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 molded brachiopod from the Lower Carboniferous of Ohio

February 20th, 2015

Syringothyris bored Wooster CarboniferousWe haven’t had a local fossil featured on this blog for awhile. Above is an external mold of the spiriferid brachiopod Syringothyris typa Winchell, 1863, from the Logan Formation (Lower Carboniferous, Osagean, about 345 million years old) of southeastern Wooster, Ohio. The outcrop is along the onramp from north Route 83 to east Route 30. Older Wooster geologists may remember this area was called “Little Arizona” because of the large roadcuts made for a highway bypass that was never completed. That original outcrop was destroyed several years ago, but the same rocks are exposed in this new section. This is the area where Heather Hunt (’09) did her Senior Independent Study work, and long before her Brad Leach (’83) worked with the same fossils.

The Logan Formation is primarily fine sandstone, with some subordinate conglomerates, silts and shales. It was likely deposited in the proximal portion of a prodelta at or below wavebase. The fossils in the Logan are mostly these large Syringothyris and the bivalve Aviculopecten, along with scattered crinoids, gastropods, bryozoans, nautiloids and ammonoids. This fauna needs more attention. Funny how the fossils in your own backyard are so often ignored.

This brachiopod was first buried in sediment and then the shell dissolved away, leaving an impression behind. Since it is an impression of the exterior of the shell, it is called an external mold. Curiously, all the external molds (and the internal molds as well) in the local Logan Formation have an iron-rich, burnt orange coating much finer than the fine sand matrix. This means that details are preserved that are of higher resolution than the matrix alone would allow. In the case of this fossil, that coating extended down into long, narrow borings in the shell, casting them (see below).
Syringothyris borings 585These borings are odd. Most of them are parallel to the ribs (plicae) of the brachiopod, and appear to have been excavated from the shell periphery towards its apex. This was in the opposite direction of brachiopod shell growth. I suspect they were made by boring annelid worms that started at the growing edge of the shell where the mantle ended. These traces need attention, like most other aspects of this local fossil fauna.

References:

Ausich, W.I., Kammer, T.W. and Lane, N.G. 1979. Fossil communities of the Borden (Mississippian) delta in Indiana and northern Kentucky. Journal of Paleontology 53: 1182-1196.

Bork, K.B. and Malcuit, R.J. 1979. Paleoenvironments of the Cuyahoga and Logan formations (Mississippian) of central Ohio. Geological Society of America Bulletin 90 (12 Part II): 1782-1838.

Leach, B.R. and Wilson, M.A. 1983. Statistical analysis of paleocommunities from the Logan Formation (Lower Mississippian) in Wayne County, Ohio. The Ohio Journal of Science 83: 26.

Wooster’s Fossils of the Week: Beautiful trace fossils from the Upper Ordovician of southern Ohio

December 19th, 2014

Trace fossils Bull Fork Ordovician OH 585Every year we highlight at least one of the fossils found and studied by Wooster’s Invertebrate Paleontology class as part of their field and laboratory exercises. This year it is this nice slab of trace fossils collected by Curtis Davies (’15) on our August 31 field trip to the emergency spillway in Caesar Creek State Park. I didn’t even notice it at the time Curtis picked it up. I only saw its full glory when he photographed the rock as part of a paleontological essay.
CurtisGalen083114aCurtis Davies is the smiling, bearded guy in the back (with Galen Schwartzberg) at the Caesar Creek outcrop. The rain had finally stopped and everyone was happy.

The traces are exposed here on the bottom of a bed of argillaceous limestone. They are preserved in what trace fossil workers (ichnologists) call convex hyporelief, which means simply that they stick out on the base (or sole) of the rock slab. These were tunnels originally excavated in soft mud by worm-like animals. The tunnels were filled with sediment that cemented up more resistant than the surrounding matrix, and thus were weathered in this relief.
Taenidium serpentinum Heer, 1877Most of the trace fossils here are the simple unlined burrow called Planolites, one of the most common traces in the Ordovician of the Cincinnati area. The trace labelled with the red “T” above, though, is rare here. Note that it is formed by a series of pulse-like movements that produced segments in the sediment infill. My estimate is that this trace can be classified as Taenidium serpentinum Heer, 1877. It is not common in the Ordovician.
Heer, Oswald, 1809-1883Oswald Heer (1809-1883), the scientist who named Taenidium serpentinum, was a Swiss geologist and botanist. As was the case for many educated Europeans, he started as a clergyman, even signing up for holy orders. The natural world captivated him, though, and starting with insects he worked his way up to become a naturalist and professor of botany at the University of Zürich. He was one of the key figures in the establishment of paleobotany (the study of fossil plants).
Taenidium serpentinum Heer, 1877 image 585Here is Heer’s figure of Taenidium serpentinum from Plate XLV in his 1877 book, Flora fossilis Helvetiae (Fossils Plants of Switzerland). You see the irony already. Heer described this trace fossil as a plant, inadvertently becoming one of the early figures in ichnology, the study of trace fossils.

Oswald Heer published many books and papers, becoming well known for his geological and paleontological explorations and descriptions. He was awarded the prestigious Wollaston Medal from the Geological Society of London in 1874. He was an earlier advocate of using fossils to sort on problems of paleogeography. He knew, for example, that Miocene fossils in Europe and North America were very similar, so he suggested in those days before Plate Tectonic Theory that the two continents were connected by a “land bridge“. This was called the “Atlantis Hypothesis”, and you can imagine the confusion that name caused among various cranks and pseudoscientists looking for Plato’s mythical continent. Heer died in Switzerland in 1883.

References:

D’Alessandro, A. and Bromley, R.G. 1987. Meniscate trace fossils and the Muensteria-Taenidium problem. Palaeontology 30: 743-763.

Heer, O. 1877. Flora fossilis Helvetiae: Die vorweltliche flora der Schweiz. Zürich, J. Wurster & Company. 182 p.

Keighley, D.G. and Pickerill, R.K. 1994. The ichnogenus Beaconites and its distinction from Ancorichnus and Taenidium. Palaeontology 37: 305-338.

Keighley, D.G. and Pickerill, R.K. 1995. Commentary: The ichnotaxa Palaeophycus and Planolites: Historical perspectives and recommendations. Ichnos 3: 301-309.

Last Fieldtrip for Climate Change

November 13th, 2014

GROUP

As the weather cools – the Wooster Geology Climate Change class ventured out in the field one more time. For the remainder of the semester we will try to get some work done. Two sites were visited – the Cedar Creek Mastodon Site and the OARDC.

excavationTwo weeks ago a pit was dug from our coring sites to the Mastodon excavation site. The mission was to link the cores to the archaeological site.

pit

The general stratigraphy of the mastodon site. The muds have a high calcium carbonate content that helped preserve the bones and tusk. Note the plow horizon about 25 cm down – the trip also focused on the agricultural history of Ohio and the role it plays in climate change.

anomalyJeff Dilyard, who hosted us at the site, explains to the class that a GPR (ground penetrating radar) survey identified an anomaly at this location. Isabel probed the area (see below) and “clunked” on a tile.

probingIsabel above used a tile probe to investigate the subsurface (note the chin method she is employing).

tileWhat is a “tile”? above is an old drainage tile from the site. This one is plugged with mud and the plugging was the reason the mastodon was discovered. New tiles were installed last year and the digging brought up the original tooth of the mastodon. Tile and draining of the Midwest allowed for our great agricultural history. In addition, the tile and draining allowed widespread plowing that released the carbon in naturally sequestered organic rich wetland soils to the atmosphere.

in_pitThe crucial end of the backhoe pit where probing and sampling links the bog cores to the mastodon site.

group_no_till

A quick stop ate the Triplett-Van Doren Experimental Plot. For over 50 years a variety of experiments have been underway here. We discussed the side-by-side no-till and mold board plowed sites and their ability to sequester carbon. Not plowing (no-till) sequesters carbon and mitigates erosion. Less carbon dioxide to the atmosphere and less sediment flux on the landscape.

no_till

A darker colored soil in the core barrel above shows more carbon in the soil relative to the one below.

DR

A quick stop at Secrest Arboretum to view the famous Dawn Redwoods. Under the proper conditions these trees can grow a meter each year. Our tree-ring data from this stand helps define the optimum conditions for their growth. Planting trees sequesters carbon and helps out in lots of other ways as well.

weather

In addition to the no-till fields and trees at Secrest – there is a meteorological record that spans more than 120 years (note how Tom – far left, seems to be the only student listening to the instructor). These instruments have been keeping track of climate and we will use it to compare with our tree ring study. Our tree ring project asks the question: during the time of European Settlement in Ohio what were the climate conditions like? (precipitation and temperature) and could the widespread deforestation and tile and draining of the region have perturbed the climate (see this video for more on this subject). This question is relevant to the ever-present striving of climate scientists to investigate the relative roles of natural climate variability and anthropogenic change.

 

 

 

 

Wooster’s Fossils of the Week: Upper Carboniferous seed casts from northeastern Ohio

October 31st, 2014

Trigonocarpus trilocularis Hildreth 1838We haven’t had a paleobotanical fossil of the week for awhile, so here are a couple of nice seed casts from the Upper Carboniferous Massillon Sandstone exposed near Youngstown, Ohio. They fall within the “form genus” Trigonocarpus Brongniart 1828. A form taxon is one that may not have any systematic or evolutionary validity, but it is a convenient resting place for taxa that share a particular morphological pattern but can’t be easily classified elsewhere. Trigonocarpus consists of seed casts that are “radially symmetrical, decorticated, and have their surface marked by three prominent ridges” (Gastaldo and Matten, 1978, p. 884). These particular seeds appear to be Trigonocarpus trilocularis (Hildreth, 1837). The taxa here are problematic, of course, because these seeds belong to larger plants that have their own names.
Trigonocarpus trilocularis Hildreth 1838_585These seeds appear to be from medullosalean trees, which were small relatives of today’s cycads. They were common in wetlands throughout North America and Europe during the Carboniferous, especially the Late Carboniferous. The seeds we have were likely attached to small stalks. You can see what appears to be a circular attachment scar above.
Samuel Prescott Hildreth (1783–1863)
Dr. Samuel Prescott Hildreth (1783-1863) was a physician and historian with a keen eye for natural history, especially including fossils and rocks. He was born in Massachusetts of strong Patriot stock and moved to the dangerous territory of Ohio in 1806, settling in Marietta in 1808. Dr. Hildreth is often cited as one of the first scientists in the country west of the Alleghany Mountains. His prolific writing is fast-moving, diverse and interesting, so he must have been a great traveling companion. Dr. Hildreth served in the Ohio Legislature and was on the first Ohio Geological Survey.
HildrethNutThe above is a figure from Hildreth (1837, p. 29) showing the fossil seed he named Carpolithus trilocularis. He wrote that “[t]his nut is probably the fruit of some antediluvian palm”, which is not far from what we think now (apart from the Flood reference!).

References:

Gastaldo, R.A. and Matten, L.C. 1978. Trigonocarpus leeanus, a new species from the Middle Pennsylvanian of southern Illinois. American Journal of Botany 65: 882-890.

Hildreth, S.P. 1837. Miscellaneous observations made during a tour in May, 1835, to the Falls of the Cuyahoga, near Lake Erie: extracted from the diary of a naturalist. American Journal of Science and Arts 31:1-84

Zodrow, E.L. 2004. Note on different kinds of attachments in trigonocarpalean (Medullosales) ovules from the Pennsylvanian Sydney Coalfield, Canada. Atlantic Geology 40: 197-206.

An Epic Geologic Competition in Cuyahoga Valley National Park

October 26th, 2014

VIRGINIA KENDALL, CUYAHOGA VALLEY NATIONAL PARK (CVNP) — What an absolutely awesome day for geology in the field!!  One of my geologic mentors once told me that “every day in the field is a day of vacation”, and today proved to be just that day.  Late October…temperatures above 60 degrees…with the fall colors everywhere!!  I could not have asked for a better day to take my Structural Geology class to “The Ledges”, part of Virginia Kendall, which is only about an hour north of campus.  Essentially, we have a National Park right in northeast Ohio, and fall is the best time to visit the area.

However, we were not just going there for a day hike.  We were on a mission.  I set up a scenario for my class:  CVNP exposes strata that in the subsurface is rich in oil and gas.  The goal for the students was to undertake a complete geologic study (including the stratigraphy, sedimentology, structure, and geomorphology) of the exposed rock in the area as an analog in order to better assess oil and gas fluid migration in the subsurface.  The class was split into two teams — seniors vs juniors.  Each team is not permitted to talk to one another about data collection, analysis, or synthesis.  Eventually, these Research and Development (R&D) Teams will share their findings with Wooster’s Production Experts (Drs. Pollock, Wiles, and Wilson) via a poster presentation later in the semester.

So, while there were literally hundreds of people out for a day hike near The Ledges, Wooster’s geologists were busy at work.  The Ledges is located just south of Happy Days Visitor Center and southeast of Peninsula, OH.

lock-29-location-map_585blogThe area between State Route 303 and Kendall Ledges Road (where there are all the green hiking trails) was our field area for the day.

DSC01285_585blog

The R&D Teams quickly noticed the amazing joint sets that are exposed all along The Ledges.  Essentially, we have ledges in this area due to the large fracture system (i.e., joints) affecting the rocks.  These joint sets are very easy to measure and to access due to a wonderful trail system next to the exposures in Virginia Kendall.  Notice above that these joints can be at various orientations and that those in the photo above appear to be nearly perpendicular to one another.

DSC01271_585blogLet me introduce the R&D Team of Woo seniors (’15), from left to right: Coleman Fitch, Zach Downes, Willy Nelson, and Leo Jones.  It appears that they are discussing their team’s strategy early in the day.  Michael Williams (’16), of the opposing team, is in the background.  Is Michael trying to eavesdrop on the opposing team?

DSC01269_585blogTwo members of our R&D team of Woo juniors (’16) are taking notes on this rock exposure.  Eric Parker (left) and Kaitlin Starr (right, white hat) appear to be focused on the gorgeous geology.

DSC01276_585blogThe other two members of the R&D team of Woo juniors (’16) were found hiding in a dark “slot canyon” among the joints.  Michael Williams is in the front, while Adam Silverstein is in the orange hoodie, peeking out from deep inside the “canyon”.  It appears that the juniors are separated from one another!!  It is OK; everyone had maps and GPS units, so perhaps their strategy for the day was to divide and conquer?

DSC01274_585blogWow!!  Check out this entrance to Ice Box Cave, which was formed by the intersection of several joint sets.  Unfortunately, we were not able to go any closer to the cave entrance than this, because…

DSC01273_585blog…the National Park Service is trying to save the bats, which are susceptible to White-Nose Syndrome.

DSC01278_585blogNow, I could not just end the blog without showing you such a wonderful photo.  Check out the amazing set of cross-beds that you can see exposed in the upper half of the photo.  These rocks, which are some of the youngest rocks exposed in CVNP, have been interpreted to be deposited by ancient stream deposits.  Superimposed on the cross-bedding is the characteristic honeycomb weathering that affects many of the sandstone exposures along The Ledges.  And, notice that some of the rocks appear to be more brown or rust colored; some scientists have identified limonite and pyrite (two iron-rich minerals) in the unit.

What an awesome day to be a geologist!!  Who else gets to spend a great fall day with friends, enjoy the weather, learn a little more about rocks, and measure joints along the way?  Geology rocks.

 

 

Wooster Geologists return to the Cedar Creek Bog and Excavation Site

October 25th, 2014

DigOverview102514WOOSTER, OHIO–Greg Wiles and I got to experience a bit of field archaeology today at the Cedar Creek Mastodon excavation site. Greg’s Climate change class has visited the site and its associated bog twice this semester: once to do some soil probing and exploration, and then again to extract a core from the bog. This time Greg and I went to consult with the chief archaeologist of the site, Nigel Brush of Ashland University. Nigel wanted our opinions on the stratigraphy of the dig, especially those parts associated with mastodon remains and flint artifacts. The hypothesis the archaeologists are testing is that the mastodon bones and flint blades are part of an ancient butchery site.  It was a joy to join our friends on this fantastic Fall day.

BonesFlagged102514Who doesn’t love an archaeology site? All that enthusiastic hard work with brushes, spades and trowels revealing hidden treasures. Those little orange flags above are tagging bits of mastodon bone that the volunteer excavators have uncovered for mapping and collection. Several schools are represented at this site, and at least a couple dozen citizen scientists.

HannahJim102514Wooster is represented at the dig by archaeology professor Nick Kardulias, along with two of his students shown above. Hannah Matulek is on the left; Jim Torpy on the right.

BoneFragment102514Here is some mastodon bone embedded in one of the excavation walls. The bones are scattered, with some large pieces and many small fragments.

Sieving102514This is the line of sieves for sorting through the excavated sediment. Pleasant enough work today, but I can imagine it’s not so fun in the rain and sleet.

GregSoilProbing102514And now for our bit of work. Greg went off into the bog with a soil probe to plan out a new trench to be dug by the landowner. This trench will help correlate the strata in the excavation with what Greg and his students have cored from the bog.

StratView102514I spent most of my time in the excavations examining the simple layering of the sediments. At the bottom we have a coarse conglomerate with cobble-sized rounded grains. The bones and artifacts lie on top of and among these clasts. Above that unit is a matrix-supported conglomeratic mud with broken rock fragments. At the top is a loam representing the disturbed (plowed) part of the section.

MudWithClasts102514This is a closer view of that middle unit with the “floating” angular rock fragments. My quick assessment (just a suggestion!) is that the coarse gravels beneath are part of a deltaic complex feeding into the bog, which was at the time a marl lake. The mud-with-clasts above it is a debris flow from the surrounding elevations that cascaded down the creek channel and its banks, entombing the bones and artifacts under a slurry of muddy debris. There is scattered charcoal throughout this unit and the top of the cobbles below. Maybe a forest fire denuded the upstream slopes and led to a rain-soaked mudslide? Then again, the charcoal could have come from an ancient barbecue of the mastodon meat.

In any case, Greg and I had a great time visiting our archaeological colleagues on such a fine day.

 

Wooster’s Fossil of the Week: A crinoid calyx from the Upper Ordovician of southern Ohio

September 26th, 2014

Xenocrinus baeri (Meek, 1872)_585This week’s contribution from the Wooster collections will be short. If all is going well, as this is posted I’m on my way to the Fourth International Palaeontological Congress in Mendoza, Argentina. I hope to have a few posts from that exotic place!

The fossil above is the crown of a monobathrid crinoid called Xenocrinus baeri (Meek, 1872). It was found by Bianca Hand (Wooster ’14) in the Bull Fork Formation (Upper Ordovician, Richmondian) on an Invertebrate Paleontology field trip to the emergency spillway at Caesar Creek State Park in southern Ohio (seen below). Thank you to my friend Bill Ausich of The Ohio State University for identifying this fossil. It is an unprepared specimen of a common species, and it is not nearly so flashy as in other collections. Still, it is one of the best finds from our class field trips, and it is cool. The calyx is on the right and mostly buried in matrix. Four filter-feeding arms extend to the left. Where the matrix is broken away on the far right you can see tiny ossicles from the pinnules on the arms. Someone using a needle very carefully under a microscope could expose more details of this crinoid, but I like leaving something to the imagination!
CaesarCreek2011References:

Schumacher, G.A. and Ausich, W.I. 198). New Upper Ordovician echinoderm site: Bull Fork Formation, Caesar Creek Reservoir (Warren County, Ohio). The Ohio Journal of Science 83: 60-64.

Wooster’s Fossils of the Week: A hardground with rugose corals from the Upper Ordovician of southern Ohio

September 5th, 2014

Hdgd small 090114The above slab is a carbonate hardground from the Liberty Formation (Upper Ordovician) of southern Ohio. Carbonate hardgrounds are cemented seafloors, so we’re actually looking at the hard rocky bottom of an Ordovician sea. I’ve long found the idea of a hardground fascinating — it is like a bit of ancient time frozen before us. This hardground is especially interesting because of the fossils associated with it. The knobby nature of the surface is probably due to a burrow system that was preferentially cemented and then exhumed by currents that washed away the loose sediment. The intersecting tunnels, now ridges, provided numerous crannies for encrusting, boring and nestling organisms to inhabit. The high points hosted encrusting bryozoans that needed currents for their filter-feeding.

brach coral 090114There are several shelly fossils found in the low points of this hardground surface. The brachiopod in the upper left is the orthid Plaesiomys subquadrata (Hall, 1847), and the conical rugose coral in the lower right is Grewingkia canadensis (Billings, 1862)

two corals 090114Here is another detailed view of the hardground showing a second rugose coral on the left. I suspect that the corals and maybe even the brachiopod are actually in place (or “in situ” to use the fancy words). I’ve seen such occurrences before and passed them off as just examples of loose fossils rolling into holes. Here, though, we can see that both corals have the calyx (the cup in which the coral polyp was located) facing upwards. These G. canadensis corals did not attach to hard substrates like some of their cousins, but lay recumbent and curved upwards on the seafloor. What better place to do so than in the cozy hollows of a hardground?

This slab is certainly a nice vignette of a marine community nearly 450 million years old.

References:

Billings, E. 1862. New species of fossils from different parts of the Lower, Middle, and Upper Silurian rocks of Canada. Paleozoic Fossils, Volume 1, Canadian Geological Survey, p. 96-168.

Hall, J. 1847. Paleontology of New York, v. 1: Albany, State of New York, 338 p.

Palmer, T.J. 1982. Cambrian to Cretaceous changes in hardground communities. Lethaia 15: 309–323.

Wilson, M.A. and Palmer, T.J. 1992. Hardgrounds and hardground faunas. University of Wales, Aberystwyth, Institute of Earth Studies Publications 9: 1–131.

Wooster’s Fossils of the Week: Rugose corals from the Upper Ordovician of Ohio

December 22nd, 2013

585px-LibertyFormationSlab092313College of Wooster student Willy Nelson spotted and collected up this beautiful Liberty Formation slab on our 2013 Invertebrate Paleontology course field trip to the Upper Ordovician of the Caesar Creek area in southern Ohio. There are many exquisite fossils on this apparent carbonate hardground (a cemented seafloor), the most prominent of which are the four linked circular corallites in the top center. They are of the species Streptelasma divaricans (Nicholson, 1875), shown in more detail below.

Streptelasma divaricans (Nicholson, 1875) 585Streptelasma divaricans is a rugose coral, a prominent order that dominated the Paleozoic coral world from the Ordovician into the Permian. Unlike most rugose corals, it usually is found attached to some hard surface like a shell, rock or hardground. S. divaricans is relatively rare in the Upper Ordovician of the Cincinnati area compared to its free-living cousin Grewingkia canadensis. In its adult form (as seen here) it can have about 60 septa (vertical partitions radiating from the center), alternating from small to large and often with a twist at the center. In life there would have been a tentacle-bearing polyp sitting in each of these septate cups (corallites) catching tiny prey as it passed by in the water currents. We presume that they lived much like modern corals today. S. divaricans was, by the way, an invading species in this Late Ordovician shallow sea community.

Streptelasma divaricans was named as Palaeophyllum divaricans in 1875 by Henry Alleyne Nicholson (1844-1899). We met Dr. Nicholson in an earlier blogpost. Astonishingly, one of our  geology majors in the paleontology course this semester is Brittany Nicholson, a direct descendant. Way cool.
WillyBrachiopodLepidocyclusperlamellosus092313Another nice fossil on Willy’s slab (in the upper right) is the rhynchonellid brachiopod Lepidocyclus perlamellosus, shown closer above.
WillyBivalve092313The curved, indented line in the middle of the slab (shown above) appears to be the outline of a bivalve shell. The original shell was made of aragonite and thus dissolved away very early (possibly even on the seafloor before burial). There is not enough shape remaining to identify it. The twig-like fossil with tiny holes above the scale is, of course, a trepostome bryozoan. You didn’t need me to tell you that!

References:

Elias, R.J. 1983. Middle and Upper Ordovician solitary rugose corals of the Cincinnati Arch region. United States Geological Survey Professional Paper 1066-N: 1-13.

Elias, R.J. 1989. Extinctions and origins of solitary rugose corals, latest Ordovician to earliest Silurian in North America. Fossil Cnidaria 5: 319-326.

Nicholson, H.A. 1875. Description of the corals of the Silurian and Devonian systems. Ohio Geological Survey Report, v. 2, part 2, p. 181-242.

Patzkowsky, M.E. and Holland, S.M. 2007. Diversity partitioning of a Late Ordovician marine biotic invasion: controls on diversity in regional ecosystems. Paleobiology 33: 295-309.

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