New Mexico Geological Society Annual Spring Meeting — Abstracts

Bulk chemical analysis of the Neoproterozoic Chuar Group (-770-746 Ma), Grand Canyon was undertaken to better understand the petrology of this near-shore marine, predominantly shale succession. The Chuar group is composed of two formations, the Galeros and the Kwagunt, subdivided into seven members. Major element (Si, AI, Fe, Mg, Mn, Ca, K, Na, Ti, P) analysis by X-ray fluorescence spectrometry (XRF) was performed on samples from five of these members. The five members, in ascending order, are the Tanner, Jupiter, and Carbon Canyon members from the Galeros Formation and the Awatubi, and Walcott members from the Kwagunt Formation.

Cross-plots of TiO₂-Al₂O₃, SiO₂-Al₂O₃, K₂O-Al₂O₃ reveal stratigraphically significant geochemical variations within the Chuar Group. TiO₂ and Al₂O₃ show a positive correlation and the Jupiter and the Awatubi members have higher TiO₂concentrations than the Carbon Canyon and the Walcott members. SiO₂ and Al₂O₃ show a negative correlation that suggests that clays (Al₂O₃-bearing) are mixed with quartz silt The Awatubi Member shows an excellent correlation (R²=0.98) suggesting that kaolinite is the dominant clay mineral in this unit. The Walcott Member contains the greatest amount of SiO₂ and therefore the most silt. Overall, K₂O and Al₂O₃ have a good positive correlation but the Walcott Member has a very strong positive correlation (R²=0.98) indicating a mineralogical control. The Tanner Member contains the largest amount of K.

Distinct chemical and mineralogical compositions for members of the Chuar Group may result from source, depositional processes and/or diagenesis. Additional geochemical and mineralogical data will help to determine the controls on the composition of the Chuar Group.