A very damp field trip

April 28th, 2012

FAIRBORN, OHIO–I actually used to brag about the great weather on my class field trips. The hubris! Today Shelley Judge and I took our combined Sedimentology & Stratigraphy and Structural Geology classes to Oakes Park Quarry near Dayton for a field trip. (Location = N39.81401°, W083.98374°.) We planned to describe and measure the exposure there of the Brassfield Formation, and then assess the joint fabric and the direction of glacial grooves on its top surface. I took three students there last week to test the concept. Since this is the last weekend of the semester, there was no do-over, so we went rain or shine.

It was 38°F and breezy when we arrived. That’s when I took my first and last picture, shown above. (It is of Tricia Hall and Scott Kugel in the middle of their stratigraphic task.) The rain came slowly at first. Not too bad. Then we heard the thunder and were quickly overwhelmed by a serious downpour. Near-freezing temperatures and a thunderstorm? That’s spring in Ohio. I haven’t been so cold and wet since I was in this place. This is why I very much prefer my field areas to be very warm and very dry.

The students were great sports, though, and we collected just enough data so that we could retreat to the bus with some geological honor intact.

The summer can’t come fast enough back here for the Wooster geologists!

Wet and Cold Wooster Geologists in the Silurian of Central Ohio

April 21st, 2012

DAYTON, OHIO–It was 37°F and raining this morning as three stalwart Wooster Geology students and I worked in a muddy quarry near Fairborn, Ohio (N 39.81472°, W 83.99471°). Our task was to scout out a beautiful exposure of the Brassfield Formation (Early Silurian, Llandovery) for a future field trip by the Sedimentology & Stratigraphy class. Until today this week was sunny and warm in Ohio. Nevertheless, our students persevered and efficiently measured and described the exposed units, and then they searched for glacial grooves and truncated corals on the top surface.

Abby, Steph and Lizzie during a relatively dry moment. The striped stick, by the way, is a Jacob’s Staff divided into tenths of meters. We use these large and simple rulers to measure the thickness of rock units. Our technician Matt Curren made us nice set of these this semester. Previous Wooster students may remember the long dowels we had in the past that Stephanie Jarvis discovered one day were not very precise! Why do we call them “Jacob’s Staffs”? Read Genesis 30:25-43. (This must be the first biblical reference in this blog!)

Dolomite at the base of the Brassfield with a pervasive fabric of burrows. These trace fossils were probably produced by shrimp-like arthropods tunneling in the seafloor sediments.

A well-sorted encrinite (limestone made almost entirely of crinoid skeletal fragments) from the lower third of the Brassfield Formation. These are mostly stem and arm pieces. The articulated portion on the left is a small stem.

A poorly-sorted encrinite. Here you can see a much greater range of bioclast size than in the previous image. There are also some brachiopod shell fragments mixed in.

The Brassfield Formation is a critical one in stratigraphy because most of the other Silurian carbonates in northeastern North America have been altered by dolomitization, which destroys the original fabric and texture of the rock. Fossils become mere ghosts in dolomitized limestone, but here they are superbly preserved.

It may have been a damp and chilly day, but how bad could it have been if we had limestones and fossils in it?

A windy, windy day in the Cretaceous

March 16th, 2012

MITZPE RAMON, ISRAEL–Melissa and I finished our work in the Jurassic of Makhtesh Gadol yesterday, so today we went out with Yoav to explore the Upper Cretaceous and Eocene exposures just a few kilometers north of Mitzpe Ramon. This is what we do near the end of each expedition so that we have more ideas for the next. It was cold and very windy on the barren hillsides this morning, but we still saw and learned a great deal.

We examined outcrops of four units: The Ora Formation (Upper Cretaceous) is primarily shales and claystones and below the stratigraphic column shown above. It has an interesting limestone unit composed mostly of rudistid bivalves and their shelly debris shown later below. The Gerofit Formation, also Upper Cretaceous, is a mix of limestones and marls unconformably above the Ora Formation. The Mishash Formation (Upper Cretaceous again) is a chert-rich unit unconformably above the Gerofit here. Andrew Retzler and Micah Risacher, who worked in the region two years ago, will immediately ask, where are the Zichor and Menuhah Formations that are supposed to be between the Gerofit and Mishash? They are absent due to a deep unconformity. On top of the Mishash, above another significant unconformity, are nummulitic limestones of the Avedat Group (Eocene). These three unconformities are all structurally and paleoenvironmentally significant — and they no doubt will be future projects for Wooster Geologists.

Some items of interest in this long section. Just below the Vroman Bank in the Ora Formation is the above cemented horizon with well-distinguished Thalassinoides burrows. These were produced by crustaceans burrowing into stiff mud in shallow waters. This unit is usually not very well exposed, but Yoav and I dropped down into an ancient cistern to see this outcrop.

This is a polished surface at the top of the Vroman Bank in the Ora Formation. Erosion in a small wadi over the centuries smoothed it off. We can see here borings known as Gastrochaenolites, some with outlines of bivalve shells still inside them. This is thus a carbonate hardground.

Some of the units in the Gerofit Formation are lithographic limestones, meaning they are very fine-grained and of uniform composition. You can see in the above photo that the stress pattern around my hammer blow is preserved as a nearly perfect sphere. This rock has been the premier building stone in Israel for millenia. It is known as “Jerusalem Stone” because so many buildings in that city are made of it and its equivalents.

Melissa is standing in what appears to be an ancient quarry for the lithographic limestone. There is a small Iron Age fort made of the stone nearby. Note how bundled up Melissa is. Not the usual image of Israel in this blog!

Finally, all our localities today were on ground that has been part of an IDF training base for decades. There is much discarded military gear around. I thought I would add this old British tin-hat to our blog’s collection of shot-up helmets! (We have German examples already, and somewhere in there is a Russian set.) I neglected to take a photo of a well-worn Egyptian helmet we found this morning.

Wooster’s Fossil of the Week: A stromatoporoid (Middle Devonian of central Ohio)

October 30th, 2011

Stromatoporoids are very common fossils in the Silurian and Devonian of Ohio and Indiana, especially in carbonate rocks like the Columbus Limestone (from which the above specimen was collected). Wooster geologists encountered them frequently on our Estonia expeditions in the last few years, and we worked with at least their functional equivalents in the Jurassic of Israel (Wilson et al., 2008).

For their abundance, though, stromatoporoids still are a bit mysterious. We know for sure that they were marine animals of some kind, and they formed reefs in clear, warm seas rich in calcium carbonate (DaSilva et al., 2011). Because of this tropical habit, early workers believed they were some kind of coral, but now most paleontologists believe they were sponges. Stromatoporoids appear in the Ordovician and are abundant into the Early Carboniferous. The group seems to disappear until the Mesozoic, when they again become common with the same form and life habits lasting until extinction in the Late Cretaceous (Stearn et al., 1999).

The typical stromatoporoid has a thick skeleton of calcite with horizontal laminae, vertical pillars, mounds on the upper surface called mamelons, and dendritic canals called astrorhizae shallowly inscribed on the mamelons. These astrorhizae are the key to deciphering what the stromatoproids. They are very similar to those on modern hard sponges called sclerosponges. Stromatoporoids appear to be a kind of sclerosponge with a few significant differences (like a calcitic instead of an aragonitic skeleton).

Stromatoporoid anatomy from Boardman et al. (1987).

Top surface of a stromatoporoid from the Columbus Limestone showing the mamelons.

There is considerable debate about whether the Paleozoic stromatoporoids are really ancestral to the Mesozoic versions. There may instead be some kind of evolutionary convergence between two groups of hard sponges. The arguments are usually at the microscopic level!

The stromatoporoids were originally named by Nicholson and Murie in 1878. This gives us a chance to introduce another 19th Century paleontologist whose name we often see on common fossil taxa: Henry Alleyne Nicholson (1844-1899). Nicholson was a biologist and geologist born in England and educated in Germany and Scotland. He was an accomplished writer, authoring several popular textbooks, and a spectacular artist of the natural world. Nicholson taught in many universities in Canada and Great Britain, finally ending his career as Regius Professor of Natural History at the University of Aberdeen.

Henry Alleyne Nicholson (1844-1899) from the University of Aberdeen museum website.

References:

Boardman, R.S., Cheetham, A.H. and Rowell, A.J. 1987. Fossil Invertebrates. Wiley Publishers. 728 pages.

DaSilva, A., Kershaw, S. and Boulvain, F. 2011. Stromatoporoid palaeoecology in the Frasnian (Upper Devonian) Belgian platform, and its applications in interpretation of carbonate platform environments. Palaeontology 54: 883–905.

Nicholson, H.A. and Murie, J. 1878. On the minute structure of Stromatopora and its allies. Linnean Society, Journal of Zoology 14: 187-246.

Stearn, C.W., Webby, B.D., Nestor, H. and Stock, C.W. 1999. Revised classification and terminology of Palaeozoic stromatoporoids. Acta Palaeontologica Polonica 44: 1-70.

Wilson, M.A., Feldman, H.R., Bowen, J.C. and Avni, Y. 2008. A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 24-29.

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

July 7th, 2011

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.

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

July 7th, 2011

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.

Wooster Geologists return to Suuriku Cliff, Saaremaa, Estonia

July 7th, 2011

KURESSAARE, ESTONIA–Today we visited one of Rob McConnell’s (’10)  Senior Independent Study field sites on the northwest coast of Saaremaa. Suuriku Cliff (N58.50875°, E21.99818°; see above image) is an exposure of the Jaani Formation (Lower Silurian, Wenlock). There are two members here: the upper Ninase (most of the cliff) and the lower Mustjala. Rob sorted out the paleoecology and environments of deposition of these two members using samples from this location and two others.

We were here today to find additional crinoid calices to continue a project Bill Ausich, Olev Vinn and I are pursuing. We found a few, too, although none very photogenic. It was also a chance for us to see more examples of Silurian limestone and fossils before we leave the island on Saturday.

Nick Fedorchuk and Rachel Matt at Suuriku Cliff. We want to show that some Saaremaa cliffs really are more than a meter high!

Panorama of Tagalaht Bay south of Suuriku Cliff near Veere. This bay is where German naval and infantry forces invaded Saaremaa on October 11, 1917, in Operation Albion.

Return to a Silurian crinoid forest

July 5th, 2011

KURESSAARE, ESTONIA–Today our Wooster Geology team visited a favorite outcrop of mine: the Äigu Beds of the Kaugatuma Formation exposed on the northwestern shore of the Sõrve Peninsula on Saaremaa. These are Late Silurian (Pridoli) limestones with a great abundance of crinoid fragments — so many that they are locally called “ringstones” (see the above image of a crinoid stem and isolated ring-like columnals). Palmer Shonk (’10) studied this outcrop for his Independent Study thesis. We returned here today to collect more field data so that Palmer, Olev Vinn, Bill Ausich and I can write a professional paper on the depositional system and paleoecology.

The limestones show significant storm beds made of skeletal debris, especially the crinoids but also corals, stromatoporoids, bryozoans, brachiopods and trilobites. The most remarkable aspect of this exposure is the presence of an in situ crinoid “forest” of holdfasts (the part of the crinoid that holds it to the sediment). Our job today was to find out more about the non-crinoid fauna since Palmer and I have already mapped out the crinoid holdfasts. We hope to soon publish a rare look at a Silurian crinoid community essentially preserved in place.

The Kaugatuma outcrop on the Sõrve Peninsula of Saaremaa. This was a Russian amphibious landing zone in 1944. You can bet you’ll read more about that story later!

The star-shaped fossil with the hole in the center is a crinoid holdfast in place at Kaugatuma. There are dozens of these scattered across the outcrop. The crinoid is Enallocrinus. The hole in the center is the hollow lumen of the crinoid stem.

Nick found this calyx of another crinoid known as Eucalyptocrinites. Such well preserved calices are rare.

Nick also found this very nice trilobite pygidium (tail piece). It is preserved well enough that we can probably later identify it to the genus level.

Back to the Big Island for the Fourth of July

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!

Saying goodbye to the little island of Hiiumaa

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.

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