Fluvial evolution of the lower Mississippi River valley during the last 100 k.y. glacial cycle: Response to glaciation and sea-level change

Abstract

The lower Mississippi valley contains multiple large braid belts for which age control has been limited. Application of the optically stimulated luminescence technique has produced a new chronology of lower Mississippi valley channel-belt formation and insight into the valley's evolution during the last glacial cycle. Fluvial deposits range from last interglacial meander belts (85 ± 7 to 83 ± 7 ka) to multiple braid belts (64 ± 5 to 11 ± 1 ka) and record large-amplitude responses of the Mississippi River to glacially induced changes in discharge and sediment supply during the last glacial cycle. Slackwater deposits in buried tributary valleys from the middle Mississippi valley and northern lower Mississippi valley suggest that the river was fl owing at a position 8-21 m below the present fl ood plain during the last interglacial, then rapidly aggraded and switched to a braided regime to form the highest and oldest braid belt by 64 ± 5 to 50 ± 4 ka, coincident with initial glaciation of the upper drainage basin. The Mississippi River remained braided until fi nal meltwater withdrawal from its headwaters in the earliest Holocene. Braid-belt formation and incision was controlled by fl uctuations in meltwater and sediment discharge, while glacio-eustatic sea level controlled the elevation to which the river was graded, causing late glacial braid belts to dip below the Holocene fl ood plain in the southern lower Mississippi valley. Moreover, avulsions in the middle Mississippi valley and northern lower Mississippi valley during the last glaciation have pinned the river over regions of shallow bedrock, preventing the modern river from incising to its last interglacial profi le. The new chronology and longitudinal profi les presented here provide insight into the response of this continental-scale river system to climatic (glacial) and base-level forcing during the last 100 k.y. glacial cycle.

Efficient retention of mud drives land building on the Mississippi Delta plain

“…Recent modeling results suggest that the suspended sand load delivered to the MD is buffered from upstream change for timescales on the order of 1000 years (Nittrouer and Viparelli, 2014a). With that in mind, the events that may have substantially changed the suspended sand load are either so recent (dams in the tributaries, rapid deforestation associated with expanding agriculture; < 200 years ago) or so long past (glacial outwash floods; > 10 000 years ago; Rittenour et al, 2007) that it is reasonable to apply modern sand loads to the Lafourche channel.…”

Fishes in Paleochannels of the Lower Mississippi River Alluvial Valley: A National Treasure

“…This response was strongest south of Vicksburg, Mississippi (Saucier 1994;Blum and Törnqvist 2000), although Rittenour et al (2007) suggested that the upstream limit of sea-level influence may be as far inland as Memphis, Tennessee. Conversely, tectonism has been more influential north of Memphis where the New Madrid Seismic Zone has been associated with development of abandoned channels as late as the early 1800s (e.g., Reelfoot Lake; Van Arsdale 2000).…”

Do Extreme Flood Deposits in Wabash and Grand River Valleys, Indiana and Michigan, Relate to Upstream Subglacial Floods?

“…Note in the inset diagram that both interstades were generally preceded by periods of high meltwater flow. The Sikeston braid belt began deposition by 19.7 ka according to Rittenour et al (2007). This age of 19.7 ka or one slightly older may be considered as a possible date of an earlier major westward flood through Erie basin and might account for both the 'glacial grooves' in western Lake Erie and the subsequent Erie Interstade.…”

“…The foraminifera are from marine sediment cores from the continental slope S of Louisiana. And at the same time, the extreme flood incised the northern lower Mississippi River Valley, mainly in Missouri and Arkansas south of the Ohio River, to initiate deposition, prior to 16.1 ka, of the Kennett braided channel belt, a zone of braided sandy river deposits, shown in red on the slide, and dated by Rittenour et al (2007) using optically stimulated luminescence methodology (OSL).…”