De Backer, T.

De Boodt, C.

De Weirdt, J.

Emsbo, P.

McLaughlin, P.

Vandenbroucke, T.

Open Marine Archive

 80 
Can chitinozoan biostratigraphy of the Maquoketa Group (Illinois 
Basin, USA) help unravel the order of events leading up to the Late 
Ordovician mass extinction?  
De Boodt Charlotte
1
, De Backer Tim
1
, Mclaughlin Patrick
2
, De Weirdt Julie
2
, Emsbo Poul
3
 and 
Vandenbroucke Thijs
3 
1
  Department of Geology, Ghent University, Krijgslaan 281 – S8, 9000 Ghent, Belgium 
E-mail: charlotte.deboodt@ugent.be 
2
 Indiana Geological and Water Survey, Indiana University, Bloomington, Indiana, USA 
3
  Central Mineral and Environmental Resources Science Center, United States Geological Survey, 
Denver, Colorado, USA 
 
Dynamic oceanographic changes during the Late Ordovician culminated in the second largest of the 
Phanerozoic’s big five mass extinctions, eradicating greater than 85% of marine species. Marine 
sedimentary rocks from this interval feature a stable carbon isotope excursion with values exceeding 
5‰, implicating a major perturbation to the global carbon cycle. Yet, a deep understanding of the 
mechanisms that drove this ancient event remain heavily debated. A detailed knowledge of the order 
of events and their environmental and biological characteristics is central to advancing understanding 
about this mass extinction. 
 
The pristine nature and accessibility of the little studied Upper Ordovician Maquoketa Group in the 
US midcontinent offers an unparalleled opportunity to advance understanding of the Late Ordovician 
mass extinction. Deposited in the tropical Illinois Basin of interior Laurentia, the Maquoketa Group 
records a complex succession of facies changes that have thwarted previous stratigraphic studies. 
Yet, the abundant shales of the Maquoketa Group, now available from across the basin due to recent 
advances in access to subsurface drill cores, yield exceptionally well preserved organic-walled 
microfossils. In particular, chitinozoans provide great opportunity for improving biostratigraphic age 
assessment. 
 
Currently thirty-six samples from the IGWS-440 drill core from northwestern Indiana (Newton County) 
are being analyzed for chitinozoan species distributions. The samples are producing a rich 
assortment of well-preserved chitinozoans, including a number of key species. The preliminary results 
show intriguing similarities and differences to other recently studied cores from closer to the basin 
margin. These data demonstrate tangible advances in revising the age assessment of the Maquoketa 
Group and are enabling coupled studies on the sequence stratigraphy, geochemistry and paleobiology 
of this interval to step closer unlocking the drivers of the Late Ordovician mass extinction. 
 
Keywords: microfossils; Ordovician; paleontology; stratigraphy; carbon isotopes  


Can chitinozoan biostratigraphy of the Maquoketa Group (Illinois Basin, USA) help unravel the order of events leading up to the Late Ordovician mass extinction?

http://www.vliz.be/imisdocs/publications/311589.pdf

Can chitinozoan biostratigraphy of the Maquoketa Group (Illinois Basin, USA) help unravel the order of events leading up to the Late Ordovician mass extinction?

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