Mercury new culprit in end-Permian event?

In a new paper in Geology Sanei et al. (abstract) address the potential impact of mercury loading from the Siberian Traps during the end-Permian event. Mercury is one of the most toxic elements on our planet, and one that cause much concern from an environmental perspective seing as it is very persistent and has long-ranging impact on biota.

Coupling new mercury data with their previously published carbon-isotope and coal-fly-ash events in the Permian-Triassic boundary succession of the Sverdrup Basin (Grasby et al., 2011) they propose that suppressed organic productivity due to deteriorating environmental conditions in the basin lead to catastrophic build-up of dissolved mercury in the sea.

The excess dissolved mercury could not be removed until conditions turned extreme euxinic and sulfide-mercury drawdown commenced.

It will be interesting to see if mercury-toxicity events are associated with other major volcanic events in Earth’s history!  

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.

Extraterrestrial impact helped cause the end-Triassic mass extinction?

In a news feature in the latest issue of Nature a team of geologists lead by Paul Olsen and Dennis Kent are in search for evidence that connect the end-Triassic mass extinction with the Rochechouart impact crater in France, which recently was dated to 201.2 ± 2.0 million years ago (Schmieder et al., 2010). Triassic-Jurassic boundary rocks in the UK are known to contain disturbed sediments close to the level of extinction, and Simms (2003) suggested that these “seismites” were in fact impact related.

The Rochechouart is a farly small impact crater, measuring only 20-25 km in diameter compared to the 180 km width of the Chixculub impact crater of the Cretaceous/Paleogene event.

Could the Rochechouart impact have helped cause the end-Triassic mass extinction event?

Well, Olsen makes sure all angles are covered:

“Perhaps it was one of a series of asteroids that hit around the same time. Alternatively, a lone French crash might have been the final straw for a world already reeling from volcanic eruptions. Or the impact may have come first, weakening ecosystems enough that when the eruptions started, life took a nosedive.”

 

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…
 
  

Hot topics within Earth and Planetary sciences (June 2011)

Every third month Science direct lists the twentyfive hottest articles within a specific field of research. The list is based on number of downloads for each article. Unfortunately there is a lagtime between the download count over a three month period and the time the list is published, e.g the Hot topics list today (12/11 2011) still displays the most downloaded papers during March to June 2011. But still, it is a good indicator if one wants to find out where the research focus was a few months ago 🙂

Based on the Science Direct list for March to June 2011 I have compiled the three hottest topics within Earth and Planetary sciences, and these are:

  1. Ecology/Paleoecology 10/25
  2. Climate/global change 8/25
  3. Water treatment/resources 3/25

This definitely tells us that there is a high demand on research concerning the ecological impact of climate and global change, whether it concerns changes that are going on today or in the past. It also indicates that there is a lot of focus on our freshwater resources and their quality.

Important issues to consider for us all.

Chalk: The white cliffs of Møn…

The Danish island Møn provides a beautiful scenic coastal landscape with green and lush forests on top of high white cliffs of chalk, with pebbly shores and the blue Baltic Sea beneath. It is also a great excursion locality if you want to study Cretaceous to Paleogene chalk, or natural erosive processes along coastal cliffs such as slumping or mudflows.

To get to the shore you have to descend down a path, partly as stairs with multiple steps.

Descending through the lush forest...

 The beach is covered with flintstone pebbles in various grey colors and sizes. Numerous trees have fallen down the slopes and their trunks are weathered white from the sea.

Dead tree on flint pebbles...

 
The cliffs are 140 meters high at the highest point. Screes are common and sometimes the shore is closed due to risk of landslides.
 

The cliffs of Møn on a slightly foggy day...

 
The chalk consists of billions of fragments of calcareous nannoplankton, coccolithophorids, that thrived in the warm Cretaceous Sea along with sharks, mosasaurs, fishes, ammonites and lots of other organisms.
 
 
I highly recommend a visit to Møn and to Geocenter Møns Klint – a wonderful exhibition centre presenting the geology of Denmark with specific focus on the chalk, and the environment and wildlife of Møn.
 
Visit their website for more information here.
 
 

End-Permian mass extinction: No problem for Parareptiles?

The end-Permian mass extinction event 250 million years ago was probably the most severe crisis in Earth history. Estimates suggest that more than 95% of life on Earth perished during this event. Marine life was hit hard. Besides the extinction of the trilobites and the tabulate and rugose corals, many other marine groups suffered near extinction including brachiopods, gastropods, cephalopods and crinoids. On land, the glossopterids, the dominant plant group in Gondwana (the southern Hemisphere) perished, and major floral changes occurred on a global scale. More than 70% of land-living vertebrate species died out.

But one group of land-living vertebrates appear almost unaffected by the end-Permian crisis, namely the parareptiles, an extinct group of reptiles, consisting of small to large tetrapods.

In a new paper in Palaeontology (read the abstract here) a group of researchers headed by Marcello Ruta recently presented various statistical analyses on diversity patterns of the Parareptilia. Their conclusion is that extinction rates for the parareptiles during the end-Permian event were no higher than before or after. However, only one clade of parareptiles crossed the Permian-Triassic boundary, and this accounted for all the Triassic parareptiles. So basically, all the other clades of parareptiles actually did die out prior to or during the end-Permian event, but as a group the parareptiles were hardly affected. It is not clear why this particular clade within the parareptiles was not affected by the end-Permian event when so many other terrestrial vertebrates were. 

The parareptiles finally did go extinct – In the Rhaetian…