Saaremaa Silurian stromatolites studied

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!

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Thriving in the shingle: the story of Sea Kale

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.

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Independent Study fieldwork begins in Estonia … with a little unexpected canine companionship

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!

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An intricate Silurian stromatoporoid reef on the island of Saaremaa, Estonia

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.

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A new Senior Independent Study project begins in Estonia

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.

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Wooster’s Fossils of the Week: Tiny little oysters (Lower Paleocene of Mississippi)

This week’s fossils are by no means rare — last year Megan Innis and I picked up dozens of them at a muddy outcrop near Starkville, Mississippi, on our Cretaceous-Paleogene boundary expedition (click “Alabama” and “Mississippi” in the tags to the right for entries from that trip). They are, though, significant indicators of a particular kind of ecological system that appeared in the oceans of southeastern North America after the cataclysm of the Cretaceous Extinction.

The specimens pictured above are Pycnodonte pulaskiensis, a local species of oyster that belongs to a very prolific genus found around the world. Pycnodonte ranges from the Lower Cretaceous (about 140 million years ago) to, it appears, today. Kase and Hayami (1992) appear to have found this oyster — or a close relative — still living in submarine caves near Japan. This makes them a kind of “living fossil”, a group with a very long history of evolutionary stability.

This longevity fits into our Pycnodonte pulaskiensis story. These fossils are very common in the lowest Paleocene sediments just above the extinction horizon that marks the fiery end of the Cretaceous. After all that devastation (and Alabama was uncomfortably close to the impact site of Chicxulub), P. pulaskiensis appeared first to reoccupy the seafloor muds. They were virtually alone in this muddy habitat, and so lived there in great numbers. We call this kind of early successional species an “opportunist” (in the good sense!) taking advantage of a recently emptied niche.

Our little oysters in the Clayton Formation near Starkville, Mississippi.

Paul Taylor, Megan Innis and George Phillips at the Cretaceous-Paleogene boundary near Starkville, Mississippi in May 2010. Our oysters were found directly below Megan's feet.

These little oysters weren’t entirely alone, though. Many of them have small beveled holes in the center of their left valves, producing the ichnofossil Oichnus. These are apparently the traces of naticid gastropod predators (see Dietl, 2003) that drilled the holes to kill and eat the oyster soft parts.  (And who can blame them?) Several shells also have encrusting foraminiferans like Bullopora and Ramulina. Small hints of a recovering ecosystem setting the stage for the modern fauna we see in the northern Gulf of Mexico today.

References:

Dietl, G.P., 2003. Traces of naticid predation on the gryphaeid oyster Pycnodonte dissimilaris: Epifaunal drilling of prey in the Paleocene. Historical Biology 16: 13-19.

Kase, T. and Hayami, I., 1992. Unique submarine cave mollusc fauna: composition, origin and adaptation. Journal of Molluscan Studies 58: 446-449.

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Wooster Geologists return to Estonia

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!

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A geological and historical tour of the Polish Jura

SOSNOWIEC, POLAND–A most memorable day traveling through part of the Polish Jura with Michał Zatoń and his delightful family of his wife Aneta and son Tomasz (4 and a half years old). The Polish Jura, also known as the Kraków-Częstochowa Upland, is a long exposure of Upper Jurassic (Oxfordian) limestones in southwestern Poland. We saw a bit of the rock yesterday — a hard white carbonate with a core of lithistid sponge mounds. The area is deeply eroded by karstic processes and so has vertical cliffs, pillars of limestone, sinkholes and caves. Since at least the 14th Century there have been stone fortifications (called “Eagles’ Nests”)  built on these rocks overlooking the deep valleys and access to inner Poland. One of these is the Castle of Pieskowa Skała shown above.

Michał Zatoń showing how the Jurassic limestones are used to effectively lengthen and strengthen the castle walls at Pieskowa Skała. When bedrock is used like this it is called evocatively “living stone”. A similar use of living stone was recorded in this blog two years ago from Jerusalem.

A large karstic pillar called Hercules’ Club near the Castle at Pieskowa Skała. It is juxtaposed with the castle most dramatically when viewed from down in the valley and is included in almost every early drawing or painting of the castle.

Another one of the Eagles’ Nests is Ojców Castle built in the second half of the 14th century by King Kazimierz the Great commemorating the exile and hiding in the area of his father Władysław Lokietek (called “The Elbow-High” because of his stature). The cliffs give this castle (now in ruins) an excellent view of the valley below.

The 14th Century King Władysław Lokietek mentioned above hid from his rivals in this karstic terrain. There is a legend that he took refuge in this particular cave now called “Grota Lokietka”. It is a good excuse to develop the cave into a tourist attraction. We walked through the slippery, dark and cold passages and chambers with a large crowd of enthusiastic Poles examining cave structures and listening to tales of cryptic royalty.

The third castle of the day is not in the Polish Jura, but I’ve included it for completion. It is Będzin Castle in Będzin, a small city next to Sosnowiec and the home of Michał and his family. It too was built in the second half of the 14th Century and obviously took advantage of the local geology, in this case exposures of Triassic limestones. More on the tragic history of Będzin in a later post. We had a very interesting, informative and touching tour of the city center near the end of the day.

I again want to thank my Polish paleontologist host, colleague and friend Michał Zatoń for arranging a wonderful and productive visit. I shall return with Wooster students someday soon. I am certain they will enjoy their visit and work here as much as I have.

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A delightful day in the Jurassic of Polish Silesia

SOSNOWIEC, POLAND–It could not have been a better day for field work: warm with a light, cooling breeze and plenty of leafy green shade. Our team consisted of me and three Polish scientists: Michał Zatoń and Wojciech Krawczyński (I work hard to get those special Polish letters in there!) of the University of Silesia, and PhD student Tomasz Borszcz of the Institute of Oceanology in Sopot, Poland (near the famed city of Gdansk on the Polish Baltic coast). Our goal was to simply see some Jurassic rocks and fossils and talk geology. Mission accomplished.

The top image shows outcrops of remarkable lithistid sponge mounds from the Oxfordian (earliest Upper Jurassic) punching up through the forest cover a few kilometers northeast of Sosnowiec. They formed relatively deep on the Jurassic seafloor and supported an associated brachiopod community.

I was able to visit for the first time one of the localities from which large Middle Jurassic oncoids (cobbles and pebbles covered with the deposits of microbial biofilms) were found and became the basis for a paper co-authored with Michał and Wojciech. In the picture above of a broken cobble you will notice bivalve borings (Gastrochaenolites) penetrating from the outside.

Lunch was in a tavern near the town square of Sławków in the Silesian Highlands. The Polish custom of carving the date of the building on the central roof beam meant we could see right away it was constructed in 1701. (It seems to be preserved in a modern shell of some kind.) I had a typical Silesian meal of rolled beef and dumplings (I think).

A view of the Silesian Highlands from a street in Sławków. This small city is the western terminus of the Broad Gauge Metallurgy Line, a rail system designed “in communist times” to transport iron ore from Ukraine to iron smelters in Poland. The rail gauge in Ukraine and points east is wider than the standard gauge in western Europe.

Our last stop of the day was to a set of deep holes in the middle of a forest. Amateur fossil collectors dug through about two meters of soil and Pleistocene sediment to expose a layer of Callovian (latest Middle Jurassic) rock rich in ammonites, belemnites and other fossils. The three paleontologists, in typical paleontological poses, are from the right Wojciech, Michał and Tomasz.

 

 

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Quality time with a Polish microscope

SOSNOWIEC, POLAND–A day in the lab with my colleague Michał Zatoń at the University of Silesia. We sorted through two very different paleontological problems with a microscope and a lot of hand waving. The first task was to come up with a hypothesis about the origin of the strange pitted tubes shown above. They are found on hiatus concretions of the Late Bathonian (Middle Jurassic) exposed in Zarki, Poland. We recently described and analyzed the sclerobionts on and in these concretions (see Zaton et al., 2011), but these tubes remained a mystery. We think now that they are remnants of egg cases laid by gastropods (snails) on the undersurfaces of the concretions, and we’ve started on the manuscript.

The coiled encrusting shell below is of a Devonian microconchid originally collected by the keen amateur Brian Bade in western New York and generously donated to our research. This group has some fascinating similarities and differences from its Polish cousins, so we have started a systematic project to determine if they represent a new genus or not. (Brian will be excited to hear this.)

Michal's office/lab in the Faculty of Earth Sciences, University of Silesia.

Tomorrow we set off for fieldwork in the area so I’ll post pictures of the wonderful Polish countryside!

Reference:

Zatoń, M., Machocka, S., Wilson, M.A., Marynowski, L. and Taylor, P.D. 2011. Origin and paleoecology of Middle Jurassic hiatus concretions from Poland. Facies 57: 275-300.

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