Rocks never forget!

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Figure1. Elephant rock, Castelsardo, Sardinia, Italy (picture by Vid Pogačnik)

Did you know that some rocks can have an incredible “magnetic memory”? The age of rocks can vary from seconds to billions of years, and besides their sometimes very old age they store information that is useful to reconstruct the history of our Planet.

We commonly use the word “memory” referring to our computer storage capacity or our own ability to remember. Rocks store information, but unlike us they are able to do it over longer periods of time. The oldest memory we have is limited to what humankind experienced but some rocks are much older than humans. Therefore it is really important to be able to extract their memories in order to better understand what we didn’t experience ourselves.  

This “magnetic memory” relates to certain minerals in rocks (e.g. magnetite, hematite) able to record the direction and the intensity of the Earth’s magnetic field when they form.

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Surprise: Catching bugs in rocks!

X-ray tomography is a powerful technique that allows us to see very tiny details inside a rock. However, the image acquisition is usually just a starting point for the image analysis. In order to get quantifiable information, one has to develop specific image processing algorithms. In the porous medium research, one of the most important processing step is the development of the task oriented image segmentation algorithm.

While trying our segmentation algorithm on a 3D image of a sedimentary rock, we found some curious piece of a former life! The “worm” you can see in the video is an orthoceras — an ancient mollusk that is often found in sediments.

This carbonate rock has been cored in the Miocene carbonate platform of Llucmajor, in Majorca. The rock has suffered a re-equilibration from aragonite to calcite (dissolution of aragonite and crystallization of calcite). This reaction led to the formation of porosity (grey parts of the picture). In this case the spatial distribution of the pores has been controlled  by the pre-existing structure of the rock. This process allowed the preservation of the shape of the fossil, even after re-equilibration and recrystallization into calcite. That is why we can see the orthoceras, although its skeleton has undergone chemical alteration.

Figure 1. This video is a series of 2D slices of a 3D volume. No orthoceras is actually swimming here

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Breaking rocks: a closer look

When I described in my last post how rocks can be broken up by volume-increasing reactions happening within them, I left you with several open questions in the end. One of them was whether reaction-driven fracturing can also occur when there is no stress from the outside and no fracture to start with. It is easy enough to imagine that minerals that grow in a crack may push against the walls of the crack, move them apart and cause further fracturing. But for this first crack, with which everything starts, we certainly need some forces from the outside that make the rock break. Or do we really?

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Rocks that pop!

  • Discovery

In 1972, the scientists onboard the French research vessel Jean Charcot, during the “Midland” cruise made an amazing discovery: Rocks that pop! From the seafloor in the Atlantic Ocean they retrieved some basaltic glassy pebbles that exploded noisily, much like firecrackers and jumped merrily to a height of up to one meter on the ship deck. A decade later, another geologic expedition aboard the RV Akademik Boris Petrov made the same surprising discovery from a complex region of the Mid-Atlantic Ridge that contains vast areas of lava flows (see previous post) as well as heavily faulted terrain with intact blocks of deep crust. These rare forms of lava rock are really interesting because of their spectacular behaviour but mostly because of their richness in gas and information they provide on the deep Earth.

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Figure 1: a) Photo of a popping rock. Volcanic glass in black and rounded vesicles. b) Photo of a thin section of popping rock (Sarda, 1990).

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Continued: The story of the deep carbon cycle…

… and the big black bear

Last summer, I was fighting my way through the boreal forests of Newfoundland in Canada, a place well renowned for its wildlife. Hence I was heavily armoured with big hammers, a huge can of strong pepper spray and some bear banger cartridges in my pocket, always smelling of mosquito repellent and making a lot of noise, in order not to surprise a sleeping black bear in the bushes. In the end, I didn’t need the bear spray or the cartridges, but every now and then signs of bears in our field area reminded us of their presence. And I took these safety measures much more seriously after we encountered a black bear close to a local landfill: you just feel small and vulnerable in front of such a huge, beautiful and elegant animal that is only 20 meters away from you, even if your car is just two meters behind you.

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Fig1. Some of the wild life a geologist might need to be worried about.

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An ocean on land

Science is not all about books or laboratories, but also includes fieldwork. Unlike what people might think, this is not a holiday (although you get to bring home a lot of beautiful pictures) but work. And it is crucial for geology! But what do we do? And why? Standing in a beautiful landscape surrounded by rocks that contain information you are looking for, science shows a very different and adventurous side. Since our blog is about oceanic rocks, fieldwork can involve going on a ship. However, an ocean can be found also on land, and as we will show you in this movie, Oman hosts oceanic rocks with plenty of interesting features.