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1 The Warnie Volcanic Province: Jurassic Intraplate Volcanism in 1 2 2 Central Australia 3 1 2 1 2 3 4 3 Jonathon P.A. Hardman , Simon P. Holford , Nick Schofield , Mark Bunch Daniel Gibbins 5 6 4 1Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, AB24 3FX, UK 7 8 2 9 5 Australian School of Petroleum, University of Adelaide, Adelaide, SA 5005, Australia 10 11 6 3Vintage Energy, 58 King William Road, Goodwood SA 5034, Australia 12 13 14 7 15 16 8 Abstract 17 18 9 The Cooper and Eromanga Basins of South Australia and Queensland are the largest onshore hydrocarbon 19 20 10 producing region in Australia. Igneous rocks have been documented infrequently within end of well reports 21 11 over the past 34 years, with a late Triassic to Jurassic age determined from well data. However, the areal 22 23 12 extent and nature of these basaltic rocks were largely unclear. Here, we integrate seismic, well, gravity, and 24 13 magnetic data to clarify the extent and character of igneous rocks preserved within Eromanga Basin 25 26 14 stratigraphy overlying the Nappamerri Trough of the Cooper Basin. We recognise mafic monogenetic 27 15 volcanoes that extend into tabular basalt lava flows, igneous intrusions and, more locally, hydrothermally 28 29 16 altered compound lava flows. The volcanic province covers ~7500 km2 and is proposed to have been active 30 between ~180-160 Ma. We term this Jurassic volcanic province the Warnie Volcanic Province (WVP) after the 31 17 32 18 Warnie East 1 exploration well, drilled in 1985. The distribution of extrusive and intrusive igneous rocks is 33 34 19 primarily controlled by basement structure, with extrusive and intrusive igneous rocks elongate in a NW-SE 35 20 direction. Finally, we detail how the WVP fits into the record of Jurassic volcanism in eastern Australia. The 36 37 21 WVP is interpreted as a product of extension and intraplate convective upwelling above the subducting Pacific 38 22 Slab. The discovery of the WVP raises the possibility of other, yet unidentified, volcanic provinces worldwide. 39 40 41 23 Keywords 42 43 24 Intraplate; volcanism; monogenetic; Australia; Jurassic 44 45 25 1. Introduction 46 47 26 Igneous rocks are frequently recognised within sedimentary basins globally, within which 48 49 27 their chronostratigraphic record can provide insights into the tectonic evolution of a region 50 51 28 (Jerram & Widdowson, 2005). Although extensive reworked volcaniclastic deposits are 52 53 29 documented throughout Central Australia during the Mesozoic (Boult et al., 1998; Barham 54 55 30 et al., 2016; Wainman et al., 2019), synchronous volcanic activity is infrequently documented 56 57 31 within the sedimentary basins of Central Australia (Allen, 1998). The Cooper and the 58 32 overlying Eromanga Basin extend for 130,000 km2 and 1,000,000 km2 respectively across 59 60 61 62 63 64 65 2

33 central, north and eastern Australia. Together, they represent the largest conventional 1 2 34 onshore hydrocarbon-producing region in Australia (Hall et al., 2016). The first gas 3 35 discovery was made in 1963 and since then, over 1,400 producing wells have been drilled, 4 5 36 with 190 gas and 115 oil fields discovered throughout both basins (Fig. 1) (Mackie, 2015). 6 7 37 The majority of discoveries within the Cooper Basin are situated within structural traps on 8 9 38 regional highs, however, a number of companies began to pursue unconventional 10 11 39 hydrocarbon plays within the basin during the late 2000s, resulting in an increase in activity 12 13 40 within the Nappamerri Trough (Hillis et al., 2001; Pitkin et al., 2012; Khair et al., 2013; Scott 14 15 41 et al., 2013; Hall et al., 2016). The Nappamerri Trough is the largest and deepest depocentre 16 42 within the Cooper Basin covering ~10,000 km2 and reaching present day depths of ~4.5 km 17 18 43 (Fig. 1A). The acquisition of new well and seismic data due to renewed exploration activity 19 20 44 has resulted in the increased recognition of igneous rocks in the Cooper and Eromanga 21 22 45 Basins. 23 24 46 Igneous rocks of suspected late Triassic-Jurassic age have been sporadically 25 26 47 encountered by drilling during the past 34 years (Short, 1984; Boothby, 1986; Bucknill, 1990; 27 28 48 Allen, 1998), though there has been no systematic study of the character, origin and 29 30 49 significance of these igneous rocks. Here, we combine extensive seismic, well and airborne 31 32 50 geophysical data to document the extent and character of Mesozoic igneous rocks 33 34 51 recognised within Eromanga Basin stratigraphy overlying the Nappamerri Trough of Cooper 35 2 36 52 Basin age. The Warnie Volcanic Province (WVP) is the suggested name for this >7,500 km 37 53 suite of igneous rocks (Fig. 1B). The province is named after the Warnie East 1 exploration 38 39 54 well, which was drilled in 1985 and encountered 65 m of basalt. We provide an in-depth 40 41 55 study of the regional implications of the WVP for the Cooper and Eromanga Basins. We find 42 43 56 that SE-NW striking intracratonic sag faulting controlled the morphology of igneous rocks 44 45 57 whilst the basin structure likely controlled the location of igneous rocks. 46 47 58 Finally, we discuss the origin of the WVP. Evidence for Triassic to mid-Cretaceous 48 49 59 volcanic activity is pervasive throughout the sedimentary basins of central Australia, 50 51 60 manifested by an influx of volcanic arc-derived sediment into the Eromanga Basin (Boult et 52 53 61 al., 1998), silicic tuffs in the Surat Basin (Wainman et al., 2015) and widespread volcanogenic 54 55 62 zircons throughout the Great Artesian Basin (Bryan et al., 1997). However, the source of 56 57 63 volcanic activity and, furthermore, the origin of intraplate volcanism can be contentious 58 64 (Conrad et al., 2011; Zhou et al., 2018). We consider the source of the WVP and the 59 60 65 tectonic implications for central Australia. We theorise that the WVP’s geodynamic origin is 61 62 63 64 65 3

66 ultimately linked to subduction at the eastern margin of Gondwana, through asthenospheric 1 2 67 shear ~1500 km from the oceanic trench, however, we also discuss other mechanisms that 3 68 can produce intraplate volcanism. Our discovery of a previously undescribed volcanic 4 5 69 province in an area that has undergone >50 years of extensive subsurface data collection 6 7 70 due to continued hydrocarbon exploration, raises the prospect of other undiscovered 8 9 71 intraplate volcanic provinces both in Australia and in other continental areas worldwide. 10 11 12 72 2. Geological Overview of the Cooper and Eromanga Basins 13 14 73 The geology of southwest Queensland and northeast South Australia, central Australia, is 15 16 74 defined by a series of intracratonic basins stacked on top of each other; the Warburton, 17 18 75 Cooper, Eromanga and Lake Eyre Basins (Fig. 2 & Fig. 3). 19 20 76 The Warburton Basin is a lower Palaeozoic sedimentary basin that hosted Silurian to 21 22 77 Carboniferous granite emplacement (Murray, 1986; Meixner et al., 2000). The Cooper 23 24 78 Basin unconformably overlies the Warburton Basin. The Cooper Basin is a northeast to 25 26 79 southwest trending intracratonic structural depression that accommodated the deposition 27 28 80 of sedimentary rocks from the late Carboniferous to the Middle Triassic (Gravestock et al., 29 81 1998). Several tectonic origins for the Cooper Basin have been suggested, including a mildly 30 31 82 compressional structural depression (Apak et al., 1997; Sun, 1997), a depression created 32 33 83 through wrenching (Kuang, 1985) and extension during post-compression flexural relaxation 34 35 84 (Kulikowski et al., 2015). Deposition throughout the early Permian was dominated by highly 36 37 85 sinuous fluvial systems situated on a major floodplain with peat rich swamps and lakes (Khair 38 39 86 et al., 2015). Later Triassic deposition took place in a period of tectonic quiescence 40 41 87 (Gravestock et al., 1998). 42 43 88 Deposition in the Cooper Basin was terminated by regional uplift, compressional folding and 44 45 89 erosion in the middle Triassic. The Cooper Basin is unconformably overlain by the 46 47 90 Eromanga Basin, which forms part of the Great Artesian Superbasin, a group of 48 49 91 interconnected basins that cover much of Queensland, South Australia and New South 50 92 Wales. The Eromanga Basin is an intracratonic sag basin whose subsidence has been 51 52 93 attributed to dynamic topography induced by subduction of the pacific plate below Australia 53 54 94 (Gallagher & Lambeck, 1989; Russell & Gurnis, 1994). 55 56 57 58 59 60 61 62 63 64 65 4

95 2.1 The Jurassic Succession of the Eromanga Basin 1 2 3 96 The Jurassic succession of the Eromanga Basin is of stratigraphic importance as it is where 4 5 97 the extrusive igneous rocks documented within this study are believed to be located. Much 6 98 of the Jurassic strata in the Eromanga Basin consists of predominantly quartzose fluviatile 7 8 99 sandstones with subordinate shales and some coals (Burger & Senior et al., 1979; Exon & 9 10 100 Burger, 1981; Draper 2002). Sediments in the Eromanga Basin can be divided into three 11 12 101 packages of decreasing age; lower non-marine, marine and upper non-marine. The focus of 13 14 102 this study is the lower non-marine package that was deposited between the early Jurassic 15 16 103 (~200 Ma) and the early Cretaceous (~155 Ma), within which the extrusive volcanics of the 17 18 104 WVP are recognised (Fig. 2). During this time, large sand-dominated, braided fluvial systems 19 105 drained into lowland lakes and swamps. Throughout deposition, it is believed that sediment 20 21 106 supply was a competing product of input from arc volcanism to the east, and sediment 22 23 107 sourced from stable cratonic regions to the south (Boult et al., 1997). In the next part of 24 25 108 this paper we briefly detail the Early to Late Jurassic stratigraphy in order to provide a 26 27 109 palaeogeographic framework for the study. The stratigraphic framework of the Jurassic 28 29 110 succession has been iterated on considerably in the last 20 years, evidenced by the 30 111 progression of Alexander & Hibburt’s stratigraphic ages (1996) to Reid et al.’s (2009), to 31 32 112 those listed on the Australian Stratigraphic Units Database. 33 34 35 113 2.1.1 Poolowanna Formation, Early Jurassic, ~200–178 Ma 36 37 38 114 In southwest Queensland, the Poolowanna Fm. sits unconformably on top of the Late 39 40 115 Triassic unconformity, which formed as a result of uplifting, tilting, and erosion of the 41 116 Cooper Basin at the end of the Early to Middle Triassic (Fig. 2). Lithologies consist of coal 42 43 117 and silt deposited in a highly sinuous fluvial setting with minor coal swamps (Hall et al., 44 45 118 2016). 46 47 48 119 2.1.2 Hutton Sandstone, Early to Middle Jurassic, ~178–166 Ma 49 50 51 120 The Hutton Sandstone is a high energy braided fluvial Jurassic sandstone that either sits 52 121 conformably on top of the Poolowanna Fm. or, where the Poolowanna is not present, 53 54 122 unconformably above Triassic sediments (Kapel, 1966; Watts, 1987). 55 56 57 58 59 60 61 62 63 64 65 5

123 2.1.3 Birkhead Formation, Middle to Upper Jurassic, ~ 166–160 Ma 1 2 124 The boundary between the Hutton and Birkhead formations is sharp to transitional across 3 4 125 the Eromanga Basin (Lanzilli, 1999) and is associated with a change in the depositional 5 6 126 setting from the high energy, braided fluvial setting of the Hutton Sandstone to a low 7 8 127 energy, fluvial-deltaic to lacustrine setting in the Birkhead Formation (Watts, 1987; Lanzilli, 9 10 128 1999). This decrease in depositional energy is also associated with a change in sediment 11 129 provenance from craton-derived sediment to lithic-rich, volcanogenic sediment from a 12 13 130 proposed volcanic arc situated to the east above the subducting Pacific plate (Lanzilli, 1999). 14 15 131 The diachronous influx of volcanogenic sediments can be traced across the Eromanga Basin 16 17 132 (Boult et al., 1997). There are several key features associated with the sediments shed from 18 19 133 the volcanic arc (Paton, 1986): 20 21 134  50% quartz with high amounts of potassium and plagioclase feldspar. Trace amounts 22 23 135 of tourmaline, pyroxene, mica and zircon are also present (Watts, 1987). 24 25 136  Common altering of the above lithics to kaolinite and chlorite or replacement of 26 27 137 carbonate cements such as siderite or dolomite. 28 29 138  Rare glassy fragments. 30 31 139 Based on the lithology of the volcanogenic sediments, it has been concluded that the 32 33 140 volcanics that formed them were of acid to intermediate affinity (Paton, 1986). 34 35 36 141 2.1.4 Adori Sandstone, Upper Jurassic, ~ 160-155 Ma 37 38 39 142 The Birkhead Formation is capped by the Adori Sandstone, marked by a transition to clean, 40 41 143 non-volcanogenic sedimentation. The Adori Sandstone is a well sorted and typically cross 42 144 bedded, fine to coarse-grained sandstone deposited in a low sinuosity fluvial system 43 44 145 consisting of channel, point bar and flood plain deposits in the Central Eromanga Basin 45 46 146 (Burger & Senior, 1979; Alexander & Hibburt, 1996). 47 48 49 147 2.2 Structural Setting of the Study Area 50 51 52 148 Structurally, the Cooper Basin can be divided into southern and northern sections 53 54 149 (Gravestock et al., 1998; Hall et al., 2016). To the north, depocentres are dominantly 55 150 Triassic, with Permian depocentres in the south (Hall et al., 2018). The northern and 56 57 151 southern sections of the Cooper Basin are separated by the Jackson-Naccowlah-Pepita 58 59 152 Trend (JNP trend) (Fig. 1). In the south west, depocentres are generally thicker, reaching a 60 61 62 63 64 65 6

153 maximum thickness of 2400 m in the Nappamerri Trough (Hall et al., 2016) and many of 1 2 154 these depocentres have experienced synclinal folding due to differential compaction (Apak 3 155 et al., 1997). The major depocentres are separated by northeast-southwest trending ridges 4 5 156 (Gravestock et al., 1998). 6 7 8 157 The area of focus in this study is the eastern Nappamerri Trough of north east South 9 10 158 Australia and south west Queensland. The Nappamerri Trough contains the deepest 11 12 159 basement within the Cooper Basin and hosts the Halifax well that intersected the deepest 13 160 Permian-age sedimentary rocks in the basin at 4,209 m. To the north, the Nappamerri 14 15 161 Trough is bounded by the Gidgealpa, Canway, Packsaddle and Innamincka ridges (Fig. 1A). 16 17 162 The southern extent of the Nappamerri Trough is bounded by the Della-Nappacoongee, 18 19 163 Dunoon and Murteree ridges (Fig. 1) (Hall et al., 2016). 20 21 164 3. Methodology 22 23 24 25 165 3.1 Identification of Volcanics Using Subsurface Data 26 27 28 166 Here we describe the main techniques that were used to investigate igneous rocks within 29 167 the Nappamerri Trough. 30 31 32 33 168 3.1.1 Seismic Data 34 35 169 Seismic reflection data has been shown by numerous studies to be especially effective at 36 37 170 imaging igneous rocks due to the high acoustic impedance of igneous material when 38 39 171 compared to surrounding sedimentary rocks and the distinctive morphology of lava flows 40 172 and intrusions (Planke et al., 2000). Here we provide a brief introduction to the different 41 42 173 types of igneous rock identified in the subsurface on seismic reflection data. 43 44 45 174 Vents identified within seismic reflection data are typically grouped into either hydrothermal 46 47 175 or volcanic vents (Reynolds et al., 2017). The morphologies of hydrothermal vents and 48 49 176 volcanoes are similar as they both exhibit eye, dome or crater shaped morphologies in 50 177 seismic data (Fig. 4)(Planke et al., 2005; Reynolds et al., 2017). This can make distinguishing 51 52 178 hydrothermal vents from volcanoes difficult when seismic reflection data are the sole data 53 54 179 source. 55 56 57 180 Volcanoes can be confidently identified using seismic reflection data where they extend into 58 181 lava flows (e.g. Fig. 4A-D). Lava flows are distinguishable as layer-parallel acoustically hard, 59 60 61 62 63 64 65 7

182 bright reflectors within the subsurface (Planke et al., 2000; Schofield & Jolley, 2013; Hardman 1 2 183 et al., 2019) (Fig. 4B). Extrusive igneous rocks are distinguishable from intrusive igneous 3 184 rocks as they do not transgress stratigraphy. 4 5 6 185 Igneous intrusions have been studied intensely using 3D seismic data (Bell & Butcher, 2002; 7 8 186 Thomson & Schofield, 2008; Archer et al., 2005; Magee et al., 2014). Igneous intrusions form 9 10 187 acoustically hard, bright reflectors that are layer parallel or transect stratigraphy. In places, 11 12 188 they can produce forced folding of the overburden with onlapping stratigraphy facilitating 13 189 age-dating of the intrusion (Trude et al., 2003). 14 15 16 190 3.1.2 Seismic Attributes 17 18 19 191 3D seismic reflection data facilitates the analysis of the geophysical properties of igneous 20 21 192 rocks in 3D. Seismic attributes such as RMS amplitude and spectral decomposition have 22 23 193 proven to be effective tools in picking the extent and morphology of lava flows in seismic 24 194 data (Figs. 4C & G) (Schofield & Jolley, 2013; Planke et al., 2017; Hardman et al., 2019). 25 26 195 Spectral decomposition involves filtering 3D seismic reflection wavelets to produce three 27 28 196 amplitude components at distinct frequencies that are displayed as separate colour channels 29 30 197 using the primary colours red, green and blue. These channels are then blended to produce 31 32 198 full colour spectrum images where the igneous rocks appear visibly different to the 33 34 199 surrounding sediments, due to their differing reflectiveness for particular frequencies (they 35 200 transmit acoustic energy efficiently at all frequencies). Furthermore, this technique can be 36 37 201 used to investigate the geometries of igneous rocks and features such as inflation lobes can 38 39 202 help with distinguishing igneous intrusions from extrusive igneous rocks. 40 41 42 203 3.1.3 Well Data 43 44 45 204 In addition to the use of seismic data, the integrated analysis of borehole data including 46 205 wireline log responses, core and cuttings is essential in accurately identifying igneous rocks 47 48 206 within the subsurface (Nelson et al., 2009; Rider & Kennedy, 2011; Watson et al., 2017). The 49 50 207 onshore response of igneous rocks in outcrop has been linked to offshore observations 51 52 208 facilitating the identification of different volcanic facies through petrophysical and 53 54 209 petrological analysis (Nelson et al., 2009; Millet et al., 2016). 55 56 210 Here, we use a combination of petrophysical and petrological data in our description of the 57 58 211 WVP. Although cuttings and core were not examined within this study, descriptions were 59 60 212 available within well reports that were integrated with petrophysical data and seismic 61 62 63 64 65 8

213 reflection data to provide a comprehensive overview of the data available. It is important to 1 2 214 recognise that the petrological descriptions taken from well reports is secondary 3 215 information and, as such, variable in quality. Wherever petrological descriptions have been 4 5 216 taken from end of well reports it is explicitly stated within the text with a reference to the 6 7 217 relevant well report. 8 9 10 218 3.2 Description of Dataset 11 12 13 219 The Cooper and Eromanga Basins have been explored extensively over the past 60 years 14 15 220 and are characterised by the largest collection of well and seismic reflection data for any 16 221 onshore sedimentary basin in Australia. Over 2000 wells have been drilled in the Cooper 17 18 222 and Eromanga Basins. Despite this, of the wells available, only 3 (Lambda 1, Orientos 2 and 19 20 223 Kappa 1) were identified as having intersected extrusive volcanic rocks with only 1 well 21 22 224 (Warnie East 1) encountering an intrusive igneous rock. To estimate the relative age of the 23 24 225 volcanic units, well data were tied, where possible, to the seismic reflection surveys 25 26 226 available. For constraining the age of the Eromanga succession within the Central 27 227 Nappamerri trough, the Halifax, Etty, Padme, Charal and Anakin wells represented key 28 29 228 datasets (location on Fig. 1C). 30 31 32 229 A large database of seismic reflection data was available through Santos Limited and the 33 34 230 Queensland Government’s Department of Natural Resources and Mines. 3D and 2D seismic 35 36 231 reflection surveys throughout the South Australian and Queensland sides of the basin were 37 232 assessed for the presence of igneous rocks (the extent of the seismic data examined is 38 39 233 visible on Fig. 1B). Notably, only four surveys available to this study (the Winnie 3D, the 40 41 234 Gallus 2D, the Madigan 3D and the Snowball 3D survey (provided for use by Santos 42 43 235 Limited)), were interpreted to contain igneous rocks and a summary of these surveys is 44 45 236 provided in Table 1. Furthermore, 3 individual 2D seismic lines were available across the 46 47 237 Lambda 1, Orientos 2 and Warnie East 1 wells. Seismic data were displayed using normal 48 238 (American) polarity, whereby a downward increase in acoustic impedance corresponds to a 49 50 239 positive (blue) reflection and a downward decrease a negative (red) reflection. The only 51 52 240 exception to this is the Snowball 3D survey that was displayed such that a downward 53 54 241 increase in acoustic impedance corresponds to a red, negative reflection (European 55 56 242 polarity). Within the Jurassic succession the average dominant frequency within the seismic 57 - 58 243 data was ~40 Hz, with volcanic rocks in the region having an acoustic velocity of 4 to 6 kms 59 60 61 62 63 64 65 9

244 1 (taken from the Lambda 1 exploration well). Using an average velocity of 5 kms-1 a vertical 1 2 245 resolution of ~30 m and a detection limit of 4 m was calculated. 3 4 246 Here we present an overview of all the available datasets that constrain the distribution and 5 6 247 age of igneous rocks within the study area. We recognise three distinct types of igneous 7 8 248 rocks within this study: 9 10  11 249 Extrusive igneous rocks 12 250  Intrusive igneous rocks 13 14 251  Altered extrusive igneous rocks 15 16 17 252 Each type is described in detail using the available well and seismic data before the regional 18 19 253 character of the Warnie Volcanic Province as a whole is discussed using regional gravity and 20 21 254 magnetic surveys. It is important we recognise that whilst this is the extent of the data that 22 255 was available during this study, the authors are aware of other seismic reflection surveys 23 24 256 within the Nappamerri Trough that were not available to download digitally and were not 25 26 257 possible to acquire within the period of time during which this study was conducted. These 27 28 258 surveys may also image igneous rocks that could fuel further work on the area. 29 30 31 259 4. Description of Extrusive Igneous Rocks 32 33 34 260 4.1 Well Data 35 36 37 261 Unaltered, basaltic, extrusive igneous rocks are recognised in the Lambda 1 and Orientos 2 38 39 262 wells in the eastern Nappamerri Trough. 40 41 263 The Lambda 1 well was drilled in 1984 by Delhi Petroleum Pty. Ltd. At a depth of 1570.9 m, 42 43 264 283 m igneous rocks were intersected, directly underlying the base of the Birkhead Fm. (Fig. 44 45 265 12). The upper 33 m of basalt are noted as heavily weathered, fractured and vesicular in the 46 47 266 Lambda 1 well report (Short, 1984). The remaining 250 m of basalt is described as fresh and 48 267 crystalline. It has low gamma ray values, with consistently high density and acoustic velocity 49 50 268 (Fig. 12A). There are localised areas where the density drops drastically, however, these are 51 52 269 associated with increases in the caliper and may therefore point to caving of the wellbore 53 54 270 when it was drilled or fractures within the basalt, rather than lithological variations. At the 55 56 271 base of the basalt ~1.5 m of core was cut, within which the fine grained, crystalline nature of 57 58 272 the basalt is apparent (Fig. 5A, see picture). 59 60 61 62 63 64 65 10

273 Similarly to Lambda 1, Orientos 2 drilled through igneous rocks situated at 1555 m, beneath 1 2 274 the Jurassic age Adori Sandstone (Fig. 14). The well drilled through 34 m of igneous rocks 3 275 before drilling was ceased, prior to the well reaching the base of the igneous rocks. The 4 5 276 igneous rocks are described as dark green, grey black with quartz inclusions and common 6 7 277 amphiboles in the end of well report (Bucknill, 1990). Similar to the Lambda 1 well, 8 9 278 Orientos 2 encountered a 14 m section of weathered basalt identifiable by low density and 10 11 279 sonic values in the well logs, followed by a high density and high velocity section, matching 12 13 280 the petrophysical response of the Lambda 1 igneous rocks. Draper (2002) noted that 14 15 281 Orientos 2 was drilled <1 km from Orientos 1, which did not intersect basalt, suggesting 16 282 that the basalt In Orientos 2 might be intrusive in origin. However, we note that Orientos 1 17 18 283 may have been drilled beyond the limit of the basalt and, as such, we do not take the 19 20 284 absence of igneous rocks in Orientos 1 to be indicative of an intrusive origin for the 21 22 285 Orientos 2 igneous rocks. 23 24 286 Nelson et al. (2009) provided compelling evidence for the use of binning velocity data in 25 26 287 estimating the type of volcanic rock present. In order to investigate the extrusive or 27 28 288 intrusive nature of the Lambda 1 igneous rocks, interval velocity histograms were created. 29 30 289 They were then binned with a bin spacing of 0.125 m order to create a velocity histogram 31 32 290 (Fig.12C). These were superimposed on the velocity histogram fields of Nelson et al., (2009) 33 34 291 that were obtained from boreholes on the Faroe Islands in the North Atlantic, in order to 35 36 292 compare the acoustic velocities of igneous rocks in the Nappamerri Trough with values 37 293 from extrusive igneous rocks in the Northwest Atlantic. It can be seen in Fig. 5C that the 38 39 294 Lambda 1 volcanics show a very strong similarity to the tabular basalt analysed by Nelson et 40 41 295 al. (2009). 42 43 44 296 Additionally, vitrinite reflectance data (Boothby, 1986) was recorded for sediments 45 297 deposited on top of the Lambda-1 volcanics (Fig. 5B). Notably, in the sediment contact with 46 47 298 the volcanics, there is no deviation towards high %RoMax, suggesting that the Lambda 1 48 49 299 volcanics had little thermal effect on the overlying organic matter. It has been observed in 50 51 300 locations such as Namibia that the thermal effect of lava flows is restricted to << 1 m depth 52 53 301 below lava contacts (Grove et al., 2017) whereas igneous intrusions have a much larger 54 55 302 thermal effect on surrounding sediments due to their inability to release heat directly to the 56 57 303 earth’s surface (see Utgard Sill Complex, Aarnes et al., 2015). If this were an intrusion, it is 58 304 expected that the VR values would be elevated (Stewart et al., 2005), and the absence of 59 60 305 such elevated values implies that the basalt is extrusive. 61 62 63 64 65 11

306 4.2 Seismic Data 1 2 3 307 Extrusive igneous rocks have been documented using the available seismic data. These 4 5 308 observations will focus on the Winnie 3D survey as it is the largest, highest quality 3D 6 309 dataset within which the full range of igneous rocks is observed. From there, we build out 7 8 310 to the other seismic surveys utilised. 9 10 11 311 In a single 2D seismic line intersecting the Lambda 1 well the tabular basalt intersected by 12 13 312 the well corresponds to a high amplitude reflection most pronounced at the location of the 14 15 313 well but also continuing ~3 km to the west of the survey (Fig. 6). The centre of the survey 16 314 (and the location of the well) corresponds with a ~1.5 km wide anticline that exhibits 17 18 315 doming on the order of ~150 ms. Below the anticline and the location of the volcanics, the 19 20 316 2D seismic reflections are visibly distorted, being most pronounced beneath the location of 21 22 317 the well where a velocity pull-up effect is visible. 23 24 2 318 Within the Winnie 3D survey, we identified ~100, <= 4 km cone shaped features 25 26 319 that often express an eye-shaped morphology, doming and velocity pull-up effects similar to 27 28 320 those observed in the location of the Lambda 1 well (Fig. 4B). The cones within the survey 29 30 321 are less than 2 km long and 750 m wide, and often elongate in a NW-SE direction (Fig. 6). 31 32 322 Due to the extrusive nature of the Lambda 1 well, their stratigraphic concordance and their 33 34 323 cone shaped morphology in seismic, we have interpreted these as monogenetic volcanoes, 35 36 324 small cumulative volume volcanic edifices built up by one continuous, or many 37 325 discontinuous, small eruptions over a short time scale (<= 10 years) (Németh & Kereszturi, 38 39 326 2015). 40 41 42 327 In the Winnie 3D survey, twelve of the volcanoes are linked with what appear to be 43 44 328 elongate, NW-SE oriented lava flows that are conformable to stratigraphy and have 45 329 dimensions of 2-7 km in length and 0.5-2.5 km in width (covering areas of 4-13.5 km2) (e.g. 46 47 330 Figs. 7 & 8). 48 49 50 331 The northwards continuation of the monogenetic volcanoes and lava flows that were 51 52 332 detailed in the Winnie 3D survey is imaged within the Gallus 2D survey (Fig. 11A-C). To 53 54 333 better constrain the distribution of the volcanics in the Gallus 2D survey, the top and 55 334 bottom of the igneous rocks were mapped. From these, we calculated the isochron 56 57 335 thickness of the igneous rocks in the area (Fig. 9A). Like the Winnie 3D survey, volcanism 58 59 336 was more pervasive towards the east, with the thickest volcanics (~300 ms, approximately 60 61 62 63 64 65 12

337 163 m) located at the eastern edge of the survey. The northernmost extent of the Warnie 1 2 338 Volcanic Province is recognised in the Madigan 3D survey where two monogenetic vents 3 339 were identified within the seismic data. Although, neither vent was penetrated by a well and 4 5 340 no surface flows were mapped away from the vents, it seems likely that they are volcanic in 6 7 341 origin due to their similarity with the other volcanoes in the Nappamerri Trough. 8 9 10 342 11 12 343 We have also interpreted one feature within the Warnie Volcanic Province as a 13 14 344 diatreme. Maar-diatreme volcanism can occur where a volcanic pipe forms through gaseous 15 16 345 explosions that cut into the country rock (Fig. 4 E-H) (White & Ross, 2011). These 17 18 346 explosions form a maar (the crater and associated ejecta ring) and a diatreme (the root to 19 20 347 the maar), consisting of a steep-sided cone shaped structure filled with pyroclastic, volcanic 21 348 and country rocks) (White & Ross, 2011). Unlike vents and associated lava flows, they 22 23 349 consist of downward dipping reflectors that truncate the underlying stratigraphy with 24 25 350 typically chaotic internal reflectors (Fig. 4F). Spectral decomposition proved to be the most 26 27 351 powerful tool for identifying maar-diatremes above the Nappamerri Trough, as the circular 28 29 352 crater morphology stood out against the surrounding sediments (Fig. 4G). One feature 30 31 353 interpreted to be a diatreme was identified within the survey, displayed in detail in (Fig. 4). It 32 2 33 354 is ~2.25 km and ~120 m deep (150 ms, TWT) and is found in the west of the Winnie 3D 34 355 survey (see Fig. 6). 35 36 37 356 38 39 357 5. Description of Intrusive Igneous Rocks 40 41 42 43 358 5.1 Well Data 44 45 46 359 Igneous rocks intersected within the Warnie East 1 well are lithologically unique amongst 47 360 the igneous rocks penetrated by wells in the WVP. Located at 2103 m depth within the 48 49 361 Permian Toolachee Fm (Fig. 10), the 65 m thick basalt is described in the end of well report 50 51 362 as fine grained and dominated by plagioclase laths intergrown with augite (Boothby, 1986). 52 53 363 The upper 12 m of the volcanics are described as altered and calcareous, containing 54 55 364 phenocrysts of augite with minor pale green talc and minor calcite veining. 56 57 365 Vitrinite reflectance data was acquired within the Warnie East 1 well. (Fig. 10B). Samples of 58 59 366 vitrain were obtained and mean maximum reflectance of vitrinite calculated (Smith, 1987). 60 61 62 63 64 65 13

367 Vitrinite reflectance samples adjacent (directly above and below) to the basalt show a 1 2 368 marked increase to 4.5% relative to surrounding Toolachee sediments that are typically 1.5- 3 369 1.75%. Whereas extrusive volcanics appear to have little thermal effect on the surrounding 4 5 370 sediments (e.g. Grove et al., 2017), igneous intrusions typically show uniform heating on 6 7 371 either side of the volcanics, as is observed here (Aarnes et al., 2015). Coupled with its 8 9 372 stratigraphic position within the Permian Toolachee Fm., where no other volcanics have 10 11 373 been documented within the Cooper Basin, we suggest that Warnie East 1 contains the sole 12 13 374 identified well intersection of an igneous intrusion in the WVP. 14 15 375 5.2 Seismic Data 16 17 18 376 Intrusive igneous rocks are also identified within the seismic data available. A 2D seismic 19 20 377 reflection line was available that runs across the location of the Warnie East 1 well (Fig. 11). 21 22 378 Unlike the Lambda 1 and Orientos 2 volcanics, the igneous rocks within the Warnie East 1 23 24 379 well sit within the Toolachee Fm., a highly reflective sequence of heterogeneous lithologies 25 26 380 consisting of sandstones, siltstones and coals. As such, the igneous rocks are difficult to 27 381 distinguish on seismic reflection survey data, although a shallow saucer-shaped reflection 28 29 382 intersects the well path of the Warnie East 1 well at the depth that igneous rocks are 30 31 383 located. The reflection is ~1.5 km wide and transects the Toolachee Fm. over a depth range 32 33 384 of 50 ms. The shallow saucer shape that the reflection event exhibits is common among 34 35 385 igneous intrusions within sedimentary basins, corroborating with the well data that suggests 36 37 386 the igneous rocks are intrusive in nature. 38 39 387 Igneous intrusions within the Winnie 3D survey are identified as igneous rocks that 40 41 388 cross-cut the Triassic to Jurassic strata; notably the Nappamerri, Hutton and Birkhead Fms 42 43 389 (e.g. Fig. 12). We identified and mapped 14 intrusions in the seismic data; these occur ~100– 44 45 390 200 ms (~105 – 210 m) below the palaeosurface. Most of the sills identified are of a similar 46 47 391 scale to the lava flows in the area (2 – 4.5 km long, 1.2 – 1.7 km wide). 48 49 392 The Winnie 3D survey also hosts a spectacular single intrusion, 14 km long and 8 50 51 393 km wide, by far the largest igneous feature in the WVP (Fig. 12). Classical intrusion-related 52 53 394 features such as inflation lobes are observed within spectral decomposition (Fig. 12C). 54 55 395 Around 20 vents cross-cut this intrusion (see pockmarks on Fig. 12C), in places leading to 56 57 396 extrusive lava flows in the overlying sediments (see surface flows on Top Birkhead overlying 58 397 the intrusion in Fig. 12B). The presence of the pockmarks on the surface of the intrusion 59 60 61 62 63 64 65 14

398 suggest emplacement of the sill predated a later stage of volcanism that occurred towards 1 2 399 the top of the Birkhead Fm. 3 4 400 5 6 401 6. Description of Altered Igneous Rocks 7 8 9 402 This study has so far dealt with igneous rocks of a very consistent lithology preserved within 10 403 or above the Central Nappamerri Trough. However, the Kappa 1 well and Snowball 3D 11 12 404 seismic reflection survey, located on the very southern edge of the mapped extent of the 13 14 405 WVP, preserve igneous rocks of a very different character (Figs. 13-15). 15 16 17 406 6.1 Well Data 18 19 20 407 The Kappa 1 well was drilled in 1997 on behalf of Santos Limited with the aim of evaluating 21 22 408 hydrocarbon presence within the Toolachee, Patchawarra and Epsilon formations (Allen, 23 409 1998). Kappa 1 is located above a large anticline and is the southernmost of a string of 24 25 410 prospects located above the northeast Della-Nappacoongee Ridge, which deepens 26 27 411 northwards into the Nappamerri Trough (Fig. 1). Between 1895 and 2115 m, the Kappa 28 29 412 well intersected a 120 m thick succession of igneous rocks below a thinned 21 m succession 30 31 413 of Hutton Sandstone (Fig. 13). Within the well report, the igneous rocks are ascribed a late 32 33 414 Permian to Middle Triassic age (Allen, 1998). 34 35 415 Although core description or in-depth petrological work was not undertaken during this 36 37 416 study, rock chips and cuttings of the igneous rocks are described extensively within the 38 39 417 Kappa 1 end of well report (Allen, 1998). Due to the large amount of alteration, the 40 41 418 volcanics are described as a chloritized basalt with abundant plagioclase, chlorite, carbonates 42 43 419 and quartz. However, the well report distinguishes two types of igneous rocks. Firstly, a 44 420 vesicular microporphyritic basalt was described that consists of olivine and pyroxene 45 46 421 phenocrysts contained within a fine grained or glassy groundmass. Secondly, a less abundant 47 48 422 coarse-grained holocrystalline basalt that is composed of randomly oriented plagioclase 49 50 423 laths, ferromagnesian crystals and accessory magnetite plus ilmenite. Importantly, and 51 52 424 pervasively throughout the succession, a fibrous chlorite is described as having replaced 53 54 425 much of the ferromagnesian minerals and groundmass as well rimming and filling vesicles 55 426 within the basalt. 56 57 58 427 The Igneous succession in Kappa 1 also has an unusual petrophysical expression. In our 59 60 428 interpretation, we have divided the volcanics into two facies based on the above description; 61 62 63 64 65 15

429 a volcaniclastic breccia and in-situ basalt (Fig. 13). The in-situ basalt (e.g. the section between 1 2 430 1900 m and 1960 m (Fig. 13)) has a ‘saw-tooth’ response with a relatively low gamma 3 -1 431 response of ~40 api. Acoustic velocities from the sonic velocity log (~4 kms ) are 4 5 432 consistently lower than those observed in the Lambda 1 and Orientos 2 wells (~ 5.5-6 kms- 6 7 433 1). The chaotic, saw-tooth response is indicative of the highly altered nature of the volcanic 8 9 434 succession in Kappa 1 and can be diagnostic of compound lava flows (Millet et al., 2016; 10 11 435 Hardman et al., 2019) (Fig. 18). The resistivity throughout the section consistently measures 12 13 436 15 Ωm. As with the Lambda 1 well, we constructed a velocity histogram for the igneous 14 15 437 rocks in the Kappa 1 well. When compared to Nelson et al.’s velocity histograms (2009) the 16 438 best match was with that of Compound-braided flows (Fig. 13B). However, the upper half of 17 18 439 Nelson et al.’s (2009) histogram is missing in the Kappa 1 volcanics, suggesting that the more 19 20 440 crystalline, high velocity material is either absent or has been altered to lower velocity 21 22 441 material. 23 24 442 The volcaniclastic breccia is described as consisting of poorly sorted, subangular, 25 26 443 volcaniclastic igneous rock of very fine sand to granule size (Allen, 1998). The log response 27 28 444 for the volcaniclastic breccia is characterised by a jagged petrophysical response when 29 30 445 compared to the in-situ basalt. Although the gamma ray values (~40 api) are similar to those 31 -1 32 446 of the in-situ basalt, the acoustic velocities (between 2800 and 4 kms ) are consistently 33 34 447 lower. Furthermore, the volcaniclastic breccia is water saturated with a resistivity of 2 – 3 35 36 448 Ωm, although this may also reflect the magnetite and ilmenite within the basalt. Finally, 37 449 below 2050 m to the base of the volcanic succession, the caliper tool widened significantly 38 39 450 suggesting that the volcaniclastics in this part of the succession are considerably 40 41 451 unconsolidated and/or fractured. 42 43 44 452 6.2 Seismic Data 45 46 47 453 The top of the Kappa 1 volcanics is interpreted to correlate with a bright, laterally 48 454 continuous reflection that was present across the whole of the Snowball 3D survey (Figs. 14 49 50 455 & 15). Above the top Kappa 1 volcanics a second reflector, deemed here the ‘Top Volcanic 51 52 456 Mounds,’ was mapped in parts of the Snowball 3D survey adjacent to a series of mound-like 53 54 457 structures, appearing in places to downlap onto the top Kappa 1 volcanics (Fig. 15). The 55 56 458 centres of these-mound shaped structures are marked by a notable brightening of the 57 58 459 reflectors and they are underlain by vertical vents similar to those seen in the other surveys. 59 460 We thus interpret these mound structures to be a series of volcanic edifices. 60 61 62 63 64 65 16

461 The volcanics present in the Snowball 3D survey are notably different to those preserved in 1 2 462 the Nappamerri Trough (e.g. Fig 7-9). Rather than isolated, monogenetic vents or flows, 3 463 they are interpreted to represent a thick package (up to ~150 ms) of mixed volcanics and 4 5 464 volcaniclastic breccias (based on evidence from Kappa 1) that thin towards the southwest of 6 7 465 the survey (Fig. 15A) (i.e. the southern edge of the Nappamerri Trough). Although the true 8 9 466 extent of them is not imaged within the survey (they are interpreted to extend beyond the 10 11 467 survey limits to the northeast), laterally they extend over 6 km. 12 13 468 7. Geophysical Surveys of the Nappamerri Trough 14 15 16 469 Alongside seismic and well data, airborne geophysical surveys were examined in 17 18 470 order to further delineate the regional distribution of the WVP (Fig. 21A). A gravity data 19 20 471 grid was downloaded from the Queensland Government’s data repository. The grid is a 21 472 compilation of open file gravity surveys collected by exploration companies and State and 22 23 473 Federal regional surveys, compiled in 2014. In southwest Queensland, the Nappamerri 24 25 474 Trough is typically characterized by a broad gravity low. However, a pronounced ~50 x 50 26 27 475 km gravity high is apparent in the northeast Nappamerri Trough (Fig. 16A). Furthermore, 28 29 476 the quantity of mapped intrusive and extrusive volcanics increases towards the centre of 30 31 477 this 50 x 50 km gravity anomaly (Fig. 1B). This corresponds with an increase in the thickness 32 478 of igneous rocks mapped within seismic data (see Figs. 2, 7 and 9). 33 34 35 479 In addition to gravity data, a 1VD magnetic intensity survey has been analysed that 36 37 480 was also downloaded from the Queensland Government’s data repository (Fig. 16B). The 38 39 481 first vertical derivate filter enhances the high frequency content in the survey, highlighting 40 41 482 magnetic anomalies caused by shallow sources such as igneous rocks that are situated at 42 483 shallower depths than the base of the Cooper Basin succession. The Nappamerri Trough is 43 44 484 generally marked by a low in the magnetic intensity whilst the bounding ridges are magnetic 45 46 485 highs. However, within the Nappamerri Trough, many small (<8 km2) circular magnetic 47 48 486 anomalies can be observed (Fig. 16B). Basalt is highly susceptible to being magnetised 49 50 487 (Tarling, 1966), which has facilitated the recognition of buried volcanic rocks elsewhere in 51 52 488 the world (Segawa & Oshima, 1975). Notably, many of the smaller magnetic anomalies do 53 489 correspond to the location of igneous rocks in the Winnie 3D survey (Fig. 16C). 54 55 56 490 When the gravity data is superimposed on top of the magnetic data, there is a clear 57 58 491 correlation between the location of igneous rocks interpreted using seismic data, the 59 60 492 magnetic anomalies and the gravity high identifiable within the Nappamerri Trough (Fig. 16D 61 62 63 64 65 17

493 & E), suggesting that regional geophysical surveys help to constrain the distribution and 1 2 494 location of the WVP and other intraplate volcanic provinces. Perhaps most interesting is 3 495 that the correlation between circular magnetic anomalies and areas with a strong gravity 4 5 496 response can be extended beyond the area of the WVP interpreted during this study (Fig. 6 7 497 16E). To the east and southeast of this study, circular magnetic anomalies appear to be 8 9 498 coincident with gravity highs. If these anomalies are proven to be volcanic in nature, the 10 2 11 499 extent of the Warnie Volcanic Province could be greater than the interpreted 7500 km . 12 13 500 8. The Age of the Warnie Volcanic Province 14 15 16 501 This study has detailed the character and extent of igneous rocks within the Cooper and 17 18 502 Eromanga basins which has facilitated a regional overview of the WVP (Fig. 17). Here we 19 20 503 synthesise the different methods used to define an age range for the eruption and 21 504 emplacement of the igneous rocks. 22 23 24 505 Previous Geochemical Analyses 25 26 506 K-Ar dating was conducted on both the Lambda 1 extrusive basalt and the Warnie East 1 27 28 507 intrusive basalt. In the Lambda 1 well, K-Ar dating was conducted on a bag of drill cuttings 29 30 508 taken from a depth of 1658 m by Murray (1994). Although the samples are described as 31 32 509 being too altered to be used for total rock analysis, fresh plagioclase within the cuttings was 33 34 510 separated for analysis and used to determine an age of 227 +/- 3 Ma, suggesting 35 36 511 emplacement of the basalt during the early Triassic (Murray, 1994). However, in Lambda-1, 37 38 512 the basalt is situated between the Jurassic Birkhead Fm. and the Triassic Nappamerri Gp., 39 513 supporting a Late Triassic to Jurassic age (Draper, 2002). K-Ar dating of basaltic volcanic 40 41 514 rocks is often unreliable (Schofield et al., 2017), due to unquantified argon loss (Kelley, 42 43 515 2002). It is noted within the well report that the loss of argon due to subsequent thermal 44 45 516 events or contamination of drill cuttings is not accounted for in the quoted error (Murray, 46 47 517 1994). 48 49 518 Within the Warnie East 1 well, K-Ar dating was conducted on a sample of drill core from 50 51 519 2163 m (Murray, 1994). Again, the rock was too altered to be used for whole rock K-Ar 52 53 520 analysis and, instead, unaltered pyroxene was used for dating. A middle Cretaceous age of 54 55 521 100 ± 9 Ma was calculated (Murray, 1994), significantly younger than the rest of the WVP 56 57 522 and the Permian host rock within which the intrusion is located. This disparity in the ages 58 59 523 determined by K-Ar dating led Draper (2002) to deem the the age dating as ‘equivocal.’ 60 61 62 63 64 65 18

524 Whilst K-Ar dating is considered be relatively unreliable, there are a number of other age- 1 2 525 dating techniques that could be conducted on cuttings or core from the Warnie Volcanic 3 526 Province. U-Pb, Re-Os and Ar-Ar could all be analysed to provide independent constraints 4 5 527 on the age of the igneous material (Liu et al., 2017). Furthermore, these geochemical 6 7 528 measurements can provide insights into the source of these volcanics (Pande et al., 2017) 8 9 529 and are an avenue for future work in the area. In the absence of more geochemical data, it is 10 11 530 important to consider the K-Ar ages with respect to other data. 12 13 531 Seismic Data 14 15 16 532 When tied to the seismic data, the Hutton Sandstone and equivalent sediments (not 17 18 533 penetrated by the Lambda 1 well) are seen to onlap the Lambda 1 volcanics. The lava flow 19 20 534 extending away from Lambda 1 sits atop Triassic Nappamerri Group sediments of the 21 535 Cooper Basin whereas the volcanics penetrated by Lambda 1 appear to cross cut the 22 23 536 Triassic stratigraphy. 24 25 26 537 The timing of igneous activity within the Winnie 3D survey was constrained by the 27 28 538 stratigraphic relationship between igneous activity and the Triassic to Jurassic stratigraphy in 29 30 539 the study area. In places, intrusions are observed to have caused forced folding of the 31 540 overburden, as evidenced by onlap of Birkhead Fm. sediments onto the deformed 32 33 541 overburden overlying the intrusions (Fig. 12B). Onlap of sedimentary rocks onto these 34 35 542 forced folds was used to constrain the age of the intrusion (Trude et al., 2003), whilst the 36 37 543 strata-concordant lava flows elsewhere in the survey were assigned an approximate age 38 39 544 based on their stratigraphic level. We estimate that volcanism lasted throughout deposition 40 41 545 of the Hutton and Birkhead formations between ~178 and 160 Ma, with the youngest 42 546 volcanics identified as surface flows emplaced on the top Birkhead marker horizon 43 44 547 (Alexander & Hibburt, 1996). 45 46 47 548 Similarly, in the Gallus 2D survey whilst none of the volcanics were intersected by any wells, 48 49 549 the approximate stratigraphic age was constrained by the nearby Halifax and Etty wells (Fig. 50 51 550 9C), placing the volcanics within the Hutton and Birkhead formations, as found for the 52 551 Winnie 3D survey. 53 54 55 552 The Madigan 3D volcanics appear to sit near the top of the Nappamerri Group, however, 56 57 553 this would place them in the middle Triassic ~240 Ma, ~60 Myrs older than the rest of the 58 59 554 WVP. An alternative explanation would be the emplacement of these vents at the very base 60 61 62 63 64 65 19

555 of the Jurassic in this region (a maximum age of ~200 Ma, Fig. 2), as they appear to cross-cut 1 2 556 all of the Triassic Nappamerri Group strata. This second explanation is preferable as it 3 557 would fit with the igneous rocks observed throughout the rest of the WVP. 4 5 6 558 We conclude that the vast majority of igneous rocks identified using seismic reflection data 7 8 559 and well data throughout this study can be constrained to a broad age range between ~180 9 10 560 and 160 Ma, spanning the Middle Jurassic. Further work is encouraged to better define the 11 12 561 age of the Warnie Volcanic Province, particularly geochemical analyse that would help 13 562 constrain both the origin and timing of volcanism. 14 15 16 563 17 18 19 564 8. Discussion 20 21 22 565 8.1 The Origin of Altered Volcanics Within the Warnie Volcanic Province 23 24 25 566 The nature of the igneous rocks within the Kappa 1 well and Snowball 3D survey is distinct 26 567 when compared to the rest of the Warnie Volcanic Province, consisting of a mixed 27 28 568 sequence of in-situ basalt and volcaniclastics breccias. What isn’t clear, however, is the 29 30 569 origin of the volcanics. Within the Kappa-1 well report, the sequence is described as 31 32 570 pyroclastic in nature (Allen, 1998). Whilst this interpretation can account for some of the 33 34 571 altered volcaniclastics, it does not explain the extensive sequence of altered basalt. An 35 36 572 alternative explanation may be differing sedimentation and eruption rates within the 37 38 573 Eromanga leading to prolonged exposure of volcanic rocks emplaced on the rim of the 39 574 Nappamerri Trough. However, Mid-Late Jurassic sedimentation rates at Kappa 1 of 2.4 40 41 575 m.my-1 (calculated by dividing the thickness of the Hutton to Adori succession by a duration 42 43 576 of 23 Myrs) are not significantly lower than those in the Warnie or Lambda wells (2.8 and 44 45 577 2.5 m.my-1 respectively). Hence, alteration does not appear to be a consequence of 46 47 578 extensive surface exposure. 48 49 579 A more compelling explanation for the Kappa 1 volcanics is hydrothermal alteration. In 50 51 580 volcanic regions, many lakes are typically fed by hot springs. In the East African Rift, 52 53 581 discharge of hydrothermal water can produce authigenic chlorite with calcite and quartz 54 55 582 forming pore filling cements (Renaut et al., 2002). These minerals, particularly chlorite, are 56 57 583 noted extensively within the petrological description of the Kappa 1 well. Additionally, the 58 59 584 Kappa 1 well lies above the Kinta structural trend which could have provided a pathway for 60 61 62 63 64 65 20

585 hydrothermal fluids into the Eromanga succession. Basin-wide hydrothermal fluid circulation 1 2 586 has been noted within the Cooper Basin (Middleton et al., 2014, 2015). In the Nappamerri 3 587 Trough, these fluids are believed to have formed due to rifting of the eastern Australian 4 5 588 margin during the mid-Cretaceous (Middleton et al., 2015), post-dating the emplacement of 6 7 589 the Warnie Volcanic Province. We propose that the Kappa 1 well represents a succession 8 9 590 of volcaniclastic and primary volcanic rocks that was highly altered by hydrothermal fluids. 10 11 12 591 13 14 592 8.2 Structural Controls on the Emplacement of the Warnie Volcanic Province 15 16 17 593 From the late Triassic to the early Jurassic, the Eromanga Basin was subject to an east-west 18 594 compressional event named the Hunter-Bowen event (Kulikowski & Amrouch, 2017), which 19 20 595 uplifted the basin and inverted the major highs. Subsequently, the basin underwent post- 21 22 596 compressional flexural relaxation with the resultant accommodation space infilled by the 23 24 597 Middle to Late Jurassic succession discussed within this manuscript (Lowe-Young, 1997). 25 26 598 During this time, a strike-slip extensional regime is thought to have been present in 27 28 599 southwest Queensland (Kulikowski et al., 2018). In this context, it is interesting to consider 29 600 whether the stress regime of the Cooper Basin helped to control the location and 30 31 601 morphology of igneous rocks within the WVP and, more broadly, the location of the WVP 32 33 602 within central Australia. 34 35 36 603 8.2.1 The Influence of Basement Structure on the Location of Igneous Rocks 37 38 39 604 Within other basins, such as those in the North Atlantic, it has been noted how the location 40 605 of igneous intrusions and volcanism is controlled by the basin structure, in particular the 41 42 606 location of major faults (Schofield et al., 2017; McLean et al., 2017; Hardman et al., 2019). To 43 44 607 investigate whether basement structure and faulting had a direct control on volcanism 45 46 608 erupted during the Jurassic, we have utilised the 3D seismic reflection datasets available. 47 48 49 609 The basin structure of the eastern Nappamerri Trough is largely obscured by the thick 50 610 Cooper and Eromanga Basin fill and the highly reflective coals of the Permian Toolachee and 51 52 611 Patchawarra Fms that make imaging of deeper sediments difficult. Of all the 3D seismic 53 54 612 reflection surveys available for this study, only the Winnie 3D survey imaged reflections 55 56 613 ~2800 ms deep within the Nappamerri Trough (Fig. 3)(approximately 4.3 km subsurface 57 58 614 depth based on the Charal-1 time-depth relationship). Notably, the exact lithology of this 59 60 615 reflection is unclear, largely due to the lack of any intersections in the Central Nappameri 61 62 63 64 65 21

616 wells. Unlike the flat-lying Cooper and Eromanga stratigraphy, these deep reflections were

1 0 2 617 often inclined at an angle of ~10 (taken with the scale set so that 1s TWT depth = 1 km 3 618 distance laterally). Although not confidently picked throughout the whole of the Winnie 3D 4 5 619 survey, the reflections can be mapped over an area of ~600 km2 (Fig. 18B). We interpret 6 7 620 these to represent the top Basement in the Nappamerri Trough. 8 9 10 621 When mapped and imaged in plan view, it is clear that the most major offset (a ~400 ms 11 12 622 step in the data visible in Fig. 18B) trends ~15 km NW-SE across the Winnie 3D survey. 13 623 The same 400 ms step has been noted by previous mapping (SA Department for 14 15 624 Manufacturing, Innovation, Trade, Resources and Energy, 2003) where it is visible on a top 16 17 625 basement map in the eastern Nappamerri Trough. We interpret offset of the top basement 18 19 626 as faulting and, so that it may be easily referred to throughout the text, name the major 400 20 21 627 ms offset the Central Nappamerri Fault. 22 23 628 In order to better relate the igneous activity in the area to the basement structure the 24 25 629 distribution of the monogenetic vents within the Winnie 3D survey is considered with 26 27 630 respect to these deep basement reflectors. Beneath the vents and volcanoes of the Winnie 28 29 631 3D survey, the seismic reflection data exhibited a velocity pull-up effect that could either 30 31 632 represent shallow high velocity material (i.e., the vents or volcanoes themselves) or a high 32 33 633 velocity feeder zone representing a vertical column of igneous rock or hydrothermally 34 634 altered host rock. This effect was particularly obvious on the well-imaged Toolachee Fm., 35 36 635 which was mapped to constrain the distribution of the pull-up effects or vents throughout 37 38 636 the area (Fig. 18A). Underlying the volcanoes are dark patches that are clearly distinguished 39 40 637 from the fluvial channels that make up the Toolachee Fm. (Fig. 18A). We have interpreted 41 42 638 these as vents that are either hydrothermal vents or basaltic dykes. The position of these 43 44 639 vents was highlighted and superimposed on top of the image of the basement reflections 45 640 (Fig. 18B). The vents broadly fall into two groups, one to the south of the Central 46 47 641 Nappamerri Fault and one to the NE of the Central Nappamerri Fault (Fig. 17 and 18B). 48 49 642 These groups fall adjacent to the Top Basement reflections or directly above visible offset in 50 51 643 the basement where it deepens to > 3600 ms and is no longer mappable, strongly implying a 52 53 644 pervasive structural control on the location of vents in the Winnie 3D survey. 54 55 56 645 We also superimposed the location of the Madigan 3D volcanoes on top of the SA 57 58 646 Department for Manufacturing, Innovation, Trade, Resources and Energy (2003) basement 59 647 map (Fig. 17). Like the igneous rocks in the Winnie 3D survey, the two volcanoes imaged in 60 61 62 63 64 65 22

648 the Madigan 3D survey sit atop the tip of the 25 km Challum Fault and atop a second, ~5 1 2 649 km fault northwest of the main Challum Fault. The volcanics seem to be located at the 3 650 stepover between two faults, suggesting it may be a small releasing bend. This reinforces the 4 5 651 idea that the location of igneous rocks was largely controlled by zones of weakness within 6 7 652 the basins. 8 9 10 653 8.2.2 The Influence of Discontinuities and Faults within the Eromanga Succession on the 11 12 654 Morphology of Igneous Rocks 13 14 655 The idea that structure was the principle control on the nature of the volcanics in the WVP 15 16 656 can be extended to the morphology of the igneous rocks. In order to consider how basin 17 18 657 structure controlled the morphology of igneous rocks within the Nappamerri Trough, the 19 658 Winnie 3D survey was used to map the length, width and elongate direction of the 20 21 659 volcanoes, lava flows and intrusions (Fig. 19). The high quality of the Winnie 3D survey 22 23 660 facilitated confident mapping of the outline of individual volcanic events, however, the Gallus 24 25 661 2D and Snowball 3D surveys were not considered as the outline of individual volcanics 26 27 662 could not be picked confidently. The data shows that igneous rocks in the area are typically 28 29 663 twice as long as they are wide (Fig. 19). Furthermore, almost all the igneous rocks are 30 31 664 elongated in a NW-SE direction, closely matching the strike of the faults within the 32 665 Nappamerri Trough. It is clear that during eruption and emplacement of the igneous rocks, 33 34 666 the basin structure exerted a strong control on the morphology of lava flows and igneous 35 36 667 intrusions. 37 38 39 668 In vertical seismic reflection sections, faulting of the Eromanga Basin stratigraphy is not 40 41 669 obvious within the Winnie 3D survey, largely due to the considerable noise within the 42 43 670 section. However, spectral decomposition produced for the Top Volcanics horizon images 44 45 671 discontinuities (shown as black lines) within the colour blend (Fig. 20). These discontinuities 46 672 are not thought to be a product of the acquisition and processing of the seismic data, due to 47 48 673 their non-linear nature and their coincidence with other geological features such as the 49 50 674 igneous rocks and the CNF. When mapped, the features form a series of largely NE-SW 51 52 675 trending lineaments (Fig. 20). Although imaging of the discontinuities is best in the SW of the 53 54 676 survey, where there are fewer igneous rocks, it is evident that many of the igneous rocks 55 56 677 are aligned with these features, suggesting they must have exerted some topographical or 57 678 structural control when the igneous rocks were erupted or emplaced into the Nappamerri 58 59 679 Trough (Fig. 20). As they do not resemble any sedimentary features such as valleys or fluvial 60 61 62 63 64 65 23

680 systems, we interpret these features to be faulting or fracturing of the Eromanga succession 1 2 681 above the Nappamerri Trough. 3 4 682 Determining the tectonic activity responsible for the faulting within the Nappamerri Trough 5 6 683 and, hence, the location and morphology of igneous rocks within the WVP is difficult due to 7 8 684 the complex structural and stress history of the Cooper Basin. Throughout the basin, a 9 10 685 conjugate set of large NNE-SSW and field scale SE-NW striking dextral strike-slip faults 11 12 686 developed under SSE-NNW strike-slip stress conditions (Kulikowski et al., 2018). This is 13 687 pertinent when applied to the central Nappamerri Trough, as Kulikowski et al. (2018) 14 15 688 identified a series of vertical SE-NW structural lineaments with normal displacement to no 16 17 689 displacement. Due to their vertical nature, it is thought that these faults developed as strike 18 19 690 slip faults during successive periods of flexural relaxation or sag. The faulting identified 20 21 691 within this study is also determined to consist of little offset with an orientation that 22 23 692 matches that of the strike-slip faulting determined by Kulikowski et al., (2018) (Fig. 20). We 24 693 surmise that sag within the basin produced a series of faults that controlled the morphology 25 26 694 of igneous rocks in the WVP. 27 28 29 695 30 31 696 8.3 The Broader Record of Jurassic Volcanism in Eastern Australia 32 33 34 697 We believe it is important to consider the WVP in the context of the broader record of 35 36 698 Jurassic volcanic activity in eastern Australia (Table 2 & Fig. 21). Coeval with the eruption of 37 38 699 the WVP, the Eromanga Basin was undergoing post-compressional flexural relaxation with 39 40 700 thermally controlled subsidence in the absence of significant fault control (Gallagher & 41 42 701 Lambeck, 1989). Subsidence has been attributed to subduction of the Pacific plate beneath 43 44 702 southern and eastern Australia, during which time rifting also initiated between Australia and 45 703 Antarctica (Griffiths, 1975; Johnstone et al., 1973). 46 47 48 704 Evidence for Jurassic volcanic activity is pervasive throughout the sedimentary basins of 49 50 705 eastern Australia, manifested by volcanic arc-derived sediment within the Eromanga Basin 51 52 706 (Boult et al., 1998), silicic tuffs in the Surat Basin (Wainman et al., 2015) and widespread 53 54 707 volcanogenic zircons within the Eromanga Basin (Bryan et al., 1997). This volcaniclastic 55 708 material is thought to be derived from an acid to intermediate volcanic arc positioned off 56 57 709 the coast of Queensland during the Jurassic, however, the remnants of this arc volcanism 58 59 710 are yet to be identified (Paton, 1986, Boult et al., 1997). Jurassic alkali basalt has been 60 61 62 63 64 65 24

711 intersected on the Marion Plateau (~400 km east of Townsville in Queensland), although 1 2 712 this may also be related to rifting in the region during the Jurassic (Isern et al., 2002). 3 4 713 Around 1500 km south of the Marion Plateau, mafic and ultramafic igneous rocks are noted 5 6 714 throughout the Eastern Highlands and Sydney Basin. Dykes of the Sydney area intrude rocks 7 8 715 as young as 235 Ma with K-Ar dating suggesting ages of between 193 and 46.9 Ma 9 10 716 (McDougall and Wellman, 1976, Embleton et al., 1985, Pells, 1985). To the north west of the 11 12 717 Syndey Basin, in New South Wales, lower Jurassic intrusions and volcanics of the Garawilla 13 718 alkali basalts are noted in the Gunnedah Basin (195-141 Ma) (Sutherland, 1978, Pratt, 1998, 14 15 719 Gurba & Weber, 2001). The intermediate to mafic Dubbo volcanics are also recognised in 16 17 720 New South Wales (236-170 Ma) (Dulhunty, 1976, Embleton et al., 1985, Black, 1998, 18 19 721 Warren et al., 1999). Further south of the Sydney and Gunnedah basins, Jurassic volcanics 20 21 722 are scattered throughout Victoria and Tasmania (Veevers & Conaghan, 1984). These include 22 23 723 voluminous tholeiitic intrusions in Tasmania (183 Ma) that are thought to have been buried 24 724 under a thick pile of largely eroded extrusive volcanics that have a detrital zircon age range 25 26 725 of 182 ± 4 Ma (Sutherland, 1978; McDougall & Wellman, 1976, Bromfield et al., 2007, Ivanov 27 28 726 et al., 2017). In Eastern Victoria, Jurassic activity included a 191 Ma dyke swarm of alkali 29 30 727 basalts (Soesoo et al., 1999). The geochemical source characteristics of the Eastern Victoria 31 32 728 alkalia basalts are suggestive of subcontinental lithospheric mantle, like the proposed source 33 34 729 of the Late Cenozoic Newer Volcanic Province in western Victoria (Elburg & Soesoo, 1999). 35 36 730 Around 1000 km south of the WVP, the Wisanger Basalt is a ~170 Ma, 20 km fragmented 37 38 731 lava flow emplaced on top of Permian fluviatile sediments on Kangaraoo Island (McDougall & 39 40 732 Wellman, 1976). Geochemically, it is similar to the Tasmanian and Antarctic tholeiitic 41 42 733 dolerite and basalts that are usually attributed to the Ferrar Large Igneous Province and 43 44 734 extension that latterly resulted in the separation of Australia and Antarctica (Compston et 45 735 al., 1968; Milnes et al., 1982). Of note in South Australia, Jurassic kimberlites record the 46 47 736 extension of Mesozoic kimberlites found along the margin of southern Gondwana, above 48 49 737 the subducting Pacific plate (Tappert et al., 2009), differing petrologically from the 50 51 738 predominantly basaltic volcanism found elsewhere in eastern Australia. 52 53 54 739 Plate reconstructions indicate that the Eromanga Basin was located at significant distances 55 740 (at least 750 km) from the oceanic trench of the subducting Pacific plate (Veevers & 56 57 741 Conaghan, 1984; Ivanov et al., 2017) (Fig. 21). We therefore believe the Warnie Volcanic 58 59 742 Province to be an intraplate volcanic province and, as the origin of intraplate volcanism can 60 61 62 63 64 65 25

743 often be contentious (Conrad et al., 2011), it is important to consider the source of this 1 2 744 volcanism and implications for the formation of intraplate volcanism. 3 4 745 8.4 The Origin of the Warnie Volcanic Province 5 6 7 746 The WVP was located far from active plate boundaries during the Jurassic (Fig. 21). When 8 9 747 considering the source of intraplate volcanism, several different mechanisms must be 10 11 748 considered: 12 13 749 • The presence of a mantle plume 14 15 750 • Asthenospheric upwelling due to extension 16 17 751 • Local scale mantle convection 18 19 752 Mantle plumes are typically associated with the eruption of voluminous flood basalt 20 21 753 provinces that often mark the earliest volcanic activity of major hot spots (Richards et al., 22 23 754 1989). Furthermore, mantle plumes cause dynamic uplift of the land’s surface of up to 24 755 several hundred kms followed by surface subsidence due to the withdrawal of mantle plume 25 26 756 material and loading of the crust with the volcanic sequence (Nadin et al., 1997; Dam et al., 27 28 757 1998; Hartley et al., 2011; Hardman et al., 2018). No evidence of major surface uplift in the 29 30 758 Cooper and Eromanga Basins is coeval with the emplacement and eruption of the WVP 31 32 759 (Hall et al., 2016). Furthermore, subsidence and sag throughout the emplacement of the 33 34 760 WVP is minor, with no large changes in sedimentary facies noted throughout the Jurassic 35 36 761 lower non-marine Eromanga succession (Alexander & Hibburt, 1996). No major crustal 37 762 and/or lithospheric extension is evidenced by the lack of major Jurassic faults, during a time 38 39 763 in which the basin underwent post-compressional flexural relaxation in a strike slip 40 41 764 extensional regime (Lowe-Young, 1997; Kulikowski et al., 2018). Furthermore, the small 42 43 765 spatial area covered by the Warnie Volcanic Province (~7500 km2 within the Nappamerri 44 45 766 Trough area) and, by extension, the volume of magma emplaced, is too low to be related to 46 47 767 a mantle plume source (Conrad et al., 2011). 48 49 768 Low-effusive volcanism occurring within tectonic plates has been also attributed to 50 51 769 several locally operating processes, such as minor upwelling plumes, downwelling drops and 52 53 770 sub-lithospheric or edge-driven convection (Courtillot et al., 2003; Ballmer et al., 2009; 54 55 771 Conrad et al., 2011). In the case of edge-driven convection, mantle flow can induce upwelling 56 57 772 and volcanism through interaction with lithospheric or asthenospheric heterogeneities 58 773 (Conrad et al., 2011; Davies & Rawlinson, 2014). In the Newer Volcanic Province in South 59 60 61 62 63 64 65 26

774 Australia, <5 kyr volcanism formed as a product of edge driven convection is noted to

1 2 2 775 consist of basaltic monogenetic volcanoes <4 km in size covering an area of up to 40,000 3 2 776 km (Demidjuk et al., 2007; Davies & Rawlinson, 2014). This style of volcanism (basaltic, with 4 5 777 individual volcanoes like Mount Gambier of a similar scale to the volcanoes imaged in the 6 7 778 Nappamerri Trough area (~1.5 x 1.5 km)) and the areal extent (7500 km2 that could be 8 9 779 extended to almost 20,000 km2 if the magnetic anomalies are found to be igneous in nature) 10 11 780 are similar in scale to the igneous rocks in the Newer Volcanic Province. Convection within 12 13 781 the asthenosphere can be induced by changes in lithospheric thickness. Although not much 14 15 782 is known about the crustal structure below the eastern Nappamerri Trough, seismic 16 783 reflection profiles have revealed that Devonian troughs to the east of the study area are 17 18 784 associated with crustal thinning of 7 – 10 km (Mathur, 1983). Furthermore, on a continental 19 20 785 scale, the Moho is observed to shallow to ~20 km below the Cooper Basin (and more 21 22 786 broadly, Central Australia) (Fig. 21)(Kennett et al., 2011). Therefore, there is observable 23 24 787 lithospheric thinning below the basins in Central Australia that could have produced edge 25 26 788 driven convection. 27 28 789 However, because Central Australia was relatively inactive during the Jurassic, we 29 30 790 must consider driving mechanisms for asthenospheric flow beneath the continent during the 31 32 791 eruption and emplacement of the WVP. As we have already detailed, the Pacific plate was 33 34 792 subducting beneath eastern Australia during the Jurassic. In intraplate volcanic provinces 35 36 793 adjacent to subduction zones (e.g. Western North America, China), there is a causal link 37 794 between subduction and intraplate volcanism, in that subduction below the continental crust 38 39 795 acts as a driving force for asthenospheric shear and, hence, the mantle upwelling that 40 41 796 produces intraplate volcanism (Conrad et al., 2011; Tang et al., 2014; Zhou et al., 2018). If 42 43 797 the extension in the area during the Jurassic is not great enough to stimulate volcanism, then 44 45 798 an alternative model may involve rapid asthenospheric shear produced by the subducting 46 47 799 Pacific Plate, localised beneath SW Queensland due to edge driven convection. 48 49 800 We propose a model for the Warnie Volcanic Province based on our understanding 50 51 801 of the lithospheric and geodynamic state of Central Australia in the Jurassic. We propose 52 53 802 that asthenospheric shear above the subducting pacific plate stimulated mantle flow below 54 55 803 Australia (Fig. 20B). Localisation of mantle flow occurred beneath southwest Queensland 56 57 804 because of edge driven convection lead to emplacement of the Warnie Volcanic Province 58 805 above the Nappamerri Trough. Despite our proposed model, we strongly believe that more 59 60 806 work needs to be conducted on the area before it can be concluded what the source of the 61 62 63 64 65 27

807 WVP is. In the Newer Volcanic Province of southeastern Australia, geochemistry, major and 1 2 808 trace element analysis, provided insights into the formation of a volcanic province through 3 809 edge driven convection (Demidjuk et al., 2007). More recent geochemical and geophysical 4 5 810 insights have furthered this discussion studies suggesting additional felsic asthenospheric 6 7 811 input (Sutherland et al., 2014), shear-driven upwelling (Oosting et al., 2016) and intermittent 8 9 812 volcanism through interaction of transient mechanisms with the passage of a mantle plume 10 11 813 (Rawlinson et al., 2017). As such, we would strongly recommend further studies to be 12 13 814 conducted on the geochemical signature of the basalts of the WVP. 14 15 815 Due to its low volume, small areal extent and predominantly basaltic nature, we do 16 17 816 not believe that the WVP was the source of the volcanically derived sediment that was 18 19 817 distributed throughout much of Australia during the Mesozoic (Boult et al., 1998; 20 21 818 MacDonald et al., 2013; Barham et al., 2016). However, our findings raise the possibility that 22 23 819 other, yet unidentified, intra-basinal volcanic sources may contribute to Mesozoic 24 820 volcanogenic sedimentation in eastern Australia. 25 26 27 821 Finally, it must be considered why the WVP has not been documented until now 28 29 822 despite the presence of igneous rocks being known for over three decades. By our 30 31 823 estimates, only 0.13% of the wells drilled in the Cooper Basin between 1959 and 2015 32 33 824 drilled the WVP (based on Hall et al., 2016’s estimate of the number of wells), with 35 years 34 825 of exploration since the first well that drilled the volcanics. This is despite the WVP 35 36 826 occupying ~6% of the geographic extent of the Cooper Basin. Largely, this is due to the lack 37 38 827 of data and attention given to the Nappamerri Trough region until recently. Acquisition of 39 40 828 the high-quality Winnie 3D seismic reflection survey facilitated confident delineation of the 41 42 829 WVP. This study also underlines the importance for collaboration between industry and 43 44 830 academia. Whilst igneous rocks have been described within industry reports and imaged 45 831 within data acquired, they have been overlooked within the literature. The obscurity of the 46 47 832 WVP in an area of such intense exploration points to the probability of other undiscovered 48 49 833 volcanic provinces globally. It is therefore an important analogue in the search for 50 51 834 undiscovered intraplate volcanism that may inform our understanding of the mantle 52 53 835 processes occurring beneath continental interiors. 54 55 836 56 57 58 59 60 61 62 63 64 65 28

837 9. Conclusions 1 2 838 We have integrated seismic, well, gravity and magnetic data and clarified the extent and 3 4 839 character of igneous rocks emplaced above the Nappamerri Trough of the Cooper Basin 5 6 840 within Eromanga Basin stratigraphy. Monogenetic volcanoes, igneous intrusions and altered

7 2 8 841 compound lava flows extending over ~7500 km are proposed to have been active between 9 10 842 ~180 – 160 Ma forming part of the proposed ‘Warnie Volcanic Province.’ Regionally, the 11 843 morphology and distribution of igneous rocks is controlled by basement structure. On a 12 13 844 continental scale, we interpret the Warnie Volcanic Province to be a product of intraplate 14 15 845 convective upwelling above the subducting Pacific slab. 16 17 18 846 19 20 847 10. Acknowledgements 21 22 848 We wish to thank Santos Ltd. for providing us with the Snowball 3D seismic survey. In 23 24 849 particular we wish to thank Jenni Clifford and Lance Holmes who provided helpful feedback 25 26 850 and 2D seismic lines covering the Lambda 1, Orientos 2 and Warnie East 1 wells. We also 27 851 wish to thank Beach Energy, in particular Rob Menpes, for the helpful discussions and 28 29 852 feedback on the manuscript in addition to helping us with the analysis of the magnetic data. 30 31 853 The work contained in this paper contains work conducted during a PhD study undertaken 32 33 854 as part of the Natural Environment Research Council (NERC) Centre for Doctoral Training 34 35 855 (CDT) in Oil & Gas [grant number NEM00578X/1] and is fully funded by NERC whose 36 37 856 support is gratefully acknowledged. Lastly, the two anonymous reviews of the manuscript 38 39 857 are thanked for their insightful and constructive comments that significantly improved the 40 858 work presented. 41 42 43 859 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 29

860 11. References 1 2 861 Aarnes, I., Planke, S., Trulsvik, M. and Svensen, H., 2015. Contact metamorphism and thermogenic 3 4 862 gas generation in the Vøring and Møre basins, offshore Norway, during the Paleocene–Eocene 5 863 thermal maximum. Journal of the Geological Society, 172, 588-598. 6 7 8 864 Alexander, E.M. and Hibburt, J.E., 1996, Petroleum Geology of South Australia, Volume 2: Eromanga 9 865 Basin. 10 11 12 866 Allen P., 1998. Kappa 1 Well Completion Report. Compiled for Santos Limited. 13 14 867 Archer, S.G., Bergman, S.C., Iliffe, J., Murphy, C.M. and Thornton, M., 2005. Palaeogene igneous 15 16 868 rocks reveal new insights into the geodynamic evolution and petroleum potential of the Rockall 17 18 869 Trough, NE Atlantic Margin. Basin Research, 17, 171-201. 19 20 870 Apak, S.N., Stuart, W.J., Lemon, N.M. and Wood, G., 1997. Structural evolution of the Permian- 21 22 871 Triassic Cooper Basin, Australia: relation to hydrocarbon trap styles. AAPG bulletin, 81, 533-555. 23 24 872 Ballmer, M.V., Van Hunen, J., Ito, G., Bianco, T.A. and Tackley, P.J., 2009. Intraplate volcanism with 25 26 873 complex age‐distance patterns: A case for small‐scale sublithospheric convection. Geochemistry, 27 874 Geophysics, Geosystems, 10. 28 29 875 Barham, M., Kirkland, C.L., Reynolds, S., O’Leary, M.J., Evans, N.J., Allen, H., Haines, P.W., Hocking, 30 31 876 R.M., McDonald, B.J., Belousova, E. and Goodall, J., 2016. The answers are blowin’in the wind: Ultra- 32 33 877 distal ashfall zircons, indicators of Cretaceous super-eruptions in eastern Gondwana. Geology, 44, 34 878 643-646. 35 36 37 879 Bell & Butcher, 2002. On the emplacement of sill complexes: evidence from the Faroe-Shetland 38 39 880 Basin. Geological Society, London, Special Publications(2002),197:307 40 41 881 Black L.p. 1998. SHRIMP zircon UIPb isotopic age dating of samples from the Dubbo 1:250000 Sheet 42 43 882 area, batch 2. Geological Survey of New South Wales, File GS1998/127 (unpublished). 44 45 883 Boothby, P.G., 1986. Warnie East 1 Well Completion Report. Compiled for Delhi Petroleum Pty 46 47 884 Ltd. 48 49 885 Boult, P.J., Ryan, M.J., Michaelsen, B.H., McKirdy, D.M., Tingate, P.R., Lanzilli, E. and Kagya, M.L., 50 51 886 1997. The Birkhead-Hutton (!) Petroleum System of the Gidgealpa Area, Eromanga Basin, Australia. 52 53 887 Boult, P.J., Lanzilli, E., Michaelsen, B.H., McKirdy, D.M. and Ryan, M.J., 1998. A new model for the 54 55 888 Hutton/Birkhead reservoir/seal couplet and the associated Birkhead-Hutton (!) petroleum 56 57 889 system. The APPEA Journal, 38, 724-744. 58 59 60 61 62 63 64 65 30

890 Bromfield, K.E., Burrett, C.F., Leslie, R.A. & Meffre, S., 2007. Jurassic volcani-clastic basaltic andesite - 1 891 dolerite sequence in Tasmania: new age constraints for fossil plants from Lune River. Australian 2 3 892 Journal of Earth Sciences, 54, 965-974. 4 5 6 893 Bryan, S.E., Constantine, A.E., Stephens, C.J., Ewart, A., Schön, R.W. and Parianos, J., 1997. Early 7 894 Cretaceous volcano-sedimentary successions along the eastern Australian continental margin: 8 9 895 Implications for the break-up of eastern Gondwana. Earth and Planetary Science Letters, 153, 85-102 10 11 896 Bucknill, M., 1990. Orientos 2 Well Completion Report. Compiled for Delhi Petroleum Pty Limited. 12 13 14 897 Burger, D. and Senior, B.R., 1979. A revision of the sedimentary and palynological history of the 15 898 northeastern Eromanga Basin, Queensland. Journal of the Geological Society of Australia, 26, 121-133. 16 17 18 899 Compston, W., McDougall, I. and Heier, K.S., 1968. Geochemical comparison of the mesozoic 19 900 basaltic rocks of Antarctica, South Africa, South America and Tasmania. Geochimica et Cosmochimica 20 21 901 Acta, 32, 129-149. 22 23 24 902 Courtillot, V., Davaille, A., Besse, J. and Stock, J., 2003. Three distinct types of hotspots in the Earth’s 25 903 mantle. Earth and Planetary Science Letters, 205, 295-308. 26 27 904 Davies, D.R. and Rawlinson, N., 2014, On the origin of recent intraplate volcanism in 28 29 905 Australia, Geology, 42, 1031-1034. 30 31 906 Demidjuk, Z., Turner, S., Sandiford, M., George, R., Foden, J. and Etheridge, M., 2007, U-series 32 33 907 isotope and geodynamic constraints on mantle melting processes beneath the Newer Volcanic 34 35 908 Province in South Australia, Earth and Planetary Science Letters, 261, 517-533. 36 37 909 Draper, J.J. ed., 2002. Geology of the Cooper and Eromanga Basins, Queensland. Department of Natural 38 39 910 Resources and Mines 40 41 911 Dulhunty, J.A. 1976. Potassium-argon ages of igneous rocks in the Wollar-Rylstone region, New 42 43 912 South Wales. Royal Society of New South Wales, Journal and Proceedings 109, 35-39. 44 45 913 Elburg, M.A. & Soesoo, A., 1999. Jurassic alkali-rich volcanism in Victoria (Australia): lithospheric 46 47 914 versus asthenospheric source. Journal of African Earth Sciences, 29, 269-280. 48 49 915 Elliot, D.H. and Fleming, T.H., 2004. Occurrence and dispersal of magmas in the Jurassic Ferrar large 50 51 916 igneous province, Antarctica. Gondwana Research, 7, 223-237. 52 53 Embleton B.J.J., Schmidt P.w., Hamilton L.H. & Riley G.H. 1985. Dating volcanism in the Sydney Basin; 54 917 55 918 evidence from K-Ar ages and palaeomagnetism. Geological Society of Australia, Journal 23, 243-248. 56 57 58 919 Exon, N.F. and Burger, D., 1981. Sedimentary cycles in the Surat Basin and global changes of sea 59 920 level. Bureau of Mineral Resources Journal of Australian Geology and Geophysics, 6, 153-159. 60 61 62 63 64 65 31

921 Fishwick, S., Heintz, M., Kennett, B.L.N., Reading, A.M. and Yoshizawa, K., 2008. Steps in lithospheric 1 922 thickness within eastern Australia, evidence from surface wave tomography. Tectonics, 27. 2 3 4 923 Gallagher, K. and Lambeck, K., 1989, Subsidence, sedimentation and sea‐level changes in the 5 6 924 Eromanga Basin, Australia, Basin Research, 2, 115-131. 7 8 925 D.I. Gravestock, J.E. Hibburt, J.F. Drexel (Eds.), Petroleum Geology of South Australia, Volume 4: 9 10 926 Cooper Basin, Department of Primary Industries and Resources (1998), 1-6 11 12 927 Greenstreet, C. 2015. From play to production: the Cooper unconventional story — 20 years in 13 14 928 the making. APPEA 2015 extended abstract. 15 16 929 Griffiths, J.R., 1975. New Zealand and the Southwest Pacific margin of Gondwanaland. In: K.S.W. 17 18 930 Campbell (Editor), Gondwana Geology. A.N.U. Press, Canberra, 619- 637. 19 20 931 Grove, C., Jerram, D.A., Gluyas, J.G. and Brown, R.J., 2017. Sandstone diagenesis in sediment–lava 21 22 932 sequences: exceptional examples of volcanically driven diagenetic compartmentalization in Dune 23 24 933 Valley, Huab Outliers, NW Namibia. Journal of Sedimentary Research, 87, 1314-1335. 25 26 934 Gurba, L.W. and Weber, C.R., 2001, Effects of igneous intrusions on coalbed methane potential, 27 28 935 Gunnedah Basin, Australia, International Journal of Coal Geology, 46, 113-131. 29 30 936 Hall, L.S., Hill, A.J., Troup, A., Korsch, R.J., Radke, B.M., Nicoll, R.S., Palu, T., Wang, L. and Stacey, A., 31 32 937 2016, Cooper Basin Architecture and Lithofacies, Geoscience Australia. 33 34 938 Hall, L.S, Palu, T.J., Murray, A.P., Boreham, C.J., Edwards, D.S., Hill, A.J., Troup, A., 2018. 35 36 939 Hydrocarbon Prospectivity of the Cooper Basin, Australia. AAPG Bulletin. 37 38 940 Hardman, J.P., Schofield, N., Jolley, D.W., Holford, S.P., Hartley, A.J., Morse, S., Underhill, J.R., 39 40 941 Watson, D.A. and Zimmer, E.H., 2018. Prolonged dynamic support from the Icelandic plume of the 41 42 942 NE Atlantic margin. Journal of the Geological Society, 175, 396-410. 43 44 943 Hardman, J., Schofield, N., Jolley, D., Hartley, A., Holford, S. and Watson, D., 2019. Controls on the 45 46 944 distribution of volcanism and intra-basaltic sediments in the Cambo–Rosebank region, West of 47 945 Shetland. Petroleum Geoscience, 25, 71-89. 48 49 50 946 Hillis, R.R., Morton, J.G.G., Warner, D.S. and Penney, R.K., 2001. Deep basin gas: A new exploration 51 947 paradigm in the Nappamerri Trough, Cooper Basin, South Australia. The APPEA Journal, 41, 185-200. 52 53 54 948 Isern, A.R., Anselmetti, F.S. and Blum, P., 2002. Constraining Miocene sea level change from 55 56 949 carbonate platform evolution, Marion Plateau, northeast Australia, Sites 1192–1199. In Proceedings of 57 950 the Ocean Drilling Program. Initial Reports, 194, 88. 58 59 60 61 62 63 64 65 32

951 Ivanov, A.V., Meffre, S., Thompson, J., Corfu, F., Kamenetsky, V. S., Kamenetsky, M.B. & Dementrova, 1 952 E. I., 2017. Timing and genesis of the Karoo-Ferrer large igneous province: New high precision U-Pb 2 3 953 data for Tasmania confirm short duration of the major magmatic pulse. Chemical Geology, 455, 32- 4 5 954 43. 6 7 955 Jerram, D.A. & Widdowson, M. 2005. The anatomy of Continental Flood Basalt Provinces: geological 8 9 956 constraints on the processes and products of flood volcanism. Lithos, 79, 385-405. 10 11 957 Johnstone, M.H., Lowry, D.C. and Quilty, P.G., 1973. The geology of South-western Australia - a 12 13 958 review. J. Proc. R. Sot. West. Aus., 56: 5-15. 14 15 959 Kapel, A., 1966. The Cooper's Creek Basin. The APPEA Journal, 6, 71-75. 16 17 18 960 Kelley, S. (2002) K‐Ar and Ar‐Ar Dating, in noble gases in geochemistry and cosmochemistry. 19 961 In: Reviews in Mineralogy and Geochemistry, 47 (Ed. by D. Porcelli, C.J. Ballentine & R. Wieler), 785– 20 21 962 818, Mineral Society America, Washington, DC. 22 23 963 Kennett, B., Salmon, M., Saygin, E. and AusMoho Working Group., AusMoho: the variation of Moho 24 25 964 depth in Australia, Geophysical Journal International, 187, 946-958, 2011, doi:10.1111/j.1365- 26 27 965 246X.2011.05194.x 28 29 966 Khair, H.A., Cooke, D. and Hand, M., 2013. The effect of present day in situ stresses and paleo- 30 31 967 stresses on locating sweet spots in unconventional reservoirs, a case study from Moomba-Big Lake 32 33 968 fields, Cooper Basin, South Australia. Journal of Petroleum Exploration and Production Technology, 3(4), 34 969 pp.207-221. 35 36 37 970 Khair, H.A., Cooke, D. and Hand, M., 2015. Paleo stress contribution to fault and natural fracture 38 971 distribution in the Cooper Basin. Journal of Structural Geology, 79, pp.31-41. 39 40 41 972 Kuang, K.S., 1985. History and style of Cooper? Eromanga Basin structures. Exploration 42 973 Geophysics, 16(3), pp.245-248. 43 44 45 974 Kulikowski, D., Amrouch, K., Al Barwani, K.H.M., Liu, W. and Cooke, D., 2015, September. Insights 46 into the Tectonic Stress History and Regional 4-D Natural Fracture Distribution in the Australian 47 975 48 976 Cooper Basin Using Etchecopar’s Calcite Twin Stress Inversion Techbique. In International Conference 49 50 977 & Exhibition. 51 52 978 Kulikowski, D. and Amrouch, K., 2017. Combining geophysical data and calcite twin stress inversion 53 54 979 to refine the tectonic history of subsurface and offshore provinces: A case study on the 55 56 980 Cooper‐Eromanga Basin, Australia. Tectonics, 36(3), pp.515-541. 57 58 59 60 61 62 63 64 65 33

981 Kulikowski, D., Amrouch, K., Cooke, D. and Gray, M.E., 2018, Basement structural architecture and 1 982 hydrocarbon conduit potential of polygonal faults in the Cooper‐Eromanga Basin, 2 3 983 Australia, Geophysical Prospecting, v. 66, p. 366-396. 4 5 6 984 Lanzilli, E., 1999. The Birkhead Formation: reservoir characterisation of the Gidgealpa south dome and 7 985 sequence stratigraphy of the Eromanga Basin, Australia (Doctoral dissertation, University of South 8 9 986 Australia). 10 11 987 Liu, P., Mao, J., Cheng, Y., Yao, W., Wang, X. and Hao, D., 2017. An Early Cretaceous W-Sn deposit 12 13 988 and its implications in southeast coastal metallogenic belt: Constraints from U-Pb, Re-Os, Ar-Ar 14 989 geochronology at the Feie'shan W-Sn deposit, SE China. Ore Geology Reviews, 81, pp.112-122. 15 16 17 990 Lowe-Young, B.S., Mackie, S.I. and Heath, R.S., 1997. The Cooper-Eromanga petroleum system, 18 991 Australia: Investigation of essential elements and processes. 19 20 992 MacDonald, J.D., Holford, S.P., Green, P.F., Duddy, I.R., King, R.C. and Backé, G., 2013. Detrital 21 22 993 zircon data reveal the origin of Australia’s largest delta system. Journal of the Geological 23 24 994 Society, 170(1), pp.3-6. 25 26 995 Mackie, S., 2015, September. History of petroleum exploration and development in the Cooper and 27 28 996 Eromanga basins. In AAPG/SEG International Conference & Exhibition, Melbourne, Australia. Search and 29 Discovery Article #10814 30 997 31 32 998 Magee, C., Jackson, C.L. and Schofield, N., 2014. Diachronous sub‐volcanic intrusion along 33 34 999 deep‐water margins: Insights from the Irish Rockall Basin. Basin Research, 26(1), pp.85-105. 35 36 1000 Mathur, S.P., 1983, Deep crustal reflection results from the central Eromanga Basin, 37 38 1001 Australia, Tectonophysics, v. 100, pp. 163-173. 39 40 1002 McDougall, I. & Wellman, P. 1976. Potassium argon ages for some Australian Mesozoic igneous 41 42 1003 rocks. Journal of the Geological Society of Australia, 23, 1-9. 43 44 1004 McLean, C.E., Schofield, N., Brown, D.J., Jolley, D.W. and Reid, A., 2017. 3D seismic imaging of the 45 46 1005 shallow plumbing system beneath the Ben Nevis Monogenetic Volcanic Field: Faroe–Shetland 47 48 1006 Basin. Journal of the Geological Society, 174(3), pp.468-485 49 50 1007 Meeuws, F.J., Holford, S.P., Foden, J.D. and Schofield, N., 2016. Distribution, chronology and causes 51 52 1008 of Cretaceous–Cenozoic magmatism along the magma-poor rifted southern Australian margin: Links 53 1009 between mantle melting and basin formation. Marine and Petroleum Geology, 73, pp.271-298. 54 55 56 1010 Meixner, T.J., Gunn, P.J., Boucher, R.K., Yeates, T.N., Richardson, L.M. and Frears, R.A., 2000. The 57 1011 nature of the basement to the Cooper Basin region, South Australia. Exploration Geophysics, 31(2), 58 59 1012 pp.24-32. 60 61 62 63 64 65 34

1013 Middleton, A.W., Uysal, I.T., Bryan, S.E., Hall, C.M. and Golding, S.D., 2014. Integrating 40Ar–39Ar, 1 1014 87Rb–87Sr and 147Sm–143Nd geochronology of authigenic illite to evaluate tectonic reactivation in 2 3 1015 an intraplate setting, central Australia. Geochimica et Cosmochimica Acta, 134, pp.155-174. 4 5 6 1016 Middleton, A.W., Uysal, I.T. and Golding, S.D., 2015. Chemical and mineralogical characterisation of 7 1017 illite–smectite: Implications for episodic tectonism and associated fluid flow, central 8 9 1018 Australia. Geochimica et Cosmochimica Acta, 148, pp.284-303. 10 11 1019 Millett, J.M., Hole, M.J., Jolley, D.W., Schofield, N. and Campbell, E., 2016. Frontier exploration and 12 13 1020 the North Atlantic Igneous Province: new insights from a 2.6 km offshore volcanic sequence in the 14 15 1021 NE Faroe–Shetland Basin. Journal of the Geological Society, 173(2), pp.320-336. 16 17 1022 Milnes, A.R., Cooper, B.J. and Cooper, J.A., 1982. The Jurassic Wisanger Basalt of Kangaroo Island, 18 19 1023 South Australia. Transactions of the Royal Society of South Australia, 106, pp.1-13. 20 21 1024 Murray, C.G., 1994. Basement cores from the Tasman fold belt system beneath the Great Artesian Basin in 22 23 1025 Queensland. Department of Minerals and Energy, Queensland. 24 25 1026 Nadin, P.A., Kusznir, N.J. and Cheadle, M.J., 1997, Early Tertiary plume uplift of the North Sea and 26 27 1027 Faeroe-Shetland basins, Earth and Planetary Science Letters, v. 148, p. 109-127. 28 29 1028 Nelson, C.E., Jerram, D.A. and Hobbs, R.W., 2009, Flood basalt facies from borehole data: 30 31 1029 implications for prospectivity and volcanology in volcanic rifted margins, Petroleum Geoscience, v. 15, 32 33 1030 p. 313-324. 34 35 1031 Németh, K., 2010. Monogenetic volcanic fields: Origin, sedimentary record, and relationship with 36 37 1032 polygenetic volcanism. What is a Volcano?, 470, p.43. 38 39 1033 Németh, K. and Kereszturi, G., 2015. Monogenetic volcanism: personal views and 40 41 1034 discussion. International Journal of Earth Sciences, 104(8), pp.2131-2146. 42 43 1035 Oostingh, K.F., Jourdan, F., Merle, R. & Chiradia, M., 2016. Spatio-temporal geochemical evolution of 44 45 1036 the SE Australian upper mantle deciphered from the Sr, Nd and Pb isotope compositions of 46 47 1037 Cenozoic intraplate volcanic rocks. Journal of Petrology, 57, 1509 - 1530. 48 49 1038 Pande, K., Cucciniello, C., Sheth, H., Vijayan, A., Sharma, K.K., Purohit, R., Jagadeesan, K.C. and 50 51 1039 Shinde, S., 2017. Polychronous (Early Cretaceous to Palaeogene) emplacement of the Mundwara 52 1040 alkaline complex, Rajasthan, India: 40 Ar/39 Ar geochronology, petrochemistry and 53 54 1041 geodynamics. International Journal of Earth Sciences, 106(5), pp.1487-1504. 55 56 1042 Paton, I.M., 1986, The Birkhead Formation-a Jurassic petroleum reservoir, in D.I. Gravestock, P.S. 57 58 1043 Moore, and G.M. Pitt, (eds.), Contributions to the Geology and Hydrocarbon Potential of the 59 1044 Eromanga Basin: Geological Society of Australia Special Publication No. 12, p. 195-201. 60 61 62 63 64 65 35

1045 Pells, P.J.N., 1985. Engineering geology of the Sydney Region, 407 pp. Routledge, London. 1 2 1046 Pitkin, M.C., Wadham, T.H., McGowen, J.M. and Thom, W.W., 2012, January. Taking the first steps: 3 4 1047 Stimulating the Nappamerri Trough resource play. In SPE Asia Pacific Oil and Gas Conference and 5 6 1048 Exhibition. Society of Petroleum Engineers. 7 8 1049 Planke, S., Symonds, P.A., Alvestad, E. and Skogseid, J., 2000. Seismic volcanostratigraphy of 9 10 1050 large‐volume basaltic extrusive complexes on rifted margins. Journal of Geophysical Research: Solid 11 1051 Earth, 105(B8), pp.19335-19351. 12 13 14 1052 Planke, S., Rasmussen, T., Rey, S.S. and Myklebust, R., 2005, January. Seismic characteristics and 15 1053 distribution of volcanic intrusions and hydrothermal vent complexes in the Vøring and Møre basins. 16 17 1054 In Geological Society, London, Petroleum Geology Conference series (Vol. 6, No. 1, pp. 833-844). 18 19 1055 Geological Society of London. 20 21 1056 Planke, S., Millett, J.M., Maharjan, D., Jerram, D.A., Abdelmalak, M.M., Groth, A., Hoffmann, J., 22 23 1057 Berndt, C. and Myklebust, R., 2017. Igneous seismic geomorphology of buried lava fields and coastal 24 25 1058 escarpments on the Vøring volcanic rifted margin. Interpretation, 5(3), pp.SK161-SK177. 26 27 1059 Pratt, W., 1998. Gunnedah Coalfield: notes to accompany the Gunnedah Coalfield regional geology 28 29 1060 (north and south maps). Report GS1998/505. New South Wales Department of Mineral Resources. 30 1061 Geological Survey of New South Wales, Sydney, 113 pp. 31 32 33 1062 Rawlinson, N., Davies, D.R. & Pila, S., 2017. The mechanisms underpinning Cenozoic intraplate 34 1063 volcanism in eastern Australia: insights from seismic tomography and geodynamic modelling. 35 36 1064 Geophysical Research Letters, 44, doi: 10.1002/2017GL074911. 37 38 Reid, A.J., Korsch, R.J., Hou, B. and Black, L.P., 2009. Sources of sediment in the Eocene Garford 39 1065 40 1066 paleovalley, South Australia, from detrital-zircon geochronology. Australian Journal of Earth 41 42 1067 Sciences, 56(S1), pp.S125-S137. 43 44 1068 Renaut, R.W., Jones, B., Tiercelin, J.J. and Tarits, C., 2002. Sublacustrine precipitation of 45 46 1069 hydrothermal silica in rift lakes: evidence from Lake Baringo, central Kenya Rift Valley. Sedimentary 47 48 1070 Geology, 148(1-2), pp.235-257. 49 50 1071 Reynolds, P., Holford, S., Schofield, N. and Ross, A., 2017. 3‐D Seismic Imaging of Ancient Submarine 51 52 1072 Lava Flows: An Example From the Southern Australian Margin. Geochemistry, Geophysics, Geosystems. 53 54 1073 Richards, M.A., Duncan, R.A. and Courtillot, V.E., 1989. Flood basalts and hot-spot tracks: plume 55 56 1074 heads and tails. Science, 246(4926), pp.103-107. 57 58 1075 Rider, M. and Kennedy, M., 2011. The Geological Interpretation of Well Logs. published by Rider- 59 60 1076 French Consulting Ltd. 61 62 63 64 65 36

1077 Russell, M. and Gurnis, M., 1994. The planform of epeirogeny: vertical motions of Australia during 1 1078 the Cretaceous. Basin Research, 6(2‐3), pp.63-76. 2 3 4 1079 "SA Department for Manufacturing, Innovation, Trade, Resources and Energy" (2003) National 5 6 1080 Geoscience Mapping Accord (NGMA) Cooper Eromanga Basins Project - Cooper Formation 7 1081 Depths. Bioregional Assessment Source Dataset. Viewed 27 November 8 9 1082 2017, http://www.energymining.sa.gov.au/petroleum/data_and_publications/seismic/cooper_and_e 10 11 1083 romanga_basin_mapping_products 12 13 1084 Schofield, N. and Jolley, D.W., 2013. Development of intra-basaltic lava-field drainage systems within 14 1085 the Faroe–Shetland Basin. Petroleum Geoscience, 19(3), pp.273-288. 15 16 17 1086 Schofield, N., Holford, S., Millett, J., Brown, D., Jolley, D., Passey, S.R., Muirhead, D., Grove, C., 18 19 1087 Magee, C., Murray, J. and Hole, M., 2017. Regional magma plumbing and emplacement mechanisms of 20 1088 the Faroe‐Shetland Sill Complex: implications for magma transport and petroleum systems within 21 22 1089 sedimentary basins. Basin Research, 29(1), pp.41-63. 23 24 1090 Scott, M.P., Stephens, T., Durant, R., McGowen, J., Thom, W. and Woodroof, R., 2013, November. 25 26 1091 Investigating hydraulic fracturing in tight gas sand and shale gas reservoirs in the Cooper Basin. In SPE 27 28 1092 Unconventional Resources Conference and Exhibition-Asia Pacific. Society of Petroleum Engineers. 29 30 1093 Segawa, J. and Oshima, S., 1975. Buried Mesozoic volcanic–plutonic fronts of the north-western 31 32 1094 Pacific island arcs and their tectonic implications. Nature, 256(5512), p.15. 33 34 1095 Short, D.A., 1984. Lambda No.1 Well Completion Report. Compiled for Delhi Petroleum Pty. Ltd. 35 36 37 1096 Soesoo, A., Bons, P. & Elburg, M., 1999 Freestone dykes—an alkali-rich Jurassic dyke population in 38 1097 eastern Victoria. Australian Journal of Earth Sciences, 46 (1-2), 1—9. 39 40 41 1098 Smith, 1987. Vitrinite Reflectance/Maceral Analysis of the Warnie East 1 Well. 42 43 1099 Stewart, A.K., Massey, M., Padgett, P.L., Rimmer, S.M. and Hower, J.C., 2005. Influence of a basic 44 45 1100 intrusion on the vitrinite reflectance and chemistry of the Springfield (No. 5) coal, Harrisburg, 46 1101 Illinois. International Journal of Coal Geology, 63(1-2), pp.58-67. 47 48 49 1102 Stewart, A.J., Raymond, O.L., Totterdell, J.M., Zhang, W. & Gallagher, R. 2013. Australian Geological 50 Provinces, 2013.01 edition. scale 1:2 500 000. Geoscience Australia, Canberra, 51 1103 52 1104 http://www.ga.gov.au/metadata-gateway/metadata/record/83860 53 54 55 1105 Sun, X., 1997. Structural style of the Warburton Basin and control in the Cooper and Eromanga 56 1106 Basins, South Australia. Exploration Geophysics, 28(3), pp.333-339. 57 58 59 60 61 62 63 64 65 37

1107 Sutherland, F.L., 1978. Mesozoic-Cainozoic volcanism of Australia. Tectonophysics, 48(3-4), pp.413- 1 1108 427. 2 3 4 1109 Sutherland, F.L., Graham, I.T., Hollis, J.D., Meffre, S., Zwingmann, H., Jourdan, F. & Pogson R.E., 2014. 5 6 1110 Multiple felsic events within post-10 Ma volcanism, Southeast Australia: inputs in appraising proposed 7 1111 magmatic models. Australian Journal of Earth Sciences, 16, 241- 267. 8 9 10 1112 Tang, Y., Obayashi, M., Niu, F., Grand, S.P., Chen, Y.J., Kawakatsu, H., Tanaka, S., Ning, J. and Ni, J.F., 11 1113 2014. Changbaishan volcanism in northeast China linked to subduction-induced mantle 12 13 1114 upwelling. Nature Geoscience, 7(6), pp.470-475 14 15 1115 Tappert, R., Foden, J., Stachel, T., Muehlenbachs, K., Tappert, M. and Wills, K., 2009. Deep mantle 16 17 1116 diamonds from South Australia: A record of Pacific subduction at the Gondwanan 18 19 1117 margin. Geology, 37(1), pp.43-46. 20 21 1118 Tarling, D.H., 1966. The magnetic intensity and susceptibility distribution in some Cenozoic and 22 23 1119 Jurassic basalts. Geophysical Journal International, 11(4), pp.423-432. 24 25 1120 Thomson, K., and Schofield, N.. "Lithological and structural controls on the emplacement and 26 27 1121 morphology of sills in sedimentary basins." Geological Society, London, Special Publications 302.1 28 29 1122 (2008): 31-44. 30 31 1123 Tracey R, Bacchin M, & Wynne P., 2008, In preparation. AAGD07: A new absolute gravity datum 32 1124 for Australian gravity and new standards for the Australian National Gravity Database. 33 34 1125 Exploration Geophysics. 35 36 1126 Trude, J., Cartwright, J., Davies, R.J. and Smallwood, J., 2003, New technique for dating igneous 37 38 1127 sills, Geology, v. 31, p. 813-816. 39 40 1128 Tucker, R.T., Roberts, E.M., Henderson, R.A. and Kemp, A.I., 2016, Large igneous province or long- 41 42 1129 lived magmatic arc along the eastern margin of Australia during the Cretaceous? Insights from the 43 1130 sedimentary record, Geological Society of America Bulletin, v. 128, p. 1461-1480. 44 45 46 1131 Veevers, J.J. and Conaghan, P.J., 1984, Phanerozoic earth history of Australia, Oxford University Press, 47 48 1132 USA. 49 50 1133 Wainman, C.C., Mccabe, P.J., Crowley, J.L. and Nicoll, R.S., 2015, U–Pb zircon age of the Walloon 51 52 1134 Coal Measures in the Surat Basin, southeast Queensland: implications for paleogeography and basin 53 1135 subsidence, Australian Journal of Earth Sciences, v. 62, p. 807-816. 54 55 56 1136 Wainman, C.C., Reynolds, P., Hall, T., McCabe, P.J. and Holford, S.P., 2019. Nature and origin of tuff 57 1137 beds in Jurassic strata of the Surat Basin, Australia: Implications on the evolution of the eastern 58 59 1138 margin of Gondwana during the Mesozoic. Journal of Volcanology and Geothermal Research. 60 61 62 63 64 65 38

1139 Warren, A.Y.E., Barron, L.M., Meekin, N.S., Morgan, E.J., Raymond, O.L., Cameron, R.G. & 1 1140 Colquhoun, G.P., 1999. Mesozoic Igneous Rocks. In Meakin, N.S. & Morgan, E.J. (Compilers). Dubbo 2 3 1141 1:250 000 Geological Sheet SI/55-4, 2nd edition, Explanatory Notes, pp. 313—328. Geological 4 5 1142 Survey of New South Wales, Sydney. 6 Watson, D., Schofield, N., Jolley, D., Archer, S., Finlay, A.J., Mark, N., Hardman, J. and Watton, T., 7 1143 8 1144 2017. Stratigraphic overview of Palaeogene tuffs in the Faroe–Shetland Basin, NE Atlantic 9 10 1145 Margin. Journal of the Geological Society, 174(4), pp.627-645. 11 12 1146 Watts, K.J., 1987, The Hutton Sandstone-Birkhead Formation Transition, ATP 269P(1), The APEA 13 14 1147 Journal, Volume 27 Number 1, p 215 - 228. 15 16 1148 White, J.D. and Ross, P.S., 2011. Maar-diatreme volcanoes: a review. Journal of Volcanology and 17 18 1149 Geothermal Research, 201(1-4), pp.1-29. 19 20 1150 Yew, C.C. and Mills, A.A., 1989. The occurrence and search for Permian oil in the Cooper Basin, 21 22 1151 Australia. 23 24 1152 Zhou, Q., Liu, L. and Hu, J., 2018, Western US volcanism due to intruding oceanic mantle driven by 25 26 1153 ancient Farallon slabs, Nature Geoscience, v. 11, p. 70. 27 28 1154 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 39

1155 12. Tables 1 2 Seismic Survey Acquisition Acquisition Areal Coverage Data Type 3 4 Date Company 5 2 6 Winnie 2012 Drillsearch Energy 1050 km 3D 7 Ltd. And 8 9 WesternGeco 10 11 Snowball 2016 Santos Ltd. 1698 km2 3D 12 Gallus 2012 Beach Energy and 420 km 2D 13 14 Icon Energy 15 16 Madigan 1996 Santos Ltd. 584 km2 3D 17 18 1156 Table 1: List of the seismic surveys that were determined to contain igneous rocks and 19 1157 utilised within this study. 20 21 Location of Igneous Rocks Name Age Key Reference 22 23 Marion Platea n/a Jurassic Isern et al., 2002 24 25 Eastern Highlands and Sydney Basin n/a 235 - 46.9 Ma Pells, 1985 26 Gunnedah Basin Garawilla Basalts 195 - 141 Ma Gurba & Weber, 2001 27 28 New South Wales Dubbo Volcanics 236 - 170 Ma Warren et al., 1999 29 Eastern Victoria n/a 191 - 179 Ma Elburg & Soesoo, 1999 30 31 Tasmania n/a 183 - 182 Ma Ivanov et al., 2017 32 Kangaroo Island Wisanger Basalt 170 Ma Milnes et al., 1982 33 34 1158 Table 2: List of Cretaceous igneous rocks in Eastern Australia. Where possible, a name and 35 1159 age range has been given. Each location is discussed within the text. 36 37 1160 38 39 1161 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 40

1162 13. Figures 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 1163 54 55 1164 Figure 1. Location map of the Warnie Volcanic Province and the data available. A Top basement 56 57 1165 map adapted from the SA Department for Manufacturing, Innovation, Trade, Resources and Energy 58 59 1166 (2003). Key structures of the southern Cooper Basin highlighted. B Location map highlighting the 60 61 62 63 64 65 41

1167 location of the Warne Volcanic Province within the Cooper Basin. Top basement map superimposed 1 1168 with the location of 3D and 2D seismic surveys utilised in this study and the location of key 2 3 1169 exploration wells. C Location map of the wells drilled within the Warnie Volcanic Province that 4 5 1170 were analysed during this study. Wells that intersected igneous rocks are highlighted in red. The 6 locations of the Central Nappamaerri Fault and the Challum Fault, structures discussed in the text, 7 1171 8 1172 are noted. 9 10 11 1173 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 42

1174 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1175 39 40 1176 41 42 1177 Figure 2. Stratigraphic column for the stratigraphy discussed within the paper, based on the work 43 44 1178 of Alexander & Hibburt (1996), Hall et al. (2016) & Reid et al. (2009). Seismic facies for each section 45 1179 is taken from the Winnie 3D survey of the eastern Nappamerri Trough. Rough stratigraphic location 46 47 1180 of the WVP highlighted. 48 49 1181 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 43

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 1182 30 31 1183 Figure 3. Seismic line from the Winnie 3D survey of the Nappamerri Trough highlighting the broad 32 33 1184 stratigraphy of the study area. A Uninterpreted line. B Interpreted line. Note the stacked nature of 34 35 1185 the Eromanga, Cooper and Warburton Basins and the stratigraphic location of the Warne Volcanic 36 1186 Province. 37 38 39 1187 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 1188 28 29 1189 Figure 4. Examples of different monogenetic vents. A Cross section through a cinder cone, adapted 30 31 1190 from Németh & Kereszturi (2015). B Seismic line across a cinder cone and lava flow, taken from the 32 1191 Winnie 3D survey, highlighting the general morphology, seismic response. Note the characteristic 33 34 1192 eye shape within the centre of the vent. C Plan view spectral decomposition of the cinder cone in B 35 36 1193 highlighting how different it is from the surrounding sediments. D Oblique view of the same cinder 37 38 1194 cone shown in TWT. E Cross section through a Maar-diatreme, adapted from Németh & Kereszturi 39 1195 (2015). F Seismic line across a proposed Maar-diatreme from the Winnie 3D survey. Note how it 40 41 1196 cuts down into the subsurface with an internally chaotic seismic response. G Plan view spectral 42 43 1197 decomposition of the Maar-diatreme within the Winnie 3D survey. H Oblique, TWT view of the 44 1198 proposed Maar-diatreme. 45 46 47 1199 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1200 26 27 1201 Figure 5. Well data for the volcanics from the Lambda-1 well. A Composite log of the volcanic 28 29 1202 succession in the Lambda-1 well. Includes an image of the core taken from the base of the volcanic 30 31 1203 successon. B Vitrinite reflectance curve for the succession above the volcanics taken from Boothby 32 1204 (1986). Little thermal effect is observed. C Velocity histogram of the Lambda-1 volcanics 33 34 1205 superimposed on Nelson et al.’s (2009) velocity histogram of Tabular basalt. 35 36 1206 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 46

1207 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1208 18 19 1209 Figure 6. West to east seismic line running across the Lambda 1 well. The extent of the Lambda 1 20 1210 vent has been inferred base on the thickness of volcanics within the well. 21 22 23 1211 24 25 1212 26 27 28 1213 29 30 1214 31 32 1215 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 47

1216 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 1217 38 39 1218 Figure 7. Spectral decomposition of a horizon mapped across the volcanics of the Winnie 3D 40 41 1219 survey. A Uninterpreted spectral decomposition. B Interpreted spectral decomposition highlight 42 1220 extrusive volcanics and the location of igneous intrusions. Note the increased number of intrusions 43 44 1221 towards the north east of the Winnie 3D survey. 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 48

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 1222 38 39 1223 Figure 8. 3D Seismic across two monogenetic vents that extend into surface flows, from the 40 1224 Winnie 3D survey. A Uninterpreted line across the vents. B Interpreted line across the vents. Note 41 42 1225 the vertical zone of disrupted seismic directly below the vents, indicative of underlying plumbing 43 44 1226 system that fed the flows. C Spectral decomposition of a horizon mapped across the vents, 45 1227 highlighting their 3D morphology. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 1228 33 34 1229 Figure 9. Seismic images of the Gallus 2D survey. A Isochron thickness map of the volcanics 35 36 1230 identified throughout the Gallus 2D survey. B Uninterpreted seismic line from the Gallus 2D survey. 37 38 1231 C Interpreted seismic line from the Gallus 2D survey. An increase in the volume of volcanics 39 1232 towards the east of the survey is apparent. 40 41 42 1233 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 50

1234 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1235 39 40 1236 Figure 10. Well data for intrusive volcanic rocks within the Warnie East 1 well. A Composite log 41 1237 across the intrusion in the Warnie East well. B Vitrinite reflectance profile across the intrusion in 42 43 1238 the Warnie East well taken from Boothby (1986). Thermal effect both above and below the well is 44 45 1239 noted. 46 47 1240 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 51

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1241 19 20 1242 Figure 11. 2D seismic line running from west to east across the Warnie East 1 well. The exact 21 22 1243 location of the igneous rocks is unclear on the line, however, a shallow saucer-shaped reflection with 23 1244 the Toolachee Fm. intersects Warnie East 1 at the depth igneous rocks are found. The lack of clearly 24 25 1245 imaged igneous rocks could point to more unimaged intrusive igneous rocks within the Cooper 26 27 1246 Basin succession. 28 29 1247 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 52

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1248 31 32 1249 Figure 12. Seismic across the large intrusion in the Winnie 3D survey. A Uninterpreted seismic 33 34 1250 line. B Interpreted seismic line, illustrating the uplift of the overburden and the numerous vents and 35 overlying volcanics associated with the intrusion. C Spectral decomposition of the intrusion, highlight 36 1251 37 1252 the pockmarks of vents that pass through the intrusion and morphological characteristics associated 38 39 1253 with the intrusion. 40 41 1254 42 43 44 1255 45 46 1256 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 53

1257 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1258 39 40 1259 Figure 13. Well data for the Kappa-1 well. A Composite log for the Kappa-1 well volcanics. B 41 42 1260 Velocity histogram for the Kappa-1 well volcanics, superimposed on top of Nelson et al.’s (2009) 43 44 1261 velocity histogram for compound-braided volcanics. 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 54

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1262 19 20 1263 Figure 14. Position of the Kappa-1 well in relation to the Snowball 3D survey. A Pseudo 21 1264 TWT/depth plot that was created using the velocity data synthesised for the wells drilled 22 23 1265 within the central Nappamerri Trough (namely Halifax, Etty, Anakin, Padme, Charal). This 24 25 1266 TWT to depth relationship was used to convert the Kappa-1 well data from depth to time in order 26 27 1267 to display it adjacent to the Snowball 3D survey. B Line across the Snowball 3D survey with the 28 position of formation tops based on the Kappa-1 well displayed. C Gamma ray curve from the 29 1268 30 1269 Kappa-1 well with formation tops marked. 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 55

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

34 1270 35 36 1271 Figure 15. Seismic across volcanics within the Snowball 3D survey. A Uninterpreted seismic line. B 37 1272 Interpreted seismic line. Thick package of mixed volcanics & sediments based off of the Kappa-1 well 38 39 1273 volcanics. C Spectral decomposition of the top mixed volcanics & sediment horizon. Location of 40 41 1274 vents noted by bright white colour with interpreted flow fields based on the cohesive dark colours 42 1275 extending away from the vents. 43 44 45 1276 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 56

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 1277 42 43 44 1278 Figure 16. Regional geophysical surveys adopted from the Queensland Government’s data 45 1279 repository. A Uninterpreted gravity anomaly with the location of the Nappamerri Trough Gravity 46 47 1280 anomaly highlighted. B Uninterpreted 1VD magnetic data. C Inset of B showing a ~6 x 5 km gravity 48 49 1281 magnetic anomaly with the interpreted extent of igneous rocks identified using seismic data 50 1282 superimposed on top of the anomaly. D Uninterpreted image of the gravity data set to 50% 51 52 1283 transparency overlain on top of the 1VD magnetic data. E Interpreted image of the combined 53 54 1284 gravity/1VD magnetic data. The extent of the Warnie Volcanic Province interpreted using well and 55 1285 seismic data within this study is indicated. Areas with circular magnetic anomalies and high gravity 56 57 1286 signatures not identified using well or seismic data are also highlighted. These areas could represent 58 59 1287 further igneous rocks within the SW Queensland. 60 61 1288 62 63 64 65 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 1289 33 34 1290 Figure 20: Regional map of the Warnie Volcanic Province. Depth to top basement map adapted 35 36 1291 from SA Department for Manufacturing, Innovation, Trade, Resources and Energy (2003). Location 37 38 1292 of extrusive volcanics and igneous intrusions based on seismic data. The igneous rocks, however, are 39 40 1293 thought to extend beyond the limit of seismic coverage towards the projected limit of the Warnie 41 1294 Volcanic Province. 42 43 44 1295 45 46 1296 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 58

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 1297 41 42 1298 Figure 17. The basement structure and it’s relation to vents within the Winnie 3D survey. A 43 44 1299 Spectral decomposition of the Top Toolachee horizon, highlighting the location of vents underlying 45 1300 the WVP. B Location of vents mapped using the Top Toolachee horizon superimposed on a TWT 46 47 1301 map of the top basement horizon. Many of the vents sit away from shallow basement reflections. 48 49 1302 Two vents are situated directly above the Central Nappamerri Fault. 50 51 1303 52 53 1304 54 55 56 1305 57 58 59 60 61 62 63 64 65 59

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1306 16 17 1307 Figure 18: Size and orientation of volcanics within the Winnie 3D and Madigan 3D surveys. A Size 18 19 1308 of vents, intrusions and volcanic flows. Note, the large Winnie 3D intrusion has not been included 20 1309 on this figure due to its sheer scale (dimensions of 8 km x 14 km) compared to the rest of the 21 22 1310 Warnie Volcanic Province. B Direction of elongation for the igneous rocks, highlighting that they are 23 24 1311 elongate in a SE-NW direction. 25 26 1312 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1313 21 22 1314 Figure 19: Mapping of faults within the Nappamerri trough. A Spectral decomposition of the Top 23 24 1315 Volcanics horizon from the Winnie 3D survey. B Interpretation of A with faults and the location of 25 1316 volcanics highlighted. C Spectral decomposition of the Top Toolachee horizon. D Interpretation of 26 27 1317 discontinuities within the Toolachee Horizon and the location of volcanics highlighted. 28 29 30 1318 31 32 1319 33 34 1320 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 61

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 1321 48 49 1322 Figure 21: A Palaeogeographic map of Australia in the middle Jurassic (Oxfordian, 160 Ma), 50 51 1323 superimposed with the location of middle to late Jurassic volcanics in eastern Australia, described in 52 1324 the text. B Oblique view of Australia, highlighting the subducting pacific slab and associated 53 54 1325 convective upwelling. Steps in lithospheric thickness have adapted from Fishwick et al., (2008). 55 56 1326 57 58 59 60 61 62 63 64 65 *Revised manuscript with changes marked Click here to view linked References

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1 The Warnie Volcanic Province: A Jurassic Volcanic ProvinceJurassic 1 2 2 Intraplate Volcanism in Central Australia 3 1 2 1 2 3 4 3 Jonathon P.A. Hardman , Simon P. Holford , Nick Schofield , Mark Bunch Daniel Gibbins 5 6 4 1Department of Geology and Petroleum Geology, University of Aberdeen, Aberdeen, AB24 3FX, UK 7 8 2 9 5 Australian School of Petroleum, University of Adelaide, Adelaide, SA 5005, Australia 10 11 6 3Vintage Energy, 58 King William Road, Goodwood SA 5034, Australia 12 13 14 7 15 16 8 Abstract 17 18 9 The Cooper and Eromanga Basins of South Australia and Queensland are the largest onshore hydrocarbon 19 20 10 producing region in Australia. Igneous rocks have been documented infrequently within end of well reports 21 11 over the past 34 years, with a late Triassic to Jurassic age determined from well data. However, the areal 22 23 12 extent and nature of these basaltic rocks were largely unclear. Here, we integrate seismic, well, gravity, and 24 13 magnetic data to clarify the extent and character of igneous rocks preserved within Eromanga Basin 25 26 14 stratigraphy overlying the Nappamerri Trough of the Cooper Basin. We recognise mafic monogenetic 27 15 volcanoes that extend into tabular basalt lava flows, igneous intrusions and, more locally, hydrothermally 28 29 16 altered compound lava flows. The volcanic province covers ~7500 km2 and is proposed to have been active 30 between ~180-160 Ma. We term this Jurassic volcanic province the Warnie Volcanic Province (WVP) after the 31 17 32 18 Warnie East 1 exploration well, drilled in 1985. The distribution of extrusive and intrusive igneous rocks is 33 34 19 primarily controlled by basement structure, with extrusive and intrusive igneous rocks elongate in a NW-SE 35 20 direction. Finally, we detail how the WVP fits into the record of Jurassic volcanism in eastern Australia. The 36 37 21 WVP is interpreted as a product of extension and intraplate convective upwelling above the subducting Pacific 38 22 Slab. The discovery of the WVP raises the possibility of other, yet unidentified, volcanic provinces worldwide. 39 40 41 23 Keywords 42 43 24 Intraplate; volcanism; monogenetic; Australia; Jurassic 44 45 25 1. Introduction 46 47 26 Igneous rocks are frequently recognised within sedimentary basins globally, within which 48 49 27 their chronostratigraphic record can provide insights into the tectonic evolution of a region 50 51 28 (Jerram & Widdowson, 2005). Although extensive reworked volcaniclastic deposits are 52 53 29 documented throughout Central Australia during the Mesozoic (Boult et al., 1998; Barham 54 55 30 et al., 2016; Wainman et al., 20198), synchronous volcanic activity is infrequently 56 57 31 documented within the sedimentary basins of Central Australia (Allen, 1998). The Cooper 58 32 and the overlying Eromanga Basin extend for 130,000 km2 and 1,000,000 km2 respectively 59 60 61 62 63 64 65 2

33 across central, north and eastern Australia. Together, they represent the largest 1 2 34 conventional onshore hydrocarbon-producing region in Australia (Hall et al., 2016). The first 3 35 gas discovery was made in 1963 and since then, over 1,400 producing wells have been 4 5 36 drilled, with 190 gas and 115 oil fields discovered throughout both basins (Fig. 1) (Mackie, 6 7 37 2015). The majority of discoveries within the Cooper Basin are situated within structural 8 9 38 traps on regional highs, however, a number of companies began to pursue unconventional 10 11 39 hydrocarbon plays within the basin during the late 2000s, resulting in an increase in activity 12 13 40 within the Nappamerri Trough (Hillis et al., 2001; Pitkin et al., 2012; Khair et al., 2013; Scott 14 15 41 et al., 2013; Hall et al., 2016). The Nappamerri Trough is the largest and deepest depocentre 16 42 within the Cooper Basin covering ~10,000 km2 and reaching present day depths of ~4.5 km 17 18 43 (Fig. 1A). The acquisition of new well and seismic data due to renewed exploration activity 19 20 44 has resulted in the increased recognition of igneous rocks in the Cooper and Eromanga 21 22 45 Basins. 23 24 46 Igneous rocks of suspected late Triassic-Jurassic age have been sporadically 25 26 47 encountered by drilling during the past 34 years (Short, 1984; Boothby, 1986; Bucknill, 1990; 27 28 48 Allen, 1998), though there has been no systematic study of the character, origin and 29 30 49 significance of these igneous rocks. Here, we combine extensive seismic, well and airborne 31 32 50 geophysical data to document the extent and character of Mesozoic igneous rocks 33 34 51 recognised within Eromanga Basin stratigraphy overlying the Nappamerri Trough of Cooper 35 2 36 52 Basin age. The Warnie Volcanic Province (WVP) is the suggested name for this >7,500 km 37 53 suite of igneous rocks (Fig. 1B). The province is named after the Warnie East 1 exploration 38 39 54 well, which was drilled in 1985 and encountered 65 m of basalt. We provide an in-depth 40 41 55 study of the regional implications of the WVP for the Cooper and Eromanga Basins. We find 42 43 56 that SE-NW striking intracratonic sag faulting controlled the morphology of igneous rocks 44 45 57 whilst the basin structure likely controlled the location of igneous rocks. 46 47 58 Finally, we discuss the origin of the WVP. Evidence for Triassic to mid-Cretaceous 48 49 59 volcanic activity is pervasive throughout the sedimentary basins of central Australia, 50 51 60 manifested by an influx of volcanic arc-derived sediment into the Eromanga Basin (Boult et 52 53 61 al., 1998), silicic tuffs in the Surat Basin (Wainman et al., 2015) and widespread volcanogenic 54 55 62 zircons throughout the Great Artesian Basin (Bryan et al., 1997). However, the source of 56 57 63 volcanic activity and, furthermore, the origin of intraplate volcanism can be contentious 58 64 (Conrad et al., 2011; Zhou et al., 2018). We consider the source of the WVP and the 59 60 65 tectonic implications for central Australia. We theorise that the WVP’s geodynamic origin is 61 62 63 64 65 3

66 ultimately linked to subduction at the eastern margin of Gondwana, through asthenospheric 1 2 67 shear ~1500 km from the oceanic trench, however, we also discuss other mechanisms that 3 68 can produce intraplate volcanism. Our discovery of a previously undescribed volcanic 4 5 69 province in an area that has undergone >50 years of extensive subsurface data collection 6 7 70 due to continued hydrocarbon exploration, raises the prospect of other undiscovered 8 9 71 intraplate volcanic provinces both in Australia and in other continental areas worldwide. 10 11 12 72 2. Geological Overview of the Cooper and Eromanga Basins 13 14 73 The geology of southwest Queensland and northeast South Australia, central Australia, is 15 16 74 defined by a series of intracratonic basins stacked on top of each other; the Warburton, 17 18 75 Cooper, Eromanga and Lake Eyre Basins (Fig. 2 & Fig. 3). 19 20 76 The Warburton Basin is a lower Palaeozoic sedimentary basin that hosted Silurian to 21 22 77 Carboniferous granite emplacement (Murray, 1986; Meixner et al., 2000; Boucher, 1997). 23 24 78 The Cooper Basin unconformably overlies the Warburton Basin. The Cooper Basin is a 25 26 79 northeast to southwest trending intracratonic structural depression that accommodated the 27 28 80 deposition of sedimentary rocks from the late Carboniferous to the Middle Triassic 29 81 (Gravestock et al., 1998). Several tectonic origins for the Cooper Basin have been suggested, 30 31 82 including a mildly compressional structural depression (Apak et al., 1997; Sun, 1997), a 32 33 83 depression created through wrenching (Kuang, 1985) and extension during post- 34 35 84 compression flexural relaxation (Kulikowski et al., 2015). Deposition throughout the early 36 37 85 Permian was dominated by highly sinuous fluvial systems situated on a major floodplain with 38 39 86 peat rich swamps and lakes (Khair et al., 2015). Later Triassic deposition took place in a 40 41 87 period of tectonic quiescence (Gravestock et al., 1998). 42 43 88 Deposition in the Cooper Basin was terminated by regional uplift, compressional folding and 44 45 89 erosion in the middle Triassic. The Cooper Basin is unconformably overlain by the 46 47 90 Eromanga Basin, which forms part of the Great Artesian Superbasin, a group of 48 49 91 interconnected basins that cover much of Queensland, South Australia and New South 50 92 Wales. The Eromanga Basin is an intracratonic sag basin whose subsidence has been 51 52 93 attributed to dynamic topography induced by subduction of the pacific plate below Australia 53 54 94 (Gallagher & Lambeck, 1989; Russell & Gurnis, 1994). 55 56 57 58 59 60 61 62 63 64 65 4

95 2.1 The Jurassic Succession of the Eromanga Basin 1 2 3 96 The Jurassic succession of the Eromanga Basin is of stratigraphic importance as it is where 4 5 97 the extrusive igneous rocks documented within this study are believed to be located. Much 6 98 of the Jurassic strata in the Eromanga Basin consists of predominantly quartzose fluviatile 7 8 99 sandstones with subordinate shales and some coals (Burger & Senior et al., 1979; Exon & 9 10 100 Burger, 1981; Draper 2002). Sediments in the Eromanga Basin can be divided into three 11 12 101 packages of decreasing age; lower non-marine, marine and upper non-marine. The focus of 13 14 102 this study is the lower non-marine package that was deposited between the early Jurassic 15 16 103 (~200 Ma) and the early Cretaceous (~155 Ma), within which the extrusive volcanics of the 17 18 104 WVP are recognised (Fig. 2). During this time, large sand-dominated, braided fluvial systems 19 105 drained into lowland lakes and swamps. Throughout deposition, it is believed that sediment 20 21 106 supply was a competing product of input from arc volcanism to the east, and sediment 22 23 107 sourced from stable cratonic regions to the south (Boult et al., 1997). In the next part of 24 25 108 this paper we briefly detail the Early to Late Jurassic stratigraphy in order to provide a 26 27 109 palaeogeographic framework for the study. The stratigraphic framework of the Jurassic 28 29 110 succession has been iterated on considerably in the last 20 years, evidenced by the 30 111 progression of Alexander & Hibburt’s stratigraphic ages (1996) to Reid et al.’s (2009), to 31 32 112 those listed on the Australian Stratigraphic Units Database. 33 34 35 113 2.1.1 Poolowanna Formation, Early Jurassic, ~200–178 Ma 36 37 38 114 In southwest Queensland, the Poolowanna Fm. sits unconformably on top of the Late 39 40 115 Triassic unconformity, which formed as a result of uplifting, tilting, and erosion of the 41 116 Cooper Basin at the end of the Early to Middle Triassic (Fig. 2). Lithologies consist of coal 42 43 117 and silt deposited in a highly sinuous fluvial setting with minor coal swamps (Hall et al., 44 45 118 2016). 46 47 48 119 2.1.2 Hutton Sandstone, Early to Middle Jurassic, ~178–166 Ma 49 50 51 120 The Hutton Sandstone is a high energy braided fluvial Jurassic sandstone that either sits 52 121 conformably on top of the Poolowanna Fm. or, where the Poolowanna is not present, 53 54 122 unconformably above Triassic sediments (Kapel, 1966; Watts, 1987). 55 56 57 58 59 60 61 62 63 64 65 5

123 2.1.3 Birkhead Formation, Middle to Upper Jurassic, ~ 166–160 Ma 1 2 124 The boundary between the Hutton and Birkhead formations is sharp to transitional across 3 4 125 the Eromanga Basin (Lanzilli, 1999) and is associated with a change in the depositional 5 6 126 setting from the high energy, braided fluvial setting of the Hutton Sandstone to a low 7 8 127 energy, fluvial-deltaic to lacustrine setting in the Birkhead Formation (Watts, 1987; Lanzilli, 9 10 128 1999). This decrease in depositional energy is also associated with a change in sediment 11 129 provenance from craton-derived sediment to lithic-rich, volcanogenic sediment from a 12 13 130 proposed volcanic arc situated to the east above the subducting Pacific plate (Lanzilli, 1999). 14 15 131 The diachronous influx of volcanogenic sediments can be traced across the Eromanga Basin 16 17 132 (Boult et al., 1997). There are several key features associated with the sediments shed from 18 19 133 the volcanic arc (Paton, 1986): 20 21 134  50% quartz with high amounts of potassium and plagioclase feldspar. Trace amounts 22 23 135 of tourmaline, pyroxene, mica and zircon are also present (Watts, 1987). 24 25 136  Common altering of the above lithics to kaolinite and chlorite or replacement of 26 27 137 carbonate cements such as siderite or dolomite. 28 29 138  Rare glassy fragments. 30 31 139 Based on the lithology of the volcanogenic sediments, it has been concluded that the 32 33 140 volcanics that formed them were of acid to intermediate affinity (Paton, 1986). 34 35 36 141 2.1.4 Adori Sandstone, Upper Jurassic, ~ 160-155 Ma 37 38 39 142 The Birkhead Formation is capped by the Adori Sandstone, marked by a transition to clean, 40 41 143 non-volcanogenic sedimentation. The Adori Sandstone is a well sorted and typically cross 42 144 bedded, fine to coarse-grained sandstone deposited in a low sinuosity fluvial system 43 44 145 consisting of channel, point bar and flood plain deposits in the Central Eromanga Basin 45 46 146 (Burger & Senior, 1979; Alexander & Hibburt, 1996). 47 48 49 147 2.2 Structural Setting of the Study Area 50 51 52 148 Structurally, the Cooper Basin can be divided into southern and northern sections 53 54 149 (Gravestock et al., 1998; Hall et al., 2016). To the north, depocentres are dominantly 55 150 Triassic, with Permian depocentres in the south (Hall et al., 2018). The northern and 56 57 151 southern sections of the Cooper Basin are separated by the Jackson-Naccowlah-Pepita 58 59 152 Trend (JNP trend) (Fig. 1). In the south west, depocentres are generally thicker, reaching a 60 61 62 63 64 65 6

153 maximum thickness of 2400 m in the Nappamerri Trough (Hall et al., 2016) and many of 1 2 154 these depocentres have experienced synclinal folding due to differential compaction (Apak 3 155 et al., 1997). The major depocentres are separated by northeast-southwest trending ridges 4 5 156 (Gravestock et al., 1998). 6 7 8 157 The area of focus in this study is the eastern Nappamerri Trough of north east South 9 10 158 Australia and south west Queensland. The Nappamerri Trough contains the deepest 11 12 159 basement within the Cooper Basin and hosts the Halifax well that intersected the deepest 13 160 Permian-age sedimentary rocks in the basin at 4,209 m. To the north, the Nappamerri 14 15 161 Trough is bounded by the Gidgealpa, Canway, Packsaddle and Innamincka ridges (Fig. 1A). 16 17 162 The southern extent of the Nappamerri Trough is bounded by the Della-Nappacoongee, 18 19 163 Dunoon and Murteree ridges (Fig. 1) (Hall et al., 2016). 20 21 164 3. Methodology 22 23 24 25 165 3.1 Identification of Volcanics Using Subsurface Data 26 27 28 166 Here we describe the main techniques that were used to investigate igneous rocks within 29 167 the Nappamerri Trough. 30 31 32 33 168 3.1.1 Seismic Data 34 35 169 Seismic reflection data has been shown by numerous studies to be especially effective at 36 37 170 imaging igneous rocks due to the high acoustic impedance of igneous material when 38 39 171 compared to surrounding sedimentary rocks and the distinctive morphology of lava flows 40 172 and intrusions (Planke et al., 2000). Here we provide a brief introduction to the different 41 42 173 types of igneous rock identified in the subsurface on seismic reflection data. 43 44 45 174 Vents identified within seismic reflection data are typically grouped into either hydrothermal 46 47 175 or volcanic vents (Reynolds et al., 2017). The morphologies of hydrothermal vents and 48 49 176 volcanoes are similar as they both exhibit eye, dome or crater shaped morphologies in 50 177 seismic data (Fig. 4)(Planke et al., 2005; Reynolds et al., 2017). This can make distinguishing 51 52 178 hydrothermal vents from volcanoes difficult when seismic reflection data are the sole data 53 54 179 source. 55 56 57 180 Volcanoes can be confidently identified using seismic reflection data where they extend into 58 181 lava flows (e.g. Fig. 4A-D). Lava flows are distinguishable as layer-parallel acoustically hard, 59 60 61 62 63 64 65 7

182 bright reflectors within the subsurface (Planke et al., 2000; Schofield & Jolley, 2013; Hardman 1 2 183 et al., 2019) (Fig. 4B). Extrusive igneous rocks are distinguishable from intrusive igneous 3 184 rocks as they do not transgress stratigraphy. 4 5 6 185 Igneous intrusions have been studied intensely using 3D seismic data (Bell & Butcher, 2002; 7 8 186 Thomson & Schofield, 2008; Archer et al., 2005; Magee et al., 2014). Igneous intrusions form 9 10 187 acoustically hard, bright reflectors that are layer parallel or transect stratigraphy. In places, 11 12 188 they can produce forced folding of the overburden with onlapping stratigraphy facilitating 13 189 age-dating of the intrusion (Trude et al., 2003). 14 15 16 190 3.1.2 Seismic Attributes 17 18 19 191 3D seismic reflection data facilitates the analysis of the geophysical properties of igneous 20 21 192 rocks in 3D. Seismic attributes such as RMS amplitude and spectral decomposition have 22 23 193 proven to be effective tools in picking the extent and morphology of lava flows in seismic 24 194 data (Figs. 4C & G) (Schofield & Jolley, 2013; Planke et al., 2017; Hardman et al., 2019). 25 26 195 Spectral decomposition involves filtering 3D seismic reflection wavelets to produce three 27 28 196 amplitude components at distinct frequencies that are displayed as separate colour channels 29 30 197 using the primary colours red, green and blue. These channels are then blended to produce 31 32 198 full colour spectrum images where the igneous rocks appear visibly different to the 33 34 199 surrounding sediments, due to their differing reflectiveness for particular frequencies (they 35 200 transmit acoustic energy efficiently at all frequencies). Furthermore, this technique can be 36 37 201 used to investigate the geometries of igneous rocks and features such as inflation lobes can 38 39 202 help with distinguishing igneous intrusions from extrusive igneous rocks. 40 41 42 203 3.1.3 Well Data 43 44 45 204 In addition to the use of seismic data, the integrated analysis of borehole data including 46 205 wireline log responses, core and cuttings is essential in accurately identifying igneous rocks 47 48 206 within the subsurface (Nelson et al., 2009; Rider & Kennedy, 2011; Watson et al., 2017). The 49 50 207 onshore response of igneous rocks in outcrop has been linked to offshore observations 51 52 208 facilitating the identification of different volcanic facies through petrophysical and 53 54 209 petrological analysis (Nelson et al., 2009; Millet et al., 2016). 55 56 210 Here, we use a combination of petrophysical and petrological data in our description of the 57 58 211 WVP. Although cuttings and core were not examined within this study, descriptions were 59 60 212 available within well reports that were integrated with petrophysical data and seismic 61 62 63 64 65 8

213 reflection data to provide a comprehensive overview of the data available. It is important to 1 2 214 recognise that the petrological descriptions taken from well reports is secondary 3 215 information and, as such, variable in quality. Wherever petrological descriptions have been 4 5 216 taken from end of well reports it is explicitly stated within the text with a reference to the 6 7 217 relevant well report. 8 9 10 218 3.2 Description of Dataset 11 12 13 219 The Cooper and Eromanga Basins have been explored extensively over the past 60 years 14 15 220 and are characterised by the largest collection of well and seismic reflection data for any 16 221 onshore sedimentary basin in Australia. Over 2000 wells have been drilled in the Cooper 17 18 222 and Eromanga Basins. Despite this, of the wells available, only 3 (Lambda 1, Orientos 2 and 19 20 223 Kappa 1) were identified as having intersected extrusive volcanic rocks with only 1 well 21 22 224 (Warnie East 1) encountering an intrusive igneous rock. To estimate the relative age of the 23 24 225 volcanic units, well data were tied, where possible, to the seismic reflection surveys 25 26 226 available. For constraining the age of the Eromanga succession within the Central 27 227 Nappamerri trough, the Halifax, Etty, Padme, Charal and Anakin wells represented key 28 29 228 datasets (location on Fig. 1C). 30 31 32 229 A large database of seismic reflection data was available through Santos Limited and the 33 34 230 Queensland Government’s Department of Natural Resources and Mines. 3D and 2D seismic 35 36 231 reflection surveys throughout the South Australian and Queensland sides of the basin were 37 232 assessed for the presence of igneous rocks (the extent of the seismic data examined is 38 39 233 visible on Fig. 1B). Notably, only four surveys available to this study (the Winnie 3D, the 40 41 234 Gallus 2D, the Madigan 3D and the Snowball 3D survey (provided for use by Santos 42 43 235 Limited)), were interpreted to contain igneous rocks and a summary of these surveys is 44 45 236 provided in Table 1. Furthermore, 3 individual 2D seismic lines were available across the 46 47 237 Lambda 1, Orientos 2 and Warnie East 1 wells. Seismic data were displayed using normal 48 238 (American) polarity, whereby a downward increase in acoustic impedance corresponds to a 49 50 239 positive (blue) reflection and a downward decrease a negative (red) reflection. The only 51 52 240 exception to this is the Snowball 3D survey that was displayed such that a downward 53 54 241 increase in acoustic impedance corresponds to a red, negative reflection (European 55 56 242 polarity). Within the Jurassic succession the average dominant frequency within the seismic 57 - 58 243 data was ~40 Hz, with volcanic rocks in the region having an acoustic velocity of 4 to 6 kms 59 60 61 62 63 64 65 9

244 1 (taken from the Lambda 1 exploration well). Using an average velocity of 5 kms-1 a vertical 1 2 245 resolution of ~30 m and a detection limit of 4 m was calculated. 3 4 246 Here we present an overview of all the available datasets that constrain the distribution and 5 6 247 age of igneous rocks within the study area. We recognise three distinct types of igneous 7 8 248 rocks within this study: 9 10  11 249 Extrusive igneous rocks 12 250  Intrusive igneous rocks 13 14 251  Altered extrusive igneous rocks 15 16 17 252 Each type is described in detail using the available well and seismic data before the regional 18 19 253 character of the Warnie Volcanic Province as a whole is discussed using regional gravity and 20 21 254 magnetic surveys. It is important we recognise that whilst this is the extent of the data that 22 255 was available during this study, the authors are aware of other seismic reflection surveys 23 24 256 within the Nappamerri Trough that were not available to download digitally and were not 25 26 257 possible to acquire within the period of time during which this study was conducted. These 27 28 258 surveys may also image igneous rocks that could fuel further work on the area. 29 30 31 259 4. Description of Extrusive Igneous Rocks 32 33 34 260 4.1 Well Data 35 36 37 261 Unaltered, basaltic, extrusive igneous rocks are recognised in the Lambda 1 and Orientos 2 38 39 262 wells in the eastern Nappamerri Trough. 40 41 263 The Lambda 1 well was drilled in 1984 by Delhi Petroleum Pty. Ltd. At a depth of 1570.9 m, 42 43 264 283 m igneous rocks were intersected, directly underlying the base of the Birkhead Fm. (Fig. 44 45 265 12). The upper 33 m of basalt are noted as heavily weathered, fractured and vesicular in the 46 47 266 Lambda 1 well report (Short, 1984). The remaining 250 m of basalt is described as fresh and 48 267 crystalline. It has low gamma ray values, with consistently high density and acoustic velocity 49 50 268 (Fig. 12A). There are localised areas where the density drops drastically, however, these are 51 52 269 associated with increases in the caliper and may therefore point to caving of the wellbore 53 54 270 when it was drilled or fractures within the basalt, rather than lithological variations. At the 55 56 271 base of the basalt ~1.5 m of core was cut, within which the fine grained, crystalline nature of 57 58 272 the basalt is apparent (Fig. 5A, see picture). 59 60 61 62 63 64 65 10

273 Similarly to Lambda 1, Orientos 2 drilled through igneous rocks situated at 1555 m, beneath 1 2 274 the Jurassic age Adori Sandstone (Fig. 14). The well drilled through 34 m of igneous rocks 3 275 before drilling was ceased, prior to the well reaching the base of the igneous rocks. The 4 5 276 igneous rocks are described as dark green, grey black with quartz inclusions and common 6 7 277 amphiboles in the end of well report (Bucknill, 1990). Similar to the Lambda 1 well, 8 9 278 Orientos 2 encountered a 14 m section of weathered basalt identifiable by low density and 10 11 279 sonic values in the well logs, followed by a high density and high velocity section, matching 12 13 280 the petrophysical response of the Lambda 1 igneous rocks. Draper (2002) noted that 14 15 281 Orientos 2 was drilled <1 km from Orientos 1, which did not intersect basalt, suggesting 16 282 that the basalt In Orientos 2 might be intrusive in origin. However, we note that Orientos 1 17 18 283 may have been drilled beyond the limit of the basalt and, as such, we do not take the 19 20 284 absence of igneous rocks in Orientos 1 to be indicative of an intrusive origin for the 21 22 285 Orientos 2 igneous rocks. 23 24 286 Nelson et al. (2009) provided compelling evidence for the use of binning velocity data in 25 26 287 estimating the type of volcanic rock present. In order to investigate the extrusive or 27 28 288 intrusive nature of the Lambda 1 igneous rocks, interval velocity histograms were created. 29 30 289 They were then binned with a bin spacing of 0.125 m order to create a velocity histogram 31 32 290 (Fig.12C). These were superimposed on the velocity histogram fields of Nelson et al., (2009) 33 34 291 that were obtained from boreholes on the Faroe Islands in the North Atlantic, in order to 35 36 292 compare the acoustic velocities of igneous rocks in the Nappamerri Trough with values 37 293 from extrusive igneous rocks in the Northwest Atlantic. It can be seen in Fig. 5C that the 38 39 294 Lambda 1 volcanics show a very strong similarity to the tabular basalt analysed by Nelson et 40 41 295 al. (2009). 42 43 44 296 Additionally, vitrinite reflectance data (Boothby, 1986) was recorded for sediments 45 297 deposited on top of the Lambda-1 volcanics (Fig. 5B). Notably, in the sediment contact with 46 47 298 the volcanics, there is no deviation towards high %RoMax, suggesting that the Lambda 1 48 49 299 volcanics had little thermal effect on the overlying organic matter. It has been observed in 50 51 300 locations such as Namibia that the thermal effect of lava flows is restricted to << 1 m depth 52 53 301 below lava contacts (Grove et al., 2017) whereas igneous intrusions have a much larger 54 55 302 thermal effect on surrounding sediments due to their inability to release heat directly to the 56 57 303 earth’s surface (see Utgard Sill Complex, Aarnes et al., 2015). If this were an intrusion, it is 58 304 expected that the VR values would be elevated (Stewart et al., 2005), and the absence of 59 60 305 such elevated values implies that the basalt is extrusive. 61 62 63 64 65 11

306 4.2 Seismic Data 1 2 3 307 Extrusive igneous rocks have been documented using the available seismic data. These 4 5 308 observations will focus on the Winnie 3D survey as it is the largest, highest quality 3D 6 309 dataset within which the full range of igneous rocks is observed. From there, we build out 7 8 310 to the other seismic surveys utilised. 9 10 11 311 In a single 2D seismic line intersecting the Lambda 1 well the tabular basalt intersected by 12 13 312 the well corresponds to a high amplitude reflection most pronounced at the location of the 14 15 313 well but also continuing ~3 km to the west of the survey (Fig. 6). The centre of the survey 16 314 (and the location of the well) corresponds with a ~1.5 km wide anticline that exhibits 17 18 315 doming on the order of ~150 ms. Below the anticline and the location of the volcanics, the 19 20 316 2D seismic reflections are visibly distorted, being most pronounced beneath the location of 21 22 317 the well where a velocity pull-up effect is visible. 23 24 2 318 Within the Winnie 3D survey, we identified ~100, <= 4 km cone shaped features 25 26 319 that often express an eye-shaped morphology, doming and velocity pull-up effects similar to 27 28 320 those observed in the location of the Lambda 1 well (Fig. 4B). The cones within the survey 29 30 321 are less than 2 km long and 750 m wide, and often elongate in a NW-SE direction (Fig. 6). 31 32 322 Due to the extrusive nature of the Lambda 1 well, their stratigraphic concordance and their 33 34 323 cone shaped morphology in seismic, we have interpreted these as monogenetic volcanoes, 35 36 324 small cumulative volume volcanic edifices built up by one continuous, or many 37 325 discontinuous, small eruptions over a short time scale (<= 10 years) (Németh & Kereszturi, 38 39 326 2015). 40 41 42 327 In the Winnie 3D survey, twelve of the volcanoes are linked with what appear to be 43 44 328 elongate, NW-SE oriented lava flows that are conformable to stratigraphy and have 45 329 dimensions of 2-7 km in length and 0.5-2.5 km in width (covering areas of 4-13.5 km2) (e.g. 46 47 330 Figs. 7 & 8). 48 49 50 331 The northwards continuation of the monogenetic volcanoes and lava flows that were 51 52 332 detailed in the Winnie 3D survey is imaged within the Gallus 2D survey (Fig. 11A-C). To 53 54 333 better constrain the distribution of the volcanics in the Gallus 2D survey, the top and 55 334 bottom of the igneous rocks were mapped. From these, we calculated the isochron 56 57 335 thickness of the igneous rocks in the area (Fig. 9A). Like the Winnie 3D survey, volcanism 58 59 336 was more pervasive towards the east, with the thickest volcanics (~300 ms, approximately 60 61 62 63 64 65 12

337 163 m) located at the eastern edge of the survey. The northernmost extent of the Warnie 1 2 338 Volcanic Province is recognised in the Madigan 3D survey where two monogenetic vents 3 339 were identified within the seismic data. Although, neither vent was penetrated by a well and 4 5 340 no surface flows were mapped away from the vents, it seems likely that they are volcanic in 6 7 341 origin due to their similarity with the other volcanoes in the Nappamerri Trough. 8 9 10 342 11 12 343 We have also interpreted one feature within the Warnie Volcanic Province as a 13 14 344 diatreme. Maar-diatreme volcanism can occur where a volcanic pipe forms through gaseous 15 16 345 explosions that cut into the country rock (Fig. 4 E-H) (White & Ross, 2011). These 17 18 346 explosions form a maar (the crater and associated ejecta ring) and a diatreme (the root to 19 20 347 the maar), consisting of a steep-sided cone shaped structure filled with pyroclastic, volcanic 21 348 and country rocks) (White & Ross, 2011). Unlike vents and associated lava flows, they 22 23 349 consist of downward dipping reflectors that truncate the underlying stratigraphy with 24 25 350 typically chaotic internal reflectors (Fig. 4F). Spectral decomposition proved to be the most 26 27 351 powerful tool for identifying maar-diatremes above the Nappamerri Trough, as the circular 28 29 352 crater morphology stood out against the surrounding sediments (Fig. 4G). One feature 30 31 353 interpreted to be a diatreme was identified within the survey, displayed in detail in (Fig. 4). It 32 2 33 354 is ~2.25 km and ~120 m deep (150 ms, TWT) and is found in the west of the Winnie 3D 34 355 survey (see Fig. 6). 35 36 37 356 38 39 357 5. Description of Intrusive Igneous Rocks 40 41 42 43 358 5.1 Well Data 44 45 46 359 Igneous rocks intersected within the Warnie East 1 well are lithologically unique amongst 47 360 the igneous rocks penetrated by wells in the WVP. Located at 2103 m depth within the 48 49 361 Permian Toolachee Fm (Fig. 10), the 65 m thick basalt is described in the end of well report 50 51 362 as fine grained and dominated by plagioclase laths intergrown with augite (Boothby, 1986). 52 53 363 The upper 12 m of the volcanics are described as altered and calcareous, containing 54 55 364 phenocrysts of augite with minor pale green talc and minor calcite veining. 56 57 365 Vitrinite reflectance data was acquired within the Warnie East 1 well. (Fig. 10B). Samples of 58 59 366 vitrain were obtained and mean maximum reflectance of vitrinite calculated (Smith, 1987). 60 61 62 63 64 65 13

367 Vitrinite reflectance samples adjacent (directly above and below) to the basalt show a 1 2 368 marked increase to 4.5% relative to surrounding Toolachee sediments that are typically 1.5- 3 369 1.75%. Whereas extrusive volcanics appear to have little thermal effect on the surrounding 4 5 370 sediments (e.g. Grove et al., 2017), igneous intrusions typically show uniform heating on 6 7 371 either side of the volcanics, as is observed here (Aarnes et al., 2015). Coupled with its 8 9 372 stratigraphic position within the Permian Toolachee Fm., where no other volcanics have 10 11 373 been documented within the Cooper Basin, we suggest that Warnie East 1 contains the sole 12 13 374 identified well intersection of an igneous intrusion in the WVP. 14 15 375 5.2 Seismic Data 16 17 18 376 Intrusive igneous rocks are also identified within the seismic data available. A 2D seismic 19 20 377 reflection line was available that runs across the location of the Warnie East 1 well (Fig. 11). 21 22 378 Unlike the Lambda 1 and Orientos 2 volcanics, the igneous rocks within the Warnie East 1 23 24 379 well sit within the Toolachee Fm., a highly reflective sequence of heterogeneous lithologies 25 26 380 consisting of sandstones, siltstones and coals. As such, the igneous rocks are difficult to 27 381 distinguish on seismic reflection survey data, although a shallow saucer-shaped reflection 28 29 382 intersects the well path of the Warnie East 1 well at the depth that igneous rocks are 30 31 383 located. The reflection is ~1.5 km wide and transects the Toolachee Fm. over a depth range 32 33 384 of 50 ms. The shallow saucer shape that the reflection event exhibits is common among 34 35 385 igneous intrusions within sedimentary basins, corroborating with the well data that suggests 36 37 386 the igneous rocks are intrusive in nature. 38 39 387 Igneous intrusions within the Winnie 3D survey are identified as igneous rocks that 40 41 388 cross-cut the Triassic to Jurassic strata; notably the Nappamerri, Hutton and Birkhead Fms 42 43 389 (e.g. Fig. 12). We identified and mapped 14 intrusions in the seismic data; these occur ~100– 44 45 390 200 ms (~105 – 210 m) below the palaeosurface. Most of the sills identified are of a similar 46 47 391 scale to the lava flows in the area (2 – 4.5 km long, 1.2 – 1.7 km wide). 48 49 392 The Winnie 3D survey also hosts a spectacular single intrusion, 14 km long and 8 50 51 393 km wide, by far the largest igneous feature in the WVP (Fig. 12). Classical intrusion-related 52 53 394 features such as inflation lobes are observed within spectral decomposition (Fig. 12C). 54 55 395 Around 20 vents cross-cut this intrusion (see pockmarks on Fig. 12C), in places leading to 56 57 396 extrusive lava flows in the overlying sediments (see surface flows on Top Birkhead overlying 58 397 the intrusion in Fig. 12B). The presence of the pockmarks on the surface of the intrusion 59 60 61 62 63 64 65 14

398 suggest emplacement of the sill predated a later stage of volcanism that occurred towards 1 2 399 the top of the Birkhead Fm. 3 4 400 5 6 401 6. Description of Altered Igneous Rocks 7 8 9 402 This study has so far dealt with igneous rocks of a very consistent lithology preserved within 10 403 or above the Central Nappamerri Trough. However, the Kappa 1 well and Snowball 3D 11 12 404 seismic reflection survey, located on the very southern edge of the mapped extent of the 13 14 405 WVP, preserve igneous rocks of a very different character (Figs. 13-15). 15 16 17 406 6.1 Well Data 18 19 20 407 The Kappa 1 well was drilled in 1997 on behalf of Santos Limited with the aim of evaluating 21 22 408 hydrocarbon presence within the Toolachee, Patchawarra and Epsilon formations (Allen, 23 409 1998). Kappa 1 is located above a large anticline and is the southernmost of a string of 24 25 410 prospects located above the northeast Della-Nappacoongee Ridge, which deepens 26 27 411 northwards into the Nappamerri Trough (Fig. 1). Between 1895 and 2115 m, the Kappa 28 29 412 well intersected a 120 m thick succession of igneous rocks below a thinned 21 m succession 30 31 413 of Hutton Sandstone (Fig. 13). Within the well report, the igneous rocks are ascribed a late 32 33 414 Permian to Middle Triassic age (Allen, 1998). 34 35 415 Although core description or in-depth petrological work was not undertaken during this 36 37 416 study, rock chips and cuttings of the igneous rocks are described extensively within the 38 39 417 Kappa 1 end of well report (Allen, 1998). Due to the large amount of alteration, the 40 41 418 volcanics are described as a chloritized basalt with abundant plagioclase, chlorite, carbonates 42 43 419 and quartz. However, the well report distinguishes two types of igneous rocks. Firstly, a 44 420 vesicular microporphyritic basalt was described that consists of olivine and pyroxene 45 46 421 phenocrysts contained within a fine grained or glassy groundmass. Secondly, a less abundant 47 48 422 coarse-grained holocrystalline basalt that is composed of randomly oriented plagioclase 49 50 423 laths, ferromagnesian crystals and accessory magnetite plus ilmenite. Importantly, and 51 52 424 pervasively throughout the succession, a fibrous chlorite is described as having replaced 53 54 425 much of the ferromagnesian minerals and groundmass as well rimming and filling vesicles 55 426 within the basalt. 56 57 58 427 The Igneous succession in Kappa 1 also has an unusual petrophysical expression. In our 59 60 428 interpretation, we have divided the volcanics into two facies based on the above description; 61 62 63 64 65 15

429 a volcaniclastic breccia and in-situ basalt (Fig. 13). The in-situ basalt (e.g. the section between 1 2 430 1900 m and 1960 m (Fig. 13)) has a ‘saw-tooth’ response with a relatively low gamma 3 -1 431 response of ~40 api. Acoustic velocities from the sonic velocity log (~4 kms ) are 4 5 432 consistently lower than those observed in the Lambda 1 and Orientos 2 wells (~ 5.5-6 kms- 6 7 433 1). The chaotic, saw-tooth response is indicative of the highly altered nature of the volcanic 8 9 434 succession in Kappa 1 and can be diagnostic of compound lava flows (Millet et al., 2016; 10 11 435 Hardman et al., 2019) (Fig. 18). The resistivity throughout the section consistently measures 12 13 436 15 Ωm. As with the Lambda 1 well, we constructed a velocity histogram for the igneous 14 15 437 rocks in the Kappa 1 well. When compared to Nelson et al.’s velocity histograms (2009) the 16 438 best match was with that of Compound-braided flows (Fig. 13B). However, the upper half of 17 18 439 Nelson et al.’s (2009) histogram is missing in the Kappa 1 volcanics, suggesting that the more 19 20 440 crystalline, high velocity material is either absent or has been altered to lower velocity 21 22 441 material. 23 24 442 The volcaniclastic breccia is described as consisting of poorly sorted, subangular, 25 26 443 volcaniclastic igneous rock of very fine sand to granule size (Allen, 1998). The log response 27 28 444 for the volcaniclastic breccia is characterised by a jagged petrophysical response when 29 30 445 compared to the in-situ basalt. Although the gamma ray values (~40 api) are similar to those 31 -1 32 446 of the in-situ basalt, the acoustic velocities (between 2800 and 4 kms ) are consistently 33 34 447 lower. Furthermore, the volcaniclastic breccia is water saturated with a resistivity of 2 – 3 35 36 448 Ωm, although this may also reflect the magnetite and ilmenite within the basalt. Finally, 37 449 below 2050 m to the base of the volcanic succession, the caliper tool widened significantly 38 39 450 suggesting that the volcaniclastics in this part of the succession are considerably 40 41 451 unconsolidated and/or fractured. 42 43 44 452 6.2 Seismic Data 45 46 47 453 The top of the Kappa 1 volcanics is interpreted to correlate with a bright, laterally 48 454 continuous reflection that was present across the whole of the Snowball 3D survey (Figs. 14 49 50 455 & 15). Above the top Kappa 1 volcanics a second reflector, deemed here the ‘Top Volcanic 51 52 456 Mounds,’ was mapped in parts of the Snowball 3D survey adjacent to a series of mound-like 53 54 457 structures, appearing in places to downlap onto the top Kappa 1 volcanics (Fig. 15). The 55 56 458 centres of these-mound shaped structures are marked by a notable brightening of the 57 58 459 reflectors and they are underlain by vertical vents similar to those seen in the other surveys. 59 460 We thus interpret these mound structures to be a series of volcanic edifices. 60 61 62 63 64 65 16

461 The volcanics present in the Snowball 3D survey are notably different to those preserved in 1 2 462 the Nappamerri Trough (e.g. Fig 7-9). Rather than isolated, monogenetic vents or flows, 3 463 they are interpreted to represent a thick package (up to ~150 ms) of mixed volcanics and 4 5 464 volcaniclastic breccias (based on evidence from Kappa 1) that thin towards the southwest of 6 7 465 the survey (Fig. 15A) (i.e. the southern edge of the Nappamerri Trough). Although the true 8 9 466 extent of them is not imaged within the survey (they are interpreted to extend beyond the 10 11 467 survey limits to the northeast), laterally they extend over 6 km. 12 13 468 7. Geophysical Surveys of the Nappamerri Trough 14 15 16 469 Alongside seismic and well data, airborne geophysical surveys were examined in 17 18 470 order to further delineate the regional distribution of the WVP (Fig. 21A). A gravity data 19 20 471 grid was downloaded from the Queensland Government’s data repository. The grid is a 21 472 compilation of open file gravity surveys collected by exploration companies and State and 22 23 473 Federal regional surveys, compiled in 2014. In southwest Queensland, the Nappamerri 24 25 474 Trough is typically characterized by a broad gravity low. However, a pronounced ~50 x 50 26 27 475 km gravity high is apparent in the northeast Nappamerri Trough (Fig. 16A). Furthermore, 28 29 476 the quantity of mapped intrusive and extrusive volcanics increases towards the centre of 30 31 477 this 50 x 50 km gravity anomaly (Fig. 1B). This corresponds with an increase in the thickness 32 478 of igneous rocks mapped within seismic data (see Figs. 2, 7 and 9). 33 34 35 479 In addition to gravity data, a 1VD magnetic intensity survey has been analysed that 36 37 480 was also downloaded from the Queensland Government’s data repository (Fig. 16B). The 38 39 481 first vertical derivate filter enhances the high frequency content in the survey, highlighting 40 41 482 magnetic anomalies caused by shallow sources such as igneous rocks that are situated at 42 483 shallower depths than the base of the Cooper Basin succession. The Nappamerri Trough is 43 44 484 generally marked by a low in the magnetic intensity whilst the bounding ridges are magnetic 45 46 485 highs. However, within the Nappamerri Trough, many small (<8 km2) circular magnetic 47 48 486 anomalies can be observed (Fig. 16B). Basalt is highly susceptible to being magnetised 49 50 487 (Tarling, 1966), which has facilitated the recognition of buried volcanic rocks elsewhere in 51 52 488 the world (Segawa & Oshima, 1975). Notably, many of the smaller magnetic anomalies do 53 489 correspond to the location of igneous rocks in the Winnie 3D survey (Fig. 16C). 54 55 56 490 When the gravity data is superimposed on top of the magnetic data, there is a clear 57 58 491 correlation between the location of igneous rocks interpreted using seismic data, the 59 60 492 magnetic anomalies and the gravity high identifiable within the Nappamerri Trough (Fig. 16D 61 62 63 64 65 17

493 & E), suggesting that regional geophysical surveys help to constrain the distribution and 1 2 494 location of the WVP and other intraplate volcanic provinces. Perhaps most interesting is 3 495 that the correlation between circular magnetic anomalies and areas with a strong gravity 4 5 496 response can be extended beyond the area of the WVP interpreted during this study (Fig. 6 7 497 16E). To the east and southeast of this study, circular magnetic anomalies appear to be 8 9 498 coincident with gravity highs. If these anomalies are proven to be volcanic in nature, the 10 2 11 499 extent of the Warnie Volcanic Province could be greater than the interpreted 7500 km . 12 13 500 8. The Age of the Warnie Volcanic Province 14 15 16 501 This study has detailed the character and extent of igneous rocks within the Cooper and 17 18 502 Eromanga basins which has facilitated a regional overview of the WVP (Fig. 17). Here we 19 20 503 synthesise the different methods used to define an age range for the eruption and 21 504 emplacement of the igneous rocks. 22 23 24 505 Previous Geochemical Analyses 25 26 506 K-Ar dating was conducted on both the Lambda 1 extrusive basalt and the Warnie East 1 27 28 507 intrusive basalt. In the Lambda 1 well, K-Ar dating was conducted on a bag of drill cuttings 29 30 508 taken from a depth of 1658 m by Murray (1994). Although the samples are described as 31 32 509 being too altered to be used for total rock analysis, fresh plagioclase within the cuttings was 33 34 510 separated for analysis and used to determine an age of 227 +/- 3 Ma, suggesting 35 36 511 emplacement of the basalt during the early Triassic (Murray, 1994). However, in Lambda-1, 37 38 512 the basalt is situated between the Jurassic Birkhead Fm. and the Triassic Nappamerri Gp., 39 513 supporting a Late Triassic to Jurassic age (Draper, 2002). K-Ar dating of basaltic volcanic 40 41 514 rocks is often unreliable (Schofield et al., 2017), due to unquantified argon loss (Kelley, 42 43 515 2002). It is noted within the well report that the loss of argon due to subsequent thermal 44 45 516 events or contamination of drill cuttings is not accounted for in the quoted error (Murray, 46 47 517 1994). 48 49 518 Within the Warnie East 1 well, K-Ar dating was conducted on a sample of drill core from 50 51 519 2163 m (Murray, 1994). Again, the rock was too altered to be used for whole rock K-Ar 52 53 520 analysis and, instead, unaltered pyroxene was used for dating. A middle Cretaceous age of 54 55 521 100 ± 9 Ma was calculated (Murray, 1994), significantly younger than the rest of the WVP 56 57 522 and the Permian host rock within which the intrusion is located. This disparity in the ages 58 59 523 determined by K-Ar dating led Draper (2002) to deem the the age dating as ‘equivocal.’ 60 61 62 63 64 65 18

524 Whilst K-Ar dating is considered be relatively unreliable, there are a number of other age- 1 2 525 dating techniques that could be conducted on cuttings or core from the Warnie Volcanic 3 526 Province. U-Pb, Re-Os and Ar-Ar could all be analysed to provide independent constraints 4 5 527 on the age of the igneous material (Liu et al., 2017). Furthermore, these geochemical 6 7 528 measurements can provide insights into the source of these volcanics (Pande et al., 2017) 8 9 529 and are an avenue for future work in the area. In the absence of more geochemical data, it is 10 11 530 important to consider the K-Ar ages with respect to other data. 12 13 531 Seismic Data 14 15 16 532 When tied to the seismic data, the Hutton Sandstone and equivalent sediments (not 17 18 533 penetrated by the Lambda 1 well) are seen to onlap the Lambda 1 volcanics. The lava flow 19 20 534 extending away from Lambda 1 sits atop Triassic Nappamerri Group sediments of the 21 535 Cooper Basin whereas the volcanics penetrated by Lambda 1 appear to cross cut the 22 23 536 Triassic stratigraphy. 24 25 26 537 The timing of igneous activity within the Winnie 3D survey was constrained by the 27 28 538 stratigraphic relationship between igneous activity and the Triassic to Jurassic stratigraphy in 29 30 539 the study area. In places, intrusions are observed to have caused forced folding of the 31 540 overburden, as evidenced by onlap of Birkhead Fm. sediments onto the deformed 32 33 541 overburden overlying the intrusions (Fig. 12B). Onlap of sedimentary rocks onto these 34 35 542 forced folds was used to constrain the age of the intrusion (Trude et al., 2003), whilst the 36 37 543 strata-concordant lava flows elsewhere in the survey were assigned an approximate age 38 39 544 based on their stratigraphic level. We estimate that volcanism lasted throughout deposition 40 41 545 of the Hutton and Birkhead formations between ~178 and 160 Ma, with the youngest 42 546 volcanics identified as surface flows emplaced on the top Birkhead marker horizon 43 44 547 (Alexander & Hibburt, 1996). 45 46 47 548 Similarly, in the Gallus 2D survey whilst none of the volcanics were intersected by any wells, 48 49 549 the approximate stratigraphic age was constrained by the nearby Halifax and Etty wells (Fig. 50 51 550 9C), placing the volcanics within the Hutton and Birkhead formations, as found for the 52 551 Winnie 3D survey. 53 54 55 552 The Madigan 3D volcanics appear to sit near the top of the Nappamerri Group, however, 56 57 553 this would place them in the middle Triassic ~240 Ma, ~60 Myrs older than the rest of the 58 59 554 WVP. An alternative explanation would be the emplacement of these vents at the very base 60 61 62 63 64 65 19

555 of the Jurassic in this region (a maximum age of ~200 Ma, Fig. 2), as they appear to cross-cut 1 2 556 all of the Triassic Nappamerri Group strata. This second explanation is preferable as it 3 557 would fit with the igneous rocks observed throughout the rest of the WVP. 4 5 6 558 We conclude that the vast majority of igneous rocks identified using seismic reflection data 7 8 559 and well data throughout this study can be constrained to a broad age range between ~180 9 10 560 and 160 Ma, spanning the Middle Jurassic. Further work is encouraged to better define the 11 12 561 age of the Warnie Volcanic Province, particularly geochemical analyse that would help 13 562 constrain both the origin and timing of volcanism. 14 15 16 563 17 18 19 564 8. Discussion 20 21 22 565 8.1 The Origin of Altered Volcanics Within the Warnie Volcanic Province 23 24 25 566 The nature of the igneous rocks within the Kappa 1 well and Snowball 3D survey is distinct 26 567 when compared to the rest of the Warnie Volcanic Province, consisting of a mixed 27 28 568 sequence of in-situ basalt and volcaniclastics breccias. What isn’t clear, however, is the 29 30 569 origin of the volcanics. Within the Kappa-1 well report, the sequence is described as 31 32 570 pyroclastic in nature (Allen, 1998). Whilst this interpretation can account for some of the 33 34 571 altered volcaniclastics, it does not explain the extensive sequence of altered basalt. An 35 36 572 alternative explanation may be differing sedimentation and eruption rates within the 37 38 573 Eromanga leading to prolonged exposure of volcanic rocks emplaced on the rim of the 39 574 Nappamerri Trough. However, Mid-Late Jurassic sedimentation rates at Kappa 1 of 2.4 40 41 575 m.my-1 (calculated by dividing the thickness of the Hutton to Adori succession by a duration 42 43 576 of 23 Myrs) are not significantly lower than those in the Warnie or Lambda wells (2.8 and 44 45 577 2.5 m.my-1 respectively). Hence, alteration does not appear to be a consequence of 46 47 578 extensive surface exposure. 48 49 579 A more compelling explanation for the Kappa 1 volcanics is hydrothermal alteration. In 50 51 580 volcanic regions, many lakes are typically fed by hot springs. In the East African Rift, 52 53 581 discharge of hydrothermal water can produce authigenic chlorite with calcite and quartz 54 55 582 forming pore filling cements (Renaut et al., 2002). These minerals, particularly chlorite, are 56 57 583 noted extensively within the petrological description of the Kappa 1 well. Additionally, the 58 59 584 Kappa 1 well lies above the Kinta structural trend which could have provided a pathway for 60 61 62 63 64 65 20

585 hydrothermal fluids into the Eromanga succession. Basin-wide hydrothermal fluid circulation 1 2 586 has been noted within the Cooper Basin (Middleton et al., 2014, 2015). In the Nappamerri 3 587 Trough, these fluids are believed to have formed due to rifting of the eastern Australian 4 5 588 margin during the mid-Cretaceous (Middleton et al., 2015), post-dating the emplacement of 6 7 589 the Warnie Volcanic Province. We propose that the Kappa 1 well represents a succession 8 9 590 of volcaniclastic and primary volcanic rocks that was highly altered by hydrothermal fluids. 10 11 12 591 13 14 592 8.2 Structural Controls on the Emplacement of the Warnie Volcanic Province 15 16 17 593 From the late Triassic to the early Jurassic, the Eromanga Basin was subject to an east-west 18 594 compressional event named the Hunter-Bowen event (Kulikowski & Amrouch, 2017), which 19 20 595 uplifted the basin and inverted the major highs. Subsequently, the basin underwent post- 21 22 596 compressional flexural relaxation with the resultant accommodation space infilled by the 23 24 597 Middle to Late Jurassic succession discussed within this manuscript (Lowe-Young, 1997). 25 26 598 During this time, a strike-slip extensional regime is thought to have been present in 27 28 599 southwest Queensland (Kulikowski et al., 2018). In this context, it is interesting to consider 29 600 whether the stress regime of the Cooper Basin helped to control the location and 30 31 601 morphology of igneous rocks within the WVP and, more broadly, the location of the WVP 32 33 602 within central Australia. 34 35 36 603 8.2.1 The Influence of Basement Structure on the Location of Igneous Rocks 37 38 39 604 Within other basins, such as those in the North Atlantic, it has been noted how the location 40 605 of igneous intrusions and volcanism is controlled by the basin structure, in particular the 41 42 606 location of major faults (Schofield et al., 2017; McCLlean et al., 2017; Hardman et al., 2019). 43 44 607 To investigate whether basement structure and faulting had a direct control on volcanism 45 46 608 erupted during the Jurassic, we have utilised the 3D seismic reflection datasets available. 47 48 49 609 The basin structure of the eastern Nappamerri Trough is largely obscured by the thick 50 610 Cooper and Eromanga Basin fill and the highly reflective coals of the Permian Toolachee and 51 52 611 Patchawarra Fms that make imaging of deeper sediments difficult. Of all the 3D seismic 53 54 612 reflection surveys available for this study, only the Winnie 3D survey imaged reflections 55 56 613 ~2800 ms deep within the Nappamerri Trough (Fig. 3)(approximately 4.3 km subsurface 57 58 614 depth based on the Charal-1 time-depth relationship). Notably, the exact lithology of this 59 60 615 reflection is unclear, largely due to the lack of any intersections in the Central Nappameri 61 62 63 64 65 21

616 wells. Unlike the flat-lying Cooper and Eromanga stratigraphy, these deep reflections were

1 0 2 617 often inclined at an angle of ~10 (taken with the scale set so that 1s TWT depth = 1 km 3 618 distance laterally). Although not confidently picked throughout the whole of the Winnie 3D 4 5 619 survey, the reflections can be mapped over an area of ~600 km2 (Fig. 18B). We interpret 6 7 620 these to represent the top Basement in the Nappamerri Trough. 8 9 10 621 When mapped and imaged in plan view, it is clear that the most major offset (a ~400 ms 11 12 622 step in the data visible in Fig. 18B) trends ~15 km NW-SE across the Winnie 3D survey. 13 623 The same 400 ms step has been noted by previous mapping (SA Department for 14 15 624 Manufacturing, Innovation, Trade, Resources and Energy, 2003) where it is visible on a top 16 17 625 basement map in the eastern Nappamerri Trough. We interpret offset of the top basement 18 19 626 as faulting and, so that it may be easily referred to throughout the text, name the major 400 20 21 627 ms offset the Central Nappamerri Fault. 22 23 628 In order to better relate the igneous activity in the area to the basement structure the 24 25 629 distribution of the monogenetic vents within the Winnie 3D survey is considered with 26 27 630 respect to these deep basement reflectors. Beneath the vents and volcanoes of the Winnie 28 29 631 3D survey, the seismic reflection data exhibited a velocity pull-up effect that could either 30 31 632 represent shallow high velocity material (i.e., the vents or volcanoes themselves) or a high 32 33 633 velocity feeder zone representing a vertical column of igneous rock or hydrothermally 34 634 altered host rock. This effect was particularly obvious on the well-imaged Toolachee Fm., 35 36 635 which was mapped to constrain the distribution of the pull-up effects or vents throughout 37 38 636 the area (Fig. 18A). Underlying the volcanoes are dark patches that are clearly distinguished 39 40 637 from the fluvial channels that make up the Toolachee Fm. (Fig. 18A). We have interpreted 41 42 638 these as vents that are either hydrothermal vents or basaltic dykes. The position of these 43 44 639 vents was highlighted and superimposed on top of the image of the basement reflections 45 640 (Fig. 18B). The vents broadly fall into two groups, one to the south of the Central 46 47 641 Nappamerri Fault and one to the NE of the Central Nappamerri Fault (Fig. 17 and 18B). 48 49 642 These groups fall adjacent to the Top Basement reflections or directly above visible offset in 50 51 643 the basement where it deepens to > 3600 ms and is no longer mappable, strongly implying a 52 53 644 pervasive structural control on the location of vents in the Winnie 3D survey. 54 55 56 645 We also superimposed the location of the Madigan 3D volcanoes on top of the SA 57 58 646 Department for Manufacturing, Innovation, Trade, Resources and Energy (2003) basement 59 647 map (Fig. 17). Like the igneous rocks in the Winnie 3D survey, the two volcanoes imaged in 60 61 62 63 64 65 22

648 the Madigan 3D survey sit atop the tip of the 25 km Challum Fault and atop a second, ~5 1 2 649 km fault northwest of the main Challum Fault. The volcanics seem to be located at the 3 650 stepover between two faults, suggesting it may be a small releasing bend. This reinforces the 4 5 651 idea that the location of igneous rocks was largely controlled by zones of weakness within 6 7 652 the basins. 8 9 10 653 8.2.2 The Influence of Discontinuities and Faults within the Eromanga Succession on the 11 12 654 Morphology of Igneous Rocks 13 14 655 The idea that structure was the principle control on the nature of the volcanics in the WVP 15 16 656 can be extended to the morphology of the igneous rocks. In order to consider how basin 17 18 657 structure controlled the morphology of igneous rocks within the Nappamerri Trough, the 19 658 Winnie 3D survey was used to map the length, width and elongate direction of the 20 21 659 volcanoes, lava flows and intrusions (Fig. 19). The high quality of the Winnie 3D survey 22 23 660 facilitated confident mapping of the outline of individual volcanic events, however, the Gallus 24 25 661 2D and Snowball 3D surveys were not considered as the outline of individual volcanics 26 27 662 could not be picked confidently. The data shows that igneous rocks in the area are typically 28 29 663 twice as long as they are wide (Fig. 19). Furthermore, almost all the igneous rocks are 30 31 664 elongated in a NW-SE direction, closely matching the strike of the faults within the 32 665 Nappamerri Trough. It is clear that during eruption and emplacement of the igneous rocks, 33 34 666 the basin structure exerted a strong control on the morphology of lava flows and igneous 35 36 667 intrusions. 37 38 39 668 In vertical seismic reflection sections, faulting of the Eromanga Basin stratigraphy is not 40 41 669 obvious within the Winnie 3D survey, largely due to the considerable noise within the 42 43 670 section. However, spectral decomposition produced for the Top Volcanics horizon images 44 45 671 discontinuities (shown as black lines) within the colour blend (Fig. 20). These discontinuities 46 672 are not thought to be a product of the acquisition and processing of the seismic data, due to 47 48 673 their non-linear nature and their coincidence with other geological features such as the 49 50 674 igneous rocks and the CNF. When mapped, the features form a series of largely NE-SW 51 52 675 trending lineaments (Fig. 20). Although imaging of the discontinuities is best in the SW of the 53 54 676 survey, where there are fewer igneous rocks, it is evident that many of the igneous rocks 55 56 677 are aligned with these features, suggesting they must have exerted some topographical or 57 678 structural control when the igneous rocks were erupted or emplaced into the Nappamerri 58 59 679 Trough (Fig. 20). As they do not resemble any sedimentary features such as valleys or fluvial 60 61 62 63 64 65 23

680 systems, we interpret these features to be faulting or fracturing of the Eromanga succession 1 2 681 above the Nappamerri Trough. 3 4 682 Determining the tectonic activity responsible for the faulting within the Nappamerri Trough 5 6 683 and, hence, the location and morphology of igneous rocks within the WVP is difficult due to 7 8 684 the complex structural and stress history of the Cooper Basin. Throughout the basin, a 9 10 685 conjugate set of large NNE-SSW and field scale SE-NW striking dextral strike-slip faults 11 12 686 developed under SSE-NNW strike-slip stress conditions (Kulikowski et al., 2018). This is 13 687 pertinent when applied to the central Nappamerri Trough, as Kulikowski et al. (2018) 14 15 688 identified a series of vertical SE-NW structural lineaments with normal displacement to no 16 17 689 displacement. Due to their vertical nature, it is thought that these faults developed as strike 18 19 690 slip faults during successive periods of flexural relaxation or sag. The faulting identified 20 21 691 within this study is also determined to consist of little offset with an orientation that 22 23 692 matches that of the strike-slip faulting determined by Kulikowski et al., (2018) (Fig. 20). We 24 693 surmise that sag within the basin produced a series of faults that controlled the morphology 25 26 694 of igneous rocks in the WVP. 27 28 29 695 30 31 696 8.3 The Broader Record of Jurassic Volcanism in Eastern Australia 32 33 34 697 We believe it is important to consider the WVP in the context of the broader record of 35 36 698 Jurassic volcanic activity in eastern Australia (Table 2 & Fig. 21). Coeval with the eruption of 37 38 699 the WVP, the Eromanga Basin was undergoing post-compressional flexural relaxation with 39 40 700 thermally controlled subsidence in the absence of significant fault control (Gallagher & 41 42 701 Lambeck, 1989). Subsidence has been attributed to subduction of the Pacific plate beneath 43 44 702 southern and eastern Australia, during which time rifting also initiated between Australia and 45 703 Antarctica (Griffiths, 1975; Johnstone et al., 1973). 46 47 48 704 Evidence for Jurassic volcanic activity is pervasive throughout the sedimentary basins of 49 50 705 eastern Australia, manifested by volcanic arc-derived sediment within the Eromanga Basin 51 52 706 (Boult et al., 1998), silicic tuffs in the Surat Basin (Wainman et al., 2015) and widespread 53 54 707 volcanogenic zircons within the Eromanga Basin (Bryan et al., 1997). This volcaniclastic 55 708 material is thought to be derived from an acid to intermediate volcanic arc positioned off 56 57 709 the coast of Queensland during the Jurassic, however, the remnants of this arc volcanism 58 59 710 are yet to be identified (Paton, 1986, Boult et al., 1997). Jurassic alkali basalt has been 60 61 62 63 64 65 24

711 intersected on the Marion Plateau (~400 km east of Townsville in Queensland), although 1 2 712 this may also be related to rifting in the region during the Jurassic (Isern et al., 2002). 3 4 713 Around 1500 km south of the Marion Plateau, mafic and ultramafic igneous rocks are noted 5 6 714 throughout the Eastern Highlands and Sydney Basin. Dykes of the Sydney area intrude rocks 7 8 715 as young as 235 Ma with K-Ar dating suggesting ages of between 193 and 46.9 Ma 9 10 716 (McDougall and Wellman, 1976, Embleton et al., 1985, Pells, 1985). To the north west of the 11 12 717 Syndey Basin, in New South Wales, lower Jurassic intrusions and volcanics of the Garawilla 13 718 alkali basalts are noted in the Gunnedah Basin (195-141 Ma) (Sutherland, 1978, Pratt, 1998, 14 15 719 Gurba & Weber, 2001). The intermediate to mafic Dubbo volcanics are also recognised in 16 17 720 New South Wales (236-170 Ma) (Dulhunty, 1976, Embleton et al., 1985, Black, 1998, 18 19 721 Warren et al., 1999). Further south of the Sydney and Gunnedah basins, Jurassic volcanics 20 21 722 are scattered throughout Victoria and Tasmania (Veevers & Conaghan, 1984). These include 22 23 723 voluminous tholeiitic intrusions in Tasmania (183 Ma) that are thought to have been buried 24 724 under a thick pile of largely eroded extrusive volcanics that have a detrital zircon age range 25 26 725 of 182 ± 4 Ma (Sutherland, 1978; McDougall & Wellman, 1976, Bromfield et al., 2007, Ivanov 27 28 726 et al., 2017). In Eastern Victoria, Jurassic activity included a 191 Ma dyke swarm of alkali 29 30 727 basalts (Soesoo et al., 1999). The geochemical source characteristics of the Eastern Victoria 31 32 728 alkalia basalts are suggestive of subcontinental lithospheric mantle, like the proposed source 33 34 729 of the Late Cenozoic Newer Volcanic Province in western Victoria (Elburg & Soesoo, 1999). 35 36 730 Around 1000 km south of the WVP, the Wisanger Basalt is a ~170 Ma, 20 km fragmented 37 38 731 lava flow emplaced on top of Permian fluviatile sediments on Kangaraoo Island (McDougall & 39 40 732 Wellman, 1976). Geochemically, it is similar to the Tasmanian and Antarctic tholeiitic 41 42 733 dolerite and basalts that are usually attributed to the Ferrar Large Igneous Province and 43 44 734 extension that latterly resulted in the separation of Australia and Antarctica (Compston et 45 735 al., 1968; Milnes et al., 1982). Of note in South Australia, Jurassic kimberlites record the 46 47 736 extension of Mesozoic kimberlites found along the margin of southern Gondwana, above 48 49 737 the subducting Pacific plate (Tappert et al., 2009), differing petrologically from the 50 51 738 predominantly basaltic volcanism found elsewhere in eastern Australia. 52 53 54 739 Plate reconstructions indicate that the Eromanga Basin was located at significant distances 55 740 (at least 750 km) from the oceanic trench of the subducting Pacific plate (Veevers & 56 57 741 Conaghan, 1984; Ivanov et al., 2017) (Fig. 21). We therefore believe the Warnie Volcanic 58 59 742 Province to be an intraplate volcanic province and, as the origin of intraplate volcanism can 60 61 62 63 64 65 25

743 often be contentious (Conrad et al., 2011), it is important to consider the source of this 1 2 744 volcanism and implications for the formation of intraplate volcanism. 3 4 745 8.4 The Origin of the Warnie Volcanic Province 5 6 7 746 The WVP was located far from active plate boundaries during the Jurassic (Fig. 21). When 8 9 747 considering the source of intraplate volcanism, several different mechanisms must be 10 11 748 considered: 12 13 749 • The presence of a mantle plume 14 15 750 • Asthenospheric upwelling due to extension 16 17 751 • Local scale mantle convection 18 19 752 Mantle plumes are typically associated with the eruption of voluminous flood basalt 20 21 753 provinces that often mark the earliest volcanic activity of major hot spots (Richards et al., 22 23 754 1989). Furthermore, mantle plumes cause dynamic uplift of the land’s surface of up to 24 755 several hundred kms followed by surface subsidence due to the withdrawal of mantle plume 25 26 756 material and loading of the crust with the volcanic sequence (Nadin et al., 1997; Dam et al., 27 28 757 1998; Hartley et al., 2011; Hardman et al., 2018). No evidence of major surface uplift in the 29 30 758 Cooper and Eromanga Basins is coeval with the emplacement and eruption of the WVP 31 32 759 (Hall et al., 2016). Furthermore, subsidence and sag throughout the emplacement of the 33 34 760 WVP is minor, with no large changes in sedimentary facies noted throughout the Jurassic 35 36 761 lower non-marine Eromanga succession (Alexander & Hibburt, 1996). No major crustal 37 762 and/or lithospheric extension is evidenced by the lack of major Jurassic faults, during a time 38 39 763 in which the basin underwent post-compressional flexural relaxation in a strike slip 40 41 764 extensional regime (Lowe-Young, 1997; Kulikowski et al., 2018). Furthermore, the small 42 43 765 spatial area covered by the Warnie Volcanic Province (~7500 km2 within the Nappamerri 44 45 766 Trough area) and, by extension, the volume of magma emplaced, is too low to be related to 46 47 767 a mantle plume source (Conrad et al., 2011). 48 49 768 Low-effusive volcanism occurring within tectonic plates has been also attributed to 50 51 769 several locally operating processes, such as minor upwelling plumes, downwelling drops and 52 53 770 sub-lithospheric or edge-driven convection (Courtillot et al., 2003; Ballmer et al., 2009; 54 55 771 Conrad et al., 2011). In the case of edge-driven convection, mantle flow can induce upwelling 56 57 772 and volcanism through interaction with lithospheric or asthenospheric heterogeneities 58 773 (Conrad et al., 2011; Davies & Rawlinson, 2014). In the Newer Volcanic Province in South 59 60 61 62 63 64 65 26

774 Australia, <5 kyr volcanism formed as a product of edge driven convection is noted to

1 2 2 775 consist of basaltic monogenetic volcanoes <4 km in size covering an area of up to 40,000 3 2 776 km (Demidjuk et al., 2007; Davies & Rawlinson, 2014). This style of volcanism (basaltic, with 4 5 777 individual volcanoes like Mount Gambier of a similar scale to the volcanoes imaged in the 6 7 778 Nappamerri Trough area (~1.5 x 1.5 km)) and the areal extent (7500 km2 that could be 8 9 779 extended to almost 20,000 km2 if the magnetic anomalies are found to be igneous in nature) 10 11 780 are similar in scale to the igneous rocks in the Newer Volcanic Province. Convection within 12 13 781 the asthenosphere can be induced by changes in lithospheric thickness. Although not much 14 15 782 is known about the crustal structure below the eastern Nappamerri Trough, seismic 16 783 reflection profiles have revealed that Devonian troughs to the east of the study area are 17 18 784 associated with crustal thinning of 7 – 10 km (Mathur, 1983). Furthermore, on a continental 19 20 785 scale, the Moho is observed to shallow to ~20 km below the Cooper Basin (and more 21 22 786 broadly, Central Australia) (Fig. 21)(Kennett et al., 2011). Therefore, there is observable 23 24 787 lithospheric thinning below the basins in Central Australia that could have produced edge 25 26 788 driven convection. 27 28 789 However, because Central Australia was relatively inactive during the Jurassic, we 29 30 790 must consider driving mechanisms for asthenospheric flow beneath the continent during the 31 32 791 eruption and emplacement of the WVP. As we have already detailed, the Pacific plate was 33 34 792 subducting beneath eastern Australia during the Jurassic. In intraplate volcanic provinces 35 36 793 adjacent to subduction zones (e.g. Western North America, China), there is a causal link 37 794 between subduction and intraplate volcanism, in that subduction below the continental crust 38 39 795 acts as a driving force for asthenospheric shear and, hence, the mantle upwelling that 40 41 796 produces intraplate volcanism (Conrad et al., 2011; Tang et al., 2014; Zhou et al., 2018). If 42 43 797 the extension in the area during the Jurassic is not great enough to stimulate volcanism, then 44 45 798 an alternative model may involve rapid asthenospheric shear produced by the subducting 46 47 799 Pacific Plate, localised beneath SW Queensland due to edge driven convection. 48 49 800 We propose a model for the Warnie Volcanic Province based on our understanding 50 51 801 of the lithospheric and geodynamic state of Central Australia in the Jurassic. We propose 52 53 802 that asthenospheric shear above the subducting pacific plate stimulated mantle flow below 54 55 803 Australia (Fig. 20B). Localisation of mantle flow occurred beneath southwest Queensland 56 57 804 because of edge driven convection lead to emplacement of the Warnie Volcanic Province 58 805 above the Nappamerri Trough. Despite our proposed model, we strongly believe that more 59 60 806 work needs to be conducted on the area before it can be concluded what the source of the 61 62 63 64 65 27

807 WVP is. In the Newer Volcanic Province of southeastern Australia, geochemistry, major and 1 2 808 trace element analysis, provided insights into the formation of a volcanic province through 3 809 edge driven convection (Demidjuk et al., 2007). More recent geochemical and geophysical 4 5 810 insights have furthered this discussion studies suggesting additional felsic asthenospheric 6 7 811 input (Sutherland et al., 2014), shear-driven upwelling (Oosting et al., 2016) and intermittent 8 9 812 volcanism through interaction of transient mechanisms with the passage of a mantle plume 10 11 813 (Rawlinson et al., 2017). As such, we would strongly recommend further studies to be 12 13 814 conducted on the geochemical signature of the basalts of the WVP. 14 15 815 Due to its low volume, small areal extent and predominantly basaltic nature, we do 16 17 816 not believe that the WVP was the source of the volcanically derived sediment that was 18 19 817 distributed throughout much of Australia during the Mesozoic (Boult et al., 1998; 20 21 818 MacDonald et al., 2013; Barham et al., 2016). However, our findings raise the possibility that 22 23 819 other, yet unidentified, intra-basinal volcanic sources may contribute to Mesozoic 24 820 volcanogenic sedimentation in eastern Australia. 25 26 27 821 Finally, it must be considered why the WVP has not been documented until now 28 29 822 despite the presence of igneous rocks being known for over three decades. By our 30 31 823 estimates, only 0.13% of the wells drilled in the Cooper Basin between 1959 and 2015 32 33 824 drilled the WVP (based on Hall et al., 2016’s estimate of the number of wells), with 35 years 34 825 of exploration since the first well that drilled the volcanics. This is despite the WVP 35 36 826 occupying ~6% of the geographic extent of the Cooper Basin. Largely, this is due to the lack 37 38 827 of data and attention given to the Nappamerri Trough region until recently. Acquisition of 39 40 828 the high-quality Winnie 3D seismic reflection survey facilitated confident delineation of the 41 42 829 WVP. This study also underlines the importance for collaboration between industry and 43 44 830 academia. Whilst igneous rocks have been described within industry reports and imaged 45 831 within data acquired, they have been overlooked within the literature. The obscurity of the 46 47 832 WVP in an area of such intense exploration points to the probability of other undiscovered 48 49 833 volcanic provinces globally. It is therefore an important analogue in the search for 50 51 834 undiscovered intraplate volcanism that may inform our understanding of the mantle 52 53 835 processes occurring beneath continental interiors. 54 55 836 56 57 58 59 60 61 62 63 64 65 28

837 9. Conclusions 1 2 838 We have integrated seismic, well, gravity and magnetic data and clarified the extent and 3 4 839 character of igneous rocks emplaced above the Nappamerri Trough of the Cooper Basin 5 6 840 within Eromanga Basin stratigraphy. Monogenetic volcanoes, igneous intrusions and altered

7 2 8 841 compound lava flows extending over ~7500 km are proposed to have been active between 9 10 842 ~180 – 160 Ma forming part of the proposed ‘Warnie Volcanic Province.’ Regionally, the 11 843 morphology and distribution of igneous rocks is controlled by basement structure. On a 12 13 844 continental scale, we interpret the Warnie Volcanic Province to be a product of intraplate 14 15 845 convective upwelling above the subducting Pacific slab. 16 17 18 846 19 20 847 10. Acknowledgements 21 22 848 We wish to thank Santos Ltd. for providing us with the Snowball 3D seismic survey. In 23 24 849 particular we wish to thank Jenni Clifford and Lance Holmes who provided helpful feedback 25 26 850 and 2D seismic lines covering the Lambda 1, Orientos 2 and Warnie East 1 wells. We also 27 851 wish to thank Beach Energy, in particular Rob Menpes, for the helpful discussions and 28 29 852 feedback on the manuscript in addition to helping us with the analysis of the magnetic data. 30 31 853 The work contained in this paper contains work conducted during a PhD study undertaken 32 33 854 as part of the Natural Environment Research Council (NERC) Centre for Doctoral Training 34 35 855 (CDT) in Oil & Gas [grant number NEM00578X/1] and is fully funded by NERC whose 36 37 856 support is gratefully acknowledged. Lastly, the two anonymous reviews of the manuscript 38 39 857 are thanked for their insightful and constructive comments that significantly improved the 40 858 work presented. 41 42 43 859 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 29

860 11. References 1 2 861 Aarnes, I., Planke, S., Trulsvik, M. and Svensen, H., 2015. Contact metamorphism and thermogenic 3 4 862 gas generation in the Vøring and Møre basins, offshore Norway, during the Paleocene–Eocene 5 863 thermal maximum. Journal of the Geological Society, 172(5), pp.588-598. 6 7 8 864 Alexander, E.M. and Hibburt, J.E., 1996, Petroleum Geology of South Australia, Volume 2: Eromanga 9 865 Basin. 10 11 12 866 Allen P., 1998. Kappa 1 Well Completion Report. Compiled for Santos Limited. 13 14 867 Archer, S.G., Bergman, S.C., Iliffe, J., Murphy, C.M. and Thornton, M., 2005. Palaeogene igneous 15 16 868 rocks reveal new insights into the geodynamic evolution and petroleum potential of the Rockall 17 18 869 Trough, NE Atlantic Margin. Basin Research, 17(1), pp.171-201. 19 20 870 Apak, S.N., Stuart, W.J., Lemon, N.M. and Wood, G., 1997. Structural evolution of the Permian- 21 22 871 Triassic Cooper Basin, Australia: relation to hydrocarbon trap styles. AAPG bulletin, 81(4), pp.533- 23 872 555. 24 25 26 873 Ballmer, M.V., Van Hunen, J., Ito, G., Bianco, T.A. and Tackley, P.J., 2009. Intraplate volcanism with 27 874 complex age‐distance patterns: A case for small‐scale sublithospheric convection. Geochemistry, 28 29 875 Geophysics, Geosystems, 10. 30 31 876 Barham, M., Kirkland, C.L., Reynolds, S., O’Leary, M.J., Evans, N.J., Allen, H., Haines, P.W., Hocking, 32 33 877 R.M., McDonald, B.J., Belousova, E. and Goodall, J., 2016. The answers are blowin’in the wind: Ultra- 34 878 distal ashfall zircons, indicators of Cretaceous super-eruptions in eastern Gondwana. Geology, 44(8), 35 36 879 pp.643-646. 37 38 39 880 Bell & Butcher, 2002. On the emplacement of sill complexes: evidence from the Faroe-Shetland 40 881 Basin. Geological Society, London, Special Publications(2002),197(1):307 41 42 43 882 BlackLACK L.p. 1998. SHRIMP zircon UIPb isotopic age dating of samples from the Dubbo 1:250000 44 883 Sheet area, batch 2. Geological Survey of New South Wales, File GS1998/127 (unpublished). 45 46 47 884 Boothby, P.G., 1986. Warnie East 1 Well Completion Report. Compiled for Delhi Petroleum Pty 48 885 Ltd. 49 50 51 886 Boult, P.J., Ryan, M.J., Michaelsen, B.H., McKirdy, D.M., Tingate, P.R., Lanzilli, E. and Kagya, M.L., 52 1997. The Birkhead-Hutton (!) Petroleum System of the Gidgealpa Area, Eromanga Basin, Australia. 53 887 54 55 888 Boult, P.J., Lanzilli, E., Michaelsen, B.H., McKirdy, D.M. and Ryan, M.J., 1998. A new model for the 56 57 889 Hutton/Birkhead reservoir/seal couplet and the associated Birkhead-Hutton (!) petroleum 58 890 system. The APPEA Journal, 38(1), pp.724-744. 59 60 61 62 63 64 65 30

891 Bromfield, K.E., Burrett, C.F., Leslie, R.A. & Meffre, S., 2007. Jurassic volcani-clastic basaltic andesite - 1 892 dolerite sequence in Tasmania: new age constraints for fossil plants from Lune River. Australian 2 3 893 Journal of Earth Sciences, 54, 965-974. 4 5 6 894 Bryan, S.E., Constantine, A.E., Stephens, C.J., Ewart, A., Schön, R.W. and Parianos, J., 1997. Early 7 895 Cretaceous volcano-sedimentary successions along the eastern Australian continental margin: 8 9 896 Implications for the break-up of eastern Gondwana. Earth and Planetary Science Letters, 153(1), pp.85- 10 11 897 102 12 13 898 Bucknill, M., 1990. Orientos 2 Well Completion Report. Compiled for Delhi Petroleum Pty Limited. 14 15 899 Burger, D. and Senior, B.R., 1979. A revision of the sedimentary and palynological history of the 16 17 900 northeastern Eromanga Basin, Queensland. Journal of the Geological Society of Australia, 26(3-4), 18 19 901 pp.121-133. 20 21 902 Compston, W., McDougall, I. and Heier, K.S., 1968. Geochemical comparison of the mesozoic 22 23 903 basaltic rocks of Antarctica, South Africa, South America and Tasmania. Geochimica et Cosmochimica 24 25 904 Acta, 32(2), pp.129-149. 26 27 905 Courtillot, V., Davaille, A., Besse, J. and Stock, J., 2003. Three distinct types of hotspots in the Earth’s 28 906 mantle. Earth and Planetary Science Letters, 205, 295-308. 29 30 31 907 Davies, D.R. and Rawlinson, N., 2014, On the origin of recent intraplate volcanism in 32 908 Australia, Geology, v. 42, pp. 1031-1034. 33 34 35 909 Demidjuk, Z., Turner, S., Sandiford, M., George, R., Foden, J. and Etheridge, M., 2007, U-series 36 910 isotope and geodynamic constraints on mantle melting processes beneath the Newer Volcanic 37 38 911 Province in South Australia, Earth and Planetary Science Letters, v. 261, p. 517-533. 39 40 41 912 Draper, J.J. ed., 2002. Geology of the Cooper and Eromanga Basins, Queensland. Department of Natural 42 913 Resources and Mines 43 44 45 914 Dulhunty,ULHUNTY J.A. 1976. Potassium-argon ages of igneous rocks in the Wollar-Rylstone 46 915 region, New South Wales. Royal Society of New South Wales, Journal and Proceedings 109, 35-39. 47 48 49 916 Elburg, M.A. & Soesoo, A., 1999. Jurassic alkali-rich volcanism in Victoria (Australia): lithospheric 50 917 versus asthenospheric source. Journal of African Earth Sciences, 29(1), 269-—280. 51 52 53 918 Elliot, D.H. and Fleming, T.H., 2004. Occurrence and dispersal of magmas in the Jurassic Ferrar large 54 919 igneous province, Antarctica. Gondwana Research, 7(1), pp.223-237. 55 56 57 58 59 60 61 62 63 64 65 31

920 EmbletonMBLETON B.J.J., SchmidtCHMIDT P.w., HamiltonAMILTON L.H. & RileyILEY G.H. 1985. 1 921 Dating volcanism in the Sydney Basin; evidence from K-Ar ages and palaeomagnetism. Geological 2 3 922 Society of Australia, Journal 23, 243-248. 4 5 6 923 Exon, N.F. and Burger, D., 1981. Sedimentary cycles in the Surat Basin and global changes of sea 7 924 level. Bureau of Mineral Resources Journal of Australian Geology and Geophysics, 6, pp.153-159. 8 9 10 925 Fishwick, S., Heintz, M., Kennett, B.L.N., Reading, A.M. and Yoshizawa, K., 2008. Steps in lithospheric 11 926 thickness within eastern Australia, evidence from surface wave tomography. Tectonics, 27(4). 12 13 14 927 Gallagher, K. and Lambeck, K..U.R.T., 1989, Subsidence, sedimentation and sea‐level changes in the 15 928 Eromanga Basin, Australia, Basin Research, v. 2, p. 115-131. 16 17 18 929 Goldstein, B., Menpes, S., Hill, A., Wickham, A., Alexander, E., Jarosz, M., Pepicelli, D., Malavazos, M., 19 930 Staritski, K., Taliangis, P., Coda, J., Hill, D. & Webb, M. 2012. Roadmap for Unconventional Gas 20 21 931 Projects in South Australia. South Australia Department for Manufacturing, Innovation, Trade, 22 23 932 Resources and Energy, Energy Resources Division, 24 25 933 D.I. Gravestock, J.E. Hibburt, J.F. Drexel (Eds.), Petroleum Geology of South Australia, Volume 4: 26 27 934 Cooper Basin, Department of Primary Industries and Resources (1998), pp. 1-6 28 29 935 Greenstreet, C. 2015. From play to production: the Cooper unconventional story — 20 years in 30 31 936 the making. APPEA 2015 extended abstract. 32 33 937 Griffiths, J.R., 1975. New Zealand and the Southwest Pacific margin of Gondwanaland. In: K.S.W. 34 35 938 Campbell (Editor), Gondwana Geology. A.N.U. Press, Canberra, pp. 619- 637. 36 37 Grove, C., Jerram, D.A., Gluyas, J.G. and Brown, R.J., 2017. Sandstone diagenesis in sediment–lava 38 939 39 940 sequences: exceptional examples of volcanically driven diagenetic compartmentalization in Dune 40 41 941 Valley, Huab Outliers, NW Namibia. Journal of Sedimentary Research, 87, 1314-1335. 42 43 942 Gurba, L.W. and Weber, C.R., 2001, Effects of igneous intrusions on coalbed methane potential, 44 45 943 Gunnedah Basin, Australia, International Journal of Coal Geology, v. 46, p. 113-131. 46 47 944 Hall, L.S., Hill, A.J., Troup, A., Korsch, R.J., Radke, B.M., Nicoll, R.S., Palu, T., Wang, L. and Stacey, A., 48 49 945 2016, Cooper Basin Architecture and Lithofacies, Geoscience Australia. 50 51 946 Hall, L.S, Palu, T.J., Murray, A.P., Boreham, C.J., Edwards, D.S., Hill, A.J., Troup, A., 2018. 52 53 947 Hydrocarbon Prospectivity of the Cooper Basin, Australia. AAPG Bulletin. 54 55 56 948 Hamilton, D.S., Holtz, M.H., Ryles, P., Lonergan, T. and Hillyer, M., 1998. Approaches to identifying 57 949 reservoir heterogeneity and reserve growth opportunities in a continental-scale bed-load fluvial 58 59 950 system: Hutton Sandstone, Jackson field, Australia. AAPG bulletin, 82(12), pp.2192-2219. 60 61 62 63 64 65 32

951 Hardman, J.P., Schofield, N., Jolley, D.W., Holford, S.P., Hartley, A.J., Morse, S., Underhill, J.R., 1 952 Watson, D.A. and Zimmer, E.H., 2018. Prolonged dynamic support from the Icelandic plume of the 2 3 953 NE Atlantic margin. Journal of the Geological Society, 175(3), pp.396-410. 4 5 6 954 Hardman, J., Schofield, N., Jolley, D., Hartley, A., Holford, S. and Watson, D., 2019. Controls on the 7 955 distribution of volcanism and intra-basaltic sediments in the Cambo–Rosebank region, West of 8 9 956 Shetland. Petroleum Geoscience, 25(1), pp.71-89. 10 11 957 Hillis, R.R., Morton, J.G.G., Warner, D.S. and Penney, R.K., 2001. Deep basin gas: A new exploration 12 13 958 paradigm in the Nappamerri Trough, Cooper Basin, South Australia. The APPEA Journal, 41(1), 14 15 959 pp.185-200. 16 17 960 Isern, A.R., Anselmetti, F.S. and Blum, P., 2002. Constraining Miocene sea level change from 18 19 961 carbonate platform evolution, Marion Plateau, northeast Australia, Sites 1192–1199. In Proceedings of 20 962 the Ocean Drilling Program. Initial Reports, (Vol. 194, p. 88.) 21 22 23 963 Ivanov, A.V., Meffre, S., Thompson, J., Corfu, F., Kamenetsky, V. S., Kamenetsky, M.B. & Dementrova, 24 25 964 E. I., 2017. Timing and genesis of the Karoo-Ferrer large igneous province: New high precision U-Pb 26 965 data for Tasmania confirm short duration of the major magmatic pulse. Chemical Geology, 455, 32- 27 28 966 43. 29 30 967 Jerram, D.A. & Widdowson, M. 2005. The anatomy of Continental Flood Basalt Provinces: geological 31 32 968 constraints on the processes and products of flood volcanism. Lithos, 79(3), 385-405. 33 34 969 Johnstone, M.H., Lowry, D.C. and Quilty, P.G., 1973. The geology of South-western Australia - a 35 36 970 review. J. Proc. R. Sot. West. Aus., 56,: 5-15. 37 38 971 Kapel, A., 1966. The Cooper's Creek Basin. The APPEA Journal, 6, 71-75. 39 40 41 972 Kelley, S., (2002.) K‐Ar and Ar‐Ar Dating, in noble gases in geochemistry and cosmochemistry. 42 973 In: Reviews in Mineralogy and Geochemistry, Vol. 47 (Ed. by D. Porcelli, C.J. Ballentine & R. Wieler), pp. 43 44 974 785–818, Mineral Society America, Washington, DC. 45 46 Kennett, B., Salmon, M., Saygin, E. and AusMoho Working Group, 2011.., AusMoho: the variation of 47 975 48 976 Moho depth in Australia, Geophysical Journnral International, 187, 946-958. , 49 50 977 2011, doi:10.1111/j.1365-246X.2011.05194.x 51 52 978 Khair, H.A., Cooke, D. and Hand, M., 2013. The effect of present day in situ stresses and paleo- 53 54 979 stresses on locating sweet spots in unconventional reservoirs, a case study from Moomba-Big Lake 55 56 980 fields, Cooper Basin, South Australia. Journal of Petroleum Exploration and Production Technology, 3(4), 57 981 pp.207-221. 58 59 60 61 62 63 64 65 33

982 Khair, H.A., Cooke, D. and Hand, M., 2015. Paleo stress contribution to fault and natural fracture 1 983 distribution in the Cooper Basin. Journal of Structural Geology, 79, pp.31-41. 2 3 4 984 Kuang, K.S., 1985. History and style of Cooper? Eromanga Basin structures. Exploration 5 6 985 Geophysics, 16(3), pp.245-248. 7 8 986 Kulikowski, D., Amrouch, K., Al Barwani, K.H.M., Liu, W. and Cooke, D., 2015, September. Insights 9 10 987 into the Tectonic Stress History and Regional 4-D Natural Fracture Distribution in the Australian 11 988 Cooper Basin Using Etchecopar’s Calcite Twin Stress Inversion Technbique. In International 12 13 989 Conference & Exhibition. 14 15 990 Kulikowski, D. and Amrouch, K., 2017. Combining geophysical data and calcite twin stress inversion 16 17 991 to refine the tectonic history of subsurface and offshore provinces: A case study on the 18 19 992 Cooper‐Eromanga Basin, Australia. Tectonics, 36(3), pp.515-541. 20 21 993 Kulikowski, D., Amrouch, K., Cooke, D. and Gray, M.E., 2018, Basement structural architecture and 22 23 994 hydrocarbon conduit potential of polygonal faults in the Cooper‐Eromanga Basin, 24 25 995 Australia, Geophysical Prospecting, v. 66, p. 366-396. 26 27 996 Lanzilli, E., 1999. The Birkhead Formation: reservoir characterisation of the Gidgealpa south dome and 28 29 997 sequence stratigraphy of the Eromanga Basin, Australia (Doctoral dissertation, University of South 30 998 Australia). 31 32 33 999 Liu, P., Mao, J., Cheng, Y., Yao, W., Wang, X. and Hao, D., 2017. An Early Cretaceous W-Sn deposit 34 1000 and its implications in southeast coastal metallogenic belt: Constraints from U-Pb, Re-Os, Ar-Ar 35 36 1001 geochronology at the Feie'shan W-Sn deposit, SE China. Ore Geology Reviews, 81, 112-122. 37 38 1002 Lowe-Young, B.S., Mackie, S.I. and Heath, R.S., 1997. The Cooper-Eromanga petroleum system, 39 40 1003 Australia: Investigation of essential elements and processes. 41 42 1004 MacDonald, J.D., Holford, S.P., Green, P.F., Duddy, I.R., King, R.C. and Backé, G., 2013. Detrital 43 1005 zircon data reveal the origin of Australia’s largest delta system. Journal of the Geological 44 45 1006 Society, 170(1), pp.3-6. 46 47 48 1007 Mackie, S., 2015, September. History of petroleum exploration and development in the Cooper and 49 1008 Eromanga basins. In AAPG/SEG International Conference & Exhibition, Melbourne, Australia. Search and 50 51 1009 Discovery Article #10814 52 53 1010 Magee, C., Jackson, C.L. and Schofield, N., 2014. Diachronous sub‐volcanic intrusion along 54 55 1011 deep‐water margins: Insights from the Irish Rockall Basin. Basin Research, 26(1), pp.85-105. 56 57 1012 Mathur, S.P., 1983, Deep crustal reflection results from the central Eromanga Basin, 58 59 1013 Australia, Tectonophysics, v. 100, pp. 163-173. 60 61 62 63 64 65 34

1014 McDougall, I. & Wellman, P. 1976. Potassium argon ages for some Australian Mesozoic igneous 1 1015 rocks. Journal of the Geological Society of Australia, 23, 1-9. 2 3 4 1016 McLean, C.E., Schofield, N., Brown, D.J., Jolley, D.W. and Reid, A., 2017. 3D seismic imaging of the 5 6 1017 shallow plumbing system beneath the Ben Nevis Monogenetic Volcanic Field: Faroe–Shetland 7 1018 Basin. Journal of the Geological Society, 174(3), pp.468-485 8 9 10 1019 Meeuws, F.J., Holford, S.P., Foden, J.D. and Schofield, N., 2016. Distribution, chronology and causes 11 1020 of Cretaceous–Cenozoic magmatism along the magma-poor rifted southern Australian margin: Links 12 13 1021 between mantle melting and basin formation. Marine and Petroleum Geology, 73, pp.271-298. 14 15 1022 Meixner, T.J., Gunn, P.J., Boucher, R.K., Yeates, T.N., Richardson, L.M. and Frears, R.A., 2000. The 16 17 1023 nature of the basement to the Cooper Basin region, South Australia. Exploration Geophysics, 31(2), 18 19 1024 pp.24-32. 20 21 1025 Menpes, S., Hill, A.J. & Pepicelli, D. 2013. Characteristics of the Gidgealpa Group Composite 22 23 1026 Resource Play in the Cooper Basin, South Australia. Unconventional Resources Technology 24 25 1027 Conference, Denver, 2013. 26 27 1028 Middleton, A.W., Uysal, I.T., Bryan, S.E., Hall, C.M. and Golding, S.D., 2014. Integrating 40Ar–39Ar, 28 29 1029 87Rb–87Sr and 147Sm–143Nd geochronology of authigenic illite to evaluate tectonic reactivation in 30 1030 an intraplate setting, central Australia. Geochimica et Cosmochimica Acta, 134, pp.155-174. 31 32 33 1031 Middleton, A.W., Uysal, I.T. and Golding, S.D., 2015. Chemical and mineralogical characterisation of 34 1032 illite–smectite: Implications for episodic tectonism and associated fluid flow, central 35 36 1033 Australia. Geochimica et Cosmochimica Acta, 148, pp.284-303. 37 38 1034 Millett, J.M., Hole, M.J., Jolley, D.W., Schofield, N. and Campbell, E., 2016. Frontier exploration and 39 40 1035 the North Atlantic Igneous Province: new insights from a 2.6 km offshore volcanic sequence in the 41 42 1036 NE Faroe–Shetland Basin. Journal of the Geological Society, 173(2), pp.320-336. 43 44 1037 Milnes, A.R., Cooper, B.J. and Cooper, J.A., 1982. The Jurassic Wisanger Basalt of Kangaroo Island, 45 46 1038 South Australia. Transactions of the Royal Society of South Australia, 106, pp.1-13. 47 48 1039 Murray, C.G., 1994. Basement cores from the Tasman fold belt system beneath the Great Artesian Basin in 49 50 1040 Queensland. Department of Minerals and Energy, Queensland. 51 52 1041 Nadin, P.A., Kusznir, N.J. and Cheadle, M.J., 1997, Early Tertiary plume uplift of the North Sea and 53 54 1042 Faeroe-Shetland basins, Earth and Planetary Science Letters, v. 148, p. 109-127. 55 56 Nelson, C.E., Jerram, D.A. and Hobbs, R.W., 2009, Flood basalt facies from borehole data: 57 1043 58 1044 implications for prospectivity and volcanology in volcanic rifted margins, Petroleum Geoscience, v. 15, 59 60 1045 p. 313-324. 61 62 63 64 65 35

1046 Németh, K., 2010. Monogenetic volcanic fields: Origin, sedimentary record, and relationship with 1 1047 polygenetic volcanism. What is a Volcano?, 470, p.43. 2 3 4 1048 Németh, K. and Kereszturi, G., 2015. Monogenetic volcanism: personal views and 5 6 1049 discussion. International Journal of Earth Sciences, 104(8), pp.2131-2146. 7 8 1050 Oostingh, K.F., Jourdan, F., Merle, R. & Chiradia, M., 2016. Spatio-temporal geochemical evolution of 9 10 1051 the SE Australian upper mantle deciphered from the Sr, Nd and Pb isotope compositions of 11 1052 Cenozoic intraplate volcanic rocks. Journal of Petrology, 57, 1509 - 1530. 12 13 14 1053 Pande, K., Cucciniello, C., Sheth, H., Vijayan, A., Sharma, K.K., Purohit, R., Jagadeesan, K.C. and 15 1054 Shinde, S., 2017. Polychronous (Early Cretaceous to Palaeogene) emplacement of the Mundwara 16 17 1055 alkaline complex, Rajasthan, India: 40 Ar/39 Ar geochronology, petrochemistry and 18 1056 geodynamics. International Journal of Earth Sciences, 106, 1487-1504. 19 20 1057 Paton, I.M., 1986, The Birkhead Formation-a Jurassic petroleum reservoir, in D.I. Gravestock, P.S. 21 22 1058 Moore, and G.M. Pitt, (eds.), Contributions to the Geology and Hydrocarbon Potential of the 23 24 1059 Eromanga Basin: Geological Society of Australia Special Publication No. 12, p. 195-201. 25 26 1060 Pells, P.J.N., 1985. Engineering geology of the Sydney Region, 407, pp. Routledge, London. 27 28 29 1061 Pitkin, M.C., Wadham, T.H., McGowen, J.M. and Thom, W.W., 2012, January. Taking the first steps: 30 1062 Stimulating the Nappamerri Trough resource play. In SPE Asia Pacific Oil and Gas Conference and 31 32 1063 Exhibition. Society of Petroleum Engineers. 33 34 1064 Planke, S., Symonds, P.A., Alvestad, E. and Skogseid, J., 2000. Seismic volcanostratigraphy of 35 36 1065 large‐volume basaltic extrusive complexes on rifted margins. Journal of Geophysical Research: Solid 37 38 1066 Earth, 105(B8), pp.19335-19351. 39 40 1067 Planke, S., Rasmussen, T., Rey, S.S. and Myklebust, R., 2005, January. Seismic characteristics and 41 42 1068 distribution of volcanic intrusions and hydrothermal vent complexes in the Vøring and Møre basins. 43 44 1069 In Geological Society, London, Petroleum Geology Conference series, (Vol. 6, No. 1, pp. 833-844).. 45 1070 Geological Society of London. 46 47 48 1071 Planke, S., Millett, J.M., Maharjan, D., Jerram, D.A., Abdelmalak, M.M., Groth, A., Hoffmann, J., 49 1072 Berndt, C. and Myklebust, R., 2017. Igneous seismic geomorphology of buried lava fields and coastal 50 51 1073 escarpments on the Vøring volcanic rifted margin. Interpretation, 5(3), pp.SK161-SK177. 52 53 1074 Pratt, W., 1998. Gunnedah Coalfield: notes to accompany the Gunnedah Coalfield regional geology 54 55 1075 (north and south maps). Report GS1998/505. New South Wales Department of Mineral Resources. 56 57 1076 Geological Survey of New South Wales, Sydney, 113. pp. 58 59 60 61 62 63 64 65 36

1077 Rawlinson, N., Davies, D.R. & Pila, S., 2017. The mechanisms underpinning Cenozoic intraplate 1 1078 volcanism in eastern Australia: insights from seismic tomography and geodynamic modelling. 2 3 1079 Geophysical Research Letters, 44, doi: 10.1002/2017GL074911. 4 5 6 1080 Reid, A.J., Korsch, R.J., Hou, B. and Black, L.P., 2009. Sources of sediment in the Eocene Garford 7 1081 paleovalley, South Australia, from detrital-zircon geochronology. Australian Journal of Earth 8 9 1082 Sciences, 56(S1), pp.S125-S137. 10 11 1083 Renaut, R.W., Jones, B., Tiercelin, J.J. and Tarits, C., 2002. Sublacustrine precipitation of 12 13 1084 hydrothermal silica in rift lakes: evidence from Lake Baringo, central Kenya Rift Valley. Sedimentary 14 15 1085 Geology, 148(1-2), pp.235-257. 16 17 1086 Reynolds, P., Holford, S., Schofield, N. and Ross, A., 2017. 3‐D Seismic Imaging of Ancient Submarine 18 19 1087 Lava Flows: An Example From the Southern Australian Margin. Geochemistry, Geophysics, Geosystems. 20 21 1088 Richards, M.A., Duncan, R.A. and Courtillot, V.E., 1989. Flood basalts and hot-spot tracks: plume 22 23 1089 heads and tails. Science, 246(4926), pp.103-107. 24 25 1090 Rider, M. and Kennedy, M., 2011. The Geological Interpretation of Well Logs. published by Rider- 26 27 1091 French Consulting Ltd. 28 29 1092 Russell, M. and Gurnis, M., 1994. The planform of epeirogeny: vertical motions of Australia during 30 31 1093 the Cretaceous. Basin Research, 6(2‐3), pp.63-76. 32 33 1094 "SA Department for Manufacturing, Innovation, Trade, Resources and Energy" (2003) National 34 35 1095 Geoscience Mapping Accord (NGMA) Cooper Eromanga Basins Project - Cooper Formation 36 37 1096 Depths. Bioregional Assessment Source Dataset. Viewed 27 November 38 39 1097 2017, http://www.energymining.sa.gov.au/petroleum/data_and_publications/seismic/cooper_and_e 40 1098 romanga_basin_mapping_products 41 42 1099 Schofield, N. and Jolley, D.W., 2013. Development of intra-basaltic lava-field drainage systems within 43 44 1100 the Faroe–Shetland Basin. Petroleum Geoscience, 19(3), pp.273-288. 45 46 1101 Schofield, N., Holford, S., Millett, J., Brown, D., Jolley, D., Passey, S.R., Muirhead, D., Grove, C., 47 48 1102 Magee, C., Murray, J. and Hole, M., 2017. Regional magma plumbing and emplacement mechanisms of 49 50 1103 the Faroe‐Shetland Sill Complex: implications for magma transport and petroleum systems within 51 52 1104 sedimentary basins. Basin Research, 29(1), pp.41-63. 53 54 1105 Scott, M.P., Stephens, T., Durant, R., McGowen, J., Thom, W. and Woodroof, R., 2013, November. 55 56 1106 Investigating hydraulic fracturing in tight gas sand and shale gas reservoirs in the Cooper Basin. In SPE 57 1107 Unconventional Resources Conference and Exhibition-Asia Pacific. Society of Petroleum Engineers. 58 59 60 61 62 63 64 65 37

1108 Segawa, J. and Oshima, S., 1975. Buried Mesozoic volcanic–plutonic fronts of the north-western 1 1109 Pacific island arcs and their tectonic implications. Nature, 256(5512), p.15. 2 3 4 1110 Short, D.A., 1984. Lambda No.1 Well Completion Report. Compiled for Delhi Petroleum Pty. Ltd. 5 6 1111 Song, B., Economides, M.J. and Ehlig-Economides, C.A., 2011, January. Design of multiple transverse 7 8 1112 fracture horizontal wells in shale gas reservoirs. In SPE Hydraulic Fracturing Technology Conference. 9 10 1113 Society of Petroleum Engineers. 11 12 1114 Soesoo, A., Bons, P. & Elburg, M., 1999 Freestone dykes—an alkali-rich Jurassic dyke population in 13 14 1115 eastern Victoria. Australian Journal of Earth Sciences, 46 (1-2), 1-—9. 15 16 1116 Smith, 1987. Vitrinite Reflectance/Maceral Analysis of the Warnie East 1 Well. 17 18 1117 Stewart, A.K., Massey, M., Padgett, P.L., Rimmer, S.M. and Hower, J.C., 2005. Influence of a basic 19 20 1118 intrusion on the vitrinite reflectance and chemistry of the Springfield (No. 5) coal, Harrisburg, 21 22 1119 Illinois. International Journal of Coal Geology, 63(1-2), pp.58-67. 23 24 1120 Stewart, A.J., Raymond, O.L., Totterdell, J.M., Zhang, W. & Gallagher, R. 2013. Australian Geological 25 26 1121 Provinces, 2013.01 edition. scale 1:2 500 000. Geoscience Australia, Canberra, 27 28 1122 http://www.ga.gov.au/metadata-gateway/metadata/record/83860 29 30 1123 Sun, X., 1997. Structural style of the Warburton Basin and control in the Cooper and Eromanga 31 32 1124 Basins, South Australia. Exploration Geophysics, 28(3), pp.333-339. 33 34 1125 Sutherland, F.L., 1978. Mesozoic-Cainozoic volcanism of Australia. Tectonophysics, 48(3-4), pp.413- 35 36 1126 427. 37 38 1127 Sutherland, F.L., Graham, I.T., Hollis, J.D., Meffre, S., Zwingmann, H., Jourdan, F. & Pogson R.E., 2014. 39 40 1128 Multiple felsic events within post-10 Ma volcanism, Southeast Australia: inputs in appraising proposed 41 42 1129 magmatic models. Australian Journal of Earth Sciences, 16, 241- 267. 43 44 1130 Tang, Y., Obayashi, M., Niu, F., Grand, S.P., Chen, Y.J., Kawakatsu, H., Tanaka, S., Ning, J. and Ni, J.F., 45 46 1131 2014. Changbaishan volcanism in northeast China linked to subduction-induced mantle 47 1132 upwelling. Nature Geoscience, 7(6), pp.470-475 48 49 50 1133 Tappert, R., Foden, J., Stachel, T., Muehlenbachs, K., Tappert, M. and Wills, K., 2009. Deep mantle 51 1134 diamonds from South Australia: A record of Pacific subduction at the Gondwanan 52 53 1135 margin. Geology, 37(1), pp.43-46. 54 55 56 1136 Tarling, D.H., 1966. The magnetic intensity and susceptibility distribution in some Cenozoic and 57 1137 Jurassic basalts. Geophysical Journal International, 11(4), pp.423-432. 58 59 60 61 62 63 64 65 38

1138 Thomson, K., and Schofield, N.. "Lithological and structural controls on the emplacement and 1 1139 morphology of sills in sedimentary basins." Geological Society, London, Special Publications 302.1 2 3 1140 (2008): 31-44. 4 5 1141 Tracey R, Bacchin M, & Wynne P., 2008, In preparation. AAGD07: A new absolute gravity datum 6 7 1142 for Australian gravity and new standards for the Australian National Gravity Database. 8 9 1143 Exploration Geophysics. 10 11 1144 Trude, J., Cartwright, J., Davies, R.J. and Smallwood, J., 2003, New technique for dating igneous 12 1145 sills, Geology, v. 31, p. 813-816. 13 14 15 1146 Tucker, R.T., Roberts, E.M., Henderson, R.A. and Kemp, A.I., 2016, Large igneous province or long- 16 1147 lived magmatic arc along the eastern margin of Australia during the Cretaceous? Insights from the 17 18 1148 sedimentary record, Geological Society of America Bulletin, v. 128, p. 1461-1480. 19 20 1149 Veevers, J.J. and Conaghan, P.J., 1984, Phanerozoic earth history of Australia, Oxford University Press, 21 22 1150 USA. 23 24 1151 Wainman, C.C., Mccabe, P.J., Crowley, J.L. and Nicoll, R.S., 2015, U–Pb zircon age of the Walloon 25 26 1152 Coal Measures in the Surat Basin, southeast Queensland: implications for paleogeography and basin 27 28 1153 subsidence, Australian Journal of Earth Sciences, v. 62, p. 807-816. 29 30 1154 Wainman, C.C., Reynolds, P., Hall, T., McCabe, P.J. and Holford, S.P., 2019. Nature and origin of tuff 31 32 1155 beds in Jurassic strata of the Surat Basin, Australia: Implications on the evolution of the eastern 33 34 1156 margin of Gondwana during the Mesozoic. Journal of Volcanology and Geothermal Research. 35 36 1157 Warren, A.Y.E., Barron, L.M., Meekin, N.S., Morgan, E.J., Raymond, O.L., Cameron, R.G. & 37 38 1158 Colquhoun, G.P., 1999. Mesozoic Igneous Rocks. In Meakin, N.S. & Morgan, E.J. (Compilers). Dubbo 39 1159 1:250 000 Geological Sheet SI/55-4, 2nd edition, Explanatory Notes, pp. 313—328. Geological 40 41 1160 Survey of New South Wales, Sydney. 42 43 1161 Watson, D., Schofield, N., Jolley, D., Archer, S., Finlay, A.J., Mark, N., Hardman, J. and Watton, T., 44 1162 2017. Stratigraphic overview of Palaeogene tuffs in the Faroe–Shetland Basin, NE Atlantic 45 46 1163 Margin. Journal of the Geological Society, 174(4), pp.627-645. 47 48 49 1164 Watts, K.J., 1987, The Hutton Sandstone-Birkhead Formation Transition, ATP 269P(1), The APEA 50 1165 Journal, Volume 27 Number 1, p 215 - 228. 51 52 53 1166 White, J.D. and Ross, P.S., 2011. Maar-diatreme volcanoes: a review. Journal of Volcanology and 54 1167 Geothermal Research, 201, 1-29. 55 56 1168 Yew, C.C. and Mills, A.A., 1989. The occurrence and search for Permian oil in the Cooper Basin, 57 58 1169 Australia. 59 60 61 62 63 64 65 39

1170 Zhou, Q., Liu, L. and Hu, J., 2018, Western US volcanism due to intruding oceanic mantle driven by 1 1171 ancient Farallon slabs, Nature Geoscience, v. 11, p. 70. 2 3 4 1172 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 40

1173 12. Tables 1 2 Seismic Survey Acquisition Acquisition Areal Coverage Data Type 3 4 Date Company 5 2 6 Winnie 2012 Drillsearch Energy 1050 km 3D 7 Ltd. And 8 9 WesternGeco 10 11 Snowball 2016 Santos Ltd. 1698 km2 3D 12 Gallus 2012 Beach Energy and 420 km 2D 13 14 Icon Energy 15 16 Madigan 1996 Santos Ltd. 584 km2 3D 17 18 1174 Table 1: List of the seismic surveys that were determined to contain igneous rocks and 19 1175 utilised within this study. 20 21 Location of Igneous Rocks Name Age Key Reference 22 23 Marion Platea n/a Jurassic Isern et al., 2002 24 25 Eastern Highlands and Sydney Basin n/a 235 - 46.9 Ma Pells, 1985 26 Gunnedah Basin Garawilla Basalts 195 - 141 Ma Gurba & Weber, 2001 27 28 New South Wales Dubbo Volcanics 236 - 170 Ma Warren et al., 1999 29 Eastern Victoria n/a 191 - 179 Ma Elburg & Soesoo, 1999 30 31 Tasmania n/a 183 - 182 Ma Ivanov et al., 2017 32 Kangaroo Island Wisanger Basalt 170 Ma Milnes et al., 1982 33 34 1176 Table 2: List of Cretaceous igneous rocks in Eastern Australia. Where possible, a name and 35 1177 age range has been given. Each location is discussed within the text. 36 37 1178 38 39 1179 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 41

1180 13. Figures 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 1181 54 55 1182 Figure 1. Location map of the Warnie Volcanic Province and the data available. A Top basement 56 57 1183 map adapted from the SA Department for Manufacturing, Innovation, Trade, Resources and Energy 58 59 1184 (2003). Key structures of the southern Cooper Basin highlighted. B Location map highlighting the 60 61 62 63 64 65 42

1185 location of the Warne Volcanic Province within the Cooper Basin. Top basement map superimposed 1 1186 with the location of 3D and 2D seismic surveys utilised in this study and the location of key 2 3 1187 exploration wells. C Location map of the wells drilled within the Warnie Volcanic Province that 4 5 1188 were analysed during this study. Wells that intersected igneous rocks are highlighted in red. The 6 locations of the Central Nappamaerri Fault and the Challum Fault, structures discussed in the text, 7 1189 8 1190 are noted. 9 10 11 1191 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 43

1192 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1193 39 40 1194 41 42 1195 Figure 2. Stratigraphic column for the stratigraphy discussed within the paper, based on the work 43 44 1196 of Alexander & Hibburt (1996), Hall et al. (2016) & Reid et al. (2009). Seismic facies for each section 45 1197 is taken from the Winnie 3D survey of the eastern Nappamerri Trough. Rough stratigraphic location 46 47 1198 of the WVP highlighted. 48 49 1199 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 44

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 1200 30 31 1201 Figure 3. Seismic line from the Winnie 3D survey of the Nappamerri Trough highlighting the broad 32 33 1202 stratigraphy of the study area. A Uninterpreted line. B Interpreted line. Note the stacked nature of 34 35 1203 the Eromanga, Cooper and Warburton Basins and the stratigraphic location of the Warne Volcanic 36 1204 Province. 37 38 39 1205 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 1206 28 29 1207 Figure 4. Examples of different monogenetic vents. A Cross section through a cinder cone, adapted 30 31 1208 from Németh & Kereszturi (2015). B Seismic line across a cinder cone and lava flow, taken from the 32 1209 Winnie 3D survey, highlighting the general morphology, seismic response. Note the characteristic 33 34 1210 eye shape within the centre of the vent. C Plan view spectral decomposition of the cinder cone in B 35 36 1211 highlighting how different it is from the surrounding sediments. D Oblique view of the same cinder 37 38 1212 cone shown in TWT. E Cross section through a Maar-diatreme, adapted from Németh & Kereszturi 39 1213 (2015). F Seismic line across a proposed Maar-diatreme from the Winnie 3D survey. Note how it 40 41 1214 cuts down into the subsurface with an internally chaotic seismic response. G Plan view spectral 42 43 1215 decomposition of the Maar-diatreme within the Winnie 3D survey. H Oblique, TWT view of the 44 1216 proposed Maar-diatreme. 45 46 47 1217 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 46

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 1218 26 27 1219 Figure 5. Well data for the volcanics from the Lambda-1 well. A Composite log of the volcanic 28 29 1220 succession in the Lambda-1 well. Includes an image of the core taken from the base of the volcanic 30 31 1221 successon. B Vitrinite reflectance curve for the succession above the volcanics taken from Boothby 32 1222 (1986). Little thermal effect is observed. C Velocity histogram of the Lambda-1 volcanics 33 34 1223 superimposed on Nelson et al.’s (2009) velocity histogram of Tabular basalt. 35 36 1224 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 47

1225 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1226 18 19 1227 Figure 6. West to east seismic line running across the Lambda 1 well. The extent of the Lambda 1 20 1228 vent has been inferred base on the thickness of volcanics within the well. 21 22 23 1229 24 25 1230 26 27 28 1231 29 30 1232 31 32 1233 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 48

1234 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 1235 38 39 1236 Figure 7. Spectral decomposition of a horizon mapped across the volcanics of the Winnie 3D 40 41 1237 survey. A Uninterpreted spectral decomposition. B Interpreted spectral decomposition highlight 42 1238 extrusive volcanics and the location of igneous intrusions. Note the increased number of intrusions 43 44 1239 towards the north east of the Winnie 3D survey. 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 49

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 1240 38 39 1241 Figure 8. 3D Seismic across two monogenetic vents that extend into surface flows, from the 40 1242 Winnie 3D survey. A Uninterpreted line across the vents. B Interpreted line across the vents. Note 41 42 1243 the vertical zone of disrupted seismic directly below the vents, indicative of underlying plumbing 43 44 1244 system that fed the flows. C Spectral decomposition of a horizon mapped across the vents, 45 1245 highlighting their 3D morphology. 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 50

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 1246 33 34 1247 Figure 9. Seismic images of the Gallus 2D survey. A Isochron thickness map of the volcanics 35 36 1248 identified throughout the Gallus 2D survey. B Uninterpreted seismic line from the Gallus 2D survey. 37 38 1249 C Interpreted seismic line from the Gallus 2D survey. An increase in the volume of volcanics 39 1250 towards the east of the survey is apparent. 40 41 42 1251 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 51

1252 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1253 39 40 1254 Figure 10. Well data for intrusive volcanic rocks within the Warnie East 1 well. A Composite log 41 1255 across the intrusion in the Warnie East well. B Vitrinite reflectance profile across the intrusion in 42 43 1256 the Warnie East well taken from Boothby (1986). Thermal effect both above and below the well is 44 45 1257 noted. 46 47 1258 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 52

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1259 19 20 1260 Figure 11. 2D seismic line running from west to east across the Warnie East 1 well. The exact 21 22 1261 location of the igneous rocks is unclear on the line, however, a shallow saucer-shaped reflection with 23 1262 the Toolachee Fm. intersects Warnie East 1 at the depth igneous rocks are found. The lack of clearly 24 25 1263 imaged igneous rocks could point to more unimaged intrusive igneous rocks within the Cooper 26 27 1264 Basin succession. 28 29 1265 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 53

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1266 31 32 1267 Figure 12. Seismic across the large intrusion in the Winnie 3D survey. A Uninterpreted seismic 33 34 1268 line. B Interpreted seismic line, illustrating the uplift of the overburden and the numerous vents and 35 overlying volcanics associated with the intrusion. C Spectral decomposition of the intrusion, highlight 36 1269 37 1270 the pockmarks of vents that pass through the intrusion and morphological characteristics associated 38 39 1271 with the intrusion. 40 41 1272 42 43 44 1273 45 46 1274 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 54

1275 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 1276 39 40 1277 Figure 13. Well data for the Kappa-1 well. A Composite log for the Kappa-1 well volcanics. B 41 42 1278 Velocity histogram for the Kappa-1 well volcanics, superimposed on top of Nelson et al.’s (2009) 43 44 1279 velocity histogram for compound-braided volcanics. 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 55

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 1280 19 20 1281 Figure 14. Position of the Kappa-1 well in relation to the Snowball 3D survey. A Pseudo 21 1282 TWT/depth plot that was created using the velocity data synthesised for the wells drilled 22 23 1283 within the central Nappamerri Trough (namely Halifax, Etty, Anakin, Padme, Charal). This 24 25 1284 TWT to depth relationship was used to convert the Kappa-1 well data from depth to time in order 26 27 1285 to display it adjacent to the Snowball 3D survey. B Line across the Snowball 3D survey with the 28 position of formation tops based on the Kappa-1 well displayed. C Gamma ray curve from the 29 1286 30 1287 Kappa-1 well with formation tops marked. 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 56

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

34 1288 35 36 1289 Figure 15. Seismic across volcanics within the Snowball 3D survey. A Uninterpreted seismic line. B 37 1290 Interpreted seismic line. Thick package of mixed volcanics & sediments based off of the Kappa-1 well 38 39 1291 volcanics. C Spectral decomposition of the top mixed volcanics & sediment horizon. Location of 40 41 1292 vents noted by bright white colour with interpreted flow fields based on the cohesive dark colours 42 1293 extending away from the vents. 43 44 45 1294 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 57

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 1295 42 43 44 1296 Figure 16. Regional geophysical surveys adopted from the Queensland Government’s data 45 1297 repository. A Uninterpreted gravity anomaly with the location of the Nappamerri Trough Gravity 46 47 1298 anomaly highlighted. B Uninterpreted 1VD magnetic data. C Inset of B showing a ~6 x 5 km gravity 48 49 1299 magnetic anomaly with the interpreted extent of igneous rocks identified using seismic data 50 1300 superimposed on top of the anomaly. D Uninterpreted image of the gravity data set to 50% 51 52 1301 transparency overlain on top of the 1VD magnetic data. E Interpreted image of the combined 53 54 1302 gravity/1VD magnetic data. The extent of the Warnie Volcanic Province interpreted using well and 55 1303 seismic data within this study is indicated. Areas with circular magnetic anomalies and high gravity 56 57 1304 signatures not identified using well or seismic data are also highlighted. These areas could represent 58 59 1305 further igneous rocks within the SW Queensland. 60 61 1306 62 63 64 65 58

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 1307 33 34 1308 Figure 20: Regional map of the Warnie Volcanic Province. Depth to top basement map adapted 35 36 1309 from SA Department for Manufacturing, Innovation, Trade, Resources and Energy (2003). Location 37 38 1310 of extrusive volcanics and igneous intrusions based on seismic data. The igneous rocks, however, are 39 40 1311 thought to extend beyond the limit of seismic coverage towards the projected limit of the Warnie 41 1312 Volcanic Province. 42 43 44 1313 45 46 1314 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 59

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 1315 41 42 1316 Figure 17. The basement structure and it’s relation to vents within the Winnie 3D survey. A 43 44 1317 Spectral decomposition of the Top Toolachee horizon, highlighting the location of vents underlying 45 1318 the WVP. B Location of vents mapped using the Top Toolachee horizon superimposed on a TWT 46 47 1319 map of the top basement horizon. Many of the vents sit away from shallow basement reflections. 48 49 1320 Two vents are situated directly above the Central Nappamerri Fault. 50 51 1321 52 53 1322 54 55 56 1323 57 58 59 60 61 62 63 64 65 60

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1324 16 17 1325 Figure 18: Size and orientation of volcanics within the Winnie 3D and Madigan 3D surveys. A Size 18 19 1326 of vents, intrusions and volcanic flows. Note, the large Winnie 3D intrusion has not been included 20 1327 on this figure due to its sheer scale (dimensions of 8 km x 14 km) compared to the rest of the 21 22 1328 Warnie Volcanic Province. B Direction of elongation for the igneous rocks, highlighting that they are 23 24 1329 elongate in a SE-NW direction. 25 26 1330 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 61

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1331 21 22 1332 Figure 19: Mapping of faults within the Nappamerri trough. A Spectral decomposition of the Top 23 24 1333 Volcanics horizon from the Winnie 3D survey. B Interpretation of A with faults and the location of 25 1334 volcanics highlighted. C Spectral decomposition of the Top Toolachee horizon. D Interpretation of 26 27 1335 discontinuities within the Toolachee Horizon and the location of volcanics highlighted. 28 29 30 1336 31 32 1337 33 34 1338 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 62

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 1339 48 49 1340 Figure 21: A Palaeogeographic map of Australia in the middle Jurassic (Oxfordian, 160 Ma), 50 51 1341 superimposed with the location of middle to late Jurassic volcanics in eastern Australia, described in 52 1342 the text. B Oblique view of Australia, highlighting the subducting pacific slab and associated 53 54 1343 convective upwelling. Steps in lithospheric thickness have adapted from Fishwick et al., (2008). 55 56 1344 57 58 59 60 61 62 63 64 65