T194 Height, the Elusive Third Dimension of Terrestrial Ecosystems: New Approaches for Determining the Structure and Complexity of Ecosystems on Land in Deep Time

Tuesday, 27 September 2016
8:00 AM - 12:00 PM
Mile High Ballroom 3C

LEAF CARBON ISOTOPES AND CELL ANATOMY AS INDICATORS OF SHADING AND CANOPY STRUCTURE IN A MIOCENE FOREST FROM ETHIOPIA

Paper number: T194-12
Program: Technical Sessions
Time: 10:45 AM – 11:00 AM

Authors

Abstract

Both leaf carbon isotope composition and cellular morphology have been proposed to represent light regime and thus canopy closure within an ecosystem. Here, we apply these proxies to exquisitely-preserved leaf fossils from the early Miocene Mush Valley site in central Ethiopia. Carbon isotope values and epidermal cell wall undulation (undulation index, UI) were measured for 21 fossil leaves of an unnamed legume morphospecies, “Legume 1.” Seven specimens of a second legume morphospecies were also analyzed using the same procedures, and carbon isotope values and total organic carbon content were measured for 85 additional fossil leaves belonging to at least eight morphospecies. A large range of both leaf carbon isotope and UI values were obtained for Legume 1, indicating that different leaves were exposed to different amounts of light, as would be expected in a closed-canopy rainforest. Average Legume 1 leaf carbon isotope discrimination falls within the range of discrimination values from modern lowland tropical forests. However, Legume 1 leaf carbon isotope values do not correlate with leaf UI values, implying that one or both of these variables is driven by factors beyond simple light exposure. We suspect that leaf carbon isotope discrimination at Mush is also affected by variables such as leaf height, branch length, and relative humidity, without affecting UI values. We also compare the Legume 1 carbon isotope values with values from several other morphotypes from the same site, as well as compound-specific carbon isotope values from plant- and algal-derived long-chain n-alkanes.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-287591

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.