GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 39-19
Presentation Time: 9:00 AM-5:30 PM


NOWACKI, Emily J. and CLARK, Christine M., Department of Geography and Geology, Eastern Michigan University, Ypsilanti, MI 48197

Volcanic ash begins to weather upon deposition, a complex process resulting in the deposition of clay minerals within the pore spaces of volcanic material. These authigenic clays can be studied to determine how weathered a particular sample may be. Previous research conducted by Almquist (2011) and O’Dowd (2017) produced an 8-step weathering classification scheme that categorized samples from pristine to highly weathered based on SEM and XRD analysis of three samples from different ages and sources. We previously introduced four additional samples of differing age and origin to this project, from the San Francisco Peaks, AZ; San Pedro Mountains, Chile; Mount St. Helens, WA (pre-1980); and the Bandelier Tuff, NM. Initially, SEM analysis was used to identify the presence of clays and observe surface morphology of each sample. Results were compared and related to their depositional environments and time of deposition, as well as the weathering classification scheme. Conclusions drawn from SEM analysis categorized the four samples from least to most weathered in the order of San Francisco Peaks, San Pedro Mountains, Mount St. Helens, and Bandelier Tuff. We present here the results of XRD analysis conducted to identify and quantify the authigenic clays and amorphous glass present in each sample. These results were added to the results from SEM analysis to better understand the alteration of the parent material. By continuing analysis of these four samples, the existing classification scheme can be extended and enhanced to consider a wider variety of volcanic material of different ages and climatic settings, and ultimately become a useful tool for researchers to help with categorizing the degradation of volcanic material.