EGU2014 Thursday: “Volcanism, Impacts, Mass extinctions and Global environmental change” – a brief review of two talks.

Thursday afternoon at the EGU2014 was totally dedicated to the session “Volcanism, Impacts, Mass extinctions and Global environmental change” in which I also presented a talk. The session contained a total of eleven oral presentations covering various subject within the above mentioned topics. The first four talks were on the volcanism of the Siberian Traps and the end-Permian mass extinction event.

In the first talk, Seth Burgess presented new high-resolution geochronological data for the intrusives of the Siberian Traps. Burgess and his colleagues had used the same analysis and standards on not only zircons from the Siberian Traps, but also on zircons from the ash-layers bracketing the end-Permian mass extinction level at the GSSP Meishan in China. According to these new datings all the dated intrusives post-date the end-Triassic mass extinction event. Seth Burgess stated that although these data could be taken as “the nail in the coffin for the theory that the intrusive activity caused the mass extinction” he didn’t believe that they did. He then went on to explain that the majority of the intrusives of the Siberian Traps are situated at depths and those that have been dated are the ones that are accessible, probably producing a biased record.

This was good news for the second speaker, Henrik Svensen, who presented a talk on the sill-induced evaporite and coal metamorphism of the Siberian Traps. Svensen and colleagues showed that the Siberian Traps contain very thick sills that have been emplaced into both coal-bearing sediments and salt deposits, with the potential for degassing of both green house gases (CH4, CO2), aerosols (SO2), and ozone destructive gases (CH3Cl, CH3Br), which could explain the end-Permian biotic crisis.

A fuzzy picture of Henrik Svensen and his audience.

 

Upcoming GTS 2012 presents major changes in the Triassic

Last week I participated in the FORCE meeting “Applications of biostratigraphy to the Norwegian Continental Shelf” in Stavanger, Norway. Besides many other interesting biostratigraphic talks, Felix Gradstein presented the upcoming 2012 edition of the Geologic Time Scale (GTS) (FORCE meeting abstracts, Gradstein et al., page 6).

Compared to the last GTS2004 there will be some remarkable changes, especially concerning the Triassic, where the ages of four Middle to Upper Triassic stages have changed between 6 and 12 million years.

The new GTS2012 will be published by Elsevier in mid 2012.

End-Permian extinction interval lasted <200.000 years

Super-interesting news from Science express (abstract):

High-precision U-Pb daiting of several well preserved Permian-Triassic boundary sections in South China, by Shu-zhong Shen and colleagues, show that after a 2‰ in δ¹³C over 90.000 years the extinction peak occurred just before 252.28 ± 0,08 Ma. It coincided with a -5‰ δ¹³C excursion that is estimated to have lasted up to 20.000 years. According to this study the extinctions in the terrestrial and marine realms were synchronous, and the most probable cause was massive release of thermogenic carbon dioxide and/or methane. Contemporaneous charcoal and soot-bearing layers provide evidence of widespread wildfires on land.

The entire extinction interval was according to Shen et al. less than 200.000 years, by far the shortest duration calculated for the end-Permian event so far.

Upper Triassic detrital zircon datings support diachronous rise of Dinosaurs

Red beds are common in Upper Triassic terrestrial sedimentary successions worldwide. Having formed in semi-arid to arid environments, these rocks are generally sparse in fossils. This is perhaps mainly because the preservation potential for fossils in such environments is poor, and not necessarily because there were no plants and animals at the time of deposition. 

The Upper Triassic Kågeröd Formation at Bälteberga Gorge, Scania. (Photo: M. Erlström)

On the Colorado Plateau in southwestern U.S.A. the Upper Triassic red bed succession of the Chinle Formation, deposited by river systems and small lakes under an arid climatic regime, contains well preserved fossil plants and vertebrate remains; archeosaurs, dinosaurs as well as the precursors of dinosaurs, the dinosauromorphs (see e.g. Irmis et al., 2007; Nesbitt et al., 2009). However, relative datings of these fossil floras and faunas have been hampered by the fact that they occur within an otherwise relatively fossil-poor terrestrial succession. They have traditionally been assigned a Carnian to early Norian age, based on fossil spores and pollen (Litwin et al., 1991).

 

A detrital zircon from the Upper Triassic of Scania (Photo: S. Lindström)

 

But now Randall Irmis and his colleagues (read the abstract here) present two new radioisotopic datings on detrital zircons that indicates that the Chinle Formation is younger than previously thought, namely between ~218 and ~212 million years old (maximum ages), i.e. mostly or wholly Norian in age.

 

This means that the early dinosaurs of North America are younger than their famous South American counterparts from the Ischigualasto Formation in northwestern Argentina.

 

This suggests that dinosaurs evolved diachronously on either side of the Equator…