Tributary response to a Mississippi River avulsion: Beheading of the White River in the Mississippi Alluvial Valley

During the last 25 ka the White River has had a complex history that has included lengthening and shortening its valley in response to Mississippi River avulsions and changing channel morphology. During the early and middle Holocene, the Mississippi River was along the east side of the valley and the White River valley extended across the entire Mississippi Alluvial Valley (MAV) to join the Mississippi River near Vicksburg, MS. The downstream section of the White River, called the Black Bayou, between the present and the past Mississippi meander belt positions, was abandoned after the Mississippi River established its modern meander belt in the center of the valley ca. 2.5 ka. In the Western Lowlands as the sediment supply decreased, the White River channel morphology evolved from a wide-shallow channel with a width to depth ratio of 268 and low sinuosity (1.3) in the late Pleistocene (17 ka) to a highly sinuous (2.1) deep-narrow channel with a width to depth ratio of 30 by 7 ka.;The Black Bayou, located east of Greenville, MS is the likely candidate for the abandoned White River channel; however, other possible origins could be an abandoned section of the Arkansas River or a Mississippi River distributary. Based on comparison of the geomorphology and elemental composition of the bayou channel sand with modern channels of these rivers, as well as dates for the time of abandonment ca. 6.5 ka, the Black Bayou is interpreted to be a beheaded section of the White River. Bulk elemental analysis of the fine sand fraction was used to distinguish point-bar deposits of the Arkansas, White, and Mississippi Rivers, when was compared to elemental concentrations of the Black Bayou. Of the 48 elements analyzed, 22 elements of the Black Bayou have concentrations that are most statistically similar to the modern White River. Optically Stimulated Luminescence dates were obtained that indicated an older segment of the Black Bayou was active 6.1 ka and was infilling by 4.2 ka and this would eliminate it being a Mississippi River distributary because the modern Mississippi meander belt did not exists at this time.;Abandoned older segments of the Black Bayou channel are filled first with Arkansas River sediment, and later Mississippi River sediment. The younger Black Bayou channel abandoned ca. 2.5 ka has only Mississippi River clay channel fill.