Archive for September, 2011

You’re never too young to be a geologist: Nursery School students visit Scovel Hall

September 30th, 2011

WOOSTER, OHIO–The Wooster Geologists have long had a special relationship with The College of Wooster Nursery School (where young children “actively construct their own knowledge of the world”). Every year our faculty and students talk to the children about rocks, fossils and dinosaurs. As you can imagine it is a most enjoyable — if a bit frantic — experience. For the past three years Professor Shelley Judge has been our primary faculty planner and organizer for these delightful events. Usually the kids walk up the hill from the nursery school about a block to Scovel Hall. There Shelley has exploration stations and, we hope, lots of college student volunteers to explain the materials.

Today the topic was simply “rocks”, and the children came to see and hold a variety of igneous, sedimentary and metamorphic samples. Shelley set it all up and we had two sessions of about 18 kids each march in line up to the lab. They went through the specimens enthusiastically, feeling which are the smoothest and which the roughest, how heavy some are compared to others, seeing the world through a crystal of calcite, and marveling at ancient giant shark teeth. They each got to try on a hardhat, look through a handlens, and wear safety googles (which they find oddly fun). Then they line up and march back to the nursery school, clearly having enjoyed the experience. As did we!

Kit Price ('13) showing some of our sedimentary rocks and fossils to the children.

Katharine Schleich ('12) explaining some extrusive igneous rocks.

Shelley Judge talking to some of the children about minerals. Notice how intently they listen to her. She has the touch!

A Midday Biology & Geology Field Trip

September 28th, 2011

Geologist Greg Wiles and Biologist Rick Lehtinen in Spangler Park outside Wooster, Ohio.

WOOSTER, OHIO–Our colleague Rick Lehtinen in the Department of Biology had a great idea: how about a casual noon trip to the local Spangler Park to enjoy the plants, animals, rocks and streams? So Greg Wiles and I took him up on it and had a splendid couple of hours down in the gorge. We talked of ash trees, buried valleys, alluvial fans, salamanders and badgers. What an excellent break from grading!

Dr. Wiles showing where the creek flow goes from supercritical to subcritical.

An American Toad found by Dr. Lehtinen.

My contribution? An analysis of this beautiful set of bivalve, crinoid and brachiopod fossils from the Logan Formation (Mississippian).

 

Wooster’s Fossil of the Week: a venerid bivalve (Upper Cretaceous of Jordan)

September 25th, 2011

This summer I joined a team describing a shell bed in the Upper Cretaceous (lower Campanian, about 80 million years old) Wadi Umm Ghudran Formation exposed northeast of Amman, Jordan (at N 32° 09.241′, E 36° 12.960′, to be exact). I hope someday to visit Jordan, so this work may be my introduction.

The fossils are diverse, including oysters, corals, gastropods and a bivalve of the Family Veneridae shown above. I was struck by how similar this fossil is to its very common modern cousin Mercenaria mercenaria (shown below).

The modern clam shell above, by the way, was one dissected by Invertebrate Paleontology students last year.

These venerid clams are infaunal, meaning they live within the sediment. Thus when east-coasters go “clamming” on a beach they are digging up clams like this from the sand at low tide. They use short tubes (siphons) like watery snorkels to suck in seawater to be filtered through their gills for suspended food particles. Since they live in the sediment their shells are usually clean of encrusters or borers while alive. After death the shells are usually cycled up to the surface and then encrusted and bored as seen below. This is an interesting feature of the Jordanian fossil shell bed — some shells are articulated and clean as the shell at the top; others are disarticulated and heavily bored. Clearly some shells were buried alive and others died long before final internment.

Venerid bivalves are heterodonts, meaning they have “different teeth”. These are not teeth for eating but rather parts of the clam’s hinge structure that hold the valves together. The shapes and sizes of these teeth are used to sort these clams into genera and species. Again, as you can see below, the teeth of the Cretaceous clam are similar to those of the modern shell, but with enough differences to make them separate genera.

The Family Veneridae is entirely marine and includes over 500 living species, many of which are delicious, I’m told. The most common clam consumed in the USA is Mercenaria mercenaria, known as the hard clam or quahog. There are 55 extinct genera in this family, which appeared first in the Early Cretaceous (Cox et al., 1969; Canapa et al., 1996).

This rather plain and common fossil will be the key to deciphering the history of our shell bed in Jordan. Sometimes the most useful fossils are the least flashy.

References:

Canapa, A., Marota, I., Rollo, F. and Olmol, E. 1996. Phylogenetic analysis of Veneridae (Bivalvia): Comparison of molecular and palaeontological data. Journal of Molecular Evolution 43: 517-522.

Cox, L.R. et al. 1969. Treatise on Invertebrate Paleontology, pt. N, Bivalvia vol. 2. The Geological Society of America, Inc. and The University of Kansas.

Wooster’s Fossil of the Week: A receptaculitid (Middle Ordovician of Missouri)

September 18th, 2011

This week’s fossil is a long-standing paleontological mystery. Above is a receptaculitid from the Kimmswick Limestone (Middle Ordovician) near Ozora, Missouri. I think I found it on a field trip with Frank Koucky in the distant mists of my student days at Wooster, but so many outcrops, so many fossils …

Below is a nineteenth century illustration of a typical receptaculitid fossil. They are sometimes called “sunflower corals” because they look a bit like the swirl of seeds in the center of a sunflower. They were certainly not corals, though, or probably any other kind of animal. Receptaculitids appeared in the Ordovician and went extinct in the Permian, so they were confined to the Paleozoic Era. Receptaculitids were bag-like in form with the outside made of mineralized pillars (meroms) with square or diamond-shaped heads. The fossils are usually flattened disks because they were compressed by burial. You may notice now that the fossil at the top of this post is a mold of the original with the dissolved pillars represented by open holes. (Paleontologists can argue if this is an external or internal mold.)So what were the receptaculitids? When I was a student we called them a kind of sponge, something like a successor of the Cambrian archaeocyathids. In the 1980s a convincing case was made that they were instead a kind of alga of the Dasycladales. Now the most popular answer is that they belong to that fascinating group “Problematica”, meaning we have no idea what they were! (Nitecki et al., 1999). It’s those odd meroms that are the problem — they appear in no other known group, fossil or recent.

I find it deeply comforting that we still have plenty of fossils in the Problematica. We will always have mysteries to puzzle over.
Another Wooster receptaculitid specimen, this time seen from the underside showing side-views of the meroms.
Diagram of a receptaculitid in roughly life position showing its inflated nature and pillar-like meroms. From Dawson (1880, fig. 25): a, Aperture (probably imaginary here). b, Inner wall. c, Outer wall. n, Nucleus, or primary chamber. v, Internal cavity.

Finally, this is what a typical receptaculitid looks like in the field (Ordovician of Estonia). Note that nice sunflower spiral of the merom ends.

References:

Dawson, J.W. 1880. The chain of life in geological time: A sketch of the origin and succession of animals and plants. The Religious Tract Society, 272 pages.

Nitecki, M.H., Mutvei, H. and Nitecki, D.V. 1999. Receptaculitids: A Phylogenetic Debate on a Problematic Fossil Taxon. Kluwer Academic/Plenum, 241 pages.

Fossils in the Wild: Invertebrate Paleontology Field Trip

September 11th, 2011

CAESAR CREEK LAKE, OHIO–The 2011 Invertebrate Paleontology class had a productive field trip on a beautiful Ohio day. Thunderstorms roamed the state, but we saw them only when we were comfortably on the bus.

We worked in the emergency spillway at Caesar Creek Lake in southwestern Ohio, roughly halfway between Cincinnati and Dayton. This site is maintained by the US Army Corps of Engineers as a fossil-collecting preserve. You obtain a free permit at the visitor center, agree to follow the rules, and extraordinary fossils await your picking. (Last time I was here it was very cold.)

The fossils are in the Arnheim, Waynesville, Liberty and Whitewater Formations of the Richmondian Stage in the Cincinnatian Series of the Ordovician System. These are shaly units with shell-rich limestones formed during storms. Brachiopods, bryozoans, crinoids, trilobites, clams, snails, nautiloids, corals — the whole Ordovician menagerie. Perfect for student collections and our later exercises.

Brachiopod-rich storm layer in the Liberty Formation. Note the circular bryozoan attachment.

Bryozoan colony and brachiopod shell interior from the Waynesville Formation.

Our fancy bus. The design insures that the back seats are rather bouncy.

Last of the summer flower field photos! It was such a beautiful day.

Wooster’s Fossils of the Week: Sponge and clam borings that revealed an ancient climate event (Upper Pleistocene of The Bahamas)

September 11th, 2011

This week’s fossils celebrate the publication today of a paper in Nature Geoscience that has been 20 years in the making. The title is: “Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral”, and the senior author is the geochronological wizard Bill Thompson (Woods Hole Oceanographic Institution). The junior authors are my Smith College geologist friends Al Curran and Brian White and me.

The paper’s thesis is best told with an explanation of this 2006 image:
This photograph was taken on the island of Great Inagua along the coast. The flat dark surface in the foreground is the top of a fossil coral reef (“Reef I”) formed during the Last Interglacial (LIG) about 123,000 years ago. It was eroded down to this flat surface when sea-level dropped, exposing the reef to waves and eventually terrestrial weathering. The student sitting on this surface is Emily Ann Griffin (’07), one of three I.S. students who helped with parts of this project. (The others were Allison Cornett (’00) and Ann Steward (’07).) Behind Emily Ann is a coral accumulation of a reef (“Reef II”) that grew on the eroded surface after sea-level rose again about 119,000 years ago. These two reefs show, then, that sea-level dropped for about 4000 years, eroding the first reef, and then rose again to its previous level, allowing the second reef to grow. (You can see an unlabeled version of the photograph here.) The photograph at the top of this post is a small version of the same surface.

The significance of this set of reefs is that the erosion surface separating them can be seen throughout the world as evidence of a rapid global sea-level event during the Last Interglacial. Because the LIG had warm climatic conditions similar to what we will likely experience in the near future, it is crucial to know how something as important as sea-level may respond. The only way sea-level can fluctuate like this is if glacial ice volume changes, meaning there must have been an interval of global cooling (producing greater glacial ice volume) that lowered sea-level about 123,000 years ago, and then global warming (melting the ice) that raised it again within 4000 years. As we write in the paper, “This is of great scientific and societal interest because the LIG has often been cited as an analogue for future sea-level change. Estimates of LIG sea-level change, which took place in a world warmer than that of today, are crucial for estimates of future rates of rise under IPCC warming scenarios.” With our evidence we can show a magnitude and timing of an ancient sea-level fluctuation due to climate change.

Much of the paper concerns the dating techniques and issues (which is why Bill Thompson, the essential geochronologist, is the primary author). It is the dating of the corals that makes the story globally useful and significant. Here, though, I want to tell how the surface was discovered in the first place. It is a paleontological tale.

In the summer of 1991 I worked with Al Curran and Brian White on San Salvador Island in The Bahamas. They were concentrating on watery tasks that involved scuba diving, boats and the like, while I stayed on dry land (my preferred environment by far). I explored a famous fossil coral exposure called the Cockburntown Reef (Upper Pleistocene, Eemian) that Brian and Al had carefully mapped out over the past decade. The Bahamian government had recently authorized a new harbor on that part of the coastline and a large section of the fossil reef was dynamited away. The Cockburntown Reef now had a very fresh exposure in the new excavation quite different from the blackened part of the old reef we were used to. Immediately visible was a horizontal surface running through the reef marked by large clam borings called Gastrochaenolites (see below) and small borings (Entobia) made by clionaid sponges (see the image at the top of this post).
Inside the borings were long narrow bivalve shells belonging to the species Coralliophaga coralliophaga (which means “coral eater”; see below) and remnants of an ancient terrestrial soil (a paleosol). This surface was clearly a wave-cut platform later buried under a tropical soil.


My colleagues and I could trace this surface into the old, undynamited part of the Cockburntown Reef, then to other Eemian reefs on San Salvador, and then to other Bahamian islands like Great Inagua in the far south. Eventually this proved to be a global erosion surface described or at least mentioned in many papers, but its significance as an indicator of rapid eustatic sea-level fall and rise was heretofore unrecognized. Finally getting uranium-thorium radioactive dates on the corals above and below the erosion surface placed this surface in a time framework and ultimately as part of the history of global climate change.

This project began 20 years ago with the discovery of small holes left in an eroded surface by humble sponges and clams. Another example of the practical value of paleontology.

References:

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral. Nature Geoscience (DOI: 10.1038/NGEO1253).

White, B.H., Curran, H.A. and Wilson, M.A. 1998. Bahamian coral reefs yield evidence of a brief sea-level lowstand during the last interglacial. Carbonates and Evaporites 13: 10-22.

Wilson, M.A., Curran, H.A. and White, B. 1998. Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250.

Wooster’s Fossil of the Week: A tabulate coral (Middle Devonian of New York)

September 4th, 2011

This week’s specimen is from a group of fossils I gave my Invertebrate Paleontology students as “unknowns” to identify. Since it is their very first week of class I expected them to struggle, but many did remarkably well. (Congratulations to Lauren Vargo and Kit Price for correctly identifying it to the genus level, and to Lauren for hitting the species itself!)

Pleurodictyum americanum Roemer 1876 is pictured above with a view of its living surface. It is a tabulate coral belonging to the Family Favositidae, thus another type of “honeycomb coral” as we’ve discussed before on this blog. This particular species is notable because it is very common in the Middle Devonian of the northeastern United States (Pandolfi and Burke, 1989). Brian Bade collected this coral, along with hundreds of others, from the Kashong Shale exposed in Livingston County, New York. He generously donated it to the paleontological teaching and research collection at Wooster.

What is most interesting about these corals is that they are almost always found with an external mold of a elongate snail shell on the underside at their origin. The snail (more officially called a gastropod) is Palaeozygopleura hamiltoniae (Hall, 1860), and it is best known for its tight relationship with Pleurodictyum americanum. Brett and Cottrell (1982) published a detailed study of P. americanum and its associates, concluding that the coral preferred to encrust P. hamiltoniae shells but only when the snail itself was dead and gone and the shell was occupied by some other organism.
Pleurodictyum americanum underside showing an external mold of the gastropod Palaeozygopleura hamiltoniae.

Closer view of Palaeozygopleura hamiltoniae.

Pleurodictyum americanum was described by Carl Ferdinand von Roemer in 1876. Roemer was a German geologist (you probably guessed) who lived from 1818 to 1891 — a time interval encompassing some of the greatest changes in the Earth Sciences, from the primacy of Charles Lyell to the general acceptance of Darwinian evolution. Roemer was educated at Göttingen to be a lawyer, but in 1840 abandoned the legal profession for the much more exciting life of a geologist. He quickly obtained one of those new-fangled German PhD degrees in 1842 and set to work.
Roemer’s original 1876 drawings of Pleurodictyum americanum.

In 1845, Roemer traveled to the USA and studied the geology of Texas and other southern states. That must have been an adventure — the Battle of the Alamo was less than ten years before. It was during the American work that he began to describe Devonian fossils, including our coral species (Roemer, 1876). Roemer became a professor of geology, paleontology and mineralogy (another field in which he had significant accomplishments) at the Universty of Breslau, where he ended his career.

Carl Ferdinand von Roemer (1818 to 1891) at the University of Breslau (now the University of Wrocław in Poland).

References:

Brett, C.E. and Cottrell, J.F. 1982. Substrate specificity in the Devonian tabulate coral Pleurodictyum. Lethaia 15: 247-262.

Pandolfi, J.M. and Burke, C.D. 1989. Environmental distribution of colony growth form in the favositid Pleurodictyum americanum. Lethaia 22: 69–84.

Roemer, F. von. 1876. Lethaea geognostica: Handbuch der erdgeschichte mit Abbildungen der für die formationen bezeichnendsten Versteinerungen, I. Theil. Lethaea palaeozoica. E. Schweizerbartsche Verlagshandlung (E. Koch), Stuttgart, Germany.

Wooster Geologists begin the 2011-2012 school year

September 1st, 2011

WOOSTER, OHIO–The cheerful group above is the Wooster Geology Club in our traditional start of the year group photograph. (The image was kindly taken by Danielle Reeder.) We are fewer than usual because an unprecedented number of our geology majors are overseas on off-campus adventures (seven juniors) and our beloved petrologist Meagen Pollock is on a semester research leave. An addition to our crew this year is the man in the upper left with a beard. He is Matt Curren, our new geological technician.

Here you can see happy students in the 8:00 a.m. Invertebrate Paleontology course enjoying their first taste of taxonomic rules and the problem of species. Or maybe they’re grinning because they just learned there is not a quiz this morning?

There are two significant changes in Scovel Hall for this year. We have a new X-Ray Laboratory under the supervision of Dr. Pollock, complete with a “clean room” for wet chemistry. (I know what the alumni are thinking: A clean room in Scovel? But yes, it really is!) We also have fancy new (and wonderfully silent) computer projection systems in our classrooms, as seen below. We are now very far beyond those old 35 mm slide projectors I grew up with.

Our courses have detailed webpages that you are encouraged to visit. You may also want to see our list of Geology Club events, including Independent Study presentations and outside speakers. Finally, you can follow this link to pdf versions of our annual reports, including our report for this past year and summer (see cover below). Patrice Reeder works very hard to produce these high quality documents.

It is going to be another eventful year for the Wooster Geologists. We again thank the generations that have gone before us to build this department, and the alumni and friends who support us so faithfully.