USING OSL DATING TO CONSTRAIN UP-DIP TO DOWN-DIP COUPLING RATES OF A MEANDER-BRAID TRANSITION: THE LAST NATURAL CHANGE IN RIVER PATTERN OF THE LOWER MISSOURI RIVER

Historically, the Lower Missouri River is known for being a temperate river that constantly and quickly reworks its floodplain with a braided network of channels; however, the river only recently became braided. Ox-bow lakes and landscape features resembling highly sinuous meandering loops mark the floodplain of the Lower Missouri River Valley as scars of what was once a fully meandering Missouri River. Two areas of the Lower Missouri River are mapped and numerous OSL dates collected with the help of students through the USGS EDMAP and NSF REU programs in conjunction with The University of Texas-Arlington and The University of Nebraska-Lincoln. OSL samples were strategically collected in order to date the last channel loops created by the meandering system and the first braids that formed after the transition completed.

Down-dip, from Kansas City, MO to the confluence with the Mississippi River, OSL results date the change from meandering to braided beginning approximately 3500 ybp and becoming fully braided approximately 1500 ybp. Up-dip, from Yankton, SD to just north of Omaha, NE, the meander-braid switch was more abrupt. Evidence of the transitional patterns that occur down-dip are absent from the up-dip floodplain record and OSL results date the pattern change up-dip between 1900-1500 ybp. The transition occurred later and more rapidly up-dip than down-dip, but did occur in both locations and completed at roughly the same time.