Paper No. 6
Presentation Time: 2:45 PM
HOLOCENE SEA-LEVEL CHANGE AND CRUSTAL MOTIONS ALONG THE US GULF COAST: IMPLICATIONS FOR PRESENT-DAY AND FUTURE RELATIVE SEA-LEVEL RISE
TORNQVIST, Torbjörn E., Earth and Environmental Sciences, Tulane University, 6823 St. Charles Ave, New Orleans, LA 70118, YU, Shiyong, Earth and Environmental Sciences, Tulane University, 6823 St. Charles Avenue, New Orleans, LA 70118-5698, WOLSTENCROFT, Martin, Department of Earth Sciences, University of Ottawa, Ottawa, K1N 6N5, Canada, KULP, Mark A., Dept. of Earth & Environmental Sciences and Pontchartrain Institute for Environmental Sciences, University of New Orleans, 2000 Lakeshore Drive, New Orleans, LA 70148, MILNE, Glenn A., Department of Earth Sciences, University of Ottawa, Ontario, ON K1N 6N5, Canada and SHEN, Zhixiong, Department of Earth and Environmental Sciences, Tulane University, 6823 St. Charles Ave, New Orleans, LA 70118, tor@tulane.edu
The Holocene relative sea-level (RSL) history of the Gulf of Mexico has been a subject of controversy that dates back to the 1960s. While one camp favors a “continuous submergence” scenario of progressive RSL rise, others have argued for one or more RSL highstands, dating as far back as 6000 years ago. These opposing scenarios have major implications for (1) the primary controls of RSL change in this region, notably the extent of glacial isostatic adjustment; (2) subsidence rates of the lithosphere beneath the Mississippi Delta relative to other portions of the US Gulf Coast; and (3) the degree of acceleration of modern sea-level rise from tide gauges compared to the pre-industrial era.
A new, high-resolution RSL reconstruction from the Louisiana Chenier Plain, >100 km west of the edge of the Mississippi Delta, enables a direct test of the highstand hypothesis. This record captures the ~6.5 to 3.0 ka time window, conclusively showing that no middle Holocene RSL highstands have existed in this region and that GIA-driven subsidence is a key variable along the US Gulf Coast. In addition, our new RSL curve allows us to quantify the differential crustal motion (a subsidence rate of 0.15 ± 0.07 mm/yr) beneath the most densely populated portions of the Mississippi Delta, relative to the adjacent Gulf Coast. Finally the rate of RSL rise along the central US Gulf Coast accelerated about fivefold during the last century, compared to the pre-industrial millennium.
We use the new RSL data, along with other recent evidence on the elastic thickness of the lithosphere in this region, to constrain a geophysical model that predicts present-day rates of subsidence due to sediment loading in the Mississippi Delta. Initial model results suggest that the footprint of the sediment loading effect may be larger than previously believed, and that growth faulting may be a significant factor in more seaward localities where modeled sediment loading effects underpredict observed subsidence rates.
