Archive for October 14th, 2012

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.

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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.

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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.

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

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

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

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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.

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

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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.