Archive for April, 2011

A muddy but successful encounter with the Mississippian-Pennsylvanian boundary in southern Ohio

April 30th, 2011

Lindsey and Richa work their way up the Pennsylvanian section with their Jacob's staffs.

JACKSON, OHIO — Usually the Sedimentology & Stratigraphy class from Wooster meets no one at this Carboniferous outcrop on US 35 in Jackson County. This morning, though, we arrived to find geology students from Wright State University (under Professor David Dominic) hard at work on the section, and the clubhouse for the Apple City Motorcycle Club had a busy (and noisy) crowd as well. We waded right in and started measuring and describing the rocks.

The recent rains had their predictable effect on the shale units, producing a thick mud in some places, but we did well enough staying on the sandstones and conglomerates when we could. I noted that the outcrop is much more overgrown than when I first visited with a Sed/Strat class in 2000. (The better exposures made for better photography of the rock units, as you will see.) Here is another set of images from the 2009 field trip to this site.

This is one of the best places in the state to see the unconformity between the Mississippian and Pennsylvanian subsystems. It is a sharp disconformity above the Logan Formation siltstones and below pebble-rich sandstones of the Sharon Conglomerate equivalent. We drew measured stratigraphic columns through this interval and then met as a group on the top of the outcrop to assess the ancient depositional environments.

We all returned home safely with muddy boots and new ideas about the local stratigraphy.

Joe and Will confer on an outcrop of black, carbon-rich shale.

If it’s spring in Ohio, it’s time for fieldwork!

April 28th, 2011

WOOSTER, OHIO–My geology colleagues have already been braving the weather to get their students into the field after the long winter. I like to wait until the end of April when it’s all sunshine and flowers. This week the Sedimentology & Stratigraphy class started its fieldwork with a visit to the Logan Formation exposed in an overgrown quarry an easy walk from campus. The Tuesday section experienced a bit of rain near the end of their work, but today’s section had a glorious day (much like last year at this time and place). In the image above we see Whitney, Jenn and Melissa describing and measuring the sandstones and conglomerates of the Logan with their fancy Jacob Staffs.

Kevin, Anna and Genevieve arrayed on the outcrop.

Oscar and Marytha conferring on the composition of the granules in the conglomerate.

The conglomerate in the midst of the very fine sandstones of the Logan Formation is the most distinctive unit.

The conglomerate has a sharp lower base and shows graded bedding.

Our little afternoon field trip is practice for this weekend’s class expedition to the Mississippian-Pennsylvanian boundary sections in Jackson County, southern Ohio. Hope we have the same kind of weather!

Wooster’s Fossil of the Week: A scaphitid ammonite (Late Cretaceous of Mississippi)

April 24th, 2011

The beauty above is Discoscaphites iris (Conrad, 1858) from the Owl Creek Formation of Ripley, Mississippi. Megan Innis and I collected it during our expedition to the Cretaceous-Paleogene boundary in the southern United States last summer. It is a significant index fossil in biostratigraphy: the Discoscaphites iris Zone is the latest in the Cretaceous (the late Maastrichtian Stage). This animal lived in the final days of the Mesozoic Era just before the mass extinction 65.5 million years ago.

Discoscaphites iris is an ammonite, a type of extinct cephalopod mollusk related to the modern octopus, squid and nautilus. It had a planispirally-coiled shell with chambers divided from each other by complexly-folded walls. If you look closely near the top of the fossil above, you will see where the shell has flaked away revealing an internal mold of sediment and a peek at the folded walls inside. “Ammonite”, by the way, is a very old term for these fossils. Pliny the Elder himself used a variant of the name, which comes from the Egyptian god Amun with his occasional coiled ram’s horn headgear.

Reconstruction of an ammonite by Arthur Weasley (via Wikipedia).

Ammonite shells were made of the carbonate mineral aragonite. This is the mineral that makes many modern mollusk shells have prismatic colors, which we call nacreous. You may know it best as “mother of pearl” or as pearls themselves. Aragonite has an unstable crystal structure and so is not common in rocks older than a few million years. The original aragonite in our ammonite fossil is thus a bonus.

In an oddly topical note, Discoscaphites iris was recently found in the Upper Cretaceous of Libya, giving it a disjunct range from the US Gulf and Atlantic coasts to the Mediterranean coast of northern Africa (Machalski et al., 2009).

Reference:

Machalski, M., Jagt, J.W.M., Landman, N.H. and Uberna, J., 2009. First record of the North American scaphitid ammonite Discoscaphites iris from the upper Maastrichtian of Libya. N. Jb. Geol. Paläont. Abh. 254: 373-378.

Achieving Wooster’s Mission

April 20th, 2011

The theme of today’s Petrology lab is summarized by the last sentence of Wooster’s Mission Statement: “Wooster graduates are creative and independent thinkers with exceptional abilities to ask important questions, research complex issues, solve problems, and communicate new knowledge and insight.” Petrology students have been hard at work on a semester-long research project that required them to do all of the above: first describe and identify an unknown rock, then use the mineralogy and textures to interpret the rock’s petrogenesis. Geologists communicate their research in a number of ways, including poster presentations. In fact, many of our students give poster presentations about their I.S. research at National GSA Meetings and in Wooster’s I.S. Symposium. So today’s Petrology lab was transformed into a “Junior GSA” Petrology Poster Session. The hallways of Scovel were buzzing with discussions about exsolution, fractional crystallization, and magma mixing. The walls were plastered with gorgeous images of perthite, compositional zoning, and reaction rims. (Imagine a petrology paradise, if you will.)

Travis Louvain ('12) explains how his sample showed a contact between two rocks.

Can you feel the excitement?

This poster session made some students look forward to GSA in the Fall.

Here’s a small sample of some of the posters:

A tale of two feldspars by Anna Mudd ('13)

Formation of Trachyte by Sarah Appleton ('12)

Of course, one of the goals of this project is to practice and improve their ability to make poster presentations, so students evaluated themselves and each other according to the Poster Rubric. The feedback they get will help improve their future poster presentations, and by using this rubric throughout their academic careers, we’ll be able to assess the development of effective communication skills in our major.

If this post has only whetted your appetite for petrology, stay tuned! Next week, we’ll unveil the petrology digital presentations.

 

Analysis of a drill core through Mississippian rocks (Senior Independent Study Thesis by Michael Snader)

April 19th, 2011

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Michael Snader, a senior geology major.

During Spring semester of 2010, I was given a core of the Black Hand Sandstone to study.  The core was drilled just outside of Wooster, Ohio, but was originally drilled in search of oil, not for studying purposes.  The Black Hand Sandstone is Mississippian (Osagean) in age and was named in 1915.  The Black Hand Sandstone is distributed only throughout Ohio and is found mostly in central Ohio.
Once studying of the core began, I first had to cut the core in order to see the inner details.  The core was roughly 65.8 meters long and had to be cut directly down the center.  Cutting was done this way so that I could use one piece to study and make thin sections of, and leave the other piece as a record.  Once cutting was done, I began looking through the core for a pattern to give me an idea of the paleoenvironment.  As I studied the core, I found a series of hiatus concretions which I believe to be evidence of regressions.  I also found crinoid fossils at various depths throughout the core which would be evidence of a deeper marine environment.  There was a large section of shale near the bottom of the core that contained concretions as well.  The concretions found within the sandstone and shale are both made of the same material and contain similar markings.  Therefore, I propose that the concretions found in the sandstone represent regressions because they exist from an eroded shale layer.  In conclusion, the concretions represent a series of regressions and show the depositional environment of the Black Hand Sandstone to be shallow marine.

Wooster’s Fossil of the Week: Oyster balls! (Middle Jurassic of Utah)

April 17th, 2011

The technical term is ostreolith, but “oyster ball” is much more descriptive. These fossils are found by the thousands in the Carmel Formation (Middle Jurassic) in southwestern Utah. As far as I know, this is the only place they’ve ever been found. Colin Ozanne (’96) worked on these ostreoliths as part of his Independent Study project, and the results of our work were published in a 1998 issue of Palaios. Colin now, by the way, is an Engineer Trial Attorney for the US Army Corps of Engineers in Buffalo, New York.

Ostreoliths are “circumrotatory accumulations” of the little oyster Liostrea strigilecula. The most common form began with a clam shell fragment as a nucleus. Oyster larvae recruited on the top shell surface and grew in the normal way. A current, though, flipped the shell over, exposing the underside that was in turn encrusted by more oyster larvae. These grew into larger oysters until, again, the shell flipped back over. A new generation of oysters then encrusted the older layer. The shell then overturned again and … you get the idea. Some ostreoliths grew this way to almost a quarter meter in diameter. The cup-shaped left valve of Liostrea was an essential feature for ostreolith development. A typical flat oyster would not build the necessary depth with each layer.

Polished section through the middle of an ostreolith showing the curved nucleus shell and calcite-filled bivalve borings.

Closer view of oysters on the surface of an ostreolith. Note how juvenile oysters are clustered within the left valves of an older generation.

Several sclerobionts (hard substrate dwellers) grew with the oysters on the ostreoliths, including the bivalve Plicatula, disciniscid brachiopods and cyclostome bryozoans. Mytilid bivalves also drilled holes (called Gastrochaenolites) in the oyster skeletons to form cavities for their filter feeding.

Ostreoliths, strange and unique as they are, tell us a lot about the depositional environment of the Carmel Formation. The sediments accumulated in these horizons under fairly high energy with periodic storm disturbances. The mytilid borings trapped ooids during formation of the ostreoliths, showing that this characteristic carbonate sediment was more common in the environment than indicated by the rocks alone.

Carmel Formation exposed at Gunlock Reservoir near St. George, Utah.

Regardless of their scientific value, though, oyster balls certainly start good conversations!

Minerals in My Toothpaste

April 16th, 2011

WOOSTER, OH – I can’t think of a more exciting thing to do on a Saturday morning than play with minerals and X-rays! Wooster’s Geology Department and the Expanding Your Horizons Program girls explored how minerals are used on a daily basis.  First, we tested the physical properties of minerals and made educated guesses about which minerals are used in common household products, like cleaners and toothpaste. Then we analyzed the products on the new X-ray diffractometer (XRD) to see whether our guesses were correct. Finally, we made our own mineral toothpaste. I don’t think we’ll be going into the toothpaste business any time soon, but the lab now smells minty fresh!

One of the EYH girls prepares a sample of powdered drywall for the XRD.

An EYH student places a prepared sample in the XRD.

After the sample is secured, an EYH student starts the run.

The XRD bombards the sample with X-rays, which diffract at specific angles. Meanwhile, the detector circles the sample and measures the intensity of X-rays at different angles. Each mineral has its own unique spectrum, sort of like an X-ray fingerprint.

Once the girls have their spectrum, they compare their sample to the spectra of known minerals to determine which minerals are in which products.

Mrs. Robertson helps the EYH girls make their own mineral toothpaste. Mmmm!

Melissa Torma ('13) and Ana Wallace ('12) volunteered to help the EYH girls and even had a chance to make their own toothpaste. (Stephanie Jarvis '11 helped, too, but had to lead the EYH girls to their next workshop before I could snap her picture).

The EYH girls search through our collection of polished stones for a souvenir. Thanks for a wonderful time, girls!

Non-stationarity in climatic response of coastal tree species along the Gulf of Alaska (Senior Independent Study Thesis by Stephanie Jarvis)

April 15th, 2011

The crew in their XtraTufs. From L-R: Stephanie, Deb, Dan, and Greg.

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Stephanie Jarvis, a senior geology and biology double major from Shelbyville, KY.  Here is a link to Stephanie’s final PowerPoint presentation on this project as a movie file (which can be paused at any point). You can see earlier blog posts from her field work by clicking the Alaska tag to the right.

For my IS field work I traveled to Glacier Bay National Park & Preserve, Alaska with my geology advisor, Greg Wiles.  Our field crew also consisted of Deb Prinkey (’01), Dan Lawson (CRREL), and Justin Smith, captain of the RV Capelin.  My focus was on sampling mountain hemlock (Tsuga mertensiana (Bong.) Carrière) at treeline sites to study climate response and forest health using tree ring analysis.  While in Glacier Bay, we also sampled interstadial wood (from forests run over from the glaciers that were now being exposed on the shore) and did some maintenance work on Dan’s climate stations throughout the park.  Back in the lab, Wooster junior Sarah Appleton kept me company and helped me out with some of the tree-ring processing, as did Nick Wiesenberg.

The view from treeline.

An interstadial wood stump, in place. The glacier ran over this tree and buried it in sediment, which is now being washed away.

Site map

I ended up processing cores from only one of the three sites I sampled this summer (the others can be fodder for future projects!).  In addition, I used data from several other sites sampled in previous years.  My data consisted of 3 mountain hemlock sites forming an elevational transect along Beartrack Mountain in Glacier Bay (one described by Alex Trutko ’08), 3 mountain hemlock sites at varying elevations from the mountains around Juneau, AK, and 2 Alaskan yellow-cedar sites (Chamaecyparis nootkatensis (D. Don) Spach) from Glacier Bay used by Colin Mennett (’10).   My purpose was to look into the assumption of stationarity in growth response to climate of trees over time and changing climatic conditions.  According to the Alaska Climate Research Center, this part of AK as warmed 1.8°C over the past 50 years.

Tree-ring base climate reconstructions are important in our understanding of climatic variations and are a main temperature proxy in IPCC’s 2007 report on climate change.  Climate reconstruction is based on the premise that trees at a site are responding to the same environmental variables today that they always have (thus, they are stationary in their response), allowing for the reconstruction of climatic variables using today’s relationship between annual growth and climate.

Greg coring a tree at treeline.

Crossdating using patterns of variations in ring width.

Temperature reconstructions using different proxies, including tree-rings, from the Intergovernmental Panel on Climate Change’s 2007 report.

Recent observations, such as divergence (the uncoupling of long-term trends in temperature and annual growth) and worldwide warming-induced tree mortality, suggest that this assumption of stationarity may not be valid in some cases.  Using mean monthly temperature and precipitation data from Sitka, AK that begin in the 1830s, I compared correlations of annual growth in mountain hemlock to climate at different elevations over time.  My results indicate that mountain hemlocks at low elevations are experiencing a negative change in response to warm temperatures with time, whereas those at high elevations are experiencing a release in growth with warming.  Low-elevation correlation patterns are similar to those of lower-elevation Alaskan yellow-cedar, which is currently in decline due to early loss of protective snowpack with warming.  An increasing positive trend in correlation to April precipitation and mountain hemlock growth indicates that spring snowpack may be playing an increased role in mountain hemlock growth as temperatures warm.  The high elevation mountain hemlock trends suggest the possibility of tree-line advance, though I was not able to determine if regeneration past the current treeline is occurring.  Tree at mid-elevation sites seem to be the least affected by non-stationarity, remaining relatively constant in their growth response throughout the studied time period.  This indicates that reconstructions using mid-elevation sites are likely to be more accurate, as the climatic variable they are sensitive to is not as likely to have changed over time.

Cedar chronologies (green lines) compared to temperature (brown line). Bar graph represents correlation coefficients between annual ring width and temperature, with colors corresponding to labels on the chronologies (orange is lowest elevation PI, blue is higher elevation ER). Asterisks represent significant correlations. Note that the relationship has changed from being positive at ER during the Little Ice Age to negative by the second half of the 20th century.

Mountain hemlock chronologies (green lines) compared to temperature (brown line). The top graph is of the Glacier Bay sites, the bottom is of the Juneau sites. Red represents the low elevation sites, green the mid-elevation, and purple the high elevation. Note that the low elevation sites are decreasing in correlation as the cedars have, while the high elevation sites have experienced a release in growth with warming.

 

Paleoecological Reconstruction of the Menuha Formation (Upper Cretaceous, Santonian), Makhtesh Ramon Region, Southern Israel (Senior Independent Study Thesis by Andrew Retzler)

April 11th, 2011

A typical Menuha Formation outcrop south of the Makhtesh Ramon structure.

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Andrew Retzler, a senior geology major from Wooster, Ohio.  Here is a link to Andrew’s final PowerPoint presentation on this project as a movie file (which can be paused at any point). You can see earlier blog posts from his field work by clicking the Israel tag to the right. Andrew also created a Wikipedia page on the Menuha Formation.

It all began with an 11-hour flight from NYC to Tel Aviv, Israel with Dr. Wilson and fellow geology senior Micah Risacher. The airport process required for international travel of this sort was an adventure in itself. Thorough baggage checks, stern looks from security personnel, and a bombardment of questions dealing with our reasons for travelling were all offset by a seemingly endless and free movie selection on the flight! Eventually, we reached our arid destination of Mitzpe Ramon, the city that would serve as our basecamp for the next two weeks.

One of the reasons behind our trip was to scour the Menuha Formation outcrops throughout the Makhtesh Ramon region (shown above). We were hoping to collect and analyze various fossils in order to reconstruct an environment that once flourished during the Cretaceous. This process also involved taking detailed measurements and notes on each outcrop to create stratigraphic columns of each locality. This would become the basis of my thesis. Of course, none of this could have been possible without the help of our all-knowing field guide, Yoav Avni, and our shark specialist, Stuart Chubb, from the Birkbeck College of London.

Although my thesis has a strong focus on the shark and other fish teeth collected from the Menuha Formation, it also incorporates oysters, trace fossils, and several benthic/planktic foraminiferans. At least ten different species were represented in the isolated teeth: Cretalamna appendiculata, Cretoxyrhina mantelli, Squalicorax falcatus?, Squalicorax kaupi, Scapanorhynchus rapax, Scapanorhynchus raphiodon?, Carcharias samhammeri, Carcharias holmdelensis, and two other fish (Hadrodus priscus and Micropycnodon kansasensis?). Many of these fish were thought to occupy outer shallow marine realms, where the continental shelf begins transitioning into the slope. A few of the sharks are also known for being top Cretaceous predators, four or more meters in length, whose diets included plesiosaurs, mosasaurs, and ichthyodectids.

Cretalamna appendiculata tooth, a shark often considered to be an ecological generalist.

Scapanorhynchus rapax tooth. Related to the extant Goblin Shark, S. rapax had the ability to protrude its mouth in order to capture prey.

Cretoxyrhina mantelli tooth. Considered a superpredator of the Cretaceous seas, this shark could reach 5-6 meters in size.

Squalicorax kaupi tooth. The Squalicorax genus is the only group to exhibit serrated dentition, like so, in the Late Cretaceous.

Hadrodus priscus pharyngeal teeth. These teeth would have been found near the back of the throat arranged in a comb-like structure to help crush exoskeletons.

LEFT: The extended left valve of a Pycnodonte vesicularis. RIGHT: Planktic, biserial foraminiferan test (possibly Heterohelix sp.) that has been replaced by silica.

The Menuha Formation consists mainly of white and yellow/brown, glauconitic chalks that were often marly or conglomeratic. This chalk comprised a variety of phosphatic peloids, microteeth, irregular echinoid spines, and benthic/planktic foraminiferans that clearly represent a shallow marine environment.

Irregular echinoid spine recovered from the partially dissolved Menuha chalk.

Microtooth from the Menuha chalk.

Correlating the paleontology with their lithological context, a shallow marine outer continental shelf/middle continental slope environment is suggested as the paleoenvironment of the Menuha Formation. This environment would have also flourished with a variety of small to medium-sized fish, squid, and larger vertebrates (plesiosaurs and mosasaurs) in order to sustain such a shark population. Unlike the deep environment that has often been suggested, my thesis provides strong evidence towards a shallow marine environment during the early formation of the Makhtesh Ramon structure. My work also marks the first identification of the fish teeth within the Menuha Formation, beginning my contributions to the scientific world.

A Paleoenvironmental Analysis of the Zichor Formation in the Cretaceous of Southern Israel (Senior Independent Study Thesis by Micah Risacher)

April 11th, 2011

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Micah Risacher, a senior geology major from Columbus, Ohio.  Here is a link to Micah’s final PowerPoint presentation on this project as a movie file (which can be paused at any point). You can see earlier blog posts from Micah’s field work by clicking the Israel tag to the right.

In the summer of 2011 Wooster geologists Mark Wilson, Andrew Retzler, and I went to the Negev Desert in southern Israel.  We were met by a colleague from England, Stewart Chubb as well as our guide and host Yoav Avni of the Geological Survey of Israel.  The small town of Mitzpe Ramon on the edge of the Makhtesh Ramon (Figure 1) would serve as our home for the next two weeks as we explored the Ramon structure.

Figure 1. A look into the Makhtesh Ramon structure.

My research includes the Zichor Formation which can be found throughout the Makhtesh Ramon structure.  However I focused on three separate locations known as the northern, southern, and western locations.  Each location had different features exposed, the southern location (Figure 2) exposed the Zichor very well, yet it was quite hard to get at it.

Figure 2. Southern section with the Zichor section labeled.

The purpose of my I.S. was to determine the paleoenvironment of this particular formation (Zichor) using the paleontology, sedimentology, and stratigraphy seen in the field/lab.  I found many well preserved echinoids (not destroyed by churning waters), Thalassinoides trace fossils, high mud content and shell fragments in the lithology, as well as several minor regression/transgression cycles.  All of these point to a primarily shallow marine environment that would slightly deepen once or twice before shallowing again.

The echinoids (Figure 3) found were so well preserved that they could be identified down to the species level and greatly helped to correlate this assemblage with others like it around the world during that time.  This process both helps to verify my results as well as put my sites in perspective with similar ones around the world.  Hopefully, this study will go a ways into settling the current dispute as to whether or not this region was a shallow or deep sea environment during the Late Cretaceous.

Figure 3. The most prevalent echinoids Hemiaster batnensis and Rachiosoma delamarri respectively; scale bars=1cm.

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