Mark Wilson July 4th, 2011
KURESSAARE, SAAREMAA, ESTONIA–The Wooster Geologists Estonia Team today braved the Baltic Sea again and took a ferry from the island of Hiiumaa to return to their previous field sites on the island of Saaremaa. We worked at Soeginina Cliff on the western coast (shown above) to finish up Nick Fedorchuk’s Independent Study field research on the Wenlock-Ludlow (Silurian) erosional sequence. It was a fun day because we now have hypotheses to test about these rocks and fossils. More on those later.
The above rock shows an advantage we have studying exposures on rocky coastlines. The waves erode blocks of limestone from the cliff and polish them up on the boulder-strewn beach. We can thus see our rocks in three dimensions rather than just the flat cross-section we would normally have. The trick, though, is to know from where in the section the boulders were derived!
We found some excellent sections through the numerous oncoids in our outcrops as well. We saw that many are formed around gastropod (snail) shells — very much like a Jurassic version I recently described as one of Wooster’s Fossils of the Week.
Tonight we will celebrate the 4th of July with a pizza dinner in downtown Kuressaare. It is as close to American food as we can get here. On this holiday we salute the Wooster Geologists Iceland Team also far from home on the front lines of science!
Mark Wilson July 3rd, 2011
KÄINA, ESTONIA–Today we had our last visit to our Silurian quarry working site (where I photographed the Paleofavosites coral fossil above, which by the way was preserved upside-down in the sequence), and then we had lunch in the town of Kärdla overlooking the Baltic. Tomorrow we take the early morning ferry back to the larger island of Saaremaa where we resume fieldwork. Here are a few last photographs from Hiiumaa.
The other Silurian outcrop on the island: Kallaste Cliff. A bit overgrown, we think.
Some purple flowers found in the woods near our field site.
Yellow flowers in the quarry itself. I do know the one on the left is a daisy!
Whitish flowers and then a moth-covered thistle. I photographed this Six-Spot Burnet moth earlier, but three on one flower deserved another image. I'm sparing you the photos of them mating!
Our hotel on Hiiumaa. For most nights we were the only ones there. The students said it reminded them of "The Shining".
A walk to the sea after lunch in Kärdla. We have enjoyed this weather very much.
Mark Wilson July 1st, 2011
KÄINA, ESTONIA–Rachel, Nick and I worked today in our lonely quarry on Hiiumaa measuring and describing this section of Lower Silurian (Llandovery, Rhuddanian) rocks and fossils. This is the fieldwork for Rachel’s Senior Independent Study.
One of the dilemmas is the nature of the lower interbedded limestones and shales. In places they show gently sloping beds and curved tops as here. Does this indicate some sort of mud mound or bioherm? Or is it a function of slumping in the quarry itself? (I'm leaning toward the latter.)
The fossils here are excellent, including corals and bryozoans. (Just because I could I expanded the image of the mite!)
Mark Wilson June 30th, 2011
KÄINA, ESTONIA–Today we moved our geological investigations from Saaremaa to the island to the north: Hiiumaa. Our friend Olev Vinn of Tartu University then led us to an abandoned quarry in the Hilliste Formation (Lower Silurian). This made Rachel Matt very happy as it is the place she has been studying as the potential site for her Senior Independent Study project. First, it is not filled with water; second, it is easy to get to; third and most important, it has a diverse mix of fossils and rocks crying out for her attention. She is shown above in front of what looks like an ancient mud mound.
The rocks and fossils are so good that the students quickly accumulated a pile of cool specimens. I had to stop them from picking up fossils because we’ve not even started to sort out the stratigraphy. A good sign!
Our friend Bill Ausich at Ohio State University will be pleased to hear that there is much crinoid debris, as shown here in this image. It is a calyx plate in the center, with stem fragments around it. Hiiumaa is the island on the Euro to the right of the top star.
There is much I can’t identify here, at least not immediately. Another good sign!
The only thing that I don’t like is that we’re on yet another island, and this one smaller than the last. So much water around so little land, and no way off except by these little ferries. Our car is the brown one in the front on the right. I’ll endure for science!
Mark Wilson June 29th, 2011
KURESSAARE, ESTONIA–Our fieldwork today at the Soeginina Cliff locality ended with an examination of a sequence of stromatolites near the top of the exposed Ludlow section. Stromatolites are layers of sediment accumulated by photosynthetic cyanobacteria. They are the earliest fossils known, some 3.5 billion years old, and these structures are still being formed today. Bacteria were present at the beginning and no doubt will be the only surviving life at the end.
In the image above, the stromatolitic portion of the outcrop begins at Nick’s upraised arm and goes almost to the top of the exposure. It is a complicated story because they seem to be sitting on an erosional surface cut into the dolomite underneath. There are also patches of what appears to be gravel under some of the stromatolite domes. A dolomitic sand fills the spaces between the stromatolite heads. Stromatolites can tell us a lot about the paleoenvironment of this area during the Silurian.
Closer view of the stromatolites at Soeginina Cliff.
Top view of the Soeginina stromatolites showing the fine layering produced by cyanobacteria. (Note the clever use for scale of a Euro with the map of Estonia on it. You can easily pick out the island of Saaremaa!)
I don’t usually come across stromatolites in my work. The last time I saw a few was with Matthew James on a great field trip to British Columbia. Part of the joy of supervising student research is that I must learn alongside them!
Mark Wilson June 28th, 2011
KURESSAARE, ESTONIA–Nick Fedorchuk began his fieldwork today at the Soeginina Cliff site we visited two days ago. The first thing we did was scout out the best place to measure the most complete section possible, and then we started the slow process of sampling and describing the rocks and fossils. On average we did about a meter an hour.
The above image shows one of the curious oncoids in the Soeginina limestones. Oncoids are usually almost spherical because they rolled around as bacteria formed layers around a nucleus. The oncoids in the lowermost Ludlow (Paadla Stage) here show an initial formation as spheroids and then they sat still on the seafloor and grew upwards to make little layered caps. The oncoid was knocked over occasionally and a new cap grew on top of the sideways oncoid. This finally made oncoids with multiple growth directions visible in cross-section.
Above is a bedding plane view of an oncoid-rich layer with shelly fossils. Some of the oncoids have formed around gastropod shells.
The trace fossils (evidence of organism behavior) are especially interesting because we can see them in bedding plane view (as above) and also in cross-sections. We will look at their distribution using various ichnofabric indices.
At the start of our day on the outcrop this happy Estonian dog joined the party. It stayed with us the whole time. It liked to splash around in the ocean and then joyfully jump on us — not conducive for taking notes or whacking rock samples, but fun nevertheless. Wolf (maybe the name we gave him was too easy) loves to gnaw on the carcasses of large, long-dead seabirds, bringing them to us as we worked. Wolf was sometimes a bit too exuberant, but he was a good friend for the day. We hope to see him tomorrow at the same place!
Mark Wilson June 27th, 2011
KURESSAARE, ESTONIA–Stromatoporoids are extinct calcareous sponges that were very common in shallow water environments of the Silurian. They are especially abundant in the middle Silurian of the Baltic Region. Today we visited a site called Katri Cliff where a reef composed of stromatoporoids is exposed. Olev Vinn is shown above studying them (with the inevitable remains of a Soviet coastal border guard post in the background).
Stromatoporoids made hard, dense skeletons of calcite, sequentially adding layers to them like onions. At Katri Cliff we found many examples of these sponges with rugose corals and tabulate corals embedded inside them. Apparently the sponge grew up around the coral skeletons, immuring them alive. The interesting question is whether the sponges and the corals had a mutual beneficial relationship or if they were actually competing for resources like space and food.
Stromatoporoid showing conical rugose corals in its skeleton.
Stromatoporoid broken in half and revealing an embedded tabulate coral.
We have placed this ancient reef on the list of possible projects for Rachel, but we won’t know what she is going to pursue until we visit the nearby island of Hiiumaa at the end of the week.
And in case you’re tired of so many fossils and seascapes in this blog, here’s another bit of history we saw today: Below are trenches built at the top of Ninase Cliff. The tragedy of 20th Century Estonian history is that we can’t immediately tell who dug these trenches. Was it Imperial Russians in 1917 defending against the invasion of Imperial Germans? Could they have been built by Soviets against the invading Nazis in 1941? Or maybe Nazis in 1944 fighting the re-invading Soviets? There is some satisfaction on this part of the coast to observe that the sea is slowly eroding these trenches back into the ancient limestone gravel from which they briefly appeared.
Mark Wilson June 26th, 2011
KURESSAARE, ESTONIA–It is always a joy to begin the fieldwork for an Independent Study project — or at least know what the fieldwork will be. This morning we visited the Soeginina Cliff locality on the Atla Peninsula of western Saaremaa and it was all we hoped it would be. Nick Fedorchuk (pictured above as a happy man with his outcrop) studied the literature about this locality during his Junior Independent Study period last semester. We confirmed today that the rocks are indeed auspicious and will work as the basis of his research.
This locality is significant because it records a time and rock boundary in the geological record. The lower portion belongs to the Wenlock Series in the Silurian System, and the upper portion is in the Ludlow Series of the Silurian. They are separated by a disconformity (an erosional horizon indicating a hiatus in the geological time record). Boundaries such as this are always interesting because they can be correlated across the globe with other rocks formed at the same time. We want to better understand what was happening in Baltica at this junction between the Wenlock and Ludlow, and then compare it to the equivalents in Sweden, Britain and North America.
The boundary rocks show a laminated unit in the uppermost Wenlock (Rootsiküla Stage) that has been interpreted as lagoonal in origin, and then a more massive limestone in the lowermost Ludlow (Paadla Stage) with oncoids (microbial accumulations) and eventually shelly beds thought to be more open shallow marine deposits. The division between them appears to be marked by a mineralized layer (see image below). Later Nick will collect rock and fossil samples to thoroughly describe this interval and sharpen the paleoenvironmental and paleoecological hypotheses.
Rachel Matt (below) does not yet know which outcrop will be the focus of her research, but we will soon!
Our last visit of the day was to Kaarma Quarry and its exposed laminated lagoonal limestones and dolomites of the Ludlow. You can see below the team in action — and what a beautiful day it was.
Mark Wilson June 25th, 2011
KURESSAARE, ESTONIA–Yesterday afternoon three Wooster geologists met in the Tallinn, Estonia, airport within an hour after flying from three different countries. (Thank you, travel agent Suzanne Easterling!) We rented a car and then drove through impressive rainstorms westwards to the coast where we boarded a ferry for the island of Saaremaa. By dinner time we had checked into a little hotel in the small city of Kuressaare. We are the third team of Wooster geologists to work in Estonia. The last one was two years ago — one of the first expeditions covered by this blog.
This morning we began our field reconnaissance with our friend and colleague Olev Vinn (shown below) of the University of Tartu. Olev is generously working with us for a week as we explore the Silurian and sort out Independent Study projects for senior geology students Nick Fedorchuk and Rachel Matt (pictured above). They are already prepared for work at particular sections, but we first want an overview of the Silurian on the island (and to be ready for surprises).
The Silurian of Saaremaa and its sister island Hiiumaa is very well exposed along the coastline in a series of cliffs (some of which, admittedly, are less than two meters high!). They encode information about the environments and communities on the ancient continent of Baltica about 430 million years ago. Saaremaa is particularly interesting to us because it was essentially off-limits to visitors between 1940 and 1991 because it was a military zone occupied by Soviets, and then Germans, and then Soviets again until Estonia regained its independence upon the collapse of the Soviet Union. The rocks and fossils here have not been studied as intensively as their equivalents elsewhere in Europe, so there are many opportunities for new discoveries and interpretations.
Today we visited Abula Cliff, Jaagarahu Quarry, and Elda Cliff on the western extension of the island looking at limestones and dolomites of the Wenlock Stage. Spherical stromatoporoids (see above) caught our fancy because they were particularly well exposed at Abula Cliff.
As you can see from the photos it was a gorgeous day. More geology tomorrow!
An old Soviet searchlight station at Elda Cliff (N58.30450°, E21.82935°). For twenty years now this coastline is free!
Mark Wilson June 19th, 2011
For some reason the Fossil of the Week I’ve had the most comments about is the Ordovician honeycomb coral from Indiana. It has an unexpected polygonal symmetry reflected in many other geological materials like desiccation cracks and columnar basalt. So this week’s fossil is another coral with a surprising shape: the chain coral Halysites.
Halysites is a tabulate coral genus originally named by Johann Fischer von Waldheim in 1828. Its corallum (colonial skeleton) consists of long vertical tubes (corallites) laterally attached to each other in ranks so that a cross-section looks like a series of chain links. Each corallite held a single coral polyp (an individual) that collected zooplankton for food. The spaces between the ranks — the empty holes — are called lacunae.
A closer view of the halysitid corallum. This specimen is replaced with silica so the surrounding limestone matrix could be removed by dissolving it in hydrochloric acid.
Halysites lived only in the Ordovician and Silurian (about 480 to 420 million years ago), so it is a rough index fossil for these periods. They were especially common in coral reefs, adding stability because their lacunae filled with sediment making them very difficult to dislodge by currents.
Thin-section of a halysitid coral with limestone matrix still in the star-shaped lacunae.
Motus, M.-A. and Klaamann, E. 1999. The halysitid coral genera Halysites and Cystihalysites from Gotland, Sweden. GFF 121: 81-90.