GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 68-4
Presentation Time: 2:30 PM


ADIATMA, Y. Datu1, SALTZMAN, Matthew R.1, YOUNG, Seth A.2, GRIFFITH, Elizabeth M.3, KOZIK, Nevin P.4, EDWARDS, Cole T.5, LESLIE, Stephen A.6 and BANCROFT, Alyssa M.7, (1)School of Earth Sciences, The Ohio State University, 275 Mendenhall Laboratory, 125 S Oval Mall, Columbus, OH 43210, (2)Earth, Ocean, and Atmospheric Science, Florida State University, 108 Carraway Building, Tallahassee, FL 32306, (3)School of Earth Sciences, The Ohio State University, Mendenhall Laboratory, 125 S Oval Mall, Columbus, OH 43210, (4)Department of Earth, Ocean, and Atmospheric Sciences, Florida State University, National High Magnetic Field Laboratory, Tallahassee, FL 32306, (5)Geological and Environmental Sciences, Appalachian State University, 572, Boone, NC 28608, (6)Department of Geology and Environmental Science, James Madison University, 801 Carrier Drive, MSC 6903, Harrisonburg, VA 22807, (7)Indiana Geological and Water Survey, Indiana University, Bloomington, IN 47405

A stepwise-change in atmospheric oxygen (O2) levels during the Ordovician has been attributed to the emergence of land plants. This phenomenon is tied to a major baseline shift in the stable carbon isotope (δ13Ccarb) curve, and an inferred increase in nutrient delivery, and enhanced primary productivity in nearshore settings, which led to enhanced organic carbon burial. The timing and magnitude of this baseline shift, however, is still elusive in part due to the lack of high-resolution δ13C data that span this period.

This study presents new high-resolution δ13C data from Middle to Upper Ordovician sections at Germany Valley (West Virginia) and Union Furnace (Pennsylvania) in the Central Appalachian Basin. The δ13C curves of the data from both sections are characterized by relative stability and low carbon isotope values (mean δ13C = -0.61 ‰) in the lower Sandbian, followed by a ~ 1.2 ‰ shift toward more positive values (mean δ13C = +0.62 ‰) in the upper Sandbian. We propose that the positive shift represents a fundamental state change in the global carbon cycle that is coincident with a major diversification of early land plants (i.e., bryophytes). This shift in δ13C baseline supports a growing number of studies that interpret enhanced organic carbon burial rates served as a mechanism for the stepwise oxygenation of the atmosphere during the Late Ordovician.