Archive for October, 2017

Wooster’s Fossils of the Week: “Ghosts” in the Upper Ordovician of Kentucky

October 13th, 2017

This year Caroline Buttler (Department of Natural Sciences, Amgueddfa Cymru – National Museum Wales) and I had a great project describing a cave-dwelling fauna in the Upper Ordovician of northern Kentucky. We hope that work will appear soon in the Journal of Paleontology. During our lab studies of thin-sections and acetate peels of massive trepostome bryozoans, we found several examples of clear calcite bodies in the middle of sediment-filled borings. These structures were described from the Ordovician of Estonia as “ghosts” of soft-bodied organisms by Wyse Jackson and Key (2007). They appear to be mineralized casts of organisms that were buried when sediment filled the borings that they occupied.

Meanwhile, Luke Kosowatz (’17) has a senior Independent Study project assessing bioerosion in the Upper Ordovician of the Cincinnati area. He and I have also found numerous examples of these ghosts in borings, so many that they have become a phenomenon in themselves for study. Above is an acetate peel made tangentially to the bryozoan surface showing the numerous tubular zooecia punctured by a few larger borings. Most of these borings are filled with sediment, but the two indicated by the arrows have these calcitic ghosts. This specimen is from the Corryville Formation near Washington, Mason County, Kentucky (38.609352°N latitude, 83.810973°W longitude; College of Wooster location C/W-10).

Above is one of our many heavily-bored trepostome bryozoans. This one comes from the Bellevue Formation (Katian) exposed on Bullitsville Road near the infamous Creation Museum (C/W-152). The irregular holes are the cylindrical boring Trypanites. The ghosts are not visible without sectioning.

Here is a close view of one of the ghostly calcitic casts in an acetate peel. The boundaries are sharp between the ghosts and the surrounding sediment.

The arrows above show ghosts in longitudinal cross-sections. Note their extended oval shapes. These are clearly organic shapes under these circumstances. (This is a thin-section.)

So what do the ghosts represent? They could be remains of the boring organisms themselves. If they are, they can be used to address a problem we have with bioerosion: What is the temporal relationship between the borings? How many were active in a given substrate at a given time? The percentage of borings with ghosts may give us a minimum amount of contemporary bioerosion. If, again, these are remnants of the borers themselves.

Maybe the ghosts are of later organisms that occupied the borings after the borers died? This happens often, with the secondary inhabitants called nestlers.

I know of no way to sort possible borers from nestlers with this kind of evidence.

The above image shows it’s possible that some of the ghosts are of organisms that had shells. The arrow is pointing to a dark line that may represent the remains of some type of shell. I’ve seen little tiny lingulid brachiopods in some borings before.

A fun mystery!

For technical interest, here is our photomicroscope we use to produce images like those in this post.

References:

Cuffey, R.J. 1998. The Maysville bryozoan reef mounds in the Grant Lake Limestone (Upper Ordovician) of north-central Kentucky, in Davis, A., and Cuffey, R. J., eds., Sampling the layer cake that isn’t: the stratigraphy and paleontology of the type-Cincinnatian. Ohio Department of Natural Resources Guidebook 13: 38-44.

Wyse Jackson, P.N. and Key, M.M. Jr. 2007. Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control. Lethaia 40: 237-252.

 

A “Dry Summer” in Wooster?

October 12th, 2017

I moved to Wooster at the very end of July.  Since that time, I’ve heard a frequent refrain that “it’s been a dry summer”.  Being a climate scientist, and knowing that everyone (including me) likes to complain about the weather, I thought I’d fact-check my neighbors.  In meteorology, “summer” usually means June, July, and August (JJA).  Based on data from the Wooster Experimental Station, 11.12 inches of rain fell during JJA 2017.  Is that dry?

It turns out, that’s nearly average.  The Wooster weather station goes back to the 1800s, and for the period 1900-2016*, the average JJA precipitation was 11.52 inches.  The minimum is 4.34 inches (1910), and the maximum is a 23.72 inches (1935).  However, my neighbors may be on to something, because digging deeper, most of that rain fell in June and July.  Early summer was really wet actually — the 9.83 inches Wooster received in June and July was greater than 75% of all years since 1900.  In August, though, we only received 1.29 inches — well below average.

September was even drier at 1.13 inches.  The main storm track that brings rain to Wooster has been farther north than normal since July, and most storms have missed us.  We also often receive rain from the remnants of hurricanes in September.  Although September had plenty of Atlantic hurricanes, Harvey is the only one that affected Wooster, dropping 0.76 inches of rain.  That’s a pittance for a tropical system, but it was also over half the rain we saw all month.

If you combine August and September, we had 2.42 inches of rain.  That’s good for 4th lowest since since 1900 (Figure 1).  Also, it’s the lowest August-September precipitation since 1922 — almost 100 years ago.  So yeah, this is rare.

Figure 1. In 2017, Wooster received 2.42 inches of precipitation in August and September. That’s 4th lowest since 1900. Data from National Centers for Environmental Prediction.

In fact, it’s so rare that Wooster is currently in a moderate drought (Figure 2). Cincinnati, Louisville, and other cities farther south are fine — they received ample rain from the tropics this year.  Much of the midwest is dry, though.  With that said, these midwest droughts are nowhere near as bad as the recent one in California (which still lingers in southern California, by the way). They are not as bad as what Montana and the Dakotas are currently facing, either.  Besides the moderate severity, they’re also currently short-term droughts — meaning it’s only been around for a few months.  Such droughts may have adverse impacts on agriculture, but there’s typically no long-term impact.  Just hope for plenty of snow this winter!

Figure 2. Droughts in the USA as of 3 October 2017. Wooster, OH is in a short-term moderate drought. Data from drought.gov.

 

*There are some data gaps before 1900 in the NCEI data, so I skipped those years.

Wooster’s Fossil of the Week: A terebratulid brachiopod from the Upper Cretaceous of southwestern France

October 6th, 2017

Yes, we’ve had a run of French Cretaceous fossils here. This is because we’re in the midst of a major project stemming from summer fieldwork in the Type Campanian of southwestern France. The fossils are delicious, and they are before us every day in the lab.

The above terebratulid brachiopod was found by Macy Conrad (’18) at our Caillaud South locality in the Biron Formation. It is so beautifully symmetrical that it just had to be a Fossil of the Week. I’ve apparently felt this way before about terebratulid brachiopods since I’ve previously written about Triassic, Jurassic and Miocene examples before in this blog. A Cretaceous example at least completes the Mesozoic set.

The above view of our articulated specimen shows the fragmentary smooth dorsal valve of the terebratulid, with the posterior portion of the ventral valve extending upwards at the top. The ventral valve has the characteristic round pedicle opening.

This is the flip side showing only the exterior of the ventral valve. A bit of chalky matrix adheres in the lower left, and the darker circles at the top are a form of silicification called beekite rings.

Here is the side view of our terebratulid, with the dorsal valve on top and larger ventral valve below. You can see why brachiopods were given the common name “lamp shells” because of the resemble to a Roman oil lamp.

References:

Coquand, H. 1858. Description physique, géologique, paléontologique et minéralogique du département de la Charente. Besançon, Dodivers, 420 p.

Platel, J.-P. 1996. Stratigraphie, sédimentologie et évolution géodynamique de la plate-forme carbonatée du Crétacé supérieur du nord du basin d’Aquitaine. Géologie de la France 4: 33-58.