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| Titel |
Geophysical modelling of subsidence on the Mississippi Delta |
| VerfasserIn |
Martin Wolstencroft, Zhixiong Shen, Torbjörn Törnqvist, Glenn Milne, Mark Kulp |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250087355
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| Publikation (Nr.) |
 EGU/EGU2014-1388.pdf |
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| Zusammenfassung |
| The Mississippi Delta (MD) is experiencing relative sea level rise of approximately 10 mm/yr
(Penland and Ramsey, 1990). This rate is caused by a combination of global sea level rise and
local subsidence of the land surface. The relative importance of processes thought to be
responsible for this subsidence is vigorously debated. Many previous studies have postulated
that isostatic subsidence of the Pleistocene basement caused by sediment loading of the MD
itself is the major contributor. GPS surveys have produced subsidence rates greater than 5
mm/yr in the MD (e.g. Dokka et al. 2006). Computational modeling studies of vertical land
motion on decadal timescales have reproduced these high rates, but required extreme
and arguably unrealistic parameter values to do so. Additionally, subsidence rates
in the MD on thousand year timescales due to delta loading are found to be an
order of magnitude lower than GPS rates (e.g. Törnqvist et al., 2006; Yu et al.,
2012).
In an attempt to understand the source of this disagreement between data types and better
understand the uncertainties in the modelling process, we carried out a sensitivity analysis
using a spherically symmetric visco-elastic deformation model. The model included
sediment, ice, and ocean load histories from the last 80 kyr. The model results were compared
with observations of vertical land motion over three different time scales (past 80 kyr, past 7
kyr, past ~15 years). We found that glacial isostatic adjustment is likely to be the dominant
contributor to present-day deformation of the Pleistocene and underlying basement.
Basement subsidence rates solely due to sediment loading were found to be less than 0.5
mm/yr. In general, sedimentary processes such as compaction of the Holocene strata
appear to contribute more to land surface lowering than subsidence of the basement
rock.
REFERENCES
Dokka, R. K., G. F. Sella, and T. H. Dixon (2006), Tectonic control of subsidence and
southward displacement of southeast Louisiana with respect to stable North America.
Geophys. Res. Lett., 33, L23308, doi:10.1029/2006GL027250.
Penland, S., and K. E. Ramsey (1990), Relative sea-level rise in Louisiana and the Gulf of
Mexico: 1908-1988, J. Coastal Res., 6, 323-342.
Törnqvist, T. E., S. J. Bick, K. van der Borg, and A. F. M. de Jong (2006), How stable is
the Mississippi Delta? Geology, 34(8), 697-700, doi:10.1130/G22624.1.
Yu, S.-Y., T. E. Törnqvist, and P. Hu (2012), Quantifying Holocene lithospheric
subsidence rates underneath the Mississippi Delta. Earth Planet. Sci. Lett., 331-332, 21–30,
doi:10.1016/j.epsl.2012.02.021. |
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