UNDERSTANDING ANTARCTIC TILL PROVENANCE THROUGH POWDER X-RAY DIFFRACTION

In January 2007, samples of till from 6 different moraines along the Reedy Glacier, East Antarctica were collected with the goal of differentiating between these samples of till and previously collected samples from the base of three West Antarctic ice streams through powder x-ray diffraction. The purpose of this study is to identify mineral phases in the < 2mm fraction in both the moraines and the material from the base of the ice streams. Understanding the differences in mineralogy of these samples will serve two purposes: (1) assess this method compared to sand petrography and (2) constrain ice flow models during the Last Glacial Maximum (LGM) into the Ross Sea. The samples were analyzed at INSTAAR, at the University of Colorado, Boulder; with a Siemens D5000 X-Ray Diffractometer (XRD). The < 2mm fraction was crushed using a McCrone Mill and the samples were back mounted on slides. The samples were analyzed by XRD at angles from 5-65° 2θ with a step size of .02° 2θ. As a result, 3002 intensity values from each sample were obtained and modeled using RockJock to determine which minerals are present.

One sample from each of six moraines along Reedy Glacier was analyzed, with the addition of 3 sub-site samples from Strickland Nunatak, located at the head of the glacier. An additional 11 samples from ice stream cores were analyzed. These sample locations were chosen to investigate the variability between the Reedy Glacier, draining the East Antarctic Ice Sheet, and ice stream samples from West Antarctica, whilst providing constraints for ice stream positions in the Ross Embayment during the LGM.

Many similarities were found when comparing the < 2mm fraction with existing coarse sand petrology data. For example, the Strickland Nunatak samples were classified as quartzite using sand petrology. RockJock found abundant quartz, ranging from 42.3% to 53.5%, but also provided greater detail with respect to other minerals. For example, RockJock identified multiple feldspars (oligoclase, andesine, and albite), which were missed in the sand fraction and identified kaolin minerals. Further analyses will reveal whether consistent differences can be identified between these East and West Antarctic tills.