Archive for March, 2013

Wooster’s Fossil of the Week: A pretty little fish from the Eocene of Wyoming

March 31st, 2013

Knightia_eocaena_033013_585Most people have seen this fossil fish type. Geologists, in fact, have probably seen Knightia eocaena Jordan, 1907, thousands of times. It is present in nearly every gift shop that sells fossils, usually as small plaques or glued to refrigerator magnets. It is the state fossil of Wyoming and, by all accounts, the most numerous fossil fish in the world. In fact, it is likely the most common vertebrate fossil ever. It is thus no surprise that Wooster has dozens of specimens, most of them donated by students and alumni.

Knightia lived in freshwater lakes throughout western North America during the Eocene. It is closely related to herring and sardines, and almost certainly had similar life habits. We know that it lived in large schools, and we suspect it had a diet of phytoplankton and insect larvae. It was low on the ecological food chain, just like its modern cousins, and so was an important food source for all sorts of larger fish, reptiles, birds and mammals.
MeagensFish585We tend to see most often beautifully preserved, complete Knightia specimens like the one at the top of the page. This is because if a fossil is very common, collectors can afford to keep only the best specimens. It is fun, though, to see what the average Knightia looks like in the fossil record. Above is a specimen collected by our petrologist Meagen Pollock from an outcrop in Wyoming. Note that the fish are contorted and often overlapping — specimens that are usually discarded by collectors. This slab shows better that these fossils occur in vast, complicated, messy death assemblages, probably because of volcanic ash falls or quick changes in lake chemistry.
Knightia_BW_TamuraThis is a digital reconstruction of Knightia (© N. Tamura). Note the deeply forked tail and flattened top of the head.

Dsjordan_wikipediaKnightia was named in 1907 by the accomplished and very problematic David Starr Jordan (1851-1931). Jordan was a well known fish expert, having been inspired by the iconic ichthyologist Louis Agassiz himself. He taught at several colleges and universities, eventually serving as president of Indiana University (at 34, the youngest university president at the time) and as the first president of Stanford University. He was a very successful university president, especially in the first years of Stanford.

But, but … David Starr Jordan was also a eugenicist, believing in compulsory sterilization of the “unfit”. On the bright side (if there is one here), he opposed war because it tended to kill the most fit members of society. Jordan also shockingly covered up the apparent murder of Jane Stanford, co-founder of the university, in 1905. Jordan does not look good at all in that story, most of which was sorted out only about ten years ago. Who would have guessed that a murder mystery could lurk in the taxonomic history of these pretty little fish?

References:

Grande, L. 1982. A revision of the fossil genus Knightia, with a description of a new genus from the Green River Formation (Teleostei, Clupeidae). American Museum Novitates 2731: 1-22.

Jordan, D.S. 1907. The fossil fishes of California; with supplementary notes on other species of extinct fishes. Bulletin, Department of Geology, University of California 5:136.

The field trip scout

March 30th, 2013

MeadvilleLodi033013WOOSTER, OHIO–One of the early spring pleasures of a geologist in the Upper Midwest is finally getting outside and scouting the field trips for the semester. Today we had bright sun and temperatures in the 50s (I know — I’m settling) so I went out to plan the late April field trip for my sedimentology and stratigraphy class. The sites I’ve been using in the last few years have become too overgrown, so it is time to find new projects in new places. Since the delightfully underbrush-free Mojave Desert is too far away, I’m looking at places in northeastern Ohio. It was a fun day.

Above is an outcrop of the Meadville Shale Member of the Cuyahoga Formation (Lower Carboniferous, late Kinderhookian) exposed in the Lodi Community Park about 20 miles north of Wooster. A tributary of the Black River (the East Fork Black River) flows through a small valley, exposing the shale in its cutbanks. I’m a bit partial to this location because from here a fellow Wooster student found a trilobite that became the basis of my first scientific publication. The unit here is moderately fossiliferous and contains numerous rock types besides shale. It will make a fine place for students to measure and describe stratigraphic sections next month. It certainly was a beautiful place to spend a sunny Saturday morning.

TurkeyVulture033013There were many turkey vultures (Cathartes aura) perched in the still-leafless trees in northern Wayne and southern Medina Counties. Here’s one keeping an eye on me. Turkey vultures are a sign in Ohio that spring really is coming (even if it is supposed to snow tomorrow morning!).

Dr. Michael Mann visits Wooster

March 28th, 2013

MichaelMann032713WOOSTER, OHIO–We were honored this week when Dr. Michael E. Mann, one of the world’s foremost climate-change experts and a leader in the efforts to educate the public about anthropogenic effects on the atmosphere, came to Wooster as part of our Richard G. Osgood, Jr., Memorial Lecture series. He gave a public lecture in the nearly-full Gault Recital Hall Wednesday evening (“The Hockey Stick and the Climate Wars: Dispatches from the Front Lines”), and then a Geology Club lecture the next day in Scovel (“The Past as Prologue: Learning from the Climate Changes in Past Centuries”). Students, faculty and staff of the Geology Department also had a wonderfully informative dinner with him in the Wooster Inn.

Michael Mann is very well known in the diverse community that studies climate change in the past, present and future. He was the senior author of a pivotal article in the Intergovernmental Panel on Climate Change (IPCC) Third Scientific Assessment Report in 2001. It set the direction for more than a decade of later climate research. He has written dozens of other papers and two books on climate change. He has received numerous awards, most recently the Hans Oeschger Medal of the European Geosciences Union.

The public Osgood lecture Dr. Mann presented on Wednesday was centered on his latest book. He described the recent scientific history of climate change research and then how he became an “accidental public figure” through the famous “Climategate” theft and publication of private email messages. His stories of attempted congressional interference in his work and that of other climate scientists were astonishing, representing what he calls “the scientization of politics” (where science — or pseudoscience — is used as a political tool).

The image at the top of the page is Dr. Mann near the end of his Osgood Lecture. The image on the screen is of his daughter enjoying a moment in the polar bear pool at the Pittsburgh Zoo and PPG Aquarium. He fears that someday such animals will be found only in zoos because humans “melted their Arctic environment.” Numerous questions and conversations followed.
MannLecture032813Dr. Mann gave a Geology Club presentation this morning in Scovel Hall on some of his scientific work (shown above). He talked about using proxies to model historical climate change and then predict future climate.
WilesMann032813For me one of the best moments was his conversation with Greg Wiles in our dendrochronology lab (above). It was great fun to see how the work of Wooster Geologists is part of the unfolding grand story of what factors control our climate, and why such research is critical in our efforts to cope with future changes.

Wooster’s Fossil of the Week: A grazed oyster from the Middle Jurassic of Gloucestershire, England

March 24th, 2013

Praeexogyra_acuminata_585This small oyster is not in itself unusual. In fact, it is one of the most common fossils in the Jurassic of western Europe: Praeexogyra acuminata (Sowerby, 1816). It may be better known by its older name: Ostrea acuminata. Local collectors call it the “sickle oyster” because of its curved shape. This specimen is from the Sharp’s Hill Formation (Middle Bathonian) exposed in the Snowshill Quarry near Moreton-in-Marsh, Gloucestershire, England. I collected it on my first trip to England in 1985.
Praeexogyra_acuminata_closerWhat attracted me to this particular shell can be seen in the above close-up: lots of little straight lines incised across its outer surface (along with a serpulid worm tube). The lines were scraped by the Aristotle’s Lantern of one or more regular echinoids (sea urchins). This is the trace fossil Gnathichnus pentax Bromley, 1975. We met this fossil last month cut into a Cretaceous oyster from Israel. One or more echinoids grazed over this Jurassic oyster, probably consuming algae and other organic materials.

Praeexogyra acuminata was an epifaunal filter-feeder, meaning it lived on the substrate sucking in seawater and sorting from it organic material for food. During the Middle Jurassic these oysters were so common that their shells formed thick deposits. It is possible that some deposits rich in these shells were formed in brackish waters rather than under fully marine conditions.

Ostrea acuminata was named by by the enthusiastic English natural historian James Sowerby (1757-1822). We met him earlier as the author of a Cretaceous bivalve genus.

References:

Bernard-Dumanois, A. and Delance, J-H. 1983. Microperforations par algues et champignons sur les coquilles des «Marnes à Ostrea acuminata (Bajocien supérieur) de Bourgogne (France), relations avec le milieu et utilisation paléobathymétrique. Geobios 16: 419-429.

Bernard-Dumanois, A. and Rat, P. 1983. Etagement des milieux sédimentaires marins. Paléoécologie des Huîtres dans les “Marnes à Ostrea acuminata” du Bajocien de Bourgogne (France). Comptes rendus de l’Académie des sciences Paris 296: 733-737.

Hudson, J.D. and Palmer, T.J. 1976. A euryhaline oyster from the Middle Jurassic and the origin of true oysters. Palaeontology 19: 79-93.

Wooster Geologist at Valley Forge, Pennsylvania

March 20th, 2013

ValleyForgeHuts032013BRYN MAWR, PENNSYLVANIA–While visiting my friends and colleagues Katherine and Pedro Marenco at Bryn Mawr College, I visited the nearby Valley Forge National Historical Park. Everyone will remember, of course that this is the place outside Philadelphia that the Continental Army made its rough winter quarters in 1777-1778. The huts above are reconstructions of the soldiers’ quarters on the windy and cold fields. Commander-in-Chief George Washington chose this place because it was easily defensible, had plenty of timber for construction and fuel, and was close enough to British-occupied Philadelphia to keep an eye on the enemy — yet not so close to be likely attacked.

LedgerOutcrop032013

As a geologist, of course, I also looked for the rocky bones beneath the landscape. They were easily found in the above cliff near the main parking area. This is the Ledger Dolomite, a Cambrian unit found throughout this part of eastern Pennsylvania.

LedgerDolomite032013The Ledger Dolomite here is distinguished by these fine laminations visible on its weathered cross-sections. These are apparently stromatolites: laminar structures built by bacterial mats. We’ve met Cambrian stromatolites before in this blog.

Smilodon_gracilisI was surprised to learn that there is also a significant middle Pleistocene fossil deposit in Valley Forge called the Port Kennedy Bone Cave. This is a sinkhole deposit within the Ledger Dolomite. A particularly large sinkhole apparently trapped a variety of animals, including the gracile sabre-tooth Smilodon gracilis, the skull of which is on display in the Valley Forge Historical Park visitor center. S. gracilis was the smallest and earliest member of its genus. The Port Kennedy Bone Cave was one of the first fossil assemblages that the famous paleontologist Edward Drinker Cope studied. The location was lost to science until its rediscovery in 2005.

ValleyForgeCannon032013This is the requisite cannon image, even though no battle was fought here. It is nevertheless a dramatic place for the privations the soldiers suffered during the darkest days of the Revolutionary War. It is hard to imagine the conditions in 1777-1778 now since highways and casinos surround the old encampment.

Wooster’s Fossil of the Week: Cast of a lower jawbone of the largest ape ever (Pleistocene, southern China)

March 17th, 2013

Gigantopithecus_blacki_mandible_010112The above is one of my favorite “fossils”, a commercially-available cast of the lower jawbone of Gigantopithecus blacki, a giant extinct ape. It was produced from an actual Pleistocene fossil found in a cave near Liucheng, Guangxi, in southern China. I like it especially because it is sometimes associated with the mythical “Bigfoot”.

Gigantopithecus blacki was the largest ape that ever lived: up to three meters tall and weighing over 500 kilograms. (G. blacki is known only from teeth and mandibles such as that shown above, so these size estimates are based on scaling.) It was a contemporary with early versions of our own species, which must have led to a few astounding encounters for our ancestors. G. blacki was two or three times heavier than the largest gorillas today.

Gigantopithecus blacki appears to have lived in bamboo forests. Striations on its teeth, and the occasional phytolith stuck in the enamel, shows that this species was a vegetarian. It may have even had a lifestyle much like today’s pandas.

The molars of Gigantopithecus blacki look surprisingly like ours with their multiple cusps and broad surfaces. This is the result of convergent evolution and not an indication of a recent common ancestry. (They are analogous features, not homologous.) G. blacki is now classified in the Subfamily Ponginae with their cousins the orangutans.

What is most fun about Gigantopithecus these days is its association with the “Bigfoot” illusion. Look at how seriously the people at the “Bigfoot Field Researchers Organization” take the possible connection of Gigantopithecus and Bigfoot. Despite their objections, we really can wonder why we’ve never found evidence of this giant ape in North America, including bones, teeth, legitimate footprints or real photographs. A living three-meter tall ape is a bit difficult for science to have missed! (Unless, of course, Bigfoot has supernatural powers.)

References:

Coichon, R. 1991. The ape that was – Asian fossils reveal humanity’s giant cousin. Natural History 100: 54–62.

Ciochon, R., et al. 1996. Dated co-occurrence of Homo erectus and Gigantopithecus from Tham Khuyen Cave, Vietnam. Proceedings of the National Academy of Sciences of the United States of America 93: 3016–3020.

Jin, C., et al. 2009. A newly discovered Gigantopithecus fauna from Sanhe Cave, Chongzuo, Guangxi, South China. Chinese Science Bulletin 54: 788-797.

Last day in the Mojave Desert for Wooster Geologists … this year

March 15th, 2013

RedRocks031513LAS VEGAS, NEVADA–We left the fine people at the Desert Studies Center in Zzyzx in the morning and drove in an all-too-irregular way through Las Vegas (sorry about that, other drivers!) to the spectacular Red Rocks National Conservation Area northwest of the city. Here we see a Paleozoic section thrust from the west over the white and red rocks of the Aztec Sandstone (Lower Jurassic). The view above is looking directly west from the visitor center. I don’t know all the names of these peaks, but I do recognize Mount Wilson on the left. (I did my dissertation in the Carboniferous rocks exposed in the background, but I don’t think they named the mountain after me.)

Our students, faculty and staff scattered for a couple of hours in this park on yet again a very pleasant day. Many of them climbed the sandstone cliffs, no doubt impressed by the large foresets showing that these sediments were deposited in massive dunes blown in from the east.

RedRocksVisitorCenter031513The redesigned visitor center at Red Rocks is excellent. Above is a view of part of the outside portion that takes advantage of the sun’s angle and cooling breezes. It includes a desert tortoise enclosure where we saw three of these endangered animals. This complex is so attractive and efficient that Yoav Avni took many photographs so that he could show Israeli planners some new ideas for their public displays.

At noon we drove back into Las Vegas and the open jaws of the McCarran Airport Complex. We turned in all four vans with no problems, got our boarding passes for our various destinations, and now are simply waiting in the airport for our flights out. An excellent and enjoyable trip in all respects. Here’s to Jason and Rob at the Desert Studies Center for their friendly and efficient management, to the rangers of the National Park Service for their helpful advice, to the faculty and staff leaders and drivers (so many miles!), and finally to the students who could not have been better ambassadors for Wooster Geology. Their enthusiasm and good humor is what makes these trips so special. We will return!

Exploring the Tecopa region … and finally the trilobites!

March 14th, 2013

SaltSpring031413ZZYZX, CALIFORNIA–This was our last full day of geological adventures in the Mojave Desert for 2013. The weather was even warmer than yesterday, with the temperature in Baker at 4:00 p.m. a delightful 94°F. We began in the usual way from our temporary home at the Desert Studies Center, heading north of Baker again to Shoshone and the Tecopa area. Our first stop was at Salt Creek Spring in the Salt Spring Hills, one of the rare riparian environments in this part of the desert. This place is also notable as the first place gold was found in southern California. This discovery in 1849 began the boom in mining throughout the Mojave Desert.

TafoniMelissa031413One of the interesting geological features we noted was the occurrence of the familiar tafoni, but this time in a deeply eroded outcrop of quartz monzonite (shown above with Melissa Torma). Our companion Yoav Avni believes this may represent a Pleistocene pluvial phase of erosion that has been exhumed in the modern landscape. Tafoni features in granite would seem to require more water than is present today in this system, thus placing these features during a wet interval makes sense.

ShoshoneMuseum031413We next returned to the little settlement of Shoshone, this time visiting the town museum (above). It is well worth touring for its local artifacts, some wildlife displays, and the bones and teeth of the Shoshone Mammoth found in the Tecopa lake sediments.

Archidiskodon_tamenensis031413The mammoth (Archidiskodon tamenensis on the sign) has been very well preserved by the lake clays and silts, especially the diagnostic teeth and jaws. It is an impressive find and an important addition to our knowledge of the ancient Lake Tecopa ecosystem.

OliviaBrownResting Springs031413The Resting Springs Welded Tuff exposed east of Shoshone is one of the most famous roadcuts in the Mojave Desert. Above we see Olivia Brown exploring the glassy black middle of the unit. The colors and hardnesses of the rocks here show degrees of welding from the intense heat developed in this pyroclastic flow. It is technically a devitrified pumice tuff, welded tuff, and vesicular vitrophyre dated by K-Ar methods as 9.5 million years old. The fiamme are fantastic.

JonahDragFold031413In the same outcrop of the Resting Springs Tuff are some impressive faults. Jonah Novek is showing above how he knows this is a normal fault because the drag fold shows downward movement of the hanging wall (the side he is standing on).

TrilobiteCollecting031413At lunchtime we arrived at Emigrant Pass east of Tecopa to collect trilobites from the Cambrian Carrara Formation exposed on the north side of the highway (which happened to be the Old Spanish Trail). After a bit of exploring, our ace field geologist Shelley Judge found the most fossiliferous outcrops. We found hundreds of the fascinating critters, leaving most for future field trips. I like the view above, by the way, because it shows Telescope Peak on the far distant skyline.

TrilobiteWhole031413The best trilobite of the day (and there were many good specimens) was collected by Olivia Brown. It is a rare whole specimen, apparently of the genus Olenellus. You can see all the thoracic segments and spines, as well as the pygidium. The way the cephalon is separated from the thorax may indicate that it is a preserved exuvium (molt). Very nice.

ChinaRanchSign031811aFollowing a geological tradition transferred from Sonoma State University geologists to us via my friend Matthew James, we visited China Ranch south of Tecopa and had date milkshakes. Delicious and refreshingly cool on what turned out to be a very hot day. We also had a good geology lesson with the fanglomerates and ancient lakebeds exposed around the date groves.

TecopaPlaya031413While driving out of Tecopa, we stopped to walk out onto the Lake Tecopa playa, which was covered by a thin crust of salts. From the left are Meagen Pollock, Melissa Torma, Shelley Judge and Olivia Brown. We observed the modern playa sediments juxtaposed with the ancient lake strata exposed as low mounds.

WadeExit031413Last of all was a stop to briefly recognize the Harry Wade exit route out of Death Valley at an historical marker on the highway back to Baker. We came full circle at this point, since we started with Death Valley and now ended looking back into that source of such hardship in 1849.

Our final scientific event of the day was an excellent tour of the night sky by the Laboratory Technician of the Vassar College Environmental Sciences and Geography Department, Rick Jones. The sky is very dark and inviting in this lonely part of the desert.

Enjoying the geology of the Mojave National Preserve

March 13th, 2013

StudentsLavaCave031313ZZYZX, CALIFORNIA–Today the Wooster Geologists explored the Mojave National Preserve. It is a beautiful, spacious, diverse place well maintained and protected by the National Park Service. Our first stop of the morning is shown above. We explored a lava tube in the cinder cones portion of the preserve. We descended into the dark tunnel by the steps above, and then studied the walls and ceiling with our flashlights, as Melissa Torma is doing below.
MelissaCave031313Lava tubes are formed when a lava flow cools on the top and sides, and then the remaining lava flows out, leaving behind the empty shell. In this particular lava tube we could see various level markings the lava left on the walls as it drained away. We also saw spatter and “lavacicles” hanging from the ceiling much like icicles or stalactites in a cave. My favorite part is where we can see from below a granitic boulder that was caught up in the flowing lava.
CambrianLimestoneOutcrop031313South of the lava tube along Kelbaker Road is a small outcrop of Cambrian limestone. We examined these rocks for a short time (above) to sort out their lithologies and the paleoenvironment in which the sediment accumulated. The clues included extensive and diverse horizontal burrow systems (shown below) and numerous oncoids with shelly nuclei.
BurrowsLimestone031313The students determined that the burrows were filled with dolomite from later diagenesis of the sediment, and that the oncoids showed the system was deposited well within the photic zone. We think this rock is a biomicrite formed around the storm wavebase on a shallow carbonate platform.

KelsoDunes031313One of our favorite places is Kelso Dunes. These massive piles of sand are stabilized at their bases but still moving about at their crests. We’ve studied them so many times in the Desert Geology and Sedimentology & Stratigraphy courses that we needed to say little about them. The students raced to the top, noting the diverse sand composition (so much more than just quartz) and eolian structures on the way.

TafoniAnanda031313Ananda Menon is here showing us one of the magnificent tuff beds at the Hole in the Wall locality in the easternmost portion of the Mojave National Preserve. The holes in the wall (is that how the place was named?) are examples of tafoni, a rock weathering pattern. We hiked the Rings Loop Trail examining the tuff units and their diverse clasts, including pumice and charcoal. We also saw good examples of Indian petroglyphs of unknown age.

QtzMonzoniteCimaDome031313While crossing Cima Dome on the way back to Zzyzx, the group visited an outcrop of quartz monzonite which forms at least part of the intrusive body under the uplift. As with most of our outcrops, it was a story of both petrology and structural deformation.

AlienFreshJerky031313Finally, at the end of the day I could not resist taking the Wooster Geologists to the unique store in Baker called “Alien Fresh Jerky“. Half the group loved it, the other seemed offended by the epic cheesiness. At least Melissa Torma and Jonah Novek enjoyed meeting members of the Galactic Peace Patrol parked in front.

Folded rocks, volcanoes, and a little of the Old West

March 12th, 2013

CalicoMemberFolds031213ZZYZX, CALIFORNIA–The spectacular set of folds above are exposed in the lower parking lot of Calico Ghost Town near Barstow, California. This is a famous site that has been visited by hundreds of geologists, but there are still many mysteries about the causes of this deformation and even the correlation of these rocks in the region. The section makes up the Calico Member of the Barstow Formation, which is apparently below the exposed units of the Barstow Formation in Owl Canyon and Rainbow Basin we saw yesterday.
ShelleyCalico031213As a true structural geologist, Shelley Judge is here explaining the folding of these beds with her hands and, later, a sketch on notepaper. “Explaining” is not quite the right word: she wrangles information and observations out of the students first before developing the deformation hypotheses. It is not just about a bit of compression!
StudentsCalico031213After exploring a wadi west of the town, we then spent the rest of the morning in Calico. The students above (from the left, Kyle Burden, Steph Bosch, Sarah Frederick, Olivia Brown and Alex Hiatt) are enjoying the main street of this reconstructed 1880s mining community. There are lots of attractions here, from sarsaparilla in the saloon to a classic old-timey mystery shack. One gentleman, hearing that we were geologists, kindly explained to us how Calico Mountain is an extinct volcano with “sandy dikes” full of metals and remnants of lava flows on its sides. It was fun to see our students grapple with the question: do we correct this nonsense or just smile and avoid the hassle? (I just let it pass because I was hungry for lunch!)
AmboyCrater031213In the afternoon we drove south and east along Interstate 40 and Route 66 (yes, the Route 66) to Amboy Crater (shown above). The day had warmed considerably — my thermometer said it was now 94°F. Nevertheless, the stalwart geology crew walked to this gorgeous cinder cone and climbed to its rim from the inside (shown below). I enjoyed learning about the subtle features of the lava flows that emanated from the cone, including pressure ridges and hexagonal cooling joints. This flows and the cinder cone look amazingly fresh. The lava flows have been dated at between 6000 and 500 years old.

InsideAmboy031213
Verbena031213The warm temperatures at Amboy brought out some reptiles, to our delight. We saw at least three desert iguanas and many flowers, including the Sand Verbena (Albronia villosa) shown above. It felt like summer, although we were still in the middle of March. Tomorrow is expected to be even warmer. (Yes!)

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