Pemiscot Bayou, a Large Distributary of the Mississippi River and a Possible Failed Avulsion

  1. N. D. Smith3 and
  2. J. Rogers4
  1. M. J. Guccione1,
  2. M. F. Burford1 and
  3. J. D. Kendall2

Published Online: 17 MAR 2009

DOI: 10.1002/9781444304213.ch16

Fluvial Sedimentology VI

Fluvial Sedimentology VI

How to Cite

Guccione, M. J., Burford, M. F. and Kendall, J. D. (1999) Pemiscot Bayou, a Large Distributary of the Mississippi River and a Possible Failed Avulsion, in Fluvial Sedimentology VI (eds N. D. Smith and J. Rogers), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444304213.ch16

Editor Information

  1. 3

    Department of Geosciences, 214 Bessey Hall, University of Nebraska, Lincoln, NE 68588-0340, USA

  2. 4

    Cape Town, South Africa

Author Information

  1. 1

    Geology Department, University of Arkansas, Fayetteville, Arkansas, USA

  2. 2

    Marathon Oil Company, Tyler, Texas, USA

Publication History

  1. Published Online: 17 MAR 2009
  2. Published Print: 7 OCT 1999

ISBN Information

Print ISBN: 9780632053544

Online ISBN: 9781444304213

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Keywords:

  • Pemiscot Bayou of Mississippi River;
  • meandering distributary system;
  • Mississippi River meander belts;
  • fluvial architecture of meander belt and architecture of distributary within the Mississippi River backswamp;
  • Pemiscot Bayou – a possible failed avulsion;
  • radiocarbon dating from Pemiscot Bayou;
  • relative age dating and diagnostic cultural artifacts along Pemiscot Bayou

Summary

Pemiscot Bayou, the largest of four major distributary systems in the northern Lower Mississippi Valley (LMV) captured approximately 25% of the Mississippi discharge 5000 yr ago. While active, the bayou developed a 1.5–5-km-wide meander belt and associated point bar, overbank and abandoned meander channel-fill deposits. Typical of distributaries, its size decreased downstream. At 27 km down-valley from the avulsion junction, the channel was 600 m wide and 12 m deep. At 58 km down-valley, the channel width was reduced to 200–300 m and 7–9 m depth. Overbank silt, deposited by sheetflow as a unit up to 3 m thick and 10 km wide, buried adjacent point-bars of fine-to-medium sand and backswamp clay. Thin-bedded fine-to-very-fine sand and silt, laminated silt and massive clay infilled the abandoned channel.

This meandering distributary system was active for approximately 2000–3000 yr, but never fully avulsed for four possible reasons:

1 the slope ratio (cross-valley gradient : down-valley gradient = 4.2) was too low;

2 the discharge ratio (relative magnitude of annual flood discharge) was too low;

3 the suspended-sediment load was too large to expand the distributary channel;

4 tectonic influence in the New Madrid seismic zone controlled development of the distributary.

These conditions were adequate to capture only 25% of the Mississippi discharge. The fate of Pemiscot Bayou as a failed avulsion was certain when the Mississippi River meander at the distributary node was cut off, but it is possible that the distributary ceased to function earlier. By 2200 yr ago the distributary channel was largely infilled. A small amount of additional channel-fill has accumulated in the past 2000yr, the most recent of which is fluvial reworking of vented sand during seismic events. Today Pemiscot Bayou is inactive and is < 1% of its former size.