Abstract Detail

Recent Topics Posters

Richey, Jon [1], Upchurch, Garland [2].

Inference of pCO₂ Levels During the Late Cretaceous Using Fossil Lauraeae.

Understanding the mechanisms of past global warming requires accurate estimates of atmospheric pCO₂ during intervals like the Late Cretaceous, which is thought to be a proxy for current climatic warming. Botanical estimates of pCO₂ for the Late Cretaceous have most commonly used Stomatal Index (SI) on leaf macrofossils (LM) of Ginkgo. Dispersed cuticle (DC) and other fossil plants have been underutilized in SI studies during this interval. Lauraceae are a family that have high potential for use in Late Cretaceous SI studies because of their quality of preservation and abundant occurrence in megafossil and dispersed cuticle assemblages. Recently, SI in fossil Lauraceae has been used to infer changes in pCO₂ across the Cenomanian-Turonian boundary, based on the relationship between SI and pCO₂ in the extant species Laurus nobilis and Hypodaphnis zenkeri. Building upon this work, we examined SI in DC and LM of the leaf macrofossil genus Pandemophyllum from: 1) the late Maastrichtian of the Raton Basin, southern Colorado (DC only), 2) The middle Cenomanian (Zone III) of the Potomac Group of Maryland at the Mauldin Mountain macrofossil locality (DC only), and 3) the latest Albian of the Dakota Formation, southeastern Nebraska, Rose Creek locality (both DC and LM). These samples fall within the Late Cretaceous decline in pCO₂ inferred from geochemical modeling and proxies. SI was calculated using counts of up to 56,000 cells per sample; pCO₂ levels and 95% confidence intervals (CI) were estimated using the relationship between SI and pCO₂ published for extant L. nobilis and H. zenkeri. Error in counts was determined using ± 1 Standard Deviation (SD) calculations. The 95% CIs of latest Albian and Maastrichtian pCO₂ estimates fall within the range of published estimates from other proxies. However, the 95% CI of the Cenomanian estimate is low relative to most other proxy estimates. This may be due to: a) a brief interval of low CO₂ within the overall Late Cretaceous trend of high CO₂, or b) transfer functions based on historic levels of pCO₂ without supplementary data from growth chamber experiments under elevated pCO₂. For the Rose Creek locality, SI calculated from DC ± 1 SD falls within SI calculated from macrofossils ± 1 SD, suggesting that DC is suitable for the SI proxy method. From this, we conclude that SI in fossil lauraceous dispersed cuticle and macrofossils show the sensitivity to high pCO₂ needed for studies of Late Cretaceous pCO₂ levels.

Broader Impacts:

1 - Texas State University - San Marcos, Department of Biology, 601 University Dr., San Marcos, TX, 78666, USA
2 - Texas State University, Department Of Biology, 601 University Drive, San Marcos, TX, 78666, USA

Keywords:
Climate Change
Stomatal Index
Lauraceae
 CO₂
Cretaceous.

Presentation Type: Recent Topics Poster
Session: P
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM
Number: PRT037
Abstract ID:1335