GeoLog

Stratigraphy, Sedimentology and Palaeontology

Imaggeo on Mondays: The odd ‘living’ rocks

Imaggeo on Mondays: The odd ‘living’ rocks

Microbialites – structures which result from the interaction between microbes and sediments – have existed in the rock record since 3700 Ma ago until the present day. The presence of microbes in environments where mineral precipitation is prevalent, usually derives in the development of such chemical sedimentary structures. This can take place in marine, non-marine, and subterranean environments. The most common type of microbialites may be referred to as stromatolites.

The stromatolites shown here formed ~72 Ma ago in an intra-arc basin – a basin, located between two chains of volcanoes formed above subducting plates, where sediments deposit –  within the Tarahumara Formation, which was emplaced during the Laramide orogeny (some 70 to 80 million years ago) in Northwestern Mexico (Sonora).

The locality has been named the Huepac Chert because of the presence of thin and thick chert – a very fine grained rock made of silicon dioxide – horizons. The chert is black and it contains a great variety of fossils, including pollen grains, fungal spores, green algae, cyanobacteria, diatoms, arthropod remains, fruits, palm roots, aquatic plants (e.g. Haloragaceae), and numerous achritarchs.

Preliminary studies of the Fe2O3/TiO2 and MnO/TiO2 ratios in the chert suggest that hydrothermal activity was frequent and that it promoted the deposition of the majority of the chert where important organisms are beautifully preserved.  Iron-rich laminae, instraclasts, and evaporation processes may be inferred for the topmost sediments covering the stromatolites, suggesting that the water level fluctuated while these structures were forming.

There is still much work to do regarding the paleoenvironments where those Cretaceous stromatolites developed. These Upper Cretaceous successions are rare in Sonora, and biostratigraphic correlations can be made only with one locality to the South (Cerro El Obispo), but no other localities with similar lithology and fossil content have been reported.

By Hugo Beraldi, researcher at the Institute of Geology of the National Autonomous University of Mexico

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

Celebrating Earth Science Week!

Celebrating Earth Science Week!

For those not so familiar with the Earth sciences, geosciences and all its subdisciplines might be shrouded in mystery:  boring, unfathomable, out of reach and with little relevance to everyday life. Nothing could be further from the truth!

Earth Science Week, an international annual celebration founded by the American Geosciences Institute in 1998, aims to change the public’s perception of the geosciences.  Since 2011, the London Geological Society also hosts a range of events and activities to raise awareness and better understanding of the Earth sciences.

In 2016, Earth Science Week takes place between 8 and16 October. For the first time, the EGU will run events to mark the special date, all of which we invite you to take part in!

Earth Science Week Photo Competition

From Wednesday 5th to Friday 14th October submit an original photo on any broad theme related to the Earth, planetary and space sciences to our open access image repository, Imaggeo.

For your image to be included in the competition be sure to include the tag #EarthSciWeek when prompted during the upload.

Upon the submission period closing, all entered images will be published to the EGU’s Facebook page. The photograph with most likes, as chosen by the public, will be crowned the competition winner.

The winner will get one free book of their choice from the EGU library and a pack of EGU goodies! We’ll also feature the top five most popular entries on our Instagram.

I’m a geoscientist – Ask me Anything: Live Twitter Q&As

Have you always wanted to know how glaciers move and carve out unbelievable landscapes? How about which emissions cause the most pollution? What are the benefits of publishing in an open access journal vs. a pay-walled publication? If politicians make all the decisions, how can we get them to take scientists more seriously?

If you’ve ever asked yourself these questions, stay tuned or, better still, take part in our daily Earth Science Week live #EGUchat with an EGU member on Twitter. Starting on Monday, every lunchtime, you’ll have the opportunity to put your questions to a range of scientists and EGU experts and discuss a variety of subjects.

Our very own Sarah Connors (@connors SL), the EGU’s Policy Fellow, will kick off a week, of what we hope will be fruitful discussions, by taking questions on all things science policy. Come Tuesday Emma Smith (@emma_c_smith) and Nanna Karlsson (@icymatters), Cryosphere Division Blog editors, will team up to shed light on the processes which operate in the iciest places on the planet.

Wednesday brings editor of the EGU’s open access journal Earth Surface Dynamics (ESurf) and Professor of Physical Geography at the University of Hull, Tom Coulthard (@Tom_Coulthard), who will shed light on the processes which shape our planet and the trials and tribulations of getting published.

If you are interested in natural hazards, how we mitigate, manage them and how they impact on our daily lives, then tune in to the chat on Thursday, where Giorgio Boni (@EguNHpresident), President of the Natural Hazards Division will be answering all your questions!

For the final chat of the week, we bring you Michelle Cain (@civiltalker), an atmospheric scientist and former Atmospheric Division Early Career Scientist Representative. Michelle will be taking questions on gaseous emissions and topics related to the Earth’s atmosphere.

Joining the conversation couldn’t be easier! To put your questions to our experts follow the hashtag #EGUchat on Twitter. Not on twitter or aren’t available during the chats? Not to worry, send us your questions in the comments below or via Twitter, Facebook or Instagram: we’ll ask the experts on your behalf.earth_sci_week_ama_twitter-01

 

Imaggeo on Mondays: The road to nowhere – natural hazards in the Peloponnese

Imaggeo on Mondays: The road to nowhere – natural hazards in the Peloponnese

The Gulf of Corinth, in southern Greece, separates the Peloponnese peninsula from the continental mainland. The structural geology of the region is complex, largely defined by the subduction of the African Plate below the Eurasian Plate (a little to the south).

The Gulf itself is an active extensional marine basin, i.e., one that is pulling open and where sediments accumulate. Sedimentary basins result from the thinning, and therefore sinking, of the underlying crust (though other factors can also come into play). The rifting in the region is relatively new, dating back some five million years, and results in rare but dangerous earthquakes.

The active tectonics result in a plethora of other natural hazards, not only earthquakes.  Minor and major faults crisscross the area and have the potential to trigger landslides, posing a threat to lives and infrastructure. A road, swept away in a landslide, in the northern Peloponnese (along the southern margin of the Corinth rift) is a clear example of the hazard.

“This photo was taken in the Valimi fault block [editor’s note: a section of bedrock bound on either side by faults], east of the Krathis valley. West of this valley, the landscape is characterised by  narrow and deep gorges as the present day rivers cut into the well-consolidated conglomerates deposited during the active extension of the basin,” explains Romain Hemelsdaël, author of this week’s imaggeo on Mondays photograph.

Characteristically, sediments deposited in actively extensional rifts where the Earth’s crust and lithosphere are being pulled apart, as at the Gulf of Corinth, change in size (both horizontally and vertically) and composition. To the east of the Krathis valley, the sediments are being uplifted and are dominated by less competent sandstones and siltstones, as opposed to the conglomerates found in the Valimi fault block.

“The present landscape along this part of the rift margin forms large valleys covered by active landslides,” clarifies Romain. “In this photograph, the road was initially constructed directly on silts which were deposited by lakes and rivers. Up the hill, a temporary track currently replaces the road but this track still remains within an active landslide.”

 

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/

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