Archive for October, 2012

Wooster’s Fossils of the Week: Bivalve Borings (Upper Miocene of Spain)

October 28th, 2012

This beautiful object has a complex history. In the center is a gray limestone cobble that eroded from an underwater ridge and rolled free on a shallow coral reef in an area now near Abanilla, southeastern Spain. It was encrusted by a scleractinian coral, which grew thickly all around the cobble because it was turned continually by wave and current action. Larvae of the bivalve Lithophaga landed on the surface of the coral and quickly began to bore downwards, creating the trace fossil Gastrochaenolites torpedo Kelly and Bromley, 1984. They bored in some cases all the way into the cobble nucleus. The whole set was then buried in transgressive sediments of the Los Banós Formation during the Late Miocene. In the summer of 1989, my student Genga Thavi (“Devi”) Nadaraju (’90) found it as part of her Keck Geology Consortium fieldwork for her Independent Study project. It now resides proudly in the trace fossil collection at Wooster.

Closer view of the gray limestone cobble in the center. Note the remnants of Lithophaga shells still in the borings.

The bivalve boring Gastrochaenolites was named in 1842 by a French geologist with a magnificent name: Alexandre Félix Gustave Achille Leymerie (1801-1878). He was a prolific author with a long career spent primarily studying Cretaceous rocks and fossils in France and northern Spain.

References:

Kelly, S.R.A. and Bromley, R.G. 1984. Ichnological nomenclature of clavate borings. Palaeontology 27: 793-807.

Leymerie, M.A. 1842. Suite de mémoire sur le terrain Crétacé du département de l’Aube. Mémoire des Société Géologique de France 5: 1-34.

Mankiewicz, C. 1995. Response of reef growth to sea-level changes (late Miocene, Fortuna Basin, southeastern Spain). Palaios 10: 322-336.

Mankiewicz, C. 1996. The middle to upper Miocene carbonate complex of Níjar, Almería Province, southeastern Spain, in Franseen, E.K., Esteban, M., Ward, W.C., and Rouchy, J.-M., eds., Models for carbonate stratigraphy from Miocene reef complexes of the Mediterranean regions: Tulsa, SEPM (Society for Sedimentary Geology), p. 141-157.

Nadaraju, G.T. 1990. Borings associated with a Miocene coral reef complex, Fortuna basin, southeastern Spain. Third Keck Research Symposium in Geology (Smith College), p. 165-168.

Taylor, P.D. and Wilson, M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62: 1-103.

An IS Meeting in the Phoenix Airport

October 21st, 2012

Phoenix, Arizona – The Wooster geologists hit a little snafu on their return trip from Arizona. Fortunately, they’ve been rebooked on a red-eye and have 12+ hours to spend in the airport. Instead of relaxing with a coffee or shopping for matching Phoenix shirts, these Wooster geologists have decided to hold a marathon IS meeting (lucky Whitney).

20121021-154035.jpg It’s actually the opportune time to debrief after an intense 3-day conference and field trip. Our conversations with physical volcanologists and experts in southwest volcanism have helped us interpret some of the curious structures that we observed in the field. We’re incorporating our new knowledge in Whitney’s GSA poster, which we planned out today.

20121021-154352.jpg This is just a sneak preview. Don’t forget to stop by her poster on Tuesday to see the final version and to learn about the emplacement of Miter lava flows.

Wooster’s Fossils of the Week: Silicified sclerobionts (Middle Permian of southwestern Texas)

October 21st, 2012

During my work at the National Museum of Natural History last week, I had my research desk amongst the many cabinets housing the famous Permian brachiopod collection made by the eminent paleontologist Richard E. Grant (1927–1995). Most of these specimens are from the Middle Permian of southwestern Texas, and they are preserved in a fantastic way. I peaked into some of these drawers and was just amazed at the beauty and delicacy of these fossils.

Many years ago I received a block of limestone from the Road Canyon Formation (Middle Permian, Roadian, about 270 million years old) found in the Glass Mountains of southwestern Texas. This rock was from an ancient reef system and so nearly completely filled with fossils. The fossils are replaced with very fine-grained quartz (“silicified”), yet the rock matrix around them is limestone (composed of calcium carbonate). The trick, then, is to dissolve away the limestone in hydrochloric acid and watch the delicate replaced fossils emerge. I did this with the Road Canyon Formation rock and recovered hundreds of extraordinary specimens. One set is shown above. Previous Fossils of the Week have included an aberrant brachiopod and a set of reef-forming brachiopods.
While at the Smithsonian, Kathy Hollis showed me a polished block of original Road Canyon Formation limestone (above) and then next to it the results after dissolving a similar block in acid (below). The complex mass of bryozoans, corals and brachiopods is preserved in exquisite detail.
Now, back to the Wooster specimens at the very top of this entry and just above. The platform is the wavy outer layer of a bivalve shell. Attached to it are encrusting organisms (sclerobionts). The long, gorgeous tube is a rugose coral. At its base is a ribbed athyrid brachiopod. Also in this vignette are bryozoans, additional corals and some really tiny productid brachiopods. Beautiful.

References:

Cooper, G.A., and Grant, R.E., 1964, New Permian stratigraphic units in Glass Mountains, West Texas: American Association of Petroleum Geologists Bulletin 48: 1581-1588.

Cooper, G.A., and Grant, R.E. 1966. Permian rock units in the Glass Mountains, West Texas, In: Contributions to stratigraphy, 1966: U.S. Geological Survey Bulletin 1244-E: E1-E9.

Olszewski, T.D. and Erwin, D.H. 2009. Change and stability in Permian brachiopod communities from western Texas. Palaios 24: 27-40.

 

A Different Kind of Conference

October 19th, 2012

Flagstaff, Arizona – The Volcanism in the American Southwest conference is different from any meeting that I’ve attended. First, most of the participants are geologists at academic institutions or government agencies, but there are also a good number of emergency managers, social scientists, aviation specialists, and meteorologists. We’ve come together to discuss the potential volcanic hazards and how best to mitigate them. I’ve learned so much about emergency response planning and how decisions are made. Did you know that each state has an emergency response plan? If you’re a scientist and you’d like to get involved in your state’s mitigation planning, you can join your Emergency Management Association.

Second, the Arizona Shakeout took place this morning during a convenient coffee break.

20121018-210132.jpg Most of us hid under tables or ducked, covered, and held at 10:18 am as we simulated an earthquake. There were even sound effects and shaking (notice the blurry photo). I can honestly say I’ve never crawled under a table with other people at a conference before.

20121018-210630.jpg Finally, our poster session was held outside under Arizona’s blue skies. Whitney, on the far right, is learning about the Smithsonian’s Global Volcanism Program. The sun was almost too bright and too warm for an outdoor poster session, but given that it’s mid-October, I’m not complaining.

A Visit to Meteor Crater

October 18th, 2012

ARIZONA – A short drive east of Flagstaff will bring you to a fabulous view of the San Francisco Peaks and a Natural Landmark called Meteor Crater.

20121017-204748.jpg
Meteor Crater was named as one of Smithsonian Magazine’s “ten most spectacular geological sites.” With a diameter of over 4000 ft and a depth of ~550 ft, the nearly perfect circular crater is truly impressive. According to the tour guide, the crater floor could host 20 simultaneous football games while 2 million fans watch from the crater walls!

20121017-210434.jpg
The crater was formed by an impact about 50,000 years ago and pieces of Fe-Ni meteorites have been found in the surrounding area since the late 1800s.

20121017-210325.jpg Here I am in the bottom of the crater searching for meteorites. Actually, that’s a backdrop in the museum.

20121017-210812.jpg This is what the center of the crater floor looks like: fenced remnants of an abandoned drill shaft. In the early 1900s, a Philadelphia mining engineer named Daniel Barringer drilled the crater floor searching for a potential ore body, which he never found because researchers think that the meteorite was destroyed during the impact.

In the mid 1960s to early 1970s, NASA used the crater to train Apollo astronauts. If you look closely at the fence, there’s an American flag and an astronaut figure in the near-right corner that honors those Apollo astronauts.

Meteor Crater is definitely worth the trip. Take the guided rim tour and ask for Eduardo; he’s very knowledgeable and will have you laughing at each stop.

My First Trip to the Grand Canyon

October 16th, 2012

ARIZONA – Contrast Dr. Wilson’s view in the Smithsonian with my view in Arizona:

20121016-074540.jpg
Believe it or not, this was my first trip to the Grand Canyon, and it didn’t fail to impress. It was a perfect day to hike the South Kaibab trail.

20121016-080012.jpg The trail begins with steep switchbacks through the ~270 million year old Kaibab Limestone and Toroweap Formation.

20121016-081141.jpg It then winds past the fantastically cross-bedded Coconino Sandstone to a place called “Ooh Ahh Point”.

20121016-081414.jpg

20121016-082002.jpg The view certainly inspired oohs and aahs. That’s O’Neill Butte in the center foreground.
Within an hour, we were eating lunch on the ~280 million year old Hermit Shale overlooking O’Neill Butte.

20121016-083053.jpg Despite the ominous signs, we made it out of the canyon in time to hike some of the rim and visit other viewpoints.

20121016-084053.jpg We arrived at the Desert View Watchtower just in time to witness a fabulous sunset. The Watchtower was designed by architect Mary Colter in the 1930s, who was meticulous about incorporating the Hopi culture and even hand selected the stone blocks for their shape and color. Overall, it was a fantastic ending to a memorable first-time visit.

Wooster Geologists at the Smithsonian

October 15th, 2012

WASHINGTON, D.C. — It is Fall Break at the College of Wooster, so some of the geologists have taken the opportunity to get out of town. Dr. Meagen Pollock is under the bright blue skies of the gorgeous state of Arizona. I am now under a string of fluorescent lights between two rows of cabinets deep in the Smithsonian National Museum of Natural History (above) in overcast and gray Washington, D.C. We are both having fun in some very different ways!

I am here on a project studying some enigmatic encrusting fossils from the Paleozoic. Paul Taylor and I want to sort out the mysterious systematic identities of Allonema, Ascodictyon and related forms commonly inhabiting hard substrates, especially in the Devonian. All we can say for certain now is that they are not bryozoans! The specimen above, for example, is USNM 43129 Allonema fusiforme (Nicholson & Etheridge, 1877) figured as Ascodictyon fusiforme in the Treatise of Invertebrate Paleontology, pt. G, p. G35, Fig. 9-3. It was collected from the Devonian of Michigan. It doesn’t look like much more than bubbles of calcite under a light microscope, but later Paul Taylor will show its glories through scanning electron microscopy. I am the advance member of the team, looking through specimens to find the best for Paul to borrow when he visits later this month. We’ll have much more to say about these fossils later.

Above are the specimen boxes for species of the genus Allonema. Note how much information is packed into the small space on the top of each box. Paul and I go through these boxes and examine the specimens they contain with light microscopes in the museum galleries.

There is some humor in the dry world of systematic paleontology.

This is my work station while at the museum. Note the nice photographic tube on the microscope, the comfortable chair, and the lack of any distractions!

I’ve saved the best part for last. Why the plural “Wooster Geologists” in the title? Because the Collections Manager of this world-class paleontological museum is one of my former students — Kathy Hollis (’03). Here is happy, efficient, uber-competent Kathy in her office, clearly in her element. We are very proud of her at Wooster. It is so cool to see her at work in one of the most paleontologically exciting places you could be. Makes up for the gray skies!

Wooster Geologist in Arizona

October 14th, 2012

ARIZONA – This Wooster Geologist has exchanged Ohio’s cool fall weather for blue skies and sunshine in Arizona. I’m here for a conference on Volcanism in the American Southwest, but I thought I’d come out early to explore some of Arizona’s geological wonders. My first stop was near the airport at Papago Park.

20121014-180554.jpg
Papago Park hosts the Phoenix Zoo, the Desert Botanical Garden, and several striking erosional landforms. The panoramic image below, from Pewe et al. (1986), shows the famous Hole in the Rock, Barnes Butte, and Contact Hill.

20121014-181423.jpg
According to Pewe et al. (1986), Papago Park is a pediment, or a gently sloping erosional surface that typically consists of bedrock with a thin sedimentary cover.

20121014-182054.jpg
Barnes Butte and Hole in the Rock are remnants of mid-Tertiary alluvial fan deposits that unconformably overlie Precambrian granite (Pewe et al., 1986).

20121014-182710.jpg
They consist of arkosic breccias with large clasts of granite and quartz in a red, sandy matrix (Pewe et al, 1986).

20121014-183332.jpg

My second stop was on the way to Flagstaff at Montezuma Castle National Monument.

20121014-183925.jpg
Although the name suggests this archaeological site was built by the Aztecs, this pueblo ruin was actually built by the Sinagua people in the early 1100s.

20121014-184535.jpg
This impressive 5-story building was constructed in a recess of the limestone cliffs overlooking Beaver Creek.

20121014-185027.jpg
On a day like today, with fantastic weather and a scenic view, I can understand why the Sinagua people decided to stay for a while. I lingered as long as I could, but I had to make it to Flagstaff today. I’ll be taking day trips out of Flagstaff until the conference starts, so stay tuned for more stories about Arizona’s geological playground.

References:
Pewe, T.L., C.S. Wellendorf, and J.T. Bales, (1986) Geologic cross sections of Papago Park pediment, Tempe quadrangle, Maricopa County, Arizona, AZ Bureau of Geology and Mineral Technology, Geological Investigation Series Map GI-2-C.

Wooster’s Fossil of the Week: A spiriferid brachiopod (Middle Devonian of northwestern Ohio)

October 14th, 2012

I begin my Invertebrate Paleontology course by giving each student a common fossil to identify “by any means necessary”. This year I gave everyone a gray little brachiopod, one of which is shown above. They did pretty well. Kevin Silver (’13) got it down to the genus quickly. Turns out a Google image search on “common fossil” is very effective!

This is Mucrospirifer mucronatus (Conrad, 1841), a beautiful spiriferid brachiopod from the Silica Shale Formation (Middle Devonian) of Paulding County, northwestern Ohio. I collected it and many others at a quarry on a crisp October day with my friend and amateur paleontological colleague Brian Bade.

The image at the head of this page is a view of the dorsal valve exterior of Mucrospirifer mucronatus; the image immediately above is the ventral valve exterior. Spiriferid brachiopods like this are characterized by extended “wings” and a long hingeline. Inside was their defining feature: a spiral brachidium that held a delicate tentacular feeding device known as the lophophore.

This is the anterior of our brachiopod. The fold in the middle helped keep incurrent and excurrent flows separate, enabling more efficient filter-feeding. (By the way, have you noted the quirky asymmetry of this specimen?)

A view of the quarry that yielded our Fossil of the Week. Note the happy amateurs picking through blast piles of the Silica Shale Formation (Middle Devonian).

A pond in the quarry. It has an unexpected beauty, muddy as it is.

Timothy Abbott Conrad (1803-1877) described Mucrospirifer mucronatus in 1841. We met him before when discussing a siliquariid gastropod. He was a paleontologist in New York and New Jersey, and a paleontological consultant to the Smithsonian Institution.

Reference:

Tillman, J.R. 1964. Variation in species of Mucrospirifer from Middle Devonian rocks of Michigan, Ontario, and Ohio. Journal of Paleontology 38: 952-964.

Wooster’s Fossils of the Week: Giant ostracods (Silurian of Estonia)

October 7th, 2012

During our Estonian expedition this summer, Richa Ekka (’13) chose as her Independent Study project focus the Soeginina Beds (lowermost Ludlow, Upper Silurian) of the Paadla Formation exposed in southeastern Saaremaa Island. These carbonate sediments, mostly dolomitized, were deposited in very shallow conditions — so shallow that in some places we have syneresis cracks and halite crystal molds. I expected the fossils to be mostly stromatolites and rare traces. We were pleasantly surprised to also find, though, a bed with numerous valves of the giant ostracod Herrmannina Kegel 1933 (shown above). I should have guessed that the hardy and extraordinarily successful ostracods would have been present.

At first we thought that these slightly-recrystallized shells must be bivalves (clams) because of their relatively large size (up to 25 mm long). But we didn’t see the typical bivalve muscle scars or hinging teeth and sockets. They had to be ostracods — but so big? The typical ostracod valve, shown below, is two mm or less in length. These Silurian examples are over 10 times that size. It would be like me meeting my 60-foot equivalent. Turns out that Herrmannina is known for its gigantism in the ostracod world — and it is not even the largest.

Cyamocytheridea sp. from the Eocene of Nederokkerzeel, Belgium. (Public Domain, Wikimedia.) This is the typical small size for an ostracod.
Today the ostracods, members of the Phylum Arthropoda, have over 8000 living species in both fresh and marine waters. Most crawl or burrow into sediments (that is, most are vagrant benthic epifaunal and infaunal), and a few are suspended in the water column (planktic). They have a wide range of feeding habits, from filter-feeding and deposit-feeding to herbivory and carnivory. (This is a key to their survival from the Early Paleozoic to today.) The living ostracod above shows that they are essentially a large head with several pairs of appendages inside two hinged valves. (The image is public domain from Anna33 at Wikipedia.) Their sex life is astonishing: ostracods have the largest sperm of any animals in both relative and absolute measures. Ostracod sperm are often ten times the length of the male body. (No, I don’t know how that works!)

Herrmannina is in the Order Leperditicopida of the Class Ostracoda. This genus was named in 1933 by Wilhelm Kegel (1890-1971), a geologist in the Preussische Geologische Landesanstalt of Berlin, Germany, who specialized in the Devonian and Carboniferous systems. I couldn’t find out much more about Dr. Kegel, but did stumble across an uncredited, undated low-resolution photo of him above. A fuzzy face from our paleontological past!

References:

Abushik, A. 2000. Silurian-earliest Devonian ostracode biostratigraphy of the Timan-Northern Ural Region. Proceedings of the Estonian Academy of Sciences, Geology 49: 112-125.

Belak, R. 1977. Ontogeny of the Devonian Leperditiid ostracode Herrmannina alta. Journal of Paleontology 51: 943-952.

Kegel, W. 1933. Zur Kenntnis palaozoischer Ostrakoden 3, Leperditiidae aus dem Mitteldevon des Rheinischen Schiefergebirges. Preussischen Geologischen Landesanstalt, Jahrbuch fur das Jahr 1932, Bd. 53, p. 907-935.

Kesling, R.V. 1958. A new and unusual species of the ostracod genus Herrmannina from the Middle Silurian Hendricks Dolomite of Michigan. Contributions, Museum of Paleontology, The University of Michigan 14, No. 9: 143-148.

Putzer, H. 1971. Wilhelm Kegel. Geologisches Jahrbuch 89: xiii-xxii.

Vannier,J., Wang, S.Q., and Coen, M. 2001. Leperditicopid arthropods (Ordovician – Late Devonian): Functional morphology and ecological range. Journal of Paleontology 75: 75-95.

Next »