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Mid-Cretaceous pCO₂ based on stomata of the extinct conifer Pseudofrenelopsis (Cheirolepidiaceae)

Matthew Haworth^*,1, Stephen P. Hesselbo^*,1, Jennifer C. McElwain^*,2, Stuart A. Robinson^*,,3 and James W. Brunt³

¹ Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK
² The Field Museum, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA
³ Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK

Stomatal characteristics of an extinct Cretaceous conifer, Pseudofrenelopsis parceramosa (Fontaine) Watson, are used to reconstruct atmospheric carbon dioxide (pCO₂) over a time previously inferred to exhibit major fluctuations in this greenhouse gas. Samples are from nonmarine to marine strata of the Wealden and Lower Greensand Groups of England and the Potomac Group of the eastern United States, of Hauterivian to Albian age (136–100 Ma). Atmospheric pCO₂ is estimated from the ratios between stomatal indices of fossil cuticles and those from four modern analogs (nearest living equivalent plants). Using this approach, and two calibration methods to explore ranges, results show relatively low and only slightly varying pCO₂ over the Hauterivian–Albian interval: a low of 560–960 ppm in the early Barremian and a high of 620–1200 ppm in the Albian. Data from the Barremian Wealden Group yield pCO₂ values indistinguishable from a soil-carbonate–based estimate from the same beds. The new pCO₂ estimates are compatible with sedimentological and oxygen-isotope evidence for relatively cool mid-Cretaceous climates.

Key Words: CO₂ • Cretaceous • Pseudofrenelopsis • Cheirolepidiaceae • Wealden Group • Potomac Group

This article has been cited by other articles:

				L. L.R. Kouwenberg, W. M. Kurschner, and J. C. McElwain Stomatal Frequency Change Over Altitudinal Gradients: Prospects for Paleoaltimetry Reviews in Mineralogy and Geochemistry, October 1, 2007; 66(1): 215 - 241. [Abstract] [Full Text] [PDF]