Modern Sedimentary Structures (Great Salt Lake)

This past summer I embarked on the "Utah Trip" lead by the extraordinary geologist Carl Brett. We saw many things over the 15 day whirl wind, but one thing I keep going back to is our trip to the shores of the Great Salt Lake. I was blown away by the similarity of these structures to those so often seen in our local sedimentary rocks. The last photo is of some Cambrian age ripples we came across later that day for comparison of preservation in the rock record.

Ohio Geological Survey Visit

Yesterday I returned from the Ohio Geological Survey (OGS) after 2 days of drilling samples and photographing a few of the sections. I had a great time and collected a lot of information that will help answer some questions we are working on in my research group for my thesis.

OGS has a whole facility dedicated to storage and analysis of core at their office just north of Columbus, OH the Horace R. Collins Laboratory.

If you have questions about the local geology when traveling to a new state or even exploring your local rocks the state geological survey is a great place to start for information. Surveys are very different state-to-state but one thing they all have in common is a group of people who know their local rocks. In addition to the informed and helpful staff they hold a wealth of information, including records that go further back then you would think. Most of the records are becoming available on their websites including maps, publications, and well logs.

Core is very expensive to drill so we rely on core available to us at geologic surveys to collect data on these packages of rock not exposed at the surface. The advantages of core is it provides access to a large continuous section of rock while being easy to sample. Thin beds that may be unrecognizable in outcrop are easily seen in core. Additionally, its size allows for instantaneous comparison of multiple sections side by side and within a single day.

While you are restricted to the diameter of the core, often a few inches or less, when analyzing bedding planes fossils are still found and can be crucial to constraining intervals with the help of biostratigraphy.

Graptolites

Trilobites! ( Triarthrus?)

Triarthrus cephalon

Fossil finds are not restricted to the bedding planes. It is very common to see cross sections of
many fossils such as the possible bryozoan pictured here. 

Big shout out to OGS especially facility coordinator Aaron Evelsizor for all of their help!

Danville, KY: Dix River

50 and partly cloudy! Maybe Kentucky missed the memo that it is still February, but Christopher and I took advantage of it for some field work. This past Saturday we took a drive down to Danville, KY to check out my favorite Upper Ordovician deposits, the Lexington Formation with our good friend Kyle of the Dry Dredgers.

At Danville, Boyle County, KY we studied ~60 meters of exposed section. Measuring bed-by-bed we collected data to draft a stratigraphic column and made some quick fossil counts.

One of the more interesting finds was how heavily faulted the entire region was. Resulting in an offset of more than a meter to just a few centimeters.

One of the MANY faults at this exposure. 

Working in heavily faulted areas adds complexity to the otherwise layer cake stratigraphy we are spoiled with in the central Kentucky outcrop belts.


Another unique feature of this particular outcrop belt is the great abundance of preserved bentonites. The literature has noted the presence of as many as 20 bentonites in the Tyrone Formation, the main member of the lower micritic section of the exposure. Including the famed Deicke K-Bentonite.

Sticky yellow clay. K-bentonite?, a sample was collected for further analysis.

Finally we found another good chronostratigraphic tie line with a deformed (ball and pillow structure) zone believed to be the expression of the capitol.

Deformed beds of the "capitol", helpful as a marker horizon when correlating
across faults.

A Bundle of Brachiopods - Zygospira

The other day when Allison and I were out in the field, we made a quick stop near Dillsboro, IN to look at an outcrop of what was probably Mount Auburn Member (of the Grant Lake Fm) or the Arnheim Formation. We knew we were not any younger than that because we came across some rather large Platystrophia ponderosa (Vinlandostrophia ponderosa) which are known the make through the Arnheim, yet disappearing before the Waynesville Formation. However we didn't see any of the true diagnostic fossils like Lapteana  or Retrosirostra carleyi. 

Outcrop of Grant Lake or Arnheim Formation near Dillsboro, Indiana

We did come across this rather interesting pair of rocks in the float that showed some sort of groove or gutter carved into what must have been a semi-harden marine floor and in this groove was dozens of small Zygospira brachiopods.

Groove or gutter filled with the small brachiopod Zygospira

Another accumulation of Zygospira from the same locality. The large brachiopod on the bottom right is a Rafinesquina.

Zygospira are known for adhering themselves to whatever hard substrate they can find. In a paper by Micheal Sandy (1996), the author describes a specimen from the Waynesville Formation of Ohio where an articulated crinoid stem is thoroughly encrusted by Zygospira. There have also been reports by local trilobite collectors that they have found Zygospira concentrated around fragments of Isotelus in mudstone deposits colloquially referred to as butter shales (more on these next week).

A closer look at one of the accumulations of Zygospira

Lastly, an interesting note is that on at least one of the blocks we see the dumbbell shaped trace fossil Diplocraterion generally thought to be the dwelling trace of a crustacean or worm.

Arrow is pointing to the Diplocraterion trace fossils associated with one of these Zygospira accumulations.

Houston Museum of Natural Science: Trilobites

I recently stopped by the Houston Museum of Natural Science (HMNS). One of the best trilobite displays I have ever seen. They were recently updated and the whole exhibit had a modern feel. The lighting was dim, but this is an issue common to most museums. This will be the first in a series of post on the displays I visited. Here are some of my favorite trilobites.

Death March: a trace and trace maker 

Amazing Growth Series