--> Abstract: A Revised Chronology For Mississippi River Subdeltas - Implications For Sequence Stratigraphy, by T. E. Tornqvist, T. R. Kidder, W. J. Autin, and J. Wallinga; #90928 (1999).

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TORNQVIST, TORBJORN, E.1, TRISTRAM R. KIDDER2, WHITNEY J. AUTIN3, and JAKOB WALLINGA4
1The Netherlands Centre for GeoResearch (ICG), Faculty of Geographical Sciences, Utrecht University, Utrecht, The Netherlands
2Department of Anthropology, Tulane University, New Orleans, LA
3Department of the Earth Sciences, SUNY College at Brockport, Brockport, NY
4The Netherlands Centre for Geo-ecological Research (ICG), Faculty of Geographical Sciences, Utrecht University, The Netherlands

Abstract: A Revised Chronology for Mississippi River Subdeltas - Implications for Sequence Stratigraphy

New 14C and archaeological data demonstrate that the chronology of the Mississippi Delta requires substantial revision. We collected 14C samples related to trunk segments of three of the four late Holocene Mississippi River subdeltas. Samples from the top of peat beds underneath clayey overbank deposits represent their beginning of activity, and constrain the period of activity of all downstream distributaries belonging to these subdeltas. We dated botanical macrofossils by accelerator mass spectrometry, to avoid contamination which usually occurs in bulk peats, and obtained highly consistent results that show an excellent match with the archaeologically based chronology. The new evidence indicates that the Lafourche subdelta cannot have existed prior to 1500 yr B.P., considerably younger than the age most commonly cited in the literature (3500 yr B.P.). The St. Bernard subdelta is also younger than generally supposed (3600 yr B.P. versus 4600 yr B.P.), whereas the Plaquemines-Modern subdelta (1300 yr B. P.), conforms much better to previous inferences. Our results thus show that the Lafourche and Plaquemines-Modern subdeltas originated almost simultaneously. The revised ages demonstrate that progradation of the highstand systems tract proceeded more rapidly than the existing chronology suggests. In addition, the previously identified maximum flooding surface may well be younger than has been assumed, and clearly postdates the glacioeustatic sea-level rise associated with Termination 1.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas