T21B-2814
Bringing organic carbon isotopes and phytoliths to the table as additional constraints on paleoelevation
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Nathan D Sheldon1, Jennifer M Cotton2, Michael T Hren3, Ethan G Hyland4, Selena Y Smith1 and Caroline A E Strömberg5, (1)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (2)University of Utah, Salt Lake City, UT, United States, (3)University of Connecticut, Center for Integrative Geosciences, Groton, CT, United States, (4)University of Washington Seattle Campus, Seattle, WA, United States, (5)University of Washington Seattle Campus, Department of Biology and Burke Museum, Seattle, WA, United States
Abstract:
A commonly used tool in paleotectonic and paleoaltimetry studies is the oxygen isotopic composition of authigenic carbonates formed that formed in lakes or soils, with both spatial (e.g., shoreline to mountain top) or temporally resolved records potentially providing constraints. However, in many cases there is a substantial spread in the oxygen isotope data for a given time period, often to the point of allowing for essentially any interpretation of the data depending upon how they have been used by the investigator. One potential way of distinguishing between different potential paleotectonic or paleoaltimetric interpretations is to use carbon isotope and plant microfossil (phytolith) analyses from the same paleosols to screen the oxygen isotope data by looking for evidence of evaporative enrichment. For example, if both inorganic (carbonate) and organic carbon isotopes are measured from the same paleosol, then in it possible to determine if the two isotope record equilibrium conditions or if they record disequilibrium driven by kinetic effects. In the former case, the oxygen isotope results can be considered reliable whereas in the latter case, the oxygen isotope results can be considered unreliable and could be culled from the interpretation. Similarly, because the distribution of C4 plants varies as a function of temperature and elevation, the presence/absence or abundance of C4 plant phytoliths, or of carbon isotope compositions that require a component of C4 vegetation can also be used to constrain paleoelevation by providing a maximum elevation constraint. Worked examples will include the late Miocene-Pliocene of Catamarca, Argentina, where phytoliths and organic carbon isotopes provide a maximum elevation constraint and can be used to demonstrate that oxygen isotopes do not provide a locally useful constraint on paleoelevation, and Eocene-Miocene of southwestern Montana where organic matter and phytoliths can be used to select between different potential uplift histories as indicated by pedogenic carbonate oxygen isotope data.
