Stones of Estonia (3)

Wednesday

In the second day of the excursion, we went to more fossiliferous (fossil-containing) sites. First, we visited the old Ungru-Sepaküla limestone quarry, in an area called Pusku. Now we had come to the early Silurian period, which came after the Ordovician, beginning around 488 million years ago.

Unfortunately, the quarry was mostly flooded, so we had to look at the carved-out exposure from above. Still, you can see quite clear, thin beddings, and two quite distinctive types of rock ad the top and the base. This might represent a stage boundary – a boundary between subdivisions within a period.

The rocks were so-called bahamitic limestones, formed in warm waters, which is good for corals, and other shelled creatures, as it is easier for them to create their shells. The teachers mentioned that the oval blobby structures you can see in the upper part of the section were formed by corals.

What was far more interesting was the heaps of quarried-out block fragments lying around.

 

This is not only where we could find some fossils, but also where peculiar rocks like these were found.

The light beige pieces are not fossils, but fragments of sedimentary rocks ripped apart while they were in the process of forming, probably by a massive storm, and then redeposited together with the other, grey sediments, and were so incorporated to form a single type of rock. It had a fancy name – intersomething conglomerates – but I did not quite catch it. They were also referred to as rip-up clasts.

But, what was by far the most fun here was that I found my very first fossil!!

A pretty large tabulate coral, nicely preserved in 3D and all! (And it was cool that it was so easy to tell what it was – the honeycomb-like structures and the overall round shape are typical for tabulates.) These are colonial creatures, important parts of coral reefs. They form their skeleton out of the mineral calcite (which basically is calcium carbonate), which also is the main constituent of limestone – the calcite in the limestone is derived from the corals, and other organisms with calcitic shells. The tabulate corals first appeared in the Ordovician, and did very well until they were wiped out in the greatest extinction event of all time – the end-Permian mass extinction 250 million years ago – which obliterated about 95% of all species alive at that time.

As with most marine invertebrates, the tabulate corals are not very interesting. They did not do much more than sit on a reef and eat. Still, they are nice to look at, and the preservation of this fossil was remarkable – by my standards, at least. It was impressive (not an impression, but an actual representation of the structure of the skeleton as it was in life). I truly could not have wished for a more spectacular fossil to be my first one! And I found it already on the second day of the trip. Wow, what if I would actually find more fossils? I was so thrilled, and I had no idea of the discoveries that awaited. 

On the way back to the bus, I learned that Aodhán Butler, one of the postdocs (I think...), did his masters degree in the University of Bristol! This is where I might end up in three years (if everything goes well, but nothing is certain, of course). He spoke very warmly of it, and said that it is one of the best things you can do if you want to workt with vertebrate paleontology, which I want very much!

Our next stop was at Pulli cliff, in the northeastern shore of Saaremaa, the largest of the islands on the western coast of Estonia. While our guide was searching for a special site on the Silurian outcrop, we could see some funny features by the shore.

The snow that had once lain over a part of the shore had been ripped up by the waves, broken into large, angular blocks, so reminiscent of actual rock blocks that I could not help taking a picture. Among the actual rocks, there were many with small, round, smooth holes, quite similar to spongy textures. Our teacher mentioned that these had been carved out by slightly acidic water. These were, however, recent features, and did not tell anything about the water chemistry back in the Silurian.

In the limestone quarry, one of the postdocs, Stephen Poropat (a sauropod expert! Yay!), told me to get used to having some sort of scale when taking photos, especially close-up ones. So I thought I could illustrate the size of the acid-eroded holes by sticking my finger into one.

Finally, we came to this place.

 

We were to study this section, with those ominously overhanging upper portions, which looked like they could fall over us at any time.

We could clearly see three different sections, marked not only as each section protruded noticeably above the underlying ones, but also by their different colours. On closer examination, we discovered a mish-mash of fossil shell fragments in both of the lower parts, so the sediments were definitely marine.

Next, we were supposed to figure out what could have caused the clear undulation, or curvature there. Something had bent up a part of the section. What could have done such a thing? Our minds raced furiously… 

When you look at the rocks on the side of the bulge, however, one can see that the beds are more massive on the flanks of the domed part. I had thought in the completely wrong direction! The dome had not been pushed out, it was the rest that had been pushed down by heavier rocks above. That shows how important it is to look at the outcrop sideways as well!

This was mostly forgotten when we came to the next site: Ninase cliff. It was more of a beach with lots of small, flat, rounded light grey pebbles.

But you just have to bend down, and you see fossils everywhere!

The stripy fan-shaped things are brachiopods, a type of marine animals quite like clams, but rather different in several aspects. There are also lots of tiny holes, which might be burrows, perhaps made by worms.

We also found crinoids (sea lilies), corals (both tabulate and rugose ones), cephalopods (a group of molluscs including squids and octopuses, and, in the Silurian, shelled forms), gastropods (slugs), and stromatoporoids (a type of sponge). You will see the crinoids, orthocones and stromatoporoids later. Here are a few pictures I took of some fossils I brought back home.

From left to right, you can see two gastropod impressions, typically coiled, and an indentation that might look like the head of a trilobite, but is actually another brachiopod (probably a craniiform, which people say look like a cranium on the inside, but it is hard to tell from this print of the exterior of the shell).

Below is another gorgeous impression of a brachiopod, which looks like a piece of candy you could pick out and eat. Luckily, it sits firmly in place.

My two favourite fossil from this locality was a large, tabulate coral, much nicer than the first I found at the Ungru-Sepaküla quarry, preserved with the shell and all, instead of just a one-side print. 

 

 

It was unbelievable that there could be so many beautifully preserved fossils here, on a well-known site, easily accessible to anyone in the vicinity. Even tough people probably have collected tons and tons of fossils here already, it was hard to find any rock without fossils. Some students even went stone-skipping with them!

This was truly an amazing day. The trance was broken only by our professor’s black whistle. I watched the sun setting as we walked back to the buss, still mesmerized by the unforgettable moment.