Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sea level as a metronome of Earth's history

19.05.2017

Sedimentary layers record the history of the Earth. They contain stratigraphic cycles and patterns that precisely reveal the succession of climatic and tectonic conditions that have occurred over millennia, thereby enhancing our ability to understand and predict the evolution of our planet.

Researchers at the University of Geneva (UNIGE), Switzerland, -- together with colleagues at the University of Lausanne (UNIL) and American and Spanish scientists -- have been working on an analytical method that combines observing deep-water sedimentary strata and measuring in them the isotopic ratio between heavy and light carbon.


This is a view of the Mediano anticline, strata dipping to the left into the lake waters. This large-scale fold structure is a witness of ancient deformation associated with the rise of the Pyrenees in the middle Eocene, 45 Million years ago. Excellent exposure of rocks in this dry area allow today's geologists to study the epic poem of the Earth written in its sedimentary archives.

Credit: © UNIGE

They have discovered that the cycles that punctuate these sedimentary successions are not, as one might think, due solely to the erosion of mountains that surround the basin, but are more ascribable to sea level changes. This research, which you can read in the journal Geology, paves the way for new uses of isotopic methods in exploration geology.

The area south of the Pyrenees is particularly suitable for studying sedimentary layers. Rocks are exposed over large distances, allowing researchers to undertake direct observation. Turbidites can be seen here: large sediment deposits formed in the past by underwater avalanches consisting of sand and gravel.

"We noticed that these turbidites returned periodically, about every million years. We then wondered what the reasons for this cyclicity were", explains Sébastien Castelltort, professor in the department of earth sciences in UNIGE's faculty of sciences.

The ups and downs of oceans regulate sedimentation cycles

The geologists focused their attention on Eocene sedimentary rocks (about 50 million years ago), which was particularly hot, and undertook the isotopic profiling of the sedimentary layers. "We took a sample every 10 metres," says Louis Honegger, a researcher at UNIGE, "measuring the ratio between 13C (heavy carbon stable isotope) and 12C (light carbon stable isotope). The ratio between the two tells us about the amount of organic matter, the main consumer of 12C, which is greater when the sea level is high. The variations in the ratio helped us explore the possible link with the sea level".

The research team found that the turbidite-rich intervals were associated with high 12C levels, and almost always corresponded to periods when the sea level was low. It seems that sedimentary cycles are mainly caused by the rise and fall of the sea level and not by the episodic growth of mountains.

When the sea level is high, continental margins are flooded under a layer of shallow water. Since the rivers are no longer able to flow, they begin to deposit the sediments they carry there. This is why so little material reaches the deep basins downstream. When the sea level is low, however, rivers erode their beds to lower the elevation of their mouth; they transfer their sediment directly to the continental slopes of the deep basins, creating an avalanche of sand and gravel.

Consequently, if the variations of the sea level are known, it is possible to predict the presence of large sedimentary accumulations created by turbidites, which often contain large volumes of hydrocarbons, one of the holy grails of exploration geology.

Measuring stable carbon isotopes: a new indicator of reservoir rocks

The research provides a new role for the use of carbon isotopes. "From now on, continues Castelltort, we know that by calculating the ratio between 13C and 12C sampled in similar slope deposits close to continents, we can have an indication of the sea level, which means it's possible to better predict the distribution of sedimentary rocks in our subsurface". In addition, this measurement is relatively simple to perform and it provides accurate data -- a real asset for science and mining companies.

The study also highlights the importance of sea levels, which are a real metronome for the Earth's sedimentary history. "Of course," concludes Honegger, "tectonic deformation and erosion are important factors in the formation of sedimentary layers; but they play a secondary role in the formation of turbidite accumulations, which are mainly linked to changes in the sea level".

Media Contact

Sébastien Castelltort
Sebastien.Castelltort@unige.ch
41-223-796-616

 @UNIGEnews

http://www.unige.ch 

Sébastien Castelltort | EurekAlert!

More articles from Earth Sciences:

nachricht Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center

nachricht NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>