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Ordovician-Silurian volcanism in northern Iran: Implications for a new Large Igneous Province (LIP) and a robust candidate for the Late Ordovician mass extinction
Abstract
Proxies such as mercury and Hg/TOC anomalies document signatures for temporal correlations between major pulses of the Late Ordovician mass extinction (LOME) event and a postulated Large Igneous Province (LIP) as the main cause of extinction. Herein, for the first time, we report a series of voluminous intraplate volcanic events of the Middle Ordovician-Silurian from northern Iran, representing the erosional and deformed remnants of a LIP as well as a robust candidate as the cause of the LOME. These volcanic rocks, distributed over a length of ca. 1700 km and more than 1000 m thickness in some cases, were erupted during initial rifting of the Paleotethys Ocean in northern Gondwana. Based on fieldwork, relative ages, and high precision U-Pb ID-TIMS dating results we have identified one plutonic (granitic) and six volcanic (mainly basaltic) phases of mostly short duration for this chain of magmatism. The onset of volcanic events at 468.70±0.30 Ma (2σ) coincided with the earliest Darriwilian, followed by a huge bimodal volcanic event between the Sandbian-Katian boundary and 450.61±0.27 million years ago, and the climax of volcanism occurred during the late Katian-Hirnantian. An approximate coincidence between the onset of basaltic eruption and weathering in northern Iran and the beginning of significant global decline in seawater ⁸⁷Sr/⁸⁶Sr during the Darriwilian Stage may be a sign of the initial volcanic activities of our newly identified LIP. We suggest that the Middle Ordovician-Silurian volcanic rocks from northern Iran, and other related places, are remnants of this newly proposed LIP (herein labeled the Alborz LIP), with high potential to be the main cause of environmental and climatic changes that led to the LOME.
Supplementary resources (2)
... After Ediacaran-Cambrian Cadomian continental arc magmatism and related active-margin extension (e.g., Taknar complex, ~ 550 Ma; Moghadam et al. 2017b), Ordovician-Silurian rift-related volcanism, stretching across Iran from Alborz-Azerbaijan in the northwest, the Alborz, to the Kopet-Dagh-Binalood of northeastern Iran, records continental rifting (e.g., Buzhan basalts, ~ 469 Ma; Derakhshi et al. 2022). The generation of Paleo-Tethys oceanic lithosphere is badly dated with MORB-like remnants preserved in the Anarak area of Central Iran (e.g., Groups 1 and 2 in the Carboniferous and Permotriassic domains of Buchs et al. 2013). ...
... The youngest detrital zircon U-Pb age cluster in the siliciclastic rocks is 544 ± 20 Ma, late Ediacaran (Chu et al. 2021). A pegmatitic gabbro yielded a Middle Ordovician age (ID-TIMS U-Pb zircon, 468.7 ± 0.30 Ma, 2 s, sample MD19-NMB; Derakhshi et al. 2022). Derakhshi et al. (2022) interpreted these igneous rocks as part of a large igneous province. ...
... A pegmatitic gabbro yielded a Middle Ordovician age (ID-TIMS U-Pb zircon, 468.7 ± 0.30 Ma, 2 s, sample MD19-NMB; Derakhshi et al. 2022). Derakhshi et al. (2022) interpreted these igneous rocks as part of a large igneous province. Herein, we focus on the geochemistry and geochronology of the mafic to felsic volcanic rocks in the Neyshabur thrust sheet. ...
Geochemical and geochronologic data are presented for meta-mafic to meta-felsic rocks along the Paleo-Tethys Suture in the Binalood Mountains east of Neyshabur, NE Iran. The rocks have a late Cambrian age (U–Pb zircon, ~ 490 Ma) and were metamorphosed in the Early Jurassic ( ⁴⁰ Ar/ ³⁹ Ar amphibole and plagioclase, 199–192 Ma). The rocks of this suite are alkaline and sub-alkaline (tholeiitic). The alkaline rocks are enriched in light relative to heavy rare earth elements, and do not show depletion of high-field strength elements on primitive mantle-normalized multi-element diagrams; they are similar to ocean island basalts (OIB). The tholeiitic rocks are depleted in Nb and Ta and have higher MgO and lower TiO 2 than the alkaline rocks. Both types have similar, high and variable ⁸⁷ Sr/ ⁸⁶ Sr (i) isotopic compositions of 0.7044 to 0.7082 and ¹⁴³ Nd/ ¹⁴⁴ Nd (i) values of 0.5118 to 0.5122. The alkaline rocks are lower-degree partial melts than the tholeiitic rocks and were generated at greater depths; they likely originated from a garnet pyroxenite-rich source. The spatial, temporal, and geochemical relationships of early Paleozoic meta-mafic to felsic rocks along the Paleo-Tethys Suture (e.g., Shahrud, Jajarm, Binalood, Torbat-e-Jam) substantiate the role of a mantle plume in continental breakup along the northern margin of Gondwana and a late Cambrian-Ordovician onset of rifting that resulted in the opening of the Paleo-Tethys Ocean. The Early Jurassic metamorphism post-dates its closure.
Graphical abstract
... It has also been suggested that the preceding late Katian Boda warming event was instigated either by explosive arc-associated volcanism or Glossary Table I in Box 1) [36,40,41]. Until recently, no direct evidence for a Late Ordovician LIP had been reported, but a potential candidate, the Alborz LIP, has recently been described from northern Iran [42]. Figure 1. ...
... Further note the four phases of the Alborz large igneous province (LIP) and the shift from primarily marine (blue) to subaerial (brown) eruptions towards the later part of the Ordovician. Sources: eruption probability [43], Alborz LIP [42], 13 C record [75], sea-surface temperature (SSE) [16,33,76] and richness [4][5][6]. Abbreviations: Ae, Aeronian; Dp, Dapingian; GICE, Gutenberg isotopic carbon excursion; H, Hirnantian; Rh, Rhuddanian; Sand, Sandbian; Tel, Telychian; V-PDB, Vienna Peedee Belemnite reference standard. ...
The Late Ordovician mass extinction event is the oldest of the five great extinc- tion events in the fossil record. It has long been regarded as an outlier among mass extinctions, primarily due to its association with a cooling climate. How- ever, recent temporally better resolved fossil biodiversity estimates complicate this view, providing growing evidence for a prolonged but punctuated biodiver- sity decline modulated by changes in atmospheric composition, ocean chemis- try, and viable habitat area. This evolving view invokes extinction drivers similar to those that occurred during other major extinctions; some are even factors in the current human-induced biodiversity crisis. Even this very ancient and, at first glance, exceptional event conveys important lessons about the intensifying ‘sixth mass extinction’.
... Lithospheric extension is recorded by rift-related bimodal magmatism and sedimentation during ca. 530-490 Ma, (e.g., Sepidbar et al., 2020), followed by rift-related alkaline magmatism and sedimentation from Ordovician (Derakhshi et al., 2022) to Carboniferous Stöcklin, 1968). However, it is still unknown whether the opening of the Paleo-Tethys Ocean was controlled by mantle-plume, or by subduction-related back-arc extension. ...
... The 461.8 Ma ages of fine-grained gabbro along with old ages of zircons (460-440 Ma) from coarse-grained gabbroic rocks may represent the initial magmas along fractures during plume upwelling, while the large-scale eruption of the mantle plume may have occurred at ca. 435 Ma. The older ages of mafic rocks are also reported by Derakhshi et al. (2022) for coarse-grained gabbro from Buzhan area in the Binaloud zone, suggesting that mantle plum activity in the Binaloud zone to be as old as 460 Ma and lasted to ca. 435 Ma, for 25 m.y. These ages are older or similar with respect to the opening of the Paleo-Tethys Ocean. ...
Documentation of continental rifting processes such as mantle plume activity is important for understanding the nature and evolution of tectonic plates. In this study, we report detailed petrological, geochronological, geochemical, Srsingle bondNd isotope, and mineral chemical data for basalt, and coarse- and fine-grained gabbro from the Binaloud zone of the Alborz, which is the easternmost extension of the Avalonian-Cadomian Orogenic Belts and the western parts of Indo-Australia Orogenic Belt, central-east Asia. Uranium–lead zircon dating of fine- and coarse-grained gabbro indicates that they have been formed at 461.8 ± 8.2 and 435.0 ± 4.5 Ma, respectively. The basalt and gabbro have large variations in elemental and isotopic compositions, with 44.0–50.0 wt% SiO2, 124–411 ppm Sr, and εNd(t) of +0.1 to +3.3. All the rocks show OIB-like or transitional OIB−/E-MORB-like geochemical characteristics, without noticeable Nbsingle bondTi depletion, diagnostic of an intraplate affinity. Whole-rock geochemical and isotopic compositions combined with mineral compositions suggest that both basalt and gabbro have been generated by a plume/asthenospheric mantle (OIB-type) source mixed with enriched subcontinental lithospheric mantle components. Partial melting of such a source in the transitional spinel-garnet stability field was followed by different degrees of fractional crystallization of olivine, clinopyroxene, and plagioclase. Our study demonstrates that roll-back of the subducting Tornquist (Eastern Ipateous ocean) oceanic lithosphere has been followed by plume activity, continental rifting and Paleo-Tethys opening during the Silurian period.
... The volcanic eruptions were documented by spikes in the mercury enrichment of sediments in different locations of the world during the biotic crisis of the Hirnantian Stage or just below the Katian-Hirnantian boundary, including the Laurentia and South China [86 ], and the Holy Cross Mountains on the southern Baltic margins [87 ]. Hirnantian volcanics and volcaniclastics, probably related to a Large Igneous Province (LIP) have been recently reported from the Alborz Mountains in northern Iran [88 ] in addition to ash beds already reported from South China [23 ]. Support for a longer more sustained phase of volcanicity has been presented more recently, suggesting volcanoes were active some 10 myr prior to the Hirnantian Age [1 ]. (ii) A hypothesis involving the rate of silicate weathering in controlling levels of atmospheric CO 2 requires the exposure of silicates to enhance weathering [89 ]; the transit of silicate-dominated massifs through the intertropical convergence zone where high rainfall would have favoured chemical weathering as would terrestrial vegetation. ...
The Late Ordovician Mass Extinction was the earliest of the ‘big’ five extinction events and the earliest to affect the trajectory of metazoan life. Two phases have been identified near the start of the Hirnantian period and in the middle. It was a massive taxonomic extinction, a weak phylogenetic extinction and a relatively benign ecological extinction. A rapid cooling, triggering a major ice age that reduced the temperature of surface waters, prompted a drop in sea level of some 100 m and introduced toxic bottom waters onto the shelves. These symptoms of more fundamental planetary processes have been associated with a range of factors with an underlying driver identified as volcanicity. Volcanic eruptions, and other products, may have extended back in time to at least the Sandbian and early Katian, suggesting the extinctions were more protracted and influential than hitherto documented.
... Baltica, Laurentia, northern Gondwana, and South China experienced volcanism during the Late Katian time Derakhshi et al., 2022;Longman et al., 2021). Large-scale volcanism may have triggered the late Boda warming event by the introduction of CO 2 to the atmosphere (Lu et al., 2021b). ...
Silica accumulation in the Yangtze Sea during the Ordovician‐–Silurian (O‐–S) transition appears to have coincided with global climatic fluctuations, widespread upwelling, and volcanism. There is a need to further evaluate their respective contributions to silica deposition and potential relationships among these factors. The current study selected siliceous deposits in the Wufeng and Longmaxi Formations from four sections spanning the inner to outer Yangtze Sea, South China, to gain a deeper understanding of the climatic and oceanographic evolution associated with silica enrichment. Al/(Al + Fe + Mn) values, the presence of radiolarians, and Si isotope values of samples recovered from the investigated shale successions offer compelling evidence that the silica is largely of biogenic origin with some terrigenous contributions. Further, various productivity and redox proxies suggest that biogenic silica (BSi) accumulated under conditions of enhanced marine productivity and anoxic bottom water conditions. Hg/TOC and Zr/Al2O3 profiles suggest intermittent volcanism during the BSi deposition in the Yangtze Sea. However, the lack of correlation between BSi and Hg/TOC values indicates that volcanic iron fertilization was not responsible for BSi accumulation. Instead, most BSi-rich samples are dominated by low MnEF × CoEF values (< 0.5), consistent with BSi deposited in modern upwelling settings. Hydrographic reconstruction based on Mo‐–U covariation indicates a more open water setting in the outer Yangtze Sea, while the coeval inner Yangtze Sea was relatively restricted. Therefore, Upwelling events appear to have been more vigorous in the outer Yangtze Sea. Published and new Chemical Index of Alteration (CIA), BSi, and MnEF × CoEF data for the Wufeng and Longmaxi Formations across the inner to outer Yangtze Sea demonstrates that temporal and spatial variations of BSi were controlled by climate-driven upwelling. In particular, cool-water upwelling contemporaneous with Hirnantian glaciation may have been responsible for the establishment of the cool-water fauna of the shallow-water Guanyinqiao Bed and enhanced silica deposition in deeper water. Moreover, a moderate negative relationship ofbetween compiled CIA and BSi contents suggests that enhanced upwelling driving BSi accumulation appears to have been favored during cooling events. Integrated analysis of BSi deposits of the Laurentia and Baltica continental margins further suggests that BSi accumulation on continental margins during the O‐–S transition was primarily influenced by global cooling. Therefore, we suggest that wind patterns or/and thermohaline circulation, influenced by climate fluctuations, induced widespread cold water upwelling events during the O‐–S transition. Moreover, elevated BSi production diluted accumulating OM resulting in the observed parabolic relationship of BSi and TOC.
... Among them, the first episode (Darriwilian) roughly corresponds to volcanic activities in the Argentine Precordillera, and the second is equivalent to three suites of famous Deicke, Millbrig and Kinnekulle K-bentonites falling in North America (Laurentia) and Europe (Baltica) which is the greatest volcanic ash falls in the Phanerozoic , and the third is nearly globally contemporaneous Xiong et al., 2017Xiong et al., , 2019this study), which indicates the Late Ordovician was an intensive period of volcanic activity worldwide (Huff, 2008). Abnormally high Hg concentrations in the Late Ordovician strata reflected an emplacement of coeval large igneous province (LIP), and subsequently, large- scale volcanism might result in the end Ordovician mass extinction (Gong et al., 2017;Jones et al., 2017;Smolarek-Lach et al., 2019;Derakhshi et al., 2022). Consequently, high-frequent and periodic volcanism would influence on many aspects such as the changes in oceanic chemical conditions, oscillation of carbon cycling, climatic cooling and pulsation of biological radiation in that time, and might be a crucially triggering factor for the initiation of glaciers and biological massive extinction at the end of the Late Ordovician (Hu et al., 2009b;Buggisch et al., 2010;Xiong et al., 2017). ...
... Furthermore, although precise isotopic dating ages are lacking, previous studies have proposed possible relics of LIPs at the Ordovician-Silurian transition (Kasbohm et al., 2021;Torsvik et al., 2021), for instance, the mafic igneous rocks in Korea of Sino-Korean Craton (445.0 ± 3.7 Ma and 452.5 ± 3.2 Ma) (Cho et al., 2014), Suordakh of Eastern Siberia Craton (458 ± 13 Ma) (Khudoley et al., 2020), and the Alborz LIP in northern Iran (443. 7 ± 2.1 Ma) (Derakhshi et al., 2022) (Fig. 2a, sites of a-c). They were located nearly vertically above the margins of the large low shearwave velocity provinces (namely, ''TUZO" and ''JASON"), which have been suggested to conform with the distribution of the past LIPs if their positions and shapes are largely unchanged (Torsvik et al., 2021) (Fig. 2a). ...
The Ordovician-Silurian transition (OST) hosted profound and frequent changes in the atmospheric-terrestrial-oceanic-climatic system (ATOCS). Previous studies have found contrasting stages for such changes, primarily based on hiatus-interrupted sections. However, the dominant driving factors and mechanisms reconciling such frequent changes remain controversial. Mercury isotopes, which undergo both mass-dependent and mass-independent fractionation, can provide critical insights into the deep-time ATOCSs, especially for those impacted by large igneous provinces (LIPs) events. Here, we build a high-resolution multi-proxy record of Hg (concentrations and isotopic compositions) combined with organic carbon isotopes (δ13Corg) and whole-rock geochemical data (including trace elements and phosphorus) from continuous cores in the Yangtze Platform, South China. Our data, combined with reported ones, indicate the occurrence of LIP eruptions against localized volcanism, and four successive, yet contrasting stages of ATOCSs during the OST. Moreover, we identified the coupling between two-pulse LIP magmatism and extreme ATOCSs, each with special pCO2, weathering rate, primary productivity, redox condition, climatic mode, and biotic evolution. For stage I, the first pulse of LIP magmatism triggered global warming, enhanced terrestrial weathering, oceanic acidification, eutrophication, anoxia, P recycling, and thereby widespread deposition of black shales. During stage II, the Hirnantian glaciation and oxygenation arose from the intense chemical weathering and black shale deposition of stage I; slashed terrestrial weathering and oceanic oxygenation facilitated CO2 accumulation. In stage III, another pulse of LIP magmatism triggered the de-glaciation, and the ATOCS was largely similar to that of stage I. This led to another round of oxygenation and positive δ13Corg excursion in stage IV. Compared with the environmental pressure by the peculiar ATOCS of each stage, their transitions might have been more devastating in triggering the prolonged Late Ordovician Mass Extinction (LOME). Moreover, limited biotic recovery was possible in the later portion of stages I and III. The multi-proxy study of continuous strata of the OST provides an excellent framework for better illuminating LIPs’ essential role in driving the “roller-coaster” behavior of the ATOCS and thus biotic crisis during the pivotal period of the OST.
... The main evidence for this rifting event is the presence of thick basalts in the base of the Ghelli Formation in the Kopet-Dagh region (north-eastern Iran; Stampfli et al. 1991;Alavi, 1996;Bagheri & Stampfli, 2008;Shahri, 2008;Shafaii Moghadam et al., 2017). Existence of such volcanic rocks, mostly of submarine basic lava composition, was in relation to the very first break-up events of the northern margin of Gondwana, which led to the opening of the Palaeotethys Ocean (Alavi, 1996;Ranjbar Moghadam et al., 2018;Alvaro et al., 2022;Derakhshi et al., 2022). These basalts, overlaying the Lashkerak Formation, were erupted onto the vast continental platform of the Alborz (i.e. the Prototethys passive margin). ...
The distribution of conventional subichnofacies in deep‐water fan systems (i.e. Ophiomorpha rudis–Paleodictyon–Nereites‐subichnofacies) depends on the presence of fully turbulent non‐cohesive flows such as low‐density turbidites and high‐density turbidites. However, changes in flow state between laminar and turbulent conditions can affect the distribution style of conventional subichnofacies. This study deals with the effects of environmental or ecological stressors as a result of hybrid sediment gravity flows (HEB) on distribution and composition of trace fossils in deep‐marine depositional system of the Ordovician Ghelli Formation in the north‐eastern Alborz. The spatial distribution and sedimentological character of hybrid sediment gravity flows, in particular their abundance in the down‐dip parts of lobe‐related facies associations, are interpreted as products of longitudinal and lateral transformation from turbidity currents to debris‐flows promoted by incorporation of significant claystone and mudstone clasts into the flow by seafloor erosion and flow bulking. Seven trace‐fossil assemblages were recognized in the channel and lobe‐related facies associations. The observed spatial distribution of trace‐fossil assemblages in the interpreted frontal and lateral lobe fringes, somewhat contrasts with conventional subichnofacies distribution models. The development of cohesive flows and rapid emplacement of turbidite, banded and debrite beds could be accompanied by fluctuations in physico‐chemical conditions and, hence, the time available for colonization and the lifestyle of producers. This study suggests that compared to the archetypal models of the subichnofacies in down‐dip parts of lobe‐related facies associations, ichnodiversity and density of bioturbation are drastically reduced, and trace fossils are limited to simple, shallow‐tier feeding strategies. Commonly, the presence of cohesive flows may have forced the producers in the Paleodictyon and Nereites‐subichnofacies to migrate into lateral lobe fringe with more participation of low‐density turbidites. This study shows that, in addition to sedimentological and architectural criteria, ichnological criteria can also be used to distinguish between frontal and lateral lobe‐fringe deposits in unconfined systems.
An unusually rich and diverse suite of virgianid brachiopods, hitherto poorly known, is systematically described here for the first time from the Ordovician-Silurian boundary interval (late Katian-Aeronian) of North Greenland. The Late Ordovician virgianids comprise typical taxa of the warm-water Tcherskidium fauna (e.g. Tcherskidium tenuicostatum, Proconch-idium schleyi, Holorhynchus giganteus and Deloprosopus dawesi sp. nov.). Among the early Silurian taxa, Virgiana hursti sp. nov. occurs as abundant shell beds, similar to other congeneric species in Laurentia, but has somewhat larger internal skeletal structures, albeit not as extravagantly developed as in the late Katian virgianids; Borealoides balderi gen. et sp. nov. shows extreme thickening of the shell wall and internal structures, approaching the extravagant calcification of Katian virgianids. The highly distinctive mid-Aeronian stricklandioid brachiopod genus, Kulumbella, characterized by a shell with criss-cross (divaricate) ribbing, also occurs in North Greenland, represented by K. heimdali sp. nov., which has the largest and most strongly biconvex shells for the genus. Palaeogeographi-cally, the Late Ordovician virgianid fauna of Laurentia was highly distinct, confined to the low-mid tropical latitudes north of the palaeoequator. In comparison, the early Silurian (Rhuddanian) Virgiana and some related taxa in Laurentia spanned the tropics of both hemispheres, forming extensive shell beds in carbonate basins, although Borealis and Borea-loides gen. nov. remained confined largely to the northern hemisphere, suggesting a certain level of provincialism extending into the earliest Silurian. A palaeoecological preference for warm-water carbonate settings would explain the unusual abundance and richness of the virgianid faunas in North Greenland.
The Ordovician–Silurian transition was a critical period in geological history, during which profound changes in climatic, biotic, and oceanic conditions occurred. To explore the provenance, palaeoclimate, and palaeoredox conditions in the Sichuan Basin during the Late Ordovician–early Silurian interval, we conducted mineralogical, geochemical, and isotopic analyses of three formations (Wufeng, Guanyinqiao and Longmaxi formations) in the Xindi No. 2 well. The ternary and bivariate diagrams indicate that the provenance is mainly felsic igneous rocks and originated mainly from a collisional setting, presumably due to an active continental margin. The chemical index of alteration (CIA) values in the lower Wufeng and Longmaxi formations are relatively high (67.48–73.57), indicating a warm and humid climate. In contrast, the CIA values declined rapidly (58.30–64.66) during the late Katian to early Hirnantian, which had a fluctuating cold and dry climate and was interrupted by a transient warm and humid climate. The palaeoredox indices (Mo concentrations and Moauth/Uauth, U/Th, V/Cr, Ni/Co, and V/V + Ni values) during the Late Ordovician–early Silurian indicate two cycles of water column euxinia. The first cycle occurred during Wufeng Formation deposition, with bottom waters evolving from oxic-suboxic to suboxic-anoxic. Most samples show relatively low redox-sensitive trace element concentrations during the Guanyinqiao Formation, pointing to oxic-suboxic conditions. The second cycle, during the late Hirnantian, transitioned from oxic to euxinic water conditions. Our δ13Corg data are comparable to previously reported records and exhibit a strong correlation between the Hirnantian isotopic carbon excursion (HICE), climate change, and redox conditions. We suggest that the variations in the δ13C values are related to two elements: (1) increased photosynthetic activity under oxic water conditions, and (2) increased carbonate weathering exposed by the glacio-eustatic sea- level. In addition, the high δ13Corg values might indicate a more shelf-proximal setting during Xindi No. 2 well deposition. The δ13Corg isotopic data effectively constrain the timing of the Late Ordovician mass extinction (LOME) and the evolution of the temporal changes in the climatic and ocean redox conditions, suggesting an apparent stratigraphic coincidence between climate and redox fluctuations and two-phase extinctions, which implies a strong causal relationship. The LOME was systematically driven by the combination of cooler glacial temperatures, glacio-eustatic sea-level fluctuations, and anoxic water conditions that caused the two pulses of extinction in the Yangtze shelf sea.
For the last two decades, the end of the voluminous phase of eruptions of the Siberian Traps large igneous province has been constrained by a U-Pb date of discordant baddeleyite collected from the Guli carbonatite intrusion with the assumption that the discordance resulted from unsupported 207Pb. In this study we have re-analysed baddeleyite from the same intrusion and found two types of discordance: (1) due to 207Pb-excess, and (2) radiogenic lead loss from high U mineral inclusions. The former implies that baddeleyite is an efficient scavenger of protactinium during crystallisation, leaving the magma depleted in this element. Together with a published high precision U-Pb date of 252.24 ± 0.08 Ma for the Arydzhansky Formation, our new date of 250.33 ± 0.38 Ma for the Guli carbonatite constrains the total duration of the voluminous eruptions of the Siberian Traps LIP at 1.91 ± 0.38 million years. The lower intercept of the (231Pa)/(235U) corrected discordance line yields a date of 129.2 ± 65.0 Ma, which points to the widespread Early Cretaceous rifting in East and Central Asia.
There is an apparent temporal correlation between large igneous province (LIP) emplacement and global environmental crises, including mass extinctions. Advances in the precision and accuracy of geochronology in the past decade have significantly improved estimates of the timing and duration of LIP emplacement, mass extinction events, and global climate perturbations, and in general have supported a temporal link between them. In this chapter, we review available geochronology of LIPs and of global extinction or climate events. We begin with an overview of the methodological advances permitting improved precision and accuracy in LIP geochronology. We then review the characteristics and geochronology of 12 LIP/event couplets from the past 700 Ma of Earth history, comparing the relative timing of magmatism and global change, and assessing the chronologic support for LIPs playing a causal role in Earth's climatic and biotic crises. We find that (1) improved geochronology in the last decade has shown that nearly all well‐dated LIPs erupted in < 1 Ma, irrespective of tectonic setting; (2) for well‐dated LIPs with correspondingly well‐dated mass extinctions, the LIPs began several hundred ka prior to a relatively short duration extinction event; and (3) for LIPs with a convincing temporal connection to mass extinctions, there seems to be no single characteristic that makes a LIP deadly. Despite much progress, higher precision geochronology of both eruptive and intrusive LIP events and better chronologies from extinction and climate proxy records will be required to further understand how these catastrophic volcanic events have changed the course of our planet's surface evolution.
An emerging consensus suggests that large igneous provinces (LIPs) are a significant driver
of dramatic global environmental and biological changes, including several Phanerozoic
mass extinctions, leading to plausible links with geological time scale (GTS) boundaries. LIP-
induced environmental changes are now being identified in the Precambrian record,
suggesting potential for the use of LIPs to define natural pre-Phanerozoic GTS boundaries.
There is now opportunity for more systematic integration of the sedimentary and LIP records …
A geochronological, isotopic, and geochemical study of the Suordakh event of mafic magmatic intrusions on the southeast Siberian margin was undertaken. U-Pb baddeleyite dating of a mafic sill intruding lower Cambrian rocks, yielded a 458 ± 13 Ma emplacement age. The chemical composition and stratigraphic setting of this dated sill differed from that previously attributed to the Suordakh event, implying that additional intrusions, previously mapped as Devonian, potentially belonged to the Suordakh event. No correlation between L.O.I. and concentration of highly mobile major and trace elements was documented, showing small or no influence of hydrothermal alteration on the chemical composition of the intrusions. A new tectonic reconstruction located an island arc and active margin relatively close to the study area. However, all samples had chemical compositions close to that of OIB and did not display Ta-Nb and Ti-negative anomalies, nor other features typical for subduction-related magmatism. The major and trace element distribution was most characteristic of within-plate basalts with the mantle source composition being transitional from spinel to garnet lherzolite. Combining four U-Pb baddeleyite dates of mafic sills and dykes from southeast Siberia, the age of the Suordakh event was estimated at 454 ± 10 Ma. The area of the Suordakh event was at least 35,000-40,000 km 2 (an estimate including sills previously interpreted as Devonian), and could be increased with additional dating in Southeastern Siberia. Similar ages for within-plate intrusions were reported from South Korea, West Mongolia, South Argentina, North Iran and Northwest Canada, and these ca. 450 Ma ages were collectively close in timing with the latest Ordovician (Hirnantian) mass extinction. More high-precision dating is necessary to fully test a link between the Suordakh event (and the other age-correlative events) and the end-Ordovician mass extinction.
A wide part of the Central Iranian and Alborz zones have affected by an extensional tectonic regime in the lower Paleozoic, especially Silurian period. Due to the some clear relation of the lithological exposes, same ages and composition we have compared early Paleozoic basaltic rocks in the two key area such as Maku in the West and Soltan Maidan in the eastern Iran. The geochemical properties obviuos the alkaline nature and intra-plate extensional regime for the studied rocks. These two areas almost show the same composition and tectioc regime with some minor diffrences. Although, magma differentiation and crustal contamination had a main role to produce different types of rocks from basalt to rhyolites in the Maku area despite of the Soltan Maidan. In the Soltan Maidan undifferentiated basaltic rocks was floated in a large area probably it infer the fast rises of origin magma comparing to the Maku area due to the violent detaching in continental lithosphere in this interval time led to sudden decompression on the rising mantle plumes, providing conditions for extensive partial melting and generation of high volumes of basaltic magma. This process more highlited Paleotethys drifting rate getting slower from the east to the west. This finding more be usfule to understand Paleotethys evolution and also can explain the varity of ophiolite types along the Paleotethys suture zone in the northern Iran.
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.
The Ordovician saw major diversification in marine life abruptly terminated by the Late Ordovician mass extinction (LOME). Around 85% of species were eliminated in two pulses 1 m.y. apart. The first pulse, in the basal Hirnantian, has been linked to cooling and Gondwanan glaciation. The second pulse, later in the Hirnantian, is attributed to warming and anoxia. Previously reported mercury (Hg) spikes in Nevada (USA), South China, and Poland implicate an unknown large igneous province (LIP) in the crisis, but the timing of Hg loading has led to different interpretations of the LIP-extinction scenario in which volcanism causes cooling, warming, or both. We report close correspondence between Hg, Mo, and U anomalies, declines in enrichment factors of productivity proxies, and the two LOME pulses at the Ordovician-Silurian boundary stratotype (Dob’s Linn, Scotland). These support an extinction scenario in which volcanogenic greenhouse gases caused warming around the Katian-Hirnantian boundary that led to expansion of a preexisting deepwater oxygen minimum zone, productivity collapse, and the first LOME pulse. Renewed volcanism in the Hirnantian stimulated further warming and anoxia and the second LOME pulse. Rather than being the odd-one-out of the “Big Five” extinctions with origins in cooling, the LOME is similar to the others in being caused by volcanism, warming, and anoxia.
Volcanic eruptions are thought to be a key driver of rapid climate perturbations over geological time, such as global cooling, global warming, and changes in ocean chemistry. However, identification of stratospheric volcanic eruptions in the geological record and their causal link to the mass extinction events during the past 540 million years remains challenging. Here we report unexpected, large mass-independent sulphur isotopic compositions of pyrite with Δ33S of up to 0.91‰ in Late Ordovician sedimentary rocks from South China. The magnitude of the Δ33S is similar to that discovered in ice core sulphate originating from stratospheric volcanism. The coincidence between the large Δ33S and the first pulse of the Late Ordovician mass extinction about 445 million years ago suggests that stratospheric volcanic eruptions may have contributed to synergetic environmental deteriorations such as prolonged climatic perturbations and oceanic anoxia, related to the mass extinction. Identification of stratospheric volcanic eruptions in the geological record and their link to mass extinction events during the past 540 million years remains challenging. Here, the authors report unexpected, large mass-independent sulphur isotopic compositions of pyrite in Late Ordovician sedimentary rocks, which they suggest originates from stratospheric volcanism linked to the first pulse of the Late Ordovician mass extinction.
Silurian trilobites of the Niur Formation in the Robat-e-Gharebil area are described and illustrated. Three genera and five species are identified, including: Calymene dastanpouri sp. nov. Calymene sp., Flexicalymene meeki, Gravicalymene hagani and Dalmanites ypacarayensis. The palaeogeographic relationships of the Eastern Alborz Range with the Northern Gondwana supercontinent during the Late Palaeozoic are also considered. The Early Silurian trilobites of lower part of the Niur Formation were comparable with those of other parts of Iran, Southern Europe, Northern Africa, Middle East and South of China. This similarity suggests that the Robat-e-Gharebil area (Kopeh Dagh region) was part of the peri- Gondwana supercontinent during the Early Silurian.
The greatest relative changes in marine biodiversity accumulation occurred during the Early Paleozoic. The precision of temporal constraints on these changes is crude, hampering our understand- ing of their timing, duration, and links to causal mechanisms. We match fossil occurrence data to their lithostratigraphical ranges in the Paleobiology Database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high-resolution time slices. In addition, we apply capture–recapture modeling ap- proaches to calculate a biodiversity curve that also considers ta- phonomy and sampling biases with four times better resolution of previous estimates. Our method reveals a stepwise biodiversity increase with distinct Cambrian and Ordovician radiation events that are clearly separated by a 50-million-year-long period of slow biodiversity accumulation. The Ordovician Radiation is confined to a 15-million-year phase after which the Late Ordovician extinc- tions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years. Based on a first-differences approach on potential abiotic drivers controlling richness, we find an overall correlation with oxygen levels, with temperature also exhibiting a coordinated trend once equatorial sea surface tem- peratures fell to present-day levels during the Middle Ordovician Darriwilian Age. Contrary to the traditional view of the Late Ordovi- cian extinctions, our study suggests a protracted crisis interval linked to intense volcanism during the middle Late Ordovician Katian Age. As richness levels did not return to prior levels during the Silurian—a time of continental amalgamation—we further argue that plate tectonics exerted an overarching control on biodiversity accumulation.
Investigation of Silurian succession equivalent to the Niur Formation at the northwest of Robat-e-Qarebil (instantly south of Western Kopeh-Dagh), is led to introduction of lithostratigraphical units in details and identification of some Llandovery conodonts. The sampled interval in this stratigraphic section is composed of shale, fossiliferous limestone, sandstone, and dolomite with 295.5 meter thickness. With a marine volcanic rock unit at the base, this succession is conformably overlaid shales and sandstones attributed to the Ordovician system and overlain by quartzarenite and red shales of the Padeha Formation. Obtained conodonts from these sequences comprise different coniform, ramiform and pectiniform elements. Nineteen species of 10 genera belong to Aspelundia expansa Interval Zone which confirms uppermost Late Rhuddanian to Aeronian for the section. This age coincides with the ages which have already been given on the basis of brachiopods, cephalopods and palinomorphs for the same outcrops at the Western Kopeh-Dagh.
The Frasnian-Famennian (F-F) global event, one of the five largest biotic crises of the Phanerozoic, has been inconclusively linked to rapid climatic perturbations promoted in turn by volcanic cataclysm, especially in the Viluy large igneous province (LIP) of Siberia. Conversely, the triggers of four other Phanerozoic mass extinction intervals have decisively been linked to LIPs, owing to documented mercury anomalies, shown as the diagnostic proxy. Here, we report multiple Hg enrichments in the two-step late Frasnian (Kellwasser) crisis interval from paleogeographically distant successions in Morocco, Germany, and northern Russia. The distinguishing signal, > 1 ppm Hg in the domain of closing Rheic Ocean, was identified in different lithologies immediately below the F-F boundary and approximately correlated with the onset of the main extinction pulse. This key Hg anomaly, comparable only with an extreme spike known from the end-Ordovician extinction, was not controlled by increased bioproductivity in an anoxic setting. We suggest, therefore, that the global chemostratigraphic pattern near the F-F boundary records a greatly increased worldwide Hg input, controlled by the Center Hill eruptive pulse of the Eovariscan volcanic acme, but likely not manifested exclusively by LIP(s). Consequently, all five major biotic crises of the Phanerozoic have now been more reliably linked to volcanic cataclysms.
The Early Paleozoic evolution of the northern margin of Gondwana is characterized by several episodes of bimodal magmatism intruded or outpoured within thick sedimentary basins. These processes are well recorded in the Variscan blocks incorporated in the Ligurian Alps because they experienced low temperature Alpine metamorphism. During the Paleozoic, these blocks, together with the other Alpine basements, were placed between the Corsica-Sardinia and the Bohemian Massif along the northern margin of Gondwana. In this framework, they host several a variegated lithostratigraphy forming two main complexes (Complexs I and II) that can be distinguished by both the protoliths and their cross-cutting relationships, which indicate that the acidic and mafic intrusives of Complex II cut an already folded sequence made of sediments, basalts and granitoids of Complex I. Both complexes were involved in the Variscan orogenic phases as highlighted by the pervasive eclogite-amphibolite facies schistosity (foliation II). However, rare relicts of a metamorphic foliation at amphibolite facies conditions (foliation I) is locally preserved only in the rocks of Complex I. It is debatable if this schistosity was produced during the early folding event - occurred between the emplacement of Complex I and II - rather than during an early stage of the Variscan metamorphic cycle.New SHRIMP and LA ICP-MS U-Pb zircon dating integrated with literature data, provide emplacement ages of the several volcanic or intrusive bodies of both complexes. The igneous activity of Complex I is dated between 507 ± 15 Ma and 494 ± 5 Ma, while Complex II between 467 ± 12 Ma and 445.5 ± 12 Ma. The folding event recorded only by the Complex I should therefore have occurred between 494 ± 5 and 467 ± 12 Ma. The Variscan eclogite-amphibolite facies metamorphism is instead constrained between ~420 Ma and ~300 Ma. These ages and the geochemical signature of these rocks allow constraining the Early Paleozoic tectono-magmatic evolution of the Ligurian blocks, from a middle-upper Cambrian rifting stage, through the formation of an Early Ordovician volcanic arc during the Rheic Ocean subduction, until a Late Ordovician extension related to the arc collapse and subsequent rifting of the PaleoThetys. Furthermore, the ~420-350 Ma ages from zircon rims testify to thermal perturbations that may be associated with the Silurian rifting-related magmatism, followed by the subduction-collisional phases of the Variscan orogeny. © 2018 China University of Geosciences (Beijing) and Peking University.
The Palaeozoic rock units mainly, Ghelli, Niur, Padeha, Khoshyeilagh and Mobark formations are well-exposed in the north of Robat-e Gharabil village. 116 out of 157 surface samples were analyzed to determine aged relationships of Ghelli Formation. The samples of Ghelli Formation are dominated by acritarchs (42 species belonging to 23 genera) and chitinozoans (26 species distributing among 15 genera). Two new acritarch species are introduced, consisting of Goniosphaeridium iranense n.sp., and Goniosphaeridium persianense n. sp. Based on the restricted stratigraphic range of chitinozoan species, Late Ordovician (Ashgill) age is assigned to the Ghelli Formation. On the other hand, the presence of diagnostic chitinozoan taxa in the Ghelli Formation consisting of Armoricochitina nigerica, Ancyrochitina merga, and Spinachitina oulebsiri chitinozoan biozones, suggest a clear palaeobiogeographic affinity between NE Alborz Mountain and North Gondwana Domain. The presence of some chitinozoan and acritarch taxa from the Baltic and Laurentia in Gondwanan chitinozoan biozones of the Robat-e Gharabil area suggests the existence of counter-clockwise marine currents that resulted in bringing planktonic organisms (acritarchs and chitinozoans) from lower latitudes (Baltica) to higher latitudes (Northern Gondwanan Domain) settings.
Asia is key to a richer understanding of many important lithospheric processes such as crustal growth, continental evolution and orogenesis. But to properly decipher the secrets Asia holds, a first-order tectonic context is needed. This presents a challenge, however, because a great variety of alternative and often contradictory tectonic models of Asia have flourished. This plethora of models has in part arisen from efforts to explain limited observations (in space, time or discipline) without regard for the broader assemblage of established constraints. The way forward, then, is to endeavour to construct paleogeographic models that fully incorporate the diverse constraints available, namely from quantitative paleomagnetic data, the plentiful record of geologic and paleobiologic observations, and the principles of plate tectonics. This paper presents a preliminary attempt at such a synthesis concerning the early Paleozoic tectonic history of Asia. A review of salient geologic observations and paleomagnetic data from the various continental blocks and terranes of Asia is followed by the presentation of a new, full-plate tectonic model of the region from middle Cambrian to end-Silurian time (500–420 Ma). Although this work may serve as a reference point, the model itself can only be considered provisional and ideally it will evolve with time. Accordingly, all the model details are released so that they may be used to test and improve the framework as new discoveries unfold.
The Silurian biostratigraphy, lithostratigraphy, and facies of Central Iran including the Kashmar (Boghu Mountains), Tabas (Derenjal Mountains, Ozbak-Kuh), Anarak (Pol-e Khavand) and Kerman regions is reviewed and updated. The current state of knowledge of the Silurian in the Zagros Basin, Alborz, Kopet-Dagh and Talysh regions, as well as in a few areas scattered across the Sabzevar Zone, and the Sanandaj-Sirjan terranes is also reviewed. Silurian volcanism in various parts of Iran is briefly discussed. The end of the Ordovician coincided with a widespread regression across Iran synchronous with the Hirnantian glaciation, and only in the Zagros Basin is there a continuous Ordovician-Silurian transition represented by graptolitic black shales of the Sarchahan Formation. In the Central-East Iranian Platform marine sedimentation re-commenced in the early to mid Aeronian. By the Sheinwoodian, carbonate platform depositional environments were established along its north-eastern margin. In other parts of Iran (e.g., Kopet-Dagh and the Sabzevar Zone), siliciclastic sedimentation continued probably into the late Silurian. The Silurian conodont and brachiopod biostratigraphy of Central Iran is significantly updated facilitating a precise correlation with the Standard Global Chronostratigraphic Scale, as well as with key Silurian sections in other parts of Iran. The Silurian lithostratigraphy is considerably revised and two new lithostratigraphical units, namely the Boghu and Dahaneh-Kalut formations, are introduced.
The second largest Phanerozoic mass extinction occurred at the Ordovician-Silurian (O-S) boundary. However, unlike the other major mass extinction events, the driver for the O-S extinction remains uncertain. The abundance of mercury (Hg) and total organic carbon (TOC) of Ordovician and early Silurian marine sediments were analyzed from four sections (Huanghuachang, Chenjiahe, Wangjiawan and Dingjiapo) in the Yichang area, South China, as a test for evidence of massive volcanism associated with the O-S event. Our results indicate the Hg concentrations generally vary in parallel with TOC, and that the Hg/TOC ratios remain low and steady state through the Early and Middle Ordovician. However, Hg concentrations and the Hg/TOC ratio increased rapidly in the Late Katian, and have a second peak during the Late Hirnantian (Late Ordovician) that was temporally coincident with two main pulses of mass extinction. Hg isotope data display little to no variation associated with the Hg spikes during the extinction intervals, indicating that the observed Hg spikes are from a volcanic source. These results suggest intense volcanism occurred during the Late Ordovician, and as in other Phanerozoic extinctions, likely played an important role in the O-S event.
Well-preserved miospore assemblages are recorded from the Late Ordovician (Katian–Hirnantian) Ghelli Formation in the Pelmis Gorge, located in the Alborz Mountain Range, Northeastern Iran. The palynomorphs were extracted from siliciclastic deposits that are accurately dated using marine palynomorphs (acritarchs and chitinozoans). The spore assemblages consist of 14 genera and 28 species (26 cryptospores and 2 trilete spore species). Six new cryptospore species are described: Rimosotetras punctata n.sp., Rimosotetras granulata n.sp., Dyadospora asymmetrica n.sp., Dyadospora verrucata n.sp., Segestrespora iranense n.sp., and Imperfectotriletes persianense n.sp. The study furthers knowledge of the development of the vegetative cover during the Late Ordovician. Various and abundant cryptospores in the Late Ordovician (Katian–Hirnantian) Ghelli Formation are probably related to the augmentation of land-derived sediments either during the global sea-level fall linked to the Late Ordovician glaciation or adaptation of the primitive land plants in a wide range of climatic conditions. These miospore taxa were produced by the earliest primitive land plants, which probably grew close to the shoreline and were washed in from adjacent areas, producing a high volume of miospores. The associated marine palynomorphs consist of acritarchs (13 genera and 18 species), chitinozoans (9 genera and 10 species), prasinophycean algae, scolecodonts, and graptolite remains, which are not discussed in detail herein. The established chitinozoan biozones of this part of the Palaeozoic sequence are the Armoricochitina nigerica Biozone, the Ancyrochitina merga Biozone, the Tanuchitina elongata Biozone, and the Spinachitina oulebsiri Biozone, suggesting a Late Ordovician age (Katian–Hirnantian). These chitinozoan biozones are widely evidenced only in the peri-Gondwanan Domain, indicating that the study area was part of this palaeo-continent in the Late Ordovician.
The Late Ordovician mass extinction (LOME), one of the five largest Phanerozoic biodiversity depletions, occurred in two pulses associated with the expansion and contraction of ice sheets on Gondwana during the Hirnantian Age. It is widely recognized that environmental disruptions associated with changing glacial conditions contributed to the extinctions, but neither the kill mechanisms nor the causes of glacial expansion are well understood. Here we report anomalously high Hg concentrations in marine strata from south China and Lau-rentia deposited immediately before, during, and after the Hirnantian glacial maximum that we interpret to reflect the emplacement of a large igneous province (LIP). An initial Hg enrichment occurs in the late Katian Age, while a second enrichment occurs immediately below the Katian-Hirnantian boundary, which marks the first pulse of extinction. Further Hg enrichment occurs in strata deposited during glacioeustatic sea-level fall and the glacial maximum. We propose that these Hg enrichments are products of multiple phases of LIP volcanism. While elevated Hg concentrations have been linked to LIP emplacement coincident with other Phanerozoic mass extinctions, the climate response during the LOME may have been unique owing to different climatic boundary conditions, including preexisting ice sheets. Our observations support a volcanic trigger for the LOME and further point to LIP volcanism as a primary driver of environmental changes that caused mass extinctions.
Sixty-four surface samples from the Lower Palaeozoic rock units (mainly Lalun, Abastu and Abarsaj formations) near Kholin-Darreh village in the Fazel Abad area, southeastern the Caspian Sea, Northern Iran, were analyzed to determine their age relationships. The samples of Lalun Formation were barren, but those of Abastu and Abarsaj formations contained well-preserved and abundant palynomorph entities, which are dominated by acritarchs (23 species belonging to 15 genera) and chitinozoans (29 species distributing among 15 genera) with remains of scolecodonts, graptolite and a few cryptospores, although not determined in detail. Based on the restricted stratigraphic range of acritarch species, an Early Ordovician (Tremadocian) age was assigned to the Abastu Formation; while based upon index chitinozoan and acritarch taxa, a Late Ordovician (Katian to Hirnantian) age was assigned to the Abarsaj Formation. Likewise, based on the presence of diagnostic chitinozoan taxa, the Abarsaj Formation can be assigned to the Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata and Spinachitina oulebsiri chitinozoan Biozones. These chitinozoan assemblages reflect a clear palaeobiogeographic affinity with the so-called "North Gondwana Domain". Two major hiata are present within the studied Lower Palaeozoic succession in the Fazel Abad area. The first hiatus appeared between the Lalun Formation (Early Cambrian) and the Abastu Formation (Tremadocian) and includes the Middle-Upper Cambrian Mila Formation. The second hiatus occurs between the Abastu Formation (Tremadocian) and the Abarsaj Formation (Katian-Hirnantian) and spans the interval of the Floian-Sandbian, which corresponds to uplift related to the initial stage of rifting of the Palaeo-Tethys Ocean.
The end-Triassic mass extinction overlapped with the eruption of the Central Atlantic Magmatic Province (CAMP), and release of CO2 and other volcanic volatiles has been implicated in the extinction. However, the timing of marine biotic recovery versus CAMP eruptions remains uncertain. Here we use Hg concentrations and isotopes as indicators of CAMP volcanism in continental shelf sediments, the primary archive of faunal data. In Triassic-Jurassic strata, Muller Canyon, Nevada, Hg levels rise in the extinction interval, peak before the appearance of the first Jurassic ammonite, remain above background in association with a depauperate fauna, and fall to pre-extinction levels during significant pelagic and benthic faunal recovery. Hg isotopes display no significant mass independent fractionation within the extinction and depauperate intervals, consistent with a volcanic origin for the Hg. The Hg and palaeontological evidence from the same archive indicate that significant biotic recovery did not begin until CAMP eruptions ceased.
The contribution of the Deccan Traps (west-central India) volcanism in the Cretaceous-Paleogene (KPg) crisis is still a matter of debate. Recent U-Pb dating of zircons interbedded within the Deccan lava flows indicate that the main eruptive phase (>1.1 × 106 km3 of basalts) initiated ∼250 k.y. before and ended ∼500 k.y. after the KPg boundary. However, the global geochemical effects of Deccan volcanism in the marine sedimentary record are still poorly resolved. Here we investigate the mercury (Hg) content of the Bidart (France) section, where an interval of low magnetic susceptibility (MS) located just below the KPg boundary was hypothesized to result from paleoenvironmental perturbations linked to the paroxysmal Deccan phase 2. Results show Hg concentrations >2 orders of magnitude higher from ∼80 cm below to ∼50 cm above the KPg boundary (maximum 46.6 ppb) and coincident with the low MS interval. Increase in Hg contents shows no correlation with clay or total organic carbon contents, suggesting that the Hg anomalies resulted from higher input of atmospheric Hg species into the marine realm, rather than organic matter scavenging and/or increased runoff. The Hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera, suggesting correlative changes in marine biodiversity. This discovery represents an unprecedented piece of evidence of the nature and importance of the Deccan-related environmental changes at the onset of the KPg mass extinction.
Mantle plumes can be recognized by their magmatic expression as large igneous provinces (LIPs). However, identification of plumes in old, structurally complicated fold belts is particularly difficult due to deformation, which obscures the LIP record. On the other hand, fold belt regions are particularly important in the search for LIPs for at least three reasons: 1) they can represent prior plate margins associated with plume-generated continental breakup and LIP magmatism; 2) the deformation may expose basement rocks (containing LIP units) covered by younger sedimentary rocks elsewhere in the continental block; and 3) they preserve deformed remnants of oceanic LIPs and hot spot chains accreted during ocean closure.
Herein we provide an initial survey of the plume /LIP record of one of the world’s great orogenic belts, the Ural fold belt. The following events are identified: The 1750 Ma Navysh event is coeval with units in Sarmatia and Karelia (other parts of Baltica) and on other crustal blocks. The 1385 Ma Mashak event is associated with a range of ore deposit types, is part of Nuna supercontinent breakup, and is postulated to have had a global environmental impact linked to the Calymmian-Ectasian boundary. The ca. 720 Ma Igonino event can be approximately matched with 720 Ma LIPs in northern Laurentia, and elsewhere, which can be linked to the onset of the Sturtian glaciation (Tonian-Cryogenian boundary). The ca. 480 Ma Kidryasovo and 450 Ma Ushat events have age matches in Siberia and other crustal blocks; the ages approximately match the end-Cambrian and end-Ordovician periods, respectively. The 370 Ma Timaiz event belongs to the c. 370 Ma Kola-Dniepr LIP which is widespread in Baltica, has an age match in Siberia and collectively can be linked with the end Devonian period. An Early Carboniferous (350–320 Ma) event follows island-arc/continent collision and slab break-up in the Magnitogorsk zone. Three orogenic/postorogenic plume intraplate episodes are also described, the ca. 285 Ma Stepninsky monzogabbro-granosyenite-granite complex, the 308–304 Ma Kalymbaevsky lamproite complex and units that are coeval with the 251 Ma Siberian Traps LIP, linked to the Ural-Siberian superplume and with the end Permian mass extinction.
LIP printing is a term adapted from forensic science to describe the use of geochemical proxies for tectonic and petrogenetic fingerprinting of Large Igneous Provinces (LIPs). Here, we investigate in detail the LIP printing of basic lavas, sills and dykes using two immobile element proxies: Th/Nb, a crustal input proxy, to monitor subduction-metasomatism and crustal assimilation and Ti/Yb, a residual garnet proxy, to monitor depth and degree of melting. The LIP printing diagram, a plot of Th/Nb against Ti/Yb for intraplate, plume-derived magmas, is characterised by two distinct arrays: a subduction-modified lithospheric mantle (SZLM) array and a MORB-OIB-OPB (plume) array (where OPB = oceanic plateau basalt). LIP basalt suites divide into three categories on this diagram: Type I plots entirely within the MORB-OIB-OPB array indicative of a significant plume source; Type II plots entirely within the SZLM array indicative of a significant sub-continental lithospheric mantle source, and Type III plots on a variety of trends between the two arrays indicative of significant plume-lithosphere interactions. Modelling demonstrates how the three LIP types, and the observed trends within and between individual LIPs, can be explained by differences in the compositions and relative contributions of lithospheric and asthenospheric (plume) mantle, in temperature and depth of melting and in the extent and nature of magma-crust interactions. This large genetic, and hence compositional, variability within and between LIPs relates to differences in geological and geodynamic setting and supports the forensic concept that ‘no two LIP prints are alike’. The potential applications of the LIP printing diagram are demonstrated here using four types of example that highlight temporal and spatial LIP print diversity: flood basalt terranes related to Atlantic breakup (NAIP, Parana-Etendeka and CAMP); giant dyke swarms (Superior Craton Late Archean to Early Proterozoic dyke swarms and the Mackenzie dyke swarm); mineralization-related LIP terranes (Bushveld and Noril’sk); and early (c. 3.5Ga) Earth and extra-Terrestrial lavas (Terrrestrial Paleoarchean basalts and komatiites, Luna Mare basalts and Martian shergottites).
Pronounced excursions of carbon and sulfur isotopes (δ¹³C and δ³⁴S) spanning the Ordovician–Silurian (O–S) transition have been recognized globally, yet the causes of these isotope events and their causal relationships to environmental changes, especially during Early Silurian time, remain the topics of debate. In this study, we present organic carbon and pyrite sulfur isotope (δ¹³Corg and δ³⁴Spyr) records and elemental concentrations from a drill core spanning from the Upper Ordovician (Katian) to Lower Silurian (Aeronian) succession of the Yangtze Platform, China. The newly presented δ¹³Corg profile records previously recognized positive excursions, including the Hirnantian isotopic carbon excursion (HICE), the middle Rhuddanian excursion, and the early Aeronian positive carbon isotope excursion (EACIE). In addition, two negative δ¹³Corg excursions are recognized during the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian stages. The δ³⁴Spyr profile exhibits a great amount of variation (−17.8‰ to +19.6‰) but mimics the δ¹³Corg record. Coupled positive δ¹³Corg and δ³⁴Spyr excursions during the middle Hirnantian and late Rhuddanian to Aeronian are associated with decreased total organic carbon (TOC) content and less reducing water column conditions, whereas the negative δ¹³Corg and δ³⁴Spyr excursions during the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian are associated with enhanced TOC values and the establishment of more strongly anoxic to euxinic conditions. The δ¹³C and δ³⁴S excursions during the O–S transition, then, cannot be explained by changes in redox conditions or the burial of organic carbon and pyrite. The heavier and less variable middle Hirnantian and late Rhuddanian to Aeronian δ³⁴Spyr values probably reflect low marine sulfate concentration. In contrast, negative Katian to early Hirnantian and late Hirnantian to middle Rhuddanian δ³⁴Spyr excursions may reflect increased sulfate concentration. The two negative δ¹³Corg and δ³⁴Spyr excursions associated with the Katian to early Hirnantian and late Hirnantian to middle Rhuddanian correspond with episodes of volcanism. We therefore propose that volcanism was the main driver of coupled negative δ¹³Corg and δ³⁴Spyr excursions. As volcanism diminished during the middle Hirnantian and late Rhuddanian to Aeronian, both δ¹³Corg and δ³⁴Spyr returned to more positive values. Our results indicate that volcanism played a crucial role in triggering carbon and sulfur isotope perturbations and environmental changes during the Late Ordovician and Early Silurian.
The ¹³C/¹²C value of dissolved inorganic carbon (DIC) in the ocean has varied through time and can be determined from the marine carbonate record as changes in δ¹³Ccarb. These variations provide insight into global carbon cycle dynamics, as well as relative age information (chronostratigraphy) that can be used to correlate sedimentary successions globally. The global carbon cycle includes both short- and long-term components, and their interactions dominate the isotopic record presented in this chapter. The partitioning and sequestration of carbon between organic and carbonate rock reservoirs, and their fluxes to and from the ocean–atmosphere–biosphere system, drive secular changes in the δ¹³C of DIC in the oceans that are ultimately recovered from the stratigraphic record. The pre-Cenozoic data presented here utilize bulk carbonate data for compilation, but a wide range of materials has been analyzed in the literature to produce previous composites. Care must be taken to consider what materials have been analyzed in comparing global carbon isotope records from the literature.
The Ordovician Period (486.9–443.1 Ma) encompasses two extraordinary biological events in the history of life on the Earth. The first, the “Great Ordovician Biodiversification Event,” is a great evolutionary radiation of marine life and the second is a catastrophic Late Ordovician extinction. Understanding the duration, rate, and magnitude of these events requires an increasingly precise time scale. The Ordovician time scale is based on the subdivision of a Lower Paleozoic CONOP9 composite graptolite range chart derived from 837 stratigraphic sections and 2651 graptolite taxa with interpolated radioisotopic dates. Thirty-seven new radioisotope dates are used in the scaling of the new Ordovician time scale. The base of the Ordovician Period is defined at the level of the first appearance of the conodont Iapetognathus fluctivagus at the Green Point Newfoundland section. Its top, the base of the Silurian Period, is set as the level of the first appearance of the graptolite Akidograptus ascensus at Dob’s Linn, Scotland. For the first time an independently time-scaled CONOP9 composite conodont range chart is presented to facilitate the application of the time scale to carbonate facies sections.
The Jalal Abad magmatic rocks are located at the southeastern edge of the Kashmar-Kerman tectonic zone, which includes Cadomian magmatic rocks and sedimentary strata intruded by several Silurian alkaline plutons and associated dikes. They have typical alkaline kaersutite and alkaline to per-alkaline pyroxene and are characterized geochemically by enrichment in LREE, Nb and Ta, and high concentrations of incompatible trace elements, demonstrating alkaline features with typical ocean island basalt signatures. Chondrite-normalized REE and multi-element spider diagrams along with High ²⁰⁶Pb/²⁰⁴Pb ratios (18.46–19.83) for the Jalal Abad gabbro, diorite, and dibasic dikes indicate involvement of an OIB-like source during the formation of these rocks. Modeling of bulk–rock trace elements and Sr–Nd isotopes suggest that magmas were generated by a pair of HIMU-EM1- like mantle source, consistent with a plume mantle origin in a within-plate rift zone. The melting took place in garnet stability field and the fractional crystallization played a major role in magmatic evolution of the mantle-derived parental magma. The Jalal Abad mafic rocks have U–Pb zircon ages of 425.5 ± 8.6 Ma and along with other Ordovician to Silurian rocks in different parts of the Iranian plate are related to the extensional tectonic regime responsible for the rifting of Cadomian fragments from northern Gondwana and the opening of Paleo-Tethys. Our findings indicate that the rifting and seafloor spreading of Paleo-Tethys and the formation of its oceanic crust were intensely influenced by a mantle plume activity in the early Paleozoic.
The Ordovician Period records an extraordinary biodiversity increase known as the Great Ordovician Biodiver- sification Event (GOBE), which coincided with a series of environmental changes to the Earth System, notably a cooling global ocean, increased oxygenation, and increased nutrient supply from volcanism and continental weathering. The co-evolution of Earth and its biota during this interval has been studied in various contexts on multiple paleocontinents. Emerging patterns depend on the lens of investigation. Here we summarize the current state of understanding by reviewing and synthesizing the fossil and sedimentary records.
Recent paleontological studies, mainly focused on rhynchonelliform (articulated) brachiopods, bryozoa, cephalopods, trilobites, graptolites, echinoderms, and reef organisms, have documented details of diversification, body size increase, development of ecosystem complexity, and intensification of inter-continental dispersal from the late Cambrian through Late Ordovician. Biomass increased markedly between the Early and Middle Ordovi- cian. Furthermore, diversification rates increase statistically during the mid-Darriwilian Age both globally and regionally.
Coincident with these biotic changes, geochemical proxies record significant changes to Earth's physical sys- tem. Oceanic temperatures decreased, and atmospheric oxygen levels increased to near modern levels in con- cert with the Middle Ordovician diversification of shelly fauna. Anoxic pulses ceased and evidence for deep ocean ventilation prevails in Middle Ordovician strata. Furthermore, a major Middle–Late Ordovician change in oceanic strontium isotopic composition indicates increased weathering of juvenile volcanic rocks and delivery of nutrients to marine settings. This multi-proxy dataset records near-simultaneous changes in fossil-rich shallow marine environments during exactly the interval of greatest diversification.
By integrating biotic and geochemical datasets, a clear picture of the co-evolution of Earth and its biota emerges indicating that the Darriwilian was the critical interval of the GOBE. We recommend restricting the term “GOBE” to indicate this short interval of rapid diversification and ecosystem change, and using “Ordovician Radiation” when referencing the sum of diversifications that occurred throughout the Ordovician Period.
The assembly of Gondwana in the Ediacaran was concluded by extensive arc magmatism along its northern margin. Extensional events in the early Paleozoic led to rifting and the eventual separation of terranes, which were later assimilated in different continents and orogens. The Sibak area of northeastern Iran records these events, including late Precambrian volcanic-sedimentary processes, metamorphism, and magmatism. A granite at Chahak in the Sibak Complex yields a zircon U–Pb age of 548.3 ± 1.1 Ma, whereas a spatially associated gabbro has an age of 471.1 ± 0.9 Ma. The latter corresponds to the earliest stages of rifting in the nearby Alborz domain, with the deposition of clastic sedimentary sequences, basaltic volcanism, and, as indicated by indirect evidence, coeval granitic plutonism. The Chahak gabbro is thus one of the earliest witnesses of the rifting processes that eventually led to the development of the Rheic Ocean and were indirectly linked to subduction of Iapetus at the Laurentian margin and the early development of the Appalachian orogen.
Life on Earth suffered its greatest bio-crisis since multicellular organisms rose 600 million years ago during the end-Permian mass extinction. Coincidence of the mass extinction with flood basalt eruptions in Siberia is well established, but the exact causal connection between the eruptions and extinction processes in South China is uncertain due to their wide spatial separation and the absence of direct geochemical evidence linking the two. The concentration and stable isotope analysis of mercury provides a way to test these links as its concentration is thought to be tied to igneous activity. Mercury/total organic carbon ratios from three Permian–Triassic boundary sections with a well-resolved extinction record in South China show elevated values (up to 900 ppb/wt.% relative to a background of <100 ppb/wt.%) that exactly coincides with the end-Permian mass extinction horizon. This enrichment does not show any correlation with redox and sedimentation rate variations during that time. Hg isotope mass-independent fractionation (Δ¹⁹⁹Hg), with sustained positive values, indicate a predominant atmospheric-derived signature of volcanic Hg in deep-shelf settings of the Daxiakou and Shangsi sections. In contrast, the nearshore environment of the Meishan section displays a negative Δ¹⁹⁹Hg signature, interpreted to be related to terrestrial Hg sources. Such temporal differences in Δ¹⁹⁹Hg values shed new light on Hg geochemical behavior in marine settings, and also on the kill mechanisms associated with volcanism that were responsible for biotic mortality at the end of the Permian.
Pb/238U ratios have been measured as a function of depth beneath natural surfaces of baddeleyite crystals using a sensitive high-resolution ion microprobe (SHRIMP II). The data are compared to model profiles calculated using a stochastic averaging algorithm to constrain the average alpha recoil distance in baddeleyite. The precision of measured profiles is hampered by relatively high common Pb corrections near the surface and difficulty in estimating penetration depth at the start of measurements. Uncertainties in U concentration gradients within the first 200 nm may also influence the model profiles. Despite these difficulties, the measured U-Pb depth profiles are consistent with an alpha recoil distance in baddeleyite of 24 ± 7 nm. Assuming this recoil distance, Pb loss from near-surface alpha recoil becomes analytically resolvable for tabular crystals with thickness of <15–20 µm. This will not significantly affect ages based on 207Pb/206Pb ratios, but 206Pb/238U ages of bulk crystals may require corrections of 0.1–0.5% depending of grain size and shape. For typical tabular crystals, alpha recoil loss is linearly correlated with surface-area-to-volume ratios allowing simple corrections to be applied if the dimensions of the crystal are accurately determined prior to analyses.
The temporal link between large igneous province (LIP) eruptions and at least half of the major extinctions of the Phanerozoic implies that large scale volcanism is the main driver of mass extinction. Here we review almost twenty biotic crises between the early Cambrian and end Cretaceous and explore potential causal mechanisms. Most extinctions are associated with global warming and proximal killers such as marine anoxia (including the Early/Middle Cambrian, the Late Ordovician, the intra-Silurian, intra-Devonian, end-Permian, and Early Jurassic crises). Many, but not all of these are accompanied by large negative carbon isotope excursions, supporting a volcanogenic origin. Most post-Silurian biocrises affected both terrestrial and marine biospheres, suggesting that atmospheric processes were crucial in driving global extinctions. Volcanogenic-atmospheric kill mechanisms include ocean acidification, toxic metal poisoning, acid rain, and ozone damage and consequent increased UV-B radiation, volcanic darkness, cooling and photosynthetic shutdown, each of which has been implicated in numerous events. Intriguingly, some of the most voluminous LIPs such as the oceanic plateaus of the Cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing LIP lethality. The missing link might be continental configuration because the best examples of the LIP/extinction relationship occurred during the time of Pangaea. Many of the proximal kill mechanisms in LIP/extinction scenarios are also potential effects of bolide impact, including cooling, warming, acidification and ozone destruction. However, the absence of convincing temporal links between impacts and extinctions other than the Chicxulub-Cretaceous example, suggests that impacts are not the main driver of extinctions. With numerous competing extinction scenarios, and the realisation that some of the purported environmental stresses may once again be driving mass extinction, we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises.
In this study we use detrital zircons to probe the Early Paleozoic history of NE Iran and evaluate the link between sediment sources and Gondwanan pre–Cadomian, Cadomian and younger events. U–Pb zircon ages and Hf isotopic compositions are reported for detrital zircons from Ordovician and Early Devonian sedimentary rocks from NE Iran. These clastic rocks are dominated by zircons with major age populations at ~ 2.5 Ga, ~ 0.8–0.6 Ga, 0.5 Ga and ~ 0.5–0.4 Ga as well as a minor broad peak at ~ 1.0 Ga.
Large Igneous Provinces (LIPs) are intraplate magmatic events, involving volumes of mainly mafic magma upwards of 100,000 km3, and often above 1 million km3. They are linked to continental break-up, global environmental catastrophes, regional uplift and a variety of ore deposit types. In this up-to-date, fascinating book, leading expert Richard Ernst explores all aspects of LIPs, beginning by introducing their definition and essential characteristics. Topics covered include continental and oceanic LIPs; their origins, structures, and geochemistry; geological and environmental effects; association with silicic, carbonatite and kimberlite magmatism; and analogues of LIPs in the Archean, and on other planets. The book concludes with an assessment of LIPs' influence onnatural resources such as mineral deposits, petroleum and aquifers. This is a one-stop resource for researchersand graduate students in a wide range of disciplines, including tectonics, igneous petrology, geochemistry, geophysics, Earth history, and planetary geology, and for mining industry professionals.