| Title: | Landscape denudation as a link between wildfires and bacterially dominated lake ecosystems of the Late Cretaceous Fort Crittenden Formation, southeastern Arizona |
| Author: | David B Finkelstein |
| Date Submitted: | 04/25/2002 |
| Address: | 1001 East 10th St.,
Biogeochemical Labs, Department of Geological Scie
Bloomington
IN
US
47405-1403
|
| Phone: | 812-855-1382 |
| Email: | dafinkel@indiana.edu |
| Co-Authors: | Pratt, Lisa M., Biogeochemical Labs, Department of Geological Sciences, Indiana University, prattl@indiana.edu |
| Affiliation: | Biogeochemical Labs, Department of Geological Sciences, Indiana University |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725492 |
| Keywords: | wildfires, bacteria, lake ecosystems, pyrolitic PAHs |
| Abstract: | Facies of the Late Cretaceous Fort Crittenden Formation reflect the terrestrial response to changing paleoclimate and tectonics during the onset of ice house conditions within the western interior of the U.S. If uplift enhances monsoonal circulation then the lacustrine strata should reflect balanced to over-filled conditions and nutrient-stimulated productivity. Stacked sequences of beach, wetland, and deep lake deposits suggest multiple episodes of lake expansion and contraction in response to either climate or tectonics. Unionid bivalves within beach, wetland and deep lake facies are consistent with a freshwater lake. High and low spired gastropods track facies changes from deep lake to wetland deposits. Mottled color, nodular textures and pseudoslickensides within wetland deposits are indicative of soil forming processes that occurred during the driest phases of wet/dry cycles. Preliminary interpretations of the stratigraphic framework support a freshwater environment indicating balanced to over-filled conditions. Organic carbon contents and the relative concentration of n-alkanes, branched and cyclic alkanes, and polycyclic aromatic hydrocarbons (PAHs) are facies controlled. The saturated hydrocarbon fraction is characterized by the presence of n-C12 through n-C39 alkanes, trace-level abundances of pristane and phytane, and a high relative abundance of branched and cyclic alkanes. Contributions of odd-chain length n-alkanes were derived from land plants and aquatic algae. The abundance of branched and cyclic alkanes points to a bacterially dominated lake ecosystem. Specific PAH compounds are indicative of a pyrogenic origin, and high abundances of PAHs indicate major forest and/or peat fires within the surrounding watershed. Humid and seasonal paleoclimate would enhance biomass build-up in the watershed. Periodic wildfires and landscape denudation results in a pyrolitic PAH signal within deep lake deposits. Enhanced fluxes of inorganic nutrients following denudation appear to have stimulated bacterial productivity. |
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