New Data Linking the End-Triassic Extinction with the Central Atlantic Magmatic Province.

Out today in Science Express. This study also provides support for the accuracy of the astrochronologically tuned time scale proposed for the Late Triassic Newark Supergroup sequence.

Blackburn, T. J., Olsen, P. E., Bowring, S. A., McLean, N. M., Kent, D. V., Puffer, J., McHone, G., Rasbury, E. T., and M. Et-Touhami. 2013. Zircon U-Pb Geochronology Links the End-Triassic Extinction with the Central Atlantic Magmatic Province. Science Express. http://www.sciencemag.org/content/early/recent / 21 March 2013 / Page 1/ 10.1126/science.1234204

Abstract - The end-Triassic extinction is characterized by major losses in both terrestrial and  marine diversity, setting the stage for dinosaurs to dominate Earth for the next 136 million years. Despite the approximate coincidence between this extinction and  flood basalt volcanism, existing geochronologic dates have insufficient resolution  to confirm eruptive rates required to induce major climate perturbations. Here we present new zircon U-Pb geochronologic constraints on the age and duration of flood basalt volcanism within the Central Atlantic Magmatic Province. This chronology demonstrates synchroneity between the earliest volcanism and extinction, tests and corroborates the existing astrochronologic time scale, and shows that the release of magma and associated atmospheric flux occurred in four pulses over ~600,000 years, indicating expansive volcanism even as the biologic recovery was under way.

CAMP Magnetostratigraphy Revisited

New paper in which the results suggest that either the SA5.r magnetozone from St. Audrie's Bay is not recorded in North American and Moroccan CAMP deposits or that the SA5.r is not reliable or useful for global-scale correlations. This has implications on the timing of the CAMP eruptions in relation to the Triassic-Jurassic boundary as well as correlations into non-marine sequences. This paper also provides a new paleo pole hypothesis for CAMP deposits in Morocco, which is more similar than past poles recovered for that unit to those determined for the North American sequence.

Font, E., Youbi, N., Fernandes, S., El Hachimi, H., Kratinova, Z., and Y. Hamim. 2011. Revisiting the magnetostratigraphy of the Central Atlantic Magmatic Province (CAMP) in Morocco. Earth and Planetary Science Letters, corrected proof. doi:10.1016/j.epsl.2011.07.007

Abstract - The origin of the Triassic–Jurassic (Tr–J) mass extinction is still a matter of debate: proponents of the idea that continental flood basalts of the Central Atlantic Magmatic Province (CAMP) are responsible for the crisis are opposed by those who favor an extraterrestrial origin linked to the impact of meteorite. Principal limitations reside in the difficulty to date and correlate CAMP lavas with the marine realm turnover. One argument widely used to suggest that CAMP lavas pre-dated the Tr–J boundary in Morocco is based on the presence of two brief magnetic reversals in the intermediate units of the Tiourjdal and Oued Lahr sections (Morocco) that were correlated to the E23r chron from the Newark basin and to the SA5n.2r/3r and SA5r chrons of the Saint Audrie Bay [Knight, K.B., Nomade, S., Renne, P.R., Marzoli, A., Betrand, H., Youbi, N., 2004. The Central Atlantic Magmatic Province at the Triassic–Jurassic boundary: paleomagnetic and ⁴⁰Ar/³⁰Ar evidence from Morocco for brief, episodic volcanism. Earth and Planetary Science Letters 228, 143–160]. However the primary origin for these negative (reverse) magnetic components is questionable since no field or reversal test was provided to constrain the primary character of the remanence as well as because the small number of samples. Here we have conducted a detailed paleomagnetic and magnetic mineralogy study of the interbedded limestones of the Tiourjdal section and of other CAMP lavas sections where the intermediate unit is complete, namely the Tizi El Hajaj, Jbel Imzar and Aït Ourir sections, to better constrain the origin and stratigraphic location of these negative magnetic components. We show that the interbedded limestones of the Tiourjdal section were entirely remagnetized by chemical processes via acid and oxidizing hydrothermal fluids generated by eruptions of CAMP lavas. In addition, magnetostratigraphic data of the Tizi El Hajaj, Jbel Imzar and Aït Ourir sections show that the entire intermediate unit encompassed a positive (normal) magnetic interval. A good quality paleomagnetic pole for the CAMP lava in Morocco is then provided (Plat = 60.0°; Plong = 241.6°; A95 = 2.6; N = 99) that is now in better agreement with its trans-Atlantic counterpart.

Atmospheric CO2 Effects of the Central Atlantic Magmatic Province Eruptions

Schaller, M. F., Wright, J. D., and D. V. Kent. 2011. Atmospheric PCO2 Perturbations Associated with the Central Atlantic Magmatic Province. Science 331: 1404-1409. DOI: 10.1126/science.1199011

Abstract - The effects of a large igneous province on the concentration of atmospheric carbon dioxide (PCO2) are mostly unknown. In this study, we estimate PCO2 from stable isotopic values of pedogenic carbonates interbedded with volcanics of the Central Atlantic Magmatic Province (CAMP) in the Newark Basin, eastern North America. We find pre-CAMP PCO2 values of ~2000 parts per million (ppm), increasing to ~4400 ppm immediately after the first volcanic unit, followed by a steady decrease toward pre-eruptive levels over the subsequent 300 thousand years, a pattern that is repeated after the second and third flow units. We interpret each PCO2 increase as a direct response to magmatic activity (primary outgassing or contact metamorphism). The systematic decreases in PCO2 after each magmatic episode probably reflect consumption of atmospheric CO2 by weathering of silicates, stimulated by fresh CAMP volcanics.

Two New Papers on the Timing of the Placement of the Central Atlantic Magmatic Province

Marzoli, A., Jourdan, F., Puffer, J. H., Cupponea, T., Tanner, L. H., Weems, R. E., Bertrand, H., Cirilli, S., Bellienia, G., and A. De Minh. 2011. Timing and duration of the Central Atlantic magmatic province in the Newark and Culpeper basins, eastern U.S.A. Lithos 122:175-188. doi:10.1016/j.lithos.2010.12.013

Abstract - New major and trace element data and 40Ar/39Ar plateau ages constrain the timing, duration and time-related geochemical evolution of the Central Atlantic magmatic province in the U.S.A. (Newark and Culpeper basins) and refine correlations with basaltic lava flows from other Late Triassic–Early Jurassic circum-Atlantic basins. The precise, statistically robust 40Ar/39Ar plateau ages were obtained on biotite and on fresh plagioclase and calculated using the latest 40K decay constants. These ages are supported by a general consistency of the Ca/K calculated from 37Ar/39Ar of the plateau steps and the Ca/K obtained by detailed electron microprobe analyses on plagioclase phenocrysts. The ages of five analyzed basalt lava flows, from all three lava flow units in the Newark basins, and the ages of two sill samples are indistinguishable, indicating a brief magmatic peak phase at 201.8 ± 0.7 Ma. Recalibrated 40Ar/39Ar plateau ages from the entire province indicate a near-synchronous onset and peak volcanic activity at the Triassic–Jurassic boundary within the circum-Atlantic basins from the U.S.A., Canada and Morocco. The early erupted magmas (Moroccan Lower to Upper basalts, the Fundy basin North Mountain Basalt, and Orange Mountain and equivalent U.S.A. flows) yield an enriched geochemical signature (e.g., with relatively high La/Yb), whereas late magmas in the U.S.A. (Hook Mountain and Hampden basalts) and Morocco (Recurrent basalt) yield relatively depleted geochemical compositions (low La/Yb). A slight, but significant age difference for eruption of Hook Mountain and Hampden basalts (200.3 ± 0.9 Ma) and Recurrent basalts (198.2 ± 1.1 Ma) is interpreted as evidence of a diachronous northward rift–drift transition during break-up of Pangea. Our data indicate also a prolonged intrusive sequence that continued until about 195 Ma at the Palisades sill and is consistent with sporadic late CAMP magmatism for dykes from the south-eastern U.S.A. and for intrusions from Guinea.

Merle, R., Marzoli, A., Bertrand, H., Reisberg, L., Verati, C., Zimmermann, C., Chiaradia, M., Bellieni, G., and M. Ernesto. 2011. 40Ar/39Ar ages and Sr–Nd–Pb–Os geochemistry of CAMP tholeiites from Western Maranhão basin (NE Brazil). Lithos 122:137-151. doi:10.1016/j.lithos.2010.12.010

Abstract - The Central Atlantic Magmatic Province (CAMP), emplaced at the Triassic–Jurassic (T–J) boundary (~ 200 Ma), is among the largest igneous provinces on Earth. The Maranhão basin in NE Brazil is located around 700 km inland and 2000 km from the site of the earliest Pangea disruption. The CAMP tholeiites occur only in the western part of the basin and have been described as low and high-Ti. Here we document the occurrence of two sub-groups among the high-Ti tholeiites in the Western Maranhão basin. The major and trace elements and the Sr–Nd–Pb isotopic ratios define three chemical groups corresponding to the low-Ti (TiO2 < 1.3 wt.%), high-Ti (TiO2 ~ 2.0 wt.%) and evolved high-Ti (TiO2 > 3 wt.%) western Maranhão basin tholeiites (WMBT). The new 40Ar/39Ar plateau ages obtained on plagioclase separates for high-Ti (199.7 ± 2.4 Ma) and evolved high-Ti WMBT (197.2 ± 0.5 Ma and 198.2 ± 0.6 Ma) are indistinguishable and identical to those of previously analyzed low-Ti WMBT (198.5 ± 0.8 Ma) and to the mean 40Ar/39Ar age of the CAMP (199 ± 2.4 Ma). We also present the first Re–Os isotopic data for CAMP basalts. The low and high-Ti samples display mantle-like initial (187Os/188Os)i ranging from 0.1267 to 0.1299, while the evolved high-Ti samples are more radiogenic ((187Os/188Os)i up to 0.184) We propose that the high-Ti WMBT were derived from the sub-lithospheric asthenosphere, and contaminated during ascent by interaction with the subcontinental lithospheric mantle (SCLM). The evolved high-Ti WMBT were derived from the same asthenospheric source but experienced crustal contamination. The chemical characteristics of the low-Ti group can be explained by partial melting of the most fertile portions of the SCLM metasomatized during paleo-subduction. Alternatively, the low-Ti WMBT could be derived from the sub-lithospheric asthenosphere but the resulting melts may have undergone contamination by the SCLM. The occurrences of high-Ti basalts are apparently not restricted to the area of initial continental disruption which may bring into question previous interpretations such as those relating high-Ti CAMP magmatism to the initiation of Atlantic ridge spreading or as the expression of a deep mantle plume. We propose that the CAMP magmatism in the Maranhão basin may be attributed to local hotter mantle conditions due to the combined effects of edge-driven convection and large-scale mantle warming under the Pangea supercontinent. The involvement of a mantle-plume with asthenosphere-like isotopic characteristics cannot be ruled out either as one of the main source components of the WMBT or as a heat supplier.

Increased fire activity at the Triassic/Jurassic Boundary Due to Climate Driven Floral Change

Belcher, C. M, Mander, L., Rein, G., Jervis, F. X., Haworth, M., Hesselbo, S. P., Glasspool, I. J., and J. C. McElwain. 2010. Increased fire activity at the Triassic/Jurassic boundary in Greenland due to climate-driven floral change. Nature Geoscience 3:426-429.

Abstract - One of the largest mass extinctions of the past 600 million years (Myr) occurred 200 Myr ago, at the Triassic/Jurassic boundary. The major floral and faunal turnovers have been linked to a marked increase in atmospheric carbon dioxide levels, probably resulting from massive volcanism in the Central Atlantic Magmatic Province. Future climate change predictions suggest that fire activity may increase, in part because higher global temperatures are thought to increase storminess. Here we use palaeontological reconstructions of the fossil flora from East Greenland to assess forest
flammability along with records of fossil charcoal preserved in the rocks to show that fire activity increased markedly across the Triassic/Jurassic boundary. We find a fivefold increase in the abundance of fossil charcoal in the earliest Jurassic, which we attribute to a climate-driven shift from a prevalence of broad-leaved taxa to a predominantly narrow leaved assemblage. Our fire calorimetry experiments show that narrow leaf morphologies are more flammable than broad leaved morphologies.We suggest that the warming associated with increased atmospheric carbon dioxide levels favoured a dominance of narrow-leaved plants, which, coupled with more frequent lightening strikes, led to an increase in fire activity at the Triassic/Jurassic boundary.

Further Support for a Causal Relationship Between the CAMP and the End-Triassic Extinction Event

Deenen, M. H. L., Ruhl, M., Bonis, M. R., Krijgsman, W., Kuerschner, W. M., Reitsma, M. and M. J. van Bergen. 2010. A new chronology for the end-Triassic mass extinction. Earth and Planetary Science Letters 291:113–125. doi:10.1016/j.epsl.2010.01.003


Abstract - The transition from the Triassic to Jurassic Period, initiating the ‘Age of the dinosaurs’, approximately 200 Ma, is marked by a profound mass extinction with more than 50% genus loss in both marine and continental realms. This event closely coincides with a period of extensive volcanism in the Central Atlantic Magmatic Province (CAMP) associated with the initial break-up of Pangaea but a causal relationship is still debated. The Triassic–Jurassic (T–J) boundary is recently proposed in the marine record at the first occurrence datum of Jurassic ammonites, post-dating the extinction interval that concurs with two distinct perturbations in the carbon isotope record. The continental record shows a major palynological turnover together with a prominent change in tetrapod taxa, but a direct link to the marine events is still equivocal. Here we develop
an accurate chronostratigraphic framework for the T–J boundary interval and establish detailed trans-Atlantic and marine–continental correlations by integrating astrochronology, paleomagnetism, basalt geochemistry and geobiology. We show that the oldest CAMP basalts are diachronous by 20 kyr across the Atlantic Ocean, and that these two volcanic pulses coincide with the end-Triassic extinction interval in the marine realm. Our results support the hypotheses of Phanerozoic mass extinctions resulting from emplacement of Large Igneous Provinces (LIPs) and provide crucial time constraints for numerical modelling of Triassic–Jurassic climate change and global carbon-cycle perturbations.

Further Evidence for a Volcanic Eruption Cause for the End-Triassic Extinction

Whiteside, J. H., Olsen, P. E., Eglinton, T., Brookfield, M. E., and R. N. Sambrotto. 2010. Compound-specific carbon isotopes from Earth’s largest flood basalt eruptions directly linked to the end-Triassic mass extinction. PNAS Published online before print March 22, 2010, doi: 10.1073/pnas.1001706107

Abstract - A leading hypothesis explaining Phanerozoic mass extinctions and associated carbon isotopic anomalies is the emission of greenhouse, other gases, and aerosols caused by eruptions of continental flood basalt provinces. However, the necessary serial relationship between these eruptions, isotopic excursions, and extinctions has never been tested in geological sections preserving all three records. The end-Triassic extinction (ETE) at 201.4 Ma is among the largest of these extinctions and is tied to a large negative carbon isotope excursion, reflecting perturbations of the carbon cycle including a transient increase in CO2. The cause of the ETE has been inferred to be the eruption of the giant Central Atlantic magmatic province (CAMP). Here, we show that carbon isotopes of leaf wax derived lipids (n-alkanes), wood, and total organic carbon from two orbitally paced lacustrine sections interbedded with the CAMP in eastern North America show similar excursions to those seen in the mostly marine St. Audrie’s Bay section in England. Based on these results, the ETE began synchronously in marine and terrestrial environments slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco, a CO2 super greenhouse, and marine biocalcification crisis. Because the temporal relationship between CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same place, this is the strongest case for a volcanic cause of a mass extinction to date.