New Mexico Geological Society Annual Spring Meeting — Abstracts

Uranium series dating of travertine at Soda Dam, New Mexico yield precise new incision rates for the Jemez River, a tributary of the Rio Grande River, through San Diego Canyon. The emerging travertine record also documents past intervals of high spring discharge, inferred to reflect wet paleoclimate intervals. Travertine deposits at Soda Dam occur along the intersection of the Soda Dam fault, part of the Jemez fault zone, and the Jemez River. Modern travertine-depositing hot springs indicate this system is part of the Valles geothermal system, which extensive volcanic and travertine deposits indicate has been active throughout the Quaternary. Previous U-series dates (Goff et al., 1987) on the Soda Dam travertines were: Soda Dam= 4.8±0.2ka, Deposit A (west side)=215±40 ka and >350 ka; Deposit B (east side)= 98±7ka near top and 58±3ka in the core; Deposit C (southeast side)= 107±5ka near base. New dates are: Deposit A= 200.6±2.1 ka for travertine rinds on river cobbles just above the bedrock strath at the cave, and 183.1±2.1ka for a sparite sill that cuts the gravels. The strath is 30 m above the river yielding an average bedrock incision rate of 150m/Ma over the last 200 ka. Outcrop B= 138.4±1.1ka near the base, and 78.2±1.6ka at the top. Outcrop C= 103.2±0.5ka at the base and 101.7±0.5ka at the top. The bedrock strath below outcrop C is 16.5 m above the river, yielding an incision rate of 160 m/Ma over the last 100 ka. Longer term average incision for the Jemez River are195 m/Ma over the last 1.2 Ma and 230 m/Ma over the last 0.64 Ma. Our results produce incision rates that are generally consistent with previously reported incision rates and suggest semi-steady bedrock river incision, with perhaps a slight slowing over the last 200 ka. Additional implications of our continued dating efforts will be to: 1) provide better paleohydrologic and paleoclimate records of key climatic transitions (200-100 ka and last 10 ka) by obtaining stable isotope and other proxy records for well dated banded vein system; 2) refine the time duration of deposit A to infer possible linkages between Soda Dam spring deposition in relationship to Valles caldera paleolakes and the evolving Valles hydrothermal system; 3) continue to refine Quaternary incision history of the Jemez River using dated strath terraces.