Triassic–Jurassic Mass Extinction as Trigger for the Mesozoic Radiation of Crocodylomorphs

A new study that contrasts that of Brusatte et al. (2008), who had found a significant dropoff in pseudosuchian disparity through the end Triassic extinction.

Toljagić, O., and R. J. Butler. 2013 Triassic–Jurassic mass extinction as trigger for the Mesozoic radiation of crocodylomorphs. Biology Letters 9: 20130095. http://dx.doi.org/10.1098/rsbl.2013.0095

Abstract - Pseudosuchia, one of the two main clades of Archosauria (Reptilia: Diapsida), suffered a major decline in lineage diversity during the Triassic–Jurassic (TJ) mass extinction (approx. 201 Ma). Crocodylomorpha, including living crocodilians and their extinct relatives, is the only group of pseudosuchians that survived into the Jurassic.We reassess changes in pseudosuchian morphological diversity (disparity) across this time interval, using considerably larger sample sizes than in previous analyses. Our results show that metrics of pseudosuchian disparity did not change significantly across the TJ boundary, contrasting with previous work suggesting low pseudosuchian disparity in the Early Jurassic following the TJ mass extinction. However, a significant shift in morphospace occupation between Late Triassic and Early Jurassic taxa is recognized, suggesting that the TJ extinction of many pseudosuchian lineages was followed by a major and geologically rapid adaptive radiation of crocodylomorphs. This marks the onset of the spectacularly successful evolutionary history of crocodylomorphs in Jurassic and Cretaceous ecosystems.

Vegetation History and Climate Change Across the Tr/J Boundary

Bonis, N. R., and W. M. Kürschner. 2012. Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary. Paleobiology 38:240-264. doi: http://dx.doi.org/10.1666/09071.1

Abstract - 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.

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.

TR-J Carbon Isotope Excursions Caused by Global Disturbance and not by Vegetation Change

Bacon, K. L., Belcher, C. M., Hesselbo, S. P., and J. C. McElwain. 2011. The Triassic–Jurassic boundary carbon-isotope excursions expressed in taxonomically identified leaf cuticles. Palaios 26:461-469. http://www.bioone.org/doi/abs/10.2110/palo.2010.p10-120r

Abstract - A negative stable carbon-isotope excursion (CIE) has been identified at sites across the globe in strata that span the Triassic–Jurassic boundary. Different studies have suggested that this negative CIE could be the result of either a change in vegetation or a massive perturbation in the global carbon cycle at this time. To determine which, 84 hand-picked leaf cuticle fragments from plant macrofossils previously identified to genus level were analyzed for stable carbon-isotope values. The samples were taken from known heights in nine plant beds spanning the Rhaetian–Hettangian (Upper Triassic–Lower Jurassic) at Astartekløft, East Greenland. We have constructed taxon-specific stable carbon-isotope curves for Ginkgoales and Bennettitales and compared these to an existing δ¹³C curve based on fossil wood from the same section. This study reveals that taxon-specific carbon-isotope curves based on the leaf data from these two seed-plant groups both record the same negative CIE as the fossil wood, despite having different ecological roles and different relative abundances in the section. Correspondence analysis of the macrofossil abundance data, where the plants are considered in their ecological groups, shows that the δ¹³C values bear no relationship to changes in vegetation. This result further suggests that vegetation change had little role in determining the δ¹³C values at this time. Considered together, the bulk cuticle and taxon-specific δ¹³C record indicate that the negative CIE at the Triassic–Jurassic boundary is likely to have been caused by a massive perturbation of the global carbon cycle and not by vegetation change.

Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction

http://news.sciencemag.org/sciencenow/2011/07/did-greenhouse-gasses-unleash-th.html?ref=hp

Ruhl, M., Bonis, M. R., Reichart, G-.R., Sinninghe Damste, J. S., and W. M. Kürschner. 2011. Atmospheric Carbon Injection Linked to End-Triassic Mass Extinction. Science 333:430-434. DOI:10.1126/science.1204255.

Abstract - The end-Triassic mass extinction (~201.4 million years ago), marked by terrestrial ecosystem turnover and up to ~50% loss in marine biodiversity, has been attributed to intensified volcanic activity during the break-up of Pangaea. Here, we present compound-specific carbon-isotope data of long-chain n-alkanes derived from waxes of land plants, showing a ~8.5 per mil negative excursion, coincident with the extinction interval. These data indicate strong carbon-13 depletion of the end-Triassic atmosphere, within only 10,000 to 20,000 years. The magnitude and rate of this carbon-cycle disruption can be explained by the injection of at least ~12 × 103 gigatons of isotopically depleted carbon as methane into the atmosphere. Concurrent vegetation changes reflect strong warming and an enhanced hydrological cycle. Hence, end-Triassic events are robustly linked to methane-derived massive carbon release and associated climate change.

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.

Revised Biostratigraphy-based Correlations for Determining the Position of the TR/J Boundary on the Colorado Plateau

This is an online published corrected proof utilizing paleomagnetic and biostratigraphic data to attempt to precisely locate the Triassic/Jurassic boundary in terrestrial strata of the Colorado Plateau in the Western U.S.  It provides corrections based on conchostracan biostratigraphy for previous proposed correlations to other global magnetostrat sections presented in a paper just published by many of the same authors this last October. Unfortunately, because of a lack of isotopic dates to calibrate the magnetostrat sections and the limitations of biostratigraphy for such correlations (e.g., Irmis et al., 2010; Olsen et al., in press), it is not yet clear how reliable these corrections are.

One interesting conclusion of this paper is that pseudosuchian extinctions and the first appearance of large theropod dinosaurs (represented by the ichnotaxon Eubrontes) may have occurred within the Late Triassic and not at or even near the Triassic-Jurassic boundary. Of course this observation is simply a result of moving the TR/J boundary upwards in terrestrial strata.

Lucas, S.G., Tanner, L.H., Donohoo-Hurley, L.L., Geissman, J.W., Kozur, H.W., Heckert, A.B., Weems, R.E.in press. Position of the Triassic-Jurassic boundary and timing of the end-Triassic extinctions on land: Data from the Moenave Formation on the southern Colorado Plateau, USA, Palaeogeography, Palaeoclimatology, Palaeoecology (2011). doi: 10.1016/j.palaeo.2011.01.009

Abstract - Strata of the Moenave Formation on and adjacent to the southern Colorado Plateau in Utah–Arizona, U.S.A., represent one of the best known and most stratigraphically continuous, complete and fossiliferous terrestrial sections across the Triassic–Jurassic boundary. We present a synthesis of new biostratigraphic and magnetostratigraphic data collected from across the Moenave Formation outcrop belt, which extends from the St. George area in southwestern Utah to the Tuba City area in northern Arizona. These data include palynomorphs, conchostracans and vertebrate fossils (including footprints) and a composite polarity record based on four overlapping magnetostratigraphic sections. Placement of the Triassic–Jurassic boundary in strata of the Moenave Formation has long been imprecise and debatable, but these new data (especially the conchostracans) allow us to place the Triassic–Jurassic boundary relatively precisely in the middle part of the Whitmore Point Member of the Moenave Formation, stratigraphically well above the highest occurrence of crurotarsan body fossils or footprints. Correlation to marine sections based on this placement indicates that major terrestrial vertebrate extinctions preceded marine extinctions across the Triassic–Jurassic boundary and therefore were likely unrelated to the Central Atlantic Magmatic Province (CAMP) volcanism.

REFERENCES

Donohoo-Hurley, L. L., Geissman, J. W., and S. G. Lucas. 2010. Magnetostratigraphy of the uppermost Triassic and lowermost Jurassic Moenave Formation, western United States: Correlation with strata in the United Kingdom, Morocco, Turkey, Italy, and eastern United States. Geological Society of America Bulletin 122: 2005-2019; doi: 10.1130/B30136.1

Irmis, R. B., Martz, J. W., Parker, W. G., and S. J. Nesbitt. 2010. Re-evaluating the correlation between Late Triassic terrestrial vertebrate biostratigraphy and the GSSP-defined marine stages. Albertiana 38:40-52.

Olsen, P. E., Kent, D. V., and J. H. Whiteside. In Press. Implications of the Newark Supergroup-based astrochronology and geomagnetic polarity time scale (Newark-APTS) for the tempo and mode of the early diversification of the Dinosauria. Environmental and Earth Science Transactions of the Royal Society of Edinburgh.

Free Access to the Journal Palaeobiodiversity and Palaeoenvironments in November 2010

For the month of November, Springer is offering open access to articles in the journal Palaeobiodiversity and Palaeoenvironments.  Recent artiles in this journal include the special issue on the "Triassic-Jurassic biodiversity, ecosystems, and climate in the Junggar Basin, Xinjiang, Northwest China".

http://www.springer.com/earth+sciences+and+geography/journal/12549

Two New Papers on the Triassic/Jurassic Boundary

Kent, D. V., and E. Irving. 2010. Influence of inclination error in sedimentary rocks on the Triassic and Jurassic apparent pole wander path for North America and implications for Cordilleran tectonics. Journal Of Geophysical Research 115: B10103, doi:10.1029/2009JB007205



Abstract - Because of paleomagnetic inclination error (I error) in sedimentary rocks, we argue that previous estimates of Triassic and Jurassic paleolatitudes of the North American craton have generally been too low, the record being derived mostly from sedimentary rocks. Using results from all major cratons, we construct a new composite apparent pole wander (APW) path for Triassic through Paleogene based on 69 paleopoles ranging in age from 243 to 43 Ma. The poles are from igneous rocks and certain sedimentary formations corrected for I error brought into North American coordinates using plate tectonic reconstructions. Key features of the new APW path are a 25° northward progression from 230 to 190 Ma to high latitudes (off northernmost Siberia) where the pole lingers until 160 Ma, a jump to the Aleutians followed by a hook in western Alaska by ∼145 Ma that leads to the 130–60 Ma stillstand, after which the pole moves to its present position. As an example of the application of this new path we use paleomagnetic results to determine that southern Wrangellia and Stikinia (W/S), the two most westerly terranes in the Canadian Cordillera, lay 630 to 1650 km farther south than at present relative to the craton during the Late Triassic and Early Jurassic. This is consistent with an exotic Tethyan origin as paleontological and mantle geochemical evidences imply. During the Late Triassic through Early Cretaceous, W/S moved northward more slowly than the craton, implying oblique sinistral net convergence over this 130 Myr interval. This was followed by dextral shear in latest Cretaceous through Eocene.


Donohoo-Hurley, L. L., Geissman, J. W., and S. G. Lucas. 2010. Magnetostratigraphy of the uppermost Triassic and lowermost Jurassic Moenave Formation, western United States: Correlation with strata in the United Kingdom, Morocco, Turkey, Italy, and eastern United States. Geological Society of America Bulletin 122: 2005-2019; doi: 10.1130/B30136.1


Abstract - A composite magnetostratigraphy based on the magnetic polarity data from four sections of the uppermost Triassic and lowermost Jurassic Moenave Formation, Utah and Arizona, USA, can be correlated to the marine successions at Saint Audrie’s Bay (UK), Oyuklu, Turkey, and the Southern Alps, Italy, and to the nonmarine sections in Morocco, northern Africa, and the Newark Basin, eastern North America, all deposited across the Triassic–Jurassic boundary. Our proposed correlation provides a stratigraphic framework to tie Triassic–Jurassic sedimentation in the American Southwest to the marine UK, Turkey, and Italy sections, and to the Pangea rift history, including extrusive igneous rocks, preserved in Morocco and in the Newark Basin. The Moenave polarity record is characterized by mostly normal polarity, as is consistent with other polarity records across the Triassic–Jurassic boundary, and is interrupted by at least two well-defined reverse-polarity magnetozones. On the basis of available paleontologic information, we interpret the oldest well defined, reverse-polarity magnetozone, M2r of the Moenave Formation, to correlate with SA5n.2r or SA5n.3r of the Saint Audrie’s Bay record, H– of the Oyuklu record, BIT5n.1r of the Italcementi Quarry record, the oldest reverse magnetozone in sedimentary rocks in Morocco, and with reverse magnetozone E23r of the Newark Basin. The youngest reverse magnetozone of the Moenave Formation, M3r, is correlated to the latest Triassic magnetozones SA5n.5r of the Saint Audrie’s Bay record, J– of the Oyuklu record, and with the interval of reverse polarity in the “intermediate unit” of the Morocco record. Magnetostratigraphic correlations and marine biostratigraphic information support placement of the Triassic–Jurassic boundary in the middle to upper Whitmore Point Member of the Moenave Formation, the Lias Group of the Saint Audrie’s Bay section, the chert-rich limestone of the Oyuklu section, above the Zu Limestone in Italy, and in the central Atlantic magmatic province extrusive zone in the Morocco and the Newark records.

Jurassic Phytosaur??

A new paper by Maisch and Kapitzke (2010) describes a mandibular fragment from a phytosaur from marine shales in England. This is supposedly the first record of a phytosaur from the Jurassic (Hettangian) as the specimen was found in-situ beneath beds that provide the lowest occurrence of the ammonoid Psiloceras. Thus some phytosaurs, in this case a marine one from Europe, purportedly survived the end-Triassic extinction.

However, as Randall Irmis (who also informed me of this paper) reminded me, this is non-sensical regarding this specimen as the base of the Jurassic is presently defined by the first appearance of Psiloceras. Thus the phytosaur bearing strata are latest Triassic in age and not Jurassic.

I'm not adverse to the possibility that some basal pseudosuchians such as phytosaurs, aetosaurs, and rauisuchians may have survived into the Triassic, especially given our poor control on the determination of the Triassic-Jurassic boundary in non-marine strata.  Obviously crocodylomorphs make it through and we have no evidence for an abrupt global-wide non-marine extinction event for other pseudosuchians. 

The specimen mentioned by Maisch and Kapitzke appears to currently hold the title of the "last phytosaur", but unfortunately it does not provide clear evidence for the survival of this clade past the end-Triassic.

Maisch, M. W. & Kapitzke, M. 2010. A presumably marine phytosaur (Reptilia: Archosauria) from the pre-planorbis beds (Hettangian) of England. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 257: 373–379.

Abstract: A mandibular fragment of a longirostrine archosaur is decribed from the lowermost Jurassic (pre-planorbis beds, lowermost Hettangian) of Watchet, Somerset, England. The specimen is compared to both marine crocodilians (Thalattosuchia) and phytosaurs, groups which are either unknown (Thalattosuchia) or only doubtfully represented (Phytosauria) in lowermost Jurassic strata so far. The specimen shows striking morphological similarity to the Late Triassic phytosaur Mystriosuchus, but differs from known teleosaurid and metriorhynchid thalattosuchians. It is consequently
determined as aff. Mystriosuchus. It supports previous assumptions that phytosaurs crossed the Triassic-Jurassic boundary, at least in Europe. It also provides additional evidence that at least some phytosaurs, particularly the longirostrine forms, may have been facultative marine animals. The persistence of amphibious, piscivorous, longirostrine phytosaurs in the earliest Jurassic of Europe may have hampered the distribution of the ecologically similar teleosaurids, which are not known from strata that are older than the latest Sinemurian to date.

...and one more from the End-Triassic Event.

Mander, L., Kuerschner, W. M., and J. C. McElwain. 2010. An explanation for conflicting records of Triassic–Jurassic plant diversity. PNAS Early Edition, www.pnas.org/cgi/doi/10.1073/pnas.1004207107. Suppl.files at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1004207107/-/DCSupplemental.

Abstract - Macrofossils (mostly leaves) and sporomorphs (pollen and spores) preserve conflicting records of plant biodiversity during the end-Permian (P-Tr), Triassic–Jurassic (Tr-J), and end-Cretaceous (K-T) mass extinctions. Estimates of diversity loss based on macrofossils are typically much higher than estimates of diversity loss based on sporomorphs. Macrofossils from the Tr-J of East Greenland indicate that standing species richness declined by as much as 85% in the Late Triassic, whereas sporomorph records from the same region, and from elsewhere in Europe, reveal little evidence of such catastrophic diversity loss. To understand this major discrepancy, we have used a new high-resolution dataset of sporomorph assemblages from Astartekløft, East Greenland, to directly compare the macrofossil and sporomorph records of Tr-J plant biodiversity. Our results show that sporomorph assemblages from the Tr-J boundary interval are 10–12% less taxonomically diverse than sporomorph assemblages from the Late Triassic, and that vegetation composition changed rapidly in the boundary interval as a result of emigration and/or extirpation of taxa rather than immigration and/or origination of taxa. An analysis of the representation of different plant groups in the macrofossil and sporomorph records at Astartekløft reveals that reproductively specialized plants, including cycads, bennettites and the seed-fern Lepidopteris are almost absent from the sporomorph record. These results provide a means of reconciling the macrofossil and sporomorph records of Tr-J vegetation change, and may help to understand vegetation change during the P-Tr and K-T mass extinctions and around the Paleocene– Eocene Thermal Maximum.

The End-Triassic Extinction Event is Really Popular Right Now....

here is another new paper...

Paris, G., V. Beaumont, A. Bartolini, M.-E. Clémence, S. Gardin, and K. Page. 2010. Nitrogen isotope record of a perturbed paleoecosystem in the aftermath of the end-Triassic crisis, Doniford section, SW England, Geochemistry, Geophysics, Geosystems 11, Q08021, doi:10.1029/2010GC003161.

Abstract - The Triassic-Jurassic transition (TJ) is characterized by successive perturbations of the carbon cycle during a time of biotic disruption as recorded by the carbon isotopic composition of organic matter (δ13Corg). The nitrogen isotopic composition of sedimentary organic matter (δ15Norg) constitutes a key parameter to explore the functioning of the ecosystem during carbon cycle perturbations and biological crises, because it provide information on seawater redox conditions and/or nutrient cycling. Here we report the first continuous δ15Norg record across the TJ transition at the Doniford Bay section (Bristol Channel Basin, UK), combined with δ13Corg, kerogen typology and carbon (δ13Cmin) and oxygen (δ18Omin) isotopic composition of bulk carbonates. The end Triassic is characterized by a major negative excursion both in δ13Corg and δ13Cmin, very low TOC (Total Organic Carbon, wt%) and high δ15Norg values, associated with a sea level lowstand. A second δ13Corg negative excursion occurs during the lower Hettangian. This interval is characterized by phases of carbonate production increase alternated with phases of exceptional accumulations of type I organic matter (up to 12%) associated with lower δ15Norg and δ13Corg. This alternation likely reflects a succession of nutrient input increase to the basin leading to enhanced productivity and eutrophication, which promoted a primary production driven by organic-walled prokaryotic organisms. The following OM export increase generates anaerobic conditions within the basin. These events occur between periods of relatively good seawater column ventilation and nutrient recycling boosting the carbonate producer recovery. Ecosystems remain perturbed in the Bristol Channel Basin during the aftermath of the end-Triassic crisis.

No Single Unambiguous Global End-Triassic Spore Spike

Bonis, N. R., Ruhl, M., and W. M. Kuerschner. 2010. Milankovitch-scale palynological turnover across the Triassic–Jurassic transition at St. Audrie’s Bay, SW UK. Journal of the Geological Society, London 167:877–888. doi: 10.1144/0016-76492009-141.

Abstract - A high-resolution palynological study of the Triassic–Jurassic boundary in the St. Audrie’s Bay section revealed a palynofloral transition interval with four pronounced spore peaks in the Lilstock Formation. Regular cyclic increases in palynomorph concentrations can be linked with periods of increased runoff, and correspond to the orbital eccentricity cycle. Spore peaks can be related to precession-induced variations in monsoon strength. An implication is that the initial carbon isotope excursion lasted for at least 20 ka. Emergence during deposition of the Cotham Member had an influence on one of the peaks, which is dominated by spore-producing pioneer plants (e.g. horsetails and liverworts). There is no compelling evidence of a global end-Triassic spore spike that, by analogy with the K–T boundary fern spike, could be related to a catastrophic mass extinction event. Climate change is a more plausible mechanism to explain the increased amount of spores.

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.

New Data on Rising Carbon Dioxide Levels Through the Triassic-Jurassic Transistion

Bonis, N. R., Van Konijnenburg-Van Cittert, J. H. A., and W. M. Kürschner. in press. Changing CO2 conditions during the end-Triassic inferred from stomatal frequency analysis on Lepidopteris ottonis (Goeppert) Schimper and Ginkgoites taeniatus (Braun) Harris, Palaeogeography, Palaeoclimatology, Palaeoecology (2010), doi:10.1016/j.palaeo.2010.05.034

End-Triassic fluctuations in atmospheric carbon dioxide (CO2) concentration were reconstructed by the use of stomatal frequency analysis on a single plant species: the seedfern Lepidopteris ottonis (Goeppert) Schimper. Stomatal index showed no distinct intra- and interpinnule variation which makes it a suitable proxy for past relative CO2 changes. Records of decreasing stomatal index and density from the bottom to the top of the Rhaetian– Hettangian Wüstenwelsberg section (Bavaria, Germany) indicate rising CO2 levels during the Triassic–Jurassic transition. Additionally, stomatal frequency data of fossil ginkgoalean leaves (Ginkgoites taeniatus (Braun) Harris) suggest a maximum palaeoatmospheric CO2 concentration of 2750 ppmv for the latest Triassic.

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.

Two New Triassic Papers in Paleo3

The latest Triassic publication fest continues.

Marsicano, C.A., Mancuso, A.C., Palma, R.M., and Krapovickas, V. 2010. Tetrapod tracks in a marginal lacustrine setting (Middle Triassic, Argentina): taphonomy and significance. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.009.

ABSTRACT - Fossil tetrapod footprints not only provide valuable information about trackmaker paleobiology but also to give insight into details of the depositional conditions of the substrate at the time of imprinting. Therefore, in the present study the mode of formation and taphonomy of footprints in different substrates was used to investigate the gait and walking dynamics of the trackmakers as well as a source of additional information on the environmental conditions of the track-bearing beds during imprinting. The analyzed section corresponds to thick Middle Triassic lacustrine/deltaic deposits of the Ischichuca/Los Rastros Formation (Ischigualasto-Villa Unión Basin) that crops out at the Quebrada de Ischichuca in northwestern Argentina. Part of the track-bearing surfaces correspond to the top of sandy distributary channel mouth bars in a distal delta front setting that were exposed along the lake margin during a lake level fall. Cross-cutting relationships observed among ripple-marks, the footprints, and invertebrate traces of a softground suite of the Scoyenia ichnofacies suggest an omission surface. Measured trackway orientations in the sandstones are perpendicular to the paleo-shoreline, with the animals coming and going along the exposed top of the bars, probably for drinking. Laterally, the distal delta front deposits interfinger with track-bearing wackestone beds of palustrine origin deposited in a restricted local embayment lateral to the delta influenced environment. Trackway orientations in the wackestones are, in contrast, consistent with the animals moving nearly parallel to the lake border, probably along a preferred route. Evidences of a relative high groundwater table at the time of imprinting in the track-bearing surfaces are revealed by the well developed rims of extruded sediment and collapsed digits in the studied tracks and the nearly absence of associated desiccation cracks on the same surfaces. Nevertheless, temporary emergence cannot be ruled out when paleosoil formation was probably promoted as can be observed in the microstructure of both sandstones and wackestones. Moreover, footprint preservation in the wackestones might have been enhanced by partial hardening of the trampled surface during subaerial exposure. Combining ichnofossil content and taphonomy with facies analysis we identified in the lower part of the Ischichuca/Los Rastros succession a relatively rapid withdrawal of the water basinward that was probably due to a forced regression during early rifting of basin evolution. Footprints can also provide valuable information about locomotion dynamics and trackmaker behavior. Thus, the sideways deformation observed in the studied footprints, attributed to basal archosaurs and putative basal dinosaurs, can be related to an outward rotation of the foot during the step cycle, a condition that might allied to the development of the parasagittal posture in Archosauria. Besides, the densely trampled surface described herein constitutes the first documented evidence of putative social behavior among therapsid dicynodonts, the most important group of herviborous animals in the early Mesozoic terrestrial ecosystems throughout Gondwana.


Preto, N., Kustatscher, E., and Wignall, P.B. 2010. Triassic climates -- state of the art and perspectives. Palaeogeography, Palaeoclimatology, Palaeoecology. doi: 10.1016/j.palaeo.2010.03.015.

ABSTRACT - The climate of the Triassic period was characterized by a non-zonal pattern, dictated by a strong global monsoon system with effects that are most evident in the Tethys realm. This strong monsoonal regime is related to the aggregation of the Pangaean supercontinent, which by Triassic time was already completed. Climate oscillations existed within this framework. The harsh hothouse climatic conditions that characterized the Late Permian, and perhaps precipitated the end-Permian mass extinction, were probably maintained during the Early Triassic and may account for the impoverished, but distinctive, faunal and floral Lower Triassic associations. Although metazoan reef builders were probably the most
affected group, carbonate production remained high at least in the western Tethys realm. The Middle Triassic was characterised locally by humid episodes, although their geographical distribution has yet to be clarified. The Carnian Pluvial Event, marks an episode of increased rainfall documented worldwide, was the most distinctive climate change within the Triassic. Different hypotheses have been proposed for its causes: changes of atmospheric or ocean circulation driven by plate tectonics; a peak of the global monsoon due to maximum continent aggregation; or triggering by the eruption of a large igneous province. Subsequently, the late Carnian and Norian seem to have been climatically stable, although minor climatic changes have recently been described even from this time period. Finally, the end Triassic extinction event is also associated with climate change, specifically warming and increased rainfall, but this evidence comes mostly from the northern parts of the Central Atlantic Magmatic Province, and the global pattern of climate change at the Triassic / Jurassic boundary has still to be resolved. Many facets of Triassic climate are intriguing and deserve further research. However, paleoclimate studies on the Triassic have so far been carried out only locally with different proxies. Those proxies will require inter-calibration, in order to depict correctly the temporal and geographical patterns of Triassic climate.

Sedimentary Organic Matter Characterization of the Triassic–Jurassic Boundary

Ruhl, M., Veld, H., and W.M. Kürschner. 2010. Sedimentary organic matter characterization of the Triassic–Jurassic boundary GSSP at Kuhjoch (Austria). Earth and Planetary Science Letters 292:17–26. doi:10.1016/j.epsl.2009.12.046


Abstract - The Triassic–Jurassic (T–J) boundary interval coincides with enhanced extinction rates in the marine realm and pronounced changes in terrestrial ecosystems on the continents. It is further marked by distinct negative excursions in the δ13Corg and 13Ccarb signature that may represent strong perturbations of the global carbon cycle. We present integrated geochemical, stable-isotope and palynological data from the Kuhjoch section, the Global boundary Stratotype Section and Point (GSSP) for the base of the Jurassic (Northern Calcareous Alps, Austria). We show that the initial carbon isotope excursion (CIE), coinciding with the marine extinction interval and the formation of black shales in the western Tethys Eiberg Basin, is marked by only minor changes in kerogen type, which is mainly of terrestrial origin. Increased Total Organic Carbon (TOC) concentrations of 9% at the first half of the initial CIE coincide with Hydrogen Index (HI) values of over 600 mg HC/g TOC. The high correlation (with R2=0.93) between HI values and terrestrial Cheirolepidiaceaen conifer pollen suggests a terrestrial source for the hydrogen enriched organic compounds. The lack of major changes in source of the sedimentary organic matter suggests that changes in the δ13Corg composition are genuine and represent true disturbances of the global C-cycle. The sudden decrease in total inorganic carbon (TIC) concentrations likely represents the onset of a biocalcification crisis. It coincides with a 4.5‰ negative shift in δ13Corg values and possibly corresponds to the onset of CAMP related volcanic activity. The second half of the initial CIE is marked by the dramatic increase of green algae remains in the sediment. The simultaneous increase of the Corg/Ntot ratio suggests increased marine primary production at the final stage of black shale formation.

Investigating the Non-Marine TR/J Boundary in Portugal

Dr. Richard Butler (Bayerische Staatssammlung für Paläontologie und Geologie, Munich), Dr. Octavio Mateus (University of Lisbon) and Steven Brusatte (American Museum of Natural History) have initiated a new field project to study terrestrial strata (Grès de Silves Formation) spanning the Triassic-Jurassic boundary in Portugal in hopes of recovering late surviving temnospondyls and possibly other Late Triassic vertebrates. Preliminary results are encouraging and you can read about them here.


Given that many Late Triassic Laurasian faunal assemblages appear very similar in content despite their stratigraphic position (e.g., Placerias Quarry vs. Coelophysis Quarry in the Chinle Formation), these types of studies are crucial to our understanding of exactly what is happening with the Triassic-Jurassic non-marine extinctions. Unfortunately many places that preserve this boundary and are accessible are non-fossiliferous (e.g., Newark Supergroup); whereas other places that may be very fossiliferous (e.g., Moenave and Kayenta Formations of Arizona) are not easily accessible.