A Revised Stratigraphic Framework for Cretaceous Sedimentary And

Home , Amerasia Basin, Isachsen Formation, Strand Fiord Formation

Canadian Journal of Earth Sciences

A revised stratigraphic framework for Cretaceous sedimentary and igneous rocks at Mokka Fiord, Axel Heiberg Island, Nunavut, with implications for the Cretaceous Normal Superchron

Journal: Canadian Journal of Earth Sciences

Manuscript ID cjes-2018-0129.R1

Manuscript Type: Article

Date Submitted by the 02-Oct-2018 Author:

Complete List of Authors: Evenchick, Carol A.; Geological Survey of Canada, GSC Pacific Galloway, DraftJennifer; Geological Survey of Canada Calgary, Saumur, Benoit; Geological Survey of Canada, 601 Booth Street; Universite du Quebec a Montreal, Sciences de la Terre et de l'Atmosphère Davis, William J.; Geological Survey of Canada,

Keyword: Sverdrup Basin, HALIP, paleomagnetism, stratigraphy, palynology

Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? :

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1 A revised stratigraphic framework for Cretaceous sedimentary and igneous rocks at Mokka

2 Fiord, Axel Heiberg Island, Nunavut, with implications for the Cretaceous Normal

3 Superchron

5 C.A. Evenchick 6 Geological Survey of Canada / Commission géologique du Canada, 1500-605 Robson Street, 7 Vancouver, BC, Canada V6B 5J3 [email protected] 8 9 J.M. Galloway 10 Geological Survey of Canada / Commission géologique du Canada, 3303 - 33 Street N.W. Calgary, 11 AB, Canada T2L 2A7 [email protected] 12 13 B.M. Saumur 14 Département des Sciences de la Terre et de l’atmosphère, Université du Québec à Montréal, C.P. 15 8888, Succursale Centre-Ville Montréal (Québec) H3C 3P8 [email protected] 16 17 W.J. Davis Draft 18 Geological Survey of Canada / Commission géologique du Canada, 601 Booth Street, Ottawa, 19 ON, Canada K1A0E8 [email protected] 20 21 Corresponding Author: Carol Evenchick, Geological Survey of Canada / Commission 22 géologique du Canada, 1500-605 Robston Street, Vancouver, BC, Canada V6B 5J3 23 [email protected], phone 604-666-7119

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24 ABSTRACT

25 New data and interpretations on geological relationships of igneous rocks at Mokka Fiord, Axel

26 Heiberg Island, Nunavut, provide insight into the timing and nature of magmatism associated with

27 the Sverdrup Basin and High Arctic Large Igneous Province (HALIP). Field relationships indicate

28 that the igneous rocks, previously interpreted to be volcanic flows, are most likely an intrusive unit

29 discordant to regional bedding. An intrusive origin helps resolve chronostratigraphic

30 inconsistencies in previous work. The host rocks are palynologically constrained to be late

31 Barremian to late Aptian in age and are interpreted to be Paterson Island or Walker Island member

32 of the Isachsen Formation. If the igneous body is intrusive, it’s previously reported Ar-Ar age

33 (102.5 ± 2.6 Ma) is no longer in conflict with accepted stratigraphic interpretations and probably

34 reflects the emplacement age of the intrusion.Draft Lingering uncertainties in interpreting the normal

35 and reverse magnetic polarities determined in the previous work remain, and both are considered

36 viable. Although this uncertainty precludes definitive conclusions on the significance of

37 paleomagnetic data at Mokka Fiord, examination of the stratigraphic, paleomagnetic, and

38 geochronologic relationships there highlight potential for the study of excursions, or reversed

39 magnetic polarity subchrons, in the Cretaceous Normal Superchron elsewhere in the HALIP.

41 Keywords: Sverdrup Basin, HALIP, paleomagnetism, stratigraphy, palynology

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43 1. Introduction

44 Cretaceous siliciclastic and igneous rocks of the Sverdrup Basin near the mouth of Mokka

45 Fiord, Axel Heiberg Island (Fig. 1), were examined to clarify conflicting and apparently

46 irreconcilable published data and interpretations regarding their age. The issue is significant

47 because stratigraphic and paleomagnetic work on Axel Heiberg Island was used to suggest that

48 further analysis of volcanic flows and host strata in the upper Isachsen Formation has the potential

49 to constrain the age of M0, the youngest of the M-sequence reversals prior to the Cretaceous

50 Normal Superchron (Wynne et al. 1988). The base of M0 is defined as the base of the Aptian

51 (Tarduno 1989; Erba 1996; Gradstein et al. 2012), but different methods of study have arrived at

52 different absolute ages for this event. In some interpretations it occurs at 125/126 Ma (e.g. Ogg

53 and Hinnov 2012; Cohen et al. 2013; OggDraft et al. 2016), whereas alternative interpretations place

54 this event at 121/122 Ma (e.g. Gilder et al. 2003; He et al. 2008; Malinverno et al. 2012;

55 Midtkandal et al. 2016).

56 Mokka Fiord was considered to be one of the Sverdrup Basin localities that exhibits

57 reversely magnetized volcanic flows which can be correlated to M0 (Embry and Osadetz 1988)

58 and as such, held the potential to constrain the age of M0 if the flows yielded a precise age

59 determination. However, more recent geochronological work by Estrada and Henjes-Kunst (2013)

60 determined an Ar-Ar age of 102.5± 2.6 Ma for one sample from the Mokka Fiord igneous body;

61 this age is in stratigraphic conflict with previous interpretations, as well as being more than 20

62 million years younger than M0. The Ar-Ar age also complicates interpretation of the significance

63 of the reversed polarity data attributed to the Mokka Fiord locality because 102 Ma is in the middle

64 of the Cretaceous Normal Superchron. One possible explanation for this, not considered in

65 previous work, is that the body cooled during a geomagnetic excursion, or a subchron, within the

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66 superchron. Resolving the significance of the reversed data is further complicated by the fact that

67 Wynne et al. (1988), the original authors of the paleomagnetic data, did not themselves interpret

68 the Mokka Fiord dataset in their discussions of reversed magnetic polarity, calling into question

69 how the data should be treated.

70 Fieldwork was undertaken with the goal of resolving the conflicts between previous

71 interpretations by better characterizing the igneous body and its host rocks. Palynological analysis

72 establishes that the host rocks are late Barremian to late Aptian in age, and are part of the Paterson

73 Island Member or Walker Island Member of Isachsen Formation. No evidence for a volcanic origin

74 was found in the igneous body, and megascopic relationships are more consistent with it being an

75 igneous intrusion. The new interpretation reconciles conflicts between previous stratigraphic and

76 radiometric work, but uncertainty in theDraft significance of the reversed magnetic polarity data

77 remains, and is discussed. The following methods were used to test previous interpretations and to

78 provide evidence for new interpretations: new field observations; analysis of field and aerial

79 photographs; palynology of stratified rocks; review of the paleomagnetic data; and, stratigraphic

80 analysis that considers recent interpretations of the Early Cretaceous timescale and revisions to

81 ages of stratigraphic units. New radiometric age dating of the igneous rock was attempted but

82 ultimately did not yield an emplacement age; analytical procedures and data table are available for

83 download from the online supplement1.

84 2. Regional Geological Setting

85 2.1. Sverdrup Basin

86 Sverdrup Basin is a 1300 km by 350 km paleo-depocentre in the Canadian Arctic

87 Archipelago (Fig. 1). The basin contains up to 13 km of nearly continuous Carboniferous to

88 Paleogene siliciclastic, evaporite, and carbonate strata (Balkwill 1978; Embry and Beauchamp

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89 2008; Fig. 2). Rifting related to the opening of the proto-Arctic Ocean during Early Jurassic to

90 earliest Cretaceous time progressed to sea-floor spreading by the Early Cretaceous (Embry and

91 Beauchamp 2008; Hadlari et al. 2016), marking the opening of the proto-Arctic Ocean.

92 Sedimentation in the Sverdrup Basin was then dominated by terrigenous clastic material that

93 recorded basin-wide transgressive-regressive cycles driven by a combination of subsidence of the

94 rifted margin, sediment supply, and eustatic sea level change (Embry 1991). This resulted in the

95 accumulation of sandstone-dominated Isachsen Formation, shale-dominated Christopher

96 Formation, sandstone-dominated Hassel Formation, and shale-dominated Kanguk Formation (Fig.

97 2). Episodic uplift of basin margins lasted into the Cretaceous, with a period of increased

98 subsidence in the Early Cretaceous when basaltic volcanism and widespread emplacement of

99 diabase dykes and sills of the High ArcticDraft Large Igneous Province (HALIP) occurred (Balkwill

100 1978; Stephenson et al. 1987; Embry and Beauchamp 2008; Evenchick et al. 2015; Saumur et al.

101 2016). Deposition in the Sverdrup Basin ended by the Paleogene as a consequence of regional

102 compression and widespread uplift during the Eurekan Orogeny (Embry and Beauchamp 2008).

103 Sverdrup Basin strata were deformed during Mesozoic episodic flow of Carboniferous evaporites

104 (e.g. Balkwill 1978; Boutelier et al. 2010; Galloway et al. 2013; Harrison et al. 2014), by

105 Hauterivian to Cenomanian magmatism and faulting (e.g. Embry and Osadetz 1988; Embry 1991;

106 Evenchick et al. 2015), and by the Eurekan Orogeny (Eocene), which produced tight folds and

107 thrust faults in the northeast basin and more gentle folds to the west (e.g. Okulitch and Trettin

108 1991; Piepjohn et al. 2016).

109 2.2. High Arctic Large Igneous Province (HALIP)

110 The HALIP initiated near 130 Ma (Barremian) and resulted in episodic igneous activity

111 until ca. 80 Ma (Campanian; Tarduno 1989; Estrada and Henjes-Kunst 2004, 2013; Tegner et al.

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112 2011; Evenchick et al. 2015; Saumur et al. 2016; Dockman et al. 2018). In Canada's High Arctic it

113 occurs within the Cretaceous Sverdrup Basin. The Canadian HALIP is expressed by an early

114 period of tholeiitic magmatism (~130-90 Ma) resulting in dykes, sills, and volcanic flows in the

115 Isachsen and Strand Fiord formations, and a later period (~80 Ma) of alkaline magmatism

116 occurring on northern Ellesmere Island as the Hansen Point Volcanics (e.g., Embry and Osadetz,

117 1988). This paper is concerned with the age and nature of igneous rock at the mouth of Mokka

118 Fiord, for which Ar-Ar age analysis yielded a plateau age of 102.5 ± 2.6 Ma (Estrada and Henjes-

119 Kunst 2013). This late Albian age is substantially younger than the lower Aptian (~121 or 125 Ma)

120 paleomagnetic and stratigraphic interpretation of previous study (Embry and Osadetz 1988).

121 Refinement of timing and nature of the HALIP has implications for understanding circum-Arctic

122 plate reconstructions and Arctic basin evolutionDraft (Døssing et al. 2013; Saumur et al. 2016).

123 2.3. Isachsen Formation

124 Igneous rocks at Mokka Fiord are reported to occur within the Valanginian to late Aptian-

125 aged Isachsen Formation (Embry and Osadetz 1988). Isachsen Formation sediments were

126 deposited in marginal marine/deltaic and fluvial environments (Tullius et al. 2014), synchronous

127 with volcanism (Embry and Osadetz 1988; Grantz et al. 2011). The formation ranges in thickness

128 from ~120 m at basin margins to 1370 m on western Axel Heiberg Island (Hopkins 1971) and is

129 divided into three members (Embry 1985). The lowermost Paterson Island Member overlies Deer

130 Bay Formation or Mackenzie King Formation with unconformable contact at basin margins and

131 conformable contact in basin centre. The member consists of fine to very coarse-grained sandstone

132 with interbeds of carbonaceous siltstone, mudstone, coal, and volcanic and

133 volcaniclastic/tuffaceous rocks, deposited in a marginal marine setting (Embry 1985; Embry and

134 Osadetz 1988; Evenchick and Embry 2012a,b; Tullius et al. 2014; Evenchick et al. 2015; Galloway

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135 et al. 2015; Hadlari et al. 2016). Rondon Member mudstones conformably overlying Paterson

136 Island Member were deposited in a marine shelf environment (Embry 1985). These are in turn

137 conformably overlain by Walker Island Member, which is composed of interbedded fine to coarse-

138 grained sandstone, siltstone, mudstone and minor coal (Embry 1985; Tullius et al. 2014; Galloway

139 et al. 2015) with local volcanic flows, and is inferred to have been deposited in marginal marine

140 delta front to delta plain and fluvial environments (Embry 1985; Embry and Osadetz 1988; Tullius

141 et al. 2014; Galloway et al. 2015). Walker Island Member is conformably overlain by mudstone

142 and fine-grained sandstone of Christopher Formation.

143 Age control for Isachsen Formation (Fig. 2) is based on limited paleontological evidence

144 described in Galloway et al. (2015) and on carbon isotope stratigraphy (Herrle et al. 2015). In

145 Galloway et al. (2015) the Paterson IslandDraft Member ranges in age from Valanginian to Barremian,

146 whereas Herrle et al. (2015) extend the range of the member into early Aptian. This difference has

147 implications for the ages of overlying members of the formation, and for interpretations presented

148 herein. The Rondon Member ranges from Barremian to early Aptian (Galloway et al. 2015) or is

149 entirely early Aptian in age if the early Aptian age for upper Paterson Island Member proposed by

150 Herrle et al. (2015) is accepted. The Walker Island Member ranges in age from Barremian to late

151 Aptian (Galloway et al. 2015) or from early Aptian to late Aptian (Herrle et al. 2015). The

152 overlying Christopher Formation ranges in age from late Aptian to late Albian (Schröder-Adams

153 et al. 2014).

154 2.4. Cretaceous Igneous Rocks

155 Isachsen Formation includes basaltic volcanic rocks and is intruded by diabase dykes and

156 sills. Some of the intrusions were likely emplaced during deposition of the Isachsen Formation

157 (e.g. Villeneuve and Williamson 2006; Evenchick et al. 2015; Dockman et al. 2018). Sills and

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158 dykes also intrude the overlying Christopher and Hassel formations and these are probably related

159 to the more-voluminous Upper Cretaceous extrusive event represented by the Strand Fiord

160 Formation (Fig. 2; Ricketts et al. 1985).

161 Volcanic rocks in Isachsen Formation are generally local units of breccia and basaltic flows

162 near the base (Paterson Island Member) or top (Walker Island Member) of the formation. Notable

163 basaltic flows in Isachsen Formation are listed in Table 1. Lack of detailed stratigraphic context is

164 a barrier to constraining the ages of these igneous rocks. The subject of this paper is an occurrence

165 near the mouth of Mokka Fiord, Axel Heiberg Island, of massive ‘basalt’, originally interpreted to

166 be a volcanic flow about 30 m thick tentatively assigned to Christopher Formation (Thorsteinsson

167 1971), and later as three volcanic flows totalling 28 m thickness within the Walker Island Member

168 of the Isachsen Formation (Embry and DraftOsadetz 1988). Below we argue that this igneous unit is

169 best interpreted as an intrusion.

170 Volcanic rocks are sparse in the Christopher Formation. They include breccia more than

171 100 m thick at Ellef Ringnes Island, and several horizons of more widespread, finer grained,

172 volcanogenic sedimentary rocks (e.g. Schröder-Adams et al. 2014; Evenchick et al. 2015).

173 Strand Fiord Formation volcanic rocks are up to 1 km thick, limited to west Axel Heiberg

174 Island, and are Cenomanian in age, consistent with the ages of diabase and gabbro intrusions on

175 Axel Heiberg Island, and gabbroic intrusions on Ellesmere Island (Fig. 2; Ricketts et al. 1985;

176 Trettin and Parrish 1987; Núñez-Betelu et al. 1992; Tarduno et al. 1997, 1998; Kingsbury 2017;

177 Dockman et al. 2018).

178 3. Geological Setting at Mokka Fiord

179 Stream-cuts between the Mokka Fiord evaporite diapir and the western shore of Mokka

180 Fiord (Fig. 3) provide limited bedrock exposure. Strata are Triassic to Upper Cretaceous

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181 siliciclastic rocks of the Sverdrup Basin; the study area is near the shore of Mokka Fiord, on the

182 southeast limb of a northeast-trending syncline with sub-horizontal plunge (Thorsteinsson 1971;

183 Fig. 3).

184 3.1. Previous Data and Interpretations

185 The initial interpretation of strata at Mokka Fiord assigned a volcanic flow tentatively to

186 the top of Christopher Formation, with the flow overlain by Eureka Sound Formation, now Eureka

187 Sound Group (Thorsteinsson 1971; stratigraphic nomenclature after Miall 1986). The history of

188 interpretation of strata at this locality is shown in Fig. 4 and outlined in Table 2, with quotes from

189 the relevant papers. Osadetz and Moore (1988) reinterpreted the section and reassigned the flow

190 to Isachsen Formation, with the overlying strata reassigned to Christopher Formation (Fig. 4). This

191 stratigraphic interpretation was based onDraft correlation of the Mokka Fiord flow with volcanic flows

192 within the Walker Island Member at central Axel Heiberg Island (Geodetic Hills), and northwest

193 Ellesmere Island (Blue Mountains); the latter are now considered to be sills (Bédard et al. 2016).

194 Wynne et al. (1988) focussed on paleomagnetism of Cretaceous volcanic rocks in the Sverdrup

195 Basin and concluded that there are two intervals of reversely magnetized volcanic flows in the

196 Isachsen Formation, one in the lower part (Paterson Island Member) and one in the upper part

197 (Walker Island Member), but that the uppermost flows of the Walker Island Member have normal

198 magnetization (Fig. 4). Wynne et al. (1988) concluded that the change from reversely to normally

199 magnetized horizons of the Walker Island Member may be used to bracket M0, and in doing so,

200 refine the age of the base of the Cretaceous Normal Superchron. Data are reported from two sample

201 sites at the Mokka Fiord locality: one site with exclusively normal magnetic polarity and the other

202 with both normal and reversed data. However, the Mokka Fiord dataset was not interpreted or

203 discussed by Wynne et al. (1988), and their text and figures dealing with magnetic reversals and

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204 the age of M0 exclude the Mokka Fiord data without explanation. A third paper (Embry and

205 Osadetz 1988) focussed on Sverdrup Basin volcanism. They assigned the volcanic rocks at Mokka

206 Fiord, which they interpreted to comprise three flows, to Walker Island Member based on

207 stratigraphic position below Christopher Formation and, citing Wynne et al. (1988), because they

208 are reversely magnetized (Fig. 4). Embry and Osadetz (1988) did not comment on the difference

209 between their assignment of reversed magnetic polarity to the rocks and the results reported by

210 Wynne et al. (1988), nor the conflict between their interpretation that the reversely magnetized

211 flow is overlain by Christopher Formation with the interpretation of Wynne et al. (1988) that the

212 highest flows in the Isachsen Formation are normally magnetized at all sites.

213 Estrada and Henjes-Kunst (2004, 2013) and Estrada (2015) conducted geochemical and

214 geochronological studies on aliquots of Draftthe same Mokka Fiord samples used in the paleomagnetic

215 study. With only hand samples to examine, Estrada and Henjes-Kunst (2004) accepted the

216 stratigraphic and other field interpretations of the 1988 papers, but when their Ar-Ar analyses

217 indicated a younger age (102.5 ± 2.6 Ma), Estrada and Henjes-Kunst (2013) reinterpreted the flows

218 to be Strand Fiord Formation (Fig. 4). The Ar-Ar age (late Albian) is older than biostratigraphic

219 and radiometric ages for the Strand Fiord Formation or associated volcaniclastic strata

220 (Cenomanian; e.g. Tarduno et al. 1998; Davis et al. 2016; Kingsbury et al. 2017; Dostal and

221 MacRae 2018). Estrada and Henjes-Kunst (2004) commented that mafic units of Mokka Fiord and

222 Blue Mountains contain low Cu, which is more akin to Strand Fiord Formation volcanic rocks than

223 those that occur within the Isachsen Formation. This conclusion was supported by Saumur and

224 Williamson (2016) for the Mokka Fiord mafic unit, based on major oxide and trace element

225 compositions that overlap with compositional arrays of Strand Fiord Formation basalts but are

226 distinct from those that occur within Isachsen Formation. Evenchick et al. (2015), in a summary

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227 of Sverdrup Basin HALIP ages, noted the conflict between the Ar-Ar geochronological result of

228 Estrada and Henjes-Kunst (2013) and the stratigraphic / paleomagnetic interpretation of Embry

229 and Osadetz (1988). They questioned the reliability of the Ar-Ar age based on the stratigraphic

230 conflict between the two studies and on the observation that Ar-Ar ages have been shown to be

231 unreliable in some cases elsewhere within the HALIP (e.g. Corfu et al. 2013).

232 3.2. Implications of the Magnetic Polarity Time Scale for Previous Interpretations

233 Figure 4 shows the interpretations of Embry and Osadetz (1988) in the context of regional

234 stratigraphy and the magnetic polarity timescale. The beginning of M0 is at the base of the Aptian

235 (Erba 1996), and is considered to be either 125/126 Ma (Fig 4A; e.g. Gradstein et al. 2012; Cohen

236 et al. 2013), or 121/122 Ma (Fig. 4B; e.g. He et al. 2008; Midtkandal et al. 2016). If the flows, as

237 interpreted by Embry and Osadetz (1988),Draft were extruded during M0, they must have been extruded

238 during deposition of the uppermost Paterson Island Member (Fig. 4B), or lower Walker Island

239 Member (Fig. 4A), depending on the accepted age of these units. The flows were interpreted to be

240 immediately overlain by mudrock of the Christopher Formation. If the flows are at the top of

241 Paterson Island Member or base of Walker Island, and overlain by Christopher Formation, then all

242 or most of the Walker Island Member must be missing, with a disconformity between upper

243 Barremian or lower Aptian rocks of Walker Island Member and upper Aptian Christopher

244 Formation. This is in contrast with regional stratigraphic relationships which suggest the contact

245 between the Christopher and Isachsen formations is conformable (e.g. Tullius et al. 2014;

246 Schröder-Adams et al. 2014; Galloway et al. 2015; Herrle et al. 2015). An additional conflict

247 between previous interpretations that is highlighted in Fig. 4 is that Wynne et al. (1988) state that

248 the highest flows in Isachsen Formation have normal polarity, whereas Embry and Osadetz (1988)

249 interpret the flows at Mokka Fiord to be at the top of Isachsen Formation but with reversed

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250 magnetism, citing Wynne et al. (1988). However, Wynne et al. (1988) do not specifically include

251 the Mokka Fiord samples within their reversely magnetized units. Wynne et al. (1988) do not

252 explain why Mokka Fiord samples are excluded from discussion and are not interpreted as

253 reversely magnetized, nor do Embry and Osadetz (1988) explain why they include them as

254 reversely polarized.

255 4. New Observations, Analytical Work, and Interpretations

256 4.1. Locality Description

257 New fieldwork at Mokka Fiord was carried out in 2015. The banks of the creek at the

258 igneous locality are about 8 to 15 m high. The igneous rocks are resistant to erosion and result in

259 a short canyon with continuous exposure from creek-level to top of the cutbank (Fig. 5A). In

260 contrast, there is little exposure of siliciclasticDraft bedrock within 500 m upstream of the igneous rocks,

261 or downstream 300 m to the shore of Mokka Fiord. Contact relationships are not exposed, and

262 away from the igneous rocks the valley has gentle slopes of slumped, barely consolidated medium-

263 grained sandstone, fine-grained sandstone, and siltstone (Fig. 5).

264 4.2. Sedimentary Rocks

265 4.2.1. Field Observations and Measurements

266 The best sedimentary rock exposure in the vicinity of the igneous body is about 200 m

267 away downstream (Fig. 5A). A steep cutbank provides 5 x 20 m of exposure; excavation with rock

268 hammers resulted in fresh outcrop (Figs. 6A, B). Several metres of laminated and cross-laminated

269 fine-grained quartz sandstone and siltstone (Fig. 6B) are capped by about 2 m of white quartz

270 sandstone; all are weakly consolidated. Bedding is gently dipping, and all measured dips are

271 subhorizontal. Dark weathered material at the top of the cutbank was not examined.

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272 Five hundred metres upstream from the igneous rocks is a large exposure of sedimentary

273 rock. It was not visited in the field, but from examination of photographs it appears to be at least

274 30 m of distinctly bedded dark weathering clastic rock, assumed to be sandstone and mudstone,

275 overlain by about 100 m of light coloured rock assumed to be predominantly sandstone (Fig. 5C).

276 The distinctly bedded dark weathering rocks are continuous with the only bedding traces that can

277 be followed southwest of the creek (Figs. 5C, 7). Based on these relationships, sedimentary rocks

278 at this exposure are interpreted to dip about 40° west northwest.

279 4.2.2. Palynology

280 One sample was collected for palynological analysis to constrain the age and stratigraphic

281 position of the clastic rocks. Sample 15EP003A01 (C-602800) is from the exposure 200 m

282 downstream from the igneous body (Fig.Draft 5A). The sample consists of dark grey/brown mudstone

283 and very fine-grained sandstone, and was collected from between thin beds and laminae of quartz

284 sandstone. The sample contains numerous and well-preserved palynomorphs (Galloway 2017).

285 The assemblage preserved in the examined unsieved preparation (P-5356-1B) includes pollen and

286 spore taxa typical of the Early Cretaceous of Arctic Canada (Galloway et al. 2012, 2013, 2015).

287 The sample contains the monocolpate angiosperm taxa Liliacidites Couper 1953 and Monocolpites

288 Van der Hammen 1954, abundant pollen with coniferous affinities (undifferentiated bisaccates,

289 Cerebropollenites mesozoicus (Couper 1958) Nilsson 1958 and Cupressaceae-Taxaceae pollen),

290 and rare Appendicisporites cf. potomacensis Brenner 1963 and Klukisporites? cf. foveolatus

291 Pocock 1965 specimens. Abundant Antulsporites clavus (Balme 1957) Filatoff 1975 and

292 Stereisporites antiquasporites (Wilson and Webster 1946) Dettmann 1963 in the sample indicate

293 that bryophytes were a common element of the terrestrial vegetation. Other abundant spore taxa

294 include Deltoidospora hallei Miner 1935 and Gleicheniidites senonicus Ross 1949. Dinocysts

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295 (undifferentiated) and acritarchs (Micrhystridium, Delfandre 1938; Pterospermopsis W. Wetzel

296 1952) are rare.

297 4.3. Igneous Rocks

298 4.3.1. Field Relationships and Petrography

299 Igneous rocks exposed at Mokka Fiord weather to a dark rusty brown colour (Fig. 5A).

300 They are strongly jointed, but otherwise massive and homogeneous (Figs. 5A, 6C). No indications

301 of flow tops or contacts to distinguish the three flows noted by Embry and Osadetz (1988) were

302 observed. The dense network of fractures has no regular pattern that could be considered columnar.

303 Fresh rock is dark grey and fine-grained, with sparse plagioclase glomerocrysts up to 5 mm across.

304 The southeast contact is covered by an apron of igneous rock talus (Fig. 5A). The northwestern

305 contact is not exposed because there is noDraft clastic bedrock present, but igneous bedrock in the creek

306 is considered to be within a couple of metres of the contact, based on the limit of resistant rock,

307 and continuity of that boundary up the dip-slope above the creek and to the northwest limit of

308 resistant rock on the plateau above (Figs. 5A, 6D). Igneous bedrock within 1 m of the northwestern

309 (upper) contact has similar character to that near the centre of the body. In thin section, the matrix

310 appears as isotropic gabbro exhibiting a weakly developed subophitic texture defined by tabular

311 plagioclase locally partly enclosed by anhedral clinopyroxene; accessory minerals include opaques

312 (~5-7% modal, mostly magnetite), minor olivine (1-2%) and retrograde interstitial biotite (10-

313 15%, after hornblende and/or pyroxenes).

314 4.3.2. Megascopic Relationships

315 Examination of field photographs and aerial photographs facilitates interpretation of the

316 extent and orientation of the igneous body based on the strong contrast in resistance to erosion

317 between the igneous and sedimentary rocks (Fig. 5A). If the limit of resistant igneous outcrop

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318 approximates its contact, the northwestern contact of the body dips about 30°- 40° northwest (Figs.

319 5A, 7); deflection of the creek to a southwest direction at the upstream limit of igneous rock is

320 interpreted to reflect the southwesterly strike of the body (Figs. 5A, 6D). The strike is also

321 indicated by the extent of outcrop and frost heaved outcrop above the creek, continuous with the

322 creek exposure (i1 in Fig. 5A). Our approximation of the dip value is consistent with Wynne et al.

323 (1988), who report a dip of 38°. Their reported dip direction of 072°, however, is highly oblique

324 to our interpretation of the southwesterly strike of the igneous body (Figs. 5A, 7), as well as the

325 south southwesterly strike of bedding farther west as shown by Thorsteinsson (1971) and in Fig.

326 5C. Considering that the strike of the igneous body reported by Wynne et al. (1988) is highly

327 oblique to the strike of sedimentary bedding, it is also in conflict with their interpretation that it is

328 a volcanic flow. Draft

329 Well-exposed sedimentary rocks 500 m upstream of the igneous rocks are continuous with

330 bedding traces across about 1.5 kilometres of gently undulating topography south of the creek

331 (Figs. 5C, 7). The bedding traces indicate a strike of about 205° (Fig. 7). Igneous bedrock at the

332 creek is continuous with frost heaved igneous rocks on the plateau above the creek, coincident

333 with a topographic feature elongate to the southwest for about 180 m, suggesting a southwesterly

334 strike (i1 in Fig. 5A). Field and aerial photographs reveal that along trend there is another elongate

335 ridge over 200 m long, and a third, smaller area (i2 and i3, respectively in Figs. 5A, B; Fig. 7). All

336 areas have similar dark colour and resistance to weathering. They are interpreted to be igneous

337 rock because of their contrast in colour and resistance to erosion with local sedimentary rocks. The

338 three areas are coincident with a topographic ridge and define a strike of about 220° (Figs. 5A, 7).

339 These relationships, as shown in plan on Fig. 7, and as viewed along i1, i2, and i3 in Fig. 5A,

340 indicate that the trace of the igneous body is oblique to bedding, and suggest to us that continuation

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341 of exposure of the igneous rocks a few hundred metres along trend would result in their intersection

342 with the bedding traces.

343 5. Discussion - Reconciliation of New Observations and Interpretations with Previous Work

344 5.1. Age of Sedimentary Rocks

345 5.1.1. Palynology Interpretation

346 Monocolpate angiosperm taxa in the sample are of limited biostratigraphic value.

347 Angiosperm pollen first appear on Ellef Ringnes and Amund Ringnes islands in the central

348 Sverdrup Basin as two species of tricolpate pollen in the uppermost beds of the Christopher

349 Formation (Hopkins 1974). Monocotyledenous angiosperms are considered to have evolved prior

350 to dicotyledenous plants; in mid-latitudes, strata containing monocotyledonous angiosperm pollen

351 are overlain by rocks containing dicotyledenousDraft angiosperm pollen (Brenner 1967; Singh 1971;

352 Leckie and Burden 2001). In Sverdrup Basin strata, monocotyledonous pollen are reported from

353 the Cenomanian Bastion Ridge and Strand Fiord formations on Axel Heiberg Island but are absent

354 from the underlying Albian Hassel Formation (Núñez-Betelu et al. 1992). It is therefore difficult

355 to precisely constrain the age of the Mokka Fiord sample based on angiosperm pollen due to a lack

356 of information on the latitudinally diachronous dispersal patterns and oldest occurrences of early

357 angiosperms in high northern latitudes (Galloway et al. 2012).

358 Pollen with coniferous affinities are typical for samples of Isachsen Formation (cf.

359 Galloway et al. 2015). Cerebropollenites mesozoicus pollen is a distinctive element in the Early

360 Cretaceous Cerebropollenites Province of the northern hemisphere (Herngreen et al. 1996).

361 Rare Appendicisporites cf. potomacensis and Klukisporites? cf. foveolatus specimens may

362 indicate that the Mokka Fiord sample is not older than late Barremian. The Cadomin and Dalhousie

363 formations in the southern Rocky Mountains and Foothills of Alberta and British Columbia contain

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364 an older assemblage that contains neither angiosperm pollen nor Appendiciporites spores that

365 White and Leckie (1999) interpret to be of Berriasian to Valanginian age, and a younger

366 assemblage that lacks angiosperm pollen but contains Appendicisporites and Klukisporites spores

367 that they interpret to be of late Barremian to ?early Aptian age.

368 5.1.2. Interpretation of Age and Stratigraphic Position of Sedimentary Rocks

369 From the paleontology interpretation it can be concluded that the sample is no older than

370 late Barremian. If the age interpretations of Herrle et al. (2015) are accepted, the Mokka Fiord

371 sample could be from as low as the mid-Paterson Island Member (lower Barremian; Fig. 4B), or

372 from Rondon (lower Aptian) or Walker Island (lower to upper Aptian) members of the Isachsen

373 Formation. Alternatively, if previous age interpretations are retained (e.g., Galloway et al. 2015;

374 Fig. 4A) the sample could be from the RondonDraft (Barremian) or Walker Island Member (uppermost

375 Barremian to upper Aptian). The sample could also be from the lowermost Christopher Formation

376 (upper Aptian to Albian; Fig. 4) but the paucity of dinocysts suggest that the sample did not come

377 from marine sediments (i.e., Rondon Member, or Christopher, Bastion Ridge, or Strand Fiord

378 formations) and thus limits the sample to have come from the mid or upper Paterson Island or

379 Walker Island member of the Isachsen Formation. We reject that the Mokka sample can be

380 assigned to Hassel Formation or younger units based on the absence of tricolpate angiosperm

381 pollen (cf. Galloway et al. 2012).

382 Osadetz and Moore (1988) and Embry and Osadetz (1988) assigned the clastic rocks to the

383 Walker Island Member, which is consistent with, but more limited than, the palynological analysis

384 presented herein. Their conclusion was based on the interpretations that the igneous body is a

385 volcanic flow correlative with others in the Isachsen Formation, that the flow has reversed

386 magnetic polarity, and that it underlies Christopher Formation. Their reasoning is challenged by

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387 our interpretation, argued below, that the igneous rock is most likely intrusive. If valid, this

388 reinterpretation negates stratigraphic correlations based on the presence of volcanic rock.

389 Independent of reinterpretation of the igneous body, correlation of shale above it with Christopher

390 Formation is weak because only two metres, at most, of non-diagnostic shale talus are present at

391 the contact area (Fig. 6D), and intervals of shale this thick are common in Isachsen Formation.

392 5.2. Interpretation of Igneous Rocks

393 We question the interpretation that the igneous body is a volcanic flow based on: 1) the

394 impressively homogeneous and massive nature of the rock in outcrop; 2) the lack of observed flow

395 features; 3) moderate dip (30-40°) of the igneous body relative to subhorizontal bedding at

396 outcrops 200 m downstream; and 4) the apparent cross-cutting relationship at a larger scale

397 between the igneous rocks and beddingDraft in sedimentary rock to the northwest. Although we find

398 these relationships compelling, we concede that they are not absolutely conclusive in the absence

399 of definitive contact relationships. For this reason, we discuss the larger scale implications of both

400 extrusive and intrusive options for origin of the igneous body within the constraints of known

401 regional Sverdrup Basin stratigraphy, and known relationships of the body. The latter are: 1) late

402 Barremian to late Aptian age of the clastic rocks 200 m downstream, as determined from

403 palynological analysis, which confirms that they are Isachsen Formation; 2) an Ar-Ar plateau age

404 of 102.5 ± 2.6 Ma (Estrada and Henjes-Kunst 2013) for the igneous body; 3) geochemical

405 similarities to mafic rocks within or associated with the Strand Fiord Formation (Saumur and

406 Williamson 2016). The Ar-Ar age was rejected in previous work (Evenchick et al. 2015) based on

407 its conflict with the stratigraphic / paleomagnetic interpretation of age of the body (Embry and

408 Osadetz 1988). But, the stratigraphic / paleomagnetic argument is suspect because the magnetic

409 polarity is in question, and, as discussed below, reverse polarity does not necessarily restrict age

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410 of the body to prior to the Cretaceous Normal Superchron. There is no longer a reason to dismiss

411 the Ar-Ar age; it is considered to record emplacement age of the body.

412 5.2.1. Interpretation of the Igneous Body as Volcanic Rock

413 The igneous body cannot be Isachsen Formation volcanic rock because its Ar-Ar age, 102.5

414 ± 2.6 Ma (late Albian; Estrada and Henjes-Kunst 2013), is significantly younger than the late

415 Aptian upper age limit of Isachsen Formation. Reversed magnetic polarity was considered to

416 constrain the age of the body to prior to the Cretaceous Normal Superchron, and therefore Isachsen

417 Formation (Embry and Osadetz 1988), but that argument is rejected for reasons noted earlier.

418 The only other volcanic succession in the Sverdrup Basin that includes flows and is

419 compatible with geochemistry of the Mokka Fiord igneous body is the Strand Fiord Formation.

420 Although the Ar-Ar age of the igneous bodyDraft is close to the age of the Strand Fiord Formation, its

421 error limits do not overlap with age determinations for volcanic rocks in the formation. As

422 discussed by Dostal and MacRae (2018), only two Ar-Ar age determinations on Strand Fiord strata

423 are within the biostratigraphic limits (Cenomanian) of the formation. These are 95.3 ± 0.2 Ma

424 (Tarduno et al. 1998) and 96.1 ± 1.6 Ma (Villeneuve and Williamson 2006). In addition, Strand

425 Fiord Formation is not known from eastern Axel Heiberg Island (Ricketts et al. 1985; Fig. 1). The

426 formation occurs as a thick, up to 1 km scale sequence of flood basalt, consisting of multiple flows

427 with conspicuous columnar jointing (Ricketts et al. 1985). In the few places that a succession of

428 flows is less than 100 m thick, near the limits of the formation, the flows are associated with

429 volcaniclastic strata (Rickets et al. 1985); no volcaniclastic strata were found in the study area

430 either in outcrop or talus blocks. If the igneous body at Mokka Fiord is Strand Fiord Formation, a

431 fault is required between the body and subhorizontal Isachsen Formation 200 m downstream to

432 account for loss of Christopher Formation between the two units. Discordance of the body with

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433 bedding to the northwest (Fig. 7) may potentially be explained by an angular unconformity. This

434 explanation is dismissed because, with the exception of one unique situation, angular

435 unconformities are not known in the Isachsen through Strand Fiord formations, despite excellent

436 exposure across the Arctic Islands, although several disconformities exist (e.g. Galloway et al.

437 2013, 2015; Hadlari et al. 2016). The unique situation, restricted to an area with a high density of

438 evaporite diapirs on western Axel Heiberg Island, resulted in local angular unconformities during

439 the formation of minibasins on the immediate flanks of evaporite diapirs (Harrison and Jackson

440 2014). This complex wall-and-basin geometry is not known to exist elsewhere in the Sverdrup

441 Basin. Another explanation for the angular discordance between the igneous body and bedding

442 could potentially be a hypothetical fault, as shown on Fig. 7. The hypothetical fault would need to

443 have significant throw to separate StrandDraft Fiord Formation from Eureka Sound Formation or

444 Isachsen Formation. In summary, interpretation of the igneous body as volcanic rock requires a

445 number of special circumstances that are not typically recognized in strata of the Sverdrup Basin.

446 It would be an unknown volcanic succession older than, and outside the geographic limits of,

447 Strand Fiord Formation, and bounded on both sides by faults.

448 5.2.2 Interpretation of the Igneous Body as Intrusive Rock

449 Interpretation of the body as intrusive rock solves contradictions of known relationships in

450 the study area. The Ar-Ar age is within the range of magmatism in the HALIP, and an intrusive

451 origin explains the observed discordance with host strata. The geochemical similarity of the Mokka

452 Fiord mafic rocks with basalts of the slightly younger Strand Fiord Formation (Estrada and Henjes-

453 Kunst, 2004; Saumur and Williamson, 2016) is consistent with the Ar-Ar age, is inconsistent with

454 interpretation as Isachsen Formation, and further reinforces an intrusive origin. There are no

455 relationships that preclude an intrusive origin, other than its description as a flow (Thorsteinsson

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456 1971), or three flows (Embry and Osadetz 1988). It should be noted that those authors did not

457 provide outcrop observations or photographs to support an extrusive origin, and no evidence of

458 flows was seen in the current study.

459 5.3. Implications of the Cretaceous Normal Superchron

460 5.3.1. Subchrons in the Cretaceous Normal Superchron

461 It is unclear why Wynne et al. (1988) did not interpret the reversed polarity data in the

462 study area. However, we must still consider it as a possibility because one of the authors of that

463 paper subsequently used the reversed polarity to support stratigraphic interpretations (Embry and

464 Osadetz (1988). We have argued that the stratigraphic interpretation is not valid, but the question

465 of reversed magnetic polarity remains in either interpretation of the igneous rocks, and is

466 particularly important because the Ar-ArDraft age, 102.5 Ma, is in the midst of the Cretaceous Normal

467 Superchron. Four short periods of reversed magnetism, which may include multiple short

468 excursions, are proposed within this period (e.g. Ogg and Hinnov 2012, their Fig. 27.6; Fig. 4).

469 Three subchrons M”-1r”, M”-2r”, and M”-3r” have been observed in deep sea drill cores but have

470 not been clearly identified in marine magnetic anomaly studies. Subchron M”-1r”, also known as

471 ISEA, is accepted as a short reversal within the Cretaceous Normal Superchron because it has been

472 recognized in both land-based and deep sea drilling studies (e.g. Tarduno 1990; Ogg and Hinnov

473 2012). Subchrons M”-2r”, and M”-3r” are suspect because they have been observed only in deep

474 sea drill cores, and have not been confirmed in independent studies. Factors that hinder the

475 reliability of magnetostratigraphic studies that rely solely on core recovered by deep sea drilling

476 are reviewed by Tarduno (1990); they include accidental inversion of core sections, which would

477 result in a false magnetic polarity. A number of reversals occur in the well-studied Albian Contessa

478 section in Italy, but it is uncertain whether those reversals represent primary magnetization at 104-

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479 107 Ma or remagnetization during a later reversed polarity chron (Tarduno et al. 1992). These

480 reversals are close in age to M”-3r” (ca. 103 Ma), and overlap, within error, with the Ar-Ar age of

481 the Mokka Fiord igneous body. A period of reversed magnetism at ~115 Ma is based on a

482 succession of dated flows in China (recalculated by He et al. 2008 from the 113 Ma interpretation

483 of Sobel and Arnaud 2000). Thus it appears that there may be two, and possibly more, short periods

484 of reversed magnetism within the Cretaceous Normal Superchron, as well as the possibility of

485 multiple excursions that could be recorded as reversed polarity. If the Mokka Fiord igneous body

486 preserves both normal and reverse polarity (e.g. Embry and Osadetz 1988) it may have cooled

487 during an excursion, or one of the subchrons. Overlap of the Ar-Ar age, 102.5 ± 2.6 Ma (Estrada

488 and Henjes-Kunst 2013), with subchron M”-3r” (ca. 103 Ma) is consistent with this possibility

489 (Fig. 4). Alternatively, the locality may Draftnot be characterized by reversed polarity, and in this case

490 there are no implications regarding reversals within the superchron.

491 5.3.2. Mokka Fiord Paleomagnetism Revisited

492 Independent of the question of the origin of the igneous body, the possibility that the Ar-

493 Ar age may provide evidence for one of the poorly documented reversals within the Cretaceous

494 Normal Superchron warrants closer examination of the paleomagnetic data. Although Embry and

495 Osadetz (1988) highlight the reverse polarity of some of the Mokka Fiord data, the original report

496 by Wynne et al. (1988) does not expressly interpret the polarity of the Mokka Fiord samples.

497 Absence of Mokka Fiord data from all cases where reversed magnetism is discussed, figured, and

498 interpreted in Wynne et al. (1988) leads us to infer that the authors were not committed to an

499 interpretation of reversed magnetization for these samples. The topic of paleomagnetic reversals

500 is a central theme in their paper, and therefore exclusion of the Mokka Fiord results is puzzling.

501 Review of Wynne et al. (1988), and examination of the original lab results archived in the

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502 Geological Survey of Canada Paleomagnetism and Petrophysics Laboratory (R. Enkin, personal

503 communication 2016) provides additional detail for discussion of the reversed magnetism

504 attributed to the Mokka Fiord samples by Embry and Osadetz (1988). The Mokka Fiord data listed

505 in Table 2 of Wynne et al. (1988) are:

506 1) 5 samples (all drill core, each split to result in 9 specimens) from site RUE41 with normal

507 polarity, declination as expected for the Cretaceous (northwest), but significantly shallower

508 inclination than expected.

509 2) 3 samples (all drill core, each split to result in 6 specimens) from site RUE42 with normal

510 polarity; two of these have results similar to RUE41, but one has southerly rather than

511 northwest declination; the average given for the 3 samples is the same as for RUE41.

512 3) 4 samples (all drill core, each splitDraft to result in 8 specimens) from site RUE42; the 4 samples

513 are consistent, with reversed magnetism, unusual declination (NNE), and significantly

514 shallower inclination than expected.

515 4) 7 samples; these are not additional samples, but the sum of the two RUE42 subsets, with the

516 reversed samples flipped to normal, and averaged.

517 The polarity of all samples, including the four reversely magnetized RUE42 samples, are robust

518 results that reflect the magnetic field at the time of cooling, and are not easily dismissed as being

519 caused by later remagnetization (R. Enkin, personal communication 2016). Another possible

520 explanation for the reversed polarities may be self-reversal, but the Mokka Fiord rocks exhibit

521 only minor secondary alteration, and magnetite grains are fresh; therefore, magnetic self-

522 reversal, as occasionally observed in oceanic basalts strongly affected by hydrothermal alteration

523 (Doubrovine and Tarduno 2006), cannot be invoked. As noted earlier, the strike of the igneous

524 body is at a high angle to that reported by Wynne et al. (1988), it cross-cuts host strata at a

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525 moderate angle, and if it is an intrusion, it is younger than the host rocks. Consideration of these

526 points would result in a more appropriate tilt correction, which may reduce the discrepancies

527 from expected declination and inclination, but will not change the magnetic polarity.

528 If the intrusion includes reversely magnetized rocks, the implications are that: 1) the 28 m

529 thick intrusion cooled in such a way, and at a time, as to retain both reversed and normal

530 magnetizations, and different declinations and inclinations; 2) considering the Ar-Ar age, it likely

531 cooled during an excursion, or possibly the M"-3r" subchron, within the Cretaceous Normal

532 Superchron (Figs. 4A, B). If the Mokka Fiord igneous rocks preserve only normal polarity there

533 are no restrictions or concerns with regard to its emplacement during the Cretaceous Normal 534 Superchron. Draft 535 5.4. Distribution of Cretaceous Volcanic and Sedimentary Rocks

536 At both Mokka Fiord (herein) and the Blue Mountains (Bédard et al. 2016), igneous bodies

537 once interpreted as Isachsen Formation volcanic flows are now considered to be igneous

538 intrusions. These new interpretations significantly reduce the extent of Isachsen Formation

539 volcanic rocks from that indicated by Embry and Osadetz (1988; their Fig 4b). Isachsen Formation

540 volcanic flows in eastern Sverdrup Basin are now limited to a north-trending region along the

541 length of Axel Heiberg Island (Fig. 1). This change impacts regional tectonic interpretations that

542 are based on the geographic distribution of volcanic flows. Within the study area, clastic rocks east

543 of the igneous body should be mapped as mid- or upper Paterson Island or Walker Island member

544 of Isachsen Formation. Rocks to the west are probably also Isachsen Formation and, considering

545 the northwest dips farther west, may be higher in the formation, and the highest strata may include

546 Christopher Formation, if no significant faults cut out or duplicate strata.

547 5.5. Future Work

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548 The work of Embry and Osadetz (1988) and Wynne et al. (1988) continue to provide an

549 important foundation for Cretaceous stratigraphic and paleomagnetic studies in Sverdrup Basin.

550 Re-examination of the field relationships at Mokka Fiord show that the igneous body is most likely

551 an intrusion; its previous interpretation as a volcanic layer resulted in an inappropriate tilt

552 correction and age assignment for these rocks. Reinterpretation of the paleomagnetic data should

553 include a more appropriate tilt correction. If, as suggested by the orientation of bedding 200 m

554 southeast, the intrusion was emplaced in subhorizontal beds, no correction is required. The strike

555 of the intrusion used by Wynne et al. (1988) for the tilt correction is inconsistent with all other

556 evidence and is likely incorrect.

557 Considering the lack of exposed contacts, this locality is not the most ideal to pursue future

558 studies. However, if additional field studiesDraft are undertaken, precise dating of the igneous body and

559 additional palynological analysis of strata to its west, and the overlying shale, would help constrain

560 its relationship to Strand Fiord magmatism and significance to the HALIP. We present a more

561 clear understanding of the strike of the body, which may guide future workers to sample close to

562 the centre, where grain size is possibly larger. Considering that Wynne et al. (1988) did not

563 interpret the reversed magnetism at Mokka Fiord, future paleomagnetic fieldwork should sample

564 with the strategy to perform all necessary tests to confirm that the results reflect the magnetic field

565 at the time of cooling of the body, including those to exclude the possibility of partial self-reversal.

566 Recognizing that different parts of the body may record different magnetic polarity, the body

567 should be sampled across its width.

568 6. Conclusions

569 The suggestion of Embry and Osadetz (1988) that further study of the Mokka Fiord site

570 could yield an age for M0 was based on the premise that the igneous unit is a volcanic flow in the

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571 upper Isachsen Formation that has reversed magnetic polarity. No evidence for volcanic flows was

572 found in our examination of this site, nor was any provided by previous workers. With the origin

573 of the igneous body in question and significance of its reversed paleomagnetic data uncertain, the

574 stratigraphic / paleomagnetic argument for its age (Embry and Osadetz 1988), which was in

575 conflict with the Ar-Ar age (102.5 ± 2.6; Estrada and Henjes-Kunst 2013), is also in question, and

576 there is no reason to dismiss the Ar-Ar age of the body based on that conflict. We provide evidence

577 that the igneous rock is best interpreted as an intrusion and not a volcanic flow. However, we

578 cannot rule out the possibility that the rocks belong to an unknown volcanic succession that is

579 older than, and outside the geographic distribution of, Strand Fiord Formation, and is also bounded

580 on both sides by hypothetical faults. The new interpretation of the body as intrusive rock removes

581 conflict between previously interpreted Draftstratigraphic position and the Ar-Ar age of 102.5 ± 2.6 Ma

582 reported by Estrada and Henjes-Kunst (2013). Sedimentary rocks 200 m southeast of the body are

583 constrained by palynological analysis to be between late Barremian and late Aptian age, and to be

584 part of mid- or upper Paterson Island Member or Walker Island Member of the Isachsen Formation.

585 The significance of the Mokka Fiord paleomagnetic data remains enigmatic because

586 Wynne et al. (1988) did not include the subset of Mokka Fiord samples with reverse polarity in

587 their discussion. If the Mokka Fiord igneous body preserves only normal polarity there are no

588 challenges to its interpretation as being emplaced during the Cretaceous Normal Superchron. If

589 the Mokka Fiord intrusion preserves both normal and reverse polarity, emplacement of the

590 intrusion may have occurred during one of the proposed short reversals, or an excursion, within

591 the Cretaceous Normal Superchron. The Ar-Ar age reported by Estrada and Henjes-Kunst (2013)

592 matches the age of the M”-3r” subchron at ~103 Ma. Considering the Ar-Ar age, and uncertainties

593 in origin and magnetic polarity of the body, the Mokka Fiord site is unlikely to provide time-

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594 stratigraphic constraints on the age of M0 as suggested by Embry and Osadetz (1988). However,

595 the presence of suitable igneous rocks in Sverdrup Basin that may record reversed magnetism

596 during the Cretaceous Normal Superchon as well as detailed stratigraphic studies which have

597 identified important events, including OAE1a (e.g. Herrle et al. 2015), highlight a potential in the

598 basin for advances in calibrating the geomagnetic time scale.

599 Acknowledgements

600 The work was conducted under the High Arctic Large Igneous Province (HALIP) activity

601 of the Western Arctic Project of GEM-2 (Natural Resources Canada), and contributes to that

602 project by elucidating the nature and age of Cretaceous igneous rocks in the Western Arctic region.

603 We thank the Polar Continental Shelf Project for logistics support in fieldwork. Thank you to Linda

604 Dancey for palynological preparation ofDraft the material and to Richard Fontaine for curation. We

605 particularly thank Randy Enkin (Geological Survey of Canada Paleomagnetism and Petrophysics

606 Laboratory) for digging out details of archived paleomagnetic data and for his opinions of their

607 meaning. Evenchick thanks Kirk Osadetz for helpful discussion of the geological issues at Mokka

608 Fiord both before and after fieldwork. The manuscript was improved with the help of comments

609 from Keith Dewing, and from reviewers John Tarduno and Henry Halls, and CJES Associate

610 Editor George Dix.

611 NRCan Contribution number / Numéro de contribution de RNCan: 20180048

612

613 Footnote

614 1Supplementary data are available with the article through the journal website at

615 http://nrcresearchpress.com/doi/suppl/xxxxxx

616

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Table 1. Volcanic rocks reported in Isachsen Formation; locations as shown in Fig. 1 (Ricketts 1985; Embry and Osadetz 1988 and references therein; Williamson et al. 2017).

Member Location Description Walker Geodetic Hills, central Axel 11 m consisting of 3 flows Island Heiberg Island

Bunde Fiord, NW Axel ~220 m of basalt flows interbedded with quartzose sandstone and Heiberg Island pyroclastic and epiclastic volcanic sediments

Li Fiord, Middle Fiord, and local 50-100 m scale exposures Strand Fiord, western Axel Heiberg Island

Mokka Fiord, Axel Heiberg 28 m of basalt consisting of 3 flows Island

Blue Mountains, Ellesmere previously interpreted to include 20 m of basalt at the top of Island Isachsen Fm; now interpreted as intrusions emplaced at the contact between Isachsen and Christopher formations (Bédard et al. 2016)

Paterson Geodetic Hills, central Axel 10.5 m of basalt Island Heiberg Island

Bjarnason Island, NW of twoDraft 10 m thick basaltic flows Geodetic Hills

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Quotes and Information from papers which present or discuss Mokka Fiord strata Comments Thorsteinsson (1971); note 1 on regional map Our observations of orientation of the igneous body are as “A basalt flow of uncertain stratigraphic position and about 100 feet thick crops out adjacent to the described by Thorsteinsson. shore of Eureka Sound, north of the entrance to Mokka Fiord. The strike of the flow more or less parallels Mokka Fiord. The flow underlies conformably the Eureka Sound Formation, but no sediments are exposed beneath it. The flow is provisionally included in the Christopher Formation.” Osadetz and Moore (1988), p. 2 follows Thorsteinsson (1971) in interpreting igneous rocks as “Another volcanic flow unit occurs below rock types typical of the lower Christopher Formation (Albian) a flow, but reinterpreted it as Isachsen Fm based on at Mokka Fiord, on eastern Axel Heiberg Island. It is believed to be roughly correlative with volcanic correlation with volcanic rocks in the formation elsewhere. rocks in the Isachsen Formation in both the Blue Mountains and Geodetic Hills. Unfortunately, the Reinterpreted overlying rocks from Eureka Sound to lower contact is not exposed and its exact stratigraphic position is uncertain.” Christopher formation Wynne, Irving, and Osadetz (1988) Table 1: Note that dip direction is significantly different than Table 1: Mokka sites RUE 41,42; Isachsen basalt; dip-direction/dip of 072/ 38 described by Thorsteinsson. Table 2: The fact that the third Table 2: Site RUE41 - 9 samples analysed from 5 cores, with a mean declination and inclination RUE42 ‘sub site’ is the first two sites combined is not stated. (relative to paleohorizontal) of 305/59. Site RUE42 – three different sub sites, with mean declination Table 3: This table lists both Mokka Fiord and Blue Mountains and inclination (relative to paleohorizontal) of: 305/78, 028/-57, 224/71. The last of these is noted as samples as Isachsen basalt equivalent. Both are now excluded from analysis of inclination because α95 is >20°). interpreted to be intrusions (this paper, Bédard et al. 2016). Table 3: The summary of rock-unit averages by locality only includes results for site RUE41 from Quote A: this statement suggests that the Mokka Fiord locality Mokka Fiord, with declination and inclination of 305/59. is normally magnetized because Embry and Osadetz (1988) ‘Reversals of magnetization’, p. 1233 (the text is split into 3 sections here for ease of reference): and Osadetz and Moore (1988) interpret the flows to be A “Eleven of the 28 flows studied from the Isachsen are reversely magnetized. The reversed flows overlain by Christopher Fm, and therefore at the top of occur at two horizons: in the lower part of the Isachsen Formation and in the upper third. The Isachsen Fm. uppermost Isachsen flows are normally magnetized (Table 2; Fig. 14). Quote B: appears to contradict quote A, which states that B “All of the flows that we sampled in the Isachsen Formation, which ranges in age from Valanginian to there are flows in the lower Isachsen with reversed Aptian (Wall 1983), lie in the upper portion of the Walker Island Member, which is late Barremian to magnetization. Aptian (Embry and Osadetz 1988), or in equivalent strata.” Quote C: the Mokka Fiord locality is not included in the list of C “… the normal magnetizations of the Strand Fiord Formation, the Christopher Formation, and the top reversely magnetized sites. of the Isachsen Formation were acquired during the Cretaceous normal polarity superchron. Hence we Outcrop relationships are not presented for the Mokka Fiord tentatively suggest that the uppermost horizon of reversed flows of the Isachsen Formation (sites locality. It is not discussed in the treatment of restoration of AXB01, AXB02, AXW10, Fig. 14) corresponds to M0, the youngest of the M sequence of reversed beds to paleohorizontal, nor is it listed in the interpretation of anomalies, and that the lower horizon of reversed flows (AXV10, AXV01, AXV02, AXV03, AXV30, reversals of magnetization. AXV31, AXV32, AXW04, Fig. 14) correspond to the M1 reversed anomaly.” Embry and Osadetz (1988), p. 1212 The "reversed polarities" and stratigraphic position with “…. at the mouth of Mokka Fiord there is a 28 m thick volcanic unit consisting of three flows. Underlying respect to Christopher Fm are used to conclude that the flow strata are not exposed, and this volcanic unit is tentatively assignedDraft to the Walker Island Member is within the Isachsen Fm. No explanations are given for why because it is overlain by shales of the Christopher Formation and has reversed polarities (Wynne et al. the data in Wynne et al. (1988) are described as reversed 1988).” polarity. Follows Osadetz and Moore (1988) reinterpretation of overlying strata as Christopher Fm. Estrada and Henjes-Kunst (2004), p. 583 Mokka Fiord rocks are included in Isachsen Formation Mokka Fiord samples: C148888 (AXV37); C107586 (82-OE-11-1.5); C107587 (82-OE-11-3) following Embry and Osadetz (1988) but the authors noted “The only remarkable difference in trace element chemistry between the basalts of the two formations that the chemistry is more like Strand Fiord Formation. The is the higher Cu content of the Isachsen Formation basalts with an average of 133 ppm compared to only other, and similar, anomaly noted in the Isachsen 64 ppm for the Strand Fiord Formation basalts (Table 1). (Exceptions: The samples of the Strand Fiord geochemistry is with the Blue Mountains samples. Formation basalts from Bals Fiord with Cu contents in the range of the Isachsen Formation, and the samples from Mokka Fiord and Blue Mountains mapped as Isachsen Formation with low Cu contents.)” Estrada and Henjes-Kunst (2013), p. 120-121; Sample C-107586 This paper uses the outcrop description of Embry and “… a 28 m thick volcanic unit consists of three basalt flows and is overlain by shales, mapped as Osadetz (1988). It is the first paper to interpret the Mokka Christopher Formation (Embry & Osadetz 1988). The underlying strata are not exposed. The basalt Fiord igneous rocks as Strand Fiord Formation; the was assigned to the upper Isachsen Formation; however, its stratigraphic position is relatively interpretation is based on Ar dating and geochemistry. uncertain (Osadetz & Moore 1988). A whole-rock separate of sample C107586 from this volcanic unit yielded within error identical total gas, plateau and inverse-isochron ages. The plateau age 102.5 ± 2.6 Ma is the best estimate for the age of this basalt (Fig. 5r). This age does not correspond to the stratigraphic age of the upper Isachsen Formation (Aptian, c. 125 to 112 Ma; Gradstein et al. 2004) but compares well to the stratigraphic age of the Strand Fiord Formation (late Albian to early Cenomanian, c. 110 to 95 Ma). A genetic relationship with the latter volcanic rocks is also supported by geochemical data. The Cu concentration of C107586 and of another sample from the same locality is low (59 ppm) and fits better to the average of the Strand Fiord Formation basalts (64 ppm) as to that of the Isachsen Formation basalts (133 ppm). Although Cu is considered a relatively mobile element, the Cu content seems to be the only geochemical parameter that is characteristically distinct for the basalts of both formations (Estrada & Henjes-Kunst 2004). Furthermore, the Rb-Sr and Sm-Nd isotope data of this sample fit better to the data of the Strand Fiord Formation basalts than to those of the Isachsen Formation basalts (see Estrada & Henjes-Kunst 2004: Fig. 6). The basalts from which C107586 was sampled are therefore interpreted to form part of the Strand Fiord Formation.” Estrada (2014); Sample C-107586 Geochemistry of the Strand Fiord and Isachsen formations (no rock descriptions or specific reference to Mokka Fiord rocks are presented) are presented and discussed. Mokka Fiord igneous rocks are included in Strand Fiord Fm, following the 2013 interpretation. Evenchick, Davis, Bédard, Hayward, and Friedman (2015), p. 1384 This interpretation follows Embry and Osadetz (1988) in using “Basalt at Mokka Fiord, Axel Heiberg Island, was originally mapped as Christopher Formation the magnetic polarity to support the Isachsen stratigraphic (Thorsteinsson, 1971). It was later reassigned to the Isachsen Formation, based in part on reversed position (incorrectly attributed to Osadetz and Moore (1988) magnetic polarity (Osadetz and Moore, 1988; Wynne et al., 1988), and then reinterpreted to be Strand and Wynne et al. (1988)), and therefore reject the Ar-Ar age Fiord Formation based on an Ar-Ar age of 102.5 ± 2.6 Ma (Estrada and Henjes-Kunst, 2013). The Ar- interpretation of Estrada and Henjes-Kunst (2013). Ar age is considered unreliable because it is inconsistent with the reversed polarity documented by Wynne et al. (1988), which requires a pre–125.9 Ma age (Gradstein and Ogg, 2012).” Table 2. Previous data and interpretations of Mokka Fiord strata

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Figure captions

Fig. 1. Geologic map of Sverdrup Basin (after Dewing et al. 2007). The study area is indicated

by the yellow star on eastern Axel Heiberg Island.

Fig. 2. Cretaceous lithostratigraphy of Sverdrup Basin (modified after Hadlari et al. 2016).

Detailed summaries and discussions of age determinations of Lower Cretaceous strata are in

Galloway et al. (2012, 2013, 2015), Schröder-Adams et al. (2014), and Herrle et al. (2015).

*Age of Rondon Member, Isachsen Formation is after Galloway et al. (2015); Herrle et al.

(2015) place Rondon Member in lower Aptian. Ages of igneous rocks are emplacement

ages; stratigraphic position is not implied.

Fig. 3. Geological setting of the study area. Geology is after Thorsteinsson (1971).The legend is

as defined in that publication, but noteDraft that Eureka Sound Formation has since been elevated

to group status (Miall 1986). The unit labels in parentheses indicate a reinterpretation of the

distribution of units based on the results in this paper. Inclusion of Kc? in the

reinterpretation is to acknowledge that dark and recessive weathering strata in the core of the

syncline may be Christopher Formation. Igneous rocks discussed in this paper outcrop in the

creek within the outline of Fig. 7, where the creek intersects the dashed line. The base map

is NTS 049G/12. Outline shows the location of Fig. 7.

Fig. 4. Stratigraphic chart of the Cretaceous part of the Sverdrup Basin, modified after Embry

and Osadetz (1988) and Evenchick et al. (2015), with previous interpretations of the

stratigraphic position of Mokka Fiord strata, and the results of the current study. Precise

stratigraphic positions of volcanic rocks in Isachsen Formation are approximate, and

depicted based on relationships to bounding units. The ages of stratigraphic units are as cited

in Fig. 2. Two combinations of interpretations of the Barremian-Aptian boundary and

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position of the top of Paterson Island Member are shown in A and B. The base of Paterson

Island Member, Early to Late Valanginian, is not shown. Stratigraphic range of the Isachsen

Formation in the study area, at right in A and B, is from palynology presented in this paper.

Magnetic polarity timescale is from Ogg and Hinnov (2012). (A) Stratigraphic relationships

using the timescale of Gradstein et al. (2012) and ages of Isachsen Formation following

Galloway et al. (2015), with late Barremian age for Rondon Member. (B) Fig. 4A modified

after Midtkandal et al. (2016, and others) for Barremian-Aptian boundary at 121-122 Ma,

and after Herrle et al. (2015) for Paterson Island Member extending into lower Aptian. The

top of Walker Island Member is moved up to allow it an age range of greater than ~2 my.

This arbitrary amount does not impact interpretations. The positions of M0r and M”-1r” are

moved up to approximately similarDraft positions within the Aptian as in Fig. 4A, with M0 at

base of Aptian, and M”-1r” above OEA1a (as in e.g. Erba 1996), which according to Herrle

(2015; his Fig. 2) overlaps Rondon and base of Walker Island members on Axel Heiberg

Island.

Fig. 5. Photographs of the south side of the creek west of the mouth of Mokka Fiord, showing

the relationships between rock units, and relative positions of features discussed in text. The

dash-dot line in A, B, and C is the same belt of bedding traces. (A) View south southwest,

almost along strike of the igneous body, identified by outcrops at i1, i2, and i3. The location

of the subhorizontal fine clastic rocks downstream of the igneous rocks, shown in Figs. 6A,

B, is indicated at left. The southern limit of the bedding traces shown in Figs. 5B, C is at

upper right. The northwest dip of the igneous body is inferred from the limit of dark brown

outcrop highly resistant to erosion, and the dip of the body is inferred from the dipslope of

resistant rock. The bend in the creek at x is considered to be controlled by the strike of the

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igneous body. The letters x and y indicate the same position in adjoining photographs.

Width of view is approximately 400 m at foreground. (B) View approximately south to the

area upstream from the igneous body. (C) View south southwest to bedded sedimentary

rocks upstream from the igneous body, with overlap with Fig. 5B identified by y. The inset

shows the distinctly bedded section that results in the surface traces of bedding indicated by

dash-dot lines. Width of view is approximately 400 m.

Fig. 6. Photographs of outcrops in the vicinity of the igneous body east of Mokka Fiord. (A)

View southwest to the only outcrop downstream from the igneous body; location is

indicated in Fig. 5A. Sub-horizontal bedding can be seen across much of the outcrop. Areas

examined are indicated by ovals. (B) Close view of laminated and cross-laminated fine-

grained quartz sandstone and siltstoneDraft from which the palynology sample was collected. The

hammer is 33 cm long. (C) Outcrop of the igneous body near its northwestern boundary and

upper contact; location is shown in Figs. 5A and 6D. A hammer 33 cm long is near centre

image. (D) Northwestern, upper contact area of the igneous body, showing extent of igneous

bedrock and quality of exposure at the contact. Position of the contact is based on the

upstream limit of igneous bedrock. Viewed to the south.

Fig. 7. Map showing interpreted relationships in the study area. The base image is the centre of

airphoto A16858-143. Intrusive rocks identified in Fig. 5 are outlined by heavy dotted lines.

Bedding traces continuous with the well-exposed bedding at the creek in Fig. 5C are

indicated by a dash-dot line. Rocks in the southwest corner labelled 'igneous rocks?' have

similar weathering characteristics to those exposed in the study area; they may be a different

intrusion, or an en echelon part of the same intrusion. The white line with black dots is a

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hypothetical fault required to accommodate the discordance between the igneous body and

bedding traces if the body is volcanic rock.

Draft

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Table 1. Volcanic rocks reported in Isachsen Formation; locations as shown in Figure 1

Member Location Description Walker Geodetic Hills, central Axel 11 m consisting of 3 flows Island Heiberg Island

Bunde Fiord, NW Axel ~220 m of basalt flows interbedded with quartzose sandstone and Heiberg Island pyroclastic and epiclastic volcanic sediments

Li Fiord, Middle Fiord, and local 50-100 m scale exposures Strand Fiord, western Axel Heiberg Island

Mokka Fiord, Axel Heiberg 28 m of basalt consisting of 3 flows Island

Blue Mountains, Ellesmere previously interpreted to include 20 m of basalt at the top of Isachsen Island Fm; now interpreted as intrusions emplaced at the contact between Isachsen and Christopher formations (Bédard et al. 2016)

Paterson Geodetic Hills, central Axel 10.5 m of basalt Island Heiberg Island

Bjarnason Island, NW of twoDraft 10 m thick basaltic flows Geodetic Hills (Ricketts 1985; Embry and Osadetz 1988 and references therein; Williamson et al. 2017).

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Table 2. Previous data and interpretations of Mokka Fiord strata

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o Area 80 enlarged

CANADA o 80

6 7 5 o 110 Ellef Ringnes 4 Axel Heiberg 1 Island 3 Island

2 o 120 Ellesmere Island Draft

200 km o 75 CONTINENTAL MARGINS NEOGENE PEARYA TERRANE CANADIAN SHIELD MID-PROTEROZOIC - SILURIAN ARCHEAN-PALEOPROTEROZOIC Sands and gravels Volcanic, deep water and Crystalline basement shallow water strata Igneous rocks discussed RIFT BASINS JURASSIC - CRETACEOUS Mokka Fiord Sandstone and shale CRETACEOUS - TERTIARY DYKES 1 Geodetic Hills inferred from maps 2 Strand Fiord or aeromag SVERDRUP BASIN CARBONIFEROUS - EOCENE 3 Middle Fiord Carbonate, sandstone Subsurface extent of sills 4 Li Fiord inferred from seismic and shale 5 Bunde Fiord 6 FRANKLINIAN MARGIN NEOPROTEROZOIC - DEVONIAN SALT-CORED STRUCTURES Bjarnason Island 7 Volcanic, Clastic foreland Diapirs Blue Mountains Deep water and carbonate Approx. spatial extent deep water strata strata platform strata of Strand Fiord Fm

Fig. 1. Geologic map of Sverdrup Basin (after Dewing et al. 2007). The study area is indicated by the yellow star on eastern Axel Heiberg Island.

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Basin Margins

Lithostratigraphy Igneous

Eureka Sound Grp

Kanguk Fm 93-84 Ma ash (4) Strand Fiord Fm 93-91 Ma granitoids, gabbro, diabase (1,5) Hassel Fm 95 Ma gabbro, diabase (6)

Bastion Ridge Fm MacDougall Point Mbr 106 Ma ash (3) Christopher Fm Invincible Point Mbr

117 Ma diabase (5) 120 Ma diabase (5) Draft 121 Ma diabase (2,5) Isachsen Fm Walker Island Mbr Rondon Mbr Paterson Island Mbr *

Deer Bay Fm

Geochronology sources: Only U-Pb zircon or baddeleyite ages are considered for the igneous events, sources are: (1) Omma et al. (2011); (2) Evenchick et al. (2015); (3) Herrle et al. (2015); (4) Davis et al. (2016);(5) Dockman et al. (2018); (6) Kingsbury et al. (2017)

Fig. 2. Cretaceous lithostratigraphy of Sverdrup Basin (modiﬁed after Hadlari et al. 2016). Detailed summaries and discussions of age determinations of Lower Cretaceous strata are in Galloway et al. (2012, 2013, 2015), Schröder-Adams et al. (2014), and Herrle et al. (2015). *Age of Rondon Member, Isachsen Formation is after Galloway et al. (2015); Herrle et al. (2015) place Rondon Member in lower Aptian. Ages of igneous rocks are emplacement ages; stratigraphic position is not implied.

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87°20'W 87°10'W Te Eureka Sound Formation Th JK Ki Kc Christopher Formation Ki Isachsen Formation Th J Kc (Ki?) JK Deer Bay Formation Mokka J undivided Jurassic formations Fiord (Ki) Th Heiberg Formation diapir Kc Te Co Otto Fiord Formation Ki

Th (Ki?) v Fig. 7 Geological boundary; defined, Co approximate, assumed Kc J Fault, defined (tick on Te (Ki) downthrown side) (Ki and Kc?)

JK v Syncline, defined

79°38'N contour on aerial photograph, Ki v interval 100' RD Kc

(Ki?) Te v KA FIO v K (Ki and Kc?) O M 1 Km

Fig. 3. Geological setting of the study area.Draft Geology is after Thorsteinsson (1971).The legend is as defined in that publication, but note that Eureka Sound Formation has since been elevated to group status (Miall 1986). The unit labels in parentheses indicate a reinterpretation of the distribution of units based on the results in this paper. Inclusion of Kc? in the reinterpretation is to acknowledge that dark and recessive weathering strata in the core of the syncline may be Christopher Formation. Igneous rocks discussed in this paper outcrop in the creek within the outline of Fig. 7, where the creek intersects the dashed line. The base map is NTS 049G/12. Outline shows the location of Fig. 7.

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A regional Mokka Fiord interpretations B regional Mokka Fiord paleomagnetism paleomagnetism

Sverdrup Basin (1971) HALIP (1988) (1988) regional ynne et al. regional ynne et al. this paper Thorsteinsson this paper Embry & Osadetz U-Pb ages W W Embry & Osadetz stratigraphy (1988); Estrada & stratigraphy (1988); Estrada &

Henjes-Kunst (2004) pre 100 Ma (2013); Estrada (2014) Henjes-Kunst (2004) (2013); Estrada (2014) Ma Estrada & Henjes-Kunst Ma Estrada & Henjes-Kunst Osadetz & Moore (1988)

Camp. Camp. Magnetic Polarity Magnetic Polarity 80 80 Eureka Snd Sant. Eureka Snd Sant. Coniac. Coniac. 90 90 Turon. Turon.

Strand Strand Kanguk Fm Cenom. Kanguk Fm Fiord Cenom. Fiord 100 100 M”-3r” ? ? M”-3r” 105 Ma ash Albian Albian 106 Ma ash

M”-2r” Hassel Fm

M”-2r” Hassel Fm 110 110 112 Ma ash E&O, based on magnetism E&O, based on stratigraphy E&O, based on magnetism 114.9+/-1.6 E&O, based on stratigraphy 114.9+/-1.6 + + + - - - 117 Ma diabase Draft M”-1r” Walker Is. Aptian + + + - - - Aptian 120 120 - - - 120 Ma diabase Walker M0r - - - 121 Ma diabase M”-1r” Island Mbr Christopher Fm - - - Christopher Fm

M0r ------Barrem. 127 Ma gabbro Rondon Mbr Barrem. Paterson Lower Cretaceous Upper Lower Cretaceous Upper 130 - - - 130 Island Mbr Paterson Haut. Island Mbr Haut. Isachsen Fm

Isachsen Fm - - - reversed magnetic polarity + + + normal magnetic polarity

volcanic flow rock Ar-Ar age of Isachsen Fm

shale-dominated Isachsen Fm sandstone-dominated (position approx.) igneous rock possible age of intrusive rock if it has reversed magnetic polarity possible age range of intrusive rock if it has normal magnetic polarity

Fig. 4. Stratigraphic chart of the Cretaceous part of the Sverdrup Basin, modified after Embry and Osadetz (1988) and Evenchick et al. (2015), with previous interpretations of the stratigraphic position of Mokka Fiord strata, and the results of the current study. Precise stratigraphic positions of volcanic rocks in Isachsen Formation are approximate, and depicted based on relationships to bounding units. The ages of stratigraphic units are as cited in Fig. 2. Two combinations of interpretations of the Barremian-Aptian boundary and position of the top of Paterson Island Member are shown in A and B. The base of Paterson Island Member, Early to Late Valanginian, is not shown. Stratigraphic range of the Isachsen Formation in the study area, at right in A and B, is from palynology presented in this paper. Magnetic polarity timescale is from Ogg and Hinnov (2012). (A) Stratigraphic relationships using the timescale of Gradstein et al. (2012) and ages of Isachsen Formation following Galloway et al. (2015), with late Barremian age for Rondon Member. (B) Fig. 4A modified after Midtkandal et al. (2016, and others) for Barremian-Aptian boundary at 121-122 Ma, and after Herrle et al. (2015) for Paterson Island Member extending into lower Aptian. The top of Walker Island Member is moved up to allow it an age range of greater than ~2 my. This arbitrary amount does not impact interpretations. The positions of M0r and M”-1r” are moved up to approximately similar positions within the Aptian as in Fig. 4A, with M0 at base of Aptian, and M”-1r” above OEA1a (as in e.g. Erba 1996), which according to Herrle (2015; his Fig. 2) overlaps Rondon and base of Walker Island members on Axel Heiberg Island.

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Quaternary(?)

Fig. 6A,B }

x sample 15EP003A01 limit of igneous outcrop at creek is inferred to indicate strike at upper contact Fig. 6C Draft sample 15EP004A03 C i3 B i3 i2 i2

y y

i1 x

Fig. 5. Photographs of the south side of the creek west of the mouth of Mokka Fiord, showing the relationships between rock units, and relative positions of features discussed in text. The dash-dot line in A, B, and C is the same belt of bedding traces. (A) View south southwest, almost along strike of the igneous body, identified by outcrops at i1, i2, and i3. The location of the subhorizontal fine clastic rocks downstream of the igneous rocks, shown in Figs. 6A, B, is indicated at left. The southern limit of the bedding traces shown in Figs. 5B, C is at upper right. The northwest dip of the igneous body is inferred from the limit of dark brown outcrop highly resistant to erosion, and the dip of the body is inferred from the dipslope of resistant rock. The bend in the creek at x is considered to be controlled by the strike of the igneous body. The letters x and y indicate the same position in adjoining photographs. Width of view is approximately 400 m at foreground. (B) View approximately south to the area upstream from the igneous body. (C) View south southwest to bedded sedimentary rocks upstream from the igneous body, with overlap with Fig. 5B identified by y. The inset shows the distinctly bedded section that results in the surface traces of bedding indicated by dash-dot lines. Width of view is approximately 400 m. https://mc06.manuscriptcentral.com/cjes-pubs Page 53 of 54 Canadian Journal of Earth Sciences

Fig. 6B

B C Draft

D debris of shale, slumped Quaternary no bedrock and/or older sand, no bedrock

upstream limit of igneous bedrock Fig. 6C (no other bedrock at creek level) igneous bedrock inferred upper contact 2m of igneous body

Fig. 6. Photographs of outcrops in the vicinity of the igneous body east of Mokka Fiord. (A) View southwest to the only outcrop downstream from the igneous body; location is indicated in Fig. 5A. Sub-horizontal bedding can be seen across much of the outcrop. Areas examined are indicated by ovals. (B) Close view of laminated and cross-laminated fine-grained quartz sandstone and siltstone from which the palynology sample was collected. The hammer is 33 cm long. (C) Outcrop of the igneous body near its northwestern boundary and upper contact; location is shown in Figs. 5A and 6D. A hammer 33 cm long is near centre image. (D) Northwestern, upper contact area of the igneous body, showing extent of igneous bedrock and quality of exposure at the contact. Position of the contact is based on the upstream limit of igneous bedrock. Viewed to the south. https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 54 of 54

87°10' W inset in Fig. 5C ‘flow’ orientation from Wynne et al. (1988) 38° ~20° Fig. ~ 6A,B ~40° i1 ~35°

i2 subhorizonal bedding

orientation of Draft intrusion as i3 interpreted herein

inferred strike of intrusion 79°38' N

hypothetical fault N

Mokka Fiord igneous rocks? 0 500 metres

Fig. 7. Map showing interpreted relationships in the study area. The base image is the centre of airphoto A16858-143. Intrusive rocks identified in Fig. 5 are outlined by heavy dotted lines. Bedding traces continuous with the well-exposed bedding at the creek in Fig. 5C are indicated by a dash-dot line. Rocks in the southwest corner labelled 'igneous rocks?' have similar weathering characteristics to those exposed in the study area; they may be a different intrusion, or an en echelon part of the same intrusion. The white line with black dots is a hypothetical fault required to accommodate the discordance between the igneous body and bedding traces if the body is volcanic rock. https://mc06.manuscriptcentral.com/cjes-pubs