GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 282-15
Presentation Time: 9:00 AM-6:30 PM


HONECK, Jacob W., Geological Sciences, University of Alabama, 201 7th Avenue, 2003 Bevill Building, Tuscaloosa, AL 35487, TOBIN, Thomas S., Geological Sciences, University of Alabama, Tuscaloosa, AL 35401, TUITE, Michael L., Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, FLANNERY, David M., School of Earth, Environmental and Biological Sciences, Queensland University of Technology (QUT), Brisbane, QLD 4000, Australia, FENDLEY, Isabel, Department of Earth and Planetary Science, University of California, Berkeley, McCone Hall, Berkeley, CA 94720, WEAVER, Lucas N., Department of Biology, University of Washington, 247 Life Sciences Building, Seattle, WA 98195 and SPRAIN, Courtney J., Department of Geological Sciences, University of Florida, Williamson Hall, Gainseville, FL 32611

Organic carbon isotope (δ13Corg) analysis of organic material has the potential to produce precise correlations in terrestrial environments. A negative δ13Corg excursion recognized worldwide has been also been observed at the Cretaceous-Paleogene (K‑Pg) boundary in the intensely studied Hell Creek area of Montana. The K-Pg boundary in this region coincides very closely with a lithological contact between two formations, and thus provides an ideal location at which to test the use of δ13Corg in high-resolution stratigraphy. Previous studies have produced stratigraphic records of δ13Corg across the K-Pg boundary in the area (Arens et al., 2014; Arens and Jahren, 2000). However, modern organic contamination, lithological control, and local spatial variability may affect δ13Corg values.

To test the effects of modern contamination and lithological control, we collected samples from a traditional hand trench, a coring device, and a deep (>1m) trench dug using a backhoe. Samples obtained using each method are collected across the same stratigraphic interval within 20 m (geographically) of each other, so their relative reliability can be assessed. Results show that core samples values are more negative, but the general trends, including the negative K-Pg excursion, are preserved in all sampling methods. There does not appear to be a significant lithological bias to δ13Corg values. Additionally, samples were also collected from hand trenches over a greater, but still fairly small (<10 km2) area to compare the effects of local spatial variability in δ13Corg signals. Results of these samples will be presented at the conference.