Stratigraphy, Sedimentology and Palaeontology

Imaggeo on Mondays: Nummulites, the living lentils

Imaggeo on Mondays: Nummulites, the living lentils

This photograph depicts a close-up of Eocene limestones from the Sardinero Formation in Cantabria (Northern Spain). The limestone is rich with foraminifera shells, most of them from the Nummulitidae family. These organisms once lived in a very shallow sea that separated Europe from Iberia in the late Mesozoic and early Cenozoic era. Later the sea basin’s  closure led to the formation of the Pyrenees.

The remarkable abundance of these Paleogene and Eocene fossils around the globe led Eugène Renevier, a Swiss geologist from the 19th century, to propose merging the two Epochs into the Nummulitic Period, a suggestion that did not succeed.

Nummulitidae were also some of the first microfossils recognized in literature. Their features were described in Book XVII of Geography, written by the Greek geographer and historian Strabo around the beginning of the 1st century. In this passage Strabo finds the Nummulitidae fossils embedded in the rocks used to build Egyptian pyramids, however he mistakes the shells for lentils dropped by rushed workers. It reads below:

One of the marvellous things I saw at the pyramids should not be omitted: there are heaps of stone-chips lying in front of the pyramids; and among these are found chips that are like lentils both in form and size; and under some of the heaps lie winnowings, as it were, as of half-peeled grains. They say that what was left of the food of the workmen has petrified; and this is not improbable.

Indeed, in my home-country, in a plain, there is a long hill which is full of lentil-shaped pebbles of porous stone; and the pebbles both of the seas and of the rivers present about the same puzzling question; but while these latter find an explanation in the motion caused by the current of water, the speculation in that other case is more puzzling.

It has been stated elsewhere that in the neighbourhood of the quarry of the stones from which the pyramids are built, which is called “Trojan”, and that there are caves at the foot of it, and a village near both these and the river which is called Troy, being an ancient settlement of the captive Trojans who accompanied Meneläus but stayed there.

Despite this initial description referring to lentil-sized Nummulitidae, the size of these fossils varies considerably among different species, and can reach up to 12 cm, some of which have been found in Cenozoic rocks in the same area where the photograph was taken. Such a size is remarkable, considering the fact that Nummulitidae are unicellular organisms.

There are lots of genera within the Nummulitidae family, the most common of which are Assilina and Nummulites. The fossils in the photograph are about 1 cm in length and pertain to the Nummulites genus. Nonetheless, more elongated and white fossils from the Discocyclinidae family are also present in the limestone; one of them can be found right below the crawling snail.

While taking some pictures of the outcrop, I noticed the snail in the lower part of the frame, slowly crawling towards the top of it. To my surprise, it chose to follow the path drawn by two large Discocyclinidae shells, and I rushed to take this photograph. Two living beings together but separated by 50 million years, embodying a sort of spacetime paradox.

By Manuel de Paz Álvarez, the University of Oviedo

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submittheir 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


Imaggeo on Mondays: The best of imaggeo in 2017

Imaggeo on Mondays: The best of imaggeo in 2017

Imaggeo, our open access image repository, is packed with beautiful images showcasing the best of the Earth, space and planetary sciences. Throughout the year we use the photographs submitted to the repository to illustrate our social media and blog posts.

For the past few years we’ve celebrated the end of the year by rounding-up some of the best Imaggeo images. But it’s no easy task to pick which of the featured images are the best! Instead, we turned the job over to you!  We compiled a Facebook album which included all the images we’ve used  as header images across our social media channels and on Imaggeo on Mondays blog post in 2017 an asked you to vote for your favourites.

Today’s blog post rounds-up the best 12 images of Imaggeo in 2017, as chosen by you, our readers.

Of course, these are only a few of the very special images we highlighted in 2017, but take a look at our image repository, Imaggeo, for many other spectacular geo-themed pictures, including the winning images of the 2017 Photo Contest. The competition will be running again this year, so if you’ve got a flare for photography or have managed to capture a unique field work moment, consider uploading your images to Imaggeo and entering the 2018 Photo Contest.

Alpine massifs above low level haze . Credit: Hans Volkert (distributed via

The forward scattering of sunlight, which is caused by a large number of aerosol particles (moist haze) in Alpine valleys, gives the mountain massifs a rather plastic appearance. The hazy area in the foreground lies above the Koenigsee lake; behind it the Watzmann, Hochkalter, Loferer Steinberge and Wilder Kaiser massifs loom up behind one other to the right of the centre line. Behind them is the wide Inn valley, which extends right across the picture.

A lava layer cake flowing . Credit: Timothée Duguet (distributed via

Check out a post from back in May to discover how layers of alternating black lavas and red soils built up to form a giant ‘mille feuilles’ cake at Hengifoss, Iceland’s third-highest waterfall.

Sediment makes the colour . Credit: Eva P.S. Eibl (distributed via

Earth is spectacularly beautiful, especially when seen from a bird’s eye view. This image, of a sweeping pattern made by a river in Iceland is testimony to it. Follow the link to learn more about river Leirá which drains sediment-loaded glacial water from the Myrdalsjökull glacier in Iceland.

Movement of ancient sand . Credit: Elizaveta Kovaleva (distributed via

Snippets of our planet’s ancient past are frozen in rocks around the world. By studying the information locked in formations across the globe, geoscientist unpick the history of Earth. The layers in one of the winning images of the 2017 photo contest may seem abstract to the untrained eye, but Elizaveta Kovaleva (a researcher at the University of the Free State in South Africa) describes how they reveal the secrets of ancient winds and past deserts in a blog post we published in November.

View of the Tuva River and central mountain range
. Credit: Lisa-Marie Shillito (distributed via

Initially, this photo may seem like any other tropical paradise: lush forests line a meandering river, but there is much more to the forests in the foreground than first meets the eye.

On the way back from Antarctica. Credit: Baptiste Gombert (distributed via

Our December 2017 header image – On the way back from Antarctica, by Baptiste Gombert – celebrated #AntarcticaDay.

Angular unconformity. Credit: André Cortesão (distributed via

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one seen above. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

Find a new way . Credit: Stefan Winkler (distributed via

Stephan Winkler’s 2017 Imaggeo Photo Contest finalist photo showcases an unusual weather phenomenon…find out more about this process in the post from last year.

On the way back from Antarctica. Credit: Alicia Correa Barahona (distributed via

August’s social media header image showcases how, in the altiplano of Bolivia, Andean ecosystems, life and the hydrological cycle come together.

Icelandic valley created during a volcanic eruption. Credit: Manuel Queisser (distributed via

The image shows a valley in the highland of Iceland carved out during a volcanic eruption with lava coming from the area visible in the upper right corner. The landscape is playing with the viewers sense of relation as there is no reference. The valley is approximately 1 km wide. The lower cascade of the water fall is ca. 30 m high. A person (ca. 3 pixels wide) is located near the base of the water fall about 50 m away. It was our October header image.

Despite being one of the driest regions on Earth, the Atacama desert is no stranger to catastrophic flood events. This post highlights how the sands, clays and muds left behind once the flood waters recede can hold the key to understanding this natural hazard.

The heart of the Canadian Rocky Mountains. Credit: Jennifer Ziesch (distributed via

“I saw one of the most beautiful place on earth: The glacially-fed Moraine Lake in the Banff National Park, Canada. The lake is situated in the Valley of the Ten Peaks. The beautiful blue colour is due to the mix of glacier water and rock flour,” says Jennifer, who took the photograph of this tranquil setting.

Symbiosis of fire, ice and water . Credit: Michael Grund (distributed via

This mesmerising photograph is another of the fabulous finalists (and winner) of the 2017 imaggeo photo contest. The picture, which you can learn more about in this blog post, was taken at Storforsen, an impressive rapid in the Pite River in northern Sweden, located close to the site of a temporary seismological recording station which is part of the international ScanArray project. The project focuses on mapping the crustal and mantle structure below Scandinavia using a dense temporary deployment of broadband seismometers.

f you pre-register for the 2018 General Assembly (Vienna, 08 – 13 April), you can take part in our annual photo competition! From 15 January up until 15 February, every participant pre-registered for the General Assembly can submit up three original photos and one moving image related to the Earth, planetary, and space sciences in competition for free registration to next year’s General Assembly!  These can include fantastic field photos, a stunning shot of your favourite thin section, what you’ve captured out on holiday or under the electron microscope – if it’s geoscientific, it fits the bill. Find out more about how to take part at

MinCup: Elevating humble minerals to new heights

MinCup: Elevating humble minerals to new heights

Throughout October and November, the world of (Earth science) Twitter was taken by storm: Day after day, Eddie Dempsey (a lecturer at the University of Hull, and @Tectonictweets for those of you more familair with his Twitter handle) pitted minerals against each other, in a knock out style popular contest. The aim? To see which mineral would eventually be crowned the best of 2017.

Who knew fiery (but good natured) rows could explode among colleagues who felt, strongly, that magnetite is far superior to quartz or plagioclase? The Mineral Cup hashtag (#MinCup) was trending, it was in everyone’s mouth. Who would you vote for today?

What started as a little fun, became a true example of great science communication and how to bring a community of researchers, scattered across the globe, together.

And then Hazel Gibson (former EGU Press Assistant, @iamhazelgibson) came along. She was an active participant in the competition, but also contributed beautiful sketches of every mineral featured, and shared them for all to see by tagging them with the #MinCup hashtag. We all know that a picture is worth more than a thousand words, so when Hazel’s hand drawn sketches where paired with an already rocking contest, it’s impact and reach was truly cemented.

Between them, Eddie and Hazel had managed to elevate the humble mineral to new heights.

Why do minerals matter?

Minerals are hugely underrated. They are often upstaged by the heavy-weights of the geosciences: volcanoes, earthquakes, hurricanes, fossils and melting glaciers (to name but a few).

But they shouldn’t be.

Minerals are the building blocks of all rocks, which in turn, are the foundation of all geology.

Whether you study the processes which govern how rivers form, or ancient magnetic fields, or fossils, chances are your work will, at some stage, involve looking at, studying, or at the very least understanding (some) minerals. Mineralogy 101 (or whatever it’s precise name was at your university) is a rite of passage for any aspiring Earth scientist. I still remember hours spent painstakingly looking down a microscope, drawing and annotating sketches trying to decipher the secrets of the Earth’s ancient past, locked in minerals.

And that’s just the beginning.

Minerals are of huge economic and, therefore societal importance, too. Many minerals are vital ingredients in house-hold products and contribute to the manufacturing processes of many others. Yet, they fail to make headlines and their true significance, often, goes unnoticed.

So, in hopes to further highlight the relevance and importance of minerals, I’ve picked a few of the #MinCup minerals and explained why they (should) matter (to you).


Gypsum will form in lagoons, where ocean waters are high in calcium and sulfate content, and where the water evaporates slowly overtime. In rocks, it is associated with sedimentary beds which can be mined to extract the mineral, but it can also be produced by evaporating water with the right chemical composition.

Gypsum has been used in construction and decoration (in the form of alabaster) since 9000 B.C.  Today, it has a wide variety of common uses. Did you know that many fruit juice companies use gypsum to aid the extraction of the liquid? It is also used in bread and dough mixes as a raising agent. And it’s uses aren’t limited to just the food and drink industry. It is also commonly used as a modelling material for tooth restorations and helps keeps us safe when added to plastic products where it acts as a fire retardant.


Geologically speaking, magnetite holds the clues to understand the Earth’s ancient magnetic field. Credit: Hazel Gibson

Typically, greyish black or black, magnetite is an important iron ore mineral. It occurs in many igneous and volcanic rocks and is the most magnetic of all minerals. For it to form, magma has to cool, slowly, so that the minerals can form and settle out of the magma.

Due to its magnetic nature, it has fascinated human-kind for centuries: it paved the way for the invention of the modern compass.  The iron content in magnetite is higher than its more common cousin haematite, making it very sought after. Iron ore is the source of steel, which is used universally throughout modern infrastructure.

Geologically speaking, magnetite holds the clues to understand the Earth’s ancient magnetic field. As magnetite-bearing rocks form, the magnetite within them aligns with the Earth’s magnetic field. Since this rock magnetism does not change after the rock forms, it provides a record of what the Earth’s magnetic field was like at the time the rock formed.


Arguably, one of the most well-known of the minerals, diamond is unique, not only for its beauty and the high prices it reaches, but also for its properties. Not only is it the hardest known mineral, it is also a great conductor of heat and has the highest refractive index of any mineral.

Though mostly sought after by the jewellery industry, only 20% of all diamonds are suitable for use as a gem. Due to it’s hardness, diamond is mined for use in industrial processes, to be used as an abrasive and in diamond tipped saws and drills. Its optical properties mean it is used in electronics and optics; while it’s conductive properties mean it is often used as an insulator too.

Diamond: perhaps the most sought after mineral of them all? Credit: Hazel Gibson


Last, but absolutely not least, let’s talk about Olivine – the winner of #MinCup 2017.

Olivine is a pretty, commonly green mineral. Because it forms at very high temperatures, it is one of the first minerals to take shape as magma cools, and given enough time, can form specimens which are easily seen with the naked eye. Changes in the behaviour of seismic waves as they traverse the Earth indicate that Olivine is an important component of the Earth’s inner layer – the Mantle.

It’s a relatively hard mineral, but overall hasn’t got highly sought-after properties and, as result, has been used rather sparingly in industrial processes. In the past it has been used in blast furnaces to remove impurities from steel and to form a slag, as well as a refractory material, but both those uses are in decline as cheaper materials come to the market.

Perhaps better known is its gemstone counterpart: peridot, a magnesium rich form of Olivine. It has been coveted for centuries, with some arguing that Cleopatra’s famous ‘emeralds’, where in fact peridote. Until the mid-90s the US was the major exporter of the gem stones, but deposits in Pakistan and China now challenge the claim.

So, do you think Olivine was the rightful winner of #MinCup 2017? With a new edition of the popular contest set to return in 2018, perhaps it’s time to shout about the properties and uses of your favourite mineral from the roof tops? Not only might it ensure it is crowned winner next year, but you’ll also be contributing to making the value of minerals known to the wider public. Heck! If you’d like to tell us all about the mineral you think should be the next champion, why not submit a guest post to GeoLog?

In the meantime, if you haven’t already got your hands on one, Hazel tells me there are a few of her charity #MinCup 2017 calendars up for grabs, so make sure to secure your copy – and contribute to a good cause at the same time.

By Laura Roberts Artal, EGU Communications Officer

Imaggeo on Mondays: Angular unconformity

Imaggeo on Mondays: Angular unconformity

It is not unusual to observe abrupt contacts between two, seemingly, contiguous rock layers, such as the one featured in today’s featured image. This type of contact is called an unconformity and marks two very distinct times periods, where the rocks formed under very different conditions.

Telheiro Beach is located at the western tip of the Algarve; Portugal’s southernmost mainland region and the most touristic too.

The area, famous for its famous rocky beaches and great seefood, shows a spectacular Variscan unconformity between the highly-folded greywackes and shales of the Brejeira Formation (Moscovian-Carboniferous) and the horizontally placed red sandstones and mudstones of the Group Grés de Silves (of Late Triassic age: 237 and 201.3 million years old). There is a hiatus of about 100 million years between the two formations.

The Variscan period ranges from 370 million to 290 million year ago and is named after the formation of a mountain belt which extends across western Europe, as a result of the collision between Africa and the North American–North European continents.

The imposing sea cliffs produce a privileged place to observe the end of the Variscan Cycle and the beginning of the Alpine Cycle.

It is possible to visit the outcrop on foot, from the top of the cliffs to the beach, although the path is of high degree of difficulty. When going down to the beach one can begin to visualise the typical lithologies of the Grés de Silves. Toward its top you can see red to green Mudstones (dominant) intercalated with rare dolomites and immediately above the unconformity plane it is possible to observe the red sandstone with cross stratification. The highly-folded turbidites (a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean) of the Brejeira Formation are located below the unconformity.

The folds feature chevron geometries (where the rocks have well behaved layers, with straight limbs and sharp hinges, so that they look like sharp Vs). The folding is the result of the final deformation phase of the Variscan compression.

The beds of sedimentary rocks show sedimentary structures attributed to sedimentation in a turbidic environment (turbititic currents), namely the Bouma sequence and sole marks like flute, groove and load casts.

                                                                                                     By André Cortesão, Environmental Engineer and Geoscientist collaborator of the University of Coimbra Geosciences Centre

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