HR: 17:15h
AN: H54A-06    [Abstracts]
TI: Vegetation-Precipitation Interactions Drive Paleoenvironmental Evolution
AU: * Fraticelli, C M
EM: carmen.m.fraticelli@exxonmobil.com
AF: ExxonMobil Upstream Research Company, 3120 Buffallo Speedway, Houston, TX 77098 United States
AU: West, B P
EM: brian.p.west@exxonmobil.com
AF: ExxonMobil Upstream Research Company, 3120 Buffallo Speedway, Houston, TX 77098 United States
AU: Bohacs, K M
EM: kevin.m.bohacs@exxonmobil.com
AF: ExxonMobil Upstream Research Company, 3120 Buffallo Speedway, Houston, TX 77098 United States
AU: Patterson, P E
EM: penny.e.patterson@exxonmobil.com
AF: ExxonMobil Upstream Research Company, 3120 Buffallo Speedway, Houston, TX 77098 United States
AU: Heins, W A
EM: bill.heins@exxonmobil.com
AF: ExxonMobil Upstream Research Company, 3120 Buffallo Speedway, Houston, TX 77098 United States
AB: In studies of climate effects on the sedimentary record, vegetation is often relegated to the role of proxy data. However, modern environmental distributions reflect strong feedbacks among vegetation communities, precipitation, and temperature that can reinforce secular climate changes. These feedbacks are strong enough to dry out tropical rainforests, green deserts, or warm high latitudes. Four distinct phases in the evolution of land plants have progressively altered the global distribution of precipitation and smoothed the climatic gradient between continent interiors and coastal margins. Each phase of land-plant evolution and its attendant climate effects have influenced sedimentary systems by modifying the relationship between climate and sediment yield. The phases are: 1) pre-Devonian, 2) Devonian-Cretaceous, 3) Cretaceous-Oligocene, 4) post-Oligocene. In the pre-Devonian, before widespread land-plant cover, precipitation patterns depended solely on latitude, the distribution of continents and oceans, and the consequent atmospheric circulation patterns. The known spatial distribution of evaporite deposits and the characteristics of fluvial systems at this time reflect how dissimilar this environment is to today. The Devonian-Cretaceous phase saw the rise and diversification of most major land-plant groups. However, these arid-intolerant floras were concentrated in high-humidity lowlands and coastal margins. Low-density vegetative cover in uplands and continental interiors was reinforced by a positive feedback among increased temperature, decreased moisture and decreased vegetation density. The climatic gradient from continental interior to coastal margin was at a maximum during this period. Continent-interior to coastal climatic gradients became less pronounced in the Cretaceous to Oligocene with the advent of arid-tolerant herbaceous angiosperms that increased the vegetative cover in dry uplands. A positive feedback among increased vegetative cover, increased moisture retention and decreased temperatures ameliorated the climatic extremes of continental interiors, enhancing chemical weathering, retarding sediment fluxes, and increasing the dissolved load of streams. The increased vegetative cover on uplands also stabilized sediment yields and increased the formation of finer-grained sediments in any given paleogeographic setting. The post-Oligocene period spans the evolution of grasslands, tundra and taiga environments, which further expanded the vegetative cover of terrestrial environments. As the nature of vegetation has changed during the Phanerozoic, the nature of the interactions between vegetation, paleoenvironments, and sediment yield has also evolved. These changes dramatically affect what paleoenvironmental conditions are predictable for the past, our understanding of ancient sediment yields, and the relationship between climate and continental depositional systems.
DE: 3344 Paleoclimatology
DE: 1815 Erosion and sedimentation
DE: 1854 Precipitation (3354)
DE: 1620 Climate dynamics (3309)
DE: 0315 Biosphere/atmosphere interactions
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting