HR: 0830h
AN: PP41C-0845    [PDF]
TI: Seasonal Wildfires as a Mechanism for Long-distance Transportation of Leaf Waxes and Pyrolytic Hydrocarbons in the Aptian-Albian Scisti a Fucoidi, Italian Appenines
AU: * Finkelstein, D B
EM: dafinkel@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 East 10th St., Bloomington, IN 47405 United States
AU: Pratt, L M
EM: prattl@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 East 10th St., Bloomington, IN 47405 United States
AU: Brassell, S C
EM: simon@indiana.edu
AF: Department of Geological Sciences, Indiana University, 1001 East 10th St., Bloomington, IN 47405 United States
AB: The Scisti a Fucoidi is a heterogenous pelagic deposit including thinly laminated black shales deposited under poorly- to moderately oxygenated conditions. Black shale deposition was coupled to Milankovitch climatic cyclicity with individual black shales occurring at $\sim$20,000 year intervals. Scisti black shales are characterized by relatively low organic carbon contents (0.41 - 5.69 wt. %) and low Tmax values (411 - $432\deg$C). These strata are at a remarkably low level of thermal maturity as evidenced by the presence of $\beta$,$\beta$-hopanes. Despite a scarcity of woody or structured terrestrial organic matter, hydrogen indices are low and long-chain n-alkanes show a strong odd/even carbon preference. Consequently, terrestrial organic matter is inferred to derive from input of leaf waxes associated with eolian dust, strong winds and an arid climate on the up-wind landmass. It is notable that Scisti black shales contain greater relative abundances of aromatic hydrocarbons than saturated hydrocarbons. Aromatic hydrocarbons are characterized by a complex mixture of diagenetic and pyrolyitc polycyclic aromatic hydrocarbons (PAH). Diagenetic PAH include methylphenanthrenes and chrysene; pyrolytic PAH include phenanthrene, anthracene, fluoranthene, pyrene, benzofluoranthene, benzo[ghi]perylene, and coronene. These PAH are inferred to be products of wildfires associated with dry continental conditions, enhancing long-distance transport of pyrolytic PAH. An abundance of pyrolytic PAH in ancient pelagic marine sediments substantiates the linkage between natural burning, atmospheric input and transport of terrestrial organic matter to distal marine basin sites. Winds associated with arid conditions and/or wildfires provide an ideal mechanism for air transport of leaf waxes and pyrolytic PAH to marine sediments. The relative abundance of leaf wax aerosols suggests that there was enough vegetation to generate these waxes and to act as fuel for fires. If landscape denudation occurred following wildfires then nutrient loads to coastal marine settings may have increased resulting in enhanced marine productivity in localized areas.
DE: 1030 Geochemical cycles (0330)
DE: 1055 Organic geochemistry
DE: 4504 Air/sea interactions (0312)
DE: 4825 Geochemistry
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting