Central Atlantic Magmatic Province Volcanism Research Articles

Mercury anomalies and the timing of biotic recovery following the end-Triassic mass extinction

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.

Beef and cone-in-cone calcite fibrous cements associated with the end-Permian and end-Triassic mass extinctions: Reassessment of processes of formation

This paper reassesses published interpretation that beef and cone-in-cone (B-CIC) fibrous calcite cements were precipitated contemporaneously just below the sea floor in unconsolidated sediment, in limestones associated with the end-Permian (P/T) and end-Triassic (T/J) mass extinctions. That interpretation introduced the concept of a sub-seafloor carbonate factory associated with ocean acidification by raised carbon dioxide driven by volcanic eruption, coinciding with mass extinction. However, our new fieldwork and petrographic analysis, with literature comparison, reveals several problems with this concept. Two key points based on evidence in the T/J transition of the UK are: (1) that B-CIC calcite deposits form thin scattered layers and lenses at several horizons, not a distinct deposit associated with volcanic activity; and (2) B-CIC calcite is more common in Early Jurassic sediments after the extinction and after the end of the Central Atlantic Magmatic Province volcanism proposed to have supplied the carbon dioxide required.Our samples from Late Triassic, Early Jurassic and Early Cretaceous limestones in southern UK show that B-CIC calcite occurs in both marine and non-marine sediments, therefore ocean processes are not mandatory for its formation. There is no proof that fibrous calcite was formed before lithification, but our Early Jurassic samples do prove fibrous calcite formed after compaction, thus interpretation of crystal growth in unconsolidated sediment is problematic. Furthermore, B-CIC crystals mostly grew both upwards and downwards equally, contradicting the interpretation of the novel carbonate factory that they grew preferentially upwards in soft sediment. Finally, Early Jurassic and Early Cretaceous examples are not associated with mass extinction.Three further key points derived from the literature include: (1) B-CIC calcite is widespread geographically and stratigraphically, not clustered around mass extinctions or the Paleocene–Eocene Thermal Maximum (PETM) event; (2) isotope signatures suggest B-CIC calcite formed under high pressure in burial at 70–120 °C, incompatible with interpretation of formation of B-CIC calcite at the redox boundary below the ocean floor; and (3) B-CIC calcite reported in P/T boundary microbialites in one site in Iran is the only occurrence known despite extensive published studies of similar shallow marine settings, demonstrating its formation is localized to the Iran site.Based on the above evidence, our opinion is that B-CIC calcite is best explained as a later diagenetic feature unrelated to rapid Earth-surface environmental change associated with mass extinctions; thus a novel carbonate factory is highly unlikely.

Volcanism and deep-ocean acidification across the end-Triassic extinction event

The end-Triassic extinction event marks one of the “big five” mass extinction events of the Phanerozoic. The ultimate cause of the extinction is considered to be volcanic activity at the Central Atlantic magmatic province (CAMP), yet the underlying nature of global environmental changes that accompanied the biotic turnover remains elusive. Here we present chemical and mineralogical studies across the end-Triassic extinction level of the deep-sea chert sequence (Inuyama, Japan). Depleted hematite content normalized by terrigenous material predated the end-Triassic extinction level with significant rock color change from brick red to purple, which is consistent with the rock magnetic records of hematite reported. This suggests the loss of authigenic hematite possibly due to the acidification of bottom-water and the underlying sediment pore-water. This timing is consistent with the initial eruption of CAMP volcanism, suggesting a catastrophic release of greenhouse gases as a cause of deep-ocean acidification. Across the end-Triassic extinction interval, MgO/Al2O3, Fe2O3/Al2O3, and Al2O3/SiO2 increased with change in color from purple to dusty red. This trend became close to those of weathered CAMP basalts in arid area, implying that it became the considerable source of aeolian dust in cherts after the end-Triassic extinction event. These temporal relations support the synchrony among the initial eruption of CAMP, deep-ocean acidification, and the end-Triassic extinction. Similar rock color changes of cherts might have potential information for the volcanisms and deep-ocean acidification in other geologic events.

The dawn of CAMP volcanism and its bearing on the end-Triassic carbon cycle disruption

The cause-and-effect relationship between the c . 201 Ma eruption of the Central Atlantic magmatic province (CAMP) and the end-Triassic abrupt climate change and mass extinction is at present based on controversial temporal correlations. Upper Triassic sedimentary strata underlying CAMP basalts in Morocco illustrate a clear mineralogical and geochemical fingerprint of early CAMP basaltic eruptions, namely unusually high contents of MgO (10–32 wt%) and of mafic clay minerals (11–84%). In the same rocks a coincident negative carbon-isotope excursion (CIE) is present, equivalent to the so-called ‘initial negative CIE’ recorded worldwide shortly before the Triassic–Jurassic boundary. The new data show that the onset of CAMP activity preceded the end-Triassic carbon cycle disruption and that the initial negative CIE is unequivocally synchronous with CAMP volcanism. The results of this study strongly support the hypothesis that the culmination of pollution of atmosphere and seawater by CAMP-derived volcanic gases was the proximate cause of the end-Triassic mass extinction. Supplementary material: The stratigraphic position of analysed samples, and the C-isotope, bulk-rock mineralogy, element analysis, Mg–Al–Si ternary diagram and trace-element analysis data are available at www.geolsoc.org.uk/SUP18707 .

Rock magnetic record of the Triassic-Jurassic transition in pelagic bedded chert of the Inuyama section, Japan

The end-Triassic mass extinction event is regarded as one of the fi ve largest extinction events of the Phanerozoic. The emerging consensus points to volcanic activity at the Central Atlantic Magmatic Province (CAMP) as the ultimate cause of the extinction, yet the underlying mecha- nisms and the nature of global environmental changes that accompanied the biotic turnover remain elusive. We present a rock magnetic study of the extinction interval found within a continuous chert sequence that provides an uninterrupted record of pelagic sedimentation in the Panthalassa Ocean. The variations in the relative abundances and characteristics of authi- genic magnetic phases indicate that the Triassic-Jurassic transition progressed in two stages. The initial stage, characterized by a disappearance of the previously ubiquitous magnetofos- sils, started a few tens of thousands of years to 100 k.y. prior to the formal Triassic-Jurassic boundary as identifi ed by the diagnostic radiolarian species. The second stage, defi ned by signifi cant changes in optical and magnetic properties of hematite pigment, lasted a few tens of thousands of years. The stepwise change in magnetic properties is suggestive of the protracted environmental deterioration, likely prompted by the early episodes of the CAMP volcanism, which was followed by a sudden ocean acidifi cation event, perhaps triggered by a catastrophic release of gas hydrates.

Environmental changes across the Triassic–Jurassic boundary and coeval volcanism inferred from elemental geochemistry and mineralogy in the Kendlbachgraben section (Northern Calcareous Alps, Austria)

The end-Triassic extinction (ETE), one of the five largest Phanerozoic mass extinctions, is associated with rapid and severe environmental change, but existing data permit alternative models of causation. Volcanism in the Central Atlantic Magmatic Province (CAMP) has been proposed as the main trigger, but direct evidence for this linkage is scarce. To help constrain scenarios for the ETE and other Triassic–Jurassic boundary (TJB) events, we obtained a temporally highly resolved, multidisciplinary dataset from the Kendlbachgraben section in the Northern Calcareous Alps in Austria. The section belongs to the same paleogeographic unit (Eiberg Basin) and share similar stratigraphy with the recently selected base Jurassic Global Stratotype Section and Point at Kuhjoch.Micromineralogic study of the topmost bed of the Rhaetian Kössen Formation revealed pseudomorphs of altered, euhedral pyroxene and amphibole crystals. Their well-faceted morphology is consistent with their origin from distal mafic volcanic ash fallout. Spherical grains were also observed in the same bed, likely representing clay-altered volcanic glass. Clay minerals of this bed include low- to medium-charged smectite and Mg-vermiculite, both typical alteration products of mafic rocks. The same bed yielded a rare earth element pattern that differs from all other levels in an enrichment of heavy REEs, hinting at some minor contribution from mafic magmatic material. These features from a layer that was deposited very near to the TJB are interpreted as direct evidence of CAMP volcanism, coeval or immediately preceding the ETE and the initial negative carbon isotope anomaly.The kaolinite-dominated clay mineral spectrum of the overlying boundary mudstone records intensive weathering under hot and humid greenhouse conditions. Redox-sensitive minor and trace elements do not support the development of widespread anoxia in the studied section. Although pyrite is common in several layers, framboid size indicates formation within a reductive zone, below the sediment/water interface, rather than in an anoxic water column.Our data provide a direct link between uppermost Triassic marine strata and CAMP-derived material. They support scenarios where CAMP volcanism induced climate and other environmental change, which in turn triggered the ETE and that is also reflected in the carbon isotope anomalies.

Rapid emplacement of the Central Atlantic Magmatic Province as a net sink for CO2

Recent evidence from the ~201.5Ma Central Atlantic Magmatic Province (CAMP) in the Newark rift basin demonstrates that this Large Igneous Province produced a transient doubling of atmospheric pCO2, followed by a falloff to pre-eruptive concentrations over ~300kyr. This paper confirms the short-term findings from the Newark basin, and tests the million-year effects of the CAMP volcanism on Early Jurassic pCO2 from strata in the corollary Hartford basin of Eastern North America (ENA) also using the pedogenic carbonate paleobarometer. We find pCO2 levels for pre-CAMP background of 2000±700ppm (at S(z)=3000±1000ppm), increasing to ~5000±1700ppm immediately above the first lava flow unit, consistent with observations from the Newark. The longer post-extrusive Portland Formation of the Hartford basin records a fourth pulse of pCO2 to ~4500±1200ppm, about 240kyr after the last lava recorded in the ENA section. We interpret this fourth increase as due to a major episode of volcanism, and revise the main CAMP duration to 840±60kyr. The Portland also records a post-eruptive decrease in pCO2 reaching pre-eruptive background concentrations of ~2000ppm in only ~300kyr, and continuing to levels below pre-CAMP background over the subsequent 1.5Myr following the final episode of eruptions. Geochemical modeling (using modified COPSE code) demonstrates that the rapidity of the pCO2 decreases, and fall to concentrations below background can be accounted for by a 1.5-fold amplification of the continental silicate weathering response due to the presence of the CAMP basalts themselves. These results demonstrate that a continental flood basalt capable of producing a short-term perturbation of the carbon system may actually have an overall net-cooling effect on global climates due to a long-term net-decrease in pCO2 to below pre-eruptive levels, as previous models have suggested followed the emplacement of the Deccan Traps.

Record of epicontinental platform evolution and volcanic activity during a major rifting phase: The Late Triassic Zamoranos Formation (Betic Cordillera, S Spain)

The study of the Late Triassic Zamoranos Formation and the comparison to coeval carbonate units provides new insights into the evolution and palaeogeography of carbonate platforms during major rifting phases in the Earth's history. The platform carbonates of the Zamoranos Formation record the last major transgression during the Triassic, and document the initial phase of the CAMP volcanism in the external Zone of the Betic Cordillera. New palynological data from the lower part of the Zamoranos Formation indicate a Middle Norian age. The entire succession is built up by limestones, dolomites, and ferruginous red detrital deposits with volcaniclastic breccias. The carbonates are interpreted as tidal and shallow marine sediments, deposited under arid conditions. The red detrital deposits appear in coastal environments in relation to a volcanic event, which triggered hydrothermal processes in these deposits and started the massive magmatic event associated with the Central Atlantic Magmatic Province (CAMP). The Zamoranos Formation was also recognized in the SW part of the Valencia Triassic and is correlated to the Imón Formation (Iberian Ranges), to the Isábena Formation (Pyrenees) and to other carbonate units of the W Tethys realm (Aquitaine, Tunisian Atlas, West Carpathians). These units indicate that an extensive epicontinental platform developed during the Late Triassic.

Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary

High-resolution palynological data sets from shallow marine Triassic-Jurassic (Tr/J) boundary beds of two principal sections in Europe (Hochalplgraben in Austria and St. Audrie's Bay in the United Kingdom) were analyzed to reconstruct changes in vegetation, biodiversity, and climate. In Hochalplgraben, a hardwood gymnosperm forest with conifers and seed ferns is replaced by vegetation with dominant ferns, club mosses and liverworts, which concurs with an increased diversification of spore types during the latest Rhaetian. Multivariate statistical analysis reveals a trend to warmer and wetter conditions across the Tr/J boundary in Hochalplgraben. The vegetation changes in St. Audrie's Bay are markedly different. Here, a mixed gymnosperm forest is replaced by monotonous vegetation consisting mainly of Cheirolepidiaceae (80–100%). This change is caused by a transition to a warmer and more arid climate. The observed diversity decrease in St. Audrie's Bay affirms this interpretation. Although both sections show major vegetation changes, neither of them demonstrates a distinctive floral mass extinction. A compilation of Tr/J boundary sections across the world demonstrates the presence of Cheirolepidiaceae-dominated forests in the Pangaean interior and increases in abundance of spore-producing plants adjacent to the Tethys Ocean. We propose that the non-uniform vegetation changes reflected in the Tr/J palynological records are the result of environmental changes caused by Central Atlantic Magmatic Province volcanism. The increase in greenhouse gases caused a warmer climate and an enhanced thermal contrast between the continent and the seas. Consequently, the monsoon system got stronger and induced a drier continental interior and more intensive rainfall near the margins of the Tethys Ocean.

Disentangling the Hettangian carbon isotope record: Implications for the aftermath of the end‐Triassic mass extinction

This study provides an organic carbon stable isotope (δ13Corg) record calibrated with detailed ammonite biostratigraphy, following the end‐Triassic biological crisis. Precise correlation between this crucial fossil group and the δ13Corg record is key to understanding feedbacks between biological and environmental events following mass extinction. The latest Triassic and Hettangian δ13Corg record shows several negative and positive excursions. The end‐Triassic negative shift coinciding with the mass extinction interval is followed by a positive excursion in the earliest Hettangian Psiloceras spelae beds, which marks the onset of recovery in the marine ecosystem. This positive trend is interrupted by a second negative δ13Corg excursion in the P. pacificum beds related to a minor ammonite extinction event. This pattern of the δ13Corg curve culminates in the uppermost Hettangian Angulata Zone major positive excursion. This indicates that both the ecosystem and the carbon cycle remained in a state of perturbation for at least 2 Ma, although the recovery of some pelagic taxa already began at the base of Jurassic. The early and late Hettangian positive δ13Corg excursions have been confused in several recent papers. Here, we show that during the Hettangian there are indeed two distinct positive δ13Corg excursions. Phases of anoxia and further pulses of Central Atlantic Magmatic Province volcanism during the Hettangian might have inhibited the full recovery for that interval of time. The main Liasicus‐Angulata organic positive CIE (carbon isotope excursion) during the Late Hettangian might be related to gradual decreasing of pCO2 due to protracted high organic burial, and coincides with a second phase of recovery, as indicated by a pulse of ammonoid diversification.

Sedimentological, palynological and geochemical studies of the terrestrial Triassic–Jurassic boundary in northwestern Poland

AbstractThe Kamień Pomorski IG-1 borehole (Pomerania, NW Poland) yields a profile through the Triassic–Jurassic (T–J) transition in continental deposits. An integrated study of the sedimentology, sequence stratigraphy, palynology, biostratigraphy and geochemistry of these deposits has been carried out on the boundary interval, which represents a time of major environmental change. Two lithological units within the transitional section are distinguished: the Lower–Middle Rhaetian Wielichowo Beds of alluvial plain facies, which shows evidence of a semi-arid climate, and the Upper Rhaetian to Lower Hettangian Zagaje Formation, lying above a marked erosional sequence boundary, composed of mudstone-claystone and sandstone deposited in a fluvial-lacustrine environment. Carbon isotope values obtained from palynomaceral separates, and thus reflecting isotopic changes in atmospheric CO2, show significant fluctuations through the Rhaetian; the most conspicuous negative δ13Corgexcursion is correlated with the Rhaetian ‘initial’ excursion and shows two sub-peaks, pointing to short-term carbon-cycle disturbances of lesser magnitude. Above the ‘initial’ negative excursion, there is a positive excursion followed again by more negative values, representing subordinate fluctuation within a positive excursion and is correlated with the T–J boundary. Seventy-two miospore taxa have been determined from the studied T–J transitional section. Two major palynological assemblages have been distinguished: the lower one, typically Rhaetian, named theCingulizonates rhaeticus–Limbosporites lundblandiiassociation, which corresponds to theRhaetipollis–Ricciisporites(=Rhaetipollis–Limbosporites) Zone; and the upper one, typically Hettangian, named theConbaculatisporites mesozoicus– Dictyophyllidites mortoni–Cerebropollenites thiergartiiassociation (with the age-diagnostic pollenC.thiergartii), which corresponds to thePinuspollenites–Trachysporites(= Trachysporites–Heliosporites) Zone. The T–J palynofloral turnover occurred in a humid period and is more conspicuous then palynofloral changes observed in Greenland, the Tethyan domain or other parts of NE Europe. The osmium isotope system is studied herein for the first time from T–J continental deposits and shows marked disturbances similar to those measured in marine deposits and attributed to volcanic fallout. Carbon and osmium isotope correlation and coeval increase in polycyclic aromatic hydrocarbon (PAH) content and darkening of miospores confirm that eruptions of the Central Atlantic Magmatic Province (CAMP) contributed to the perturbances in climate and crisis in the terrestrial biosphere. A series of periodical atmospheric loading by CO2, CH4or alternatively by SO2, sulphate aerosols and toxic compounds is inferred to have caused a series of rapid climatic reversals, directly influencing the ecosystem and causing the Triassic floral crisis. A floral turnover period commenced at the ‘initial’ δ13C excursion, with the onset of CAMP volcanism. Obtained values of initial187Os/186Os between 2.905 and 4.873 and very low iridium content (about 5 ppt) lend no support to a role for an extraterrestrial impact at the T–J boundary event. The position of the ‘initial’ negative carbon isotope excursion about 12 m below the T–J boundary, position of sequence boundaries (emergence surfaces) and other isotope excursions allow reliable correlation with marine profiles, including St Audrie's Bay (UK), Csövár (Hungary) and the GSSP profile at Kuhjoch (Austria).

The quest for chron E23r at Partridge Island, Bay of Fundy, Canada: CAMP emplacement postdates the end-Triassic extinction event at the North American craton

The Partridge Island stratigraphic section at the Bay of Fundy, Maritime Canada, reveals a continental sedimentary succession with the end-Triassic mass extinction level closely followed by basalts of the Central Atlantic Magmatic Province (CAMP). New Paleomagnetic data show that a short reverse magnetic polarity chron, correlative to E23r of the Newark Geomagnetic Polarity Time Scale (GPTS), is present below the extinction event. Organic carbon isotope data and basalt geochemistry further indicate that the onset of CAMP emplacement in the Bay of Fundy was roughly synchronous with emplacement in the Newark basin, but slightly postdates the oldest CAMP volcanism in Morocco by ∼20 ka. These results confirm the potential for long-distance CAMP correlations based on geochemical trace elements, indicate substantiate provincialism of latest Triassic palynoflora, and suggest a very concise period (<<100 ka) of CAMP emplacement in the northern Atlantic region.

Correlating the end-Triassic mass extinction and flood basalt volcanism at the 100 ka level

New high-precision U/Pb geochronology from volcanic ashes shows that the Triassic-Juras- sic boundary and end-Triassic biological crisis from two independent marine stratigraphic sections correlate with the onset of terrestrial fl ood volcanism in the Central Atlantic Mag- matic Province to <150 ka. This narrows the correlation between volcanism and mass extinc- tion by an order of magnitude for any such catastrophe in Earth history. We also show that a concomitant drop and rise in sea level and negative δ 13 C spike in the very latest Triassic occurred locally in <290 ka. Such rapid sea-level fl uctuations on a global scale require that global cooling and glaciation were closely associated with the end-Triassic extinction and potentially driven by Central Atlantic Magmatic Province volcanism.

Latest Triassic onset of the Central Atlantic Magmatic Province (CAMP) volcanism in the Fundy Basin (Nova Scotia): New stratigraphic constraints

In this paper we investigate the stratigraphic relationship between the emplacement of the CAMP basalts and the Triassic–Jurassic (Tr–J) boundary in the Fundy Basin (Nova Scotia, Canada). This is one of the best exposed of the synrift basins of eastern North America (ENA) formed as a consequence of the rifting that led to the formation of the Atlantic Ocean. The Triassic palynological assemblages found in the sedimentary rocks below (uppermost Blomidon Formation) and just above the North Mountain Basalt (Scots Bay Member of the McCoy Brook Formation) indicate that CAMP volcanism, at least in Nova Scotia, is entirely of Triassic age, occurred in a very short time span, and may have triggered the T–J boundary biotic and environmental crisis. The palynological assemblage from the Blomidon Formation is characterised by the dominance of the Circumpolles group (e.g. Gliscopollis meyeriana, Corollina murphyae, Classopollis torosus) which crosses the previously established Tr–J boundary. The Triassic species Patinasporites densus disappears several centimetres below the base of the North Mountain basalt, near the previously interpreted Tr–J boundary. The lower strata of the Scots Bay Member yielded a palynological assemblage dominated by Triassic bisaccate pollens (e.g Lunatisporites acutus, L. rhaeticus Lueckisporites sp., Alisporites parvus) with minor specimens of the Circumpolles group. Examination of the state of preservation and thermal alteration of organic matter associated with the microfloral assemblages precludes the possibility of recycling of the Triassic sporomorphs from the older strata. Our data argue against the previous definition of the Tr–J boundary in the ENA basins, which was based mainly on the last occurrence of P. densus. Consequently, it follows that the late Triassic magnetostratigraphic correlations should be revised considering that chron E23r, which is correlated with the last occurrence of P. densus in the Newark basin, does not occur at the Tr–J boundary but marks rather a late Triassic (probably Rhaetian) reversal.

The nonmarine Triassic–Jurassic boundary in the Newark Supergroup of eastern North America

For the last three decades, the position of the Triassic–Jurassic boundary (TJB) in nonmarine strata has largely been based on its palynostratigraphic placement just below the oldest basalts of the Central Atlantic magmatic province (CAMP) in the Newark Supergroup of eastern North America. This boundary, however, is demonstrably older than the TJB as it is defined in marine strata. Thus, the palynostratigraphic change used to place this TJB in the Newark most resembles a late Norian change in the European section and does not correspond to any palynological event at the marine-defined TJB. Conchostracan biostratigraphy suggests that the TJB is in the Newark extrusive zone above the oldest CAMP basalt, and vertebrate biostratigraphy is consistent with this placement of the TJB. Radioisotopic ages indicate that the TJB defined in marine strata is no older than 200 MA, but the oldest CAMP basalts of the Newark Supergroup consistently yield ages averaging about 201 Ma. Magnetostratigraphic correlation of the Newark section to the TJB section at St. Audrie's Bay in England also indicates that the onset of CAMP volcanism in the Newark Supergroup is older than the marine TJB. Correlations based on carbon and osmium isotopes are also consistent with this correlation. Thus, all data indicate that the TJB in the Newark Supergroup is above the lowest CAMP basalt in the Newark extrusive zone. Correct placement of the TJB in the Newark Supergroup allows key nonmarine and marine events to be sequenced across the TJB, indicating the following succession of events: crurotarsan (“thecodont”) extinction, the palynofloral turnover in the Newark, the first CAMP eruptions, the extinctions of Rhaetian ammonites and conodonts, and the first appearance of Jurassic psiloceratid ammonites.

40Ar/ 39Ar ages and duration of the Central Atlantic Magmatic Province volcanism in Morocco and Portugal and its relation to the Triassic–Jurassic boundary

The Central Atlantic Magmatic Province (CAMP) is the world's largest known continental igneous province and is contemporaneous with the Triassic–Jurassic (T–J) boundary that marks one of the five largest biological extinctions in the last 600 Ma. Although constraints on the duration of the CAMP volcanism remain yet poorly defined, the assumption that the CAMP may have had a causal relationship with the climatic and biotic crisis was suggested [Marzoli, A., Bertrand, H., Knight, K., Cirilli, S., Buratti, N, Verati, C., Nomade, S., Renne, P.R., Youbi, N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., Bellieni, G., 2004. Synchrony of the Central Atlantic magmatic province and the Triassic–Jurassic boundary climatic and biotic crisis. Geology 32, 973–976.]. In this paper, we present new 40Ar/ 39Ar ages on basaltic flows from Moroccan (central High Atlas, Oujda and Argana) and Portuguese (Algarve and Santiago do Cacém) basins where CAMP lava flows are interlayered with T–J sedimentary sequences. In the Moroccan basins, where the basalts were erupted across the T–J boundary, well defined 40Ar/ 39Ar plateau ages ( n = 12) for more than 90% of the total erupted volume of CAMP basalts range from 197.8 ± 0.7 Ma to 201.7 ± 2.4 Ma and display a main restricted peak at 199.1 ± 1 Ma providing a precise estimate of the 40Ar/ 39Ar age of the T–J boundary, concordant with the current U–Pb age [199.6 ± 0.3 Ma; Pálfy, J., Mortensen, J.K, Carter, E.S., Smith, P.L., Friedman, R.M., Tipper, H.W., 2000. Timing the end-Triassic mass extinction: First on land, then in the sea? Geology 28, 39–42.]. The topmost lava flows (recurrent unit) yield a significantly younger mean age of 196.6 ± 0.6 Ma, highlighting late episodic eruption of CAMP magmas. These late basalts represent a small magma volume (< 10% of the total), which was erupted most likely due to asthenospheric upwelling and lithospheric extension within the T–J central High Atlas basins. In the Portuguese basins, stratigraphical and palynological studies of the associated continental sedimentary sequence underlying the volcanic units suggest an age close to the T–J boundary for the CAMP basaltic flows. This is confirmed by new 40Ar/ 39Ar data for the Portuguese basalts, which provide the first accurate radio-isotopic ages for lava flows in the European CAMP, with two plateau ages yielding a mean value of 198.1 ± 0.4 Ma. These plateau ages (plus three concordant mini-plateau ages) suggest synchronous rifting and volcanism both in south-western Europe and Morocco (central High Atlas and Oujda basins). In summary, the eruptive history of the CAMP, with an early extremely widespread and intense peak at 199.1 Ma and a tail of episodic eruption events until 196.6 Ma is consistent with the biotic turnover at the T–J boundary, which was likely caused by devastating effects of extensive volcanic eruptions.

Response of the marine infauna to Triassic–Jurassic environmental change: Ichnological data from southern England

The trace fossil record through the Triassic–Jurassic boundary interval is examined at three sites in central and southern England (St. Audrie's Bay, Somerset; Pinhay Bay, Devon; and Long Itchington, Warwickshire). The lower ‘Pre-Planorbis Beds’ of the Blue Lias Formation record low ichnotaxonomic diversity, low bioturbation intensity, small burrow diameters, and an absence of deep tier bioturbation. The stepwise reappearance of ichnotaxa following this interval is similar at the three sites, suggesting similar rates of recovery in the benthic marine ecosystem and highlighting the potential contribution of these trace fossils to stratigraphic correlation. Mass extinction in the Late Triassic is increasingly linked to the emplacement of the Central Atlantic Magmatic Province (CAMP). Timing of the onset of CAMP volcanism in the UK is currently imperfectly known, but potentially occurred within either the Westbury Formation or the Lilstock Formation. If the onset of CAMP was within the Lilstock Formation, the modestly diverse trace fossil assemblage of the Langport Member of the Lilstock Formation suggests that emplacement of CAMP had little lasting effect on the marine benthos in central and southern England. The decline in benthic activity recorded in the ‘Pre-Planorbis Beds’ appears to be unrelated to the onset of CAMP and any associated environmental change. It is more likely related to an episode of marine anoxia. An episode of marine anoxia also provides a suitable causal mechanism for the reduction of infaunal tiering.