Emplacement Of Large Igneous Provinces Research Articles

Local melt contamination and global climate impact: Dating the emplacement of Karoo LIP sills into organic-rich shale

The emplacement of Large Igneous Provinces (LIPs) is commonly correlated with global climate change, and environmental and biological crises. To establish this complex causative link, chemical proxies from marine sedimentary sections must be temporally tied to LIP activity through high-precision geochronology. The temporal link is often ambiguous, especially as periods of environmental change are commonly shorter than the full duration of magmatic and volcanic activity in a LIP. Most importantly, temporal relations need to be established through precise and accurate U-Pb geochronology; however, mafic rocks are often undersaturated in zircon or baddeleyite. New U-Pb age determinations of pegmatitic pods from Karoo LIP dolerite sills into the Ecca Group of the Karoo Basin yield single crystal dates with uncertainties below 50 ka, which allow for a new, detailed assessment of this intrusive event. These samples yield complicated age spectra and Hf geochemistry, which indicate that localized assimilation of sedimentary rocks enabled zircon saturation within these mafic melts. Zircon crystallization age interpretations from these data indicate that sill emplacement within the Ecca Group was coeval across the basin within uncertainty of U-Pb dating, and therefore represents a period of particularly high magma flux. Since the Ecca Group is locally exceptionally rich in organic matter, the widespread and rapid sill-related contact metamorphism generated a significant volume of thermogenic volatiles. Given the temporal overlap of the emplacement of sills between 183.147 ± 0.059 Ma and 183.187 ± 0.133 Ma and the timing of the global Toarcian Oceanic Anoxic Event (TOAE), our data support a causal link between this discrete period of high flux emplacement of Karoo sills into the Ecca Group and the global climate change that took place during the Early Jurassic.

Two-pronged kill mechanism at the end-Triassic mass extinction

AbstractHigh-resolution biomarker and compound-specific isotope distributions coupled with the degradation of calcareous fossil remnants reveal that intensive euxinia and decalcification (acidification) driven by Central Atlantic magmatic province (CAMP) activity formed a two-pronged kill mechanism at the end-Triassic mass extinction. In a newly proposed extinction interval for the basal Blue Lias Formation (Bristol Channel Basin, UK), biomarker distributions reveal an episode of persistent photic zone euxinia (PZE) that extended further upward into the surface waters. In the same interval, shelly taxa almost completely disappear. Beginning in the basal paper shales of the Blue Lias Formation, a Lilliput assemblage is preserved consisting of only rare calcitic oysters (Liostrea) and ghost fossils of decalcified aragonitic bivalves. The stressors of PZE and decalcification parsimoniously explain the extinction event and inform possible combined causes of other biotic crises linked to emplacement of large igneous provinces, notably the end-Permian mass extinction, when PZE occurred on a broad and perhaps global scale.

Background Earth system state amplified Carnian (Late Triassic) environmental changes

Past major biological turnovers are coeval to large injections of CO2 into the atmosphere–ocean system that are often linked to the emplacement of Large Igneous Provinces. The impact of these CO2 pulses on ecosystems is however different at different times, and this difference is contingent on the initial boundary conditions. Here, we show how delayed vegetation recovery from the Permo–Triassic mass extinction (ca. 252 Ma) and continuing amalgamation of Pangaea, determined the style of the Late Triassic Carnian Pluvial Episode (ca. 233 Ma), a global climate change event linked to a major biological turnover and to the emplacement of the Wrangellia LIP. Our new biogeochemical modelling can reproduce changes in C and Sr isotopes only when we assume that high terrestrial productivity recovers in the Carnian, ∼15 Myrs after the Permo–Triassic crisis, consistent with the re-appearance of large coal swamps. In the model, this early Carnian expansion of the terrestrial organic C reservoir results in a drop of atmospheric pCO2 and global temperatures. Furthermore, climate modelling shows how the resulting low pCO2 conditions, coupled to the aridity of Pangaea, made the Carnian Earth system more susceptible to hydrological cycle enhancements following C inputs from coeval volcanism, thus explaining the nature of the Carnian Pluvial Episode.

The life cycle of large igneous provinces

Extremely voluminous magmatic systems known as large igneous provinces (LIPs) punctuate Earth’s history, and the gases they release plausibly link large-scale geodynamic and magmatic processes with major climate shifts in Earth’s geological record. However, quantifying the relationships between magmatism, gas release and environmental changes remains challenging. In this Review, we explore the major insights and outstanding questions regarding the linked evolution of mantle melting, expansive magmatic systems and the redistribution of volatiles from the solid Earth to the atmosphere. The evolution of mantle melt generation during LIP episodes sets the fundamental tempo of magma emplacement throughout the crust. The progression of crustal LIP magmatism and associated hydrothermal activity help shape the chemical evolution of the continental lithosphere and surface environment. Percolation of magmatic and metamorphic volatiles can decouple the tempo of gas release — a potential key driver of environmental changes — from the tempo of extrusive volcanic activity. LIPs demonstrate how large-scale magmatic systems interact with the surrounding lithosphere to propel evolving regimes of magma and volatile transfer through the crust. New, temporally resolved constraints on the evolution of LIP plumbing systems are needed to keep pace with increasingly precise timelines of palaeoenvironmental change during LIP emplacement. Major environmental disruptions throughout Earth’s history are often linked to extensive magmatic events, termed large igneous provinces. This Review explores the coupled evolution of mantle melting, magmatism and volatile release over the life cycle of large igneous provinces.

Ecosystem change and carbon cycle perturbation preceded the end-Triassic mass extinction

During the Phanerozoic, major global upheavals in life history and the carbon cycle are predominantly linked to the emplacement of large igneous provinces, but the delineation of a cause and effect framework remains unclear. The end-Triassic mass extinction (ETE) is temporally associated with emplacement of the Central Atlantic magmatic province (CAMP). A better understanding of precursor events to the ETE is essential if the mechanisms for this mass extinction are to be fully delineated. Here, we present new high-resolution data integrating petrographic, biotic, mercury, and carbon isotope analyses of the pre-extinction interval at the Ferguson Hill locality, Nevada (USA). We document the “precursor” carbon isotope excursion along with low Hg concentrations and sulphidic sediments prior to the ETE. A combination of proxies reveals disruptions to shallow marine ecosystems and biogeochemical cycles prior to the main phase of CAMP volcanism. We propose that episodic anoxic conditions led to the restructuring of shallow marine benthic ecosystems towards overall lower diversity, including more low oxygen tolerant taxa preceding the ETE. The timing of the initial marine ecosystem restructuring in eastern Panthalassa could be related to the early phase of CAMP emplacement, and implies that an early intrusive event initiated the ecosystem changes. These restructured marine ecosystems reflect the deteriorating environmental conditions leading up to the ETE that ultimately resulted in the ETE.

Coronene, mercury, and biomarker data support a link between extinction magnitude and volcanic intensity in the Late Devonian

The Late Devonian biodiversity crisis, one of the big five Phanerozoic diversity depletions, is composed of a series of extinction events broadly coincident with the invasion of land by plants and vertebrates. These extinctions may have been triggered by volcanism, as sedimentary mercury enrichments are associated with the two main extinctions, the Kellwasser and Hangenberg crises. However, the sources of this mercury and its relation to volcanic style are not known. Furthermore, any links between the magnitudes of volcanic emissions and biodiversity loss have not been explored. To address these issues, we develop a new suite a geochemical data from shallow water sedimentary rocks in France, Belgium, and China for three Late Devonian crises – the Kellwasser and Hangenberg events, as well as for the preceding Frasnian extinction. We report paired coronene – mercury data as a refined proxy for large igneous province (LIP) emplacement, and we use cadalene and dibenzofuran biomarkers as proxies for terrestrial ecological disturbance. Coronene is a highly condensed six-ring polycyclic aromatic hydrocarbon (PAH), which requires significantly higher energy to form as compared to smaller PAHs; coronene enrichment has been found only in LIP volcanic emission and projectile impact events. Our data show that coronene and mercury coincidentally peaked at only the environmental and biotic events, demonstrating that pulses of LIP volcanism are tightly associated with the Late Devonian crises. In addition, mercury concentration is highly correlated with cadalene and dibenzofuran abundance during the events only in nearshore settings, indicating fluxes of soil erosion. Finally, we observe a correlation between coronene index and extinction magnitude for the three events, suggesting a link between temperatures of sills and lavas during LIP emplacement, pressure of evolved volatiles, and global climatic effects.

Chapter 1.1 Tectonic history of Antarctica over the past 200 million years

Abstract The tectonic evolution of Antarctica in the Mesozoic and Cenozoic eras was marked by igneous activity that formed as a result of simultaneous continental rifting and subduction processes acting during the final stages of the southward drift of Gondwana towards the South Pole. For the most part, continental rifting resulted in the progressive disintegration of the Gondwana supercontinent from Middle Jurassic times to the final isolation of Antarctica at the South Pole following the Cenozoic opening of the surrounding ocean basins, and the separation of Antarctica from South America and Australia. The initial rifting into East and West Gondwana was proceeded by emplacement of large igneous provinces preserved in present-day South America, Africa and Antarctica. Continued rifting within Antarctica did not lead to continental separation but to the development of the West Antarctic Rift System, dividing the continent into the East and West Antarctic plates, and uplift of the Transantarctic Mountains. Motion between East and West Antarctica has been accommodated by a series of discrete rifting pulses with a westward shift and concentration of the motion throughout the Cenozoic leading to crustal thinning, subsidence, elevated heat flow conditions and rift-related magmatic activity. Contemporaneous with the disintegration of Gondwana and the isolation of Antarctica, subduction processes were active along the palaeo-Pacific margin of Antarctica recorded by magmatic arcs, accretionary complexes, and forearc and back-arc basin sequences. A low in magmatic activity between 156 and 142 Ma suggests that subduction may have ceased during this time. Today, following the gradual cessation of the Antarctic rifting and surrounding subduction, the Antarctic continent is situated close to the centre of a large Antarctic Plate which, with the exception of an active margin on the northern tip of the Antarctic Peninsula, is surrounded by active spreading ridges.

Bushveld superplume drove Proterozoic magmatism and metallogenesis in Australia

Large-scale mantle convective processes are commonly reflected in the emplacement of Large Igneous Provinces (LIPs). These are high-volume, short-duration magmatic events consisting mainly of extensive flood basalts and their associated plumbing systems. One of the most voluminous LIPs in the geological record is the ~ 2.06 billion-year-old Bushveld Igneous Complex of South Africa (BIC), one of the most mineralised magmatic complexes on Earth. Surprisingly, the known geographic envelope of magmatism related to the BIC is limited to a series of satellite intrusions in southern Africa and has not been traced further afield. This appears inconsistent with the inferred large size of the BIC event. Here, we present new radiometric ages for alkaline magmatism in the Archean Yilgarn Craton (Western Australia), which overlap the emplacement age of the BIC and indicate a much more extensive geographic footprint of the BIC magmatic event. To assess plume involvement at this distance, we present numerical simulations of mantle plume impingement at the base of the lithosphere, and constrain a relationship between the radial extent of volcanism versus time, excess temperature and plume size. These simulations suggest that the thermal influence of large plume events could extend for thousands of km within a few million years, and produce widespread alkaline magmatism, crustal extension potentially leading to continental break-up, and large ore deposits in distal sectors. Our results imply that superplumes may produce very extensive and diverse magmatic and metallogenic provinces, which may now be preserved in widely-dispersed continental blocks.

Pulsed volcanic combustion events coincident with the end-Permian terrestrial disturbance and the following global crisis

Abstract Eruption of the Siberian Traps large igneous province (LIP) is thought to have triggered the Permian-Triassic biological crisis, the largest of the Phanerozoic mass extinctions. Mercury concentration enrichments have been widely used as a proxy for volcanic inputs to sediments, especially for ancient LIP eruptions. However, detailed correlations of magmatic pulses with extinction events in the terrestrial and marine realms are not fully resolved. Here we use paired coronene (a six-ring polycyclic aromatic hydrocarbon, a high-temperature combustion proxy) and mercury spikes as a refined proxy for LIP emplacement. In records from stratigraphic sections in south China and Italy, we identify two sets of paired coronene-mercury spikes accompanied by land plant biomarker spikes, followed by a rapid decrease coinciding with terrestrial ecological disturbance and extinction of marine metazoans. Each short-term episode is likely caused by high-temperature combustion of sedimentary hydrocarbons during initial sill emplacement of the Siberian Traps LIP. These data indicate that discrete volcanic eruptions could have caused the terrestrial ecosystem crisis followed by the marine ecosystem crisis in ∼60 k.y., and that the terrestrial ecosystem was disrupted by smaller global environmental changes than the marine ecosystem.

Complex Interactions Between Large Igneous Province Emplacement and Global‐Temperature Changes During the Cenomanian‐Turonian Oceanic Anoxic Event (OAE 2)

AbstractSuper greenhouse temperatures at the onset of the Cenomanian‐Turonian oceanic anoxic event (OAE 2) have been widely linked with large igneous province (LIP) volcanic activity. However, the extent to which volcanism influenced subsequent climate changes throughout OAE 2, such as global cooling during the Plenus Cold Event (PCE) early in the OAE, and the subsequent return to very warm conditions through the second part of the crisis remain less clear. Here, new osmium‐isotope (187Os/188Os) data are presented from the northeastern margin of the proto‐North Atlantic Ocean (ODP Leg 174AX Bass River, NJ, USA). The results are consistent with previously published OAE 2 records and are similarly interpreted as documenting LIP activity while further demonstrating the ability to use osmium‐isotope stratigraphy as a global chemostratigraphic marker in open‐ocean records. Correlations of 187Os/188Os and sea‐surface temperature trends at Bass River and other sites show that the earliest PCE cooling coincided with intense volcanism, but that LIP activity began to decline during or soon after the cold pulse. These temporal relationships support previous hypotheses that the PCE was regionally diachronous and likely caused by enhanced carbon sequestration via organic‐matter burial and silicate weathering, rather than a period of volcanic quiescence, while the persistently warm conditions later in OAE 2 were linked to reduced silicate weathering rather than sustained volcanism. These findings highlight the complex interactions between LIP emplacement and climate responses during OAE 2, reemphasizing the need for similar correlations between volcanism and paleotemperature proxy data for other major events in Earth's history.

Volcanic controls on seawater sulfate over the past 120 million years

Changes in the geological sulfur cycle are inferred from the sulfur isotopic composition of marine barite. The structure of the 34S/32S record from the Mesozoic to present, which includes ∼50- and 100-Ma stepwise increases, has been interpreted as the result of microbial isotope effects or abrupt changes to tectonics and associated pyrite burial. Untangling the physical processes that govern the marine sulfur cycle and associated isotopic change is critical to understanding how climate, atmospheric oxygenation, and marine ecology have coevolved over geologic time. Here we demonstrate that the sulfur outgassing associated with emplacement of large igneous provinces can produce the apparent stepwise jumps in the isotopic record when coupled to long-term changes in burial efficiency. The record of large igneous provinces map onto the required outgassing events in our model, with the two largest steps in the sulfur isotope record coinciding with the emplacement of large igneous provinces into volatile-rich sedimentary basins. This solution provides a quantitative picture of the last 120 My of change in the ocean's largest oxidant reservoir.

Lu-Hf systematics of 4.0 – 2.3 Ga old zircons from the Turee Creek Group (Pilbara Craton, W. Australia): Implications on the rise of atmospheric oxygen and global glaciation during the Paleoproterozoic

We investigated the Hf isotopic systematics of detrital zircons in a succession of siliciclastic sediments and glacial diamictites from the early Paleoproterozoic sequence of the Boolgeeda Iron Formation (Hamersley Group) and overlying Turee Creek Group of the Pilbara Craton, Western Australia. About 400 detrital zircons yielding >95% concordant U-Pb ages were analyzed for Hf isotopes to constrain their magmatic sources. 70% of the analyzed zircons display super-chondritic initial Hf isotopic compositions, demonstrating crystallization in mantle-derived magmas. Most of the data are comprised between model age lines at ~2.5 and 3.2 Ga, which suggests a sub-continuous crust generation by extraction from the depleted mantle during this time period. A single grain yields a 4.0 Ga age, which represents the first Hadean age for a zircon from the Pilbara Craton. Our results are significantly different from zircon Hf isotope data of the Glenburgh Terrane, in the southern border of the Turee Creek Group, or older successions of the Pilbara, Kaapvaal and Superior cratons, but show overlap with some of the Yilgarn Craton. This together with the occurrence of a Hadean zircon crystal preserved in the Boolgeeda glacial diamictite with similar Hf isotopic signature than the Jack Hills zircons makes the Yilgarn Craton a possible source material for the Boolgeeda glacial horizon. Alternatively, the majority of the zircons analyzed show ages which are consistent with those of the underlying 2.45–2.78 Ga Hamersley and Fortescue groups, formed by sedimentary successions interleaved with thick subaerial volcanic sequences associated with the emplacement of Large Igneous Provinces. Such subaerial volcanic rocks could account for the relatively juvenile character of the zircon analyzed. A local provenance of the siliciclastic material delivered to the Turee Creek Basin would support the role of large subaerial magmatic provinces as triggers of the rise of atmospheric oxygen and the onset of glaciations at the beginning of the Proterozoic.

Stable climate in India during Deccan volcanism suggests limited influence on K–Pg extinction

Large igneous provinces (LIPs) have been temporally correlated to mass extinctions throughout the Phanerozoic, including the emplacement of the Deccan Volcanic Province (DVP; 66.3–65.6 Ma) in western and central India, which has been invoked as either a cause or exacerbating factor in the Cretaceous-Paleogene (K-Pg) extinction. However, relatively little is known about local paleoclimatic and paleoenvironmental responses to volcanism. To investigate the DVP's role as a driver of local environmental change and to provide climatic background for known ecological shifts, new inter-basaltic paleosol profiles at the eastern edge of the DVP are used in conjunction with profiles from the literature to reconstruct paleoclimate and terrestrial environments before and after the K–Pg. These profiles provide a novel opportunity to study the sediments within basalt flows before, during, and after a mass extinction event and in the midst of a LIP emplacement event. Paleoclimate proxies and the Floral Humidity Province proxy reflect little long-term change in either climate or environment across the K–Pg, with stable precipitation values and temperatures accompanied by a constant forest signal. These interpretations are corroborated by macrofloral records and sedimentology from India, which suggest some environmental turnover but generally support a forested, fluvio-lacustrine environment throughout the duration of volcanism. Our results support the possibility of rapid recovery times for terrestrial ecosystems during volcanism and suggest that while DVP eruptions may have exacerbated long-term environmental perturbation, the emplacement of the DVP is not likely to have caused the terrestrial mass extinction at the K–Pg boundary.

U-Pb zircon age constraints on the earliest eruptions of the Deccan Large Igneous Province, Malwa Plateau, India

Climate instability driven by emission of volatiles during emplacement of large igneous provinces (LIPs) is frequently invoked as a potential cause of mass extinctions. However, documenting this process in the geologic record requires a holistic understanding of eruption rates, the location of eruptive centers, and potential sources of climate-changing volatiles. We present new chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon geochronology from Malwa Plateau basalts on the northern margin of the Deccan LIP, India. These basalts have been previously interpreted as either an extension of the province's main volcanic stratigraphy or as an independent eruptive center active up to millions of years prior to the main eruptive phase. Our data instead demonstrate that the lower Malwa Plateau basalts are temporally correlative with the first pulse of Deccan volcanism and provide new constraints on its initiation and duration. Paleomagnetic data further indicate that upper Malwa Plateau basalts may be age-equivalent to the second, third, and fourth pulses of Deccan volcanism. The relative thicknesses of age-equivalent packages of basalt are consistent with eruption of the Deccan LIP from a southward-migrating eruptive center. The first eruptive pulse is coeval with a ∼200 kyr Late Maastrichtian warming event preserved globally in contemporaneous stratigraphic sections. We propose that the first pulse of Deccan magmatism was more voluminous in the north, where it erupted through organic-rich sedimentary rocks of the Narmada-Tapti rift basin. Thermal metamorphism of these sediments could have been a source of sufficient CO2 to drive the Late Maastrichtian warming event, which if true would reconcile the apparent dampened warming signals associated with later Deccan eruptive pulses.

Reconstruction of the chaotic behavior of the Solar System from geologic records

Astronomical solutions for planetary orbits beyond several tens of million years (Myr) ago have large uncertainties due to the chaotic nature of the Solar System, mainly Myr-scale cycles related with the Earth-Mars secular resonance. Our only accessible archive for unraveling the Earth's orbital variations in the geologic past are sedimentological records, yet their reliability and uncertainties are still debated. Here, we describe Myr-scale orbital signals of early Mesozoic monsoon records from two different sedimentary settings (lake level records of the equatorial Pangea and biogenic silica burial flux of deep-sea Panthalassa), along with a marine carbon isotope compilation. Although most of the dominant multi-Myr cycles are not exactly of the same frequency, 1.8 Myr cycles during ∼216–210 Ma are detected from the two mutually-independent sedimentary settings, and differ from available astronomical solutions. This finding provides not only convincing evidence for the chaotic nature of the Solar System in the geological past, but also additional constraints on astronomical models. On the other hand, besides the orbital cycles, tectonic forcing and consequent climatic perturbations could also have affected the proxies on multi-Myr timescales during episodes of large igneous province emplacement, such as Siberian trap volcanism (252–245 Ma), Wrangellia (233–225 Ma), Central Atlantic Magmatic Province (202–200 Ma), and Karoo-Ferrar volcanism (184–180 Ma). If we can distinguish orbital signals from other effects, such as tectonic and volcanic processes, the multi-Myr cycles in geologic records have the potential to reconstruct the chaotic evolution of the Solar System.

Basalt hills of Torres, southern Brazil: World-class geology, its heritage value, and tourism perspectives

The geological heritage of Brazil represents a wide spectrum of unique phenomena. Field investigations in the Torres locality (vicinity of Torres town, Rio Grande do Sul State, Brazil) have highlighted the value of the exposed geological features. These include columnar basalts of the Cretaceous Paraná-Etendeka large igneous province, basalt hills and cliffs, non-karst caves, rockfalls, etc. These features are assigned to six geological heritage types, namely igneous, tectonic, geomorphological, sedimentary, palaeogeographical, and engineering types. Three of them (igneous, palaeogeographical, and engineering types) demonstrate global uniqueness. These unique features are exposed at three points, which are proposed as geosites, namely Torre Sul and Torre da Guarita, Morro das Furnas, and Morro do Farol (also geomorphosites). The former of them appears to be the most valuable due to its diversity, and it is ranked as global. The Torres locality provides exceptional opportunities for understanding the events before Gondwana breakup and during the time span of major large igneous province emplacement. The world class geological heritage of Torres indicates a significant potential for geotourism. The presence of state parks popular among visitors, and the notable biodiversity of the study area, would support geotourism growth. However, urban pressure and tourist crowding create risks for local community, and particularly for geosites. Thus, a special plan for sustainable (geo)tourism development in the Torres locality is required.

Deep Carbon and the Life Cycle of Large Igneous Provinces

Carbon is central to the formation and environmental impact of large igneous provinces (LIPs). These vast magmatic events occur over geologically short timescales and include voluminous flood basalts, along with silicic and low-volume alkaline magmas. Surface outgassing of CO2 from flood basalts may average up to 3,000 Mt per year during LIP emplacement and is subsidized by fractionating magmas deep in the crust. The large quantities of carbon mobilized in LIPs may be sourced from the convecting mantle, lithospheric mantle and crust. The relative significance of each potential carbon source is poorly known and probably varies between LIPs. Because LIPs draw on mantle reservoirs typically untapped during plate boundary magmatism, they are integral to Earth's long-term carbon cycle.

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.

Geomagnetic Secular Variations at the Permian‐Triassic Boundary and Pulsed Magmatism During Eruption of the Siberian Traps

AbstractThe tempo of Large Igneous Province emplacement is crucial to determining the environmental consequences of magmatism on the Earth. Based on detailed flow‐by‐flow paleomagnetic data from the most representative Permian‐Triassic Siberian Traps lava stratigraphy of the northern Siberian platform, we present new constraints on the rate and duration of the volcanic activity in the Norilsk and Maymecha‐Kotuy regions. Our data indicate that volcanic activity there occurred during a limited number of short volcanic pulses, each consisting of multiple individual eruptions, and that the total duration of discrete eruption pulses did not exceed ~10,000 years (hiatuses are not included). Our study confirms the occurrence of a thick interval in the lower part of the Norilsk lava sections, which contains a record of geomagnetic reversal and excursion. Based on combined evidence from paleomagnetic secular variation and typical timescales for such reversals, we conclude that the ~1‐km‐thick lava stratigraphy, corresponding to ~20,000 km3 of basalt, of the Kharaelakh, Norilsk, and Imangda troughs was formed during a brief, but voluminous, eruptive period of several thousand years or less. Our data further suggest that the ore‐bearing Norilsk‐type intrusions are coeval or nearly coeval with the boundary between the Morongovsky and Mokulaevsky formations. We calculated a new Siberian Permian‐Triassic paleomagnetic pole Norilsk‐Maymecha‐Kotuy (NMK): PLat = 52.9°, PLong = 147.1°, A95 = 4.3°, K = 23.2, and N = 49 lava flows. It is shown that geomagnetic field variations circa 252 Ma were similar to those observed in the latest Cenozoic.

Does large igneous province volcanism always perturb the mercury cycle? Comparing the records of Oceanic Anoxic Event 2 and the end-Cretaceous to other Mesozoic events

Mercury (Hg) is increasingly being used as a sedimentary tracer of Large Igneous Province (LIP) volcanism, and supports hypotheses of a coincidence between the formation of several LIPs and episodes of mass extinction and major environmental perturbation. However, numerous important questions remain to be answered before Hg can be claimed as an unequivocal fingerprint of LIP volcanism, as well as an understanding of why some sedimentary records document clear Hg enrichment signals whilst others do not. Of particular importance is evaluating the impact of different volcanic styles on the global mercury cycle, as well as the role played by depositional processes in recording global Hg-cycle perturbations. Here, new mercury records of Cretaceous Oceanic Anoxic Event 2 (OAE 2: ∼94 Ma) and the latest Cretaceous (∼67–66.0 Ma) are presented. OAE 2 is associated with the emplacement of multiple, predominantly submarine, LIPs; the latest Cretaceous with subaerial volcanism of the Deccan Traps. Both of these connections are strongly supported by previously published trends towards unradiogenic osmium- (Os) isotope values in globally distributed sedimentary records. Hg data from both events show considerable variation between different locations, attributed to the effectiveness of different sediment types in registering the Hg signal, with lithologically homogeneous records documenting more clear Hg enrichments than sections with major changes in lithology such as limestones to claystones or organic-rich shales. Crucially, there is no geographically consistent signal of sedimentary Hg enrichment in stratigraphic records of either OAE 2 or the latest Cretaceous that matches Os-isotope evidence for LIP emplacement, indicating that volcanism did not cause a global Hg perturbation throughout the entire eruptive history of the LIPs formed at those times. It is suggested that the discrepancy between Os-isotope and Hg trends in records of OAE 2 is caused by the limited dispersal range of Hg emitted from submarine volcanoes compared to the global-scale distribution of Os. A similar lack of correlation between these two proxies in uppermost Cretaceous strata indicates that, although subaerial volcanism can perturb the global Hg cycle, not all subaerial eruptions will do so. These results highlight the variable impact of different volcanogenic processes on the efficiency of Hg dispersal across the globe. Factors that could influence the impact of LIP eruptions on the global mercury cycle include submarine versus subaerial volcanism, volcanic intensity or explosivity, and the potential contribution of thermogenic mercury from reactions between ascending magma and surrounding organic-rich sediments.