Tunnels (again)

August 9th, 2010

MAASTRICHT, THE NETHERLANDS–After mentioning the excavations in the Maastricht Formation limestones (latest Cretaceous) in the last post, I expected to be moving on the next day to a quarry. I hadn’t read the guidebook closely enough: we were planning to spend the afternoon in them! Thinking of my last geology-in-tunnels experience in Russia, I was a bit apprehensive. This time, though, the tunnels were relatively dry, much wider and taller (no sliding on your belly for 30 feet!), and far more stable.

A portion of the tunnel map painted on a wall near the entrance.

The tunnels under Maastricht are incredibly complex, the product of hundreds of years of mining. The walls often show charcoal drawings of amazing complexity, some dating back to the 17th Century. On our particular route was a Roman Catholic chapel fashioned out of a few galleries by painting the rock walls, adding statuary and carving a pulpit. It was a refuge for the Catholic community when revolutionary French soldiers took over the town at the end of the 18th Century.

Our tour had a geological purpose. We saw, in three dimensions, what may be the most complete Cretaceous-Paleogene boundary known. I learned a great deal about the end-Cretaceous extinction event, especially that the story is getting more complex and surprising. More on that in a later post.

Geology and Art History

August 9th, 2010

Tunnels in the Maastrichtian Formation (Late Cretaceous) in Maastricht, The Netherlands. Location = N50.82667°, E5.67978°.

MAASTRICHT, THE NETHERLANDS–The tunnels dug into the soft Maastrichtian Formation limestones in this city have a long history starting with the Romans. At first the excavations were intended only to extract building stone, but with all the battles, sieges and other military actions in this region, residents realized that these dry and deep caves also provided places of refuge. Bakeries, chapels, storehouses and dormitories were constructed in these spaces for times of war since the Middle Ages.

During World War II, the Dutch hid several works of art in these tunnels to protect them from the Germans. These included the magnificent Night Watch by Rembrandt and The Street by Vermeer. They were guarded by Dutch military police successfully throughout the occupation. We can view this art today because of the extent, thickness and composition of this Cretaceous limestone sequence — and the courage of Dutch patriots.

Rembrandt's The Night Watch (from Wikipedia).

Wooster Geologist in The Netherlands

August 8th, 2010

An outcrop of the Type Maastrichtian in Maastricht, The Netherlands. The square tunnels were dug in the Middle Ages for building stone. The rock is a limestone.

MAASTRICHT, THE NETHERLANDS–This is the first day of the International Bryozoology Association post-conference field trip. We took a train south from Kiel to Hamburg, Germany, and then connected with another train to Cologne. After spending a half-hour at the Cologne Cathedral (right next door to the train station), we took a bus west to Maastricht, The Netherlands, on the Maas River. We then spent the rest of the day in the ENCI cement quarry exploring the very fossiliferous Maastricht Formation, which is the type section of the Maastrichtian Stage described yesterday.

One of my favorite fossils in the Maastricht quarry. This is an external mold of an aragonitic shell in which the borings were filled with calcitic sediment. The result is a set of casts of the original borings.

Wooster geologist in New Zealand!

July 13th, 2010

CHRISTCHURCH, NEW ZEALAND–And it’s not me! Wooster geology student Andrew Collins is in a study abroad program on the South Island of New Zealand.  He has promised to share with us his geological experiences now and then. Andrew recently traveled to a town called Springfield near Christchurch and visited some amazing Paleogene limestone exposures on Castle Hill. This is an extreme example of karstic weathering.

Paleogene limestone on Castle Hill, South Island, New Zealand. Photograph by Andrew Collins.

Beautiful, eh? Andrew will share more New Zealand geology with us through this blog and his own.

This summer we’ve had Wooster geologists in Alaska, the southern USA, Ohio, Israel, Iceland and Utah … and we’re only halfway through our field season. Gotta love it!

Wooster Geologist in Ohio!

December 16th, 2009

CAESAR CREEK STATE PARK, OHIO–I’ve definitely extended my field season as far as possible.  (And what a season it has been.)  My last fieldwork at the end of this research leave was in Ohio, about three hours south of Wooster.  I visited Caesar Creek State Park this morning where a large cut through an Upper Ordovician section has been set aside as a fossil preserve of sorts.  It is an emergency spillway for Caesar Creek Lake, which is maintained by the US Army Corps of Engineers.  Many Wooster paleontology field trips have stopped here.  Fossils can be collected, but only with a permit (obtained at the visitor center) and following significant regulations.  The fossils are diverse and abundant, including all the stars of the Ordovician seafloor.

My task was to find, photograph and measure an old trace fossil friend: the boring Petroxestes pera.  This is a slot-shaped excavation in carbonate hard substrates formed by bivalves (probably in this case the modiomorphid Corallidomus).

The boring Petroxestes pera (the name means "purse-shaped rock-grinding") in a hardground at Caesar Creek State Park.

The boring Petroxestes pera (the name means "purse-shaped rock-grinding") in a hardground at Caesar Creek State Park.

These elongated holes are among the first bivalve borings.  Some of my students and I think they may have been formed in clusters, and they also may be oriented relative to each other and their local environment.  In any case, I found plenty.  It was an astonishingly cold morning, though, so I didn’t waste any time on the outcrop!

Yes, this photo is here mainly to show just how tough Wooster Geologists are.  And there are some very nice brachiopods and bryozoans!

Yes, this photo is here mainly to show just how tough Wooster Geologists are. And there are some very nice brachiopods and bryozoans!

Mysterious out-of-place rocks in the Ordovician of Kentucky

December 15th, 2009

MAYSVILLE, KENTUCKY–Our short geological expedition to northern Kentucky today was to look at some odd blocks of limestone that sit suspended in the sediments as if they were dropped in while the sequence was accumulating.

An eroded, bored and encrusted limestone block in the Fairview Formation (Upper Ordovician) of northern Kentucky at the Route 11 outcrop (N38.61243°, W83.75575°).

An eroded, bored and encrusted limestone block in the Fairview Formation (Upper Ordovician) of northern Kentucky at the Route 11 outcrop (N38.61243°, W83.75575°).

These rocks are bored by worms and encrusted by bryozoans on their top and sides, and they often sit at high angles to the surrounding strata.

Bryozoans encrusting a side of the block above. The beautiful pinkish bryozoan on the left is the holdfast of a ptilodictyoid which in life held an erect bifoliate portion of the colony. The field of view here is about 10 cm wide.

Bryozoans encrusting a side of the block above. The beautiful pinkish bryozoan on the left is the holdfast of a ptilodictyoid which in life held an erect bifoliate portion of the colony. The field of view here is about 10 cm wide.

It is difficult to imagine a mechanism which deposited large, lithified limestone blocks in the middle of a shallow carbonate ramp. They are almost certainly related to “seismite” structures in the outcrop (see next post), but how these earthquakes would have transported such rocks is a mystery.  We also do not know how quickly the limestone had been lithified before emplacement.  We do know that the sides of these blocks were exposed on the seafloor long enough to accumulate encrusters and borers.

Plenty yet to discover in these well-studied rocks.  It is a continuing lesson for scientists: the more you see the more questions you have.

Wooster Geologist in Kentucky

December 15th, 2009

MAYSVILLE, KENTUCKY–Today I visited the University of Cincinnati for a meeting of Aaron House’s thesis committee, on which I serve.  (Aaron is a 2004 geology graduate from The College of Wooster.)  It all went very well and soon after Aaron took me and two other geologists on a short field trip to an Upper Ordovician outcrop near the Ohio River town of Maysville.

Outcrop of the upper Fairview Formation (Upper Ordovician) on Kentucky Route 11 near Maysville, Kentucky (N38.61243°, W83.75575°).

Outcrop of the upper Fairview Formation (Upper Ordovician) on Kentucky Route 11 near Maysville, Kentucky (N38.61243°, W83.75575°). A distant Aaron House for scale.

Many Wooster students and alumni will immediately recognize all the elements of a typical roadside outcrop of the Cincinnatian Group in winter: gray rocks matching the gray sky, the muddy ditch at the base, and the thin verge of grass extending to the road.  Alternating limestones, siltstones and shales give the outcrop its jagged appearance.

Some of the best Ordovician fossils in the world are found in these sedimentary sequences, and the stratigraphy holds many mysteries despite over a century and a half of intensive study by geologists.  Wooster students have completed dozens of Independent Study theses with these rocks, and there are many more to come.  Aaron House is now pursuing a masters degree by assessing and interpreting the preservation of mollusk fossils in the Cincinnatian.

A full geological circle

July 8th, 2009

View from a room in the St. Barbara Hotel, downtown Tallinn, Estonia.

View from my room in the St. Barbara Hotel, downtown Tallinn, Estonia (N59.431802°, E24.743355°).

The Wooster Geology Estonia team is now safely in Tallinn preparing for our visit to the paleontological collections in the university museum tomorrow. For me a private joy is that our hotel building is made of Ordovician limestone, the very same stone that I studied a month ago in Russia.

Goal!

June 8th, 2009

BABINO, LENINGRAD REGION, RUSSIA–Today we visited an active quarry, which is a different experience from the riverbank exposures and abandoned quarries we have been frequenting.  Quarry mud has a special character — a kind of purified mud, the kind of mud all mud aspires to be.  There are also very large trucks splashing by, giant rock saws whining, cranes lifting large blocks, and small groups of curious workmen who want to see what we are doing there with our hammers that now seem so small.  Active quarries can produce the very best exposures for geologists, especially those interested in the boundaries between rock units as we are.  This quarry at Babino N60.03035°, E32.38613°) is particularly good because they quarry Ordovician limestone by first cutting it vertically, and then lifting the rocks away in sections, revealing smooth surfaces perpendicular to bedding.

Cut surface through Ordovician section, Babino Quarry.

Cut surface through Ordovician section, Babino Quarry.

I want most to see the boundary between the Lower and Middle Ordovician rocks, and look at the trace fossils above and below it.  This boundary — a plane in the rocks which extends across northeastern Russia, Scandinavia, and parts of northern Europe — could not be better displayed than the way we saw it here.  It is an erosional surface which has been cemented into a carbonate hardground and then bored (to some extent that we are debating) and abraded smooth.  Above it is a significant change in the fossil fauna, a change which can be seen around the world.  In no place is this boundary better presented to geologists than here.

Lower/Middle Ordovician boundary in the Babino Quarry.

Lower/Middle Ordovician boundary in the Babino Quarry.

The trace fossils along this boundary are complex and may show both boring and burrowing behavior.  The distinction depends on when the sediments were soft, firm and cemented, and on the varieties of organisms which did the work.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

Borings in the Lower/Middle Ordovician boundary at Babino Quarry.

I can’t take these specimens home for further examination.  I’d very much like to make thin-sections (slices of rock shaved down until almost transparent for microscopic analysis) of all the critical intersections, but that will have to wait.  Andrey collected many samples he can cut up and share from his lab in Moscow.

Ordovician Hardgrounds

June 7th, 2009

SASS RIVER, LENINGRAD REGION, RUSSIA–The main geological attractions for me on this expedition are the abundant carbonate hardgrounds in the Lower and Middle Ordovician in this part of the world.  A carbonate hardground is a cemented seafloor.  What were soft sediments on the bottom were cemented with carbonate minerals (calcite in the Ordovician) so that they became a rocky surface several centimeters thick.  The sediment is usually carbonate mud and shells, so the result is essentially a limestone seafloor.  Many invertebrate animals colonize these hard surfaces by wither encrusting them or boring into them.  Those eocrinoids illustrated earlier, for example, often encrusted Early and Middle Ordovician hardgrounds.

Today at the Sass River Carbonate Mound locality (N60.02316°, E32.62471°) we saw numerous hardgrounds bored by a shallow variety of a trace fossil called Trypanites.

Borings in Ordovician hardground fragments.

Borings in Ordovician hardground fragments.

These are the most common borings in hardgrounds.  This particular type of Trypanites is remarkably shallow — often appearing as pits rather than the usual penetrating cylinder.  Another difference between these hardground fossil faunas and those I know best in North America and western Europe.

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