Mineralogy of Mars
mpollock November 19th, 2009
As promised, here’s another digital presentation. The Mineralogy of Mars is presented by Colin Mennett (’10).
A very bored Permian brachiopod
Mark Wilson November 15th, 2009
COLLEGE STATION, TEXAS–I never get tired of that too-obvious joke. I found the above productid brachiopod on the last outcrop of our little Texas expedition. It has been drilled by barnacles, which leave a distinctive slit-shaped hole with a tiny little comma shape at one end. It may not look special here photographed on my backpack in the sunlight, but it is. Hard substrate communities in the Permian are still poorly known. This specimen tells us that a future trip may reveal many more such specimens.
Paleontologists (and anyone else) should be able to tell me whether these borings were produced during the life of the brachiopod or after its death. Your determination can be posted in the comments below!
Two West Texas outcrops: which looks more inviting?
Mark Wilson November 15th, 2009
COLLEGE STATION, TEXAS–The upper one is the base of the Valera Formation on US Highway 84 (N31.88196°, W99.47115°) and the lower one is the lower Bead Mountain Formation on Route 6 near Albany; both are Permian and both have delicious microconchid fossils along with much else. You can imagine which is the more pleasant to work on.
I have been very impressed with the Permian geology of this part of Texas. The fossils and sedimentary rocks are very accessible and sufficiently mysterious to generate at least two paleontology and sedimentology projects, including future Independent Study work by Wooster students. Sure there are fire ants, rattlesnakes, and very fast country road driving, but it wouldn’t be Texas without them! (And the barbecue … all beef, dry-rubbed barbecue …)
The puzzle of gypsum
Mark Wilson November 15th, 2009
Our Permian sections on this Texas trip have had thick beds of gypsum only a meter or three beneath our fossiliferous limestones and shales.
An outcrop of sedimentary gypsum below the Valera Formation (Permian).
Gypsum (calcium sulfate) is an evaporite mineral, indicating when the Permian shallow sea in this case was much saltier than normal (hypersaline). Our fossils show a restricted nature (lower diversity than normal, and generally smaller shells), but they were still living in at least close to normal salinities. This is especially the case with our numerous echinoids. We even have evidence of some evaporites within our fossiliferous limestones. It is a curious juxtaposition of deposition al environments.
A new family of fossil clams from the Triassic of Israel
Mark Wilson November 15th, 2009
The latest issue of the journal Palaeontology has an article describing a new family of large clams from the Triassic of southern Israel. The authors include Allison Mione (’05), who pursued this project as part of her geology Independent Study.
A specimen of the new clam family Ramonalinidae from the Triassic of southern Israel in Makhtesh Ramon.
The Ramonalinids: a new family of mound-building bivalves of the Early Middle Triassic
by Thomas E. Yancey, Mark A. Wilson and Allison C.S. Mione
Abstract: Ramonalina n. gen. is a large thick-shelled bivalve abundant in mounds preserved in the Gevanim Formation (late Anisian, Middle Triassic) of southern Israel. This bivalve was an edgewise-recliner with a flattened anteroventral (functionally basal) surface and partially fused valves. It is the basis of a new family, the Ramonalinidae, which is descended from the myalinids through adaptation to edgewise positioning. Ligamental attachment was inadequate to hold valves together on large adults, resulting in valve displacement followed by shell secretion in the apical area that fused valves together and caused irregular growth on abapical areas. The ramonalinids formed large, nearly monospecific mounds on firm mud substrates in shallow marine waters. These are the largest Middle Triassic bivalve mounds known.
(I am very proud!)
You’re never alone on an outcrop
Mark Wilson November 13th, 2009
Molted skin layer from a rattlesnake apparently in the cavity underneath the nice piece of Permian limestone. I didn't poke around in there to wake him up, and I let that limestone stay where it was.
A West Texas outcrop
Mark Wilson November 13th, 2009
BROWNWOOD, TEXAS–It was nearly a five hour drive from College Station, Texas, through the Hill Country to our first Permian exposure in West Texas. (We passed, by the way, through Killeen and Fort Hood.) It was worth the trip for all the strange features we found on this outcrop of the Valera Formation.
Tom Yancey, a paleontologist at Texas A&M University, seated on our little outcrop of the Valera Formation in West Texas (N31.48454°, W99.69368°).
We spent several hours measuring, describing and sampling this outcrop in ideal weather. We found plenty of examples of what we came here for: fossil microconchids, otherwise known as “worm tubes”.
Microconchid tubes from the Valera Formation at the above outcrop.
We were surprised to also find abundant sea urchin (echinoid) spines in one of the limestone units here. These usually indicate normal marine salinity, but they are unaccompanied by other indicators such as brachiopods and bryozoans. A thick gypsum below our exposed rocks shows that we are likely dealing with elevated seawater salinity during the Permian in this area. A mystery. (And we love mysteries in this business.)
A barbed echinoid spine from the Valera Formation (Permian). In the lower left with the apparent hole in it is an echinoid test plate.
Tomorrow we visit a similar outcrop with microconchids. Now we have some hypotheses to test. Fieldwork is such a joy!
Wooster Geologist in Texas
Mark Wilson November 12th, 2009
Halbouty Geosciences Building on the campus of Texas A&M University
COLLEGE STATION, TEXAS–I arrived this afternoon in beautiful central Texas to give a talk at Texas A&M University on bioerosion. If you click the link you can see my PowerPoint slides. The talk went well enough and there were many questions. It is a fun topic because it is at an intersection of geology and biology.
Tomorrow Tom Yancey and I drive to Brownwood, Texas, to begin a field project in the Permian. There are some very curious “worm tube” clusters that I hope to post photos of soon. I’m excited to be able to work in the Permian, which I haven’t done since my dissertation days.
The weather is absolutely perfect here!
Mineralogy of Hydrothermal Vents…in HD
mpollock November 6th, 2009
Our mineralogy students have been researching some fascinating topics and have recently created a suite of impressive digital presentations. Stay tuned over the next few weeks as we unveil their projects on the blog. The first presentation is by Megan Innis (’11) on the mineralogy of hydrothermal vents. Make sure your volume is turned up. Enjoy!
It was a dark and stormy night…Halloween in Mineralogy
mpollock October 30th, 2009
Tomorrow is Halloween, but Mineralogy students celebrated the holiday today by dressing as their favorite optical property. Guess what the people in the picture below are dressed as (hint: they are all under crossed polars!).
Becky Alcorn, Colin Mennett, Nick Fedorchuk, and Megan Innis are dressed as interference colors! Can you determine their birefringence?
The people below appear every 90 degrees when the stage is rotated under crossed polars…
Colin Mennett, Elizabeth Deering, Micah Risacher, and Becky Alcorn are at extinction!
Andrew Retzler (below) is dressed as muscovite under conoscopic illumination…
Retzler dressed as a Bxa interference figure.
Okay, here’s a tough one. Lindsey Bowman’s costume represents the microscope set up when the analyzer is in the optical path…
Lindsey is a "crossed polar." Get it? Grumpy = crossed Polar!
Wooster Mineralogy students bring a whole new meaning to optics!
