Saturday, December 19, 2009

This week I was ambitious and decided to drill four of my samples for Uranium dating. I only got two done, with lots of support from Eileen Embid. (The drill is pictured above)

There are studies that have already assessed the timing of travertine accumulation in the Rio Salado, the Grand Canyon, and Springerville, AZ (Sower et al., 2008; Embid et al., in prep.; Crossey et al., 2009). My study focuses specifically on the active spring deposits in the Tierra Amarilla anticline, just south of the Rio Salado and their correlation with results from the surrounding area.

To better understand the paleohydrologic processes and to estimate the growth record of the mound system, geologic mapping and U-series geochronology is being incorporated. The active and extinct mound springs we propose to study are morphologically similar to mounds elsewhere in the southwestern U.S., including in Springerville, AZ and the Grand Canyon.

U-series chronology of travertine samples will be determined in the Radiogenic Isotope Laboratory at the University of New Mexico. The chemistry lab and mass spectrometry lab are class 100 clean labs. The travertine samples will be cut and drilled samples will be obtained along growth bands with an automated drill. The carbonate powder, typically around 200 mg, will be dissolved in HNO3 and spiked with a mixed 229Th-233U-236U spike. You can see my fresh travertine powder above and Eileen is putting in a vial for safe keeping until January when we will run the samples in the lab.

The Micromass Sector 54 thermal ionization mass spectrometer with a high-abundance sensitivity filter will be utilized for all U and Th measurements (Rasmussen, 2001). The timing of travertine accumulation will be determined and than correlated with nearby accumulations (Springerville, AZ and Grand Canyon). We will define the time interval over which these springs have been active and these dates will relate to the surrounding region and the incision rates of the Rio Salado. We hypothesize that this region will provide unique dates that do not correlate with the Grand Canyon or the Springerville area (i.e., controls are local).

Eileen Embid just finished her Master's at UNM working with travertine from Springerville,AZ. If you want to see more information on her and the other graduate students in our research group here is our link: