Wooster Geologists in Sweden

Mark Wilson July 11, 2011 11:23 am

STOCKHOLM, SWEDEN–I had not realized how much water is in the city of Stockholm. Almost a third of the city’s area is water because the center is built on 14 islands connected by bridges and ferries. “The Venice of the North” some call it.

Rachel, Nick and I are here for a very short visit. We’ll spend tomorrow in the Naturhistoriska Riksmuseet (Royal Museum of Natural History), so for now we just explored the neighborhood around our hotel. It is called Östermalm and is one of the older parts of Stockholm.

The Nordiska museet (Nordic Museum) has a glorious array of building stones, all from Sweden. The simple blocks are sandstones and fine-grained metamorphic rocks, and the carved pieces are limestones.

The local bedrock is 1750-1900 million years old, formed during the Svecofennian (Svecokarelian) orogeny. The outcrops I saw, like this example of “living stone” at the base of a building, are metavolcanics (metamorphosed volcanic rocks, usually basalt). Apparently the bedrock of Stockholm is an engineering geologist’s dream because of its stability, moisture repelling capabilities, and uniform strength — great for bridge abutments and subway tunnels.

I spent my Stockholm afternoon in the museums found in an easy walk around our hotel. I was impressed with the Viking runestones on display in the Historiska muséet (History Museum), and I was touched by this one. The runes are translated as: “Una/Unna had this stone raised in memory of her son Eysteinn who died in christening robes. May God help his soul.” They are carved in a glacial granite boulder, the kind of rock we saw scattered across the Estonian western islands. Note the dark xenoliths.

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A Day in Tallinn, Estonia

Mark Wilson July 10, 2011 1:27 pm

TALLINN, ESTONIA–Like our Wooster Geology colleagues in Iceland, we also have a nearly-final day in a city. Tallinn is the capital of Estonia, the medieval town square of which is shown above. We started here briefly at the airport, and will leave from the same place early  tomorrow morning. The only difference is that we have one more big city to go: Stockholm, Sweden.

Tallinn, or at least a significant settlement in this place, goes back to the 11th Century, and before that there are Bronze Age artifacts. After the Danes conquered it in the 13th Century, it became known as Reval until the Estonian War of Independence in 1918-1920 when the Estonians could finally give it their own name: Tallinn (or Tallinna). It was a member of the Hanseatic League, being an important trade link between northern Europe and Russia. (And so the merchants in the town square are dressed in the Medieval garb of “Old Hansa”.) This year it is a European Capital of Culture. Tallinn does not sit on a major river but takes advantage of Ordovician limestone heights to raise it above the coastal swamps and bogs.

We enjoyed a day off in the city under (as you might have predicted) sunny skies. Tomorrow is another travel day, and then back to work one more time in Stockholm!

The newly renovated Freedom Square in Tallinn. The memorial is for the Estonian War of Independence (1918-1920).

Rachel and Nick can be barely made out here on the other side of Freedom Square.

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Wooster’s Fossil of the Week: Ancient shrimp burrows (Middle Jurassic of Israel)

Mark Wilson July 10, 2011 1:01 am

This week we have a trace fossil, the burrow Thalassinoides. It is represented by one of my favorite images, reproduced above, showing a very large Thalassinoides suevicus in the Zohar Formation (Middle Jurassic, Callovian) of Makhtesh Qatan in the Negev of southern Israel. Holding the scale is Wooster geologist and Independent Study student Allison Mione (’05) during our 2004 Israel expedition. These burrows were originally described as giant desiccation cracks, but I.S. student Kevin Wolfe (’05), Israeli geologist Yoav Avni and I reinterpreted them as burrows in a rocky shore complex (see Wilson et al., 2005).

Thalassinoides is a complex trace fossil that is today made primarily by thalassinidean crustaceans (a type of shrimp; see below). We know a lot about how the burrows are made today by shrimp, and our knowledge is growing about how the ancient systems were excavated, at least in the Mesozoic and later. We have fossil shrimp preserved in Thalassinoides from the Jurassic (Sellwood, 1971) and the Cretaceous (Carvalho et al., 2007).

Pestarella tyrrhena, a modern thalassinidean shrimp. Image from Wikipedia.

Reconstruction of Mecochirus rapax in a Cretaceous Thalassinoides. A) In its burrowing life mode; B) Predominantly horizontal Thalassinoides suevicus burrow systems showing two successive event levels, with Mecochirus in life position. From Carvalho et al. (2007, fig. 3).

The burrow systems in the Zohar Formation of Israel were critical in working out the depositional environment of these carbonate sediments. We could see that first the water was comparatively deep (below wavebase) with worm burrows (Planolites). Then relative sea level dropped and the Thalassinoides burrows cut through the Planolites fabric, showing that the sediment was become stiffer. Finally bivalve borings (Gastrochaenolites) in the same rock indicated that the sediment had cemented into a shallow water hardground. This hardground showed tidal channels cut into its top surface (Wilson et al., 2005).

This work was done with virtually no “body fossils”, meaning evidence of the actual bodies of the organisms living in and on the sediment. Trace fossils, evidence of organism activity, were the only indications of this significant environmental change. This is why the study of trace fossils (ichnology) should be a part of the education of every paleontologist and sedimentologist.

References:

Carvalho, C.N., Viegas, P.A. and Cachao, M. 2007. Thalassinoides and its producer: Populations of Mecochirus buried within their burrow systems, Boca Do Chapim Formation (Lower Cretaceous), Portugal. Palaios 22: 104-109.

Sellwood, B.W. 1971. A Thalassinoides burrow containing the crustacean Glyphaea undressieri (Meyer) from the Bathonian of Oxfordshire. Palaeontology 14: 589-591.

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171–178.

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A Day in Akureyri

mpollock July 9, 2011 1:37 pm

AKUREYRI, ICELAND – Since we finished Travis’ field work a day early, we were able to spend Friday in Akureyri, Iceland’s second-largest city. Akureyri has an idyllic location, nestled between a fjord and snow-capped mountains in north-central Iceland.

 

Snow-capped peaks make a scenic background for Akureyri.

Our first stop was at the Botanical Gardens, which hosted a surprising variety of plants, given Akureyri’s rugged climate. We saw some familiar flowers that reminded us of the field:

 

This yellow flower was common in our field areas (it's Icelandic name is Argentina egedii Skeljamura).

We saw this delicate purple flower often, too (Viola canina Tysfjola).

This sweet flower grew in the jagged spaces between rock piles (Silene uniflora Holurt).

There were other flowers that were more exotic:

 

The vivid blue petals of this Meconopsis grandis Fagurblasol were stunning.

And then there were flowers that were much too familiar:

 

A well-established specimen of our friend, the dandelion.

Next to the Botanical Gardens, we contemplated statues on the campus of Akureyri’s University.

 

Dr. Pollock interpreted this sculpture to mean that basalt is the foundation of the world.

Next, we admired the Akureyrarkirkja, a columnar basalt-themed church that was designed by the same architect who built Reykjavik’s famous Hallgrimskirkja.

 

The Akureyrarkirkja.

Finally, we visited the historic district for some food and shopping.

 

View of historic Akureyri. We highly recommend Cafe Paris, in the blue building on the right. The soup and bread is delicious!

 

 

 

Perhaps a little light reading for the trip home?

 

Lindsey and Dr. Pollock find hats for their next field experience.

A day in Akureyri was the perfect way to celebrate the successful end of two I.S. field projects. We happily headed back to our cabin in Blonduos, where we packed up for our journey back to Hafnarfjordur and started working on our GSA abstracts, which our Estonian colleagues have inspired.

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Return to Vatnsdalfjall

mpollock July 9, 2011 12:46 pm

BLONDUOS, ICELAND – Meagen and guest blogger, Travis

We returned to Vatnsdalfjall for the second day of field work on the Monocline. The weather was the best we’ve experienced in Iceland yet.

View of the steeply dipping Monocline as it dives under the Hjallin Lens.

After a long hike through fields of sadness (so named by a previous IS student), we finally made it to our first exposure. We found lots of interesting amygdules (filled vesicles):

Vesicles half-filled with chalcedony in horizontal layers suggests that the lavas were tilted before the chalcedony precipitated.

Zeolites come in a variety of habits, including these hair-like fibers that are about 1 cm long.

We sampled and made observations all of the way to the top of the Monocline. We were quite pleased with ourselves when we made it to the top, and slightly surprised to see that it was already 8 pm! In the land of the midnight sun, field work could last for 24 hours a day.

Lindsey and Travis getting ready to head down the mountain at 8 pm at night.

After such a hard day of work, we relaxed in the evening and made plans to visit Akureyri the next day.

Travis relaxes in the hot tub.

 

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Suur Strait (Moon Sound, Moonzund)

Mark Wilson July 9, 2011 12:38 pm

TALLINN, ESTONIA–The Wooster Geology team in Estonia successfully returned to the Estonian capital city of Tallinn today, which means we crossed by ferry the Suur Strait between the western Estonian islands (notably Muhu) and the Estonian mainland. This is an interesting strip of water with a complicated geological and human history.

There is an Estonian dream of building a bridge or digging a tunnel across the Suur Strait to eliminate the need for the ferry line and more efficiently connect Muhu and Saaremaa to the main part of Estonia. It will not be an easy task (and it is probably too expensive to ever be attempted), but it has led to considerable study of the strait and its oceanographic, biologic and geologic characteristics. The currents are complicated as they move between the Gulf of Riga to the south and the Baltic Sea proper in the north, and it freezes solid in the winter (when it is crossed by a 9 km long ice road). The strait hosts one of the most significant bird migration routes in northern Europe, and the marine fauna and flora here is still poorly surveyed.

The floor of the Suur Strait is highly variable from exposed Silurian limestone bedrock to thick mantles of glacial till. As you can deduce from the Google Earth image, some parts of the strait are very shallow, and the deepest regions are no more than 21 meters of water. Because of isostatic rebound, the region gets shallower about 2 mm per year as the land rises.

Suur Strait as viewed from northeastern Muhu (July 2007).

Historically, the Suur Strait has been the “backdoor” to the Gulf of Riga to the south. Any navy that controls the Baltic wants to keep that backdoor open for itself, but close it to enemies. This was especially the case during World War I when the Imperial German Navy sought to trap elements of the Imperial Russian Baltic Fleet in the Gulf on October 17, 1917, during Operation Albion. Most escaped north through the Suur Strait (known then in English as Moon Sound) following carefully dredged channels lined with mines. One Russian battleship, the Slava, was severely damaged and took on too much water to pass back through the shallow strait and was scuttled.

The Suur Strait was crossed by the Germans in 1941 as they invaded the western Estonian islands (Operation Beowulf), and again by the Russians when they re-invaded in 1944 (Moonzund Landing Operation).

We made it across on one of the car ferries which ply the Suur Strait between Kuivastu and Virtsu. Like the Russian warships of old, it also follows a dredged channel through the shallow and storied waters.

View from our ferry west across the Suur Strait towards Kuivastu on Muhu island. Last ferry ride of the trip!

Reference:

Saaremaa Fixed Link – Report of Preliminary Environmental Impact Assessment – Final Draft – 15.07.2005 (Google this and you can get a thorough report as a pdf.)

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A visit to Kaali Crater for our last day on Saaremaa

Mark Wilson July 8, 2011 9:59 am

KURESSAARE, ESTONIA–A dramatic geological site on our last Saaremaa day: the meteorite craters at Kaali. We hiked around the largest crater (shown above) and then visited one of the smaller subsidiary craters nearby (shown below). The main Kaali crater is 110 meters in diameter and about 22 meters deep. The meteorite was between 20 to 80 metric tonnes and was traveling 10-20 km/s. It broke up into pieces 5-10 km above the ground before the multiple impacts. The date of this event is disputed. We have seen ranges in the literature from 4000 to 2700 years ago. Some archaeologists have evidence that an ecological catastrophe followed the impacts with massive wildfires and a drop in crop production for a century. Others think there is a connection between the Kaali event and Baltic mythology. (I think it is a delightful coincidence that the Estonian place name “Kaali” used for this fiery event is coincidentally the same name as the fearsome Hindu goddess.)

To our surprise, the Kaali Museum had a thorough display on the geology of Saaremaa, including this polished cross-section through Nick’s critical Wenlock/Ludlow section.

Our last stop was a virtually abandoned little harbor at Turja on the southeastern coast of the island. It was a nice place for lunch as we contemplated how our fieldwork did not include bears and wolverines (as with our Wooster colleagues in Alaska) or gale-force winds and thick fogs (as experienced by our Iceland friends). We were quite fortunate to gather such excellent geological data with so few such adventures!

Tomorrow we drive to Tallinn to spend a day and a half, and then to Stockholm for a day in the Natural History Museum looking at comparative Silurian material. On Wednesday of next week we fly home.

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Paleoecology of the Hilliste Formation (Lower Silurian, Llandovery, Rhuddanian) Hiiumaa Island, Estonia: An example of a shallow marine recovery fauna — An abstract submitted to the Geological Society of America for the 2011 annual meeting

Mark Wilson July 7, 2011 2:24 pm

KURESSAARE, ESTONIA–Editor’s note: The Wooster Geologists in Estonia found enough material, and had enough time, to write abstracts for posters at the Geological Society of America Annual Meeting in Minneapolis this October. The following is from student guest blogger Rachel Matt in the format required for GSA abstracts:

PALEOECOLOGY OF THE HILLISTE FORMATION (LOWER SILURIAN, LLANDOVERY, RHUDDANIAN) HIIUMAA ISLAND, ESTONIA: AN EXAMPLE OF A SHALLOW MARINE RECOVERY FAUNA

MATT, Rachel M., WILSON, Mark A., FEDORCHUK, Nicholas D., Dept of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691-2363, VINN, Olev, Dept of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia

The Hilliste Formation (Lower Silurian, Llandovery series and Rhuddanian stage) is well exposed in a quarry in western Estonia. During the deposition of this unit, Estonia was part of the paleocontinent Baltica, which was located near the equator. The Hilliste Formation thus records the recovery of tropical invertebrate marine communities following the mass extinction at the end of the Ordovician. Globally, pre-extinction levels of marine diversity were not met until the Wenlock, about 15 million years after the end of the Ordovician; this formation was deposited about three million years following the event. The Hilliste Formation contains a diverse fauna including brachiopods (orthids, atrypids, rhynchonellids, pentamerids, and strophomenids), corals (favositids, halysitids, heliolitids and rugosans), stromatoporoids, bryozoans, gastropods, crinoids, ostracodes and trilobites. We measured, described and sampled the Hilliste Formation at Hilliste Quarry on Hiiumaa Island, western Estonia. The unit records a regression from depths between normal and storm wavebase to depths at or above normal wavebase. The evidence for this paleoenvironmental interpretation includes more argillaceous beds in the bottom two-thirds of the formation and more biosparite/grainstone upwards. The top third of the formation consists of massive biosparite/grainstone with little clay and overturned and fragmented corals and stromatoporoids indicating high depositional energy. The fauna changes stratigraphically upwards from one dominated by brachiopods and gastropods to a community primarily of corals, stromatoporoids and crinoids. This fauna provides additional information about biotic recovery in eastern Baltica and its implications for the migration of Early Silurian Baltic taxa into other regions.

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Stratigraphy and paleoecology at the Wenlock/Ludlow boundary on Saaremaa Island, Estonia — An abstract submitted to the Geological Society of America for the 2011 annual meeting

Mark Wilson July 7, 2011 2:15 pm

KURESSAARE, ESTONIA–Editor’s note: The Wooster Geologists in Estonia found enough material, and had enough time, to write abstracts for posters at the Geological Society of America Annual Meeting in Minneapolis this October. The following is from student guest blogger Nick Fedorchuk in the format required for GSA abstracts:

STRATIGRAPHY AND PALEOECOLOGY AT THE WENLOCK/LUDLOW BOUNDARY ON SAAREMAA ISLAND, ESTONIA

FEDORCHUK, Nicholas D., WILSON, Mark A., MATT, Rachel M., Dept of Geology, The College of Wooster, 944 College Mall, Wooster, OH 44691-2363, VINN, Olev, Dept of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia

The boundary between the Wenlock Series and the Ludlow Series can be easily observed on the island of Saaremaa in western Estonia. Here, the boundary is distinguished by a major disconformity that can be correlated to a regional regression described in several previous studies. During this time, western Saaremaa was a lagoonal facies that reflected sea-level changes within the Baltic Basin. We measured and described this Wenlock-Ludlow boundary interval at Soeginina Cliff on the western shore of Saaremaa. Here this boundary consists of the Vesiku Beds of the Rootsiküla Formation (Wenlock) overlain by the Soeginina Beds of the Paadla Formation (Ludlow). The Vesiku Beds (Wenlock) record a carbonate lagoonal environment with finely laminated beds and Thalassinoides burrows (indicating oxygenated bottom conditions). The fauna is much less diverse than that in normal marine sediments of the Wenlock. The top surface of these beds (the primary discontinuity surface) shows a microtopography and dissolution consistent with exposure and abrasion. The top 20 centimeters also show diagenetic alteration of the laminated sediments, probably from fluids traveling through the Thalassinoides burrow systems. The Soeginina Beds (Ludlow) show pulsating transgressive sediments with multiple discontinuity surfaces. Large oncoids are common in these beds. They have distinctive shapes because they were initially spherical and later stabilized and grew like small stromatolites upwards. These forms may indicate periodic energy reductions in these transgressive waters. There are also storm beds with biogenic debris including oncoids nucleated on gastropods. This boundary interval is topped by thin dolomites and stromatolites. This example of the Wenlock-Ludlow boundary can be correlated with other such disconformities recorded in a variety of depositional environments, such as in the equivalent reef complexes of Gotland, Sweden.

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Inside a secret Soviet missile base — 20 years later

Mark Wilson July 7, 2011 1:52 pm

KURESSAARE, ESTONIA–When I was growing up the Soviet Union was simply an unchangeable fact of life. The United States had an implacable enemy, and we were locked in a struggle that would last my lifetime, at least. That lifetime was almost certainly going to be short, of course, because sooner or later someone would push the nuclear button and, in the words of the Kingston Trio, “… we will all be blown away”.

Thus it is very much an existential treat to have lived into my sixth decade and be able to walk through the remains of a secret Soviet missile base to get to the Suuriku Cliff locality this morning. The Evil Empire collapsed, the Baltic States were liberated, and massive overgrown concrete bunkers stand as evidence of a nearly unimaginable past only 20 years old. I am privileged as a geologist to be able to travel to such places and feel the turning points of history.

While constructing this Google Earth image of Tagalaht Bay to show the location of this Soviet base (one of dozens on the island, by the way), I saw something cool in the south: ancient shorelines. Saaremaa, like most of the Baltic region, is experiencing post-glacial isostatic rebound. The land is rising at least 2 mm per year (and in some places much more), so the sea is retreating. These shorelines are only a few thousand years old.

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