BRIDGING THE LIMESTONE TO SHALE TRANSITION: UPPER ORDOVICIAN (KENTUCKY AND OHIO)

The abstract I submitted to the North Central Geological Society of America meeting this coming May was accepted. I hope to see a few of you at the meeting!

Correlation of shallow marine limestones into deeper shale-dominated settings remains an area of great uncertainty in many sedimentary basins impairing the accuracy of depositional models. The Lexington Platform-Sebree Trough transition (Kentucky-Ohio) represents a well preserved Upper Ordovician example of this problem. In this study, outcrops and cores in central Kentucky and new drill cores from Cincinnati, Ohio were logged using litho-, bio-, and chemo-stratigraphy to develop detailed correlation of chrono-stratigraphic packages across a major facies transition from a the carbonate-dominated Lexington Limestone platform succession to the dark, mudrock-dominated deposits at the transition to the Sebree trough. A number of facies-crossing markers provide useful, first-order controls on stratigraphy: these include abrupt facies offsets, K-bentonites, fossil epiboles (e.g. Prasopora bryozoans), and deformed beds, probably representing regional seismites. These correlations are corroborated by gamma ray, carbon isotope curves, and elemental abundance profiles. This research expands the regional correlation of the Lexington Formation and its members into more distal settings and provides strong evidence that depositional sequences, and distinctive faunal epiboles, and chemo-stratigraphic signatures are of regional extent. Thus, despite local abrupt facies variations, associated with far field tectonics, there is strong evidence for allocyclic, probably eustatic control of large and small-scale cycles. However, the degree of environmental change across this gradient varies strongly with stratigraphic levels. Thus, lower units (Curdsville, Logana members) persist across the profile with relatively little change. In contrast, the upper Lexington units display much more abrupt northward change to shaly facies, suggesting increasing rates of subsidence in the Sebree trough through deposition of the Lexington sediments.

YOUNG, Allison L., Geology, University of Cincinnati, 500 GeoPhys, Cincinnati, OH 45221, younga9@mail.uc.edu, BRETT, C.E., Department of Geology, University of Cincinnati, 500 Geology/Physics Building, Cincinnati, OH 45221-0013, and MCLAUGHLIN, Patrick I., Wisconsin Geological Survey, University of Wisconsin - Extension, 3817 Mineral Point Rd, Madison, WI 53705

Ordovician Atlas

You have probably noticed that in past posts about the local paleontology, I have often linked specific fossil genera to an 'Ordovician Atlas' page. I thought I would share a little bit about this resource because I think it is a wonderful way to learn about the paleontology of the Cincinnati Arch.

This Ordovician Atlas is part of a collaborative NSF-funded initiative to produce digital atlases for multiple intervals of Earth history.

The Ordovician Atlas website is a series of interactive pages which allow you to search different fossil taxa that can be found in the strata along the Cincinnati Arch. Whether it be arthropods, brachiopods, echinoderms, cnidaria, mollusks or bryozoans, the Ordovician Atlas is a great resource for identifying taxa, identifying that strata you might find them in, ecological niches, descriptions or publication relevant to the taxa in question.


I know personally when dealing with fossils genera that I may be unfamiliar with, I always check the Ordovician Atlas to see if they have a listing. Below I have posted a few screenshots from the website to show some of the features present for individual genera, in this case Isotelus.

Example of the Isotelus page showing the Linnaean classification, geologic range and location map. 

Some of the pages shows these nice paleoecological diagrams depicting the range of habitats and organism may have lived. This image is for Isotelus maximus

These two images show the stratigraphic distribution of the general in question (Isotelus maximus) along with basic fossil descriptions.

Lastly, many of these pages will have a list of references and descriptions from those references, of the fossil in question.

The site contains more than just information about the various Cincinnatian genera. There is a page about the local geologic setting, the Richmondian Invasion (a person interest of mine) and various educational resources for the teachers among you. For those of you who like to go collecting, they have a page dedicated to listing good sites for doing just that!

I want to thank Dr. Alycia Stigall and the students in her lab for the great work they have put in and continue to put into this great resource.


I also would like to point you to this recent publication which discusses the program further.

Stigall, Alycia L., Jennifer E. Bauer, and Hannah-Maria R. Brame. "The Digital Atlas of Ordovician Life: digitizing and mobilizing data for paleontologists and the public." Estonian Journal of Earth Sciences 63.4 (2014): 312œ316.

Keep checking back for more additions to the Ordovician Atlas. If you are Twitter savvy, @PaleoDigAtlas is one source for updates to not just the Ordovician Atlas but the entirety of the 'Digital Atlas of Ancient Life' project.