Team Yorkshire explores Scarborough

June 5th, 2015

1 Scarborough060515SCARBOROUGH, ENGLAND (June 5) — It was a spectacular day on the coast of northeastern England. When Paul Taylor arrived by train at 10:30 this morning, the clouds broke and the sunlight streamed through. Mae and Meredith explored Scarborough in the morning, plotting out where the stores and other useful places are, and Paul and I began to sort through geological action plans.

2 Peter Rawson Paul TaylorPeter Rawson, on the left with Paul Taylor, joined us for lunch to give us local field advice. He is the senior author of the Geologists’ Association’s Guide to the Yorkshire Coast, so there was no one better to have as an advisor. We had lunch in one of the classic spa buildings and made our field plans for the next few days.

Rotunda Museum frontAfter lunch we visited the Rotunda Museum (above), which is devoted to the geology of the area. It was built in 1829 out of the Jurassic Hackness stone. William “Strata” Smith suggested the unusual design, and much of the museum is devoted to his accomplishments and legacy.

4 Rotunda Interior 060515Paul, Mae and Meredith are examining the upper levels inside the circular Rotunda Museum.

5 Smith stratigraphy RotundaThe motif around the rim of the main room in the Rotunda is the 19th Century version of the local stratigraphy, including some places we will be visiting tomorrow.

6 Smith fossils RotundaMany of William Smith’s original fossils (loaned by the Natural History Museum) are on display.

7 Smith figureWe could in several cases match the specimens with Smith’s illustrations of them.

8 Trap inspectionAfterwards we went down to the marina and inspected the crab and fish traps sitting on the wharves. What were we looking for?

9 Electra pilosa PDTBryozoans, of course! Here is an Electra pilosa, the most common species. (Photo by Paul Taylor.) We also saw many serpulids, barnacles, oysters and other sclerobionts. A good view of the present to inform our coming interpretations of past hard substrate communities.

10 Anne Bronte gravestoneFor a cultural interlude we visited the grave of Anne Brontë in the castle church cemetery. The sandstone markers are exfoliating, with most now unreadable. (Choose granite!)

11 Scarborough Castle 060515We walked up to Scarborough Castle and will explore it later when we have the chance. There are 3000 years of human history here. In 1914 it was heavily shelled by — you guessed it — the German Navy.

12 Scarborough downtown 060515In the evening it was back to the busy downtown for a seafood dinner. Our plans are in place, the context is set. Tomorrow we start our fieldwork.

 

Wooster’s Fossil of the Week: A chaetetid demosponge from the Upper Carboniferous of southern Nevada

June 5th, 2015

1 Chaetetid Bird Spring Upper Carboniferous Nevada 585I collected this lump of a specimen during my dissertation research in the Bird Spring Formation (Carboniferous-Permian) of southern Nevada. It was found in a richly-fossiliferous Upper Carboniferous (Moscovian) portion near Mountain Springs Pass, which is about 40 km southwest of Las Vegas. It is a chaetetid, which at the time I interpreted conventionally as a singular extinct sponge in the genus “Chaetetes“. Since then we’ve learned a lot more about chaetetids. (And about the stratigraphy of the Bird Spring Formation. I wish we had sequence stratigraphy way back then!)
2 Chaetetid Bird Spring closer Upper Carboniferous Nevada 585Excellent and thorough work, especially by Ron West, has shown that the chaetetids are “hyper-calcified” members of the Class Demospongiae of the Phylum Porifera. They are sponges indeed, but the tubular chaetetid skeleton is found in at least three orders of the demosponges, including living ones. The chaetetid skeleton, which consists of very thin tubes (as shown above) is polyphyletic, meaning several groups of organisms converged on the same form.
3 Chaetetid Bird Spring closest 585In this oblique section of a chaetetid you can see the calcitic tubules, somewhat blurred by recrystallization.
4 Chaetetid Bird Spring cross-section Upper Carboniferous Nevada 585Here is a cross-section through one of the Bird Spring chaetetids. The tubules are very thin and long, somewhat resembling hair. Chaeto– comes from the Greek chaite for “hair or hairy”.

Now we know from systematic studies that the fossil “chaetetids” cannot be classified from their tubular skeletons alone. Without evidence of the spicules (which are rarely found, or at least recognized) and original mineralogy of the skeleton (many are recrystallized or, like the one at the top of this entry, replaced with silica) we can only refer to skeletal specimens such as ours as “chaetetid hyper-calcified demosponges”.

This is enough, though, for me to reintroduce them into my Invertebrate Paleontology classes. I had removed them from the teaching collections several years ago because of the confusion as to their status. Now they are at least demosponges, hyper-calcified at that.

References:

Almazán, E., Buitrón, B., Gómez-Espinosa, C. and Daniel Vachard. 2007. Moscovian chaetetid (boundstone) mounds in Sonora, Mexico. In: Vennin, E., Aretz, M., Boulvain, F. and Munnecke, A., eds., Facies from Palaeozoic reefs and bioaccumulations. Mémoires du Muséum national d’Histoire naturelle 195: 269–271.

Martin, L.G., Montañez, I.P. and Bishop, J.W. 2012. A paleotropical carbonate-dominated archive of Carboniferous icehouse dynamics, Bird Spring Fm., southern Great Basin, USA. Palaeogeography, Palaeoclimatology, Palaeoecology 329: 64-82.

West, R.R. 1994. Species in coralline demosponges: Chaetetida. In: Oekentorp-Küster, P., ed., Proceedings of the VI International Symposium on Fossil Cnidaria and Porifera, Munster Cnidarian Symposium, v. 2. Courier Forschungsinstitut Senckenberg 172: 399–409.

West, R.R. 2011a. Part E, Revised, Volume 4, Chapter 2A: Introduction to the fossil hypercalcified chaetetid-type Porifera (Demospongiae). Treatise Online 20: 1–79.

West, R.R. 2011b. Part E, Revised, Volume 4, Chapter 2C: Classification of the fossil and living hypercalcified chaetetid-type Porifera (Demospongiae). Treatise Online 22: 1–24.

West, R.R. 2012c. Part E, Revised, Volume 4, Chapter 2D: Evolution of the hypercalcified chaetetid-type Porifera (Demospongiae). Treatise Online 35: 1–26.

Wilson, M.A. 1985. Conodont biostratigraphy and paleoenvironments at the Mississippian-Pennsylvanian boundary (Carboniferous: Namurian) in the Spring Mountains of southern Nevada. Newsletters on Stratigraphy 14: 69-80.

Wooster’s Fossil of the Week: Petrified conifer wood

May 29th, 2015

1Petrified Wood 052615 585This is one of the most beautiful fossils in Wooster’s teaching collections. It is a polished section of petrified wood. It has vibrant colors and exquisite detail, as you’re about to see. Unfortunately any label that accompanied this specimen disappeared long ago. No matter how fantastic a fossil is, without its original location and stratigraphic context it has little scientific value. It works for our teaching collection, but I can’t tell you the age of the specimen, nor where it was found.
2Petrified wood close 052615 585Petrified wood is one of the most common types of fossil known to the public because of its abundance, attractiveness, hardiness (many a house out west has been built with petrified logs), and variety. Through the process of permineralization, minerals (quartz and chalcedony in this case) have infiltrated the porous organic structure, giving us three-dimensional, highly detailed preservation. This wood was first buried in low-oxygen sediments before it could decay on the forest floor. Groundwater circulated through the conductive tissue of the wood, depositing minerals in and around the cell walls of lignin and cellulose.

3Season of wood 052615 585It is hard to believe as we look closer and closer at the specimen that this is a fossil and not modern wood. Here we see the structure of the annual rings. The light-colored section is the new growth, the darker is when growth slowed at the end of the season. Our Wooster dendrochronologists, Greg Wiles and Nick Wiesenberg, could tell from this view that our tree was some kind of conifer.

4Polished petrified wood cells 585An even closer view of the same specimen. Now the perspective is dominated by vertical elements (rays) extending from the core of the tree outwards.

5Wood cells closest 052615 585This is as close as I could get with our photographic equipment. The cell walls and intervening rays are very distinct. Again, we’re looking at minerals here, not the original wood!

Again, fully label your fossils when you collect them. Because it has no locality information, this unlabeled specimen has little scientific worth. Too bad!

References:

Hickey, L.J. 2010. The Forest Primeval: The Geologic History of Wood and Petrified Forests. Yale Peabody Museum Series, 62 pp.

Wooster’s Fossils of the Week: A Silurian encrinite from southwestern Ohio

May 22nd, 2015

BrassfieldEncrinite585_041915The above rock was collected on our Sedimentology & Stratigraphy class field trip last month. It is an average piece of weathered Brassfield Formation (Early Silurian, Llandovery) from Oakes Quarry Park near Fairborn, Ohio (N 39.81472°, W 83.99471°). It is made almost entirely of crinoid fragments, and has a pleasant pinkish hue, most of which comes from the crinoid bits themselves. If you look closely you can see crinoid thecal plate fragments as well columnals and pluricolumnals.

This kind of limestone in which echinoderm ossicles make up the bulk of the grains is known as an encrinite. I first learned about encrinites from my colleague Bill Ausich of The Ohio State University, who has written the best assessments of encrinites on a regional scale. Encrinites are well-washed biosparite grainstones typically deposited between fair weather and storm wave bases on shallow shelves in low latitudes. They are surprisingly common from the Ordovician into the Jurassic, but then the disappear from the rock record as crinoids declined in abundance in shallow environments.

We’ve seen encrinites before in this blog from the Silurian of Estonia, the Triassic of Poland, and the Jurassic of Utah.

References:

Ausich, W.I. 1986. Early Silurian inadunate crinoids (Brassfield Formation, Ohio). Journal of Paleontology 60: 719-735.

Ausich, W.I. 1997. Regional encrinites: a vanished lithofacies. In: Paleontological events: stratigraphic, ecologic and evolutionary implications, p. 509-519. Columbia University Press, New York.

Ausich, W.I. and Deline, B. 2012. Macroevolutionary transition in crinoids following the Late Ordovician extinction event (Ordovician to Early Silurian). Palaeogeography, Palaeoclimatology, Palaeoecology 361: 38-48.

Hunter, A.W. and Zonneveld, J.P. 2008. Palaeoecology of Jurassic encrinites: reconstructing crinoid communities from the Western Interior Seaway of North America. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 58-70.

Tang, C.M., Bottjer, D.J. and Simms, M.J. 2000. Stalked crinoids from a Jurassic tidal deposit in western North America. Lethaia 33: 46-54.

Wooster’s Fossil of the Week: A ptilodictyine bryozoan from the Silurian of Ohio

May 15th, 2015

Phaenopora superba Brassfield 585The fossil above was found by Luke Kosowatz (’17) on our Sedimentology & Stratigraphy class field trip last month. We were measuring and sampling the Brassfield Formation (Early Silurian, Llandovery) near Fairborn, Ohio, and Luke pulled this beauty out of the rubble. This limestone is full of echinoderms and corals, so this lonely bryozoan was immediately a star.
Peela 050815This is the specimen that we sectioned and made an acetate peel from last month. The interior view, shown above, was critical to its identification. This peel was made perpendicular to the surface. It shows that the bryozoan is bifoliate, meaning it has two sides with zooids (the filter-feeding bryozoan polypides) and stood upright on the seafloor like a fan or leaf. Both sides had the characteristic bumps called monticules.
Phaenopora closerThe next critical view is this close-up of a slightly weathered surface of the bryozoan. It shows a regular arrangement of the larger zooecia (autozooecia) with two smaller zoooecia (metazooecia) between each pair. These clues enabled my friend Andrej Ernst, a paleontologist and bryozoan expert in the Department of Geosciences at the University of Hamburg, to identify this bryozoan as the ptilodictyine Phaenopora superba (Billings, 1866).
CNSPhoto-GEOLOGISTElkanah Billings (1820-1876) originally described this bryozoan species in 1866. He was Canada’s first government paleontologist, and he very much looked the part. Billings was born on a farm near Ottawa. He went to law school and became a lawyer in 1845, but he gave up dusty books for the life of a field paleontologist. In 1856 Billings joined the Geological Survey of Canada. He named over a thousand new species in his career. The Billings Medal is given annually by the Geological Association of Canada to the most outstanding of its paleontologists.

References:

Billings, E. 1866. Catalogues of the Silurian fossils of the island of Anticosti: with descriptions of some new genera and species. Dawson brothers.

Ross, J.P. 1960. Larger cryptostome Bryozoa of the Ordovician and Silurian, Anticosti Island, Canada: Part I. Journal of Paleontology 34: 1057-1076.

Ross, J.P. 1961. Larger cryptostome Bryozoa of the Ordovician and Silurian, Anticosti Island, Canada: Part II. Journal of Paleontology 35: 331-344.

Wooster’s Fossil of the Week: A Jurassic coral with beekite preservation from southern Israel

May 8th, 2015

MicrosolenaCW366_585This week’s fossil is again in honor of Annette Hilton (’17), now retired as my Sophomore Research Assistant this year. She has been assessing with great skill a large and diverse collection of scleractinian corals from the Matmor Formation in Hamakhtesh Hagadol in the Negev Desert of southern Israel. These specimens were collected during paleoecological studies by the Wooster paleontology lab and our Israeli colleagues. Above is a fantastic specimen of Microsolena Lamouroux 1821. We are looking at the top of a gumdrop-shaped corallum, with the corallites (which held the polyps) as shallow pits with radiating septa.
MicrosolenaReverseBeekiteCW366_585This is the reverse view of the coral, showing its concentric growth lines. The jumble in the center is shelly debris on which the coral originally established itself on the muddy seafloor. Note that the preservation here includes numerous little circles. These are centers of silica replacement called beekite rings (a form of chalcedony).
BeekiteMicrosolenaReverseCW366_585Above is a closer view of the beekite preservation. The silica circles have concentric rings of their own. This kind of preservation (a type of silicification) is common in the Matmor Formation. Corals like this one started as aragonitic skeletons and then were replaced by calcite and silica. I suspect the calcitization took place first because of the fine degree of preservation for most of the corallum.
Henry Beeke (1751–1837)So how do we get a term like beekite? Meet Rev. Henry Beeke (1751-1837), a rather unlikely scholar to make it to this blog. Beeke was an Oxford graduate in divinity, with a strong concentration in history. He became a prestigious Regius Professor of Modern History at Oxford. He was sought after as an expert of economics and taxation at the beginning of the 19th Century. As with many divines of the time, Beeke also pursued natural history, specializing in botany. At some point in his career he was noted as having described what we now call beekite, but I can’t find where in the literature. All I have is a brief mention of “Beekite, a new mineral, named after Dr. Beeke, at the Corbors” in Blewitt (1832, p. 15). Henry Beeke had the distinction of seeing this mineral variety named after him during his lifetime, which is rare in science.

References:

Blewitt, O. 1832. The panorama of Torquay: a descriptive and historical sketch of the district comprised between the Dart and Teign. Second edition. London: Simpkin and Marshall, 289 pages.

Church, A.H. 1862. XV. On the composition, structure, and formation of Beekite. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 23(152): 95-103.

Nose, M. and Leinfelder, R. 1997. Upper Jurassic coral communities within siliciclastic settings (Lusitanian Basin, Portugal): implications for symbiotic and nutrient strategies. Proceedings of the 8th International Coral Reef Symposium 2: 1755-1760.

Pandey, D.K., Ahmad, F. and Fürsich, F.T. 2000. Middle Jurassic scleractinian corals from northwestern Jordan. Beringeria 27: 3-29.

Pandey, D.K. and Fürsich, F.T. 2001. Environmental distribution of scleractinian corals in the Jurassic of Kachchh, western India. Journal Geological Society of India 57: 479-495.

Pandey, D.K. and Fürsich, F.T. 2005. Jurassic corals from southern Tunisia. Zitteliana 45: 3-34.

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.

Wilson, M.A., Feldman, H.R. and Krivicich, E.B. 2010. Bioerosion in an equatorial Middle Jurassic coral–sponge reef community (Callovian, Matmor Formation, southern Israel). Palaeogeography, Palaeoclimatology, Palaeoecology 289: 93-101.

Wooster’s Fossil of the Week: How to make brilliant acetate peels, with a Jurassic coral example

May 1st, 2015

1_Image_1986My retiring Sophomore Research student, Annette Hilton (’17), is excellent at making acetate peels. These peels, like the one above she made from a mysterious Callovian (Middle Jurassic) coral, show fine internal details of calcareous fossils and rocks.

2_Image_1987This is a closer view of the acetate peel of the coral showing incredible detail in the radiating septa and connecting dissepiments. This is a solitary coral from the Matmor Formation of southern Israel. We thought we knew what it was until we examined this peel and saw features we can’t match with any coral taxa. (Experts are invited to tell us what it is!) This view looks like it is from a thin-section, but it is all acetate and was made in about 20 minutes.

An acetate peel is a replica of a polished and etched surface of a carbonate rock or fossil mounted between glass slides for microscopic examination. Peels cannot give the mineralogical and crystallographic information that a thin-section can, but they are faster and easier to make. For most carbonate rocks most of the information you need for a petrographic analysis can be recovered from an acetate peel. In many paleontological applications, an acetate peel is preferred to a thin-section because you get essentially two dimensions without sometimes confusing depth.

To make a peel you need the following:

A trim saw for rock cutting.
A grinding wheel with diamond embedded disks (with 45µm and 30µm plates)
Grinding grit (3.0 µm) in a water slurry on a glass plate.
Acetate paper.
A supply of 5% hydrochloric acid in a small dish.
A supply of water in another small dish.
A squeeze bottle of acetone.
Glass biology slides (one by three inches)
Transparent tape.
Scissors
A carbonate rock or fossil

We’re now going to show you how we make peels. This process was worked out by my friend Tim Palmer and me back in the 1980s. See the reference at the end of this entry.

DSC_5123Annette is in her required safety gear about to start the process by cutting a fossil. She needs to cut a flat surface that is usually perpendicular to bedding in a carbonate rock, or through a fossil at some interesting angle.

DSC_5124The specimen approaches the spinning diamond-embedded blade of the rock saw. Annette is holding the rock sample steady on a carriage she is pushing towards the blade. It is important to hold the specimen still as the blade cuts through it.

DSC_5126My camera is faster than I thought. Not only do you see those suspended drops of water, the spray is frozen in the air! The cut is almost complete.

DSC_5128Now we use a diamond-embedded grinding wheel (45 µm or 30 µm) to polish the surface cut with the saw. This will be the side from which we make the acetate peel.

DSC_5129A closer view of the rock (which contains an embedded bryozoan, by the way) being polished flat on the spinning wheel.

DSC_5130The best peels are made from surfaces that have the finest polish. We are using a 3.0 µm grit-water slurry on a glass plate to again polish the rock surface as smooth as possible, removing all saw and grinding marks.

DSC_5133Keep the plate wet and push down hard to polish the cut surface in the grit slurry. With carbonate rocks and fossils it takes no more than five minutes here to get an excellent polish.

DSC_5134Wash the specimen thoroughly in water to remove all grit. Check the polished surface for grinding marks. If you see any, return to the glass plate and slurry for more polishing.

DSC_5135We’re ready for the simple etching process. We use a Petri dish half-filled with 5% hydrochloric acid and a another dish with water. (Yes, I have a dirty hood in my lab.)

DSC_5136Annette is suspending the polished surface of the specimen downward into the acid bath. She dips it in only a couple millimeters or so. The acid reacts with the carbonate and fizzes. Her fingers are safely above the action, but if you’re nervous you can use tongs to hold the specimen. We usually keep the specimen in the acid for about 15 seconds, and then quench it with the water in the second dish. The etching time will vary with the strength of the acid and carbonate content of the specimen.

DSC_5140This is the kit you need to make the acetate peel itself. Note that we use a thin acetate rather than the thick sheets preferred by others.

DSC_5143The tricky part. When the specimen is dry, cut a piece of acetate somewhat larger than the etched surface. We then hold this acetate and the specimen in one hand, and the squeeze bottle of acetone in the other. The next step is to flood the etched surface, which is held flat and upwards, with the acetone and quickly place the acetate on the wetted surface. The acetate will adhere fast, so smooth it out with your fingers across the etched surface. At this point the acetone is partially dissolving the acetate, causing it to flow into the tiny nooks and crannies of the etched surface. The acetone evaporates and the acetate hardens into this microtopography.

DSC_5145If you did it correctly, you now have a sheet of acetate adhering entirely to the etched surface. With practice you learn how to avoid bubbles between the acetate and specimen. Opinions vary and how long to let the system thoroughly dry. We found that we can proceed to the next step in about five minutes.

DSC_5147Now you peel! Slowly and firmly pull the acetate off the specimen.

DSC_5152Carefully trim the acetate with scissors. Place this peel between two glass slides, squeeze tight, and seal the assemblage like a sandwich with transparent tape. You have now made an acetate peel. Easy!

DSC_5153Here’s our finished product. Twenty minutes from rock saw to peel. You’ll have to wait until another blog post to see what this particular peel shows us!

Reference:

Wilson, M.A. and Palmer, T.J. 1989. Preparation of acetate peels. In: Feldmann, R.M., Chapman, R.E. and Hannibal, J.T. (eds.), Paleotechniques. The Paleontological Society Special Publication 4: 142-145. [The link is to a PDF.]

 

Wooster’s Fossil of the Week: A twisted scleractinian coral from the Middle Jurassic of southern Israel

April 24th, 2015

1 Epistreptophyllum Matmor CW366 585Another exquisite little coral this week from the collection of Matmor Formation (Middle Jurassic, southern Israel) corals Annette Hilton (’17) and I are working through. We believe this is Epistreptophyllum Milaschewitsch, 1876. It is a solitary (although more on that in a moment) scleractinian coral found in marly sediments at our location C/W-366 in Hamakhtesh Hagadol. I’m always impressed at how well preserved these corals are considering their original aragonitic skeletons were replaced long ago.
2 Epistreptophyllum lateral bentOne cool thing about this specimen is the near 90° bend it took during growth. Apparently it was toppled over midway through its development but survived and grew a twist so it could keep its oral surface (where the polyp resided) upwards. Another interesting observation is the small bud visible near the base. Gill (1982) suggested that the solitary Epistreptophyllum in the Jurassic of Israel may have been able to branch into separate individuals. Pandey and Lathuilière (1997) doubted this and suggested that Gill had misidentified his Israeli specimens. Maybe so, but we’re pretty sure we have Epistreptophyllum here, and we definitely have budding. We’re always open to other ideas!
3 Epistreptophyllum orientedHere is another view of the specimen in its living position after the fall. I love the sweep of the vertical ribs as it made the bend.
4 Epistreptophyllum septaTo complete the tour of this specimen, here’s a view of the oral surface where the polyp lived. The radiating lines are the septa that extended vertically through the interior of the corallite.
5 Milaschewitsch plate 50Epistreptophyllum was named in 1876 by Constantin Milaschewitsch. Here is Plate 50 from that massive work. Epistreptophyllum is marked by the red rectangles. (Note the misspelling of the genus in the caption for figure 2.) I wish I knew more about Mr. Milaschewitsch, but his particulars are thus far not available. I can tell he worked in Moscow and St. Petersburg, Russia, but that’s all. If anyone knows more about this man, please add your information in the comments.

References:

Gill, G.A. 1982. Epistreptophyllum (Hexacorallaire Jurassique), genre colonialou solitaire? Examen d’un matériel nouveau d’Israel. Geobios 15: 217-223.

Milaschewitsch, C. 1876. Die Korallen der Nattheimer Schichten. Palaeontographica 21: 205-244.

Pandey, D.K. and Lathuilière, B. 1997. Variability in Epistreptophyllum from the Middle Jurassic of Kachchh, western India: an open question for the taxonomy of Mesozoic scleractinian corals. Journal of Paleontology 71: 564-577.

A beautiful day for Wooster Geologists in the Silurian of Ohio

April 18th, 2015

aDSC_5072FAIRBORN, OHIO–It’s field trip season at last for the Wooster Geologists. Several geology classes have now been out in Ohio, taking advantage of windows of spectacular weather. Today was one of those days for 25 students in the Sedimentology & Stratigraphy class. We returned to the Oakes Quarry Park exposures in southwestern Ohio (N 39.81472°, W 83.99471°). Three years ago here in April it was 37°F and raining. This year the conditions were perfect. We studied outcrops of the Brassfield Formation (Early Silurian, Llandovery) in the old quarry walls. The students measured stratigraphic columns of these fossiliferous biosparites as part of an exercise, and then explored the glacially-truncated top of the unit.

bDSC_5079The Brassfield is intensely fossiliferous. Large portions of it are virtually made of crinoid fragments. In the random view above you can see columnals, as well as a few calyx plates. This is why this unit is very popular among my echinodermologist friends at Ohio State.

DSC_5056Kevin Komara, Brian Merritt and Dan Misinay (Team Football) are here contemplating the quarry wall, planning how to measure their sections.

DSC_5063One of our Teaching Assistants, Sarah Bender, is here pointing out one of the many thin intercalated clay units in the Brassfield biosparites.

DSC_5065Fellow Californian Michael Williams directed the action. No, actually he’s doing the time-honored technique of following a measured unit with his finger as he finds a place he can safely climb to it and the units above. He is holding one of our measuring tools, a Jacob’s Staff. Why do we call them “Jacob’s Staffs”? Read Genesis 30:25-43. (Yes, today’s students are mystified by Biblical references.)

DSC_5066Here’s Rachel Wetzel, giving me a heart attack. Don’t worry, insurance companies and parents, she’s fine.

DSC_5068Rachel is again on the left. Team Ultimate Frisbee (Meredith Mann and Mae Kemsley) are in the front, and Sharron Ostermann is above. This is the recommended way to get to the top of the exposure!

DSC_5070We carried our lunches in “to go” boxes from the dining hall. Our Teaching Assistants Sarah Bender and Kaitlin Starr enjoyed a sunny picnic on the rocks.

yDSC_5077The top level of the quarry was cleared of soil and brush many years ago to expose a glacially truncated and polished surface of the Brassfield. Looking for glacial grooves and fossils here are (from the left) Tom Dickinson, Jeff Gunderson (another Californian!), Andrew Conaway, and Luke Kosowatz (who seems to also be making a little pile of rocks as a memorial to a great day).

zDSC_5074One of the many corals we found in the top of the Brassfield was this halysitid (“chain coral”), an indicator fossil for the Late Ordovician and Silurian.

Everyone returned safely to Wooster with their completed stratigraphic columns, lithological descriptions, and a few fossils. Thank you to Mark Livengood, our bus driver. Good luck to the other field trip groups later this month!

Wooster’s Fossil of the Week: A Middle Jurassic trace fossil from southwestern Utah

April 17th, 2015

1 Gyrochorte 2 CarmelTime for a trace fossil! This is one of my favorite ichnogenera (the trace fossil equivalent of a biological genus). It is Gyrochorte Heer, 1865, from the Middle Jurassic (Bathonian) Carmel Formation of southwestern Utah (near Gunlock; locality C/W-142). It was collected on an Independent Study field trip a long, long time ago with Steve Smail. We are looking at a convex epirelief, meaning the trace is convex to our view (positive) on the top bedding plane. This is how Gyrochorte is usually recognized.
2 Gyroxhorte hyporelief 585A quick confirmation that we are looking at Gyrochorte is provided by turning the specimen over and looking at the bottom of the bed, the hyporelief. We see above a simple double track in concave (negative) hyporelief. Gyrochorte typically penetrates deep in the sediment, generating a trace that penetrates through several layers.
3 Gyrochorte Carmel 040515Gyrochorte is bilobed (two rows of impressions). When the burrowing animal took a hard turn, as above, the impressions separate and show feathery distal ends.
4 Gyrochorte 585Gyrochorte traces can become complex intertwined, and their detailed features can change along the same trace.
5 Gibert Benner fig 1This is a model of Gyrochorte presented by Gibert and Benner (2002, fig. 1). A is a three-dimensional view of the trace, with the top of the bed at the top; B is the morphology of an individual layer; C is the typical preservation of Gyrochorte.

Our Gyrochorte is common in the oobiosparites and grainstones of the Carmel Formation (mostly in Member D). The paleoenvironment here appears to have been shallow ramp shoal and lagoonal. Other trace fossils in these units include Nereites, Asteriacites, Chondrites, Palaeophycus, Monocraterion and Teichichnus.

So what kind of animal produced Gyrochorte? There is no simple answer. The animal burrowed obliquely in a series of small steps. Most researchers attribute this to a deposit-feeder searching through sediments rather poor in organic material. It may have been some kind of annelid worm (always the easiest answer!) or an amphipod-like arthropod. There is no trace like it being produced today.

We have renewed interest in Gyrochorte because a team of Wooster Geologists is going to Scarborough, England, this summer to work in Jurassic sections. One well-known trace fossil there is Gyrochorte (see Powell, 1992).
6 Heer from ScienceOswald Heer (1809-1883) named Gyrochorte in 1865. He was a Swiss naturalist with very diverse interests, from insects to plants to the developing science of trace fossils. Heer was a very productive professor of botany at the University of Zürich. In paleobotany alone he described over 1600 new species. One of his contributions was the observation that the Arctic was not always as cold as it is now and was likely an evolutionary center for the radiation of many European organisms.

References:

Gibert, J.M. de and Benner, J.S. 2002. The trace fossil Gyrochorte: ethology and paleoecology. Revista Espanola de paleontologia 17: 1-12.

Heer, O. 1864-1865. Die Urwelt der Schweiz. 1st edition, Zurich. 622 pp.

Heinberg, C. 1973. The internal structure of the trace fossils Gyrochorte and Curvolithus. Lethaia 6: 227-238.

Karaszewski, W. 1974. Rhizocorallium, Gyrochorte and other trace fossils from the Middle Jurassic of the Inowlódz Region, Middle Poland. Bulletin of the Polish Academy of Sciences 21: 199-204.

Powell, J.H. 1992. Gyrochorte burrows from the Scarborough Formation (Middle Jurassic) of the Cleveland Basin, and their sedimentological setting. Proceedings of the Yorkshire Geological Society 49: 41-47.

Wilson. M.A. 1997. Trace fossils, hardgrounds and ostreoliths in the Carmel Formation (Middle Jurassic) of southwestern Utah. In: Link, P.K. and Kowallis, B.J. (eds.), Mesozoic to Recent Geology of Utah. Brigham Young University Geology Studies 42, part II, p. 6-9.

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