HR: 0830h
AN: H51E-1123    [PDF]
TI: Flood Plain Aggradation Rates Based on Tree-Ring Growth-Suppression Dates
AU: Friedman, J M
EM: jonathanfriedman@usgs.gov
AF: US Geological Survey, 3215 Marine St, Boulder, CO 80303 United States
AB: When woody riparian plants are partially buried subsequent tree rings of the buried stems resemble those of roots. Annual rings in a buried stem are narrower and have larger vessels then those in unburied sections of the same stem. We have used this phenomenon to date flood plain sediments exposed in trenches, along two ephemeral streams in New Mexico (Rio Puerco and Chaco Wash) where the sediments are predominantly silt and very fine sand and the plants are predominantly tamarisk and willow. Cross dating down the stem allows dating of the first growth-season following burial by thick beds, and constrains the age of all stratigraphic units deposited since germination of the tree. We observed that the anatomical reaction to burial increases with bed thickness and cumulative deposition. Beds that are thicker than 30 cm can be dated to the year of the deposition event. Beds 10 to 30 cm thick can usually be dated to within several years. The period of deposition of multiple very thin beds can be constrained to the decade. Results can be improved by analyzing multiple stems from one tree and multiple trees linked together by the stratigraphy. Along our study streams, sites far from the channel tend to have moderate and relatively steady point-aggradation rates. Levees next to the channel tend to have the thickest deposits per flood and variable long-term rates, which can differ from the whole flood plain aggradation rates by several fold. Cross-sectionally averaged flood plain aggradation has been as large as a meter per decade along our study streams.
DE: 0400 Biogeosciences
DE: 1800 HYDROLOGY
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2003 Fall Meeting