T15 Fossils Plants as Paleoenvironmental Recorders I

Sunday, 4 November 2012
8:00 AM - 12:00 PM
202AB

CARBONIFEROUS ATMOSPHERIC CO2 AND CLIMATE: AN INTEGRATED FOSSIL CUTICLE AND PALEOSOL CARBONATE ANALYSIS

Paper number: T15-9
Program: Technical Sessions
Time: 10:00 AM – 10:15 AM

Authors

Abstract

The Paleozoic icehouse has long been attributed to a substantial drop in atmospheric pCO2 to present-day levels driven by the evolution of vascular plants and consequent increased continental weathering. Recent studies reveal a dynamic ice age involving repeated discrete glaciations separated by periods of greatly diminished ice. How paleo-atmospheric CO2 varied during this period of dynamic climate, however, remains elusive. Here we present a cyclothem-scale reconstruction of Pennsylvanian (314 to 303 Ma) atmospheric CO2 contents developed through integration of stomatal indices (SI) of fossil cuticles and δ13C of soil-formed carbonates and associated or occluded organic matter. The SI record is based on two long-ranging taxa of wetland pteridosperms, Macroneuropteris scheuchzeri and Neuropteris ovata, from the Illinois Basin. Dryland taxa, Megalopteris and Lesleya, from two cameo intervals, provide constraints on the response of stomata to varying environmental conditions. The mineral-based proxy record was developed using pedogenic carbonates from the same set of Illinois Basin cyclothems and contemporaneous successions in the Appalachian and Donets basins. Recent correlation of the cyclothemic successions of the Midcontinent and Appalachian and Donets basins permits integration of the CO2records and comparison to independent paleosol, geochemical, and stratigraphic proxies of climate and glacioeustasy.

Similar SI trends are defined by M. scheuchzeri and N. ovata although variants of the latter exhibit offsets in SI. Intra- and inter-pinnule SI variation falls within the standard error of the mean for each leaf. Temporal variation in stomatal morphology, trichome density, and cuticle δ13C further correlate to SI trends providing insight into the origin of the stomatal trends. Integration of the mineral-based CO2 estimates with the SI trends delineates repeated short-term variations in atmospheric pCO2 that agree well with recent independent estimates of glaciation and glacioeustasy. Both records suggest that widespread reduction in the areal extent of tropical wetland forests in the late Pennsylvanian and associated aridification may have been linked to a multi-million year increase in CO2 concentration through a substantial decrease in organic C sequestration at this time.