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? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 54 Canadian Journal of Earth Sciences 1 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 4 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 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 54 2 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. 40 41 Keywords: Sverdrup Basin, HALIP, paleomagnetism, stratigraphy, palynology 42 https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 54 Canadian Journal of Earth Sciences 3 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 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 54 4 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 https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 54 Canadian Journal of Earth Sciences 5 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.