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…
During Saturday core drilling at Sose bugt continued slowly. Because the sedimentary succession is fairly unconsolidated we are drilling with a technique that encase the cored sediments in 1,5 m long pipes. This means that it is only possible to investigate the cored sediments at the top or bottom of each core section. Typical Early Jurassic whitish sands and grey clays had been cored during the first three days of drilling. On Saturday we were closing in on two prominent seismic horizons, one which we suspected could be the top of the Triassic redbeds. At 91 m there were still grey clays but also coal. But at 95 m the top of the core showed dark grey clays, while the bottom consisted of light green sand and clay typical for the Upper but not the uppermost Triassic. We had finally reached the Triassic! 🙂
Drilling will continue for a few more hours tomorrow until the geophysical logging equipment arrives. We are all very excited and can’t wait to get the cores back to GEUS so that we can study them. Almost 95 m of Lower Jurassic and hopefully also uppermost Triassic (Rhaetian) near coastal sedimentary strata which we think will provide us with additional information on the end-Triassic mass extinction and the biotic recovery that followed.
Our core drilling through the Triassic-Jurassic boundary at Sose Bugt on Bornholm is progressing faster than expected. The drilling commenced Wednesday and we have already reached a depth of 64 m. Just like the outcrop succession along the beach, the deposits that mainly consist of sand, heteroliths and clay are faurly unconsolidated. The biggest challenges so far have been a siderite and a loose sand layer. None of these two were successfully cored.
Our on-site technician is providing updates for us and we are ready to take the next ferry to Bornholm as soon as we get close to our target depth. With the current drilling speed this may happen sooner than expected 🙂
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! 🙂
This year I am attending the European Geisciences Union General Assembly or for short the EGU2014 meeting in Vienna, Austria, 27 April – 2 May. The EGU meetings are BIG! Geoscientists everywhere! More than 600 sessions, workshops and short courses. A multitude of geotopics with something for everyone.
I arrived yesterday, so I have only attended half a session so far, but I have seen plenty of posters and met many colleagues. Today I am especially looking forward to the Arthur Holems Medal lecture by Kevin C.A. Burke on “Plume Generation Zones on the core mantle boundary: their origin and what they tell us about how the Earth works – and how it has worked”. And also to spend the afternoon at session SSP2.3: “Late Palaeozoic and Mesozoic stratigraphy, paleoceanography and paleoclimate” (sponsored by the IAS).
I am also co-author on a poster in the session “Rifts and rifted margins: The sedimentary, volcanic and crustal architecture”, so I have to check out that. The poster is entitled “Pre-breakup age of East Greenland Ridge strata” by Tove Nielsen, Morten Bjerager, Sofie Lindström, Henrik Nøhr-Hansen, Tine L. Rasmussen (Abstract).
It’s going to be a busy but fun day 🙂
Last week I attended the Geological Society of America (GSA) annual meeting and 125th anniversary which was held at the Colorado Convention Center in Denver, Colorado, USA – A multitude of scientific sessions and thousands of geoscientists! As always with large conferences, it is both fantastic and confusing to have so many interesting sessions presented almost simultaneously.
I participated in the session T238. New insights into Triassic-Jurassic Transition events and end-Triassic Mass Extinction (blue text are links to program and abstracts). This session was graciously hosted by Rowan C. Martindale and Morgan F. Schaller who had put together an interesting programme bringing forth some of the latest research and ideas concerning TJ-boundary research. We who participated got to hear interesting talks on the carbon cycle, specifically on Late Triassic pCO2 variations by Morgan Schaller et al. and on Late Triassic ocean stability and orbital control by Sylvain Richoz et al. The pedogenic carbonate results of Schaller et al.’s research suggest a long-time (30-million-years) fall in the atmospheric CO2-content from the Carnian to the late Rhaetian prior to the eruption of the Central Atlantic Magmatic Province (CAMP). Richoz et al., on the otherhand, demonstrate a relatively stable marine C-isotope curve from the Norian to the Rhaetian, displaying only a gentle decrease, i.e. possibly an on-going input of light carbon to the atmosphere (increased CO2) during the Late Triassic prior to CAMP eruption.
Regarding the plant record, Wolfram Kürschner presented some new data indicating environmental mutagenesis in Late Triassic conifers in more equatorial areas, where a sudden size increase in Classopollis pollen may be due to whole genome doubling (polyploidy) as a consequence of environmental stress. Karen Bacon talked about the fact that many present-day plants get thicker leaves when subjected to increased levels of CO2, and especially if exposed to low O2 at the same time, and put this in relation to findings in the plant records across the TJ-boundary in East Greenland. In one of the solicited talks, Jennifer McElwain presented an extensive review of her and her co-workers palaeobotanical research on the TJ-boundary of East Greenland over the last 25 years. The impact of her research did however, receive some criticism from the next solicited speaker Spencer Lucas who meant that not only is there no palaeobotanical evidence for a global or even regional mass extinction at the end of the Triassic, but not for the terrestrial terapods either! But then Lucas did not seem to acknowledge the palynological support for a floral mass extinction. His critique does emphasize that there is a need of more thorough palaeobotanical work across the TJ-boundary from other parts of the world.
Lucas also presented major criticism on the impact of the cyclostratigraphic scheme for the Newark Basin, which he said had caused “a decade-long miscorrelation” with other TJ-boundary succession. This led to a slightly heated discussion between Lucas and the next speaker, Paul Olsen, one of the researchers behind the Newark Basin cyclostratigraphy. In his talk, Paul Olsen discussed the impact a volcanic winter due to SO2-degassing from the CAMP would have on terrestrial vertebrates.
After a short break it was finally my turn. My talk, entitled “Supraregional seismites in Triassic – Jurassic boundary strata“, presented widespread evidence of episodic seismic activity in NW Europe during the end-Triassic mass extinction interval. My co-authors and I have found evidence of at least four separate seismic events in the form of soft-sediment deformations within TJ-boundary successions from Sweden, Denmark and Germany, and the implications of these on the CAMP and the end-Triassic mass extinction where discussed during the talk, which was going as scheduled when it was interrupted by a ca 5 minute long false fire alarm. Eventually I could continue and finish my talk but unfortunately with no time for questions.
One of the most interesting talks was that on the Cotham Marble where Yadira Ibarra et al. showed that the calcified microbial mats, containing prasinophycean algal cysts (Tasmanites) and a sparse shelly fauna, must have formed in a calcium carbonate supersaturated environment. The Cotham Marble is synchronous to the so called initial C-isotope excursion. Kathleen Rittersbuch et al. presented new data on earliest Jurassic siliceous sponge dominance based on fieldwork in the Peruvian Andes. Correlations with siliceous sponge records in Nevada, the Austrian Alps and Morocco indicate that this was a globally relevant phenomena.
Aviv Bachan and Jonathan Payne presented modeling of hypothesized carbon cycle perturbation scenarios for the TJ-boundary, focusing on the large positive C-isotope excursion (CIE) following the sharp negative CIE. They found that the modelled scenario most similar to the recorded C-isotope record is that with temporary increase in pCO2 coincident with the volatile release, as well as a temporary decrease in carbonate saturation, indicating that the release of volatiles during the emplacement of the Central Atlantic Magmatic Province could have been the driver of the environmental perturbation.
The final talk of the session was that of Bas van de Schootbrugge et al. who presented our palynological reworking data that indicate increased weathering and erosion, i.e. mass-wasting, synchronous to the terrestrial deforestation during the end-Triassic mass extinction. The massive reworking registered in both Germany, Denmark and Sweden, emphasizes the severity of the environmental impact on the land environment, and it seems likely that increased input of sediment, soil and organic matter to the ocean must have played a part in the extinction scenario.
We celebrated the end of an interesting the session by having lunch at the Rock-Bottom Restaurant in downtown Denver. Good food and great company! 🙂