ABSTRACT: Oversize Oxbows: Tentative Dates, Effects and Risks

TANNER, WILLIAM F., Geology Department, Florida State University, Tallahassee, FL

An oversize oxbow is a river-channel remnant having a channel width greater than the modern one. Many such lakes, two to six times as wide as the modern stream, represent runoff up to 125 in./year (317 cm/yr). These oxbows are not due to stream piracy or glacial meltwater.

Sea level history is known at 50-year intervals from work in Denmark. The best times for oversize oxbows were 6,500-5,600 B.P. (mid-Holocene high) and 1,800 B.P., and the best times for undersize channels, 5,000-4,000 B.P. and 800-200 B.P. (Little Ice Age). Data from the Rio Grande delta system suggest that many oversize channels formed at various times in the last 3,000 years, and represent common, rather than rare, conditions.

A modest northward shift of the boundary between dominant dry westerly winds over the southern states, and dominant wet easterly winds over the Gulf of Mexico, should increase east-west air flow from the Atlantic Ocean across those states, and increase rainfall. Reversal of the Dog Island (Florida) sand transport system, some 250 years ago, suggests this shift.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)