HR: 1330h
AN: G43A-07    [Abstracts]
TI: Using Holocene Relative Sea-Level Data for High-Precision Measurement of Differential Crustal Movements in the Mississippi Delta
AU: * Tornqvist, T E
EM: tor@uic.edu
AF: Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7059 United States
AU: Bick, S J
EM: bick@unavco.org
AF: Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL 60607-7059 United States
AU: van der Borg, K
EM: k.vanderborg@phys.uu.nl
AF: Robert J. Van de Graaff Laboratory, Utrecht University, P.O. Box 80000, Utrecht, NL-3508 TA Netherlands
AU: de Jong, A F
EM: a.f.m.dejong@phys.uu.nl
AF: Robert J. Van de Graaff Laboratory, Utrecht University, P.O. Box 80000, Utrecht, NL-3508 TA Netherlands
AU: Greenberg, J
EM: greenberg@unavco.org
AF: UNAVCO, Inc., 6350 Nautilus Drive, Boulder, CO 80301-5554 United States
AB: Due to the immense concern about wetland loss and coastal erosion in southern Louisiana, there is vigorous debate about the driving mechanisms that cause this environmental catastrophe. One frequently invoked component is tectonic subsidence of the Mississippi Delta and its surroundings as a consequence of lithospheric flexure due to ongoing sediment loading by the deltaic depocenter. We have collected relative sea-level data covering the past 8500 years from three study areas in different sections of the Mississippi Delta, to assess whether significant differential crustal movements occur. Our sea-level index points were obtained from basal peat that accumulated during the initial transgression of the pre-existing, consolidated Pleistocene basement, thus ruling out the role of compaction of Holocene strata. The study areas differ in their distance to the present shoreline; in addition, a presumed major growth-fault system may be located between two of them. The rationale of our analysis is that given spatially uniform eustatic and glacio-hydro-isostatic signals, any difference between relative sea-level curves from the three study areas can be attributed to differential tectonic subsidence rates. The extremely favorable conditions for sea-level research on the US Gulf Coast (largely due to the low tidal range) and the long time span of observation allow us to calculate tectonic movements with exceptionally high accuracy and precision. Our results show that differential crustal movements among the three study areas have been on the order of ~0.1 mm/yr, values that are statistically indistinguishable. We compare our new evidence with a recently published compilation of relative sea-level data from the Caribbean, to a large extent based on data from areas that are widely believed to be tectonically very stable (e.g., Florida, Bahamas, Belize). All our sea-level index points nearly coincide with the Caribbean data, showing that considerable parts of the Mississippi Delta may be surprisingly tectonically stable. Thus, we suggest that the rapid rates of coastal-wetland loss are largely due to a combination of compaction of the thick Holocene strata, as well as human action, like the extraction of oil, gas, and groundwater.
DE: 1035 Geochronology
DE: 1645 Solid Earth
DE: 1890 Wetlands
DE: 4556 Sea level variations
DE: 8105 Continental margins and sedimentary basins
SC: Geodesy [G]
MN: 2005 Joint Assembly