then applied to the specimen in a laboratory ﬁeld and (AF) demagnetised again; this is similar to Wilson’s method (described below), but uses AF instead of thermal demagnetisation. If the demagnetisation curves of the NRM and TRM are identical, then “it is assumed that the coercivity spectrum of the NRM has remained unaltered during heating” (Valet, 2003). However, this is rarely the case and an ‘anhysteretic remanent magnetisation’ (ARM) is often used.

This method was initially proposed by van Zijl et al. (1962), and subsequently used on Icelandic lavas by Smith (1967a,b) and Lawley (1970), and partially by Schweitzer and Soﬀel (1980). After being revised by Shaw, modiﬁed versions of the method were also used in Iceland by Shaw (1975), Shaw et al. (1982), Senanayake et al. (1982), and Roberts and Shaw (1984), and partially by Tanaka et al. (2012).

4.10.3. Microwave methods

Walton et al. (1993) proposed to use microwave excitation for demagnetisation, instead of conventional heating (as in the Thellier type methods). Specimens subjected to microwave treatment were described as acquiring a TRM “almost identical to one gained by natural heating”, with some signiﬁcant advantages over the conventional method, such as reduced alteration (Valet, 2003). The same protocols as for Thellier methods can be used. So far, the microwave method has seen limited use in Iceland (e.g., Brown et al., 2006; Stanton et al., 2011).

4.10.4. Other methods

‘Multi-specimen’ experiments have also been used in Iceland (e.g., Michalk et al., 2008; Muxworthy and Taylor, 2011). These experiments are based on the ‘MSP- DB’ (multispecimen parallel differential pTRM) method where multiple specimens are taken from a single unit and each specimen is exposed to heating at the same temperature but in different laboratory fields, as proposed by Dekkers and Böh- nel (2006). Whereas classic Thellier type experiments rely on the assumption of ‘single domain’ remanence behaviour, the MSP-DB method is intended to be appli-

42 4.11. Dipole moments (VDM and VADM) cable for ‘multi-domain’ remanences, although this is questionable (see Tauxe, 2010, chap. 10).

Muxworthy (2010) trialled another domain-state independent method in Iceland, originally proposed by Wilson (1961). In this method the NRM of the specimen is thermally demagnetised, and then a full TRM is applied in a known field (i.e. no stepwise pTRMs are applied). The specimen is then thermally demagnetised again in order to compare the TRM and NRM demagnetisation curves. This method is “chemically an ‘all or nothing’ approach” (Muxworthy, 2010), in that it is not possible to determine any effects of alteration during heating. Wilson’s method was also partially used in Iceland by Schweitzer and Soffel (1980).

The master table ﬁelds listed in Table 4.10 relate to the palaeointensity experiments.

Table 4.10: Master table - palaeointensity Data ﬁeld Description Format (units) PI method ID Integer ID corresponding to entry in PI_METHODS integer (ID) (Table A.15) table. Absolute ﬁeld strength (palaeointensity) reported in Abs. PI number (µT) microtesla (10−6 T). σ (abs. PI) Standard deviation of absolute palaeointensity. number (µT) σ % (abs. Percentage standard deviation of absolute palaeointensity. number (%) PI) # PI samples Number of samples used in PI calculation. integer # PI Number of specimens used in PI calculation. integer specimens Alteration Integer ID corresponding to entry in ALT_ID table. check ID integer (ID) Relates to type of alteration check. (Table A.16)

4.11. Dipole moments (VDM and VADM)

Palaeointensity results can also be described in terms of an equivalent geocentric dipole moment. This ‘virtual dipole moment’ (VDM) expresses what “would have produced the observed intensity at a specific [palaeo]latitude” (see Tauxe, 2010, chap. 2) if the site inclination is known. The ‘virtual axial dipole moment’ (VADM) is a slightly different calculation which uses the site co-latitude instead of the magnetic co-latitude (if the site inclination is not known). The master table fields listed in Table 4.11 relate to the VDM and VADM calculations for each site (if given).

43 4. Data types and experimental methods

Table 4.11: Master table - dipole moments Data ﬁeld Description Format (units) number VDM Site average of virtual dipole moment (VDM). (1022Am2) number σ (VDM) Standard deviation of VDM. (1022Am2) # VDM Number of samples used in VDM calculation. integer samples number VADM Site average of virtual axial dipole moment (VADM). (1022Am2) number σ (VADM) Standard deviation of VADM. (1022Am2) # VADM Number of samples used in VADM calculation. integer samples

44 5. Online implementation and functionality

5.1. ICEPMAG website

The ICEPMAG website (Fig. 5.1), described in this section, was designed to allow any user quick access to the contents of the ICEPMAG database through a web interface (http://icepmag.org/). This interface allows for rapid searches of Ice- landic data with a range of custom ﬁlters, including: geographic constraints (by region, location and between speciﬁed coordinates); age constraints; authors and years of publication; rock and sample/specimen types; dating methods; palaeointensity methods; directional polarity and statistical constraints. The design and functionality borrows heavily from GEOMAGIA50.

Figure 5.1: Home page of the ICEPMAG website (screenshot)

45 5. Online implementation and functionality

5.1.1. Home page

ICEPMAG’s home page (Fig. 5.1) contains a description of the project and the latest news, updates and error corrections, as well as instructions about how to use and reference the database. The sidebar contains links to the query form (see Section 5.1.3), the study page (see Section 5.1.2), as well as pages displaying website usage statistics, a list of credits, and links to other databases (not shown in this document).

5.1.2. Study page

The study page (Fig. 5.2) lists details about the papers included in the ICEPMAG database. The studies can be sorted by ID (as assigned in Table A.2), lead author name, title, year and journal title, or searched by author or title. The table contains hyperlinks to the paper’s DOI and corresponding MagIC contribution page. This allows for the user to quickly identify any study contained in the database and look up its abstract or full paper for further details. Both links are persistent and unique so will always be accessible.

Figure 5.2: Example of study page containing details of the papers included in ICEPMAG (searched authors for ‘Brown’)

5.1.3. Query form

The query form allows users to search the ICEPMAG database with a number of customisable ﬁlters. The ﬁrst part of the form (Fig. 5.3) allows the user to specify how the data should be displayed. By default, ‘Detailed query’ is selected, which

46 5.1. ICEPMAG website relates to the number of columns to be displayed on the results page. Unchecking this box will reduce the number of columns displayed in the results table - only the data ﬁelds listed as ‘Default’ in the master table (see Table A.1) will be displayed. Checking the ‘Detailed query’ box will displayed additional master table ﬁelds listed as ‘Optional’ in Table A.1, depending on which constraints are selected (described in the following sections). This was done so the user can specify how detailed the results page will be, and adjust it according to the search parameters.

Checking ‘Site location map’ will output an interactive location map displayed all the sites returned from the search (see Section 5.1.5). Checking ‘VGP plot’ will plot the VGP locations for all the sites returned from the search (see Section 5.1.6), if they contain VGP data. Checking ‘Download data’ will produce a downloadable *.csv ﬁle containing the full results of the search (see Section 5.1.7).

Figure 5.3: Query form - outputs (screenshot)

The query ﬁelds shown in Fig. 5.4 allow for the user to selectively search for direction and/or intensity data. The three options are conjunctive, i.e. selecting multiple options will only return results that contain both or all of the options. E.g., selecting ‘directional data’ and ‘palaeointensity measurements’ will only return sites that contain results for both direction and intensity, i.e. fewer sites would be returned than if only one option was selected. This allows the user to quickly target type of data that is required. By default, ‘All’ is selected.

Figure 5.4: Query form - include result options (screenshot)

Geographic query ﬁelds (Fig. 5.5) allow the user to search for data by region (see Section 4.2), location, or by specifying a range of latitudes and longitudes. Regions and locations can be searched for and selected either through an ‘autocomplete’

47 5. Online implementation and functionality function or by scrolling through dropdown menus. Multiple locations or regions can be selected by holding down the control or shift keys. Default coordinates are shown which express the geographic extents of Icelandic data, however, longitudes can also be entered as negative values (e.g., -26◦ and -13◦ W) and will be converted by the website when running the query. By default, ‘None’ is selected.

Figure 5.5: Query form - geographic constraints (screenshot)

Age constraints (Fig. 5.6) allow the user to search for sites by the estimated age of the rock. This includes options for ages greater than, less than or between certain values. The default units are Ma (millions of years). This allows to user to quickly select an age range of interest. With international standards in mind, precise (e.g., radiocarbon) ages are calculated back from the year 1950 AD, so any recent results (i.e. samples from eruptions since 1950) are stored in ICEPMAG as negative values. The ‘0’ value is adjusted when a search is run so these results are also returned. By default, ‘None’ is selected.

Figure 5.6: Query form - age constraints (screenshot)

Publication constraints (Fig. 5.7) allow for the user to search for data by individual study (author/s and year) via an autocomplete function or by scrolling through a dropdown menu. Multiple references can be selected by holding down the control or

48 5.1. ICEPMAG website shift keys. Studies queried can also be constrained by year of publication (between certain years). This allows to user to quickly search for data from particular studies, authors or research period. By default, ‘None’ is selected.

Figure 5.7: Query form - publication constraints (screenshot)

By expanding the ‘Other constraints’ option, the user can perform a more advanced search of the database. Fig. 5.8 displays the options available for searching by rock/geology type, sampling method and specimen type. Within each type or method field, the options are inclusive, i.e. selecting multiple options from within a type will return results containing any of the selected options (e.g., selecting ‘lava’ and ‘tuff’ will return results from both lavas and tuffs). However, across multiple fields, the options are conjunctive, e.g., selecting ‘tuff’ and ‘portable drill cores’ will only return tuff samples collected with a portable drill.

Figure 5.8: Query form - rock, sample and specimen types (screenshot)

Fig. 5.9 displays options for searching ICEPMAG by palaeointensity and/or dating methods (see Sections 4.10 and 4.4 for further details). This allows the user to

49 5. Online implementation and functionality quickly search for samples subjected to speciﬁc laboratory protocols or constrain the search to sites with more accurate dating information.

Figure 5.9: Query form - palaeointensity and dating methods (screenshot)

The fields shown in Fig. 5.10 allow to the user to query data with a number of statistical constraints. This is useful for filtering for data (e.g., specifying a upper limit for α95 or a lower limit for κ) and testing quality criteria on Icelandic data. The user can also quickly search for sites with a specified polarity, e.g., can quickly isolate transitional data or split normal and reverse data to look for asymmetries in directional polarity.

Figure 5.10: Query form - site statistics and polarity (screenshot)

50 5.1. ICEPMAG website

5.1.4. Results page

After selecting all the options described above and clicking on the ‘Perform Query’ button at the bottom of the query page (Fig. 5.10), the user is directed to the results page. A new tab is opened in the browser, with a webpage showing a series of on- page tables containing the output retrieved from the MySQL server. If the user has entered any invalid search terms (e.g., longitudes outside the possible range) then an error message is displayed. At top of the results page (Fig. 5.11), the user can select between four tabs which are linked to the results table (‘paleomagnetic data’), location map (see Section 5.1.5), VGP plot (see Section 5.1.6) and downloadable data (see Section 5.1.7). Underneath these tabs, a summary of the query parameters selected by the user is displayed.

Figure 5.11: Results page - an example of query parameters (screenshot)

Results table

An example of the query results table is shown in Fig. 5.12, as returned from the query parameters in Fig. 5.11. A basic search (i.e. not selecting ‘detailed query’) will return a table with 22 columns corresponding to the ‘Default’ columns listed in Table A.1. The integer IDs are hyperlinked to the corresponding relational tables.

A detailed search (i.e. selecting ‘detailed query’) will return a table with up to an additional 9 columns (with integer IDs for relational tables) corresponding to the ‘Optional’ colums listed in Table A.1, based on the advanced options selected on the query page. An example of these columns is displayed in Fig. 5.12, as returned from the query parameters in Fig. 5.11.

51 5. Online implementation and functionality

Figure 5.12: Results page - an example of basic search query results (screenshot)

Figure 5.13: Results page - an example of additional results columns from a detailed search (screenshot)

Basic query relational tables

A number of relational tables are displayed underneath the results table. Fig. 5.14 shows an example of the reference table that relates to the results of the query (i.e. sites matching the search criteria were published in the listed studies). This is only a subset of the full relational table (Table A.2) that corresponds to the results of the query in Fig. 5.12. The DOIs provide hyperlinks to the referenced paper.

Figure 5.14: Results page - an example table of references returned by a query (screenshot)

The example tables shown in Fig. 5.15 relate to the location and region IDs displayed in the main results table. These are subsets of the full relational tables displayed in

52 5.1. ICEPMAG website the appendix (Tables A.2 and A.3) returned by the query parameters in Fig. 5.12.

Figure 5.15: Results page - an example of the region and location tables returned by a query (screenshot)

The example table shown in Fig. 5.16 relate to the palaeointensity and dating method IDs displayed in the main results table. These are subsets of the full relational tables listed in Tables A.7 and A.15, as returned by the query parameters in Fig. 5.12.

Figure 5.16: Results page - an example of palaeointensity and dating method tables (screenshot)

Detailed query relational tables

If ‘detailed query’ is selected, then additional relational tables will also be displayed below the results table. An example of these additional tables is shown in Fig. 5.17, as returned by the query parameters in Fig. 5.11. These relate to the: demagnetisation methods; alteration checks; geological, sample and specimen types; direction calculations for specimens, samples and sites; and directional polarity. These are subsets of the full relational tables listed in the appendix Tables A.6, A.8 - A.14, and A.16.

53 5. Online implementation and functionality

Figure 5.17: Results page - an example of the additional relational tables returned from a detailed query (screenshot)

5.1.5. Location map

If ‘Site location map’ has been selected on the query page, sites returned from the query will be plotted on an embedded interactive map (as in Fig. 5.18 - results from the query parameters in Fig. 5.11). Hovering over a pin will display details about the location and corresponding study. Location and reference tables (e.g., Fig. 5.14 and 5.15) are displayed underneath the map for convenience. This map allows the user to quickly view matching sites and their sampling locations in Iceland.

54 5.1. ICEPMAG website

Figure 5.18: Results page - an example of a location map produced from a query (screenshot)

5.1.6. VGP plot

If ‘VGP plot’ has been selected on the query page, sites containing VGP data will be plotted on a global map. This allows to user to easily view all the VGP data returned from a query and get a sense of the pole distribution. An example of this is provided in Fig. 5.19 which shows all the VGP data returned from sites in the the Westfjords. The returned image can be downloaded as a PNG or SVG ﬁle by clicking on the links underneath.

55 5. Online implementation and functionality

Figure 5.19: Results page - an example of a VGP plot produced from a query (all VGP calculations from the Westfjords region)

5.1.7. Data download

If ‘Download data’ was selected on the query page, the website will produce a downloadable *.csv file containing all the ‘Default’, ‘Optional’ and ‘Only in csv download’ fields listed in Table A.1. The file can be downloaded by clicking on the link in the ‘Download data’ tab (Fig. 5.20). This allows the user to analyse and plot the data returned from a query with their own software.

Figure 5.20: Results page - an example of the link to a downloadable spreadsheet (screenshot)

56 6. Overview of ICEPMAG data

This section provides some plots and histograms of the data contained in the database. These ﬁgures give a broad overview of data contained in the database and the distributions of various data ﬁelds, as well as demonstrating the functionality of ICEP- MAG and the types of analyses that can be performed.

6.1. Geographic distributions

Fig. 6.1 displays all unique site locations for Iceland. There are significant clusters of sites around the Capital Region in the southwest, the Westfjords (northwest peninsula), and the Eastern Region, and the central north to a lesser extent. This is clearly reflected in the distribution of site latitudes and longitudes (Fig. 6.2). The distribution shows a significant bias away from the central longitudinal bands and along the southern coastline - these areas are coincident with the location of Iceland’s central spreading ridge and more recently active volcanic zones (see Fig. 1.2).

As shown in Fig. 6.2 and 6.3, ICEPMAG’s data are dominated by studies carried out in the older lavas of the Westfjords (>2,500 sites) and Eastern Region (>3,000 sites). This is due mainly to two large campaigns by Watkins and Walker (1977) in the east and McDougall et al. (1984) in the northwest, as shown in Fig. 6.4 (references #8 and #33). These studies report results from over a thousand lavas each.

Fig. 6.3 shows that relatively few results have come from the Southern Region, despite covering a large geographic area. The Southern Region contains a good proportion of Iceland’s major glaciers and active volcanoes. Access is diﬃcult to many areas in the Southern Region, which is frequently exposed to seismic and volcanic activity as well as glacial ﬂooding, and long sequences of lavas suitable for palaeomagnetic study are rare. Even fewer sites have come from the Southern Peninsula (Reykjanes) - this is a much smaller geographic area and is dominated by recent volcanism (<1 Ma).

57 6. Overview of ICEPMAG data

Figure 6.1: Map of ICEPMAG site locations (all results) - clustering can be seen in the Westfjords, Eastern and Capital regions

Figure 6.2: Histogram of all ICEPMAG sites by latitude and longitude

58 6.1. Geographic distributions

Figure 6.3: Histogram of site distribution by geographic region (see Table A.3 and Fig. 4.1)

Figure 6.4: Histogram of sites by reference ID (see Table A.2)

59 6. Overview of ICEPMAG data

6.2. Temporal distributions

Fig. 6.5 displays the estimated age distribution for all sites in Iceland. Sites are distributed reasonably well over the last 16 Ma, although there are a number of peaks dominated by several large studies (>100 sites each): • 2 - 3 Ma (Doell, 1972; Kristjánsson et al., 1980, 1991; Helgason and Duncan, 2001; Tanaka and Yamamoto, 2016) • 8 - 10 Ma (Saemundsson et al., 1980; Helgason, 1982; McDougall et al., 1984; Kristjánsson and Jóhannesson, 1999; Kristjánsson et al., 2006) • 12 - 14 Ma (Piper et al., 1977; McDougall et al., 1984; Kristjánsson et al., 1995; Kristjánsson and Jóhannesson, 1996; Kristjánsson, 2009)

Figure 6.5: Histogram - sites by age (all results)

As shown in Fig. 6.6, many of the measured Holocene sites in ICEPMAG come from recent lavas (<250 years old); the majority of these are palaeointensity studies (e.g., Smith, 1967b; Schweitzer and Soﬀel, 1980; Stanton et al., 2011).

60 6.3. Palaeointensity results

Figure 6.6: Histogram - sites by age (Holocene only)

6.3. Palaeointensity results

Fig. 6.7 shows the distribution of sites by palaeointensity method. The Shaw method (including its modiﬁcations) has been the most popular palaeointensity method in Iceland (used extensively by Shaw himself on lavas from the Eastern Region). The Thellier method and its derivatives (i.e. ZI/Coe, IZZI and MT4) have also been widely utilised - further details on palaeointensity methods are provided in Section 4.10.

Figure 6.7: Histogram - sites by palaeointensity method

The geographic distribution of palaeointensity results is shown in Fig. 6.8 and 6.9. In contrast to all site results (Fig. 6.2), palaeointensity studies have targeted the younger lavas/neo-volcanic zone towards the central longitude bands and spreading

61 6. Overview of ICEPMAG data ridge. However, the geographic distribution of the palaeointensity sites is also dominated by a number of individual studies. Two large palaeointensity studies were carried out in the Eastern Region by Shaw and others (Roberts and Shaw, 1984; Shaw et al., 1982), which contribute 128 and 68 palaeointensity results to ICEP- MAG, respectively. The other peak in distribution towards the southwest relates to a study of the ‘R3-N3’ reversal in the Esja-Hvalfjörður area (Goguitchaichvili et al., 1999a). To date there have not been any studies published on palaeointensity for the northwestern regions.

Figure 6.8: Geographic distribution of all palaeointensity results

Biases in the geographic distributions of palaeointensity results are reﬂected in the age distribution (Fig. 6.10). Many of the palaeointensity sites are younger than 1 Ma, and their frequency decreases towards 10 Ma. The palaeointensity results between 12 - 14 Ma are from three studies in Eastern Iceland (Lawley, 1970; Roberts and Shaw, 1984; Linder and Leonhardt, 2009).

62 6.4. Other distributions

Figure 6.9: Histogram - all palaeointensity results by latitude and longitude

Figure 6.10: Histogram - palaeointensity sites by age (all results)

6.4. Other distributions

Fig. 6.11 shows the distribution of studies by publication year (in 5 year intervals). The number of sites published each year is shown in Fig. 6.12. The period 1975 - 1985 was dominated by a number of large studies (e.g., Watkins and Walker, 1977; Kristjánsson et al., 1980; Saemundsson et al., 1980; McDougall et al., 1984). It can be seen that the number of sites published in a year has decreased signiﬁcantly since the 1980s. The most recent large study (∼500 studies) was published in 2009 on lavas from the Westfjords (Kristjánsson, 2009).

63 6. Overview of ICEPMAG data

Figure 6.11: Histogram - number of studies by reference year (5 year intervals)

Figure 6.12: Histogram - number of sites published by reference year

Distribution of the number of samples collected per site is shown in Fig. 6.13. In Iceland, the number of samples collected per site has typically been ﬁve or less; many of the larger studies considered 3 to 4 samples per site (or fewer) to be adequate for palaeodirectional work. As noted by McDougall et al. (1984) “...larger numbers of samples per ﬂow is not necessary because of the very good stability of original remanence in Icelandic lavas, the generally large secular variation, and the exceptionally large size of the present survey” (McDougall et al., 1984). However, more recent papers might disagree, e.g., the global compilation of Cromwell et al. (2018) only includes two studies from Iceland.

McDougall’s view is supported by the distribution of α95 and κ values for direction determinations in ICEPMAG (Fig. 6.14 and 6.15): ∼4,500 sites have a 95%

64 6.4. Other distributions

Figure 6.13: Histogram - number of samples collected per site (<12)

◦ ◦ ◦ conﬁdence interval (α95) ≤ 5 , and 2,000 sites have α95 values between 6 and 10 . Kristjánsson (2013) showed that collecting more than four samples from an Icelandic lava is unnecessary as directions calculated from four samples typically have an α95 ◦ value in the order of 5 . Van der Voo (1990) and Butler (1998) suggest that an α95 of less than ∼15◦ is adequate for deﬁning a VGP.

Figure 6.14: Histogram - sites by α95 value (<40)

65 6. Overview of ICEPMAG data

Figure 6.15: Histogram - sites by precision parameter κ (<4000)

The reliability of remanence directions from Icelandic lavas may be aided by relatively low tectonic action; lava piles in Iceland experience slow spreading due to the action of the central ridge but generally do not experience any signiﬁcant upheaval (aside from being buried and uplifted). Bedding angles in Iceland typically dip towards the spreading ridge at an angle between 2 - 10◦ from the horizontal. As shown in Fig. 6.16, the bedding dip angle reported for sites in ICEPMAG is mostly 12◦ or less. The higher dip values come from: • Mosfellssveit, southwest Iceland (Kristjánsson et al., 1991) - up to 30◦ • Langidalur, Northern Iceland (Kristjánsson et al., 1995) - up to 28◦ • Skorradalur, western Iceland (Kristjánsson, 1995) - up to 18◦

Figure 6.16: Histogram - sites by estimated bedding dip (all results)

66 7. Conclusion

7.1. Summary

The past direction and intensity of Earth’s magnetic field can be preserved over geological time in the magnetisation of rocks. The lavas of Iceland provide excellent material for studying the past behaviour and long-term variation of the geomagnetic field. Palaeomagnetic research in Iceland commenced in the 1920s, although not on a significant scale until the 1950s, and contributed to some key concepts fundamental to the fields of palaeomagnetism and geomagnetism, and essential for the progression of other Earth sciences.

Early pioneers of palaeomagnetism, including Jan Hospers, Trausti Einarsson, Þorb- jörn Sigurgeirsson and Ari Brynjolfsson, used Iceland as a testing ground for emerg- ing ideas about geomagnetic field behaviour. The work of these scientists resulted in several world firsts including: detailed demonstrations of polarity reversals; formation of the geocentric axial dipole (GAD) hypothesis; successful isolation of primary remanence directions using alternating field (AF) demagnetisation; geomagnetic polarity mapping and construction of long reversal records; calculation of virtual geomagnetic poles (VGPs) from palaeodirections; and plotting of transitional pole paths.

Since the 1960s, palaeomagnetic samples have been collected from thousands of lava ﬂows across Iceland. The main focus of these studies has been to obtain accurate palaeodirections and natural remanence intensities (NRMs) from long sequences of lavas for the purposes of magnetostratigraphy and geochronology. Many studies have investigated hundreds of lavas at a time. By far the largest of these studies have been those of Watkins and Walker (1977) in Eastern Iceland and McDougall et al. (1984) in Northwest Iceland, both of which include results from over a thousand lava ﬂows respectively. However, comparatively few investigations have been carried out on the palaeointensity of Icelandic lavas.

ICEPMAG compiles palaeomagnetic data from over 9,200 Icelandic sampling sites (mostly lavas) - one of the largest collections of this type from a single location anywhere in the world. ICEPMAG is based on the design of the GEOMAGIA50

67 7. Conclusion database and was constructed to allow easy transfer of information to the MagIC global palaeomagnetic database by utilising the same vocabulary and data ﬁelds. All the sites in ICEPMAG contain either direction calculations (direction and inclination) or palaeointensity measurements. Of the sites in ICEPMAG: 8,649 contain direction only, 218 intensity only, and 337 both direction and intensity.

ICEPMAG is presented in the form of a publicly available website which allows users to query the database. Searches can be customised with a range of constraints including: geographic constraints (region, location or between certain coordinates), age constraints, authors and years of publication, rock and sample/specimen types, dating methods, palaeointensity methods, directional polarity and statistical constraints. The ICEPMAG website also produces interactive maps, VGP plots and downloadable spreadsheets derived from search results. Data compiled into the ICEPMAG database will also be adapted and uploaded in the MagIC database. At the time of writing, MagIC only contains 2,634 sites from Iceland; ICEPMAG will contribute an additional 6,570 sites to the MagIC database.

The geographic distribution of all Icelandic sites shows a bias away from the southern regions and central longitudinal bands which are coincident with more recently active volcanic zones and the central spreading ridge running through the country. The majority of results come from the older lavas of the Westfjords (>2,500 sites) and the Eastern Region (>3,000 sites). Temporally, the sites are distributed reasonably well over the last 16 Ma, with peaks between 2 - 3 Ma, 8 - 10 Ma and 12 - 14 Ma. Most of the Holocene sites come from recent lavas (<250 years old).

In Iceland, the number of samples collected per site has typically been ﬁve or less, however, the distribution of α95 values shows reasonable accuracy in direction deter- ◦ minations: ∼4,500 sites have a 95% conﬁdence interval (α95) ≤ 5 , and 2,000 sites ◦ ◦ have α95 values between 6 and 10 .

The distributions of palaeointensity results are more clustered towards younger lavas and the central latitude bands of Iceland; most of the palaeointensity results come from lavas younger than 7 Ma. In Iceland the most popular palaeointensity techniques have been the Shaw and Thellier methods, and their various derivatives (e.g., ZI, IZZI and MT4).

The ICEPMAG database is intended to promote the use of Icelandic palaeomagnetic data in global analyses of palaeomagnetic field behaviour. Iceland is one of very few high latitude (>60◦) locations where long sequences of lavas suitable for detailed palaeomagnetic study are exposed, and presents excellent opportunities for investi- gating long-term palaeodirectional variations. Results from analyses of palaeomagnetic data from Iceland are therefore vital for understanding the long-term nature of Earth’s magnetic field and the processes which generate the field.

68 7.2. Path forward

7.2. Path forward

7.2.1. MagIC uploads

After completion and ﬁnalisation of ICEPMAG v1.0, the dataset will be adapted for uploading into the MagIC global palaeomagnetic database. MagIC is a contribution- based database, so ICEPMAG’s master spreadsheet will be separated into individual spreadsheets for each study. This will be achieved with Python scripting and will tie- in with recent eﬀorts to better integrate the GEOMAGIA50 and MagIC databases. ICEPMAG has been designed with this process in mind so the adaptation will be straightforward.

7.2.2. Updates and error checking

Data from future palaeomagnetic studies can be appended to ICEPMAG’s master spreadsheet and ‘pushed’ to the MySQL server in order to update the database and website. The MagIC tranfer script, developed for adapting ICEPMAG’s dataset into formatted spreadsheets suitable for uploading to MagIC, can also be utilised to add new contributions to the global database.

During compilation of the ICEPMAG dataset, eﬀorts were made to identify and correct obvious errors in data (e.g., clear typographical errors, numbers exceeding possible values) as they were transferred from various sources. However, it is likely that there are still some errors in the database which will need to be corrected. Visualisation and processing of ICEPMAG data, enabled through the MagIC and ICEPMAG websites, will aid in detecting these errors. Identiﬁed errors can be corrected in ICEPMAG’s master spreadsheet and pushed to the MySQL server and re-uploaded to both websites. The updating and error checking process, which closes the loop in the construction of ICEPMAG, is illustrated in Fig. 7.1.

A signiﬁcant opportunity also exists to improve the accuracy and precision of geological and stratigraphic age estimations in ICEPMAG. There is a paucity of detailed age information for palaeomagnetic sites in Iceland; the vast majority of age determinations in the database are only estimates with approximate precision in the order of ± 1 to 2 Myr, and fewer than 200 sites report an accurate standard deviation or error range. The functionality and usefulness of the data contained in ICEPMAG could be improved with a comprehensive review and update of age estimations. With more accurate dating information it would be possible to better correlate long sequences of palaeomagnetic variations across Iceland and with global datasets for the past 16 Ma.

69 7. Conclusion

Add new studies

Update Compile Update spreadsheets database MySQL server

Upload to MagIC ICEPMAG website

Error detection and QA/QC

Figure 7.1: Error checking and update process for ICEPMAG

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A. Appendix

83 A. Appendix Continued on next page AREAS (not shown) Merged with Location ID ) Default None ) Default None ° ° Not used in ICEPMAG For MagIC EXT_DATABASES (not shown) external_database_- id n_samplesn_specimens N/A N/A CSV download only None alt_id CSV download only None AltID Optional ALT_ID (Table A.16) column. MASTER COLUMN =column column name name as it in appearsthe the on master website the table. (Default ICEPMAG = website. HTMLonly field USAGE HEADER = describes is = only how always abbreviated appears the displayed,TABLE in field Optional = downloadable is = name text displayed on of depends file, For relational on MagIC SQL user = table. input, not CSV used download in the ICEPMAG website). ID Table A.1: Master data fields/column names and relational tables. DATA FIELD = simple text name of No. of samples collected No. of specimens measured Alteration check type ID #12 DATA FIELD3 Unique identifier Reference ID4 External Database5 ID MASTER Region COLUMN UID ID67 Area HTML ID HEADER8 ref_id Location ID9 Site name10 Site latitude11 USAGE Site longitude region_id Height12 Elevation UID13 area_id location_id14 RefID site_name List lat of15 sample lon names ID Sampling TABLE type (SQL) ID RegID1617 samples height LocID elevation18 Specimen names Not19 Specimen used sample_type_id type in Site ID ICEPMAG name Default20 Result type ID Default21 Result quality ID22 Method specimens code Lat. SampTypeID ID Lon. ( 23 Geologic specimen_type_id ( class Default ID N/A N/A24 Geologic type N/A ID25 Lithology result_type_id Default ID result_quality_id SpecTypeID None Default Bedding dip26 method_code_id REFS Bedding (Table geologic_class_id dip A.2) direction Optional N/A27 Not geologic_type_id used28 in Not ICEPMAG used REGIONS Not in (Table bed_dip_direction A.3) used Cooling ICEPMAG GeoClassID in rate ICEPMAG check lithology_id ID For Cooling MagIC Default LOCATIONS rate (Table GeoTypeID For A.4) CSV bed_dip CSV MagIC None download download For only only N/A MagIC CSV cool_id download only SAMPLE_TYPES (Table A.8) None None None Not used Optional RESULT_QUALITY_ID CSV (not in download shown) ICEPMAG only RESULT_TYPE_ID cooling_rate (not SPECIMEN_TYPES Optional shown) MAGIC_CODE_ID (Table (not A.9) shown) For N/A None MagIC Not used in ICEPMAG CSV download only Not GEOLOGIC_CLASS_ID used (Table For A.5) in MagIC ICEPMAG GEOLOGIC_TYPE_ID None (Table LITHOLOGIES A.6) (not shown) For MagIC CSV download only COOL_ID (not shown) None None

84 Table A.1 – continued from previous page # DATA FIELD MASTER COLUMN HTML HEADER USAGE ID TABLE (SQL) 29 Dating method ID date_id DatID Default DATE_ID (Table A.7) 30 Age estimate age Age (Ma) Default None 31 Stdev of age age_sigma N/A CSV download only None Estimated age range 32 age_low Age_min (Ma) Default None (minimum) Estimated age range 33 age_high Age_max (Ma) Default None (maximum) 34 Age unit ID age_unit_id Not used in ICEPMAG For MagIC AGE_UNIT_ID (not shown) 35 Demag type ID demag_type_id DemagID Optional DEMAG_TYPE_ID (Table A.10) Peak demagnetisation 36 demag_step_max N/A CSV download only None step Specimen direction specimen_dir_calc_- SPECIMEN_DIR_CALC_ID (Table 37 SpecDCID Optional calculation ID id A.11) Sample direction sample_dir_ave_- SAMPLE_DIR_AVE_METHOD_ID 38 SampDAMID Optional average method ID method_id (Table A.12) Site direction average site_dir_ave_- SITE_DIR_AVE_METHOD_ID 39 SiteDAMID Optional method ID method_id (Table A.13) 40 Tilt correction dir_tilt_correction N/A CSV download only None 41 Declination dir_dec Dec. (°) Default None 42 Inclination dir_inc Inc. (°) Default None Declination 43 dir_dec_alt N/A CSV download only None (alternative) Inclination 44 dir_inc_alt N/A CSV download only None (alternative) Declination 45 dir_dec_unc N/A CSV download only None (uncorrected) Inclination 46 dir_inc_unc N/A CSV download only None (uncorrected) 47 Alpha95 dir_alpha95 α95 (°) Default None 48 Theta63 dir_theta63 N/A CSV download only None 49 Direction R dir_r N/A CSV download only None 50 Direction K dir_k K Default None 51 K ratio dir_k_ratio N/A CSV download only None 52 Direction N samples dir_n_samples N_dir Default None 53 Direction N specimens dir_n_specimens N/A CSV download only None 54 Polarity ID dir_polarity PolID Optional DIR_POLARITY_ID (Table A.14) Direction NRM origin 55 dir_nrm_origin Not used in ICEPMAG For MagIC DIR_NRM_ORIGIN_ID (not shown) ID 56 Contact test ID contact_test Not used in ICEPMAG For MagIC CONTACT_TEST_ID (not shown) 57 VGP latitude vgp_lat VGP_lat (°) Default None 85 Continued on next page A. Appendix Continued on next page ) Default None ° T) Default None T) Default None µ µ ( int σ Table A.1 – continued from previous page vgp_lat_altvgp_long_alt N/A N/Avadm CSV download only CSV download only None magn_vol_sigma None N/Amagn_mass_sigma N/A N/Ah_ﬁeld CSV downloadpi_method_id only CSV download only None None CSV downloadint_abs_sigma only N/A IntID None int_abs_sigma_perc N/Aint_n_specimens N_int CSV Default download only None CSV download only None PI_METHOD_ID (Table A.15) Default None VGP latitude (alternative) VGP longitude (alternative) Virtual axial dipole moment Stdev magnetisation (vol) Stdev magnetisation (mass) Magnetising ﬁeld strength Paleointensity method ID Absolute Paleointensity Sigma Absolute Paleointensity Sigma % No. specimens incalc PI #58 DATA FIELD59 VGP longitude60 6162 MASTER COLUMN vgp_long63 VGP DP64 VGP HTML DM HEADER65 VGP Alpha9566 VGP No. Samples67 Virtual dipole moment USAGE Stdev. VDM68 VGP_lon No. ( vdm samples in69 vgp_n_samples vgp_dp VDM vgp_alpha95 vgp_dm7071 Stdev. vdm_n_samples VADM No. samples72 N/A vdm_sigma in ID VADM Magnetisation TABLE (vol) (SQL) N/A73 N/A vadm_n_samples74 N/A Magnetisation N/A vadm_sigma magn_volume N/A (mass)75 N/A N/A76 magn_mass77 Demagnetisation level Susceptibility (vol) N/A78 N/A CSV Stdev download magn_demag_level of only susceptibility79 CSV download only CSV None download N/A only80 susc_mean N/A susc_sigma CSV Koenigsberger download only ratio CSV None CSV download download only81 only None CSV None CSV download download82 only None only None Absolute q_koenig Paleointensity None None 83 CSV int_abs N/A N/A download CSV only download only84 None None 85 CSV CSV download No. download only samples only in86 PI N/A calc None None int_n_samples Anisotropy Int. ( CSV CSV download download only only N/A None None aniso_type_id CSV download only None Not used in ICEPMAG CSV download Not only utilised None ANISO_TYPE_ID (not shown)

86 Table A.1 – continued from previous page # DATA FIELD MASTER COLUMN HTML HEADER USAGE ID TABLE (SQL) Anisotropy tilt 87 aniso_tilt_correction Not used in ICEPMAG Not utilised None correction 88 V1 aniso_v1 Not used in ICEPMAG Not utilised None 89 V2 aniso_v2 Not used in ICEPMAG Not utilised None 90 V3 aniso_v3 Not used in ICEPMAG Not utilised None 91 # perc an PI calc aniso_perc Not used in ICEPMAG Not utilised None 92 # total an PI calc aniso_total Not used in ICEPMAG Not utilised None 93 # p an PI calc aniso_p Not used in ICEPMAG Not utilised None 94 # pp an PI calc aniso_pp Not used in ICEPMAG Not utilised None 95 # t an PI calc aniso_t Not used in ICEPMAG Not utilised None 96 # l an PI calc aniso_l Not used in ICEPMAG Not utilised None 97 # f an PI calc aniso_f Not used in ICEPMAG Not utilised None 98 # ll an PI calc aniso_ll Not used in ICEPMAG Not utilised None 99 # ff an PI calc aniso_ff Not used in ICEPMAG Not utilised None 100 # vg an PI calc aniso_vg Not used in ICEPMAG Not utilised None 101 # fl an PI calc aniso_fl Not used in ICEPMAG Not utilised None 102 # test an PI calc aniso_test Not used in ICEPMAG Not utilised None 103 # ftest12 an PI calc aniso_ftest12 Not used in ICEPMAG Not utilised None 104 # ftest23 an PI calc aniso_ftest23 Not used in ICEPMAG Not utilised None 87 A. Appendix Kristjansson 2010 Dossing et al 2016 Kristjansson et al 1980 Tanaka et al 1995 Brown et al 2006 Linder and Leonhardt 2009 Kristjansson et al 1998 Helgason and Duncan 2001 Kristjansson et al 1991 Udagawa et al 1999 Roberts and Shaw 1984 McDougall et al 1984 13963 N/A 9265 Doell 1972 9325 9759 Continued on next page 10.1111/j.1365- 246X.2006.03034.x 10.1111/j.1502- 3885.1998.tb00863.x 10.1111/j.1365- 246X.1972.tb05763.x 10.1016/S0031- 9201(99)00073-4 10.1111/j.1365- 246X.1984.tb01913.x 10.1029/JB089iB08p07029 7265 7029- 7060 26 459-479 456 98-111 10.1016/j.epsl.2016.09.022 N/A 115 147-171 4776 89-102 10.5636/jgg.47.89 637-651 89 7307 177 88-101 10.1016/j.pepi.2009.07.013 N/A Geophys. J. Royal Astron. Soc. Earth Planet. Sci. Lett. Phys. Earth Planet. Inter. J. Geomag. Geoel. Geophys. J. Royal Astr. Soc. J. Geophys. Res. Phys. Earth Planet. Inter. 2010 Jökull1972 2016 60 149-1641980 N/A J. Geophys.1999 47 31-421995 N/A 10.7288/V4/MagIC/91211984 8511 1984 2006 Geophys. J.2009 Int. 1671998 53-69 Boreas2001 Geology1991 27 Jökull 29 1-13 179-182 41 10.1130/0091-7613(2001)029 47-60 N/A N/A 12028 Paleomagnetic observations at three locations in the Pleistoceneof lava southwest sequences and south Iceland Palaeomagnetic Studies of IcelandicFlows Lava High northern geomagnetic fieldand behavior new constraints onPaleomagnetic the and Gilsá 40Ar/39Ar event: results0.5-3.1 of Ma basalts fromIceland Jökuldalur, Stratigraphy and paleomagnetism ofEsja, the Eyrarfjall and AkrafjallSW-Iceland mountains, Age and magnetism ofarea, lavas Eastern in Iceland: Jökuldalur Gilsá event revisited Paleosecular variation of directionintensity and from two Pliocene-Pleistocene lava sections in SouthwesternThe Iceland relationship between theand magnitude direction of theduring geomagnetic the field late Tertiary in Eastern Iceland Magnetostratigraphy and geochronology of Northwest Iceland Microwave paleointensity from thegeomagnetic R3-N3 field reversal Paleomagnetic full vector recordconsecutive of Mid four Miocene geomagnetic reversals Stratigraphy, palaeomagnetism and agevolcanics of in the upperThjorsardalur regions valley, central of southern the Iceland Glacial-interglacial history of theregion, Skaftafell southeast Iceland Paleomagnetic stratigraphy of the Mosfellssveit area, SW-Iceland: astudy pilot = MagIC reference code, SHORT = abbreviated name for website menu) Table A.2: Relational table - Reference IDs (DOI = Digital Object Identifier for permanent link, MAGIC Døssing, A., Muxworthy, A. R., Supakulopas, R., Riishuus, M. S., Niocaill, C. M. Kristjánsson L., I. B. Fridleifsson and N. D. Watkins Udagawa S., H. Kitagawa, A. Gudmundsson, O. Hiroi, T. Koyaguchi, H. Tanaka, L. Kristjánsson and M. Kono Tanaka H., M. Kono and S. Kaneko Roberts N. and J. Shaw McDougall I., L. Kristjánsson and K. Saemundsson Brown M.C., J. Shaw and A.T. Goguitchaichvili Linder J. and R. Leonhardt Kristjánsson L., R. A. Duncan and A. Gudmundsson Helgason J. and R. A. Duncan Kristjánsson L., H. Johannesson and I. B. Fridleifsson ID1 AUTHORS Kristjánsson2 L. TITLE Doell, R.R 3 4 YEAR5 PUBLICATION VOL6 PAGES DOI7 8 9 10 MAGIC SHORT 11 12 13

88 Table A.2 – continued from previous page ID AUTHORS TITLE YEAR PUBLICATION VOL PAGES DOI MAGIC SHORT Kristjansson Kristjánsson L. Paleomagnetic studies in Skardsheidi, and 14 and A. 2001 Jökull 50 33-48 N/A N/A South-Western Iceland Gudmundsson Gudmundsson 2001 Kristjánsson L., A. Stratigraphy and paleomagnetism of a Geol. Kristjansson et 15 Gudmundsson 3-km thick Miocene lava pile in the 1995 84 813-830 10.1007/BF00240570 N/A Rundschau al 1995 and H. Mjoifjördur area, eastern Iceland Haraldsson Goguitchaichvili No evidence for strong fields during the Earth Planet. 10.1016/S0012- Goguitchaichvili 16 A., M. Prévot 1999 167 15-34 15281 R3-N3 Icelandic geomagnetic reversal Sci. Lett. 821X(99)00010-2. et al 1999a and P. Camps Kristjansson Kristjánsson L. Secular variation and reversals in a Earth, Planets, and 17 and H. composite 2.5 km thick lava section in 1999 51 261-276 10.1186/BF03352230 6209 Space Johannesson Johannesson central Western Iceland 1999 Saemundsson K., L. K-Ar dating, geological and paleomagnetic J. Geophys. 3628- Saedmundsson 18 Kristjánsson, I. study of a 5-km lava succesion in northern 1980 85 10.1029/JB085iB07p03628 7226 Res. 3646 et al 1980 McDougall and Iceland N. D. Watkins Kristjánsson L., H. Johannesson Stratigraphy, age and paleomagnetism of Kristjansson et 19 1992 Jökull 42 31-44 N/A N/A and I. Langidalur, northern Iceland al 1992 McDougall A new study of paleomagnetic directions in the Miocene lava pile between Kristjansson 20 Kristjánsson L. 2009 Jökull 59 33-50 N/A N/A Arnarfjördur and Breidafjördur in the 2009 Vestfirdir peninsula, Northwest Iceland Kristjánsson L., Paleomagnetism and geology of the 10.1016/0040- Kristjansson et 21 R. Pätzold and Patreksfjördur-Arnarfjördur region of 1975 Tectonophys. 25 201-216 5397 1951(75)90027-X al 1975 J. Preston Northwest Iceland Kristjansson Kristjánsson L. Stratigraphy and paleomagnetism of the and 22 and H. lava pile south of Isafjardardjup, 1996 Jökull 44 3-16 N/A N/A Johannesson Johannesson NW-Iceland 1996 Kristjánsson L., A detailed palaeomagnetic study of the B. S. Hardarson 991- 10.1111/j.1365- Kristjansson et 23 oldest (ca. 15 Myr) lava sequences in 2003 Geophys. J. Int. 155 6515 and H. 1005 246X.2003.02111.x al 2003 Northwest Iceland Audunsson Kristjánsson L., A. A paleomagnetic study of stratigraphic Gudmundsson, relations in the lava pile of Nordurardalur Kristjansson et 24 2006 Jökull 56 37-55 N/A N/A A. Hjartarson and Austurdalur, Skagafjördur, North al 2006 and H. Iceland Hallsteinsson Kristjansson Kristjánsson L. Stratigraphy and paleomagnetism of lava and 25 and A. sequences in Sudurdalur, Fljotsdalur, East 2005 Jökull 55 17-32 N/A N/A Gudmundsson Gudmundsson Iceland 2005 Kristjánsson L., H. Johannesson, J. Brunhes-Matuyama paleomagnetism in Can. J. Earth Kristjansson et 26 1988 25 215-225 N/A 13692 Eiriksson and three lava sections in Iceland Sci. al 1988 A. I. Gudmundsson 89 Continued on next page A. Appendix Kristjansson et al 1990 Kristjansson 2014 McDougall et al 1976 Kristjansson et al 2004 Kristjansson 2003 Kristjansson and Sigurgeirsson 1993 Watkins and Walker 1977 Kristjansson 1995 Watkins et al 1977 Watkins et al 1975 Marshall et al 1988 Goguitchaichvili et al 1999b N/A 13315 Piper et al 1977 13476 14575 14865 Shaw et al14353 1982 11875 Continued on next page 10.1111/j.1502- 3885.1990.tb00420.x 10.2475/ajs.276.9.1078 N/A 10.1016/0040- 1951(77)90067-1 10.1111/j.1365- 246X.1995.tb05724.x 10.1029/JB087iB08p06396 15898 Helgason10.1111/j.1365- 1982 246X.1977.tb01307.x 10.1111/j.1365- 246X.1982.tb06970.x 10.1016/0012- 821X(75)90063-1 10.1029/88JB0015810.1016/S0031- 13006 9201(99)00064-3 1078- 1095 6396- 6404 11681- 11698 93 582-595 10.1007/s00531-004-0409-445 15209 275-288 10.5636/jgg.45.27587 N/A 49 609-632 68 211-218 27 436-444 93 115 53-66 Internat. J. Earth. Sci. J. Geomag. Geoel. J. Geophys. Res. Geophys. J. Royal Astr. Soc. Geophys. J. Royal Astr. Soc. Earth Planet. Sci. Lett. J. Geophys. Res. Phys. Earth Planet. Inter. 1990 Boreas2014 Jökull1976 19 Am. J. 39-55 Sci.2004 64 276 1-142003 Jökull N/A1993 521982 21-321977 N/A N/A Tectonophys.1977 401982 227-244 1975 14557 1988 1995 Geophys. J.1999 Int. 121 435-443 Table A.2 – continued from previous page Palaeomagnetism of Pliocene-Pleistocene sediments and lava flowsFlatey, on North Tjörnes Iceland and Paleomagnetic studies on thebetween lava Skalavik pile and Alftafjorour, Northwest Iceland Geochronology and paleomagnetism ofMiocene-Pliocene a lava sequence at Bessastadaa, Eastern Iceland Stratigraphy and paleomagnetism ofkm a composite 2.9 lava sectionNorthern in Iceland: Eyjafjördur, a reconnaissance study Paleomagnetic observations on Late Quaternary basalts around Reykjavikon and the Reykjanes peninsula, SW-Iceland The R3-N3 and R5-N5transition palaeomagnetic zones in Iceland revisited Magnetostratigraphy of Eastern IcelandMagnetostratigraphy of the exposedsection lava east of theReydarfjördur, 1977 IRDP Iceland drill holeDyke in magnetisation, magnetostratigraphy and upper crustal Am. structureReydarfjördur J. in area Sci. of the eastern Iceland Upper Miocene and Pliocenevariation in secular the BorgarfjördurWestern area Iceland of 277The magnitude of thein 513-584 paleomagnetic Iceland field between 2 and 6 Myr ago 10.2475/ajs.277.5.513A detailed survey ofthe the Gilsa type geomagnetic location polarity for event Preliminary paleointensity measurements and detailed magnetic 12067 analysesfrom of the basalts Skalamaelifell excursion, Southwest Iceland New palaeomagnetic results fromNeogene Icelandic lavas An attempt to determinegeomagnetic the field absolute intensity duringGauss-Matuyama the reversal Eiriksson J., A. I. Gudmundsson, L. Kristjánsson and K. Gunnarsson McDougall I., N. D. Watkins and L. Kristjánsson Kristjánsson L., A. Gudmundsson and B. S. Hardarson Kristjánsson L. and M. Sigurgeirsson Watkins N. D. and G. P. L. Walker Piper J. D. A., M. G. Fowler and I. L. Gibson Watkins N. D., I. McDougall and L. Kristjánsson Shaw J., P. Dagley and A. E. Mussett Watkins N. D., L. Kristjánsson and I. McDougall Marshall M., A. Chauvin and N. Bonhommet Goguitchaichvili A., M. Prévot, J. Thompson and N. Roberts ID AUTHORS27 TITLE28 Kristjánsson L. 29 30 31 YEAR Kristjánsson L. PUBLICATION32 VOL33 PAGES DOI34 Helgason J. 35 36 37 MAGIC SHORT 38 39 40 Kristjánsson L. 41

90 Table A.2 – continued from previous page ID AUTHORS TITLE YEAR PUBLICATION VOL PAGES DOI MAGIC SHORT Geophys. J. Dagley P. and Paleomagnetic evidence for transitional 10.1111/j.1365- Dagley and 42 1974 Royal Astron. 36 577-598 16068 E. A. Lawley behaviour of the geomagnetic field 246X.1974.tb00614.x Lawley 1974 Soc. The intensity of the geomagnetic field in Earth Planet. 10.1016/0012- 43 Lawley E. A. Iceland during Neogene polarity transitions 1970 10 145-149 15441 Lawley 1970 Sci. Lett. 821X(70)90076-2 and systematic deviations Schweitzer C. Paleointensity measurements on Schweitzer and 44 1980 J. Geophys. 47 57-60 N/A 14469 and H. Soffel postglacial lavas from Iceland Soffel 1980 Geophys. J. Strong geomagnetic fields during a single 10.1111/j.1365- 45 Shaw J. 1975 Royal Astr. 40 345-350 12453 Shaw 1975 Icelandic polarity transition 246X.1975.tb04136.x Soc. 99-105 On the suitability of igneous rocks for Earth Planet. (cf. p. 10.1016/0012- 46 Smith P. J. 1967 2 14360 Smith 1967a ancient geomagnetic field determination Sci. Lett. 329- 821X(67)90108-2 330) Camps, P., Singer, B.S., The Kamikatsura event and the Carvallo, C., Matuyama-Brunhes reversal recorded in Earth Planet. Camps et al 47 Gogui- 2011 310 33-44 10.1016/j.epsl.2011.07.026. 14385 lavas from Tjörnes Peninsula, northern Sci. Lett. 2011 tchaichvili, A., Iceland Fanjat, G. and Allen, B. Stanton, T., Riisager, P., New palaeointensity data from Holocene Phys. Earth Stanton et al 48 Knudsen, M.F. 2011 186 1-10 10.1016/j.pepi.2011.01.006 12459 Icelandic lavas Planet. Inter. 2011 and Thordarson, T. Tanaka, H., Palaeointensity determinations from 10.1111/j.1365- Tanaka et al 49 Hashimoto, Y. historical and Holocene basalt lavas in 2012 Geophys. J. Int. 189 833-845 16276 246X.2012.05412.x 2012 and Morita, N. Iceland Cromwell, G ., New paleointensity results from rapidly Tauxe, L. and J. Geophys. 2913- Cromwell et al 50 cooled Icelandic lavas: Implications for 2015 120 10.1002/2014JB011828 14348 Halldorsson, Res. 2934 2015 Arctic geomagnetic field strength S.A. Magma flow and palaeo-stress deduced Eriksson P.I., from magnetic fabric analysis of the Geol. Soc. Riishuus M.S., Eriksson et al 51 Alftafjordur dyke swarm: implications for 2015 London Spec. 396 107-132 10.1144/SP396.6 N/A and Elming 2015 shallow crustal magma transport in Publ. S.-A. Icelandic volcanic systems Helgason J. and Stratigraphy, 40Ar-39Ar dating and Helgason and 52 2013 Jökull 63 33-54 N/A N/A R. A. Duncan erosional history of Svinafell, SE-Iceland Duncan 2013 New evidence on an episode of Stud. Geophys. Kristjansson 53 Kristjánsson, L. geomagnetic instability, recorded in middle 2015 59 309-324 10.1007/s11200-014-0910-6 N/A Geod. 2015 Miocene lava flows in Northwest Iceland Palaeointensities from Pliocene lava Tanaka and Tanaka, H. and sequences in Iceland: emphasis on the 54 2016 Geophys. J. Int. 205 694-714 10.1093/gji/ggw031 N/A Yamamoto Yamamoto, Y. problem of Arai plot with two linear 2016 segments Jicha, B.R., Kristjánsson, L., Brown, New age for the Skalamaelifell excursion Earth Planet. 55 M.C., Singer, and identification of a global geomagnetic 2011 310 509-517 10.1016/j.epsl.2011.08.007 N/A Jicha et al 2011 Sci. Lett. B.S., Beard, event in the late Brunhes chron B.L, Johnson, C.M.

91 Continued on next page A. Appendix Li and Beske-Diehl 1991 Senenayake et al 1982 Beske-Diehl and Li 1993 Ferk and Leonhardt 2009 Kristjansson 2004 Verard et al 2012 Helgason et al 1990 Oliva-Urcia and Kontny 2012 Muxworthy 2010 Muxworthy and Taylor 2011 Brynjolfsson 1956 Michalk et al 2008 Goguitchaichvili et al 1999c Kristjansson 1985 5118 N/A N/A N/A Smith 1967b Continued on next page 10.1111/j.1365- 246X.1990.tb01748.x 10.1111/j.1365- 246X.2011.05163.x 10.1111/j.1365- 246X.2008.03740.x 10.1029/1999JB900260 N/A 10.1029/JB090iB12p10129 N/A 10.1111/j.1365- 246X.1967.tb03120.x 29219- 29238 10-27 10.1016/j.pepi.2012.03.012 N/A 10129- 10135 1953 1-172 N/A N/A Hospers 1953 18 597-600173 10.1029/91GL00816 409-420 34 N/A 141-14698 10.5636/jgg.34.141177 403-417 19-30 10.1029/92JB01253104 N/A 10.1016/j.pepi.2009.07.011 N/A N/A 200- 201 90 5612 641-657179 10.1007/s11200-011-9013-9 239-258 21-31 N/A 10.1016/j.pepi.2010.01.003 N/A 43 143-133 10.1007/BF00623094 N/A PhD thesis - University of Cambridge Geophys. Res. Lett. Geophysical J. Internat. J. Geomag. Geoel. J. Geophys. Res. Phys. Earth Planet. Inter. J. Geophys. Res. Phys. Earth Planet. Inter. J. Geophys. Res. Stud. Geophys. Geod. Geophys. J. Royal Astr. Soc. Phys. Earth Planet. Inter. Naturwis- senschaften 19641991 Geol. Mijnb. 432008 403-413 N/A1982 1993 2009 1999 126622004 Wensink 1964 Jökull2012 1990 54 Geophys. J.1985 Int. 57-632012 103 N/A1967 13-24 2010 2011 Geophys. J. Int. 187 N/A 1956 118-127 Table A.2 – continued from previous page Secular variation of earthPlio-Pleistocene magnetism basalts in of Eastern Iceland Magnetic properties of deutericin hematite young lava flows from Iceland Evaluation of the multispecimendifferential parallel pTRM method:historical a lavas test from on Iceland and Mexico Comparison between the ThellierShaw and paleointensity methods usingless basalts than 5 million years old Magnetic properties of hematiteflows in from lava Iceland: Responsehydrothermal alteration to The Laschamp geomagnetic excursion recorded in Icelandic lavas Thermodetrital and crystallodetrital magnetization in an Icelandic hyaloclastite A reconnaissance study ofdirections paleomagnetic in the TjörnesIceland Beds, Northern Variations of magnetic propertieslava in flow thin profiles: Implicationsrecording for of the the Laschamp Excursion A study of thesubglacial palaeomagnetism basalts, of SW-Iceland:comparison a with oceanic crust Magnetic and thermal effectsintrusions of in dike Iceland Remanent magnetization of maghemitized basalts from Krafla drill cores, NE-Iceland The intensity of thefield Tertiary geomagnetic Revisiting a domain-state independent method of palaeointensity determination Evaluation of the domain-statemultiple-specimen corrected absolute palaeointensity protocol: a testIceland of historical lavas from Ergebnisse bei partieller Entmagnetisierung des naturlichen Magnetismus islandischer Basalt Li H. and S. Beske-Diehl Michalk, D.M., A. R. Muxworthy, H. N. Böhnel, J. Maclennan, N. Nowaczyk Senenayake W. E., M. W. McElhinny and P. L. McFadden Beske-Diehl S. and H. Li Ferk A. and R. Leonhardt Goguitchaichvili A., M. Prévot, J. -M. Dautria and M. Bacia Vérard, C., Leonhardt, R., Winklhofer, M., Fabian, K. Helgason J., N. A. van Wagoner and P. J. C. Ryall Oliva-Urcia, B. and Kontny, A. Muxworthy, A. R. Muxworthy, A. R. and Taylor, S. N. ID56 AUTHORS Wensink57 H. TITLE58 59 60 61 YEAR62 PUBLICATION VOL63 PAGES Kristjánsson L. 64 DOI65 6667 Kristjánsson L. 68 MAGIC Smith SHORT 69 P. J. 70 71 Hospers J.72 Brynjolfsson A. Palaeomagnetic Studies of Icelandic Rocks 1953

92 Table A.2 – continued from previous page ID AUTHORS TITLE YEAR PUBLICATION VOL PAGES DOI MAGIC SHORT BSc. Honours thesis - Paleomagnetic measurements in 73 Bragason H. O. 1981 University of 1981 33-44 N/A N/A Bragason 1981 Jokuldalur Iceland (in Icelandic) Kristjánsson L. Kristjansson On uncertainties in the interpretation of 74 and H. 2007 Raust 4 17-25 N/A N/A and Audunsson remanence directions in lava flows Audunsson 2007 Levi S., H. Audunsson, R. Late Pleistocene geomagnetic excursion in A. Duncan, L. Earth Planet. 10.1016/0012- 75 Icelandic lavas: confirmation of the 1990 96 443-457 N/A Levi et al 1990 Kristjánsson, P. Sci. Lett. 821X(90)90019-T Laschamp excursion -Y. Gillot and S. P. Jakobsson Extension of the Middle Miocene Kleifakot geomagnetic instability event in Extension Kristjansson 76 Kristjánsson L. of the Middle Miocene Kleifakot 2016 Jökull 66 83-94 N/A N/A 2016 geomagnetic instability event in Ísafjörður , Northwest Iceland Pinton, A., Paleomagnetism of Holocene lava flows Giordano, G., from the Reykjanes Peninsula and the Bulletin of Pinton et al 77 2018 80 1-19 10.1007/s00445-017-1187-8 N/A Speranza, F., Tungnaá lava sequence (Iceland): Volcanology 2018 Þórðarson, Þ. implications for flow correlation and ages 93 A. Appendix

Table A.3: Relational table - Region IDs (NAME = English name, ICE_NAME = Icelandic name) ID NAME ICE_NAME 1 Capital Region Höfuðborgarsvæði 2 Southern Peninsula Suðurnes 3 Western Region Vesturland 4 Westfjords Vestﬁrðir 5 Northwestern Region Norðurland vestra 6 Northeastern Region Norðurland eystra 7 Eastern Region Austurland 8 Southern Region Suðurland

Table A.4: Relational table - location IDs. NAME = location name with Icelandic characters (e.g., ‘þ’, ‘ð’, ‘ö’, ‘á’) replaced by standard characters (e.g., ‘th’, ‘d’, ‘o’, ‘a’) for parsing through the MySQL database. ICE_NAME = location name with Icelandic characters. ID NAME ICE_NAME 0 Unknown Unknown 1 Thorisgil (Brynjudalur) Þórisgil (Brynjudalur) 2 Stora-Saudafell (Kjosarskard) Stóra-Sauðafell (Kjósarskarð) 3 Hrutagil (Kjosarskard) Hrútagil (Kjósarskarð) 4 Storoxl (Kjosarskard) Stóröxl (Kjósarskarð) 5 Thvera-Fossnes (Thjorsardalur) Þverá-Fossnes (Þjórsárdalur) 6 Askja (Dyngjufjoll) Askja (Dyngjufjöll) 7 Skaftareldahraun (Lakagigar) Skaftáreldahraun (Lakagígar) 8 Bakkabrunir (Skagafjordur) Bakkabrúnir (Skagafjörður) 9 Skagaheidi (Skagafjordur) Skagaheiði (Skagafjörður) 10 Laxargljufur Laxárgljúfur 11 Dettifoss Dettifoss 12 Gulfoss Gulfoss 13 Reydara Reyðará 14 Raudsgja (Tjornes) Rauðsgjá (Tjörnes) 15 Lon (Tjornes) Lón (Tjörnes) 16 Knarrarbrekkutangi (Svinafell) Knarrarbrekkutangi (Svínafell) 17 Breidavik (Tjornes) Breiðavík (Tjörnes) 18 Valadalstorfa (Tjornes) Valadalstorfa (Tjörnes) 19 Trollagil (Tjornes) Tröllagil (Tjörnes) 20 Fossgil (Tjornes) Fossgil (Tjörnes) 21 Sandolar (Tjornes) Sandólar (Tjörnes) 22 Sandolastong (Tjornes) Sandólastöng (Tjörnes) 23 Kerling (Tjornes) Kerling (Tjörnes) 24 Furuvik (Tjornes) Furuvík (Tjörnes) 25 Litli-Stakkur (Tjornes) Litli-Stakkur (Tjörnes) 26 Skeifa (Tjornes) Skeifá (Tjörnes) 27 Stod (Snaefellsnes) Stöð (Snæfellsnes) 28 Hvalvik (Tjornes) Hvalvík (Tjörnes) 29 Hofdakulur (Snaefellsnes) Höfðakúlur (Snæfellsnes) 30 Trollafjall (Reydarfjordur ) Tröllafjall (Reyðarfjörður ) 31 Akrafjall (Hvalfjordur) Akrafjall (Hvalfjördur) 32 Kuludalur (Hvalfjordur) Kuludalur (Hvalfjördur) 33 Hvalfjardareyri (Hvalfjordur) Hvalfjardareyri (Hvalfjördur) 34 Fossardalur (Hvalfjordur) Fossardalur (Hvalfjördur) 35 Morastadir (Hvalfjordur) Morastadir (Hvalfjördur) 36 Middalur (Hvalfjordur) Middalur (Hvalfjördur) 37 Kerlingargil (Hvalfjordur) Kerlingargil (Hvalfjördur) 38 Thornyjartindur (Hvalfjordur) Thornyjartindur (Hvalfjördur) 39 Kistufell (Hvalfjordur) Kistufell (Hvalfjördur) 40 Grafardalur-Hatindur (Hvalfjordur) Grafardalur-Hatindur (Hvalfjördur) 41 Svinaskard (Hvalfjordur) Svinaskard (Hvalfjördur) Continued on next page

94 Table A.4 – continued from previous page ID NAME ICE_NAME 42 Krengilsa (Jokuldalur) Krengilsá (Jökuldalur) 43 Budara (Jokuldalur) Budará (Jökuldalur) 44 Thvera (Jokuldalur) Þverá (Jökuldalur) 45 Adalbol (Hrafnkelsdalur) Aðalból (Hrafnkelsdalur) 46 Eiriksstadir (Jokuldalur) Eiríksstaðir (Jökuldalur) 47 Ingolfsfjall (Olfusa) Ingólfsfjall (Ölfusá) 48 Reynivallahals (Hvalfjordur) Reynivallaháls (Hvalfjördur) 49 Skalavik (Gunnarsvik) Skálavík (Gunnarsvík) 50 Spillir (Sugandafjordur) Spillir (Súgandafjörður) 51 Nupur (Sugandafjordur) Nupur (Súgandafjörður) 52 Botnsfjall (Sugandafjordur) Botnsfjall (Súgandafjörður) 53 Botnsnama (Sugandafjordur) Botnsnama (Súgandafjörður) 54 Burfell (Tjornes) Búrfell (Tjörnes) 55 Lambadalur (Dyrafjordur) Lambadalur (Dýrafjörður) 56 Urdarfjall (Dyrafjordur) Urdarfjall (Dýrafjörður) 57 Botnshestur (Westfjords) Botnshestur (Westfjords) 58 Hornataer (Westfjords) Hornataer (Westfjords) 59 Blankur (Westfjords) Blankur (Westfjords) 60 Baejara-Middegisfjall (Westfjords) Baejara-Middegisfjall (Westfjords) 61 Burstafell (Westfjords) Burstafell (Westfjords) 62 Kaldbakur (Westfjords) Kaldbakur (Westfjords) 63 Kaldrananes (Westfjords) Kaldrananes (Westfjords) 64 Kjolur (Westfjords) Kjolur (Westfjords) 65 Trollatunga-Middalur (Westfjords) Trollatunga-Middalur (Westfjords) 66 Stekkjargil (Westfjords) Stekkjargil (Westfjords) 67 Heydalur (Steingrimsfjordur) Heydalur (Steingrimsfjordur) 68 Thorpagil (Steingrimsfjordur) Thorpagil (Steingrimsfjordur) 69 Thorpagil-Galmastrond (Westfjords) Thorpagil-Galmastrond (Westfjords) 70 Galmastrond (Westfjords) Galmastrond (Westfjords) 71 Broddanes (Westfjords) Broddanes (Westfjords) 72 Ennistigi (Westfjords) Ennistigi (Westfjords) 73 Hnappseyri (Westfjords) Hnappseyri (Westfjords) 74 Ennisa-Ennisbunga (Westfjords) Ennisa-Ennisbunga (Westfjords) 75 Ospakseyri (Westfjords) Ospakseyri (Westfjords) 76 Stekkjarlaekur (Westfjords) Stekkjarlaekur (Westfjords) 77 Hofdarond (Westfjords) Hofdarond (Westfjords) 78 Gudlaugshofdi (Westfjords) Gudlaugshofdi (Westfjords) 79 Skuggahlidarbjarg Skuggahlíðarbjarg 80 Kattara (Westfjords) Kattara (Westfjords) 81 Vikura (Westfjords) Vikura (Westfjords) 82 Muli (Westfjords) Muli (Westfjords) 83 Kolbeinsarnes (Westfjords) Kolbeinsarnes (Westfjords) 84 Borgir-Hvalsa (Westfjords) Borgir-Hvalsa (Westfjords) 85 Hvallatradalur (Westfjords) Hvallatradalur (Westfjords) 86 Kjaransstadahorn (Westfjords) Kjaransstadahorn (Westfjords) 87 Fjallfoss (Westfjords) Fjallfoss (Westfjords) 88 Thverarfjall (Westfjords) Thverarfjall (Westfjords) 89 Nonarafjall (Westfjords) Nonarafjall (Westfjords) 90 Brjanslaekur (Westfjords) Brjanslaekur (Westfjords) 91 Fjardarhornsdalur (Westfjords) Fjardarhornsdalur (Westfjords) 92 Baejarnesfjall (Westfjords) Baejarnesfjall (Westfjords) 93 Langagil (Hamarsdalur) Langagil (Hamarsdalur) 94 Leidaroxl Leiðaröxl 95 Krossvatnshaedir Krossvatnshæðir 96 Valthjofsstadur Valþjófsstaður 97 Holl Hóll 98 Nipokollur (Nordfjordur) Nipokollur (Norðfjörður) 99 Eystri-Seljatungnakvisl (Thjorsardalur) Eystri-Seljatungnakvísl (Þjórsárdalur) 100 Brunaskogaheidi (Thjorsardalur) Brúnaskógaheiði (Þjórsárdalur) 101 Geldingaa (Thjorsa) Geldingaá (Þjórsá) Continued on next page

95 A. Appendix

Table A.4 – continued from previous page ID NAME ICE_NAME 102 Kongsas (Thjorsa) Kóngsás (Þjórsá) 103 Hvanngiljakvisl (Thjorsa) Hvanngiljakvísl (Þjórsá) 104 Gaesaalda (Thjorsa) Gæsaalda (Þjórsá) 105 Kjaloldur (Thjorsa) Kjalöldur (Þjórsá) 106 Joofell (Skaftafell) Joöfell (Skaftafell) 107 Stora-Skrida (Skaftafell) Stóra-Skriða (Skaftafell) 108 Raudhellar (Skaftafell) Rauðhellar (Skaftafell) 109 Vestara-Meinﬁl (Skaftafell) Vestara-Meinﬁl (Skaftafell) 110 Midfellstindur (Skaftafell) Miðfellstindur (Skaftafell) 111 Hafrafell (Skaftafell) Hafrafell (Skaftafell) 112 Skaftafellsheidi (Skaftafell) Skaftafellsheiði (Skaftafell) 113 Ulfarsfell (Mosfellssveit) Ulfarsfell (Mosfellssveit) 114 Varma (Mosfellssveit) Varmá (Mosfellssveit) 115 Hafrahlid (Mosfellssveit) Hafrahlid (Mosfellssveit) 116 Gufunes (Mosfellssveit) Gufunes (Mosfellssveit) 117 Korpa (Mosfellssveit) Korpa (Mosfellssveit) 118 Lagafell (Mosfellssveit) Lágafell (Mosfellssveit) 119 Kaldakvisl (Mosfellssveit) Kaldakvísl (Mosfellssveit) 120 Helgafell (Mosfellssveit) Helgafell (Mosfellssveit) 121 Brattatorfa-Litlahorn (Skardsheidi) Brattatorfa-Litlahorn (Skarðsheiði) 122 Skardshyrna-Heidarhorn (Skardsheidi) Skarðshyrna-Heiðarhorn (Skarðsheiði) 123 Thorishlidarfjall Selardalur (Arnarfjordur) Thorishlidarfjall Selardalur (Arnarfjörður) 124 Suladalur-Thverfjall (Skardsheidi) Súládalur-Þverfjall (Skarðsheiði) 125 Drageyraroxl (Skardsheidi) Drageyraröxl (Skarðsheiði) 126 Strandartindur (Seydisfjordur) Strandartindur (Seyðisfjörður) 127 Hvita Ytri (Mjoifjordur) Hvita Ytri (Mjóifjörður) 128 Hvita Innri (Mjoifjordur) Hvita Innri (Mjóifjörður) 129 Mjoafjardara (Mjoifjordur) Mjoafjardara (Mjóifjörður) 130 Storurdargil (Mjoifjordur) Storurdargil (Mjóifjörður) 131 Hesteyri (Mjoifjordur) Hesteyri (Mjóifjörður) 132 Grytukollur (Seydisfjordur) Grytukollur (Seyðisfjörður) 133 Toarfjall (Mjoifjordur) Toarfjall (Mjóifjörður) 134 Dalatangi (Mjoifjordur) Dalatangi (Mjóifjörður) 135 Dalir (Mjoifjordur) Dalir (Mjóifjörður) 136 Bjarnarhafnarfjall (Snaefellsnes) Bjarnarhafnarfjall (Snæfellsnes) 137 Eyrarfjall (Snaefellsnes) Eyrarfjall (Snæfellsnes) 138 Hafursfell (Snaefellsnes) Hafursfell (Snæfellsnes) 139 Trollakirkja (Snaefellsnes) Tröllakirkja (Snæfellsnes) 140 Kolbeinsstadafjall (Snaefellsnes) Kolbeinsstadafjall (Snæfellsnes) 141 Fagraskogarfjall (Snaefellsnes) Fagraskógarfjall (Snæfellsnes) 142 Dagmalafjall (Snaefellsnes) Dagmálafjall (Snæfellsnes) 143 Olafsfjardarmuli (Trollaskagi) Olafsfjardarmuli (Tröllaskagi) 144 Kerahnjukur (Trollaskagi) Kerahnjukur (Tröllaskagi) 145 Holshyrna (Trollaskagi) Holshyrna (Tröllaskagi) 146 Steindyr (Trollaskagi) Steindyr (Tröllaskagi) 147 Hofsa-Hofasarkot (Trollaskagi) Hofsa-Hofasarkot (Tröllaskagi) 148 Heljarfjall (Trollaskagi) Heljarfjall (Tröllaskagi) 149 Holabyrda (Trollaskagi) Holabyrda (Tröllaskagi) 150 Bolugil (Trollaskagi) Bolugil (Tröllaskagi) 151 Solheimafjall (Trollaskagi) Solheimafjall (Tröllaskagi) 152 Bakkadalur (Trollaskagi) Bakkadalur (Tröllaskagi) 153 Bolstadarhlid (Langidalur) Bólstaðarhlíð (Langidalur) 154 Aesustadafjall (Langidalur) Æsustaðafjall (Langidalur) 155 Gunnsteinsstadafjall (Langidalur) Gunnsteinsstaðafjall (Langidalur) 156 Gautsdalur (Langidalur) Gautsdalur (Langidalur) 157 Holtastadafjall (Langidalur) Holtastaðafjall (Langidalur) 158 Vatneyri (Patreksfjordur) Vatneyri (Patreksfjörður) 159 Haenuvikurnupur (Patreksfjordur) Haenuvikurnupur (Patreksfjörður) 160 Hafnarmuli Orlygshofn (Patreksfjordur) Hafnarmuli Orlygshofn (Patreksfjörður) 161 Tunga Orlygshofn (Patreksfjordur) Tunga Orlygshofn (Patreksfjörður) Continued on next page

96 Table A.4 – continued from previous page ID NAME ICE_NAME 162 Skapadalsfjall (Patreksfjordur) Skapadalsfjall (Patreksfjörður) 163 Smaelingjadalur (Talknafjordur) Smaelingjadalur (Talknafjörður) 164 Faskrudardalur (Talknafjordur) Faskrudardalur (Talknafjörður) 165 Baejargil Dufansdalur (Arnarfjordur) Baejargil Dufansdalur (Arnarfjörður) 166 Reykjafjordur (Arnarfjordur) Reykjafjörður (Arnarfjörður) 167 Fossa Fossfjordur (Arnarfjordur) Fossa Fossfjordur (Arnarfjörður) 168 Miklidalur (Bardastrond) Miklidalur (Barðaströnd) 169 Skalladalsfjall Vatnsdalur (Patreksfjordur) Skalladalsfjall Vatnsdalur (Patreksfjörður) 170 Kollsvik (Westfjords) Kollsvík (Westfjords) 171 Sudur Fossa (Raudasandur) Suður Fossá (Rauðasandur) 172 Baejarfjall Sveinseyri (Talknafjordur) Baejarfjall Sveinseyri (Talknafjörður) 173 Mulahyrna (Bardastrond) Mulahyrna (Barðaströnd) 174 Audi-Hrisdalur (Arnarfjordur) Audi-Hrisdalur (Arnarfjörður) 175 Bildudalur (Arnarfjordur) Bildudalur (Arnarfjörður) 176 Botnsdalur (Talknafjordur) Botnsdalur (Talknafjörður) 177 Skorarnupur (Arnarfjordur) Skorarnupur (Arnarfjörður) 178 Seljadalur (Arnarfjordur) Seljadalur (Arnarfjörður) 179 Vatnshlid (Altafjordur) Vatnshlíð (Áltafjörður) 180 Rjukandi (Hestfjordur) Rjukandi (Hestfjörður) 181 Hvalskurdara (Skotufjordur) Hvalskurdara (Skötufjörður) 182 Kotgil (Mjoifjordur) Kotgil (Mjóifjörður) 183 Kleifakotsmuli (Isafjordur) Kleifakotsmúli (Ísafjörður) 184 Gjorfidalur (Isafjordur) Gjörfidalur (Ísafjörður) 185 Efrabolsdalur (Langidalur) Efrabolsdalur (Langidalur) 186 Lambatungudalur/Steinsgil (Langidalur) Lambatungudalur/Steinsgil (Langidalur) 187 Torfdalur (Langidalur) Torfdalur (Langidalur) 188 Fljotavik (Westfjords) Fljótavík (Westfjords) 189 Gardafjall (Westfjords) Garðafjall (Westfjords) 190 Straumnesfjall (Westfjords) Straumnesfjall (Westfjords) 191 Hvarfnupur (Westfjords) Hvarfnúpur (Westfjords) 192 Kerling-Skalavik (Westfjords) Kerling-Skálavík (Westfjords) 193 Stigahlid (Westfjords) Stigahlíð (Westfjords) 194 Tradarhorn (Westfjords) Tradarhorn (Westfjords) 195 Bolungarvik (Westfjords) Bolungarvík (Westfjords) 196 Nesdalur-Bardi (Westfjords) Nesdalur-Barði (Westfjords) 197 Hofn (Westfjords) Höfn (Westfjords) 198 Hafnardalur (Westfjords) Hafnardalur (Westfjords) 199 Skalavikurheidi (Westfjords) Skalavikurheidi (Westfjords) 200 Nordureyri (Sugandafjordur) Norðureyri (Súgandafjörður) 201 Flateyri (Onundarfjordur) Flateyri (Önundarfjörður) 202 Thorfinnur (Onundarfjordur) Þorfinnur (Önundarfjörður) 203 Gardsgil (Nordurardalur) Garðsgil (Norðurárdalur) 204 Geldingsgil (Nordurardalur) Geldingsgil (Norðurárdalur) 205 Mosgil (Austurdalur) Mosgil (Austurdalur) 206 Fjoslaekur (Austurdalur) Fjóslækur (Austurdalur) 207 Midhus farm (Austurdalur) Miðhús farm (Austurdalur) 208 Brennigil (Austurdalur) Brennigil (Austurdalur) 209 Vidivallahals (Fljotsdalur) Víðivallaháls (Fljótsdalur) 210 Stulua (Fljotsdalur) Stuluá (Fljótsdalur) 211 Arnaldsstadir (Fljotsdalur) Arnaldsstaðir (Fljótsdalur) 212 Marklaekur (Fljotsdalur) Marklækur (Fljótsdalur) 213 Nupakot (Eyjafjoll) Núpakot (Eyjafjöll) 214 Grasafjoll (Tjornes) Grasafjöll (Tjörnes) 215 Grisatungufjoll (Tjornes) Grísatungufjöll (Tjörnes) 216 Torfholl (Tjornes) Torfhóll (Tjörnes) 217 Horgi (Tjornes) Hörgi (Tjörnes) 218 Rakkadalsbjarg (Tjornes) Rakkadalsbjarg (Tjörnes) 219 Hoskuldsvik (Tjornes) Höskuldsvík (Tjörnes) 220 Baejargil (Tjornes) Bæjargil (Tjörnes) 221 Heydalur (Mjoifjordur) Heydalur (Mjóifjörður) Continued on next page

97 A. Appendix

Table A.4 – continued from previous page ID NAME ICE_NAME 222 Laekjarvik (Tjornes) Lækjarvík (Tjörnes) 223 Engidalur (Tjornes) Engidalur (Tjörnes) 224 Engidalsgja (Tjornes) Engidalsgjá (Tjörnes) 225 Skarfaflos (Tjornes) Skarfaflös (Tjörnes) 226 Bessastadaa (Lagarfljot) Bessastaðaá (Lagarfljót) 227 Hengifoss (Lagarfljot) Hengifoss (Lagarfljót) 228 Gloppufjall (Trollaskagi) Gloppufjall (Tröllaskagi) 229 Almenningsfjall (Trollaskagi) Almenningsfjall (Tröllaskagi) 230 Storagil (Trollaskagi) Storagil (Tröllaskagi) 231 Kotlugja (Trollaskagi) Kotlugja (Tröllaskagi) 232 Holar (Trollaskagi) Holar (Tröllaskagi) 233 Vatnsendi (Trollaskagi) Vatnsendi (Tröllaskagi) 234 Granastadir (Trollaskagi) Granastadir (Tröllaskagi) 235 Oskjuhlid (Reykjavik) Öskjuhlið (Reykjavík) 236 Alfsnes (Reykjavik) Álfsnes (Reykjavík) 237 Gardabaer (Reykjavik) Garðabær (Reykjavík) 238 Leirdalur (Reykjavik) Leirdalur (Reykjavík) 239 Setberg (Reykjavik) Setberg (Reykjavík) 240 Nonhaed (Reykjavik) Nónhæð (Reykjavík) 241 Heidmork (Reykjavik) Heiðmörk (Reykjavík) 242 Hafnarfjordur (Reykjavik) Hafnarfjörður (Reykjavík) 243 Laekjarbotnar (Reykjavik) Lækjarbotnar (Reykjavík) 244 Lyklafell (Reykjavik) Lyklafell (Reykjavík) 245 Artunshofdi (Reykjavik) Ártúnshöfði (Reykjavík) 246 Hofdab-Kotas (Reykjavik) Höfðab-Kotás (Reykjavík) 247 Breidholt (Reykjavik) Breiðholt (Reykjavík) 248 Gunnarsholt (Reykjavik) Gunnarsholt (Reykjavík) 249 Arnarnes (Reykjavik) Arnarnes (Reykjavík) 250 Mosfellsbaer (Reykjavik) Mosfellsbær (Reykjavík) 251 Kyrgil-Mosfell (Reykjavik) Kýrgil-Mosfell (Reykjavík) 252 Leirvogsa (Reykjavik) Leirvogsá (Reykjavík) 253 Saltvik (Reykjavik) Saltvík (Reykjavík) 254 Alftanes (Reykjavik) Álftanes (Reykjavík) 255 Dysjar (Reykjavik) Dysjar (Reykjavík) 256 Grimsnes (Reykjavik) Grímsnes (Reykjavík) 257 Asfjall (Reykjavik) Ásfjall (Reykjavík) 258 Laugarnes (Reykjavik) Laugarnes (Reykjavík) 259 Grafarvogur (Reykjavik) Grafarvogur (Reykjavík) 260 Mikligardur (Reykjavik) Míkligarður (Reykjavík) 261 Kidagil (Hvalfjordur) Kidagil (Hvalfjördur) 262 Mulafjall (Hvalfjordur) Mulafjall (Hvalfjördur) 263 Husagil (Hvalfjordur) Husagil (Hvalfjördur) 264 Flugugil (Hvalfjordur) Flugugil (Hvalfjördur) 265 Sela (Hvalfjordur) Sela (Hvalfjördur) 266 Kyrgil (Hvalfjordur) Kyrgil (Hvalfjördur) 267 Modruvallahals (Hvalfjordur) Mödruvallahals (Hvalfjördur) 268 Villingadalur (Skardsheidi) Villingadalur (Skarðsheiði) 269 Thjorsarbru (Thjorsa) Þjórsárbrú (Þjórsá) 270 Stokkseyri (Thjorsa) Stokkseyri (Þjórsá) 271 Ames island (Thjorsa) Ames island (Þjórsá) 272 Olfusa (Thjorsa) Ölfusá (Þjórsá) 273 Ranga (Thjorsa) Ranga (Þjórsá) 274 Thjofafoss (Thjorsa) Þjófafoss (Þjórsá) 275 Gerpir Gerpir 276 Vadlavik Vaðlavík 277 Hundsvik Hundsvík 278 Neskaupstadur Neskaupstaður 279 Hjaleigulaekur Hjáleigulaekur 280 Gaesadalur Gaesadalur 281 Slenjadalur Slenjadalur Continued on next page

98 Table A.4 – continued from previous page ID NAME ICE_NAME 282 Skagafell Skagafell 283 Melrakkanes Melrakkanes 284 Hengill Hengill 285 Akrafjall (Akranes) Akrafjall (Akranes) 286 Karfagil Karfagil 287 Thrandargil Thrandargil 288 Hvammabrunir Hvammabrúnir 289 Geithellnadalur Geiþellnadalur 290 Stampahraun (Reykjanes) Stampahraun (Reykjanes) 291 Melgraefur Melgraefur 292 Grundarlaekur Grundarlaekur 293 Kleifara Kleifará 294 Nordurdalur Norðurdalur 295 Laugara Laugará 296 Kollur (Reydarfjordur ) Kollur (Reyðarfjörður ) 297 Teigargerdistindur (Reydarfjordur ) Teigargerdistindur (Reyðarfjörður ) 298 Holmatindur (Reydarfjordur ) Holmatindur (Reyðarfjörður ) 299 Arnorsstadahnjukur (Jokuldalur) Arnórsstaðahnjúkur (Jökuldalur) 300 Hnjuksa (Jokuldalur) Hnjúksá (Jökuldalur) 301 Kerling (Trollaskagi) Kerling (Tröllaskagi) 302 Tregagilsa (Jokuldalur) Tregagilsá (Jökuldalur) 303 Skalamaelifell (Reykjanes) Skálamælifell (Reykjanes) 304 Fitjaa (Skorradalur ) Fitjaa (Skorradalur ) 305 Djupivogur (Hamarsdalur) Djúpivogur (Hamarsdalur) 306 Laki Laki 307 Myvatn fires Mývatn fires 308 Kapelluhraun Kapelluhraun 309 Elgja Elgjá 310 Tvibollahraun Tvíbollahraun 311 Obrinnisholahraun Óbrinnishólahraun 312 Younger Laxardalur Younger Laxárdalur 313 Burfellshraun (Myvatnsoraefi) Búrfellshraun (Mývatnsöræfi) 314 Older Laxardalur Older Laxárdalur 315 Leitahraun (Reykjavik) Leitahraun (Reykjavík) 316 Botnahraun Botnahraun 317 Burfellshraun (Heidmork) Búrfellshraun (Heiðmörk) 318 Thjorsa Þjórsá 319 Rauduborgir-Raudholar-Sveinar Rauðuborgir-Rauðhólar-Sveinar 320 Krafla Krafla 321 Hekla Hekla 322 Svinahraunsbruni Svínahraunsbruni 323 Nesjahraun Nesjahraun 324 Skjolgil (Svinafell) Skjólgil (Svínafell) 325 Storutjarnir Storutjarnir 326 Festarfjall (Reykjanes) Festarfjall (Reykjanes) 327 Borgarhraun (Reykjanes) Borgarhraun (Reykjanes) 328 Siglubergshals (Reykjanes) Siglubergsháls (Reykjanes) 329 Burfell (Sugandafjordur) Búrfell (Súgandafjörður) 330 Einihlidar (Reykjanes) Einihlídar (Reykjanes) 331 Hraunssels-Vatnsfell (Reykjanes) Hraunssels-Vatnsfell (Reykjanes) 332 Hofdi (Reykjanes) Höfdi (Reykjanes) 333 Langihryggur (Reykjanes) Langihryggur (Reykjanes) 334 Seltangar Seltangar 335 Skala Skala 336 Hujuska Hujuska 337 Svidinhornadalur Sviðinhornadalur 338 Bleiksholl (Reykjanes) Bleikshóll (Reykjanes) 339 Einbui (Reykjanes) Einbúi (Reykjanes) 340 Natthagakriki (Reykjanes) Nátthagakriki (Reykjanes) 341 Fagradalsfjall (Reykjanes) Fagradalsfjall (Reykjanes) Continued on next page

99 A. Appendix

Table A.4 – continued from previous page ID NAME ICE_NAME 342 Kibadalur (Hvalfjordur) Kibadalur (Hvalfjördur) 343 Hallbjarnarstadaa (Tjornes) Hallbjarnarstaðaá (Tjörnes) 344 Kambsgja (Tjornes) Kambsgjá (Tjörnes) 345 Hallbjarnarstadakambur (Tjornes) Hallbjarnarstaðakambur (Tjörnes) 346 Svartihryggur (Hvalfjordur) Svartihryggur (Hvalfjördur) 347 Stapafell (Reykjanes) Stapafell (Reykjanes) 348 Kleifarvatn (Reykjanes) Kleifarvatn (Reykjanes) 349 Kalfstindar Kalfstindar 350 Oshlid (Westfjords) Óshlíð (Westfjords) 351 Sudavik-Isafjordur (Westfjords) Sudavik-Isafjordur (Westfjords) 352 Ogurnes (Westfjords) Ogurnes (Westfjords) 353 Grimsstadamuli (Myrar) Grimsstadamuli (Mýrar) 354 Hestfjall (Borgarfjordur) Hestfjall (Borgarfjörður) 355 Hesthals road (Borgarfjordur) Hesthals road (Borgarfjörður) 356 Lokufjall (Hvalfjordur) Lokufjall (Hvalfjördur) 357 Blikdalsa (Kjalarnes) Blikdalsa (Kjalarnes) 358 Njorvadalsa (Reydarfjordur ) Njorvadalsa (Reyðarfjörður ) 359 Sudurbotnahraun Suðurbotnahraun 360 Kvislahraun Kvíslahraun 361 Myvetningahraun Mývetningahraun 362 Batshraun Bátshraun 363 Eldhraun Eldhraun 364 Krokarhraun Krókarhraun 365 Thjorsarhraun Thjórsárhraun 366 Svinhagi Svínhagi 367 Hellisheidhi Hellisheidhi 368 Svinahraun Svinahraun 369 Hraunjardhir Hraunjardhir 370 Ellidhaa Ellidhaá 371 Thingvellahraun Thingvellahraun 372 Storagja Stóragjá 373 Bardhardalur Bárdhardalur 374 Sandfell Sandfell 375 Hnappa (Jokuldalur) Hnappá (Jökuldalur) 376 Gilsa (Jokuldalur) Gilsá (Jökuldalur) 377 Yzta-Rjukandi (Jokuldalur) Yzta-Rjúkandi (Jökuldalur) 378 Garda vid Hjardarhaga (Jokuldalur) Garðá við Hjarðarhaga (Jökuldalur) 379 Thyrli (Hvalfjordur) Þyrli (Hvalfjördur) 380 Dynjandisheidi (Westfjords) Dynjandisheiði (Westfjords) 381 Gardur (Midnes) Garður (Miðnes) 382 Sandgerdi (Midnes) Sandgerði (Miðnes) 383 Midnesheidi (Midnes) Miðnesheiði (Miðnes) 384 Helguvik (Midnes) Helguvík (Miðnes) 385 Keﬂavik (Midnes) Keﬂavík (Miðnes) 386 Osar (Midnes) Ósar (Miðnes) 387 Galgar (Midnes) Gálgar (Miðnes) 388 Helgafell (Sydridalur) Helgafell (Syðridalur) 389 Eyrarfjall (Hvalfjordur) Eyrarfjall (Hvalfjördur) 390 Eyrarfjall (Altafjordur) Eyrarfjall (Áltafjörður) 391 Eyrarfjall (Hnifsdalur) Eyrarfjall (Hnífsdalur) 392 Eyrarfjall (Skutulsfjordur) Eyrarfjall (Skutulsfjördur) 393 Leitahraun (Kirkjubaejarklaustur) Leitahraun (Kirkjubæjarklaustur) 394 Thjorsa (Holsa) Þjórsá (Hólsá)

100 Table A.5: Relational table - geologic class IDs ID NAME 0 Unspeciﬁed 1 Igneous 2 Sedimentary

Table A.6: Relational table - geologic type IDs ID NAME 0 Unspeciﬁed 1 Lava 2 Volcanic dike 3 Sediment layer 4 Tuﬀ 5 Baked laterite

Table A.7: Relational table - dating method IDs ID NAME 0 Unspeciﬁed 101 Geological estimate 102 K-Ar age 103 40Ar/39Ar age 104 Historical age 105 Tephrochronology 106 Radiocarbon C14 107 U-Th age

Table A.8: Relational table - sample type IDs ID NAME 1 Mini-cores (diameter 1cm) 2 Portable drill cores (diameter 2.54cm) 3 Block or hand samples 4 Existing samples (remeasurement 5 Conventional drill cores (diameter 4.4cm)

Table A.9: Relational table - specimen type IDs ID NAME 0 Unspeciﬁed 1 2.54cm diameter cores cut into 2-2.4cm lengths 2 3.55cm diameter discs cut with trepanning tool 3 1cm diameter mini-cores cut into 1cm lengths

101 A. Appendix

Table A.10: Relational table - demagnetisation type IDs ID NAME SHORT_NAME -1 None None 1 Alternating ﬁeld AF 2 Microwave MW 3 AF and thermal AF-TH 4 Thermal and microwave TH-MW 5 Thermal TH

Table A.11: Relational table - specimen direction calculation IDs (NAME taken from MagIC vocabulary) ID NAME DESCRIPTION 0 Unspeciﬁed - No demagnetization carried out but only NRM values 1 LP-DC0 reported Bulk demagnetization carried out on all samples but 2 LP-DC2 no vector diagrams shown Vector diagrams or stereoplots with M/Mo justify 3 LP-DC3 demagnetization procedures used Principal component analysis carried out from analysis 4 LP-DC4 of Zijderveld diagrams Magnetic vectors isolated using two or more 5 LP-DC5 demagnetization methods with principle component analysis

Table A.12: Relational table - sample direction average method IDs ID NAME 0 Unspeciﬁed 1 Averaged Decl - Incl

Table A.13: Relational table - site direction average method IDs ID NAME DESCRIPTION 0 Unspeciﬁed Unknown or no directions calculated 1 Fisher Mean calculated with Fisherian statistics Mean with lowest alpha95 value (or highest vector 2 a95 min sum R) chosen Kappa-maximising/minimum-scatter criterion used by 3 Kmax Watkins et al (1977) Combined analysis of directions and remagnetization 4 Combined planes of McFadden and McElhinny (1988)

102 Table A.14: Relational table - directional polarity IDs ID NAME SHORT_NAME -1 Unspeciﬁed U 0 Undetermined or mixed M or ? 1 Normal N 2 Transitional (|VGPlat|<40) T 3 Reverse R

Table A.15: Relational table - palaeointensity method IDs ID NAME DESCRIPTION -1 Unspecified No measurement or not specified 1 Thellier classic Koenigsberer-Thellier-Thellier (KTT) 2 ZI (Coe) Thellier modified by Coe et al (1967) 3 Shaw see Shaw (1974) 4 Microwave see Walton (1993) 5 MT4 modified Thellier type four (Leonhardt et al 2004) 6 Wilson see Wilson (1961) 7 Van Zijl see Van Zijl et al (1962) 8 IZZI modified Thellier (Tauxe and Staudigel 2004) 9 MSP-DB Multispecimen parallel differential pTRM (Dekkers and Boehnel 2006)

Table A.16: Relational table - alteration check IDs ID NAME DESCRIPTION 0 Unspeciﬁed No measurement or not speciﬁed 1 PTRM pTRM check 2 AFARM AF demagnetization of ARM 3 PMRM Partial microwave induced TRM check 4 SUSC Susceptibility does not change after successive heatings

103