Large Igneous Province Eruptions Research Articles

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.

Pervasive Hydrothermal Events Associated with Large Igneous Provinces Documented by the Columbia River Basaltic Province

The degree and extent of crustal hydrothermal alteration related to the eruption of large igneous provinces is poorly known and not easily recognizable in the field. We here report a new δ18O dataset for dikes and lavas from the Columbia River Basalt Group (16–15 Ma) in the western USA, and document that dikes on average are 1–2‰ more depleted in δ18O than basalt flows. We show that this observation is best explained with the involvement of heated meteoric waters during their cooling in the crust. The largest 6–8‰ depletion is found around and inside a 10 m-thick feeder dike that intruded the 125 Ma Wallowa tonalitic batholith. This dike likely operated as a magma conduit for 4–7 years, based on the extent of heating and melting its host rocks. We show that this dike also created a hydrothermal system around its contacts extending up to 100 m into the surrounding bedrock. A model that considers (a) hydrothermal circulation around the dike, (b) magma flow and (c) oxygen isotope exchange rates, suggests that the hydrothermal system operated for ~150 years after the cessation of magma flow. In agreement with a previously published (U-Th)/He thermochronology profile, our model shows that rocks 100 m away from such a dike can be hydrothermally altered. Collectively, our sample set is the first documentation of the widespread hydrothermal alteration of the shallow crust caused by the intrusion of dikes and sills of the Columbia River Basalt Province. It is estimated that heating and hydrothermal alteration of sediments rich in organic matter and carbonates around the dikes and sills releases 18 Gt of greenhouse gases (CH4 and CO2). Furthermore, hydrothermal δ18O depletion of rocks around dikes covers 500–600 km3, which, when scaled to the total CRB province constitutes 31,000 km3 of low-δ18O rocks. These volumes of crust depleted in δ18O are sufficient to explain the abundant low-δ18O magmas in eastern Oregon and western Idaho. This work also demonstrates that the width and magnitude of δ18O depletion around dikes can identify them as feeders. Given this, we here interpret Paleoproterozoic dikes in Karelia with the world’s lowest δ18O depletions (−27.8‰) as feeders to the coeval large igneous province aged 2.2–2.4 Ga that operated under the Snowball Earth glaciation conditions.

Evidence for the Carnian Pluvial Episode in Gondwana: New multiproxy climate records and their bearing on early dinosaur diversification

The Triassic hothouse world experienced dynamic changes in climate and ecosystems that set the Earth's climate and biotic states for much of the Mesozoic Era. A critical time interval was the Carnian Stage (~237–227 Ma), which not only saw the first appearance of dinosaurs in the fossil record but witnessed a large igneous province eruption (Wrangellia LIP) and a sudden climate shift, the Carnian Pluvial Episode (CPE). Compelling hypotheses suggest that the Wrangellia eruptions caused the CPE, which in turn set the stage for the origin and initial diversification of dinosaurs. Unfortunately, testing these hypotheses is difficult because most relevant Carnian sedimentary archives possess few if any absolute age constraints, and there are little detailed paleoclimatic data for the CPE outside of the Tethys region. There is little existing evidence for the CPE in Gondwana, even though this region contains by far the best fossil record of early dinosaurs and their close relatives. We present new high-resolution geochronologic and paleoclimatic data from Carnian-aged strata in the Ischigualasto-Villa Unión Basin of northwest Argentina, which also preserves fossils of the earliest-known dinosaurs. New CA-TIMS UPb zircon age of 234.47 ± 0.44 Ma from the lower Los Rastros Formation demonstrates that most of the overlying lacustrine strata within this basin was deposited during or after the CPE, including large dinosauriform footprints. Multiproxy paleoenvironmental data (sedimentology, clay mineralogy, C and O stable isotopes, and fossils) from the same strata are the first detailed paleoclimate data for the CPE in Gondwana, and provide evidence that the CPE interval in western Gondwana was indeed warmer and more humid than before or after. These data are consistent with the interpretation of the CPE as a global event, but direct linkages in Gondwana and the Tethys with the origin and initial diversification of dinosaurs are less clear.

Toxic mercury pulses into late Permian terrestrial and marine environments

Abstract Large spikes in mercury (Hg) concentration are observed globally at the latest Permian extinction (LPE) horizon that are thought to be related to enhanced volcanic emissions of the Siberian Traps large igneous province (LIP). While forming an effective chemostratigraphic marker, it remains unclear whether such enhanced volcanic Hg emissions could have generated toxic conditions that contributed to extinction processes. To address this, we examined the nature of enhanced Hg emissions from the Siberian Traps LIP and the potential impact it may have had on global ecosystems during the LPE. Model results for a LIP eruption predict that pulses of Hg emissions to the atmosphere would have been orders of magnitude greater than normal background conditions. When deposited into world environments, this would have generated a series of toxic shocks, each lasting >1000 yr. Such repeated Hg loading events would have had severe impact across marine trophic levels, as well as been toxic to terrestrial plant and animal life. Such high Hg loading rates may help explain the co-occurrence of marine and terrestrial extinctions.

High resolution osmium data record three distinct pulses of magmatic activity during cretaceous Oceanic Anoxic Event 2 (OAE-2)

Oceanic Anoxic Event 2 (OAE-2) occurred at the Cenomanian-Turonian boundary (∼94.1 Ma) and was a time of profound global changes in ocean chemistry and the carbon cycle. This event was characterized by a positive carbon isotope excursion (CIE) caused by massive organic carbon burial, global greenhouse temperatures, ocean deoxygenation, and changes in ocean life driven by large igneous province (LIP) activity. LIPs throughout the Phanerozoic have had dynamic magma flux, with episodes of major eruptions interspersed with periods of relatively less intense eruptions. A possible trigger for LIP activity throughout the Phanerozoic has been attributed to extraterrestrial impacts because there are multiple contemporaneous occurrences of large craters, LIP activity, and mass extinctions in the geologic record. At the Cenomanian-Turonian boundary, there is a 25 km diameter (rim-to-rim) complex crater in NW Alberta, Canada known as the Steen River impact structure dated at 91 ± 7 Ma (Carrigy and Short, 1968). An alternative explanation for those craters found contemporaneous with LIP activity and mass extinctions is that they were created by large explosive events related to LIP activity. Explosive events associated with mantle plume incubation beneath cratonic lithosphere have been suggested to create geologic features commonly attributed to impacts (e.g., shocked quartz, microspherules, etc.). Currently, the trigger for LIP activity during OAE-2, as well as the duration of LIP activity and the temporal variation and magnitude of eruption rates are not well constrained.To address the issue of LIP eruption rates and the trigger for LIP activity, we examined osmium (Os) abundances and isotopes as well as highly siderophile element (HSE; for this study: Re, Ru, Pd, Os, Ir, Pt) abundance data from a continuous sedimentary section spanning OAE-2. The section is from the Eagle Ford Group in the Iona-1 core, deposited in the Cretaceous Western Interior Seaway (KWIS). We found three high Os concentration intervals with mantle-like initial Osi isotope (initial 187Os/188Os) values of ∼0.16. These intervals are interpreted to reflect high-flux LIP magmatic pulses. Between the pulses, lower Os abundances with more radiogenic Osi values of ∼0.20 are observed, which we interpret as low-flux LIP activity between the high-flux periods. This trend of high-and-low flux Os concentration pulses with mantle-like Osi values during the high flux periods is found in another KWIS core (USGS Portland #1) deposited to the north of Iona-1, and in core Deep Sea Drilling Project (DSDP) Site 530 Hole A (hereafter DSDP 530A; drilled off-shore Namibia in the Angola Basin) deposited in the Southern Hemisphere. Before and throughout the Iona-1 core OAE-2 interval, HSE abundance patterns indicate a mantle source for the unradiogenic Os, and are not consistent with an extraterrestrial impact trigger or contribution to LIP activity during OAE-2.This evidence for multiple high-flux pulses of LIP activity driving ocean deoxygenation has implications for the modern ocean, which is currently experiencing deoxygenation. These results provide new constraints on subsequent high-flux periods that extended the event. The first high-flux period started ∼60 Kyr after our selection of the onset of the CIE. The second and third high-flux periods started ∼270 and ∼400 Kyr after the onset of the CIE, respectively. After the third high-flux period, δ13Corg and Os isotope ratios shifted back to pre-excursion values over ∼585 kyr. In the Iona-1 core, OAE-2 lasted for 1.04 ± 0.12 Myr based on our selection of the CIE.

Deep CO2 in the end-Triassic Central Atlantic Magmatic Province

Large Igneous Province eruptions coincide with many major Phanerozoic mass extinctions, suggesting a cause-effect relationship where volcanic degassing triggers global climatic changes. In order to fully understand this relationship, it is necessary to constrain the quantity and type of degassed magmatic volatiles, and to determine the depth of their source and the timing of eruption. Here we present direct evidence of abundant CO2 in basaltic rocks from the end-Triassic Central Atlantic Magmatic Province (CAMP), through investigation of gas exsolution bubbles preserved by melt inclusions. Our results indicate abundance of CO2 and a mantle and/or lower-middle crustal origin for at least part of the degassed carbon. The presence of deep carbon is a key control on the emplacement mode of CAMP magmas, favouring rapid eruption pulses (a few centuries each). Our estimates suggest that the amount of CO2 that each CAMP magmatic pulse injected into the end-Triassic atmosphere is comparable to the amount of anthropogenic emissions projected for the 21st century. Such large volumes of volcanic CO2 likely contributed to end-Triassic global warming and ocean acidification.

The lead-up to the Sturtian Snowball Earth: Neoproterozoic chemostratigraphy time-calibrated by the Tambien Group of Ethiopia

AbstractThe Tonian-Cryogenian Tambien Group of northern Ethiopia is a mixed carbonate-siliciclastic sequence that culminates in glacial deposits associated with the first of the Cryogenian glaciations—the Sturtian “Snowball Earth.” Tambien Group deposition occurred atop arc volcanics and volcaniclastics of the Tsaliet Group. New U-Pb isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates demonstrate that the transition between the Tsaliet and Tambien Groups occurred at ca. 820 Ma in western exposures and ca. 795 Ma in eastern exposures, which is consistent with west to east arc migration and deposition in an evolving back-arc basin. The presence of intercalated tuffs suitable for high-precision geochronology within the Tambien Group enable temporal constraints on stratigraphic data sets of the interval preceding, and leading into, the Sturtian glaciation. Recently discovered exposures of Sturtian glacial deposits and underlying Tambien Group strata in the Samre Fold-Thrust Belt present the opportunity to further utilize this unique association of tuffs and carbonate lithofacies. U-Pb ID-TIMS ages from zircons indicate that Tambien Group carbonates were deposited from ca. 820 Ma until 0–2 m.y. before the onset of the Sturtian glaciation, making the group host to a relatively complete carbonate stratigraphy leading into this glaciation. New δ13C and 87Sr/86Sr data and U-Pb ID-TIMS ages from the Tambien Group are used in conjunction with previously published isotopic and geochronologic data to construct newly time-calibrated composite Tonian carbon and strontium isotope curves. Tambien Group δ13C data and U-Pb ID-TIMS ages reveal that a pre-Sturtian sharp negative δ13C excursion (referred to as the Islay anomaly in the literature) precedes the Sturtian glaciation by ∼18 m.y., is synchronous in at least two separate basins, and is followed by a prolonged interval of positive δ13C values. The composite Tonian 87Sr/86Sr curve shows that, following an extended interval of low and relatively invariant values, inferred seawater 87Sr/86Sr rose ca. 880–770 Ma, then subsequently decreased leading up to the ca. 717 Ma initiation of the Sturtian glaciation. These data, when combined with a simple global weathering model and analyses of the timing and paleolatitude of large igneous province eruptions and arc accretion events, suggest that the 87Sr/86Sr increase was influenced by increased subaerial weathering of radiogenic lithologies as Rodinia rifted apart at low latitudes. The following 87Sr/86Sr decrease is consistent with enhanced subaerial weathering of arc lithologies accreting in the tropics over tens of millions of years, lowering pCO2 and contributing to the initiation of the Sturtian glaciation.

Triassic marine Os isotope record from a pelagic chert succession, Sakahogi section, Mino Belt, southwest Japan

Pelagic cherts preserved in accretionary complexes represent former seafloor sediment that can retain geochemical evidence of paleoceanographic conditions that predate the oldest extant oceanic crust. The ratio of Os isotopes in seawater, in particular, is of wide interest as a source of insight into notable geologic events such as oceanic anoxic events, rapid global warming episodes, and eruption of large igneous provinces, but marine Os isotope records from before 80 Ma are scarce. We present a record of secular variations of marine Os isotope ratios from a thick, continuous succession of Middle and Upper Triassic pelagic chert in the Sakahogi section of the Mino Belt accretionary complex. Initial Os isotope ratios (187Os/188Os) have a wide range in this succession, from 0.197 to 0.813. The variations in this Os record are quite similar to those in the marine Sr isotope record for the same time period, although their amplitudes differ owing to the differing residence times of Os and Sr in the ocean. Together, our results and previous data trace a continuous Os isotope record for ca. 50 Myr starting in Anisian time. We document the following six notable features in the Os record, which also appear in the Sr record, and their interpretation: (1) a negative (unradiogenic) shift associated with euxinia in the latest Anisian reflecting late-stage Siberian Traps eruptions, (2) wide fluctuations from the latest Anisian to Ladinian induced by volcanism and by the late Ladinian humid pulse and volcanism of the Italian Volcanic Center, (3) a continuous decrease in the early Carnian during eruptions of the Wrangellia large igneous province, (4) stable unradiogenic values from the early to early middle Norian associated with a prolonged arid period, (5) a negative spike in the middle Norian associated with the Manicouagan impact event, and (6) a broad rise and fall from the earliest late Norian to the Rhaetian ages, attributed to the Cimmerian-Indosinian orogeny and subsequent volcanism of the Central Atlantic Magmatic Province.

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.

The Carnian Pluvial Episode and the origin of dinosaurs

We present new evidence for a major inflection point in the history of tetrapods on land, a jump in the diversification of archosauromorphs, primarily dinosaurs, at 232–230 Ma. This corresponds to a long-noted changeover in Triassic terrestrial tetrapod faunas from those dominated by synapsids, many of them holdovers from the Permian, to those dominated by dinosaurs. The dinosaur explosion is shown here to correspond in timing to the Carnian Pluvial Episode (CPE), dated at 232 Ma, a time of increased rainfall and perturbation of oceans and atmospheres, followed by substantial aridification. The rock record through the CPE confirms that this event shared many characters with other mass extinctions driven by eruption of large igneous provinces, in this case the Wrangellia flood basalts of the west coast of North America. If this was a catastrophic extinction event, then the environmental perturbations of the CPE explain the sharp disappearance of various terrestrial tetrapods, and the subsequent sharp rise of dinosaurs and perhaps other clades too, especially those that constitute much of the modern terrestrial faunas, such as lissamphibians, turtles, crocodiles, lizards and mammals. Supplementary material: The sampled tetrapod faunas, geological ages, and details of the R code method and results are available at https://doi.org/10.6084/m9.figshare.c.4111439

Massive volcanism, evaporite deposition, and the chemical evolution of the Early Cretaceous ocean

Early Cretaceous (145–100 Ma) rocks record a ∼5‰ negative shift in the sulfur isotope composition of marine sulfate, the largest shift observed over the past 130 m.y. Two hypotheses have been proposed to explain this shift: (1) massive evaporite deposition associated with rifting during opening of the South Atlantic, and (2) increased inputs of volcanically derived sulfur due to eruption of large igneous provinces. Each process produces a very different impact on marine sulfate concentrations, which in turn affects several biogeochemical phenomena that regulate the global carbon cycle and climate. Here we present sulfur isotope data from Resolution Guyot, Mid-Pacific Mountains (North Pacific Ocean), that track sympathetically with strontium isotope records through the ∼5‰ negative sulfur isotope shift. We employ a linked sulfur-strontium isotope mass-balance model to identify the mechanisms driving the sulfur isotope evolution of the Cretaceous ocean. The model only reproduces the coupled negative sulfur and strontium isotope shifts when both hydrothermal and weathering fluxes increase. Our results indicate that marine sulfate concentrations increased significantly during the negative sulfur isotope shift and that enhanced hydrothermal and weathering input fluxes to the ocean played a dominant role in regulating the marine sulfur cycle and CO 2 exchange in the atmosphere-ocean system during this interval of rapid biogeochemical change.

High‐Resolution Floating Point Time Scale (FPTS) of the Permian Capitanian Stage in South China

AbstractHere we present a magnetic susceptibility (χ) dataset from the Permian Capitanian strata exposed in the Tieqiao section, Laibin area, South China, a supplementary reference section for the Guadalupian‐Lopingian (Middle‐Upper Permian) Global Boundary Stratotype Section and Point (GSSP). The succession consists of alternating thin‐bedded chert with micritic limestone of basinal and slope facies, with a carbonate cap indicating shallow‐water platform deposition. χ datasets, which are mostly negative (diamagnetic), suggest that the Laibin area was isolated from terrigenous sources during most of the Capitanian. A sudden increase in the χ signal just below the Guadalupian‐Lopingian (G‐L) boundary is recorded. Although regression at the terminal Capitanian might have contributed to the increase, the coincidence of the increase with the onset of the Emeishan Large Igneous Province (LIP) eruptions demonstrate pronounced volcanic effects controlling χ in this part of the section. χ and thermomagnetic susceptibility measurements indicate that the dominant magnetic constituents in this study are diamagnetic calcite and chert, with subordinate paramagnetic and ferrimagnetic minerals, derived from eolian and volcanic sources, and producing the cyclicity observed in the dataset.Spectral (time‐series) analyses of χ data were performed using Multi Taper Method (MTM) and Fourier Transform (FT) analysis. Five frequencies that are consistent with Milankovitch‐band orbital forcing were compared to the dataset: eccentricity E1 and E2 (100 and 405 ka, respectively), obliquity O2 (44.10 ka), and precession P1 (17.70 ka) and P2 (20.95 ka). Interpretation of these results indicates that the duration for the Capitanian in the Tieqiao section was ∼3.85 Ma. Likewise, the mean sediment accumulation rate (SAR) for the whole Capitanian was ∼2.91 cm·ka−1. In addition, graphic comparison of the Tieqiao χ data to a floating point time scale for Upper Wordian through Capitanian time allows estimates of the duration for conodont zones identified from the section; these ranging from 26.6 ka to 2.3 Ma before extinction of individual conodont species. Therefore, timing of the onset age of Emeishan LIP eruptions is estimated to yield an age of 262.7 Ma, with placement of these eruptions at 1.4 Ma below the G‐L boundary.

Large igneous provinces and organic carbon burial: Controls on global temperature and continental weathering during the Early Cretaceous

There is an abundance of evidence for short intervals of cold climatic conditions during the Early Cretaceous. However, the lack of a high-resolution, long-term Early Cretaceous paleotemperature record hampers a full-scale synthesis of these putative “cold snap” episodes, as well as a more holistic approach to Early Cretaceous climate changes. We present an extended compilation of belemnite-based oxygen, carbon and strontium isotope records covering the Berriasian–middle Albian from the Vocontian Basin (SE France). This dataset clearly demonstrates three intervals of cold climatic conditions during the Early Cretaceous (late Valanginian–earliest Hauterivian, late early Aptian, latest Aptian–earliest Albian). Each of these intervals is associated with rapid and high amplitude sea-level fluctuations, supporting the hypothesis of transient growth of polar ice caps during the Early Cretaceous. As evidenced by positive carbon isotope excursions, each cold episode is associated with enhanced burial of organic matter on a global scale. Moreover, there is a relatively good match between the timing and size of large igneous province eruptions and the amplitude of Early Cretaceous warming episodes. Altogether, these observations confirm the instrumental role of atmospheric CO2 variations in driving Early Cretaceous climate change. From a long-term perspective, the coupling of global paleotemperature and seawater strontium isotopic ratio during the Early Cretaceous is best explained by temperature-controlled changes of continental crust weathering rates.

Submarine palaeoenvironments during Emeishan flood basalt volcanism, SW China: Implications for plume–lithosphere interaction during the Capitanian, Middle Permian (‘end Guadalupian’) extinction event

Plume-induced lithospheric uplift and erosion are widely regarded as key features of large igneous province (LIP) emplacement, as is the coincidence of LIP eruption with major extinction and oceanic anoxic events (OAE). The Emeishan LIP, which erupted during the Capitanian (previously termed ‘end Guadalupian’) extinction event, has provided the most widely discussed example of axisymmetric doming above a rising mantle ‘plume’; advocates have argued that in excess of 500m of uplift occurred over >30000km2 causing extensive radially distributed erosion and alluvial fan formation. However, the recognition of submarine hydromagmatic and phreatomagmatic-style volcanism, as well as syn-volcanic marine sediments interbedded in the eruptive succession, now requires further examination to this simple plume–uplift model.Here we present data from newly discovered sections from the center of the putative uplifted area (around Lake Er Hai, SW Yunnan Province,) that provide a more complete history of the Emeishan volcanism. These reveal that platform carbonate deposition was terminated by rapid subsidence, followed quickly by the onset of volcanism. Importantly, these eruptions also coincide with widespread losses amongst fusulinacean foraminifera and calcareous algae. For at least the lower two thirds of the 4–5km thick lava pile, eruptions continued at or below sea level, as testified by the presence of voluminous mafic volcaniclastic deposits, pillow lavas, and development of syn-volcanic reefal limestones in the Emeishan inner zone. Only in the later stages of eruption did terrestrial lava flows become widely developed. This onset of volcanism in a submarine setting and the consequent violent, phreatomagmatic-style eruptions would have had a profound effect on marine fauna and exacerbated any volcanically induced climate effects during the Capitanian. The late Permian of SW China at the time of the Emeishan was an extended area of thinned lithosphere with epeiric seas, which appear to have been sustained through the onset of LIP emplacement. Therefore, while there remains substantial geochemical support of a plume origin for Emeishan volcanism, LIP emplacement cannot be ubiquitously associated with regional pre-eruption uplift, particularly where complex lithospheric structure exists above a plume.

Period-Tripling and Fractal Features in Multi-Billion Year Geological Records

Period-tripling is a common but rarely studied feature of natural processes. Its detection in long-term geological events is often restricted by poor preservation, inadequate time-resolution, and insufficient record lengths. This work includes an analysis of the highest-resolution and most complete multi-billion year sequence of geological and paleobiological records to determine the hierarchy of nonlinear (fractal) and periodic components. Using wavelet, spectral, and nonlinear analysis methods, a similar set of cycles emerged from these different records. The analyses indicate that the period-tripling pattern persists in geological and paleobiological events on time-scales of $$\sim $$ 30 to $$\sim $$ 1600 million years. The observed quasi-periodic tripling pattern could theoretically arise similar to bifurcations in a logistic map with a growth potential parameter of $$\mu =3.83$$ . Many of the period-tripled cycles exhibit half-cycle counter-parts. Most likely, the half-cycles developed from oscillations involving low-dynamic states versus the high-dynamic states of the full-cycles. Moreover, the period-tripling process contributes to fractal clustering of geological and biological events such as the eruptions of large igneous provinces. This is verified with the box-counting method for a model with a single dominant variable (a one-dimensional vector of $$d=0.815$$ ), for observational spans of less than 180 million years, and for a Cantor set model with a box dimension of ln(6)/ln(9).

A new interpretation of the sedimentary environment before and during eruption of the Emeishan LIP, Southwest China

The environment where the Permian Emeishan large igneous province (LIP) of Southwest China erupted remains controversial, especially regarding whether it was terrestrial, involving a 1 km scale domal uplift, or submarine. Slightly younger Daqiao conglomerate and Binchuan pillow lavas suggest that the Emeishan LIP erupted in a submarine environment. We show that at Binchuan, sandstone and rhyolite lie beneath the pillow lavas. In the Daqiao cross-section, there is an eastwards-verging syncline that reverses the succession of basalt and conglomerate. The conglomerate is not a basal conglomerate, and it does not contain any magmatic hydrovolcanic deposits. The basalt underlying the conglomerate is not the first of the LIP eruptions; that first eruption is found ~420 m below, on top of the Permian Maokou limestone. All together, these observations show that the deposits, including the conglomerate and pillow lava, do not represent the environment at the very start of the LIP volcanic eruptions, but represent conditions that existed before and possibly during the Emeishan LIP eruptions. Based on field investigations, the petrology of the rocks, and structural features, we conclude that submarine sedimentation and subaerial basalt eruptions coexisted in time and space in the region during or prior to the Emeishan LIP basalt eruptions.

Mesozoic eruptions of Large Igneous Provinces and environmental changes

Mesozoic eruptions of Large Igneous Provinces and environmental changes

The links between large igneous provinces, continental break-up and environmental change: evidence reviewed from Antarctica

ABSTRACTEarth history is punctuated by events during which large volumes of predominantly mafic magmas were generated and emplaced by processes that are generally accepted as being, unrelated to ‘normal’ sea-floor spreading and subduction processes. These events form large igneous provinces (LIPs) which are best preserved in the Mesozoic and Cenozoic where they occur as continental and ocean basin flood basalts, giant radiating dyke swarms, volcanic rifted margins, oceanic plateaus, submarine ridges, and seamount chains. The Mesozoic history of Antarctica is no exception in that a number of different igneous provinces were emplaced during the initial break-up and continued disintegration of Gondwana, leading to the isolation of Antarctica in a polar position. The link between the emplacement of the igneous rocks and continental break-up processes remains controversial. The environmental impact of large igneous province formation on the Earth System is equally debated. Large igneous province eruptions are coeval with, and may drive environmental and climatic effects including global warming, oceanic anoxia and/or increased oceanic fertilisation, calcification crises, mass extinction and release of gas hydrates.This review explores the links between the emplacement of large igneous provinces in Antarctica, the isolation of Antarctica from other Gondwana continents, and possibly related environmental and climatic changes during the Mesozoic and Cenozoic.

On the location of plumes and lateral movement of thermochemical structures with high bulk modulus in the 3-D compressible mantle

The two large low shear velocity provinces (LLSVPs) at the base of the lower mantle are prominent features in all shear wave tomography models. Various lines of evidence suggest that the LLSVPs are thermochemical and are stable on the order of hundreds of million years. Hot spots and large igneous province eruption sites tend to cluster around the edges of LLSVPs. With 3-D global spherical dynamic models, we investigate the location of plumes and lateral movement of chemical structures, which are composed of dense, high bulk modulus material. With reasonable values of bulk modulus and density anomalies, we find that the anomalous material forms dome-like structures with steep edges, which can survive for billions of years before being entrained. We find that more plumes occur near the edges, rather than on top, of the chemical domes. Moreover, plumes near the edges of domes have higher temperatures than those atop the domes. We find that the location of the downwelling region (subduction) controls the direction and speed of the lateral movement of domes. Domes tend to move away from subduction zones. The domes could remain relatively stationary when distant from subduction but would migrate rapidly when a new subduction zone initiates above. Generally, we find that a segment of a dome edge can be stationary for 200 million years, while other segments have rapid lateral movement. In the presence of time-dependent subduction, the computations suggest that maintaining the lateral fixity of the LLSVPs at the core-mantle boundary for longer than hundreds of million years is a challenge.

Climate changes caused by degassing of sediments during the emplacement of large igneous provinces: COMMENT

Many mass extinctions and biotic crises coincide with eruptions of large igneous provinces (LIPs), but a causal link remains disputed because many LIPs apparently had no severe deleterious impact on the biosphere ([Wignall, 2005][1]). [Ganino and Arndt (2009)][2] presented exciting data showing that