Mark Wilson June 30th, 2011
KURESSAARE, ESTONIA–We have gotten to know the western coastline of Saaremaa very well and would like to simply share some of the gorgeous flowers found there. All of these grow in alvars, which are environments on limestone bedrock with thin and nutrient poor soils. They often dry out completely in the summer, so they tend to host endemic species well adapted to these specific conditions and generally out-competed elsewhere.
Saaremaa is especially blessed with plant diversity. There are 1200 species of vascular plants on the island, about 80% of all the vascular plant species in Estonia. About 10% of these species are rare and protected
I don’t have any identifications for these flowers. They are here for their beauty and as a break from all the rocks!
Mark Wilson June 29th, 2011
Like a lonely little onion in a petunia patch, a boulder of red granite sits on the cobblestone beach off Soeginina Cliff, western Saaremaa, Estonia.
KURESSAARE, ESTONIA–Hard-rock geologists sometimes complain that I flood this blog with too many sedimentary rocks and fossils (and just wait until I get to the Estonian wildflowers!). There are actually quite a few igneous and metamorphic rocks on Estonia — just like there are in Ohio — in the Pleistocene glacial till. They show up well on the beaches here in contrast to the sedimentary rocks around them.
A closer view of the above rock, just to show it really is granite.
Granite in action! A granitic vein through some unfortunate rock.
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 29th, 2011
KURESSAARE, ESTONIA–A very common perennial plant at the foot of the cliffs we are studying in Estonia is Sea Kale (Crambe maritima Linnaeus). It is beautiful with large, thick leaves and central stalks with bursts of white flowers, each with a purplish throat and yellow pistil. Turns out there is a bit of geological context and history of this edible plant in Western Europe.
Sea kale lives in a place where few other plants can survive. Shingle and cobblestone beaches have very little soil and are usually saturated at depth with brackish water from rain mixed with seawater. If the cobbles are mostly calcareous, as they are on Saaremaa, nutrient levels are low. Sea kale does well in this place because it is halophytic (tolerant of higher salinity than most terrestrial plants) and can collect enough nutrients because it has so few competitors. Its seeds float and so the plant can disperse via coastal sea currents. It is pollinated by numerous species of flies, beetles and bees, so it has no dependence on a particular pollen vector.
Sea kale was a popular vegetable in Europe during the 19th Century and before, but it fell out of favor as more easily cultivated plants became marketable. The new geological angle on sea kale is its ability to grow nutritious tissues in salty water. As freshwater resources become more scarce, biologists are looking at more ways to cultivate sea kale in marginal marine environments, and geologists are helping identify and preserve limestone shingle and cobble beaches for its continued growth. One of those places is Vilsandi National Park in western Saaremaa where we’ve been working this week.
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 May 1st, 2011
The fossils above are about as simple as fossils can be. They are internal molds (sediment-fills) of conical shells that were made of the carbonate mineral aragonite. The aragonite shells dissolved away after death and burial, leaving the cemented sediment behind. While not complex, these fossils have historic value in paleontology. They represent an extinct group called hyoliths, and they were found where the very first hyoliths were described by Eichwald in 1840: the Middle Ordovician of Estonia. I collected them on my first field trip to the Baltic States in 2006. (My original interest in picking them up, by the way, was in the faint squiggles on the outside of the molds — a trace fossil known as Arachnostega.)
Hyoliths are rather common in some rock sequences. They are among the earliest shelly fossils known, found in the lowest Cambrian rocks (about 540 million years old). They peaked in abundance in the Cambrian and lived throughout the Paleozoic Era, finally going extinct at the end of the Permian Period (around 250 million years ago).
Reconstruction of a living hyolith (by "Smokeybjb" via Wikipedia).
For as many hyolith fossils we have, they remain an enigmatic group. They had conical shells, usually a bit flattened, with a hinged lid (operculum) over the open end. Extending from the space between the operculum and cone were two calcareous rods called helens (a name deliberately chosen so as not to evoke a particular function). Some rare hyolith fossils show evidence of internal features, including muscle scars and a twisted intestinal tract. We still can’t definitely place them in a particular animal group, though, and even their life habits are obscure. They probably were deposit-feeders (digesting organic material from seafloor mud), but the support for this is speculative.
The hyoliths of Estonia tell us one more thing: they are different enough from other hyoliths around the world to show us that the paleocontinent of Baltica likely had its own biogeographic province. In other words, Baltica was isolated as an island continent during the Middle Ordovician (around 460 million years ago), much like Australia today.
Baltica is the small green continent shown on this global reconstruction of the Cambrian (public domain from Wikipedia).
Mark Wilson January 16th, 2011
Fossils don’t get much more spherical than Echinosphaerites aurantium, an extinct creature common in the Early and Middle Ordovician of North America and Europe. These are cystoids, a somewhat informal category of filter-feeding, stalked echinoderms that are relatives of the better known crinoids. My students and I found bucketloads of them in the oil shales of the Baltic country Estonia three years ago. They are like stony golf balls.
A typical cystoid has a sac-like theca forming the bulk of the body. This theca is made of dozens to hundreds of plates of the mineral calcite fitted together like tiles. On one end of the theca is a small stem to attach it to the substrate; the other end has short brachioles, which are filter-feeding arms surrounding a tiny mouth at their base. An anus is present on the side, distinguished by a circlet of special plates.
If you look carefully at the specimen on the left in the above illustration, you’ll see at least two sclerobionts (hard-substrate dwellers) attached to the theca. The black branching form is a graptolite (like our last Fossil of the Week) called Thallograptus sphaericola (the species name means “sphere dweller”) and the raised disk is a bryozoan.
Every once in awhile the cystoids in Estonia were buried quickly and did not fill with sediment. The hollow space within became a kind of geode with crystals of calcite growing from the thecal plates inward. Each plate is a single crystal of calcite, so the crystals grew syntaxially (maintaining crystallographic continuity). These specimens are spectacular if broken open carefully so they don’t shatter into a thousand sparkles.