This spring an entire issue of the Danish Geoscience journal Geoviden was dedicated to our research project “The Triassic–Jurassic boundary: Impact of a Large Igneous Province on the geobiosphere”. Geoviden is a popular science magazine aimed at high school students and everyone else interested in geology and geography. Our issue is called “A crisis in the history of life” and presents the background, hypothesis and progress of our Geocenter Denmark financed project. Unfortunately for non-Scandinavian readers it is in Danish. It is richly illustrated and covers various aspects of our research. It can be downloaded for free using this link, so feel free to check it out: Geoviden No 1 2016: “En krise i livets historie”
The Sose Bay area on the Danish island of Bornholm is a beautiful place. Here, the lush greens of the partly forested coastline with its white sandy beaches meets the Baltic Sea, and at the horizon there is nothing but sky.
Early Jurassic rocks crop out along the coast; the sands and clays still soft after 200 million years, revealing a multitude of sedimentary structures when scraped free of their weathered surfaces.
The most continuous sedimentary succession in the coastal cliff is exposed east of Sose Odde. It comprises a c. 24 m thick section including restricted marine, eustarine, lacustrine and fluvial deposits, and was described in detail by Surlyk et al. (1995). The outcropping succession belongs to the Sose Bugt Member of the Rønne Formation, which was assigned a Hettangian–Sinemurian (Early Jurassic) age based on its fossil palynological (spores, pollen, microalgae) content. In 2014, Clemmensen et al. described the presence of steep-walled, flat- to concave-bottomed depressions, with a raised ridge at each side, that were interpreted as dinosaur tracks.
The dinosaur tracks are found in layers interpreted to have been deposited in small streams on a large coastal plain. Clemmensen et al. (2014) suggest that the dinosaurs may have preferred to use shallow channels as paths. The succession also contains thin coal seams and layers penetrated by numerous vertical roots, remnants of 200 million year old vegetation.
So these are the sediments that lie immediately beneath our feet when we walk the fields at Sose Bay, below a thin cover of Quaternary sediments. But what lies beneath? Would sediments deposited before, during and after the end-Triassic mass extinction be present?
In order to find out, we performed a core drilling in the Sose Bay area, with the aim to reach typical red and green coloured Late Triassic sediments – and hopefully Triassic–Jurassic boundary sediments.We drilled with a core drilling technique that sealed the sedimentary cores in plastic pipes.
By checking the bottom of each pipe when they were brought to the surface, it was possible to see when the red and green Triassic had been reached. At a depth of 110 m below ground, we reached red Triassic sediments.
But because the cores were sealed in red plastic pipes, we still had no idea how complete the drilled succession would be. All we could do was wait until the cores had been transported back to GEUS.
To be continued…
On Tuesday next week we launch our new core drilling project. This time we are going to drill through the lowermost Jurassic sedimentary succession at Sose Bugt on the Danish island of Bornholm, with the aim to reach uppermost Triassic rocks. Despite many excellent geological studies in the area it is not clear if the Triassic-Jurassic boundary is preserved on the Sose Fault block, but the presence of Hettangian-Sinemurian strata in the coastal cliffs at Sose Bugt and Upper Triassic green and red clays along parts of the coast make it an ideal area to drill for the TJB.
Our core drilling project is funded by Geocenter Denmark and is a part of our research project on the end-Triassic mass extinction event. The core drilling will provide us with new research material, hopefully both of the mass extinction interval and of the recovery in the earliest Jurassic.
Quite excited about this! 🙂
Me and my colleagues at the Geological Survey of Denmark and Greenland (GEUS), the Department og Geography and Geology (IGN) at Copenhagen University, and the Department of Earth Sciences (IG) at Århus University, have received a large strategic research grant from Geocenter Denmark to continue our research on the Triassic-Jurassic boundary. This three-year project will focus on the Danish Basin, where we are fortunate enough to have preserved not only a thick marginal marine to fully marine TJ-boundary succession in the subsurface of southern Sweden and Denmark, but also marginal marine to terrestrial strata outcropping in Scania (S Sweden) and on the Danish island Bornholm.
The new project is partly a continuation of our three-year (2010-2013) starting grant from Geocenter Denmark which also dealt with the TJ-boundary of the Danish Basin, the results of which were published in Lindström et al. 2012 in Geology and Petersen and Lindström 2012 in PlosOne, and participated to Richoz et al. 2012 in Nature Geoscience.
By joining forces, our team now incorporates sedimentology, palynology, micropalaeontology, isotope geochemistry, inorganic and organic geochemistry, organic petrography, magmatic petrography and diagenesis.
We are delighted to be able to continue our research on the TJ-boundary and the events leading up to, and succeeding the end-Triassic mass extinction.
On-going anthropogenic carbon emissions has reached levels 40% higher than pre-industrial ones in 1750, due to human burning of fossil fuels. Despite international discussions and various national efforts to decrease carbon emissions, the amount of heat-trapping carbon dioxide in the atmosphere reached a record 390.9 parts per million (ppm) in 2011, according to a report recently released by the UN’s World Meteorological Organization (WMO). As a result, 30% more atmospheric heat was kept from escaping to space than in 1990. The increased amounts of CO2 in the atmosphere has lead to a 1°C increase in average temperatures worldwide. This may not sound much, but with the long retention time of CO2 in the atmosphere the average temperature will continue to rise for a long time even if we should manage to limit our carbon emissions extensively. The World bank estimates an average temperature rise to as much as 4°C by 2060 unless we start reducing our carbon emissions significantly! The effects of such a dramatic global warming would mean serious threats to the human civilization, with extreme weather, heat waves and sea-level rise, but that is not all…
The geological record testifies to the effects of global warming. Numerous scientific articles dealing with the causes and consequences of the mass extinctions at the end-Permian (252 million years ago) and end-Triassic (201 million years ago) have provided evidence of the dire effects of intense global warming. Both events are linked to massive volcanism from large igneous provinces (LIPs) that emitted huge amounts of CO2 and methane to the Earth’s atmosphere. As discussed by Payne and Clapham (Annual Review of Earth and Planetary Sciences, May 2012) such mass extinction events in the geological record may serve as an important ancient analog for the twenty-first century! Climate change and increased temperatures, possibly coupled with destruction of the ozone layer, can account for the extinctions on land, whereas changes in ocean oxygen levels, CO2, ocean acidification, and temperature made life difficult for marine animals, resulting in the demise of as much as 96% and 80% of all species for the end-Permian and end-Triassic events, respectively.
Recent scientific reports provide warning signals. One of the most well documented consequences of the increased CO2-levels at the end-Permian and end-Triassic events is referred to as the biocalcification crisis. The increased CO2-levels caused upper ocean acidification due to lowering of the pH of surface waters, causing problems for calcareous organisms such as calcareous phytoplankton and reef-building organisms, e.g. bivalves and corals. Scientists have long discussed the on-going coral bleeching as one result of our anthropogenic carbon emissions, but now Bednarsek et al. (Nature Geoscience, advanced on-line publication 2012) report alarming evidence of dissolution of shells on living pteropods (shell-bearing free-swimming sea-snails) in the Southern Ocean, providing further warning signals of on-going ocean acidification.
In addition, Arneborg et al. (Nature Geoscience, advanced on-line publication 2012) show increased inflow of warm and salty bottom waters to the central Amundsen shelf in Antarctica where the thinning of glaciers have persisted over the last decades. The Amundsen shelf is part of the West Antarctic Ice Sheet that contains enough ice to raise global sea level by several metres and, because it is grounded mainly below sea level, it is extra sensitive to ocean warming.
These reports, among many others, should serve as serious warning signals to world leaders that we need to take immediate action to reduce carbon emissions. So far, we have not managed to act efficiently on reducing emissions. At the UN-sponsored climate meeting in Copenhagen in 2009 the relatively weak agreement was to a non-binding target of limiting the world’s greenhouse-gas-triggered temperature increase to no more than 2°C (3.6°F) above preindustrial levels to limit the potential damage. The 2011 numbers provided by the UN’s World Meteorological Organization (WMO) clearly show that we are failing to keep even that!
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.”