HR: 1340h
AN: PP33B-0944    [Abstracts]
TI: Modeling of Seawater Geochemistry in Snowball Earth-Hothouse Earth Environments
AU: * Marion, G M
EM: giles.marion@dri.edu
AF: Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512 United States
AU: Catling, D C
EM: dcatling@u.washington.edu
AF: University of Washington, Box 351640, Seattle, WA 98195 United States
AU: Kargel, J S
EM: jkargel@usgs.gov
AF: U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001 United States
AB: Abundant evidence exists that during the Neoproterozoic era, the Earth was covered by glaciers and sea-ice into the tropics. This cold phase of Earth's geologic history has come to be known as "Snowball Earth," which interestingly alternated with unusually warm intervals, now called "Hothouse Earth." The cause(s) of these alternating phases of Earth's geologic history are controversial. For example, were these alternating climates caused by obliquity changes, continental drift, weathering, changes in the carbon cycle, or some combination of these factors? Remnants of these geologic times are clearly imprinted in geologic formations with banded iron formations and carbonate deposits overlying glacial tillites. Banded iron formations strongly suggest that seawater was anoxic in order for ferrous iron to have accumulated to concentrations high enough to precipitate distinct iron layers. Carbonate deposits suggest that the oceans were supersaturated with carbonate minerals. One of the mechanisms proposed for bringing the Earth out of these deep freezes is the release of greenhouse gases from gas hydrates that could have contributed to atmospheric warming. To better understand and constrain the possible interpretations of what occurred during these glacial/interglacial periods, we used the FREZCHEM model to simulate processes potentially controlling seawater geochemistry. The FREZCHEM model is structured to predict the equilibrium aqueous geochemistry of chloride, sulfate, carbonate, and nitrate salts, strong acids, and gas hydrates over the temperature range from $<$-70 to 25øC and the pressure range from 1 to 1000 bars. During the Snowball Earth phase, defining seawater solids are likely to have been siderite(FeCO3), methane hydrate, and ice. Warming of a Snowball Earth to a Hothouse Earth and reacting with oxygen causes the conversion of siderite to ferrihydrite [Fe(OH)3] and the precipitation of dolomite. Only shallow gas hydrate deposits ($<$ 1 km) are likely to have influenced global warming during these alternating climate shifts.
DE: 9619 Precambrian
DE: 4825 Geochemistry
DE: 4842 Modeling
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting