--> ABSTRACT: Sedimentology and Facies of a Mississippi River Meander Belt: A Fluvial Model Based on a Significant Fluvial System, by Wayne A. Pryor and Douglas W. Jordan; #91030 (2010)

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Sedimentology and Facies of a Mississippi River Meander Belt: A Fluvial Model Based on a Significant Fluvial System

Wayne A. Pryor, Douglas W. Jordan

The meander belt of the Mississippi River, in southeastern Missouri, consists of four distinct facies groups: (1) river channel/point bar, (2) chute, (3) crevasse splay/levee, and (4) abandoned channel fill. A depositional model and vertical sequences have been developed from drill cores, vibra-cores, trenches, fathometer surveys, and mapping of these principal facies. This model and the vertical sequences compare very well to ancient sequences because the Mississippi River is a large, significant river with ancient analogs.

The meander belt has a 4,500-year history of lateral migration, point bar deposition, and abandonment of channel systems. It is 15 mi wide and approximately 100 ft thick. The Mississippi River is a big river, with discharge rates of 200,000 to 1,500,000 ft3/sec and flow velocities exceeding 7 ft/sec. In the study area the channel is up to 5,000 ft wide, averages 75 ft deep, and the principal point bar is 18,500 ft long. Large, long-crested dunes of sand and fine gravel up to 16 ft in height with planar cross-bedding are the principal bed forms in the channel/point bar. The chute is 13,000 ft long, 200 to 800 ft wide, and up to 15 ft deep. Chute deposits are composed of tangentially cross-bedded sands and ponded mud sheets. The natural levee systems are composed of coalescin crevasse splays. The studied splay has continuously developed over a 57-year period and is a wedge-shaped body 5,600 ft long, 7,000 ft wide, up to 50 ft thick, and is composed of series of individual lobes of sand and gravel interbedded with distal silts and muds. Abandoned channel deposits include oxbow lake organic muds interbedded with varying amounts of cross-bedded sands and silts. No clay drape deposit has been observed during three years of study. The vertical sequences observed in cores through the various facies systems have systematic variations and associations that serve as models for meander belt fluvial systems. Rumors of the demise of the fluvial vertical sequence model are greatly exaggerated.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.