Sverdrup Basin Research Articles

Rift Competition in the Canadian Arctic: The Sverdrup Basin Case Study

Rift Competition in the Canadian Arctic: The Sverdrup Basin Case Study

Exploring the role of High Arctic Large Igneous Province volcanism on Early Cretaceous Arctic forests

The Hauterivian–Aptian Isachsen Formation at Glacier Fiord, Axel Heiberg Island, in the Sverdrup Basin of the Canadian Arctic Archipelago was deposited contemporaneous with initiation of the High Arctic Large Igneous Province (HALIP). New palynological biostratigraphy and paleoenvironmental reconstruction, in coordination with the emerging geochronology of HALIP igneous rocks, permits exploration of the effects of volcanism on Arctic vegetation during the Early Cretaceous. Four informal terrestrial palynofloral zones are defined and used to reconstruct vegetation change over the Isachsen Formation's ca. 17 million year history and explore the role of the HALIP in these changes. Climate warming during the Hauterivian promoted expansion of a hinterland community dominated by members of the Pinaceae. By the middle Barremian, this community was replaced by mixed heathland and mire, represented by up to 70% fern spores in the uppermost Paterson Island Member, that may be, in part, in response to environmental disturbance associated with volcanic flows of the HALIP. Above the fern spore spike, dinoflagellate cyst assemblages suggest an early Aptian age and a marine setting for mudstones of the Rondon Member in which Ocean Anoxic Event 1a is recorded. An interval of floral instability is recorded in the overlying Walker Island Member, characterized by fluctuations in Pinaceae and Cupressaceae pollen and fern spores, possibly as a result of post-OAE 1a temperature variabilty and landscape disturbance associated with lava flows of the HALIP that were repeatedly extruded onto the subsiding delta plain during deposition of the member.

Evidence for widespread wildfires and their environmental impact in the Late Cretaceous Canadian Arctic

Wildfires are important in modern ecology but the complex interplay between wildfires and vegetation or climate is less well understood in ancient environments, in particular those of the Arctic regions. This includes the impacts of paleo-wildfires on surrounding marine basins by affecting sedimentation rates and nutrient input via soil degeneration and intensification of continental run-off. The Late Cretaceous was an important time of global climate shift, with the rise of angiosperm vegetation marking a turning point in global flora, and globally abundant wildfires due to high atmospheric oxygen levels and elevated temperatures. This study investigates Late Cretaceous samples from the Canadian Arctic Islands to examine the evidence for widespread wildfires and how these wildfires may have influenced or been influenced by contemporaneous climate and vegetation shifts. Organic geochemical, and organic petrological data show evidence of enhanced wildfires beginning in the Turonian, including increases in semi-fusinite macerals and pyrogenic PAH (polycyclic aromatic hydrocarbon) indicators of natural combustion. This increasing wildfire influence corresponds with a rise in broad-leafed Arctic forests, as evidenced by angiosperm-derived terpenoid biomarkers, with both wildfire and angiosperm abundances peaking in the Early Campanian. Additionally, geochemical and petrographic data shows a shift in the type of organic matter deposited over time, correlating to the evidence of increased wildfire activity. This study proposes that the distance between wildfire region and marine depocenter is assessed via a new provenance method based on the degree of photo-oxic degradation of selected PAH isomers upon airborne transport. The increasing effects of wildfires on the Arctic ecosystem over the Turonian-Campanian were likely driven by relatively warm temperatures, elevated atmospheric oxygen, volcanism related to the High Arctic Large Igneous Province (HALIP), and abundant fuel availability. Widespread wildfires are proposed to have fostered the expansion of angiosperm vegetation into the Canadian Arctic in the Late Cretaceous by allowing them to outcompete gymnosperms in post-fire regrowth. Intensified erosion and continental run-off associated with the destruction of the vegetation cover by wildfires is thought to have acted as a driving force in the increasing terrigenous organic matter deposition in the Sverdrup Basin during the Late Cretaceous. Taken together, the results of this study suggest that increasing wildfires related to global climatic conditions in the Late Cretaceous contributed to the expansion of angiosperm flora in the Arctic, and had a substantial impact on the deposition of sediments in the surrounding Sverdrup Basin.

High Arctic Large Igneous Province Alkaline Rocks in Canada: Evidence for Multiple Mantle Components

Abstract The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135–90 Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (∼96 Ma) scatter around major fault and basement structures. They are represented by the newly defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanic rocks. The younger alkaline group is represented by the Wootton Intrusive Complex (92·2–92·7 Ma), and the Audhild Bay Suite (83–73 Ma), both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba–K–Zr–Ti that are nearly orthogonal to predicted fractionation- or melting-related variations, which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet lherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5–Ba–Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba–Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low 87Sr/86Sri. These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare earth element (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar–Hassel rocks, whereas other samples trend towards possible High-P2O5 + Zr (PZr) and High-P2O5 + K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases such as apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1) could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K–Rb–U–Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provides little support for a ubiquitous fossil sedimentary subduction-zone component in the HALIP mantle source.

Geochemical Systematics of High Arctic Large Igneous Province Continental Tholeiites from Canada—Evidence for Progressive Crustal Contamination in the Plumbing System

Abstract Cretaceous High Arctic large igneous province (HALIP) sub-alkaline magmatic rocks in Canada are mostly evolved (MgO 2–7 wt%), sparsely plagioclase + clinopyroxene ± olivine-phyric tholeiitic basalts. There were two main HALIP continental flood basalt (CFB) eruption episodes: 135–120 Ma (Isachsen Fm.) and 105–90 Ma (Strand Fiord Fm.), both associated with cogenetic doleritic sills and dykes. Building on a large modern database, 16 HALIP tholeiite types are defined and grouped into genetic series using Ce vs Sm/YbNMORB distributions. Comparison with model melting curves implies that higher-Sm/Yb HALIP basalt types record low-degree melting of garnet-bearing mantle sources. More voluminous intermediate- and low-Sm/Yb HALIP basalt types separated from the mantle at shallower levels after further extensive melting in the spinel-peridotite field. Within a given Sm/Yb range, increases in incompatible elements such as Ce are coupled with progressive clockwise rotation of normalized incompatible trace element profiles. Trace element modeling implies this cannot be due to closed-system fractional crystallization but requires progressive and ubiquitous incorporation of a component resembling continental crust. The fractionation models imply that low-Sm/Yb HALIP basalts (∼7 wt% MgO) initially crystallized olivine gabbro assemblages, with lower-MgO basalts successively crystallizing gabbro and ilmenite-gabbro assemblages. In contrast, higher-Sm/Yb basalts fractionated more clinopyroxene and ilmenite, but extensive plagioclase fractionation is still required to explain developing negative Sr–Eu anomalies. Back-fractionation models require about 40 % addition of olivine to bring the most primitive HALIP basalts (∼7 % MgO) into equilibrium with Fo89 mantle. Inverse fractionation–assimilation modeling shrinks the CFB signature, making decontaminated model parental melts more similar to enriched mid-ocean ridge basalt. The progressive increase of the contamination signature within each HALIP tholeiitic differentiation series is not consistent with models involving derivation of HALIP basalts from a mantle source previously enriched by subduction. Strong interaction of basalt with Sverdrup Basin sedimentary rocks may cause localized over-enrichment in K–Rb–Th–U, but cannot explain strong Ba enrichment in the absence of concomitant K–Rb–Th–U enrichment. The localized Ba enrichment could reflect either a Ba-rich lithospheric mantle component that is strongly manifested in the coeval HALIP alkaline suites, or syn- to post-emplacement fluid-mediated transfer from Ba-rich host rocks.

Carbon isotope and sequence stratigraphy of the upper Isachsen Formation on Axel Heiberg Island (Nunavut, Canada): High Arctic expression of oceanic anoxic event 1a in a deltaic environment

Abstract The Early Cretaceous oceanic anoxic event (OAE) 1a documents a major perturbation of the global carbon cycle with severe consequences for the ocean-climate-biosphere system. While numerous studies over the past decades have provided a relatively detailed picture of the environmental repercussions of OAE 1a at low and mid-latitudes, studies from high latitudes, in particular the High Arctic, are limited. In this study, we present a high-resolution carbon isotopic and sequence stratigraphic framework for the lower to lower upper Aptian interval of the Isachsen Formation of the High Arctic Sverdrup Basin (Canada). These data enable us to precisely locate the stratigraphic position of OAE 1a in a deltaic sedimentary environment. The carbon isotope record allows, for the first time, identification of the different carbon isotope segments (CISs) of OAE 1a in the Sverdrup Basin and thereby correlation of the High Arctic record with sections from lower latitudes. Based on this improved chemostratigraphy, we revise the age of upper Paterson Island, Rondon, and Walker Island Members, important regional lithostratigraphic marker units. Whole-rock geochemical data record two episodes of marine incursion into the Sverdrup Basin during OAE 1a (CISs Ap3 and Ap6), which are interpreted as regional maximum flooding surfaces. This information is used in conjunction with detailed sedimentological logs and geochemical grain-size proxies to refine the sequence stratigraphic framework for the upper Isachsen Formation. We propose that transgressive-regressive cycles in the Sverdrup Basin were controlled mainly by the combined effects of eustatic sea-level changes and regional tectonic uplift, potentially related to the emplacement of Alpha Ridge, which culminated at ca. 122 Ma during CIS Ap9.

Upper Paleozoic stratigraphy and detrital zircon geochronology along the northwest margin of the Sverdrup Basin, Arctic Canada: insight into the paleogeographic and tectonic evolution of Crockerland

The upper Paleozoic succession along the northwest margin of the Canadian Arctic Sverdrup Basin is little studied and poorly understood yet has the potential to yield insights into the paleogeographic and tectonic evolution of the Arctic regions including Crockerland. Carboniferous and Permian drill cuttings were collected from five exploration wells on Brock, Mackenzie King, and Ellef Ringnes islands. Seven unconformity-bounded sequences were identified and correlated. Reflection seismic interpreted on Ellef Ringnes Island indicates that a major syn-sedimentary fault offsets the Mississippian succession bounding a down-to-the-north half-graben. Late Pennsylvanian (Gzhelian) fault reactivation, associated with the Melvillian Disturbance, created a depression that extended northward and was bordered to the south by a structural high. Episodic minor fault reactivation occurred until the Early–Middle Permian boundary. During the latest Early Permian (Kungurian), sand derived from Crockerland prograded southward onto the Sverdrup Basin’s northwest margin and continued into the Roadian. After a lull during the Wordian, clastic progradation resumed in the Capitanian. Detrital zircon U–Pb ages recovered from Kungurian and Roadian samples on Brock and Ellef Ringnes islands display Devonian Clastic Wedge (DCW) signatures. A Moscovian–Artinskian carbonate blanket likely covered Crockerland and sheltered DCW material from erosion, implying it was a subsiding, carbonate bank throughout most of the Pennsylvanian – Early Permian. Base level fall in the Kungurian, associated with a transition to a more humid climate, breached these carbonate rocks to allow erosion and transportation of DCW material. Recycling of the DCW started earlier (Artinskian) and peaked later (Wordian) along the southern margin of the basin.

Macrofauna and biostratigraphy of the Rollrock Section, northern Ellesmere Island, Canadian Arctic Islands – a comprehensive high latitude archive of the Jurassic–Cretaceous transition

The Rollrock Section in the Sverdrup Basin of Arctic Canada is one of the northernmost outcrops where the Jurassic-Cretaceous transition is accessible. The over 500 m thick sedimentary succession exposes the Oxfordian to Valanginian Ringnes and Deer Bay formations. Macrofauna from 15 discrete horizons includes ammonites, Buchia bivalves and belemnites. These fossils improve the biostratigraphy of the Tithonian and Berriasian in the Sverdrup Basin, provide correlation to the remainder of the Boreal Realm and set reliable calibration points. The occurrence of Buchia rugosa in the Ringnes Formation moves the upper formation boundary from the top of the Kimmeridgian into the lower Tithonian. Dorsoplanites maximus and D. sachsi document the middle Tithonian Dorsoplanites maximus Zone in Arctic Canada for the first time. The late Tithonian to early Berriasian Buchia terebratuloides is considered to be the best approximate indicator of the Jurassic-Cretaceous transition in the Rollrock Section. The middle early Berriasian Praetollia maynci and the late early Berriasian Borealites fedorovi tie the respective horizons to the successive Chetaites sibiricus and Hectoroceras kochi zones. Two species of the belemnite Arctoteuthis, collected from an interval with common glendonites, suggest a Valanginian age for the upper Deer Bay Formation. The dearth of Late Jurassic to earliest Cretaceous macrofossils in the Sverdrup Basin is inferred to be predominantly a function of diagenetic carbonate loss. Abundant dropstones and glendonites in the middle Tithonian to middle Valanginian interval suggest cold climatic conditions, and make the Rollrock Section a prime candidate for studying the Arctic environmental perturbations of this time.

Bottom water redox conditions and benthic foraminiferal morphogroup response in the Late Cretaceous Sverdrup Basin, Arctic Canada: Implications for Oceanic Anoxic Event 3

Oceanic anoxic events (OAEs) represent significant perturbations in the global carbon cycle and therefore studying these events is critical for understanding drivers of carbon burial and variable oxygen conditions under a Cretaceous greenhouse climate mode. Here we present whole rock geochemical and benthic foraminiferal morphogroup data from two localities in the Sverdrup Basin in the High Arctic of Canada to investigate bottom water redox conditions during the Coniacian to Santonian OAE 3 interval. Major element geochemistry reflects lithological change and is related to shoreline proximity. Evidence for bottom water anoxia in the Late Cretaceous of the Sverdrup Basin is lacking and benthic dysoxia was limited to the Coniacian interval at the basin margin. Dysoxic conditions were characterized by elevated Mo concentrations and small epifaunal trochamminid species adapted to tolerate low oxygen levels. Elevated total organic carbon (TOC) in the Sverdrup Basin was related to relative sea-level changes, with increased erosion and terrestrial organic matter flux during transgression that promoted primary production. During transgressions to highstands, the Sverdrup Basin may have acted as a minor sink of carbon due to increased organic matter flux, potentially contributing to CO2 drawdown in the Late Cretaceous. Our comparison of six records across the Sverdrup and Western Interior basins demonstrates that no distinct OAE 3 interval can be determined based on the timing of benthic dysoxia to anoxia, TOC increases, and carbon isotopic excursions. Instead, organic burial records are driven by local tectonics influencing transgressive/regressive phases that are accentuated in shallows seas.

High latitude meteoric δ 18 O compositions from the Cenomanian Bastion Ridge Formation, Axel Heiberg Island, Canadian Arctic Archipelago: a palaeoclimate proxy from the Sverdrup Basin

Abstract Stable isotope analyses of a siderite-cemented siltstone from the Cenomanian Bastion Ridge Formation, Axel Heiberg Island, Canada, produce a range of δ 18 O values from −21.9 to −18.4‰ Vienna Pee Dee Belemnite (VPDB), and δ 13 C values ranging from 2.0 to 4.4‰ VPDB. A meteoric siderite line of −18.95 ± 0.33‰ VPDB is calculated from siderite cements of the authigenic component. At estimated palaeolatitude of 68–72° N and palaeotemperature range from 12.6 to 13.7°C, the calculated δ 18 O range of palaeoprecipitation is −23.3 to −23.0‰ Vienna Standard Mean Ocean Water (VSMOW). This result is compatible with other published meteoric water δ 18 O datasets from Cretaceous Arctic studies, but is near the lower end of the range of estimated δ 18 O values. The modern δ 18 O empirical relationship of Dansgaard and Earth System models simulating meteoric δ 18 O values does not yield results for palaeopolar regions that match proxy δ 18 O datasets. Orographic effects of contemporaneous mountain belts and seasonal biases in groundwater recharge have been proposed to explain this paradox regarding depleted meteoric water δ 18 O values from proxy data in greenhouse worlds. Evidence for local to regional orographic effects and alpine snowmelt biasing groundwater recharge is lacking for the Sverdrup Basin deposits, further indicating that the Dansgaard relationship does not apply to ancient greenhouse worlds.

Finding the VOICE: organic carbon isotope chemostratigraphy of Late Jurassic – Early Cretaceous Arctic Canada

AbstractA new carbon isotope record for two high-latitude sedimentary successions that span the Jurassic–Cretaceous boundary interval in the Sverdrup Basin of Arctic Canada is presented. This study, combined with other published Arctic data, shows a large negative isotopic excursion of organic carbon (δ13Corg) of 4‰ (V-PDB) and to a minimum of −30.7‰ in the probable middle Volgian Stage. This is followed by a return to less negative values ofc. −27‰. A smaller positive excursion in the Valanginian Stage ofc. 2‰, reaching maximum values of −24.6‰, is related to the Weissert Event. The Volgian isotopic trends are consistent with other high-latitude records but do not appear in δ13Ccarbrecords of Tethyan Tithonian strata. In the absence of any obvious definitive cause for the depleted δ13Corganomaly, we suggest several possible contributing factors. The Sverdrup Basin and other Arctic areas may have experienced compositional evolution away from open-marine δ13C values during the Volgian Age due to low global or large-scale regional sea levels, and later become effectively coupled to global oceans by Valanginian time when sea level rose. A geologically sudden increase in volcanism may have caused the large negative δ13Corgvalues seen in the Arctic Volgian records but the lack of precise geochronological age control for the Jurassic–Cretaceous boundary precludes direct comparison with potentially coincident events, such as the Shatsky Rise. This study offers improved correlation constraints and a refined C-isotope curve for the Boreal region throughout latest Jurassic and earliest Cretaceous time.

Diversity of igneous rocks from the Isachsen Dome, Ellef Ringnes Island, Canadian High Arctic

The sedimentary deposits of the central Sverdrup Basin on Ellef Ringnes Island were affected by both salt diapirism and igneous activity of the Cretaceous High Arctic Large Igneous Province (HALIP). Occurrences of mafic igneous rocks on the centre of salt domes are usually assigned to the Cretaceous magmatism. Petrographic, geochemical, Sr–Nd isotope, and geochronological (Ar–Ar dating) studies on six rock fragments collected on the top of Isachsen Dome reveal a larger variability in the composition and the age compared to HALIP-related rocks from elsewhere on Ellef Ringnes Island. A blocky fragment of tholeiitic hornblende dolerite with an Ar–Ar age of 121 Ma is interpreted to originate from an in-situ intrusion and was uplifted by evaporite diapirism. The other samples are small, sub-rounded pebbles, which represent three different parent rock types. A kaersutite-bearing alkali basalt was possibly formed during the Triassic or Permian. A leucocratic, albitised rock fragment has experienced contact metasomatism at 102 Ma, and three very similar tholeiitic basalt fragments probably derived from the margin of a dyke were auto-hydrothermally affected at 69 Ma. The inferred source area of these exotic pebbles is the segment of the Arctic continental margin in the northeast that was repeatedly affected by igneous events between the Carboniferous and latest Cretaceous and that was uplifted and eroded during the Eocene. The rock fragments were probably deposited as Palaeogene sediments above the rising Isachsen diapir shortly before or as the head of the salt dome has pierced the Earth’s surface. Glacial transport up the top of Isachsen Dome during the Late Wisconsinan glaciation is not very likely due to the contrast between the north to northwest directed ice-flow direction reported in the literature and the assumed northeastern source area of the pebbles; however, it cannot be completely excluded.

Influence of igneous intrusions on the thermal maturity of organic matter in the Sverdrup Basin, Arctic Canada

The influence of igneous intrusions on the trend of thermal maturity with depth in two drillholes, one on Ellesmere Island and the other on Ellef Ringnes Island, Arctic Canada, was assessed using vitrinite and solid bitumen reflectance, Rock-Eval pyrolysis/TOC, and gas composition analysis in order to assess the impact of igneous intrusions on the hydrocarbon system in the area. Thick sequences of Permo-Pennsylvanian strata in Sabine Peninsula, Melville Island, were intruded by two igneous intrusions in the Panarctic Chads Creek B-64 (influenced by one intrusion) and the Panarctic Drake Point D-68 (influenced by two intrusions). Sedimentary strata in Chads Creek B-64 were intruded by a 120 m-thick diabase sill (with temperature of ~1100 °C) of unknown age. This resulted in increased reflectance of vitrinite from 0.90% to 1.65% and of pyrobitumen from 2.90% to almost 5.80% near the sill contact at depth of 3600 m. Solid bitumen outside of the thermal aureole zones and having reflectance values <1.50% followed the extrapolated trend for solid bitumen present in the country rocks. In Panarctic Drake Point D-68, the intrusives are granodiorite sills of 45 m and 75 m thickness and were emplaced during the Upper Jurassic (152 Ma) and Lower Cretaceous (131 Ma). The intrusion temperature was 800 °C. The Vitrinite Rr prior to sill emplacement was <1.0% outside the aureole and increased to approximately 2.0% near the intrusive zone. The rocks were well-lithified prior to sill emplacement. Solid bitumen underwent carbonization after being exposed to a temperature of at least 800 °C. Solid bitumen reflectance also showed a sudden increase from a minimum of 1.50% outside the aureole to approximately 7.0% near the sill contact, a 5× increase as compared to an increase of 2× for vitrinite. This indicates that solid bitumen is a very sensitive indicator of temperature variation, more sensitive than vitrinite. Solid bitumen reflectance prior to the sill emplacement can only be inferred from the solid bitumen below the lower, younger sill because of poor control on solid bitumen in the interval just above the upper, older sill. Reflectance trends above and below the sills appear to be symmetrical despite the superimposition of the effects of one sill on the other. The metamorphic effects of the sill, as determined vertically by the reflectance trend, can be observed for a distance of up to seven times its thickness. The upper, older sill is approximately 45 m thick and the thermal aureole zone above it has a width of 330 m. The thickness of the aureole below the sill is difficult to establish because it has been obliterated by the effect of the lower, younger sill. The thickness of the lower sill is 75 m. An additional factor that influenced solid bitumen reflectance in this case may have been the thickness of the sill, which, in turn, affects the cooling time of the intrusive body. The granodiorite sills are approximately 45–75 m thick and the diabase sill is almost 120 m.

Controls on the formation of microbially induced sedimentary structures and biotic recovery in the Lower Triassic of Arctic Canada

Abstract Microbially induced sedimentary structures (MISS) are reportedly widespread in the Early Triassic and their occurrence is attributed to either the extinction of marine grazers (allowing mat preservation) during the Permo-Triassic mass extinction or the suppression of grazing due to harsh, oxygen-poor conditions in its aftermath. Here we report on the abundant occurrence of MISS in the Lower Triassic Blind Fiord Formation of the Sverdrup Basin, Arctic Canada. Sedimentological analysis shows that mid-shelf settings were dominated by deposition from cohesive sand-mud flows that produced heterolithic, rippled sandstone facies that pass down dip into laminated siltstones and ultimately basinal mudrocks. The absence of storm beds and any other “event beds” points to an unusual climatic regime of humid, quiet conditions characterized by near continuous run off. Geochemical proxies for oxygenation (Mo/Al, Th/U, and pyrite framboid analysis) indicate that lower dysoxic conditions prevailed in the basin for much of the Early Triassic. The resultant lack of bioturbation allowed the development and preservation of MISS, including wrinkle structures and bubble textures. The microbial mats responsible for these structures are envisaged to have thrived, on sandy substrates, within the photic zone, in oxygen-poor conditions. The dysoxic history was punctuated by better-oxygenated phases, which coincide with the loss of MISS. Thus, Permo-Triassic boundary and Griesbachian mudrocks from the deepest-water settings have common benthos and a well-developed, tiered burrow profile dominated by Phycosiphon. The presence of the intense burrowing in the earliest Triassic contradicts the notion that bioturbation was severely suppressed at this time due to extinction losses at the end of the Permian. The notion that Early Triassic MISS preservation was caused by the extinction of mat grazers is not tenable.

The Capitanian (Guadalupian, Middle Permian) mass extinction in NW Pangea (Borup Fiord, Arctic Canada): A global crisis driven by volcanism and anoxia

Abstract Until recently, the biotic crisis that occurred within the Capitanian Stage (Middle Permian, ca. 262 Ma) was known only from equatorial (Tethyan) latitudes, and its global extent was poorly resolved. The discovery of a Boreal Capitanian crisis in Spitsbergen, with losses of similar magnitude to those in low latitudes, indicated that the event was geographically widespread, but further non-Tethyan records are needed to confirm this as a true mass extinction. The cause of this crisis is similarly controversial: While the temporal coincidence of the extinction and the onset of volcanism in the Emeishan large igneous province in China provides a clear link between those phenomena, the proximal kill mechanism is unclear. Here, we present an integrated fossil, pyrite framboid, and geochemical study of the Middle to Late Permian section of the Sverdrup Basin at Borup Fiord, Ellesmere Island, Arctic Canada. As in Spitsbergen, the Capitanian extinction is recorded by brachiopods in a chert/limestone succession 30–40 m below the Permian-Triassic boundary. The extinction level shows elevated concentrations of redox-sensitive trace metals (Mo, V, U, Mn), and contemporary pyrite framboid populations are dominated by small individuals, suggestive of a causal role for anoxia in the wider Boreal crisis. Mercury concentrations—a proxy for volcanism—are generally low throughout the succession but are elevated at the extinction level, and this spike withstands normalization to total organic carbon, total sulfur, and aluminum. We suggest this is the smoking gun of eruptions in the distant Emeishan large igneous province, which drove high-latitude anoxia via global warming. Although the global Capitanian extinction might have had different regional mechanisms, like the more famous extinction at the end of the Permian, each had its roots in large igneous province volcanism.

Enigmatic massive sulphide mineralization in the High Arctic Large Igneous Province, Nunavut, Canada

Modern mineral exploration strategies should take into account nontraditional metallogenic models for a given geological environment. Here we document the first detailed study of a massive sulphide showing associated with the High Arctic Large Igneous Province (HALIP) and Sverdrup Basin and in fact, only the second example of mineralization described from Axel Heiberg Island, Queen Elizabeth Islands, Canadian Arctic Archipelago. The Between Lake showing (western Axel Heiberg Island) is a small massive sulphide occurrence within scree/talus below a large ridge of gabbro. It was originally described by explorationists as an orthomagmatic sulphide occurrence hosted within a dioritic dyke. New petrographic and mineralogical analyses indicate that the showing consists predominantly of pyrrhotite with lesser pyrite, trace chalcopyrite, and rare sphalerite. No Ni- or Pb-bearing sulphide minerals were detected. Geochemically, the showing contains some Co and Cu, rare Zn, and generally very low Ni contents (&lt;9 ppm). Sulphur isotope ratios of sulphide minerals range from +3.6 to + 6.6‰, somewhat heavier than expected for magmatic-derived S but isotopically lighter than S associated with local evaporite diapirs (+5.8‰ to +12.2‰). Orthomagmatic sulphides hosted in the diorite typically exhibit even lighter isotopic ratios of –3.9‰ to –1.00‰. The data are consistent with potential mafic–siliciclastic volcanogenic massive sulphide mineralization, or the like, the first documented in the HALIP. High heat flow associated with extensive HALIP magmatism was likely the driving force for such mineralization. Mineral prospectivity in Canada’s High Arctic had been predicated upon the potential presence of magmatic Ni – Cu – platinum group element sulphide mineralization. Rather than negating this potential, our findings provide evidence for additional metallogenic potential for this region of Nunavut.

Mixed local and ultra-distal volcanic ash deposition within the Upper Cretaceous Kanguk Formation, Sverdrup Basin, Canadian Arctic Islands

AbstractThe Upper Cretaceous Kanguk Formation of the Sverdrup Basin, Canadian Arctic Islands, contains numerous diagenetically altered volcanic ash layers (bentonites). Eleven bentonites were sampled from an outcrop section on Ellesmere Island for U–Pb zircon secondary ion mass spectrometry dating and whole-rock geochemical analysis. Two distinct types of bentonite are identified from the geochemical data. Relatively thick (0.1 to 5 m) peralkaline rhyolitic to trachytic bentonites erupted in an intraplate tectonic setting. These occur throughout the upper Turonian to lower Campanian (c. 92–83 Ma) outcrop section and are likely associated with the alkaline phase of the High Arctic Large Igneous Province. Two thinner (&lt;5 cm) subalkaline dacitic to rhyolitic bentonites of late Turonian to early Coniacian age (c. 90–88 Ma) are also identified. The geochemistry of these bentonites is consistent with derivation from volcanoes within an active continental margin tectonic setting. The lack of nearby potential sources of subalkaline magmatism, together with the thinner bed thickness of the subalkaline bentonites and the small size of zircon phenocrysts therein (typically 50–80 μm in length) are consistent with a more distal source area. The zircon U–Pb age and whole-rock geochemistry of these two subalkaline bentonites correlate with an interval of intense volcanism in the Okhotsk–Chukotka Volcanic Belt, Russia. It is proposed that during late Turonian to early Coniacian times intense volcanism within the Okhotsk–Chukotka Volcanic Belt resulted in widespread volcanic ash dispersal across Arctic Alaska and Canada, reaching as far east as the Sverdrup Basin, more than 3000 km away.

Influence of the High Arctic Igneous Province on the Cenomanian/Turonian boundary interval, Sverdrup Basin, High Canadian Arctic

Emplacement of Large Igneous Provinces (LIPs) had a major effect on global climate, ocean chemistries as traced in sedimentary records and biotic turnovers. The linkage between LIPs and oceanic anoxic events has been documented with the Cenomanian/Turonian boundary event and Oceanic Anoxic Event 2 (OAE2). The Caribbean LIP and High Arctic Large Igneous Province (HALIP) are regarded as possible triggers. The pericratonic Arctic Sverdrup Basin is the partial location of the HALIP, where little is known about sedimentary, geochemical and biotic responses to the HALIP phases. Sedimentary strata at Glacier Fiord, Axel Heiberg Island, exhibit a dynamic Cretaceous polar carbon burial history within the lower to middle Cenomanian Bastion Ridge Formation and upper Cenomanian to Turonian part of the Kanguk Formation. We present the first initial 187Os/188Os (Osi) composition profile for a polar Cenomanian/Turonian boundary interval (∼100–93.9 Ma) linked to recently dated magmatic phases of the Strand Fiord Formation, part of the HALIP. The carbon isotope record coupled with the Osi profile show two events in the upper Cenomanian interval marked by positive carbon perturbations and shifts to more non-radiogenic Osi compositions. The earlier short-lived event is interpreted as result of weathering of the surrounding Strand Fiord volcanics causing a local non-radiogenic Osi signal. Coinciding transgressive shorelines let to an increase in marine and terrestrially derived organic matter. Subsequently, injection of mantle-derived basalts into organic rich sediments is credited with causing the release of methane documented in a distinct negative carbon isotope excursion. We speculate that the methane release of the HALIP was an important contribution for rapid global warming caused by increasing atmospheric CO2 levels associated with the OAE2 event likewise recognized in the Sverdrup Basin. As climate cooled in the middle and late Turonian, carbon burial decreased under increasingly oxygenated benthic conditions. Epifaunal foraminiferal species, adapted to low oxygen conditions, persisted during the OAE2. Our Cenomanian to Turonian multiproxy record of the Sverdrup Basin distinguishes between local and global signals within a restricted High Arctic basin. Our results demonstrate the interplay between basin tectonism and sea-level change, increased weathering during transgressive phases, seafloor processes such as hydrothermal activity and methane release and biotic response to a complex paleoceanography. With future reliable dated frameworks this unique polar record will facilitate correlations to other polar basins and records of lower paleolatitudes.

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

New data and interpretations on geological relationships of igneous rocks at Mokka Fiord, Axel Heiberg Island, Nunavut, provide insight into the timing and nature of magmatism associated with the Sverdrup Basin and High Arctic Large Igneous Province (HALIP). Field relationships indicate that the igneous rocks, previously interpreted to be volcanic flows, are most likely an intrusive unit discordant to regional bedding. An intrusive origin helps resolve chronostratigraphic inconsistencies in previous work. The host rocks are palynologically constrained to be late Barremian to late Aptian in age and are interpreted to be Paterson Island or Walker Island member of the Isachsen Formation. If the igneous body is intrusive, it’s previously reported Ar–Ar age (102.5 ± 2.6 Ma) is no longer in conflict with accepted stratigraphic interpretations and probably reflects the emplacement age of the intrusion. Lingering uncertainties in interpreting the normal and reverse magnetic polarities determined in the previous work remain, and both are considered viable. Although this uncertainty precludes definitive conclusions on the significance of paleomagnetic data at Mokka Fiord, examination of the stratigraphic, paleomagnetic, and geochronologic relationships there highlight potential for the study of excursions, or reversed magnetic polarity subchrons, in the Cretaceous Normal Superchron elsewhere in the HALIP.

Lac des Bois, a locality in the northern Western Interior Seaway (Canada) with Tethyan faunal connections during the Cenomanian/Turonian Thermal Maximum

Early Turonian fishes are known from only a few localities in the Northern Hemisphere, including three in the present-day European/Mediterranean region and three in northern Canada. One of the latter localities, Lac des Bois (66°52.087ʹ N), preserves a diverse marine fauna composed of trace fossils, foraminifera, molluscs and actinopterygian fishes including early acanthomorphs. The molluscan fauna, as well as a radiometric date from bentonites recovered from the site, support an age of latest Cenomanian/early Turonian for the locality. This interval spans the global Oceanic Anoxic Event 2, a time characterized globally by high temperatures and high carbon burial. Although the Cenomanian/Turonian boundary interval has been documented in North America in the Arctic Sverdrup Basin and the southern Interior Seaway, the present study provides the first account of a faunal assemblage that inhabited the northern Western Interior Seaway during this interval. Organic-rich shales and sandstones indicate limited organic decomposition and low oxygen conditions, although the presence of trace fossils (Skolithos, Planolites, Taenidium and Alcyonidopsis, as well as fugichnia) indicates that the sea floor was not completely anoxic. The presence of coiled planktic foraminifera indicates warmer water and extends the known migration limit of these Tethyan-derived forms some 6° further north. Surprisingly, the fish fauna of localities in the Bohemian Cretaceous Basin (Czech Republic) bears a close resemblance to that of Lac des Bois, although acanthomorph fish have not been recorded from the former. This suggests faunal connections between the two regions, either through the northern Polar Sea, or through the postulated Hudson Strait.